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Gallium Nitride-based Compound Semiconductor Multilayer Structure And Production Method Thereof Inventor Store
Patents sorted by company.	10/05/06 | Class 257 Monitor | RSS | Browse: Prev - Next Gallium nitride-based compound semiconductor multilayer structure and production method thereof Abstract: The object of the present invention is to provide a gallium nitride-based compound semiconductor multilayer structure useful for manufacturing a gallium nitride-based compound semiconductor light-emitting device which requires a low operating voltage and from which a good emission output can be obtained. The present gallium nitride-based compound semiconductor multilayer structure comprises a substrate having thereon an n-type layer, a light-emitting layer and a p-type layer, the light-emitting layer having a multiple quantum well structure in which a well layer and a barrier layer are alternately stacked repeatedly and the light-emitting layer being provided between the n-type layer and the p-type layer, wherein the well layers consisting of the multiple quantum well structure comprise a well layer having an ununiform thickness and a well layer having a uniform thickness. ...
Agent: Sughrue Mion, PLLC - Washington, DC, USInventors: Hisao Sato, Hisayuki MikiUSPTO Applicaton #: #20060219998 - Class: 257012000 (USPTO) - 10/05/06 - Class 257 Related Patent Categories: Active Solid-state Devices (e.g., Transistors, Solid-state Diodes), Thin Active Physical Layer Which Is (1) An Active Potential Well Layer Thin Enough To Establish Discrete Quantum Energy Levels Or (2) An Active Barrier Layer Thin Enough To Permit Quantum Mechanical Tunneling Or (3) An Active Layer Thin Enough To Permit Carrier Transmission With Substantially No Scattering (e.g., Superlattice Quantum Well, Or Ballistic Transport Device), HeterojunctionThe Patent Description & Claims data below is from USPTO Patent Application 20060219998, Gallium nitride-based compound semiconductor multilayer structure and production method thereof.Allium Gallium CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is an application filed under 35 U.S.C.
.sctn.111(a) claiming benefit, pursuant to 35 U.S.C. .sctn.119(e)(1), of
the filing date of the Provisional Application No. 60/670,236 filed on
Apr. 12, 2005, pursuant to 35 U.S.C. .sctn.111(b).
[0002] The present invention relates to a gallium nitride-based compound
semiconductor multilayer structure useful for producing a high-power
light-emitting device which emits ultraviolet to blue light, or green
light, and to a method for producing the semiconductor multilayer
[0003] In recent years, gallium nitride-based compound semiconductors have
become of interest as materials for producing a light-emitting device
which emits light of short wavelength. Generally, a gallium nitride-based
compound semiconductor is grown on a substrate made of an oxide crystal
such as a sapphire single crystal, a silicon carbide single crystal, or a
Group III-V compound single crystal, through a method such as
metal-organic chemical vapor deposition (MOCVD), molecular-beam epitaxy
(MBE), or hydride vapor phase epitaxy (HVPE).
[0004] At present, the crystal growth method that is most widely employed
in the industry includes growing a semiconductor crystal on a substrate
such as sapphire, SiC, GaN, or AlN, through metal-organic chemical vapor
deposition (MOCVD). Specifically, an n-type layer, a light-emitting
layer, and a p-type layer are grown on the aforementioned substrate
placed in a reactor tube, by use of a Group III organometallic compound
and a Group V source gas at about 700.degree. C. to about 1,200.degree.
[0005] After growth of the above layers, a negative electrode is formed on
the substrate or the n-type layer, and a positive electrode is formed on
the p-type layer, whereby a light-emitting device is fabricated.
[0006] Conventionally, such a light-emitting layer is formed from InGaN
whose composition is controlled so as to modulate the light emission
wavelength. The active layer is sandwiched by layers having a bandgap
higher than that of InGaN, thereby forming a double-hetero structure, or
is incorporated into a multiple quantum well structure on the basis of
the quantum well effect.
[0007] In a gallium nitride-based compound semiconductor light-emitting
device having a light-emitting layer of a multiple quantum well
structure, when the thickness of a well layer is adjusted to 2 to 3 nm,
satisfactory output is attained, but a problematically high operating
voltage is required. In contrast, when the thickness of the well layer is
2 nm or less, the operating voltage is lowered, but the output is poor.
[0008] Further, a quantum dot structure as described below, in which
light-emitting layers are formed in a dot form, is suggested to improve
the emission output.
[0009] For example, in Japanese Laid-Open Patent Application (kokai) No.
10-79501, Japanese Laid-Open Patent Application (kokai) No. 11-354839,
etc., a light-emitting device containing a light-emitting layer having a
quantum dot structure is disclosed. The quantum dot structure is formed
according to the anti-surfactant effect. According to Japanese Laid-Open
Patent Application (kokai) No. 11-354839, the size of each light-emitting
device is preferably such that 0.5 nm.ltoreq.height.ltoreq.50 nm, 0.5
nm.ltoreq.width.ltoreq.200 nm, and
10.sup.6.ltoreq.density.ltoreq.10.sup.13 cm.sup.-2. In examples, the
light-emitting device having a height of 6 nm and a width of 40 nm is
[0010] However, a part which is not covered with quantum dots is a region
having an extremely low resistance in comparison with a dot region,
whereby the current is preferentially applied thereto and the non-dot
part does not contribute to light-emission. Therefore, the quantum dot
structure thus suggested has a problem that the emission output with
respect to the applied current is decreased as a whole, although the
emission efficiency of each light-emitting dot is improved.
[0011] Japanese Laid-Open Patent Application (kokai) No. 2001-68733
discloses a quantum box structure containing In. According to Japanese
Laid-Open Patent Application (kokai) No. 2001-68733, the quantum box
structure is formed by annealing, in hydrogen, a quantum well structure
once produced, whereby the well layer is sublimated. In examples, the
quantum box has a size of not more than 200 .ANG., for example, the size
of 20 .ANG..times.20 .ANG..times.20 .ANG.. The density of the
light-emitting box is not defined. However, it can be seen from the
drawings that the area which is covered with the light-emitting box is
the same as or smaller than the area which is not covered with the
light-emitting box.
[0012] In short, in these technologies, it is defined that the region
where no quantum dot or quantum box is formed has a structure where no
dot or box is formed. Therefore, the region where no quantum dot or
quantum box is formed is a region having an extremely low resistance in
comparison with the region where a quantum dot or a quantum box is
formed, whereby the current is preferentially applied to the region where
no quantum dot or quantum box is formed.
[0013] The structure, in which no light-emitting elements are provided in
a region not covered with a dot or a box, has a problem that the emission
output is decreased although the operating voltage is effectively
decreased, and it cannot be practically used.
[0014] Japanese Laid-Open Patent Application (kokai) No. 2001-68733 also
discloses that a quantum box structure is fabricated by forming a
conventional quantum well structure and annealing the structure in
hydrogen, thereby decomposing an InGaN crystal provided on through-hole
dislocations. However, annealing a quantum well structure in hydrogen
induces release of In from a portion intended to serve as a quantum box
structure, thereby blue-shifting the emission wavelength, which is not
[0015] Also, in US Patent Application Publication No. US2003/0160229A1, a
light-emitting layer having a multiple quantum well structure in which
the thickness of the well layer is partially changed is suggested to
obtain a highly efficient light-emission. In the specification thereof,
at least from the attached drawings, it is found that all the well layers
are irregular in thickness.
[0016] The object of the present invention is to provide a gallium
nitride-based compound semiconductor multilayer structure useful for
manufacturing a gallium nitride-based compound semiconductor
light-emitting device which requires a low operating voltage and from
which a good emission output can be obtained.
[0017] The present invention provides the following.
