U.S. Patent Mar. 8, 2022 Sheet 19 of 25 US 11,271,137 B2

(A) Current Density vem} B)
80 3.0010" 8.0510" 9.02108

WPE (Normalized)

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Current (Aj

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FIG. 19


US 11,271,137 B2

21

the efficiency droop effect. Hence, ZnO is most likely not the
critical compound for creating a droop-free LED. A ZnO fin,
however, due to its sub-200 nm width is expected to have a
lower potential drop and resistive loss across its width, two
factors that are known to impact the IQE. The comb like
structure of the p-GaN contact is also effective for current
spreading layer and effective hole injection into the fins. The
linear rise of output power versus injected current at high
current density (FIG. 17¢) shows the effectiveness of the fins
in charge injection. Furthermore, the minimal impact of
temperature on the defect-related SRH carrier loss in ZnO
fin, at low injection current (FIG. 18d) is consistent with the
low defect density of the fins. There is no electron blocking
layer in the presented fin heterojunction. Nevertheless, there
is no electron leakage and charge recombination in the
p-GaN at high current densities. Hence, our results suggest
the absence or negligible presence of the critical factors that
reduce the efficiency of conventional LEDs including elec-
tron leakage. Auger recombination, defect-related recombi-
nation and temperature degradation.

While one or more embodiments have been shown and
described, modifications and substitutions may be made
thereto without departing from the spirit and scope of the
invention. Accordingly, it is to be understood that the present
invention has been described by way of illustrations and not
limitation, Embodiments herein can be used independently
or can be combined.

All ranges disclosed herein are inclusive of the endpoints,

and the endpoints are independently combinable with each °

other. The ranges are continuous and thus contain every
value and subset thereof in the range. Unless otherwise
stated or contextually inapplicable, all percentages, when
expressing a quantity, are weight percentages. The

10

2

suffix “(s)” as used herein is intended to include both the ~

singular and the plural of the term that it modifies, thereby
including at least one of that term (e.g., the colorant(s)
includes at least one colorants). “Optional” or “optionally”
means that the subsequently described event or circumstance
can or cannot occur, and that the description includes
instances where the event occurs and instances where it does
not. As used herein, “combination” is inclusive of blends,
mixtures, alloys, reaction products, and the like

As used herein, “a combination thereof” refers to a
combination comprising at least one of the named constitu-
ents, components, compounds, or elements, optionally
together with one or more of the same class of constituents,
components, compounds, or elements.

All references are incorporated herein by reference.

The use of the terms “a” and “an” and “the” and similar
referents in the context of describing the invention (espe-
cially in the context of the following claims) are to be
construed to cover both the singular and the plural, unless
otherwise indicated herein or clearly contradicted by con-
text. “Or” means “and/or.” It should further be noted that the
terms “first,” “second,” “primary.” “secondary,” and the like
herein do not denote any order, quantity, or importance, but
rather are used to distinguish one element from another. The
modifier “about” used in connection with a quantity is
inclusive of the stated value and has the meaning dictated by
the context (e.g., it includes the degree of error associated
with measurement of the particular quantity). The conjunc-
tion “or” is used to link objects of a list or alternatives and
is not disjunctive; rather the elements can be used separately
or can be combined together under appropriate circum-
stances.

40

22

What is claimed is:

1. A light article comprising:

a substrate;

a truncated cuboidal fin disposed on the substrate and
comprising:

a laterally-grown nanocrystal comprising a longitudinal
length and a lateral length that are different;

a charge injection facet arranged along a longitudinal
fin axis of the truncated cuboidal fin, and

a truncation facet disposed opposing the charge injec-
tion facet and arranged parallel to the longitudinal fin
axis;

a side-injector disposed on the charge injection facet of
the truncated cuboidal fin and that provides electrons to
an active layer; and

the active layer interposed between the side-injector and
the substrate and that:
receives electrons from the side-injector;
receives holes from the substrate; and
produces light in response to combining the electrons

and the holes.

2. The light article of claim 1, wherein the truncated
cuboidal fin further comprises an initiation facet disposed
along a lateral fin axis of the truncated cuboidal fin and from
which the charge injection facet and the truncation facet
propagate during growth.

3. The light article of claim 2, wherein the truncated
cuboidal fin further comprises a terminal facet disposed
parallel to the lateral fin axis of the truncated cuboidal fin
and at which the charge injection facet and the truncation
facet terminate along the longitudinal fin axis during growth.

4. The light article of claim 3, wherein the truncated
cuboidal fin further comprises a top facet disposed parallel
to the longitudinal fin axis of the truncated cuboidal fin and
at which the charge injection facet and the truncation facet
terminate along a height fin axis of the truncated cuboidal fin
during growth.

5. The light article of claim 1, wherein the active layer is
interposed between the truncated cuboidal fin and the sub-
strate.

6. The light article of claim 1, wherein the active layer is
interposed between the truncated cuboidal fin and the side-
injector.

7. The light article of claim 1, further comprising an
electrical via disposed on the side-injector.

8. The light article of claim 1, further comprising an
electrical via disposed on the substrate.

9. The light article of claim 1, further comprising:

a side-injection drain electrode disposed on the side-

injector;
a side-injection source electrode disposed on the side-
injector and in electrical communication with the side-
injection drain electrode through the side-injector;
a dielectric member disposed on the side-injector between.
the side-injection drain electrode and the side-injection
source electrode; and
a gate electrode disposed on the dielectric member such
that:
the gate electrode is in electrical communication with
the side-injection drain electrode and the side-injec-
tion source electrode through the dielectric member;
and

the dielectric member is interposed between the gate
electrode and the side-injector;

wherein the side-injector comprises a semiconducting
material.


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US 11,271,137 B2

Sheet 13 of 25

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U.S. Patent Mar. 8, 2022 Sheet 23 of 25 US 11,271,137 B2

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U.S. Patent Mar. 8, 2022 Sheet 4 of 25 US 11,271,137 B2

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US 11,271,137 B2

17

enabling the development of a new generation of LEDs for
macro- and micro-scale applications

Since the breakthroughs in GaN blue light emitting diode
(LED) technology and the subsequent realization of white
LEDs, great progress has been made in wide bandgap
(WBG) semiconductor LED lighting for general illumina-
tion, display, and many other applications including biologi-
cal sensing, surface disinfection and sterilization, visible-
blind photodetectors, visible light communication, acoustic-
optoelectronics, and terahertz electronics. A technical
challenges of WBG LED technology is efliciency droop. ie.,
a decline in internal quantum efficiency (IQE) with increas-
ing current density. This phenomenon has limited the per-
formance of some conventional LEDs. Efficiency droop has
been linked to Auger recombination, phase space filling,
stimulated emission, delocalization-activated nonradiative
recombination, and incomplete carrier localization. The
droop increases with junction temperature, although it is
pronounced even at lower temperatures. This Example
describes a p-n heterojunction ZnO—GaN fin LED that
intrinsically does not show the droop effect even at
extremely high current densities. ZnO has a Wurtzite crystal
structure and a bandgap (E,) of 3.36 eV, similar to GaN
(B,=3.43 eV). It has a considerably larger exciton binding
energy of about 60 meV (relative to 24 meV in GaN) making
it more effective for high temperature light sources and
opto-electronics resistant to radiation damage.

The fin LED architecture shown in FIG. 15a includes a
lateral ZnO nanofin (1) epitaxially grown on p-GaN. The

fins are grown via an Au-catalyzed vapor-liquid-solid 3

(VLS)-growth process that is directed on the surface, where
the Au nanodroplets formed at the periphery of the catalyst
pattern nucleate the nanofins (FIG. 155). On c-GaN, ZnO fin
grows upright in the direction and laterally in the m-direc-

tion. A ZnO fin could have one or two large non-polar (11. 3

20) side facets. Fabrication of the fins is completed by
connecting n-type fins to the n-metal electrodes. We used a
“facet-selective contact” method (FIG. 15c-d) in which one
of the fin side facets is first passivated with a dielectric layer
(2), deposited at an angle (FIG. 15d). The other non-polar
side facet remains accessible to receive the n-contact metal
electrode (3). The design provides large-area low-resistance
contacts. The side-facet selective contact also results in
facile formation of clean metal-semiconductor interfaces as
shown in the cross-section of FIG. 15/,

FIG. 16 presents the optical image (a) and the magnified
scanning electron microscope (SEM) image (b) of a fin LED
(under operation) containing a single fin and its n- and
p-metal contacts. Electrically-addressable fin LED pixels
can be fabricated using standard photolithography. FIG. 16c
shows an example of a linear array. In this optical image, the
fin LED pixels containing 1 to 10 fins are spaced 120 um
apart across a 1 cm range. For better current spreading in the
p-GaN layer, the p-contact microelectrodes (yellow high-
lights) are spaced every 150 wm.

Fin LED pixels are bright enough so that the individual
pixels in the wire-bonded linear array can be directly mea-
sured in front of a metrology-grade charge-coupled device
(CCD)-array spectroradiometer with no focusing optics
(FIG. 17a). For each pixel, a bright emission appears at the
location of the p-n heterojunction at forward bias. The
electroluminescence (EL) spectra of individual fin LED
pixels were measured at different currents. FIG. 175 shows
a series of the representative spectra obtained from a pixel
containing eight nanofins, with an average fin length of 5 jum.
and height of 1 um. When the current increases, two peaks
at 3.369 eV (368.5 nm) and 3.280 eV (378.5 nm) appear.

