GaN中転位と不純物の複合体
原嶋 庸介
奈良先端科学技術⼤学院⼤学

Dislocation causes a leakage current

d CL dark spots.
he leakage spots
the dislocations
mesa edge, andleakage spots(emission microscopy)

Appl. Phys. Lett. 112, 182106 (2018)
position of dislocation(etch pit)

presentabsent
S. Usami, et al., APL, 112, 182106 (2018).

FIG. 6. Positional correlation between leakage spots and etch pits. Almost• medium
The leakage
and the dislocations
are Instronglyallpits correspondto leakage spots.
contrast,correlated.
large (whitearrowed) pits and small pits do not match the leakage spots. This result indicates that the dislocations formed in the medium pits play a crucial role in
the reverse leakage. The rough morphology at the center of the mesa wasformed by the electrode residue. The circular mesa shape became hexagonal
during the KOH etching. The dashed line denotes the (previous) mesa edge,3

Mg condensation at the threading screw dislocations(a) STEM
TSD position

3D(b) Atom Probe-40 -20 020 40

Mg Condensation-100-50

300nm
0T. Nakano, Y. Harashima, et al.,APL, 117, 012105 (2020).

50100• Does impurity interact with the dislocations?
4ContentsMg

p-typeHSi転位n-type

1. dislocation + Mg
2. dislocation + Mg + H
3. dislocation + Si
これらから以下を考察• band structure of complex of dis.+Mg• leakage current model

Models of TSD-Mg complexes•

To avoid distortion
at cell boundary,Ø supercell,vacuum,fictitious hydrogentermination,
are used.
ØØ

Schematic of a supercell
Fictitious hydrogen

Dislocation line
41Å
GaN

•

Structure optimization.

•VASP
Ø Generalized Gradient Approximation (GGA)ØThreading screw dislocation(TSD)49Å

Heyd-Scuseria-Ernzerhof (HSE) hybrid functional

Vacuum~900 atoms
T. Nakano, Y. Harashima, et al.,APL, 117, 012105 (2020).
6

Energetics of TSD

s t a b leco re str u c tu

res7Interaction with Mg•D(0|2)

S(0|6)

Binding energy:

Eb = Edis + Ebulk/Mg
Edis/Mg (d) + Ebulk

boundstrongly

S(0|3)• Mg condensation at TSD.
Ø Formation of Mg—TSD complexes.

8Electronic levels derived from dislocations• Density of States
bandgap
highest occupied state-Screw dislocation D(0|2)
no dislocation• A level is present in the gap.
• This state is fully occupied and this is the highest occupied state.

9

Highest occupied levels and Mg
Conduction
band• The highest occupied level is elevatedtowards the conduction band as the Mg
approaches the dislocation.
Ø Although Mg is an acceptor,
the complex acts as a donor.

Valence band

Ø A local n-region
in a p-type semiconductor.
10

GaN exhibits two main luminescence peaks
the expected value for a shallow acceptor because ofy related to the presence of the Mg dopants:
large charge-state-dependent lattice relaxations aroundeV, which we will refer to as the ultraviolet
Mg impurity [see Fig. 1(a)]. Furthermore, we propose t(UVL) [10], and a broader luminescence
the UVL generally assumed to be associated withat 2.8 eV, which has been labeled the blue
isolated Mg acceptors is instead due to Mg-H complex(BL). The UVL is usually observed in as[Fig. 1(b)]. We will show that these assignments
ed GaN and has commonly been attributed
consistent with the experimental data, and also offrom a shallow donor to the supposedly
cceptor [4–7];
otherorigins
have
been sugSIMSof GaN
p-ndiode
S. Usami, PhD Thesis
(a)
(b)
[10].
Annealingorelectron-beamirradia00 hPa1000 hPa
pGaN
activating
the Mg acceptors by removing
2~3um
2~3um
Mg
NH3.1e16
H2.9e16
uritiesC6.24e15
leads to a significant decrease in theC7.1e15
Ga cMg
GaO6.2e15
O5.5e15
he UVL[4,6,7];
simultaneously
thedeep,Si1.6e16Si2.1e16
Mg2.4e15erges Mg1.2e15[3,4,7].
The
microscopic
originsofNHFe1.4e15
Fe1.2e15
Hong been debated.
Because the BL appears
SiSiC,OC,O
energy than thebandgapofGaN(2.8vsFeFe
Mg
centershave
traditionallybeen
invokedtoMg
Mg
gin [5,7,11]. In particular, it has often been
J. Lyons,al., PRL,
108, 156403(2012).
(µm)
Depth (µm)
FIG. 1 (color online).
(a)etLocal
structure
showing
the dist
ombination from deep donors to shallow Mg
D.L. (Atms/cm ) H3e16, C4e15, O6e15, Si7e14, Mg1e15, Fe1e15
tion around a neutral Mg acceptor in GaN. The localization
the donor centershavenever been
• H
passivates
Mg experiacceptors in GaN.
the hole on the axial nitrogen neighbor is illustrated by the spPa ΍πβpn ϥόϑВϬί SIMS jƿʋǁ
ified[8].1000hPa ř̻Ø Does H affect the propertiesdensityof Mg-dislocation
complexes?
isosurface (yellow),
set to 5% of the maximu
y on the evolution of photoluminescence(b) Structure of the Mg-H complex in GaN in the positive cha
11ductivity upon annealing, Occam’s razor
Wa=¼¯Å9state. The spin density shows the more delocalized
nature of
the UVL to Mg-H complexes, and the BLcomplex. Large green spheres denote Ga atoms, medium li
uch an interpretation
has been
disregarded, 100blue
0΃750΃1000hPa ίȇÔЃϛʗÐpn ϥόϑВϬί͘Ǐĺµm ΍spheres N atoms, and the orange (darker) sphere denoause it seems to conflict with accepted
the Mg .
ΊΧǜȾθςГʰ¶ȲДˡ;χ˃ΤΡ΄ΟτΠτί͘ǏĺΨˏƍʄòχ Ga

Hole passivation by HMg 1E+20Mg
Fe 1E+19SiH
1E+18CO
1E+17

1E+161E+151E+143435012345

Summary
TSD: Threading Screw Dislocation

1. First-principles calculations for TSD and Mg, H, Si in GaN

2. Electronic band structure of the cylindrical depletion region.
• The Fermi level in the local n-region is pinned at the dislocation level.
3. One dimensional hopping conduction model having two hopping levels.
• The sudden increase of the current due to reverse bias is reproduced.

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