[0018] (1) A gallium nitride-based compound semiconductor multilayer
structure comprising a substrate having thereon a n-type layer, a
light-emitting layer and a p-type layer, the light-emitting layer having
a multiple quantum well structure in which a well layer and a barrier
layer are alternately stacked repeatedly and the light-emitting layer
being provided between the n-type layer and the p-type layer, wherein the
well layers consisting of the multiple quantum well structure comprise a
well layer having an ununiform thickness and a well layer having a
[0019] (2) The gallium nitride-based compound semiconductor multilayer
structure according to (1) above, wherein the thickness of the well layer
closest to the p-type layer is uniform.
[0020] (3) The gallium nitride-based compound semiconductor multilayer
structure according to (1) or (2) above, wherein the thickness of the
well layer closest to the n-type layer is uniform.
[0021] (4) The gallium nitride-based compound semiconductor multilayer
structure according to any one of (1) to (3) above, wherein the thickness
of a well layer having a uniform thickness is 1.8 to 5 nm.
[0022] (5) The gallium nitride-based compound semiconductor multilayer
structure according to any one of (1) to (4) above, wherein the thickness
of a thin part of a well layer having an ununiform thickness is not more
than 2.7 nm.
[0023] (6) The gallium nitride-based compound semiconductor multilayer
structure according to any one of (1) to (5) above, wherein the multiple
quantum well structure comprises 3 to 10 stacks of the well layer and the
[0024] (7) The gallium nitride-based compound semiconductor multilayer
structure according to any one of (1) to (6) above, wherein the barrier
layer comprises a gallium nitride-based compound semiconductor selected
from the group consisting of GaN, AlGaN and InGaN having a In ratio
smaller than that of InGaN which forms the well layer.
[0025] (8) The gallium nitride-based compound semiconductor multilayer
structure according to (7) above, wherein the barrier layer comprises
[0026] (9) The gallium nitride-based compound semiconductor multilayer
structure according to any one of (1) to (8) above, wherein the barrier
layer contains a dopant.
[0027] (10) The gallium nitride-based compound semiconductor multilayer
structure according to (9) above, wherein the dopant is at least one
selected from the group consisting of C, Si, Ge, Sn, Pb, O, S, Se, Te,
Po, Be, Mg, Ca, Sr, Ba and Ra.
[0028] (11) The gallium nitride-based compound semiconductor multilayer
structure according to (9) or
[0029] (10) above, wherein the concentration of the dopant is from
1.times.10.sup.17 to 1.times.10.sup.18 cm.sup.-3.
[0030] (12) The gallium nitride-based compound semiconductor multilayer
structure according to any one of (1) to (11) above, wherein the
thickness of the barrier layer is from 7 to 50 nm.
[0031] (13) The gallium nitride-based compound semiconductor multilayer
structure according to (12) above, wherein the thickness of the barrier
layer is at least 14 nm.
[0032] (14) The gallium nitride-based compound semiconductor multilayer
structure according to any one of (1) to (13) above, wherein the well
layer contains In.
[0033] (15) The gallium nitride-based compound semiconductor multilayer
structure according to (14) above, wherein a thin layer containing no In
is provided on at least the substrate side of the barrier layer.
[0034] (16) A gallium nitride-based compound semiconductor light-emitting
device, wherein the device has a negative electrode and a positive
electrode, the negative electrode and the positive electrode being
provided on the n-type layer and the p-type layer of a gallium
nitride-based compound semiconductor multilayer structure according to
any one of (1) to (15) above, respectively.
[0035] (17) A lamp in which the gallium nitride-based compound
semiconductor light-emitting device according to (16) above is used.
[0036] (18) A method for manufacturing the gallium nitride-based compound
semiconductor multilayer structure according to any one of (1) to (15)
above, wherein after a well layer is formed, the layer thus formed is
partly decomposed or sublimated to provide an ununiform thickness.
[0037] (19) The method for manufacturing a gallium nitride-based compound
semiconductor multilayer structure, according to (18) above, wherein the
substrate temperature T1 during forming the well layer and the substrate
temperature T2 during decomposing or sublimating a part of the well layer
satisfy the formula: T1.ltoreq.T2.
[0038] (20) The method for manufacturing a gallium nitride-based compound
semiconductor multilayer structure, according to (18) or (19) above,
wherein the decomposition or sublimation of a part of the well layer is
conducted in an atmosphere containing a nitrogen source and containing no
III group metal source.
[0039] (21) The method for manufacturing a gallium nitride-based compound
semiconductor multilayer structure, according to any one of (18) to (20)
above, wherein the decomposition or sublimation of a part of the well
layer is conducted during forming the barrier layer.
[0040] According to the present invention, whose main subject is to have a
uniform thickness in well layers of a multiple quantum well structure
which forms a light-emitting layer, a gallium nitride-based compound
semiconductor light-emitting device which maintains a good emission
output, and exhibits a low operating voltage, can be obtained.
[0041] Further, a gallium nitride-based compound semiconductor
light-emitting device obtained by the present invention exhibits less
deterioration of the peak inverse voltage characteristics.
[0042] The light emitted from the well layer can be prevented from being
shifted to a shorter wavelength, by forming a well layer having an
ununiform thickness in the presence of a nitrogen source.
[0043] FIG. 1 is a schematic view of a cross-section of the gallium
nitride-based compound semiconductor multilayer structure fabricated in
[0044] FIG. 2 is a schematic view of an electrode configuration of the
light-emitting diode fabricated in Example and Comparative Example.
[0045] FIG. 3 is an exemplary cross-section TEM photograph of the gallium
[0046] FIG. 4 is another exemplary cross-section TEM photograph of the
gallium nitride-based compound semiconductor multilayer structure
fabricated in Example 1.
[0047] FIG. 5 is another exemplary cross-section TEM photograph of the
[0048] FIG. 6 is another exemplary cross-section TEM photograph of the
[0049] FIG. 7 is another exemplary cross-section TEM photograph of the
[0050] FIG. 8 is another exemplary cross-section TEM photograph of the
[0051] FIG. 9 is another exemplary cross-section TEM photograph of the
[0052] FIG. 10 is another exemplary cross-section TEM photograph of the
[0053] FIG. 11 is another exemplary cross-section TEM photograph of the
[0054] FIG. 12 is another exemplary cross-section TEM photograph of the
[0055] FIG. 13 is another exemplary cross-section TEM photograph of the
[0056] FIG. 14 is another exemplary cross-section TEM photograph of the
[0057] FIG. 15 is another exemplary cross-section TEM photograph of the
[0058] FIG. 16 is another exemplary cross-section TEM photograph of the
[0059] FIG. 17 is another exemplary cross-section TEM photograph of the
[0060] FIG. 18 is another exemplary cross-section TEM photograph of the
[0061] The n-type layer, light-emitting layer, and p-type layer of a
gallium nitride-based compound semiconductor light-emitting device are
widely known to be formed from a variety of gallium nitride-based
compound semiconductors represented by formula:
Al.sub.xIn.sub.yGa.sub.1-x-yN (0.ltoreq.x<1; 0.ltoreq.y<1;
0.ltoreq.x+y<1). No particular limitation is imposed on the gallium
nitride-based compound semiconductor for forming the n-type layer, the
light-emitting layer, and the p-type layer employed in the present
invention, and a variety of gallium nitride-based compound semiconductors
represented by formula: Al.sub.xIn.sub.yGa.sub.1-x-yN (0.ltoreq.x<1;
0.ltoreq.y<1; 0.ltoreq.x+y<1) may also be employed.
[0062] No particular limitation is imposed on the type of the substrate,
and there may be employed conventionally known substrate species such as
sapphire, SiC, GaP, GaAs, Si, ZnO, and GaN.
[0063] In order to form a gallium nitride-based compound semiconductor on
any of the above substrates (excepting a GaN substrate) which are not
theoretically lattice-matched with the gallium nitride-based compound, a
low-temperature buffer method (disclosed in, for example, Japanese Patent
3026087 and Japanese Laid-Open Patent Application (kokai) No. 4-297023)
and a lattice-mismatch crystal epitaxial growth technique (disclosed in,
for example, Japanese Laid-Open Patent Application (kokai) No.