S

3

40

45

35

18

These wavelengths agree with the neutral donor bound
exciton (D°X) recombination in ZnO. Observation of these
two peaks at room temperature and their agreement with the
room temperature cathodoluminescence (CL) data high-
lights the high quality of the ZnO fins and underlines the low
concentration of the donor states relative to what is typically
observed in unintentionally n-doped ZnO nanowires. A low
concentration of donor states is also evidenced by the flow
of holes from p-GaN to the n-ZnO and their recombination
in the ZnO fin. Furthermore, the narrow full-width at half-
maximum (FWHM) of only 5 nm and 18 nm for these two
emissions shows the low defect density of the fins. At lower
injection currents, the appearance of the red shoulder at
about 420 nm indicates radiative e-h recombination in GaN,
due to the slow movement of holes toward the p-n interface.
As the drive current increases, the intensity of the ultraviolet
(UV) EL peaks at 368 nm and 378 nm continues to rise while
the e-h recombination in GaN is suppressed

To further explore the impact of drive current on the
output power and spectral properties of fin LEDs, the total
spectral radiance flux (W/nm) of a pixel containing three fins
was investigated up to 100 mA (the limit of the measurement
setup) using the integrating sphere described in FIG. 17a

5 The pixel was operated under a direct current (DC) bias for

the operation times of 50 s, 25 s, 10s, 5s, 2.5 s, 1 s and 0.5
s and for the current range of 1 mA, 2 mA, 5 mA, 10 mA,
20 mA, 50 mA, and 100 mA, respectively. During each
measurement, a 10-minute rest time was given so that the fin
LED can reach the equilibrium temperature of 25 (£0.1) °C.
established by a temperature-controlled stage. The total
spectral radiance-current (L-I) graph of FIG. 17¢ (dark
circles) shows that the 100 times increase in the injected
current results in +108 times increase in the output optical
power of the fin LED. This observation indicates that at high
currents, carrier loss due to non-radiative events is well
controlled. Loss of carriers inside the active region at high
current injections is one of the main processes that promotes
the efficiency droop. As current is increased, the rise of
intense UV EL peaks in the range of 368 nm to 390 nm (3.37
eV to 3.18 eV) in FIG. 18a shows that the radiative
recombination occurs in the ZnO fin, as shown in the band
structure of the ZnO—GaN heterojunction (FIG, 185). In
contrast to other types of LEDs, flow of electrons (electron
leakage) to the p-GaN is not observed in fin LEDs. Such
leakage is an important factor in promoting the droop effect
at high current densities.

In FIG. 18c, we see that as current is raised, the EL UV
peaks redshift, approximately, in a linear fashion. For
instance, the 368.4 nm peak redshifts approx. 3 nm (27
meV) at 10 mA, and 17 nm (144 meV) at 100 mA, reaching
385.4 nm. This shift is attributed to the junction temperature,
as the temperature-dependent EL studies of the fin LEDs
also show a linear redshift in the UV peak position (supple-
mentary materials, FIG. 20). Based on these measurements,
the 17 nm redshift in the fin LED corresponds to a drastic
rise in the junction temperature of about 340° C. during its
0.5 s operation. Also, at low injection current of 2 mA, the
temperature-dependent EL analysis from 25° C. to 110° C.
(FIG. 18d) shows no significant variation in the charge
recombination in the ZnO fin. This could be attributed to the
minor contribution of defect-related Shockley-Read-Hall
(SRH) non-radiative carrier recombination in the fin. Mean-
while, a gradual suppression of e-h recombination in GaN is
observed as temperature is raised (supplementary materials,
FIG. 21). These results underline the tolerance of fin LEDs
to non-radiative recombination processes both at low and
high current densities. The resilience of fin LEDs to high
temperature is also in line with a higher exciton binding


U.S. Patent Mar. 8, 2022 Sheet 20 of 25 US 11,271,137 B2

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US 11,271,137 B2

1
LIGHT ARTICLE

CROSS REFERENCE TO RELATED
APPLICATIONS

The application claims priority to U.S. Provisional Patent
Application Ser. No. 62/916,978 filed Oct. 18, 2019, the
disclosure of which is incorporated herein by reference in its
entirety.

STATEMENT REGARDING FEDERALLY
SPONSORED RESEARCH

This invention was made with United States Government
support from the National Institute of Standards and Tech-
nology (NIST), an agency of the United States Department
of Commerce. The Government has certain rights in the
invention. Licensing inquiries may be directed to the Tech-
nology Partnerships Office, NIST, Gaithersburg, Md.,
20899; voice (301) 301-975-2573; email tpo@nist.gov; ref-
erence NIST Docket Number 19-007US1

BRIEF DESCRIPTION

Disclosed is a light article comprising: a substrate; a
truncated cuboidal fin disposed on the substrate and com-
prising: a laterally-grown nanocrystal comprising a longi-
tudinal length and a lateral length that are different; a charge
injection facet arranged along a longitudinal fin axis of the

truncated cuboidal fin; and a truncation facet disposed 3

opposing the charge injection facet and arranged parallel to
the longitudinal fin axis; a side-injector disposed on the
charge injection facet of the truncated cuboidal fin and that
provides electrons to an active layer; and the active layer

interposed between the side-injector and the substrate and 3:

that: receives electrons from the side-injector; receives holes
from the substrate; and produces light in response to com-
bining the electrons and the holes.

Disclosed is a process for making a light article, the
process comprising: forming a catalyst pattern on a sub-
strate, the catalyst pattern comprising a catalyst; forming a
mask on a masked portion of the catalyst pattern while
providing an exposed portion of the catalyst pattern in an
absence of the mask on the exposed portion of the catalyst
pattern; controllably quenching growth of nanostructures
from the masked portion of the catalyst pattern by the mask
disposed on the masked portion of the catalyst pattern;
propagating the catalyst from the exposed portion of the
catalyst pattern along a single crystal index of the substrate;
forming a truncated cuboidal fin selectively along the single
crystal index of the substrate in the presence of the catalyst
as the catalyst propagates along the single crystal index of
the substrate, such that the truncated cuboidal fin comprises:
a laterally-grown nanocrystal comprising a longitudinal
length and a lateral length that are different; a charge
injection facet arranged along a longitudinal fin axis of the
truncated cuboidal fin, the longitudinal fin axis being dis-
posed along the single crystal index; and a truncation facet
disposed opposing the charge injection facet and arranged
parallel to the longitudinal fin axis, such that in forming the
truncated cuboidal fin a translation order and orientation
order of the laterally-grown nanocrystal is controlled by a
crystal symmetry of the substrate; subjecting the truncated
cuboidal fin to angular-directed passivation in which the
truncation facet is contacted by a passivation composition,
and the charge injection facet is not contacted by the
passivation composition; forming, from the passivation

8

2

40

&

2

composition, a passivation layer on the truncation facet in
response to subjecting the truncated cuboidal fin to angular-
directed passivation; subjecting the truncated cuboidal fin to
angular-directed deposition in which the charge injection
facet is contacted by a deposition composition, and the
truncation facet is not contacted by the deposition compo-
sition; and forming, from the deposition composition, a
side-injector on the charge injection facet in response to
subjecting the truncated cuboidal fin to angular-directed
deposition to form the light article.

Disclosed is a process for producing light with a light
article, the process comprising: providing electrons to side-
injector, side-injector disposed on charge injection facet
opposing truncation facet of truncated cuboidal fin; com-

5 municating electrons from side-injector to active layer:

providing holes to substrate; communicating holes from
substrate to active layer; receiving, by active layer, electrons
from side-injector and holes from substrate; combining, in
active layer, electrons and holes; and producing light from
combining electrons and holes in active layer.

BRIEF DESCRIPTION OF THE DRAWINGS.

The following description should not be considered lim-

iting in any way. With reference to the accompanying

drawings, like elements are numbered alike

FIG. 1 shows a plan view of a light article in panel A, a
perspective view of the light article in panel B, a cross-
section along line A-A in panel C of the light article shown
in panel A, a side view along a lateral fin axis of a truncation
facet of the light article in panel D, and a side view of a
side-injector disposed on a charge injection facet of the light
article in panel E;

FIG. 2 shows electrons from the side-injector combining
with holes from the substrate in the active layer to produce
light by the light article shown in FIG. 1;

FIG. 3 shows a plan view of a light article in panel A, a
perspective view of the light article in panel B, a cross-
section along line A-A in panel C of the light article shown
in panel A, a side view along a lateral fin axis of a truncation
facet of the light article in panel D, and a side view of a
side-injector disposed on a charge injection facet of the light
article in panel E;

FIG. 4 shows electrons from the side-injector combining

5 with holes from the substrate in the active layer to produce

light by the light article shown in FIG. 3;

FIG. 5 shows an electrical via disposed on the side-
injector and an electrical via disposed on the substrate of the
light article shown in FIG. 1;

FIG. 6 shows an electrical via disposed on the side-
injector and an electrical via disposed on the substrate of the
light article shown in FIG. 3;

FIG. 7 shows formation of a light article that includes a
side-injection drain electrode, side-injection source elec-

5 trode, dielectric member, and gate electrode;

FI
array;

FIG. 9 shows a truncated cuboidal fin;

FIG. 10 shows a light article disposed on a substrate;

FIG. 11 shows formation of a light article;

FIG. 12 shows cylindrical pillar-shaped nanowires having
a common electrode disposed on in panel A; a cylindrical
pillar-shaped nanowire in panel B; a light article in panel C;
a plurality of light articles in panel D; optical images in

8 shows a plurality of light articles disposed in an

5 panel E of a linear array of light articles arranged as

n-ZnO/p-GaN nanoLED pixels in which top and lower
panels show different pixels under an average driving cur-


U.S. Patent Mar. 8, 2022 Sheet 22 of 25 US 11,271,137 B2

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Or

FIG. 22


US 11,271,137 B2

19
energy of ZnO compared to GaN. It should be noted that the
typical commercial LEDs are limited to an upper operating
temperature of ~150° C.

These fin LEDs can sustain unprecedented current den-
sities; for instance, on the order of 1 MA/cm? for a fin LED
pixel that contains three nanofins, each with a metal-semi-
conductor area of 6.7x107* cm? (2.8 umx0.8 jum). To put this
in perspective, typical planar LEDs are already in their
efliciency-droop regime at 100 A/cm? drive current. The
highest reported current density values for nanowire-based
LEDs fall in the range of 7 kA/cm? to 20 kA/cm?, where the
efficiency droop overwhelms the overall device efficiency.

