GaN中の転位、不純物とリーク電流
原嶋 庸介
筑波⼤学 計算科学研究センター

リーク電流と転位

d CL dark spots.
the 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).

6. Positional correlation between leakage spots and etch pits. Almost• FIG.
リーク電流の発⽣箇所(左図)には転位(右図)がある
all medium pits correspond to leakage spots. In contrast, large (white• arrowed)
転位(右図)にはリーク電流(左図)を発⽣させないものもある
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,2etch pit shapes and the histogram of the etch pit diameters
the number of nodes, n , satisfies the relation ghkil $ buvtw ¼ n .
are shown in Fig. 5. As shown in the histogram, three sizes
Figures 7(a)–7(c) show the bright-field LACBED patternsof etch pits were clearly observed on this substrate, namely,for various reciprocal lattice vectors obtained from areas conlarge, medium, and small. The densities of large, medium,taining threading dislocations. D and L in the figures denoteand small etch pits were 3.1 " 105 cm# 2, 8.1 " 105 cm# 2, andthe dislocation and Laue reflection lines, respectively. The
6.6 " 106 cm# 2, respectively, and the total etch pit density
LACBED pattern in Fig. 7(a) was taken using the 000!6 reflec6#2(EPD) was 7.7 " 10 cm . The total EPD was lower thantion, and six nodes were observed. (A bright interval between
the CL dark-spot density. This means that there are dislocaneighboring dark fringes was counted as one node.) The signtion types for which no etch pits were formed. Figure 6of n was determined from the sense of the bend of the reflecshows the positional relationship between the leakage spots
tion line.31,32 Similarly, six and five nodes were observed from[Fig. 6(a)] and the etch pits [Fig. 6(b)]. It was found that all
the LACBED pattern using the 11!2 !6 and 21!35 reflections inthe medium pits correspond to leakage spots. In contrast,Large-Angle Convergent-Beam Electron Diffraction
large pits and small pits do not match leakage spots. The cir(LACBED)
cular mesa became hexagonal during the etching. The results
revealed~ghkil · ~buvtw= nthat the specific dislocation component that constitutes the medium pits is related to the reverse leakage.

Burgers vector of the threading dislocation

Bargers vectorn : the number of nodes.
6w =

66w =

6u+v

2t

2u + v

3t + 5w = 51µmu+v+t=0)~buvtw = [0001]
screw dislocation

3FIG. 5. Etch pit shapes and histogram of etch pit size. The histogram clearly S. FIG.
7. Bright-field LACBED
patterns
for 182106
several reciprocallattice vectors
Usami,., APL,112,(2018).
shows the presence of three types of etch pits. Each type of etch pit has a difobtained from the areas containing TDs: (a) g ¼ 000!6, (b) g ¼ 11!2 !6, and (c)ferent diameter and different wall angle. These differences are caused by theg ¼ 21!35. D and L denote the dislocation and Laue reflection lines, respecdifference in dislocation components.
tively. (d) The cross-sectional TEM image of a large pit.

et alMg condensation at the threading screw dislocations
TSD: Threading Screw Dislocation(a) STEM
TSD position

3D(b) Atom Probe-40 -20 020 40Mg Condensation-100-50300nm• リーク電流発⽣箇所には貫通らせん転位とMg不純物が存在する

050100T. Nakano, Y. Harashima, et al.,APL, 117, 012105 (2020).

4らせん転位-Mg 複合体のモデル•セルの境界での歪みを除く
Ø 超格⼦
Ø 真空層
Ø 擬⽔素終端超格⼦の模式図

貫通らせん転位の構造

Fictitious hydrogen

Dislocation line41Å

•

構造最適化GaN49Å

Vacuum~900 atoms•VASP
Ø Generalized Gradient Approximation (GGA)Ø Heyd-Scuseria-Ernzerhof (HSE) hybrid functional5転位芯構造の安定性•

2種類の転位線 (D, S)•e.g.) D(0|2): Double,
Gaを0個、Nを2個、取り除く•

今回は全部で16パターンの転位芯構造を考慮した

6

転位芯構造の安定性•Formation energy:

Ef = EE refµ N nNµGa nGa•

Equilibrium condition:µGaN = µGa + µN•

Ga-rich and N-rich conditions arecontrolled by a chemical potential.

•The N-removed core structures arestable for both double and single.

7転位芯構造の安定性•Formation energy:

Ef = EE refµ N nNµGa nGa•

Equilibrium condition:µGaN = µGa + µN•

Ga-rich and N-rich conditions arecontrolled by a chemical potential.

•The N-removed core structures arestable for both double and single.

8Complex of threading screw dislocation and Mg

Mg
dislocation line

ddis Mg9

転位に対するMgの束縛エネルギー
D(0|2)•S(0|6)

束縛エネルギー:

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

boundstrongly

S(0|3)• Mg はらせん転位に凝集する• Mg̶らせん転位複合体が形成される

10

電⼦準位
• Density of Statesbandgap
highest occupied state• 転位由来の電⼦準位が現れる• 最⾼占有準位は完全に占有される-Screw dislocation D(0|2)
no dislocation

11

最⾼占有準位とMg
Conduction
band• Mgがらせん転位に近づくと最⾼占有準位が伝導帯に向かって押し上げられる• Mgはアクセプターだが、Mg̶らせん転位の複合体はドナーとして振る舞う

Ø p型半導体層に局所的なn型領域ができる
Valence bandØ 局所n型領域とp型バルク層のバンド構造も必要
12課題p-typeü p層中のらせん転位̶Mg複合体の電⼦状態
ü p層中のらせん転位̶Mg̶H複合体の電⼦状態
Ø 3体であるØ Hは格⼦間に⼊る*RSDFTを導⼊dislocation• 転位とp層バルクのバンド構造
ü n層中のらせん転位̶Si複合体の電⼦状態

n-type• p-n接合でのhopping伝導• 最終的にはリーク電流の制御法の指針を提案したい13

ü が第⼀原理計算

まとめp-typedislocation

済 ü p層中のらせん転位̶Mg複合体の電⼦状態

ü p層中のらせん転位̶Mg̶H複合体の電⼦状態• 転位とp層バルクのバンド構造

n-typeü n層中のらせん転位̶Si複合体の電⼦状態• p-n接合でのhopping伝導14