2003-243302), which is called "seeding process (SP)," may be employed.
Among these methods, from the viewpoint of productivity and other
factors, the SP method is a particularly advantageous lattice-mismatch
crystal epitaxial growth technique which can produce AlN crystal film at
such a high temperature that enables formation of GaN crystals.
[0064] When a lattice-mismatch crystal epitaxial growth technique such as
a low-temperature buffer method or an SP method is employed, the gallium
nitride-based compound semiconductor for an undercoat layer on which a
semiconductor is formed is preferably GaN which is undoped or lightly
doped (dopant concentration is about 5.times.10.sup.17 cm.sup.-3). The
undercoat layer preferably has a thickness of 1 to 20 .mu.m, more
preferably 5 to 15 .mu.m. An n-type layer, a light-emitting layer and a
p-type layer are stacked on the undercoat layer in this order.
[0065] In the present invention, the well layers included in a multiple
quantum well structure for forming a light-emitting layer always comprise
a well layer having a uniform thickness and a well layer having an
ununiform thickness. In the present invention, "uniform thickness" means
that the thicknesses of all parts of a layer are included in the range of
.+-.10%, preferably .+-.7%, with respect to the average thickness.
"Ununiform thickness" means that the thickness of at least a part of a
layer is not in the range of .+-.10% of the average thickness. "Average
thickness" is an arithmetic average of the maximum thickness and the
minimum thickness of the layer. In a well layer having an ununiform
thickness, a part having a thickness larger than the average thickness is
designated to "a thick part" and a part having a thickness smaller than
the average thickness is designated to "a thin part".
[0066] Whether the thickness of each well layer is uniform or ununiform is
measured and determined by a cross-sectional TEM photograph of a gallium
nitride-based compound semiconductor. For example, the variation in the
thicknesses of each well layer can be measured by observing the
cross-section in a TEM photograph of 200,000 to 2,000,000 magnifications.
FIGS. 3 to 10 are cross-sectional TEM photographs of 1,000,000
magnifications of a chip produced according to Example 1. The thickness
can be calculated based on the magnification. The maximum thickness and
the minimum thickness of each well layer in each figure are described in
the table attached to each figure. Whether the thickness of each well
layer is uniform or ununiform can be determined from the maximum
thickness and the minimum thickness of each well layer calculated from
the eight figures. A thick part has a thickness larger than the average
thickness which is an arithmetic average of the maximum thickness and the
minimum thickness, and a thin part has a thickness smaller than the
average thickness. In the drawings, A represents a thick part and B
represents a thin part. The maximum thickness and the minimum thickness
of each well layer is calculated by observing plural parts of a
cross-sectional TEM photograph at, for example, least eight parts at a
pitch of 20 .mu.m.
[0067] When the thicknesses of all well layers in the multiple quantum
well structure forming a light-emitting layer are ununiform, in
comparison with the case in which the thicknesses of all well layers are
uniform, the operating voltage is lower and the emission output is the
same or lower. However, if the thicknesses of all well layers are not
ununiform and the thickness of a part of well layers is uniform, the
operating voltage is decreased and the emission output is increased. The
reason for the above is not known. Particularly, when the thickness of
the well layer closest to the p-type layer or the n-type layer is
uniform, the emission output is effectively increased. When the
thicknesses of the well layer closest to the p-type layer and of the well
layer closest to the n-type layer are uniform, the emission output is
effectively increased but the operating voltage is not effectively
decreased. Therefore, well layers having uniform thicknesses can include
the well layer closest to the p-type layer and the well layer closest to
the n-type layer, and preferably include one of them. It is particularly
preferable to have the well layer closest to the p-type layer as a well
layer having an uniform thickness.
[0068] If the number of well layers having uniform thicknesses is
increased, the operating voltage is not effectively decreased.
Accordingly, the number of well layers having uniform thicknesses is at
least 1 and preferably not more than 60%, more preferably not more than
40%, of the total number of well layers.
[0069] The thickness of a well layer having a uniform thickness is
preferably 1.8 to 5 nm. If the thickness is out of this range, the
emission output is decreased. The thickness is more preferably in the
range of 2.0 to 3.5 nm.
[0070] The thickness of a thick part of a well layer having an ununiform
thickness is preferably about 1.8 to 5 nm. If the thickness of the thick
part is out of this range, the emission output is decreased. The
thickness is more preferably in the range of 2.3 to 3.5 nm. The width of
the thick part is preferably 10 to 5,000 nm, more preferably 20 to 1,000
[0071] The area of the thick part preferably accounts for 30 to 90% the
entire area of the well layer. When the area falls within the range,
lowering of operating voltage and increasing emission output can be
attained. More preferably, the area of the thick part accounts for 60 to
90% the entire area of the well layer. The area ratio of the thick part
and that of the thin part can be calculated from the width as measured
from a cross-section TEM photograph.
[0072] The thin part has a width of 1 to 200 nm, more preferably 5 to 150
[0073] The difference in thickness between the thick part and the thin
part preferably falls within a range of about 1 to 3 nm. The thickness of
the thin part preferably falls within a range of 1.0 to 2.7 nm.
[0074] The well layer may include a thin part having a thickness of 0. In
other words, the well layer may include an area that is not covered with
a well layer. However, such an area is preferably narrow in order to
prevent lowering of emission output. Thus, the area preferably accounts
for 30% or less the entire area of the well layer, more preferably 20% or
less, particularly preferably 10% or less. The area ratio can be
calculated from the width as measured from a cross-section TEM
[0075] The well layer is preferably formed of a gallium nitride-based
compound semiconductor containing In, because the In-containing gallium
nitride-based compound semiconductor is of a crystal for readily
attaining a structure having a thick part and a thin part. In addition,
the In-containing gallium nitride-based compound semiconductor can emit
high-intensity light in a blue light region.
[0076] The barrier layer may be formed of GaN, AlGaN, and InGaN which has
an In content lower than that of InGaN forming a well layer. Among them,
GaN is preferred.
[0077] The barrier layer may comprise a stacked structure of plural
layers. When the well layer is a gallium nitride-based compound
semiconductor containing In, it is preferable to provide a thin layer
containing no In on at least one side of the barrier layer attached to
the well layer of the substrate side. It is preferable that the
decomposition and sublimation of In in the well layer can be inhibited
and that the emission wavelength can be stably controlled, by forming the
thin layer. The thin layer is preferably provided at a substrate
temperature same as the growing temperature of the well layer.
[0078] When a dopant is doped into the barrier layer, the operating
voltage is preferably decreased. As an element for the dopant, C, Si, Ge,
Sn, Pb, O, S, Se, Te, Po, Be, Mg, Ca, Sr, Ba and Ra can be exemplified.
Among those, Si and Ge are preferable and Si is the most preferable.
[0079] The concentration of the dopant is preferably 5.times.10.sup.16 to
1.times.10.sup.18 cm.sup.-3. If the concentration is less than
5.times.10.sup.16 cm.sup.-3, the operating voltage is not effectively
decreased. If the concentration is more than 1.times.10.sup.18 cm.sup.-3,
the peak inverse voltage characteristics tend to be degraded. The
concentration is more preferably 1.times.10.sup.17 to 5.times.10.sup.17
[0080] The thickness of the barrier layer is preferably at least 7 nm,
more preferably at least 14 nm. If the barrier layer is thin, the gap
between the thicknesses of a thick part and a thin part of a well layer
cannot be filled and as a result, formation of the thick part and the
thin part of the well layer is prohibited, leading to lowering the
emission efficiency and deterioration in characteristics due to aging. If
the barrier layer is too thick, the operating voltage is increased and
the emission output is decreased. Therefore, the thickness of the barrier
layer is preferably not more than 50 nm.
[0081] The repetition of stacking in the multiple quantum well structure
is preferably about 3 to about 10 times, more preferably about 3 to about
6 times. The composition and structure can be changed in each well layer
and barrier layer.