The total radiant flux (output optical power) at 100 mA.
reaches 1 W (#10%) for the fin LED as shown in FIG. 17c.
This translates to an output power density of 45 W/cm?
based on a p-n junction area of ~2.4x10"* cm?. This power
density is on par with the output power of the brightest
commercial planar UV-A LEDs of ~50 W/cm’. The nanow-
ire LEDs have so far shown output powers that are an order
of magnitude smaller than those for the planar LEDs. Recent
measurements using ensembles of free-standing nanowire
LEDs show power density values in the range of 0.001
W/em?, 0.5 W/em?, and 3 W/cm?, respectively, for axial
InGaN/GaN nanowires, InGaN/AlGaN dot-in-a-wire core-
shell nanowires, and core-shell AllInGaN nanowires. Full
three-dimensional Finite-Difference Time-Domain (FDTD)
modeling (FIG. 18¢) shows that the fin LEDs have an
intrinsic light extraction efficiency (LEE) of about 15%. The
rest of the light is trapped in the p-GaN substrate, due to a
higher refractive index of GaN (2.5) relative to ZnO (2.2).

LEE could be increased to more than 80% by improving the 3

chip design with the commensurate expected increase of the
measured output power of 45 W/em? by a factor of 5. By
increasing the IQE of a fin LED from its current value of
about 35% to 90% (which is the IQE of current GaN LEDs)

and an increase in the fin LED drive current from 100 mA. ;

to 1000 mA, it is estimated that the output power can be
increased by a factor of 100 relative to existing planar LEDs.

FIG. 19a shows the normalized wall-plug efficiency
(WPE), ratio of output power to input electrical power, of a
fin LED. There is no sign of decline in the performance of
the fin LEDs at high current densities. This is remarkable;
normally LEDs show a strong drop in efficiency as current
density increases, long before reaching such high densities
The IQE of the ZnO—GaN heterojunction is a determining
parameter in the overall performance of the LED. We
attribute the IQE improvement to two factors: (a) the fin
shape forming a heterodimensional contact with GaN facili-
tating the current gradient saturation and (b) the high quality
of ZnO crystal evidenced by the narrow bandwidth transi-
tions observed by the CL and EL spectroscopy. To support
this interpretation, we present a three-parameter model
based on the radiative and nonradiative processes (ABC)
including the SRH and Auger recombination in which the
energy is eventually released as heat. According to the ABC
model (supplementary materials, Eq. 1), the IQE is given by:

-—__Ne
THN, +0gNE

ay
0

Here N,=n/n,, is the dimensions electron-hole pair den-
sity,

cA
No= Fe

¢,-CA/B?, and c, is the dimensionless Auger recombination
constant, This model (FIG. 22) describes the impact of rise

3

35

60

6:

20

of non-radiative Auger recombination and decline of IQE. In
the steady state, the current density flux gradient is estimated
as J=I/(qd), where J=An+Bn74Cn’. Here I is the current
density, y is the electron charge, and d is the characteristic
length of the recombination region. The current density flux
gradient (J) could be rewritten as j-N,+N,7+c,N,>. Here,
the dimensionless current flux density is j=J/(An,).

We consider two limiting cases: (1) The low injection
regime when the generation occurs close to the heterointer-
face. In this case, the Auger recombination is negligible. (2)
High injection regime, when the generation occurs in the fin
and the Auger recombination is dominant. In the low injec-
tion case, we neglect the Auger recombination contribution
in the current flux density. In this case, the SRH defect-

s related carrier recombination is more dominant, however, it

does not cause the efficiency droop. In the high injection
regime, the Auger recombination is dominant, and the
equation for the current flux density becomes j=N,+N,,"+
c,N,°=c,N,*. At this regime,

a)

This equation applies when c,N,>>1 or (je,2)!3>>1. The
general expression for IQE could be interpolated as

1 @)
oe
Ligh + Uthow

A difference between conventional LED and fin LED is
dependence of current gradient j on the injection level. For
conventional LEDs, the length of the recombination region,
d, is nearly independent of injected current, I. For the fin
LEDs (FIG. 196), d increases with I and the current gradient
j saturates leading to the saturation of the Auger recombi-
nation. For the conventional LED, we obtain the dependen-
cies shown in FIG. 19c. In this graph, as the Auger recom-
bination constant c¢, increases, the IQE declines (top to
bottom). For the case of the fin LED, we assume that at high
injections the electron hole pairs spread out, i.e., d increases
(FIG. 196) and the electron-hole flux gradient j,,, saturates at
acertain value of j,. Therefore, for the high injection regime

5 of a fin LED

@

Tight = ss
ca jo

Then using the interpolation

ne 1 ©)
Uitnightin + Vion:

we obtain the droop-free dependencies at high injection
levels shown in FIG. 19d.

The model highlights the two factors stated above in
improving the IQE at high current densities, namely, the fin
shape facilitating the current gradient saturation and the high
quality of ZnO crystal. In addition, ZnO fins do not host the
threading dislocations originated at the underlying GaN
substrate. This is due to their growth mechanism that gov-
erns the lateral growth in the surface-directed VLS process
versus the epitaxy used in growth of conventional LEDs
Previously ZnO—GaN thin film-based LEDs have shown


US 11,271,137 B2

Sheet 17 of 25

Mar. 8, 2022

U.S. Patent

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U.S. Patent Mar. 8, 2022 Sheet 9 of 25 US 11,271,137 B2

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FIG. 9


US 11,271,137 B2

13

tals. A metal catalyst droplet such as gold (Au) acts as a
nucleation center that leads the in-plane nanocrystal growth.
Integration of n-ZnO/p-GaN nanoLEDs is a complex case of
chaos control because ZnO nanofins grow in six possible
directions according to the C, symmetry of GaN, in contrast,
to simpler two-direction growth on a-sapphire that has a C,
symmetry.

In surface-directed VLS process, although the lattice
structure of the substrate can impose the ultimate boundary
conditions to have a strict control over order of grown
nanocrystals, experimental results show that the growth
kinetics could substantially scramble the Au droplet trajec-
tory on the surface when there are multiple competing
nucleation centers at a given site. This phenomenon often
results in growth of multiple nanowires per site and ran-
domness of directionality (FIG. 13). Control of this chaos
during growth occurs by reducing the number of nucleation
centers (or metal catalyst droplets) per site via high-resolu-
tion lithography.

Microscale patterns (FIG. 13a-b) as large as 3 jum?
typically produce dozens of standing and horizontal nanoc-
rystals per site, where a poor directionality is observed for
the lateral ones. The loss of directionality appears at the
early stage of the lateral growth within a radius of few
microns of the catalyst pattern (FIG. 13c). The origin of this
scrambling effect to the growth competition can be between
free-standing and lateral nanocrystals, where surface collec-
tion areas of nanocrystals for capturing gas phase materials
overlap. Loss of directionality is observed in the lateral

growth of other semiconductors such as ZnO, GaN, or ZnSe 3

on sapphire when large size catalyst patterns used, limiting
their use in scalable device integrations based on the sur-
face-directed VLS.

To enable using microscale catalyst patterns for creating

device quality nanocrystals, we impose control mechanisms. 3

to minimize the undesired growth kinetics affecting direc-
tionality of the nanocrystals. As shown, these fabrication
strategies achieve control to electrically charge 1, 2, ora few
nanocrystals per site on a large scale. In FIG. 13d, the
scrambling of the lateral nanocrystals at the early stage of
the growth is suppressed by reducing the number of free-
standing nanowires via masking part of the Au catalyst
patterns using a benign material such as chromium (Cr) or
silicon oxide (SiO,). This treatment controllably reduces the
active Au catalyst area and quenches most of the free-
standing nanowire growth (FIG. 13e). It reduces competition
with the lateral growth and allows lateral nanocrystals to
predictably grow in their intended crystallographic direc-
tions. In the case of (0001) GaN substrate with six allowed-
directions along its m-directions, nanofins grow in two or
three dominant orientations of [-1010], [-1100], and [10-
10] at the catalyst site (FIG. 13e-/). The laterally grown
nanocrystals are interconnected at the initial catalyst site via
a thick polycrystalline semiconductor film. The defective
layer is eliminated via a chemical etch step (FIG. 13c). The
outcome of these two steps provide isolated nanofins with
sub-200 nm dimensions that are formed at predefined sites
using micropatterning, showing that this method is a high-
resolution but low-cost method for large scale generation of
semiconductor nanostructures. In the case of ZnO nanofins,
hydrochloric acid is used in a wet chemical-etch process to
remove the initial catalyst site and separate the nanofin
crystals (FIG. 13 g, h, i).

To place electrical contacts specifically on nanofins with
certain crystallographic directions at a large scale, specific
group(s) of nanofins were targeted with known orientation
(s). This is possible as the global (translational) and local

S

2

40

14

(orientation) orders of lateral nanocrystals are controlled by
the crystal symmetry of the substrate. Facet passivation is
programmable and carried out via angled-deposition of a
thin dielectric layer along the direction of the nanofins that
are to be fully passivated. An example for the three dominant
directions of ZnO nanofins on GaN is shown in FIG. 137
where directed oxide deposition (FIG. 13K, indicated by
arrow) on nanofins at [-1010] direction resulted in their full
passivation as seen from the cross section of the nanofin in
the inset (coated facets marked with x). The other two
directions of [-1100] and [01-10], also presented in the
insets, are only passivated from one-side. Therefore, for a
population of ZnO nanofins with these three orientations, the
first round of oxide deposition leaves two orientations
electrically accessible and by the 2” round of directed
deposition along another nanofin direction, e.g., [-1100], the
remaining orientation of nanofins, i.c., [01-10] becomes
accessible. A thin layer of conductive indium tin oxide is
deposited as the top contact to highlight the open facets in
contrast to the oxide-coated ones.

Control measures developed in steps 1 and 2 (FIG. 13),
enable the nanocrystals to be receptive of additional layers
for device fabrication using conventional optical lithogra-
phy. Traditional photolithography techniques use two steps
of deposition and etch in fabrication processes. Here, an
additional step forms single crystalline nanostructures com-
mensurate with the deposition and etch steps. In the third
step shown in FIG. 13, a top metal electrode can be
introduced to the open side facet of the nanofins (see FIG.
13i) by depositing the metal layer opposite to that of the
oxide layer. The interface area between metal and semicon-
ductor is large and defined by the width of the metal
electrode (W) and height of the nanowire or nanofin (H)
Conventional techniques for in-situ integration of free-
standing nanowires as nanoLEDs or nanolasers involve
exposing the upper ends of the nanowires via etching a
supporting matrix for receiving a common metal contact
(FIG. 12a). In some conventional methods, free-standing
nanowires are overgrown to merge and form a continuous
upper surface that can receive the top contact. In these
conventional methods, charge carrier injection area is lim-
ited to the small cross-section of the nanowires, causing a
bottleneck in charge transport accompanied by heating and
lower efficiencies than thin film LEDs.