[0082] The n-type layer generally has a thickness of about 1 to about 10
.mu.m, preferably about 2 to about 5 .mu.m. The n-type layer is formed of
an n-type contact layer for forming a negative electrode and an n-type
cladding layer which has a bandgap larger than that of a light-emitting
layer and which is in contact with the light-emitting layer. The n-type
contact layer may also serve as the n-type cladding layer. The n-type
contact layer is preferably doped with Si or Ge at high concentration.
The thus-doped n-type layer preferably has a carrier concentration which
is controlled to about 5.times.10.sup.18 cm.sup.-3 to about
2.times.10.sup.19 cm.sup.-3.
[0083] The n-type cladding layer may be formed from a semiconductor such
as AlGaN, GaN, or InGaN. Needless to say, when InGaN is employed, the
InGaN preferably has such a composition as to have a bandgap greater than
that of the InGaN forming the light-emitting layer. The carrier
concentration of the n-type cladding layer may be equal to or greater or
smaller than that of the n-type contact layer. The n-type cladding layer
preferably has a surface having high flatness by appropriately regulating
growth conditions including growth rate, growth temperature, growth
pressure, and dopant concentration, so as to attain high crystallinity of
the light-emitting layer formed thereon.
[0084] The n-type cladding layer may be formed by alternatingly stacking
layers repeatedly, each layer having a different specific composition and
lattice constants. In this case, in addition to the composition, the
amount of dopant, film thickness, etc. of the layer stacked may be
[0085] The p-type layer generally has a thickness of 0.01 to 1 .mu.m and
is formed of a p-type cladding layer which is in contact with the
light-emitting layer and a p-type contact layer for forming a positive
electrode. The p-type cladding layer may also serve as the p-type contact
layer. The p-type cladding layer is formed from a semiconductor such as
GaN or AlGaN and doped with Mg serving as a p-type dopant. In order to
prevent overflow of electrons, the p-type cladding layer is preferably
formed from a material having a bandgap greater than that of the material
for forming the light-emitting layer. Furthermore, in order to
effectively inject carriers into the light-emitting layer, the p-type
cladding layer preferably has high carrier concentration.
[0086] Similar to the n-type cladding layer, the p-type cladding layer may
be formed by alternatingly stacking layers repeatedly, each layer having
a different specific composition and lattice constants. In this case, in
addition to the composition, the amount of dopant, film thickness, etc.
of the layer stacked may be modified.
[0087] The p-type contact layer may be formed from a semiconductor such as
GaN, AlGaN, or InGaN, and is doped with Mg serving as an impurity
element. When removed from a reactor, the as-removed Mg-doped gallium
nitride-based compound semiconductor generally exhibits high electric
resistance. However, the Mg-doped compound semiconductor exhibits p-type
conductivity through activation such as annealing, electron-beam
irradiation, or microwave irradiation.
[0088] The p-type contact layer may be formed from boron phosphide doped
with a p-type impurity element, which exhibits p-type conductivity even
though the aforementioned treatment for attaining p-type conductivity is
[0089] No particular limitation is imposed on the method for growing the
gallium nitride-based compound semiconductor for forming the
aforementioned n-type layer, light-emitting layer, and p-type layer, and
any of widely known methods such as MBE, MOCVD, and HVPE may be employed
under widely known conditions. Of these, MOCVD is preferred.
[0090] Regarding sources for forming the semiconductor, ammonia,
hydrazine, an azide, or a similar compound may be used as a nitrogen
source. Examples of the Group III organometallic compound include
trimethylgallium (TMGa), triethylgallium (TEGa), trimethylindium (TMIn),
and trimethylaluminum (TMAl). Examples of employable dopant sources
include silane, disilane, germane, organic germanium compound,
biscyclopentadienylmagnesium (Cp.sub.2Mg), other organometallic
compounds, and hydrides. Nitrogen or hydrogen may be employed as a
[0091] A well layer having an ununiform thickness is preferably formed by
growing a well layer to a predetermined thickness and then decomposing or
sublimating a part of the well layer. A gallium nitride-based compound
semiconductor containing In can be easily decomposed or sublimated and is
[0092] The In-containing well layer is preferably grown at a substrate
temperature of 650 to 900.degree. C. When the substrate temperature is
lower than 650.degree. C., a well layer of high crystallinity cannot be
formed, whereas when the substrate temperature is higher than 900.degree.
C., the amount of In incorporated into the well layer decreases, thereby
not fabricating a light-emitting device which emits light of the intended
[0093] After the In-containing gallium nitride-based compound
semiconductor has been grown to a predetermined thickness by continuously
supplying a Group III metal (containing In) source and a nitrogen source,
supply of the Group III metal source is stopped. The substrate
temperature is maintained or elevated under the above conditions, thereby
decomposing or sublimating a portion of the compound semiconductor. The
carrier gas is preferably nitrogen. Decomposition or sublimation is
preferably performed when the substrate temperature has been elevated
from the above growth temperature to 700 to 1,000.degree. C. or while the
substrate temperature is elevated.
[0094] The barrier layer is preferably grown at a substrate temperature
higher than that employed for the growth of the well layer. The substrate
temperature is preferably about 700 to about 1,000.degree. C. When the
temperature at which the well layer is grown is represented by T1 and the
temperature at which the barrier layer is grown is represented by T2, T1
and T2 satisfy the relationship: T1.ltoreq.T2. During increasing
temperature after growth of the well layer from T1 to T2, supply of the
Group III source is stopped while the nitrogen source and a
nitrogen-containing carrier gas are supplied continuously, whereby a
thick part and a thin part are effectively formed in the well layer and
as a result, a well layer having an ununiform thickness is formed. During
the course of the above procedure, change of carrier gas is not needed.
If the carrier gas is changed to hydrogen, the wavelength of emitted
light is blue-shifted. As such variation in wavelength is difficult to
control reliably, the variation reduces device productivity.
[0095] The rate of increasing temperature from T1 to T2 is preferably
about 1 to about 200.degree. C./min, more preferably about 5 to about
150.degree. C./min. The time required for increasing temperature from T1
to T2 is preferably about 30 sec to about 10 min, more preferably about 1
min to about 5 min.
[0096] The growth of the barrier layer may include a plurality of steps
which are performed at different growth temperatures. For example, a
barrier layer having a predetermined thickness is formed at T2 on a well
layer, followed by forming thereon another barrier layer at a growth
temperature T3. When T3 is lower than T2, deterioration of
characteristics caused by aging can be prevented, which is preferred. T3
may be equal to T1.
[0097] Further, as described above, when a well layer contains In, a thin
layer containing no In is preferably provided on the substrate side of
the barrier layer. In that case, a well layer comprising a gallium
nitride-based compound semiconductor containing In is grown at the
temperature T1 and then only the supply of a In source stops at the same
substrate temperature to grow the barrier layer comprising a gallium
nitride-based compound semiconductor at the temperature T1 first.
[0098] Negative electrodes of a variety of compositions and structures
have been widely known, and no particular limitation is imposed on the
negative electrode which may be employed in the present invention.
Examples of employable contact materials for the negative electrode which
is to be in contact with an n-type contact layer include Al, Ti, Ni, Au,
Cr, W, and V. Needless to say, the negative electrode may have a
multilayer structure in its entirety, thereby imparting the electrode
with a bonding property and other properties.
[0099] Positive electrodes of a variety of compositions and structures
positive electrode which may be employed in the present invention.
[0100] Examples of light-permeable positive electrode materials include
Pt, Pd, Au, Cr, Ni, Cu, and Co. Through partial oxidation of the positive
electrode, light permeability is known to be enhanced. Examples of
employable reflection-type positive electrode materials include the
aforementioned materials, Rh, Ag, and Al.
[0101] The positive electrode may be formed through a method such as
sputtering or vacuum vapor deposition. Particularly when sputtering is
employed under appropriately controlled sputtering conditions, ohmic
contact can be established even though the electrode film is not annealed
after formation of the film, which is preferred.
[0102] The light-emitting device may have a flip-chip-type structure
including a reflection-type positive electrode or a face-up-type
structure including an light-permeable positive electrode or a
lattice-like or comb-like positive electrode.
[0103] According to a well layer having an ununiform thickness which
includes a thick part and a thin part, an interface between the well
layer and a barrier layer composed of a material different from that of
the well layer in a boundary area between the thick part and the thin
part is slanted to the substrate surface. Therefore, the amount of light
extracted in the direction normal to the substrate surface increases.
Particularly when the light-emitting device has a flip-chip-type
structure including a reflection-type electrode, emission intensity is
[0104] An operating voltage of a light-emitting device obtained by using
the inventive gallium nitride-based compound semiconductor multilayer
structure may be freely lowered to some degree. However, when it is
largely lowered, the emission output is also lowered. The operating
voltage, at which the emission output is not lowered, is 2.5 V or more at
a current of 20 mA. More preferably, the operating voltage is 2.9 V or
more. It is necessary that the operating voltage is 3.5 V or less,
because a very high operating voltage is disadvantageous when a
light-emitting device is incorporated in equipment.
[0105] A take-off voltage, at which a current increases rapidly in a
current-voltage curve, is a diode characteristic. The take-off voltage of
a light-emitting device obtained by using the inventive gallium
nitride-based compound semiconductor multilayer structure may be lowered.
However, in regard to the take-off voltage, when it is lowered very
largely, a emission output is also lowered together. The take-off
voltage, at which the emission output is not lowered, is 2.3 V or more at
a current of 20 mA. More preferably, the take-off voltage is 2.5 V or
more. It is necessary that the take-off voltage is 3.4 V or less, because
a very high take-off voltage is disadvantageous when a light-emitting
device is incorporated in equipment.
[0106] The inventive gallium nitride-based compound semiconductor
multilayer structure is employed in, for example, a light-emitting diode
(LED) and a laser diode (LD).
[0107] A semiconductor light-emitting device is fabricated from the
inventive gallium nitride-based compound semiconductor multilayer
structure and, through conventional means well known in the art, a
transparent cover was attached to the semiconductor light-emitting
device, thereby fabricating a lamp. Also, a phosphor-containing cover was
attached to the semiconductor light-emitting device, thereby fabricating
a white light lamp.
[0108] A semiconductor light-emitting device having a high emission output
may be fabricated from the inventive gallium nitride-based compound
semiconductor multilayer structure. A very bright LED lamp may be
fabricated from the inventive gallium nitride-based compound
semiconductor multilayer structure by the above-mentioned technique.
Further, an electronic machine such as a portable telephone, a display
and an instrument panel, in which a chip fabricated by the
above-mentioned technique is incorporated, and machines such as a car, a
computer and a game machine, in which the electronic machine is
incorporated, may be operated at low electric power and may attain a high
performance. Specially, apparatuses such as a portable telephone, a game
machine and a car part, which are operated by a battery, may attain the
effect of saving energy.
[0109] The present invention will next be described in more detail by way
of examples, which should not be construed as limiting the invention.
[0110] FIG. 1 schematically shows a gallium nitride-based compound
semiconductor multilayer structure for producing a semiconductor
light-emitting device which structure was fabricated as Example 1
(configuration of well layers and barrier layers in the light-emitting
layer being omitted). As shown in FIG. 1, an SP layer formed of AlN is
stacked on a sapphire substrate having a c-plane through a
lattice-mismatch crystal epitaxial growth method. On the SP layer, the
following layers are sequentially formed: an undoped GaN undercoat layer
(thickness: 8 .mu.m); a highly-Ge-doped GaN contact layer (electron
concentration: 1.times.10.sup.19 cm.sup.-3, thickness: 2 .mu.m); an
Si-doped In.sub.0.02Ga.sub.0.98N cladding layer (electron concentration:
1.times.10.sup.18 cm.sup.-3, thickness: 20 nm); a light-emitting layer of
a multiple quantum well structure including 6 Si-doped GaN barrier layers
(electron concentration: 3.times.10.sup.17 cm.sup.-3, thickness of each
layer: 15 nm) and 5 undoped In.sub.0.08Ga.sub.0.92N well layers
(thickness of each layer: 3 nm); an Mg-doped p-type
Al.sub.0.05Ga.sub.0.95N cladding layer (thickness: 16 nm); and an
Mg-doped p-type Al.sub.0.02Ga.sub.0.98N contact layer (hole
concentration: 8.times.10.sup.17 cm.sup.-3, thickness: 0.2 .mu.m).
[0111] The aforementioned gallium nitride-based compound semiconductor
multilayer structure was fabricated by means of MOCVD through the
[0112] Firstly, a sapphire substrate was placed in a stainless reactor
furnace that can heat a plurality of substrates by means of a carbon
susceptor heated by an induction heater. The susceptor has a mechanism
such that the susceptor itself is rotatable and it rotates the
substrates. The sapphire substrate was placed on the carbon susceptor for
heating, the operation being performed in a nitrogen-substituted glove
box. After introduction of the substrate, the reactor furnace was purged
[0113] After passage of nitrogen for 8 minutes, the substrate temperature
was elevated, over 10 minutes, to 600.degree. C. by means of the
induction heater, and the pressure inside the furnace was adjusted to 15
kPa (150 mbar). While the substrate temperature was maintained at
600.degree. C., the substrate surface was thermally cleaned by allowing
the substrate to stand for 2 minutes under flow of hydrogen and nitrogen.
[0114] After completion of thermal cleaning, a valve of a nitrogen carrier
gas feeding pipe was closed, and only hydrogen was supplied to the
reactor furnace.
[0115] After the carrier gas was changed to hydrogen, the substrate
temperature was elevated to 1,150.degree. C. After confirming that a
constant temperature of 1,150.degree. C. was attained, a gas containing
TMAl vapor was supplied to the reactor furnace by opening the
corresponding valve. The supplied TMAl was caused to react with N atoms
which had been released through decomposition of deposits on an inner
wall of the reactor furnace, thereby depositing AlN on the sapphire
[0116] After supply of TMAl for 7 minutes and 30 seconds, the valve was
closed to stop supply of the gas containing TMAl vapor to the reactor
furnace. The conditions were maintained for 4 minutes, whereby the TMAl
vapor remaining in the furnace was completely removed. Subsequently,
ammonia gas was supplied to the furnace by opening the corresponding
[0117] Four minutes after the start of supply of ammonia gas, the
susceptor temperature was lowered to 1,040.degree. C. under ammonia flow
and simultaneously the pressure inside the furnace was adjusted to 40 kPa
(400 mbar). During lowering of the susceptor temperature, the flow rate
of TMGa was regulated by means of a flow controller.
[0118] After confirmation that the substrate temperature was lowered to
1,040.degree. C. and the substrate maintained a constant temperature of
1,040.degree. C., TMGa was supplied into the furnace by opening the
corresponding valve, so as to grow undoped GaN. The growth was performed
for about 4 hours, thereby forming the aforementioned GaN layer.
[0119] Thus, an undoped GaN undercoat layer having a thickness of about 8
.mu.m was formed.
[0120] Additionally, a highly Ge-doped n-type GaN contact layer was grown
on the undoped GaN undercoat layer. After the growth of the undoped GaN
undercoat layer, the supply of TMGa into the furnace was stopped, the
substrate temperature was increased to 1080.degree. C. in one minutes,
and the temperature was kept for three minutes to stabilize the same.
During the process, the flow rate of TMGe was controlled. The flow rate
was determined in advance and was controlled so that the electron
concentration of the Ge-doped GaN contact layer was about
2.times.10.sup.19 cm.sup.-3. Ammonia was continuously supplied into the
furnace at the same flow rate.