FIG. 14a shows an electroluminescence (EL) spectrum of
this pixel acquired with a calibrated spectrometer with a
resolution of 0.3 nm. Based on the appearance of two intense
emissions at 370 nm, and 380 nm, two main charge recom-
bination channels exist in these p-n heterojunctions. Narrow
full-width at half-maximum (FWHM) of only 5 nm and 18
nm are observed for these emissions, despite the absence of
any charge confinement mechanism such as quantum wells
in such p-n junctions. Energetically, these electronic transi-
tions overlap well with the room temperature cathodolumi-
nescence (CL) of ZnO nanofins/GaN heterostructure (FIG.
14a, filled curve) an indication of charge recombination in
the ZnO side of the heterojunction. The first emission at 368
nm (3.36 eV) is assigned to the free-exciton recombination
within ZnO band gap, while the peak at 379 nm (3.28 eV)
is assigned to donor-bound exciton recombination. The
absence of EL emission at reverse bias revealed negligible
mid-gap defect states in ZnO at the interface in contrast to
the previous reports. The strong ZnO excitonic peak at 368
nm and its comparable intensity with the 379 nm peak is
indicative of lower concentration of donor sites (such as
oxygen) than what is observed in n-type ZnO nanowires
Furthermore, the observation of flow of holes under forward



US 11,271,137 B2

7

densities to form abrupt interfaces for electron-hole recom-
bination and light emission. Alternatively, the same junction
could be used for charge separation and light detection.
Exemplary dopants include silicon and germanium for
n-type doping, and magnesium for p-type doping. According
to an embodiment, substrate 201 includes 700 nm thick
p-doped GaN on 1300 nm thick undoped GaN.

Truncated cuboidal fin 202 is formed on substrate 201 to
form a p-n junction. Exemplary truncated cuboidal fins 202
include a semiconductor such as a third-generation semi-
conductor, e.g,, gallium nitride or zinc oxide. The dopant
concentration of truncated cuboidal fin 202 can be from
undoped (<1x10"! cmTM°) to highly doped (>5x10'® cmTM>). It
should be appreciated that a transverse cross-sectional shape
in a plane parallel to height fin axis 207 and lateral fin axis
206 (e.g., as shown in panel C of FIG. 1 and in FIG. 9) of
truncated cuboidal fin 202 is determined by growth of
laterally-grown nanocrystal 204 on substrate 201 and
approximates a right trapezoid Growth of truncated cuboidal
fin 202 starts at initiation facet 211 in a presence of catalyst
227, and growth of truncated cuboidal fin 202 propagates
along longitudinal fin axis 205 on substrate 201. Growth of
truncated cuboidal fin 202 longitudinally terminates at ter-
minal facet 210. Accordingly, with reference to FIG. 10,
truncated cuboidal fin 202 includes charge injection facet
208 that can be substantially normal to the surface of
substrate 201 on which truncated cuboidal fin 202 forms,
substantially normal to lateral fin axis 206, and substantially
parallel to height fin axis 207. Truncation facet 209 is at an
oblique angle to lateral fin axis 206 and canted toward
charge injection facet 208 in a direction of height fin axis
207.

Laterally-grown nanocrystal 204 can include a gallium
nitride single crystal. Since laterally-grown nanocrystal 204

selectively grows along a crystalline direction on substrate 3

201, longitudinal fin axis 205 of truncated cuboidal fin 202
is disposed along a selected crystal index of substrate 201
Exemplary crystal indexes of substrate 201 along which
laterally-grown nanocrystal 204 grows such that longitudi-
nal fin axis 205 is directed along such index include [-1010],
[-1100}, [01-10], and the like as shown, e.g,, in FIG. 13.

It is contemplated that laterally-grown nanocrystal 204
can include a semiconductor and a dopant. Such dopants
provide a p-n junction interface for recombination of elec-
trons and holes to generate or detect light. Exemplary
dopants include K, Mg, Li, and the like. According to an
embodiment, laterally-grown nanocrystal 204 includes
n-doped II-VI and III-V semiconductors such as ZnO, AIN,
GaN, CdS and the like.

Side-injector 203 is formed on charge injection facet 208
of truncated cuboidal fin 202. Side-injector 203 injects
charges, e.g., electrons 222, into truncation facet 209 as
shown in FIG. 2 or into active layer 217 as shown in FIG.
4. It is contemplated that, instead of electrons 222, side-
injector 203 can inject holes 223 into truncated cuboidal fin
202 or active layer 217. Whether side-injector 203 injects
electrons 222 or holes 223 can depend upon doping of
side-injector 203 relative to other components of light article
200. In this respect, side-injector 203 injects electrons 222
when side-injector 203 is n-doped and injects holes 223
when p-doped. Side-injector 203 can include an electrical
conductor or an electrical semiconductor in which the dop-
ant is disposed.

P-dopants include materials that support transport of holes
223 such as phenylamines, triphenyl-amines, fluorenes, ben-
zidines, and the like. Examples of such p-dopants include:
4,4',4"tris(N-3-methylphenyl-N-phenyl-amino) triph-

30

40

8

enylamine (m-MTDATA), 4.4,4"-tris(N-(2-naphthyl)-N-
phenyl-amino)triphenylamine (2-TNATA), | MeO-TPD
(N.N,N',N'-tetrakis(4-methoxy-phenyl)benzidine), (2,2',7,
7'-tetrakis-(N,N-diphenylamino)-9,9"-spirobifluoren  (spiro-
TTB), _N,N’-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-benzi-
dine, N.N'-bis(naphthalen-1-yl)-N.N'-bis(phenyl)-9,9-spiro-
bifluorene, 9,9-bis[4-(N.N-bis-bipheny|-4-yl-amino)
phenyl]-9H-fluorine, _N,N'-bis(phenanthren-9-yl)-N,N'-bis
(phenyl)-benzidine, 2,2'-bis[N,N-bis(biphenyl-4-y)amino]
9,9-spiro-bifluorene, 1,3,5-tris{4-[bis(9,9-dimethyl-
fluorene-2-yl)amino|pheny!}benzene, _tri(terphenyl-4-yl)
amine, and  N,N'-Bis(naphthalen-1-yl)-N,N'-bis(phenyl)-
benzidine (NPD). The p-dopant can have a reduction
potential from 0 V vs. a ferrocene/ferrocenium redox couple
(referred to as Fe/Fe+) to 0.4 V vs. Fe/Fe+. Reduction
potentials can be considered as measures for a LUMO of a
molecule.

N-dopants include materials that support transport elec-
trons 222 such as phosphorous, arsenic, antimony, alkali
metals (e.g., Li, Cs, and the like), donor-type organic mol-
ecules that can provide increased electron conductivity in
the doped material in comparison with a non-doped mate-
rial, and the like.

Electrons 222 and holes 223 combine in active layer 217
to produce light 221. Active layer 217 can include a quantum
well, a plurality of quantum dots, and the like. Exemplary
quantum wells can include alternating layers of semicon-
ductor material such as alternating layers of InGaN and
GaN. Quantum dots can be disposed in a matrix that
supports production of light 221 from combining electrons
222 and holes 223. Exemplary quantum dots include Group
II-VI compound semiconductor nanocrystals such as CdS,
CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, and HgTe;
Group III-V or IV-VI compound semiconductor nanocrys-
tals such as GaP, GaAs, GaSb, InP, InAs, and InSb; PbS,
PbSe, and PbTe; CulnSe2; metal oxide nanoparticles such as
ZnO, TiO2; or a core-shell structured nanocrystal such as
CdSe/ZnSe, CdSe/ZnS, CdS/ZnSe, CdS/ZnS, ZnSe/ZnS,
InP/ZnS, and ZnO/MgO; and the like. The quantum dots can
be semiconductor nanocrystals that are undoped or doped,
e.g., with a rare earth element such as Eu, Er, Tb, Tm, or Dy,
or doped with a transition metal element such as Mn, Cu,
Ag; ora combination thereof. A thickness of catalyst 227 can
be from 1 nm to 100 nm that is deposited on substrate 201
by a patterning method, e.g., optical lithography, or nano-
imprinting.

Light 221 produced from active layer 217 can have a
wavelength from deep UV to near infrared, specifically from
deep UV to visible, and more specifically from 250 nm to
420 nm.

In an embodiment, side-injector 203 includes an electrical
semiconductor with electrically conductive electrodes, side-
injection source electrode 226, side-injection drain electrode

5 218, and gate electrode 219, are disposed on side-injector

203 in a field-effect transistor light emitting diode configu-
ration. Side-injection source electrode 226, side-injection
drain electrode 218, and gate electrode 219 independently
can include aluminum, copper, titanium, tantalum, tungsten,
molybdenum, chromium, neodymium, scandium, silver,
titanium, or an alloy thereof; a conductive film such as
indium tin oxide (ITO), indium zine oxide (IZO), or the like;
or a laminate thereof. Electrodes (218, 219, 226) indepen-
dently can include a single layer structure or a stacked

5. structure of layers. A thickness of electrodes (218, 219, 226)

independently can be from 10 nm to 200 nm, specifically
from 90 nm to 120 nm.


U.S. Patent Mar. 8, 2022 Sheet 6 of 25 US 11,271,137 B2

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U.S. Patent Mar. 8, 2022 Sheet 24 of 25 US 11,271,137 B2

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FIG. 24


a2 United States Patent

Nikoobakht et al.