[0121] After stabilizing the temperature for three minutes, a Ge-doped
n-type GaN having the thickness of 10 nm and an undoped GaN having the
thickness of 10 nm were grown alternately in this order for 100 periods
to grow a n-type GaN contact layer of about 2 .mu.m. The Ge-doped GaN
layer was produced by supplying TMGa and tetramethylgermanium (TMGe) into
the furnace. The undoped GaN layer was produced by supplying TMGa. Thus,
an n-type GaN contact layer having an average carrier concentration of
about 1.times.10.sup.19 cm.sup.-3.
[0122] After the growth of the last undoped GaN layer, the supply of TMGa
into the furnace was stopped by switching the TMGa valve. The carrier gas
was changed from hydrogen to nitrogen by switching the valve while
ammonia was continuously introduced. Then, the temperature of the
substrate was lowered from 1080.degree. C. to 720.degree. C.
[0123] During the lowering of the temperature inside the furnace, the flow
rate of SiH.sub.4 was modified. The flow rate of interest had been
predetermined in advance, and the flow was regulated so as to control the
electron concentration of the Si-doped InGaN cladding layer to
1.times.10.sup.18 cm.sup.-3. Ammonia was supplied continuously into the
furnace, but the flow rate was unchanged.
[0124] Then, after the condition in the furnace was stabilized, the valves
for TMIn, TEGa and SiH.sub.4 were switched at the same time to start
supplying the materials into the furnace. The materials were continuously
supplied for predetermined time to form a Si-doped
In.sub.0.02Ga.sub.0.98N clad layer having a thickness of 20 nm. After
that, the valves for TMIn, TEGa and SiH.sub.4 were switched to stop
supplying the materials. Then, the setting for the supplying amount of
SiH.sub.4 was changed. The flow rate was determined in advance and was
controlled so that the electron concentration of the Si-doped GaN barrier
layer was 3.times.10.sup.17 cm.sup.-3. The Si-doped GaN barrier layer was
[0125] TEGa and SiH.sub.4 were begun to be supplied into the furnace while
keeping the substrate temperature at 720.degree. C., a thin barrier layer
A comprising a Si-doped GaN was formed for predetermined time, and the
supply of TEGa and SiH.sub.4 was stopped. Then, the substrate temperature
was increased to 920.degree. C. while the growth stopped. After the
temperature was stabilized, TEGa and SiH.sub.4 were begun to be supplied
into the furnace by switching the valves for TEGa and SiH.sub.4 while the
pressure in the furnace and the flow rates and kinds of ammonia gas and
of the carrier gas were maintained. A barrier layer B was grown at the
substrate temperature of 920.degree. C. for predetermined time. After
that, the substrate temperature was decreased to 720.degree. C. and TEGa
and SiH.sub.4 were continuously supplied to grow a barrier layer C. Then,
the supply of TEGa and SiH.sub.4 was stopped by switching valves again to
finish the growth of the GaN barrier layer. Thus, the Si-doped GaN
barrier layer comprising a three-layered structure of A, B and C, and
having a total thickness of 15 nm was formed.
[0126] After the growth of the GaN barrier layer, the supply of TEGa and
SiH.sub.4 stopped for 30 seconds. Then, TEGa and TMIn were started to be
supplied into the furnace by switching the valves for TEGa and TMIn while
the pressure in the furnace and the flow rates and kinds of ammonia gas
and of the carrier gas were maintained to form a well layer. After
supplying TEGa and TMIn for predetermined time, only the supply of TMIn
was stopped by switching the valve again to finish the growth of the
In.sub.0.08Ga.sub.0.92N well layer. At that moment, the
In.sub.0.08Ga.sub.0.92N well layer having a thickness of 3 nm was formed.
After that, SiH.sub.4 was supplied to form a second barrier layer.
[0127] The above described processes were repeated 5 times to form five
Si-doped GaN barrier layers and five In.sub.0.08Ga.sub.0.92N well layers.
In the manufacturing processes of the well layers and the barrier layers,
after the barrier layer A was formed at 720.degree. C., the growth of the
semiconductor layer was stopped by stopping the supply of a III group
material during the heating process to 920.degree. C., in order to form
the barrier layer B.
[0128] After the fifth In.sub.0.08Ga.sub.0.92N well layer was formed, the
process for producing the sixth barrier layer started. In the production
of the sixth barrier layer, SiH.sub.4 was again supplied. After the thin
barrier layer A comprising a Si-doped GaN was formed, the substrate
temperature was increased to 920.degree. C. while TEGa and SiH.sub.4 were
continuously supplied into the furnace. The barrier layer B was grown at
the substrate temperature of 920.degree. C. for predetermined time. Then,
the substrate temperature was decreased to 720.degree. C. and TEGa and
SiH.sub.4 were continuously supplied to grow the barrier layer C. After
that, the supply of TEGa and SiH.sub.4 was stopped by switching the
valves again to finish the growth of the GaN barrier layer. Thus, the
Si-doped GaN barrier layer comprising a three-layered structure of A, B
and C, and having a total thickness of 15 nm was formed.
[0129] According to the above described method, a light-emitting layer of
a multiple quantum well structure containing well layers (the first to
fourth layers) having ununiform thicknesses and a well layer having an
uniform thickness (the fifth layer) was formed.
[0130] On the outermost Si-doped GaN barrier layer of the light-emitting
layer, an Mg-doped p-type Al.sub.0.05Ga.sub.0.95N cladding layer was
[0131] After completion of the growth of the last Si-doped GaN barrier
layer, by stopping the supply of TEGa and SiH.sub.4, the substrate
temperature was elevated to 1,000.degree. C. The carrier gas was changed
to hydrogen, and the pressure inside the furnace was adjusted to 15 kPa
(150 mbar). After the pressure inside the furnace became constant,
sources (TMGa, TMAl, and Cp.sub.2Mg) were supplied to the furnace by
opening the corresponding valves. The growth was performed for about
three minutes, after which supply of TEGa, TMAl and Cp.sub.2Mg was
stopped, thereby terminating the growth of an Mg-doped p-type
Al.sub.0.05Ga.sub.0.95N cladding layer. As a result, an Mg-doped p-type
Al.sub.0.05Ga.sub.0.95 cladding layer having a thickness of 16 nm was
[0132] On the Mg-doped p-type Al.sub.0.05Ga.sub.0.95N cladding layer, an
Mg-doped p-type GaN contact layer was formed.
[0133] After completion of the growth of the Mg-doped
Al.sub.0.05Ga.sub.0.95N cladding layer by stopping supply of TMGa, TMAl,
and Cp.sub.2Mg, the pressure inside the furnace was adjusted to 20 kPa
(200 mbar). After the pressure inside the furnace became constant,
sources (TMGa, TMAl and Cp.sub.2Mg) were supplied to the furnace by
opening the corresponding valves. The flow rate of Cp.sub.2Mg had been
hole concentration of the Mg-doped Al.sub.0.02Ga.sub.0.98N contact layer
to 8.times.10.sup.17 cm.sup.-3. Thereafter, the growth was performed for
about 12 minutes, after which supply of TMGa, TMAl and Cp.sub.2Mg was
stopped, thereby terminating the growth of the Mg-doped GaN layer. As a
result, the Mg-doped Al.sub.0.02Ga.sub.0.98N contact layer was formed to
a thickness of 0.2 .mu.m.
[0134] After completion of the growth of the Mg-doped
Al.sub.0.02Ga.sub.0.98N contact layer, the electricity supply to the
induction heater was stopped, and the substrate temperature was lowered
to room temperature over 20 minutes. During the process of lowering the
temperature, the atmosphere in the reactor furnace was formed exclusively
of nitrogen. When the substrate temperature was confirmed to have been
lowered to room temperature, the thus-fabricated gallium nitride-based
compound semiconductor multilayer structure was removed to the
[0135] Through the above-described procedure, the gallium nitride-based
compound semiconductor multilayer structure for producing a semiconductor
light-emitting device was fabricated. Even though the Mg-doped
Al.sub.0.02Ga.sub.0.98N layer had not undergone annealing for activating
the p-type carrier, the Al.sub.0.02Ga.sub.0.98N layer exhibited p-type
[0136] By use of the aforementioned gallium nitride-based compound
semiconductor multilayer structure, a light-emitting diode, which is a
type of semiconductor light-emitting device, was fabricated.
[0137] On the surface of the p-type AlGaN contact layer of the
thus-fabricated gallium nitride-based compound semiconductor multilayer
structure, there was formed a reflection-type positive electrode having a
structure in which Pt, Rh, and Au were successively formed on the contact
layer side through a method well-known in the art.
[0138] Subsequently, the aforementioned gallium nitride-based compound
semiconductor multilayer structure was dry-etched so as to expose a
negative electrode portion of the highly-Ge-doped n-type GaN contact
layer. Ti and Al were successively formed on the exposed portion of the
contact layer in this order, thereby forming a negative electrode.
Through these operations, electrodes of the shape shown in FIG. 2 were
[0139] The back of the sapphire substrate of the gallium nitride-based
compound semiconductor multilayer structure which had been provided with
the positive electrode and the negative electrode in the above manner was
ground and polished, thereby providing a mirror surface. Subsequently,
the gallium nitride-based compound semiconductor multilayer structure was
cut into square (350 .mu.m.times.350 .mu.m) chips, and each chip was
affixed on a sub-mount such that the electrodes were in contact with the
sub-mount. The thus-formed sub-mounted chip was placed on a lead frame
and wired to the lead frame with gold wire, thereby fabricating a
[0140] When an operating current was applied to the positive electrode and
the negative electrode of the thus-fabricated light-emitting diode in a
forward direction, the diode exhibited a forward voltage (an operating
voltage) of 3.2 V at a current of 20 mA, an emission wavelength of 460
nm, and an emission output of 10.8 mW. Such characteristics of the
light-emitting diode can be attained without variation among
light-emitting diodes cut and produced from virtually the entirety of the
above-fabricated gallium nitride-based compound semiconductor multilayer
[0141] Also, the reverse voltages at the current of 10 .mu.A before and
after the power supply at the current of 30 mA and for 100 hours were
measured and compared with each other. The changing rate of the reverse
voltages was 0%.
[0142] FIGS. 3 to 10 show examples of photographs observed at 1,000,000
magnifications by a cross-sectional TEM. Eight parts spaced at 20 .mu.m
distance from each other in a cross section were observed. The serial
numbers for the well layers are assigned 1 to 5 from the surface side
(the semiconductor side) of the nitride semiconductor multilayer
structure. Thus, the well layer 1 is located on the p-type layer side and
the well layer 5 is located on the n-type layer side. In the figures, A
represents a thick part and B represents a thin part. Tables, attached to
FIGS. 3 to 10, show the maximum thickness and the minimum thickness of
each well layer at the respective parts.
[0143] Considering the eight parts shown in FIGS. 3 to 10, the maximum
thickness, the minimum thickness, the average thickness, and the ratio of
the difference between the maximum thickness and the average thickness to
the average thickness (the ratio of the difference between minimum
thickness and the average thickness to the average thickness) were
calculated and shown in Table 1.
thickness thickness thickness Ratio of
Well layer (nm) (nm) (nm) difference
1 3.1 2.8 2.95 .+-.5.1%
2 3.2 1.8 2.50 .+-.28.0%
3 3.1 1.9 2.50 .+-.24.0%
4 3.1 1.6 2.35 .+-.31.9%
5 3.2 1.7 2.45 .+-.30.6%
[0144] From Table 1, it can be seen that the range of the thicknesses of
the well layer 1 from its average thickness is .+-.5.1% and is in the
range of 10%, and that the layer is a well layer having a uniform
thickness in the present invention. It can also be seen that the ranges
of the thicknesses of the well layers 2 to 5 from their average
thicknesses are .+-.28.0%, .+-.24.0%, .+-.31.9% and .+-.30.6%,
respectively, and are more than 10%, and that the layers are well layers
having ununiform thicknesses in the present invention. In each of the
well layers 2 to 5, a part having a thickness larger than its average
thickness is a thick part and a part having a thickness smaller than its
average thickness is a thin part.
[0145] From FIGS. 3 to 10, the thickness of the barrier layer was about 15
nm. The barrier layer completely filled the gab between the thicknesses
of the thin part and the thick part of the well layer.
[0146] FIGS. 11 to 18 are TEM photographs in which the neighborhoods of
the parts in FIGS. 3 to 10 was observed at 200,000 magnifications. In
these figures, it can be seen that the well layer 1 has a uniform
[0147] From these TEM photographs, the widths of the thick parts and of
the thin parts of the well layers 2 to 5 were measured and the
distributions of the same were evaluated. The thick or thin part of each
well layer was determined based on the average thickness of each well
layer calculated from FIGS. 3 to 10. The results are shown in Table 2.
For example, in the well layer 2 in the TEM photograph of FIG. 11, the
widths were, in this order from the left side of the field of view in the
TEM photograph, 250 nm in the thick part, 60 nm in the thin part, 105 nm
in the thick part, 35 nm in the thin part, and 75 nm in the thick part.
In Table 2, the thicknesses are described as thick part (250 nm)--thin
part (60 nm)--thick part (105 nm)--thin part (35 nm)--thick part (75 nm).
TEM Well Variation
photograph layer Distribution of thick part and thin part Thin part Thick
2 Thick part(250 nm)-thin part(60 nm)-thick part(105 nm)-thin part(35
nm)-thick part(75 nm) 35-60 nm 75-250 nm
3 Thick part(260 nm)-thin part(45 nm)-thick part(220 nm) 45 nm 220-260 nm
4 Thick part(160 nm)-thin part(100 nm)-thick part(220 nm) 100 nm 160-220
5 Thick part(260 nm)-thin part(70 nm)-thick part(120 nm) 70 nm 120-260 nm
2 Thick part(410 nm)-thin part(35 nm)-thick part(50 nm)-thin part(30 nm)
30-35 nm 50-410 nm
3 Thick part(470 nm)-thin part(30 nm) 30 nm 470 nm
4 Thick part(185 nm)-thin part(40 nm)-thick part(235 nm)-thin part(80 nm)
40-80 nm 185-235 nm
5 Thick part(145 nm)-thin part(50 nm)-thick part(245 nm)-thin part(40 nm)
40-50 nm 145-245 nm
2 Thick part(270 nm)-thin part(65 nm)-thick part(20 nm)-thin part(55 nm)
55-65 nm 20-270 nm
3 Thick part(320 nm)-thin part(80 nm)-thick part(70 nm)-thin part(50 nm)
50-80 nm 70-320 nm
4 Thick part(270 nm)-thin part(90 nm)-thick part(120 nm)-thin part(30 nm)
30-90 nm 120-270 nm
5 Thick part(310 nm)-thin part(40 nm)-thick part(200 nm) 40 nm 200-310 nm
2 Thick part(190 nm)-thin part(60 nm)-thick part(120 nm)-thin part(60
nm)-thick part(75 nm) 60 nm 75-190 nm
3 Thick part(320 nm)-thin part(40 nm)-thick part(60 nm)-thin part(60 nm)
40-60 nm 60-320 nm
4 Thin part(60 nm)-thick part(65 nm)-thin part(90 nm)-thick part(140
nm)-thin part(55 nm) 55-90 nm 65-140 nm
5 Thick part(300 nm)-thin part(45 nm)-thick part(65 nm)-thin part(60 nm)
45-60 nm 65-300 nm
2 Thick part(450 nm)-thin part(50 nm)-thick part(40 nm)-thin part(35 nm)
35-50 nm 40-450 nm
3 Thick part(580 nm) -- 580 nm
4 Thick part(520 nm)-thin part(70 nm) 70 nm 520 nm
5 Thick part(540 nm)-thin part(55 nm) 55 nm 540 nm
2 Thin part(40 nm)-thick part(250 nm)-thin part(100 nm)-thick part(130
nm)-thin part(60 nm) 40-100 nm 130-250 nm
3 Thick part(500 nm)-thin part(75 nm) 75 nm 500 nm
4 Thick part(580 nm) -- 580 nm
5 Thick part(600 nm) -- 600 nm
2 Thin part(65 nm)-thick part(45 nm)-thin part(30 nm)-thick part(320
nm)-thin part(100 nm) 30-100 nm 45-320 nm
3 Thick part(330 nm)-thin part(50 nm)-thick part(180 nm) 50 nm 180-300 nm
4 Thick part(60 nm)-thin part(100 nm)-thick part(300 nm)-thin part(50 nm)