US 11,271,137 B2
Mar. 8, 2022

US011271137B2

(10) Patent No.:
(45) Date of Patent:

(54)
(71)

(72)

(73)

(*)

(21)

(22)
(65)

(60)

(51)

(52)

LIGHT ARTICLE

Applicant: Government of the United States of
America, as represented by the
Secretary of Commerce, Gaithersburg,
MD (US)

Inventors: Babak Nikoobakht, Potomac, MD
(US); Robin Paul Hansen, Rockville,

MD (US)

GOVERNMENT OF THE UNITED
STATES OF AMERICA, AS
REPRESENTED BY THE
SECRETARY OF COMMERCE,
Gaithersburg, MD (US)

Assignee:

Notice: Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.C. 154(b) by 49 days.

Appl. No.: 16/804,203

Filed: Feb. 28, 2020

Prior Publication Data
US 2021/0119081 Al Apr. 22, 2021

Related U.S. Application Data

Provisional application No. 62/916,978, filed on Oct.
18, 2019.

Int. Cl.

HOIL 33/24 (2010.01)

HOIL 33/32 (2010.01)

HOIL 33/00 (2010.01)

HOIL 33/06 (2010.01)

B82Y 20/00 (2011.01)

US. Cl.

CPC . HOIL 33/24 (2013.01); HOLL 33/007

(2013.01); HOLL 33/06 (2013.01); HOIL
33/325 (2013.01); B82Y 20/00 (2013.01)

(58) Field of Classification Search
CPC combination set(s) only.
See application file for complete search history.

(56) References Cited
U.S. PATENT DOCUMENTS

2017/0263834 Al* 9/2017 Yamaguchi HOLL 33/62

2017/0359865 Al* 12/2017 Kim HOSB 33/04

OTHER PUBLICATIONS

Nikoobakht, B., et al., “Formation of Planar Arrays of One-
Dimensional p-n Heterojunctions Using Surface-Directed Growth
of Nnowires and Nanowalls”, ACS Nano, 2010, p. 5877-5886, vol
4No 10

* cited by examiner

Primary Examiner —Moin M Rahman
(74) Attorney, Agent, or Firm — Office of Chief Counsel
for National Institute of Standards and Technology

(67) ABSTRACT

A light article includes: a substrate; a truncated cuboidal fin
disposed on the substrate and including: a laterally-grown
nanocrystal including a longitudinal length and a lateral
length that are different; a charge injection facet arranged
along a longitudinal fin axis of the truncated cuboidal fin;
and a truncation facet disposed opposing the charge injec-
tion facet and arranged parallel to the longitudinal fin axis;
a side-injector disposed on the charge injection facet of the
truncated cuboidal fin and that provides electrons to an
active layer; and the active layer interposed between the
side-injector and the substrate and that: receives electrons
from the side-injector: receives holes from the substrate; and
produces light in response to combining the electrons and
the holes.

18 Claims, 25 Drawing Sheets



U.S. Patent Mar. 8, 2022 Sheet 11 of 25 US 11,271,137 B2

212
A B02
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“Lgo1
232
202
225
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A201
212
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| a—_-208
[ >L201

FIG. 11


U.S. Patent Mar. 8, 2022 Sheet 10 of 25 US 11,271,137 B2

FIG. 10


US 11,271,137 B2

11

Light article 200 and processes herein unexpectedly
includes truncated cuboidal fin 202 that is free of threading
dislocation (TD) defects. These defects reduce an efliciency
of LEDs and lasers semiconductors as their dimensions are
miniaturized.

The articles and processes herein are illustrated further by
the following Examples, which are non-limiting.

EXAMPLES

Example 1. Breaking the Limit of Charge Injection
in Nanocrystals: A Facet- and Orientation-Selective
Electrical Charging

Bottom-up nanocrystal growth methods and high-resolu-
tion top-down approaches can generate nanocrystals. In
bottom-up growth, chaos at nanoscale, and in top-down
growth, high cost of nanopatterning prohibited uniform
charging of nanocrystals and scaling nanowire-devices. A
side-facet charge injection design provides power-up of
individual 1D-nanocrystals according to their orientation
and at large scales. Direct measurement of total radiant flux
of nano-light emitting diodes (nanoLEDs) of [-VI/III-V
materials showed a record output power density of 710
W/cm?, 230 times more than that of free-standing nanowires
and 7 times more than thin film conventional LEDs. High
brightness is attributed to effective side-facet charge injec-
tion that provides injection current density of 70 kA/cm?

without decline in output power. Site-specific formation and 3

charging of individual nanocrystals eliminate ultrafine
lithography, making this method economic with impact on
development of nanotechnologies that have remained cost-

prohibitive due to small volumes and high manufacturing

cost.
There is plenty of room at the bottom provided by
controlling placement of miniaturized matter at nanoscale.
The drive for miniaturization is in realization of devices with
higher degree of intelligence and autonomy. Nanoscale
materials include nanowires and one-dimensional (1D-)
nanostructures as a building block, and such can function as
transistors, field emission devices, solar cells, secondary
batteries, chemical sensors, photonic sensors, light sources
for micro displays and smart lighting. These nanotechnolo-
gies have a high cost for controlling order at nanoscale. The
devices and processes in this Example are cost-effective
fabrication strategies that control the chaos at nanoscale.
Fabrication technologies for transitioning microscale light
sources to nanoscale in form of nanodiodes and nanolasers
provide on-chip applications. Technological advance here
includes bandgap engineering using small and wide-band-
gap semiconductors and nanowires or one-dimensional (1D)
nanostructures that have structural tunability in combination
with other low-D materials such as quantum dots (QDs),
quantum wells (QWs), or quantum disks (Qdisks) for UV to
near-infrared light sources, coherent light sources below
diffraction limit and single photon light sources. Integration
of individual nanowires to a complex hierarchy is challeng-
ing due to intrinsic randomness of nanocrystal growth.
Nanopatterning using high-resolution techniques can pro-
vide limited scalability. To overcome these technological
problems, a process for making a light article 200 suppresses
unpredictability in bottom-up growth in an absence of
nanopatterning and providing efficient charge injection to
nanocrystals. The architecture and method of integration
herein provides cost effective and high throughput nanofab-

3

40

&

12

rication of 1D- and 2D-nanocrystals to electronic-photonic
circuitries at a chip scale including optical sources at nano-
and microscale.

FIG. 12(a-b) shows conventional architectures for pow-
ering up free-standing, cylindrical nanowires. In the design
of FIG. 12a, nanowires are integrated into a device by
placing a common top electrical contact on top of the
nanowires, and arrays of edge-emitting nanowire diodes or
electrically-driven arrays of nanowire lasers were made. In
creating such assemblies of nanoLEDs or nanolasers, bot-
tom-up growth methods have been used, while in controlling
uniformity of shape, diameter and spacing of nanowires,
top-down nanofabrication methods have been a must to use.
For in-situ charging of individual free-standing nanowires,
top-down nanofabrication has been the main remedy (FIG.
126). However, its limited scalability has prohibited the
top-contact architecture to create large scale hierarchies for
utilizing or scrutinizing their individual properties. In the
top-contact architecture, the surface area of the metal-
semiconductor interface at the ends of a nanowire is fixed
and cannot be adjusted creating a bottleneck for charge
injection, causing reduced power generation, device heating
and potential instability.

FIG. 12c shows a light article that includes a laterally

5 grown nanocrystal (1) that is facet-specifically passivated

with a dielectric layer (2) to receive a metal electrode (3) for
charge injection to side facet of the nanocrystal where the
nanocrystal has a predictable orientation. As described
below, a charge injection area on the nanocrystal side facet
can be increased to several square microns proportional to
the length (L) and height (H) of the nanocrystal, increasing
injection efliciency and reducing junction heating. Addition-
ally, without high-resolution lithography nanocrystals, with
sub-200 nm dimension are formed that are electrically-
addressable at very large scales (FIG. 12d).

A large-scale side-facet charge injection is shown in the
optical image of FIG. 12e for charging up a linear array of
60 pixels (devices) with a pitch of 120 jum across a 1 cm
length, where each pixel contains 1 to 10 nanofin LEDs.
NanoLEDs are located toward the end of the top metal
contacts and that is why under forward bias, bright spots
appear at the end of the microelectrodes (inset of FIG. 12e)
and FIG. 12/. Tilted view of a representative pixel in FIG.
12g shows each nanoLED (labeled 1) is a ZnO nanofin
laterally grown in [01-10] of p-GaN forming an elongated
p-n heterojunction at its interface with c-plane of GaN. A
ZnO nanofin is first oxide-passivated (labeled 2) from all
facets except one to intentionally form an interface with the
top metal electrode (labeled 3). By controlling nanofins
orientation order, uniform and predictable interfaces can be
made between its side facet and the top contact of the SEM
cross-section shown in FIG. 124. The linewidth of the top
metal contact that defines the metal-semiconductor interface
area can be chosen to be as wide as selected to cover the
entire side-facet of the nanofin.

To selectively place the top metal contacts on a certain
side facet of nanofins, fabrication processes ensured predict-
able formation of a pristine semiconductor surface for an
unimpeded charge injection channel. Lateral epitaxy made
nanowires and nanofins to control the crystallographic direc-
tions of the side facets and an adjustable heterojunction
length relative to free-standing nanowires, Surface-directed
vapor-liquid-solid (VLS) growth was used to grow nanoc-
rystals. The surface-directed VLS growth is a substrate-
assisted nanocrystal growth that provided translational and
rotational orders of nanocrystals on a large-scale, eliminat-
ing architectural disadvantages of free-standing nanocrys-


US 11,271,137 B2

9

Dielectric member 216 is interposed between gate elec-
trode 219 and side-injector 203 and is an insulator with a
high relative dielectric constant. Dielectric member 216 can
include gallium oxide, hafnium oxide, an oxide containing
aluminum and hafnium, oxynitride containing aluminum
and hafnium, an oxide containing silicon and hafnium,
oxynitride containing silicon and hafnium, and the like. A
thickness of dielectric member 216 can be from 2 nm to 200
nm, specifically from 20 nm to 30 nm.

To provide an electrical bias, electrical current, and the
like to side-injector 203 and active layer 217, electrical via
220 can be included in light article 200. Electrical via 220
is electrically conductive and can include aluminum, copper,
titanium, tantalum, tungsten, molybdenum, chromium, neo-
dymium, scandium, silver, titanium, or an alloy thereof.

In making light article 200, several elements are involved.
Catalyst 227 is disposed on substrate 201 in catalyst pattern
228 to form truncated cuboidal fin 202 and can include gold,
copper, silver, and the like. Catalyst pattern 228 can be a
selected size or shapes such as spherical or polygons. In an
embodiment, catalyst 227 and catalyst pattern 228 respec-
tively are gold and a patterned photoresist. Mask 229 can be
disposed on a portion of catalyst 227 to eliminate growth of
laterally-grown nanocrystal 204 on such portion. Mask 229
can be an inert material such as silicon oxide or chromium
with a thickness range of 10 nm to 200 nm.

Passivation layer 224 is disposed on truncated cuboidal
fin 202 to cover a selection portion of truncated cuboidal fin
202 to eliminate formation of side-injector 203 on such

portion of truncated cuboidal fin 202. Passivation layer 224 3

can include an organic layer such as a photoresist or a

dielectric material such as silicon oxide and the like.
Light article 200 can be made in various ways. In an

embodiment, with reference to FIG. 11, a process for making

light article 200 includes: forming catalyst pattern 228 on 3:

substrate 201, the catalyst pattern 228 including catalyst 227
by metal deposition on a patterned photoresist that contains
pattern openings with the shape of rectangle or square;
forming mask 229 on masked portion 230 of catalyst 227
while providing exposed portion 231 of catalyst pattern 228
in an absence of mask 229 on exposed portion 231 of
catalyst pattern 228 by typical photolithography patterning
methods; controllably quenching growth of nanostructures
from masked portion 230 of the catalyst pattern 228 by mask
229 disposed on masked portion 230 of catalyst pattern 228;
propagating catalyst 227 from exposed portion 231 of cata-
lyst pattern 228 along a single crystal index of substrate 201
by lateral nanoepitaxy; forming truncated cuboidal fin 202
selectively along single crystal index 232 of substrate 201 in
the presence of catalyst 227 as catalyst 227 propagates along
single crystal index 232 of substrate 201, such that truncated
cuboidal fin 202 includes: laterally-grown nanocrystal 204
including longitudinal length 213 and lateral length 214 that
are different; charge injection facet 208 arranged along
longitudinal fin axis 205 of truncated cuboidal fin 202,
longitudinal fin axis 205 being disposed along single crystal
index 232; and truncation facet 209 disposed opposing
charge injection facet 208 and arranged parallel to longitu-
dinal fin axis 205, such that in forming truncated cuboidal fin
202 a translation order and orientation order of laterally-
grown nanocrystal 204 is controlled by a crystal symmetry
of substrate 201; subjecting truncated cuboidal fin 202 to
angular-directed passivation by a directed thermal deposi-
tion method such as electron-beam deposition, in which
truncation facet 209 is contacted by passivation composi-
tion, and charge injection facet 208 is not contacted by
passivation composition; forming, from passivation compo-

40

&

0

10

sition, passivation layer 224 on truncation facet 209 in
response to subjecting truncated cuboidal fin 202 to angular-
directed passivation by a directed thermal deposition method
such as electron-beam deposition; subjecting truncated
cuboidal fin 202 to angular-directed deposition as stated
above, in which charge injection facet 208 is contacted by
deposition composition, and truncation facet 209 is not
contacted by deposition composition; and forming, from
deposition composition, side-injector 203 on charge injec-
tion facet 208, by depositing thin semiconductor layers with
proper doping and band gap energies, in response to sub-
jecting truncated cuboidal fin 202 to angular-directed depo-
sition to form light article 200.

The process for making a light article also can include:
forming side-injection drain electrode 218 disposed on side-
injector 203 by photopatterning and directed thermal depo-
sition methods; forming side-injection source electrode 226
disposed on side-injector 203 and in electrical communica-
tion with side-injection drain electrode 218 through side-
injector 203 by photopatterning and directed thermal depo-
sition methods; forming dielectric member 216 disposed on
side-injector 203 between side-injection drain electrode 218
and side-injection source electrode 226 by photopatterning

s and directed thermal deposition methods; and forming gate

electrode 219 disposed on dielectric member 216 by pho-
topatterning and directed thermal deposition methods, such
that: gate electrode 219 is in electrical communication with
side-injection drain electrode 218 and side-injection source
electrode 226 through dielectric member 216; and dielectric
member 216 is interposed between gate electrode 219 and
side-injector 203, wherein side-injector 203 includes a semi-
conducting material

The process for making light article 200 also can include
connecting the devices to individual drivers to power up the
light sources in an individual or array format.

Light article 200 has numerous advantageous and unex-
pected benefits and uses. In an embodiment, with reference
to Example 1 and Example 2, a process for producing light
with light article 200 includes: providing light article 200;
providing electrons 222 to side-injector 203, side-injector
203 disposed on charge injection facet 208 opposing trun-
cation facet 209 of truncated cuboidal fin 202; communi-
cating electrons 222 from side-injector 203 to active layer

5 217; providing holes 223 to substrate 201; communicating

holes 223 from substrate 201 to active layer 217; receiving,
by active layer 217, electrons 222 from side-injector 203 and
holes 223 from substrate 201; combining, in active layer
217, electrons 222 and holes 223; and producing light from
combining electrons 222 and holes 223 in active layer 217.

In an embodiment, as shown in FIG. 8, a plurality of light
articles 200 can be arranged in an array and individually
addressed to selectively produce light from individual light
articles 200. Using the same design, article 200 can be used

5 as a light sensor. The bandgape of the layer 208 can be

adjusted to sensitize truncated cuboidal fin 202 for different
wavelengths ranging from UV, visible and infrared.
Examples of materials for layer 208 is metal silicides
including PtSi, NiSi and the like. The photodetector can
work under no bias, i.e., photovoltaic mode, or could be
operated under a small bias, i.e., photoconductive mode.
Light article 200 and processes disclosed herein have
numerous beneficial uses, including bright light point
sources in micro-displays, smart light sources, nanolasers,

5 and visible light communication. Advantageously, light

article 200 overcomes limitations of technical deficiencies of
conventional planar p-n junctions such as efficiency droop.


US 11,271,137 B2

Sheet 7 of 25

Mar. 8, 2022

U.S. Patent

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U.S. Patent Mar. 8, 2022 Sheet 21 of 25 US 11,271,137 B2

— 7 d t v ¢ t t :
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20 40 60 80 100 120
Temperature (°C)

FIG. 21


US 11,271,137 B2

3

rent of 3 mA with an average turn on voltage of 9V, wherein
an inset shows simultaneous operation of three adjacent
pixels; in panel E 8 light articles as nanoLEDs that were
powered with a top electrode; in panel F a scanning electron
microscope (SEM) image of an oblique view of several light
article as nanofin LEDs epitaxially grown on c-plane of GaN
along its m-directions; and in panel H (top panel) an
FIB-SEM cross-section of adjacent light articles as nanofin
LEDs that received a top contact from their side and (bottom
panel) different layers of light article 200 as a nanofin LED;

FIG. 13 shows in panel A, B, and C non-selective for-
mation of truncated cuboidal fins; in panels D, E, F, G, H,
and I selective formation of a truncated cuboidal fin along a
single crystal index of a substrate in a presence of a catalyst
as the catalyst propagates along the single crystal index of
the substrate; and formation of a light article from a trun-
cated cuboidal fin in panels J, K, and L;

FIG. 14 shows in panel A EL spectra of a group of 8 light
articles as nanoLEDs for an injection current increase from
1 mA to 10 mA, wherein the filled curve is for CL emission
of a ZnO/GaN heterojunction at 2 k eV; panel B shows an
output power and power density versus injection current
density without device cooling; panel C shows an EL peak
at 370 nm redshifted 1.5 nm at 10 mA injection current, and
the 380 nm peak showed no change; panel D shows, from
top to bottom, normalized EL spectra of devices #44 (at 2
mA drive current), #35 (at 2 mA drive current), and #17 (at
10 mA drive current) compared with EL of 14 pixels turned
ON in parallel (at an average 3 mA drive current): panel E
shows a dependence of redshift of the UV EL peaks at 370
nm and 380 nm on a number of operating pixels; panel F
shows an optical image of the nanoLED pixel array with
their 2D EL image in panel G; and panel G, upper part,
shows an EL image of individually operated pixels at

indicated driving currents, wherein the EL spectrum is 3

overlapped with the 2D image to show UV peak positions
and uniformity across different pixels, and the lower part
shows behavior of groups of 4, 7 and 14 pixels, wherein the
latter shows a redshift relative to the rest of the pixels. The
faint color in the 2D map from 400 nm to 430 nm is emitted
photons generated in a p-GaN side of the heterojunction;

FIG. 15 shows aspects of architecture and fabrication
steps for making a light article that includes an n-ZnO
truncated cuboidal fin LED on a p-GaN substrate, wherein
in panel A, a fin LED pixel includes a truncated cuboidal fin
as an n-ZnO fin (1), a dielectric member as a dielectric layer
(2), and a side-injector as an n-metal contact (3); panel B
shows surface-directed ZnO fin epitaxially grown on c-plane
GaN from an Au catalyst pattern via surface-directed VLS
growth process; panel C shows isolated fins formed by
removing the initial catalyst site via photolithography and
wet etch; panel D shows a truncation facet passivated via
photolithography and angled-oxide deposition, wherein an
open facet has an approximate area of HxW, where “H” is
height and “W” is width. The maximum length of W can be
the fin longitudinal length (L); panel E shows a charge
injection facet receives the n-metal contact; and panel F
shows an electron micrograph of a cross-section of a light
article as an LED, wherein an inset shows the truncated
cuboidal fin, n-metal contact side-injector, and GaN sub-
strate;

FIG. 16 shows a light article LED pixel in panel A as an
optical image for a single truncated cuboidal fin with side-
injector 203 electrode on a left side as a p-metal contact and
a marked area of the light article LED under forward bias;
panel B shows an SEM image with different layers of the
pixel and GaN crystallographic directions; and panel C

0

30

40

&

4

shows an optical image of a linear array of light article as
LED pixels, wherein bright spots are fin LED pixels that are
ON, and light vertical lines are positions of p-contact
electrodes relative to n-contacts. ZnO truncated cuboidal
fins grew in [1T00] Gay and [0T10] gay:

FIG. 17 shows electroluminescence and output power of
light articles as fin LEDs, wherein panel A shows a wire-
bonded array of fin LEDs mounted in front of a 44 mm
diameter integrating sphere that is connected to a calibrated
metrology-grade CCD-array spectroradiometer using an
optical fiber bundle. Fin LED pixel (1); chip carrier (2)
mounted on a stage (3); detector (4). Panel B shows a total
spectral radiance flux (W/nm) of a representative pixel
containing 8 light article LEDs as injection current increased
from 1 mA to 10 mA. Each spectrum is an average of five
measurements with a total time of 325 s. UV emissions are
shown at 368.5 nm (3.369 eV) and 378.5 nm (3.280 eV). The
filled spectrum is the cathodoluminescence (CL) of a single
ZnO fin at 2 keV; panel C shows total output power (left
axis) and voltage-current data (right axis) of a representative
pixel containing 3 light article fin LEDs at different injection
currents of 1 mA to 100 mA.