50-100 nm 60-300 nm
5 Thin part(40 nm)-thick part(330 nm)-thin part(60 nm) 40-60 nm 330 nm
2 Thin part(80 nm)-thick part(95 nm)-thin part(95 nm)-thick part(140
nm)-thin part(70 nm) 70-95 nm 95-140 nm
3 Thick part(130 nm)-thin part(60 nm)-thick part(250 nm)-thin part(100
nm) 60-100 nm 130-250 nm
4 Thin part(70 nm)-thick part(275 nm)-thin part(90 nm)-thick part(100
nm)-thin part(40 nm) 40-90 nm 100-275 nm
5 Thin part(100 nm)-thick part(85 nm)-thin part(35 nm)-thick part(105
nm)-thin part(60 nm) 35-100 nm 85-105 nm
[0148] The distributions of the widths of the thin parts and of the thick
parts of each well layer calculated from Table 2 is 30 to 100 nm in the
well layer 2, 30 to 100 nm in the well layer 3, 30 to 100 nm in the well
layer 4 and 35 to 100 nm in the well layer 5, for the thin part, and 20
to 450 nm in the well layer 2, 60 to 580 nm in the well layer 3, 60 to
580 nm in the well layer 4 and 65 to 600 nm in the well layer 5, for the
[0149] In the present comparative example, a gallium nitride-based
compound semiconductor multilayer structure was produced according to the
same method as for Example 1, except that the thicknesses of all the well
layers are uniform. Namely, a gallium nitride-based compound
semiconductor multilayer structure was produced according to the same
method as for Example 1, except that for the first to fifth barrier
layers, after the barrier layer A was formed the substrate temperature
was increased to 920.degree. C. while TEGa and SiH.sub.4 were
continuously supplied into the furnace, the same as for the sixth layer.
[0150] A light-emitting diode was manufactured and evaluated using the
according to the same method as for Example 1. As a result, the forward
voltage at the current of 20 mA was 3.9 V. The emission wavelength was
460 nm and the emission output was 9 mW.
[0151] The initial value of the reverse voltage at 10 .mu.A and the
reverse voltage at 10 .mu.A after the power supply at the current of 30
mA and for 100 hours were compared with each other. The changing rate of
the reverse voltage was -0.5%.
[0152] In the present comparative example, a gallium nitride-based
layers are ununiform. Namely, a gallium nitride-based compound
method as for Example 1, except that for the sixth barrier layers, after
the barrier layer A was formed the substrate temperature was increased to
920.degree. C. while TEGa and SiH.sub.4 were stopped, same as for the
first to fifth layers.
[0153] A light-emitting diode was manufactured and evaluated using the
voltage at the current of 20 mA was 3.15 V. The emission wavelength was
[0154] The initial value of the reverse voltage at 10 .mu.A and the
the reverse voltage was -7%.
[0155] In Example 2, a gallium nitride-based compound semiconductor
multilayer structure was produced according to the same method as for
Example 1, except that only the well layer closest to the n-type layer
has a uniform thickness. Namely, a gallium nitride-based compound
method as for Example 1, except that for the second barrier layer, after
920.degree. C. while TEGa and SiH.sub.4 were continuously supplied into
the furnace, same as for the sixth layer of Example 1, and that for the
sixth barrier layer, after the barrier layer A was formed the substrate
temperature was increased to 920.degree. C. while the supply of TEGa and
SiH.sub.4 into the furnace was stopped, same as for the first to fifth
layers of Example 1.
[0156] A light-emitting diode was manufactured and evaluated using the
voltage at the current of 20 mA was 3.3 V. The emission wavelength was
460 nm and the emission output was 10.8 mW.
[0157] In Example 3, a gallium nitride-based compound semiconductor
Example 1, except that only the third well layer from the p-type layer
method as for Example 1, except that for the fourth barrier layer, after
[0158] A light-emitting diode was manufactured and evaluated using the
voltage at the current of 20 mA was 3.2 V. The emission wavelength was
460 nm and the emission output was 9.7 mW.
[0159] In Example 4, a gallium nitride-based compound semiconductor
Example 1, except that the two well layers closest to the p-type layer
and to the n-type layer, respectively, have uniform thicknesses. Namely,
a gallium nitride-based compound semiconductor multilayer structure was
produced according to the same method as for Example 1, except that for
the second barrier layer, after the barrier layer A was formed the
substrate temperature was increased to 920.degree. C. while TEGa and
SiH.sub.4 were continuously supplied into the furnace, same as for the
[0160] A light-emitting diode was manufactured and evaluated using the
voltage at the current of 20 mA was 3.45 V. The emission wavelength was
460 nm and the emission output was 11.4 mW.
[0161] In Example 5, a gallium nitride-based compound semiconductor
Example 1, except that the first and second two well layers from the
p-type layer, respectively, have a uniform thickness. Namely, a gallium
nitride-based compound semiconductor multilayer structure was produced
according to the same method as for Example 1, except that for the fifth
barrier layer, after the barrier layer A was formed the substrate
[0162] A light-emitting diode was manufactured and evaluated using the
460 nm and the emission output was 10.2 mW.
[0163] In Example 6, a gallium nitride-based compound semiconductor
Example 1, except that the first to third three well layers from the
according to the same method as for Example 1, except that for the fourth
and fifth barrier layers, after the barrier layer A was formed the
[0164] A light-emitting diode was manufactured and evaluated using the
voltage at the current of 20 mA was 3.35 V. The emission wavelength was
[0165] In Example 7, in a manner similar to Example 1, a positive
electrode and a negative electrode were provided on the gallium
nitride-based compound semiconductor multilayer structure obtained in
Example 1. However, the positive electrode had a structure in which a
transparent electrode, in which Au and NiO were stacked in this order
from the p-type AlGaN contact layer, and a pad electrode, in which Ti,
Au, Al and Au were stacked in this order from the p-type AlGaN contact
layer, were successively formed on the p-type AlGaN contact layer side.
[0166] In a manner similar to that of Example 1, the fabricated
light-emitting diode was evaluated. As a result, the diode exhibited a
forward voltage of 3.2 V at a current of 20 mA, an emission wavelength of
460 nm, and an emission output of 5.5 mW. Such characteristics of the
[0167] In Comparative Example 3, a light-emitting diode having the same
electrode structure as employed in the diode of Example 7 was fabricated
by use of the gallium nitride-based compound semiconductor multilayer
structure fabricated in Comparative Example 1.
[0168] In a manner similar to that of Example 1, the fabricated
forward voltage of 3.9 V at a current of 20 mA, an emission wavelength of
460 nm, and an emission output of 5 mW.
[0169] In Comparative Example 4, a light-emitting diode having the same
structure fabricated in Comparative Example 2.
[0170] In a manner similar to that of Example 1, the fabricated
forward voltage of 3.15 V at a current of 20 mA, an emission wavelength
of 460 nm, and an emission output of 5 mW.
[0171] The light-emitting device produced from the gallium nitride-based
compound semiconductor multilayer structure of the present invention
operates at low voltage while maintaining satisfactory light emission
output. Thus, the present invention is of remarkably great value in the
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