FIG, 18 shows electroluminescence of light articles as fin
LEDs at high current density and heat. Panel A shows a total
spectral radiance flux (W/nm) of a representative pixel
containing 3 fin LEDs as injection current increased from 1
mA to 100 mA. The respective acquisition time at each drive
current was 50 s, 25 s, 10 s, 5s, 2.5 s, 1 s and 0.5 s. Panel
B shows ZnO—GaN band structure. Panel C shows UV
peak position redshifts (in eV) as current increased. The
expanded uncertainty of the measured peak position is less
than 0.5 nm, with coverage factor of k=2. Panel D shows a
change in EL of the fin LED pixel at a low current load of
2 mA as temperature increased from 25° C. to 110° C. using
a temperature-controlled stage. The emission at 420.2 nm
(2.955 eV) due to electron and hole recombination in a side
of GaN does not redshift, but is suppressed as temperature
reaches 110° C. The intensity of the first UV emission
related to electron and hole recombination in the ZnO fin at
368.5 nm (3.369 eV) was nearly constant, but redshified 4.8
nm and nearly overlapped with a second UV peak. Panel E
shows an FDTD simulation of light extraction from a fin
LED viewed from the longitudinal side of the fin. A single
dipole is oriented 45 degrees at the interface. Light rays
leave more from the charge injection facet of the truncated
cuboidal fin, and a model showed about 8% emission from
side facets and 7% from the top facet;

FIG. 19 shows efficiency of light article as fin LEDs at
high current density, wherein panel A shows a normalized
wall-plug efficiency of a fin LED from 1 mA to 100 mA;
panel B shows fin LED charge spreading length “d” at low
and high current injection regimes: panel C shows calculated
IQE versus dimensionless current flux j for conventional
LEDs, wherein dimensionless Auger recombination con-

5 stant c, varies from 0 to 0.6; panel D shows calculated IQE

versus dimensionless current flux j for fin LED, wherein
dimensionless Auger recombination constant c, varies from
0 to 0.6, and a parameter used in the calculation is dimen-
sionless injection current flux

FIG. 20 shows a redshift in UV EL peak at 368 nm of light
articles as fin LEDs as a mount temperature was increased
from 25° C. to 110° C., wherein a pixel included 3 fin LEDs
and was driven at 2 mA of DC current at each temperature;

FIG. 21 shows pixel containing 3 light articles as fin

3 LEDs driven at 2 mA of DC current, wherein impact of

temperature on intensity of EL peak for ZnO at 386 nm (dark
points) and GaN peak at 420 nm. As temperature changed


U.S. Patent Mar. 8, 2022 Sheet 3 of 25 US 11,271,137 B2
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US 11,271,137 B2

Sheet 16 of 25

Mar. 8, 2022

U.S. Patent

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U.S. Patent

Mar. 8,2022 Sheet 2 of 25 US 11,271,137 B2
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US 11,271,137 B2

23

10. The light article of claim 1, wherein the substrate
comprises gallium nitride

11. The light article of claim 1, wherein the active layer
comprises a quantum well,

12. The light article of claim 1, wherein the active layer
comprises a plurality of quantum dots.

13. The light article of claim 1, wherein the laterally-
grown nanocrystal comprises a gallium nitride single crys-
tal; and

the longitudinal fin axis of the truncated cuboidal fin is

disposed along a [1100] index of the substrate.

14. The light article of claim 1, wherein the truncated
cuboidal fin comprises zinc oxide.

15. The light article of claim 1, wherein the side-injector
comprises an electrical conductor.

16. The light article of claim 1, wherein the side-injector
comprises an electrical semiconductor.

17. A light article comprising:

a substrate;

a truncated cuboidal fin disposed on the substrate and

comprising:

a laterally-grown nanocrystal comprising a longitudinal
length and a lateral length that are different:

a charge injection facet arranged along a longitudinal
fin axis of the truncated cuboidal fin; and

a truncation facet disposed opposing the charge injec-
tion facet and arranged parallel to the longitudinal fin
axis:

a side-injector disposed on the charge injection facet of 3

the truncated cuboidal fin;
an active layer interposed between the side-injector and
the substrate;

2

24

a side-injection drain electrode disposed on the side-
injector;
side-injection source electrode disposed on the side-
injector and in electrical communication with the side-
injection drain electrode through the side-injector;
a dielectric member disposed on the side-injector between.
the side-injection drain electrode and the side-injection
source electrode; and
a gate electrode disposed on the dielectric member such
that:
the gate electrode is in electrical communication with
the side-injection drain electrode and the side-injec-
tion source electrode through the dielectric member;
and

the dielectric member is interposed between the gate
electrode and the side-injector;

wherein the side-injector comprises a semiconducting
material.

18. A process for producing light with the light article of

claim 1, the process comprising:

providing electrons to side-injector, side-injector disposed
on charge injection facet opposing truncation facet of
truncated cuboidal fin;

communicating electrons from side-injector to active
layer;

providing holes to substrate;

communicating holes from substrate to active layer;

receiving, by active layer, electrons from side-injector and
holes from substrate;

combining, in active layer, electrons and holes; and

producing light from combining electrons and holes in
active layer.

.


U.S. Patent Mar. 8, 2022 Sheet 25 of 25 US 11,271,137 B2

4.8)

FIG. 25


U.S. Patent

Mar. 8, 2022

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US 11,271,137 B2

15

bias from p-GaN to the ZnO and their recombination in the
nanofin also supports the lower carrier concentration in ZnO.
at the vicinity of its interface with GaN. The second pathway
for electron-hole (“e-h’”) recombination is in the p-GaN side
of the heterojunction that results in the red shoulder seen in
the EL spectra of FIG. 14a. Deconvoluting the electronic
transitions reveals two emissions at about 403 nm and 430
nm that have been attributed to Mg ion acceptor to valence
band.

Fabricated NanoLED pixels under a direct current (DC)
forward bias are bright enough to be visually seen without
using any light collecting optics or reducing the background
light (FIG. 12e). This allowed measurement of their total
radiant flux in a 7 ft diameter integrating sphere. Our
measurements show that at a 10 mA drive current a pixel
containing 8 nanofin LEDs with a total heterojunction length
of 39 wm and a width of 160 nm can generate 718
Wicm?+10%, a power density 7 times more than that of a
commercial 100 W/cm? thin film LED (FIG. 144). This
output power translates to about 1 1 W power per 1 jum of
nanoLED length that is 230 times stronger than the power
density generated by the state-of-art top-facet charge injec-
tion design used in the free-standing nanowire LEDs. As
shown in FIG. 146, using the side-facet charge injection
design and a charge injection area of about 3 um?, can
receive current densities ranging from 70 to 90 kA/cm?. This
is at least ten times more than the previously reported values
in charging free-standing single nanoLED pixels with an
average diameter of 240 nm. As the injection current

increases, the intensity of the two UV peaks and output 3

power increase linearly (FIG. 146) with no obvious shift at
the 379 nm peak (FIG. 14c, dots) indicating the remarkable
efficiency of nanofin LEDs in dissipating self-heating under
an unusually high current density.

Device heat generation can cause a redshift in the LED’s 3

emitting wavelength due to the lattice expansion and band-
gap reduction. Self-heating has been a disadvantage in
powering up nanoLEDs as their packing density on the
increase, resulting in drop in their output power. In our
nanoLEDs, it is noted that as the injection current increase,
the 370 nm ZnO exitonic emission that is more sensitive to
the ZnO lattice temperature shows a slight redshift of about
1.5 nm at 57 kA/cm? that we attribute to the lattice expan-
sion and a subtle Joule heating at the junction. Blueshift in
the UV EL emissions was not observed. Blueshift can be due
to band-filling or piezoelectric field effects that are reported
in GaN-based LEDs, ZnO/GaN film LEDs, or nanowire
heterojunctions. Absence of the blueshift in our nanofin
LEDs is attributed to a reduced polarization-related electric
fields in the nanocrystal due to the side-charge injection to
the non-polar (11-20) facet of ZnO. This is an advantageous
feature in creating sub-200 nm Wurtzite crystals such as
ZnO or GaN as it could suppress or eliminate the polariza-
tion-related electric fields and increase charge recombina-
tion efficiency of nanoscale heterojunctions. Currently, crys-
tals with non-polar facets can be prepared with selective area
growth (SAG) methods in form of nanofins or nanopillars;
however, in addition to the high cost of scaling-up, extension
of threading dislocations (TDs) to the nanocrystals cannot be
eliminated. TD defects are shown to impact the radiative
recombination efficiency in the device active region.
Statistical information can be extracted using the archi-
tecture because nanofins can be powered in different regions
along the device array. This can occur while current mea-
surements are either performed on single nanoLEDs
sampled from a large group or on large ensembles. In FIG.
14d, EL spectra of pixel #17 with 8 nanofin LEDs is

0

40

0

16

compared with pixels #35 and #44 containing single
nanoLEDs that are spaced 2.16 mm and 3.24 mm apart.
These three pixels show similar UV peaks at 368 nm and
379 nm demonstrating the uniformity in chemical structures
of the formed nanoscale heterojunctions irrespective of the
number and length of nanofins and their spatial locations. As
seen in device #17, at an injection current of 10 mA,
corresponding to a 56 kA/em?, the exitonic peak at 368 nm
only redshifts about 1.5 nm relative to single nanofin LEDs
#35 and #44 operated at 2 mA. This is an example of
detecting a microscale heating effect in nanoLEDs that
corresponds to a 46° C. rise in temperature. Here, an
injection current regime leads to heating and droop that can
reduce LED output power, but our results shows the poten-
tial of this charge injection architecture for driving
nanoLEDs in the absence of cooling mechanisms or pulsed-
biasing. This figure also compares the local heating effect of
pixel #17 with a group of 14 pixels (~220 nanofins) oper-
ating in parallel for a similar duration of time. Although the
average driving current is 3 mA, we observe a 4 nm redshift
in the more sensitive exitonic emission at 370 nm, corre-
sponding to a temperature rise of 123° C. No suppression of
this peak’s intensity is observed, illustrating the strength of
ZnO as a material for high temperature LED applications
The 4 nm redshift is assigned to a global heating due to
simultaneous operation of 14 pixels across the 1 cm chip.

During operation of individual pixels as shown in FIG.
14e, no discernable wavelength shift was observed; how-
ever, the increase in the redshift becomes detectable as the
number of operating pixels increased. For instance, redshifts
of 1 nm and 2.5 nm at the 370 nm peak was measured,
respectively, when four and seven pixels were turned ON.
The peak at 380 nm showed the same trend but with a
smaller redshift as seen in the figure. We attribute the global
heat accumulation on the chip, primarily, to the poor heat
conduction of the thermally-insulative chip carrier package
used in this experiment. By constructing a two-dimensional
(2D) EL map of nanoLED pixels across the 1 cm chip, our
results can be used to deduce valuable analytical information
such as spatial uniformity of chemical composition/structure
of the ZnO/GaN heterojunctions or physical properties such
as device heating or contact resistance on spectral charac-
teristics of the nanoLEDs. As evident in this map, appear-
ance of nearly identical UV peak energies at 370 nm and 380
nm (red curve) for all pixels demonstrate the high quality of
ZnO nanocrystal over the entire chip.

Example 2. Droop-Free Fin Light-Emitting Diodes
(LEDs)

Efficiency droop refers to a decline in brightness of LEDs
at high electrical currents and is a technological barrier for
realization of high-brightness LEDs. We present a fin LED
architecture that eliminates efliciency droop. These fin LED

5 nanoscale heterojunctions can sustain record current densi-

ties of more than 1 million A/cm, 10000 times more than
what is attainable in conventional LEDs and junction tem-
peratures over 340° C., about 200° more than allowed
temperatures in typical LEDs, without any decline in efli-
ciency. At estimated 15% light extraction efficiency, fin
LEDs generate an output power density of 45 W/cm? at 100
mA, comparable to planar LED performance and a factor of
10 higher than free-standing nano LEDs. Modeling suggests
that spreading of the electron-hole recombination region in

5 fin LEDs at high injection levels suppresses the non-radia-

tive Auger recombination processes. The fin geometry is
estimated to result in at least 10 to 100 times brighter LEDs,


US 11,271,137 B2

5

from 25° C. to 110° C., for ZnO, emission intensity first
showed an increase, then reached a terminal value that
matched its initial value, and for the GaN peak, emission
intensity decreased as temperature increased;

FIG. 22 shows a graph of IQE versus wn, for c, from 0
to 0.6 for a light article:

FIG. 23 shows a graph of IQE versus j for a low injection
case for a light article;

FIG. 24 shows a graph of IQE vs. dimensionless current
flux j for conventional LEDs, wherein dimensionless Auger
recombination constant c, varied from 0 to 0.6 at a step
increment of 0.1; and

FIG. 25 shows a graph of IQE vs. dimensionless current
flux j for a light article as a fin LED, wherein dimensionless
Auger recombination constant c, varied from 0 to 0.6 at a
step increment of 0.1, and a parameter used in the calcula-
tion was dimensionless injection current flux j,=5:

DETAILED DESCRIPTION

A detailed description of one or more embodiments is
presented herein by way of exemplification and not limita-
tion.

It has been discovered that a light article herein can
include uniformly charged nanocrystals so that large area
interfaces per nanocrystal can be formed for electrically
powering or operating such nanocrystals with metal-inter-
faces, including metal-semiconductor and semiconductor-
semiconductor. The light article is structurally uniform to
provide nanodevices such a nano light emitting diode (na-
noLED) in which, in an array of such light articles, the light
articles have identical electro-optical properties on very
large areas. Advantageously, the light article is made by
facet-selective passivation of nanocrystals to provide facet-

selective charge injection. As a result, high-performance 3

nanoscale light emitting diodes, lasers, and transistors can be
fabricated that provide a broad range of applications from
deep-ultraviolet laser sources to detectors for trace detection
of chemicals.

Making the light article can occur by forming individual
nanowires in-plane of a surface a substrate with controlled
orientation and location, and the resulting light article can be
electrically powered. With light articles selectively arranged
ona substrate, a uniformly luminous interface can be formed
in which the light article have similar electro-optical prop-
erties. Beneficially, embodiments include selectively choos-
ing a nanocrystal facet for metallization or overgrowth with
another semiconductor thereon. Moreover, articles and pro-
cesses herein overcome conventional technological limits of
scale production of second generation or third generation
semiconductor (non-silicon based) devices.

In an embodiment with reference to FIG. 1, FIG. 2, FIG.
3, and FIG. 4, light article 200 includes substrate 201;
truncated cuboidal fin 202 disposed on substrate 201 and
including: laterally-grown nanocrystal 204 that includes
longitudinal length 213 and lateral length 214 that are
different; charge injection facet 208 arranged along longi-
tudinal fin axis 205 of truncated cuboidal fin 202; and
truncation facet 209 disposed opposing charge injection
facet 208 and arranged parallel to longitudinal fin axis 205;
side-injector 203 disposed on charge injection facet 208 of
truncated cuboidal fin 202 and that provides electrons 222 to
active layer 217; and active layer 217 interposed between
side-injector 203 and substrate 201 and that: receives elec-
trons 222 from side-injector 203; receives holes 223 from
substrate 201; and produces light 221 in response to com-
bining electrons 222 and holes 223. Truncated cuboidal fin

S

20

30

40

&

6

202 includes initiation facet 211 disposed along lateral fin
axis 206 of truncated cuboidal fin 202 and from which
charge injection facet 208 and truncation facet 209 propa-
gate during growth. Truncated cuboidal fin 202 further
includes terminal facet 210 disposed parallel to lateral fin
axis 206 of truncated cuboidal fin 202 and at which charge
injection facet 208 and truncation facet 209 terminate along
longitudinal fin axis 205 during growth. Truncated cuboidal
fin 202 also includes top facet 212 disposed parallel to
longitudinal fin axis 205 of truncated cuboidal fin 202 and at
which charge injection facet 208 and truncation facet 209
terminate along height fin axis 207 of truncated cuboidal fin
202 during growth.

According to an embodiment, as shown in FIG. 2, active
layer 217 is interposed between truncated cuboidal fin 202
and substrate 201. In some embodiments, as shown in FIG.
4, active layer 217 is interposed between truncated cuboidal
fin 202 and side-injector 203.

In an embodiment, with reference to FIG. 5 and FIG. 6,
light article 200 includes electrical via 220 disposed on
side-injector 203 and electrical via 220 disposed on substrate
201

In an embodiment, with reference to FIG. 7, light article
200 includes side-injection drain electrode 218 disposed on
side-injector 203; side-injection source electrode 226 dis-
posed on side-injector 203 and in electrical communication
with side-injection drain electrode 218 through side-injector
203; dielectric member 216 disposed on side-injector 203
between side-injection drain electrode 218 and side-injec-
tion source electrode 226; and gate electrode 219 disposed
on dielectric member 216. In this manner gate electrode 219
is in electrical communication with side-injection drain
electrode 218 and side-injection source electrode 226
through dielectric member 216. Dielectric member 216 is
interposed between gate electrode 219 and side-injector 203,
wherein side-injector 203 includes a semiconducting mate-
rial.

Light article 200 includes substrate 201 and structurally
supports various components of light article 200 such as
truncated cuboidal fin 202. Exemplary substrata 201 include
a material that can communicate electrons or electron holes
such as a semiconductor (e.g., a third generation semicon-
ductor such as gallium nitride GaN), silicon carbide (SiC),
aluminum nitride (AIN), gallium nitride (GaN), diamond, or
zinc oxide (ZnO)), a material that is electrically insulating
(e.g, glass, ceramic, polymer, and the like), and the like.
Moreover, substrate 201 can include a p- or n-doped semi-
conductor layer with dopant concentration, e.g., of 5x10'7
cmTM or stack of quantum wells (QWs) including one to
several QWs. A thickness of substrate 201 can be from 10
nm to 3000 nm, specifically from 200 nm to 700 nm, and
more specifically 700 nm. This layer could be grown over an
undoped semiconductor as a supporting substrate that can be
500 nm to 2000 nm. The undoped supporting layer can be

5 grown on even a thicker substrate such as sapphire or silicon

wafer with a thickness range of 100 jim to 500 jum. Longi-
tudinal length 213 of truncated cuboidal fin 202 along
longitudinal fin axis 205 can be from 100 nm to 100 ym,
specifically from 3 jum to 40 um, and more specifically about
5 um, Lateral length 214 of truncated cuboidal fin 202 along
lateral fin axis 206 can be from 50 nm to 1000 nm,
specifically from 160 nm to 220 nm. Height length 215 of
truncated cuboidal fin 202 along height fin axis 207 can be
from 50 nm to 4000 nm, specifically from 1000 nm to 2000

5 nm, and more specifically from 1100 nm to 1200 nm. It is

contemplated that substrate 201 can include a semiconductor
and a dopant. Such dopants provide electron and hole


U.S. Patent Mar. 8, 2022 Sheet 12 of 25 US 11,271,137 B2

SNE

FIG. 12


271,137 B2

Sheet 15 of 25 US 11

Mar. 8, 2022

U.S. Patent

ST DM