Tables

Table Ia

 List of techniques for evaluating GaN polarity in chronological order. The relationship between growth conditions and the resulting polarity is also represented.
Year Who [Ref]

(growth method)

Substrate or buffer layer Process or Feature of HT-GaN Method (probe) polarity
88 Sasaki [12]

(LP-MOCVD)

Si-SiC Smooth surface XPS

(photoelectron)

-c
C-SiC Rough surface +c
94 Sun [15]

(MOCVD)

c-sapphire Hexagonal Chemical stability

(H2 annealing)

+c
M-sapphire Ridgelike
Si-SiC Hexagonal -c
96 Ponce [18]

(MOCVD)

Bulk Ga       Smooth  Homo-epitaxy of HT- GaN CBED

(e-beam)

+c
Bulk Ga       Rough -c
Sapphire Smooth surface +c
96 Liliental-Weber

[19]

- Bulk GaN    Smooth CBED +c
                 Rough -c
96 Romano [20]

(MBE)

Nitride c- sapphire


CBED -c
(MOCVD) c-sapphire +c
(HVPE) c-sapphire(ZnO buffer) +c
96 Rouviere [21]

(MOCVD)

a,c-sapphire (GaN600°C + no anneal)

a,c-sapphire (AlN 800°C + 1000°C)

Hexagonal (1150°C growth) CBED -c
Smooth (950°C growth) +c
Smooth (900°C growth) +c
96 Daudin [45]

(MOCVD)

GaN buffer layer deposited on sapphire at 500°C Smooth
(Both LT-layers were annealed in N2 at 1000°C for 5min)		 Ion channel

(2MeV He+ beam)

+c
GaN buffer layer deposited on sapphire at 600°C Rough
(Both LT-layers were annealed in N2 at 1000°C for 5min)		 +c + -c mix
97 Smith [28]

(MBE)

Sapphire nitrided for 30min at 1000°C
 (GaN ~10nm at 685°C)

200nm Epi-layer at 775°C, and then supply Ga Surface reconstruction

(e-beam)

-c
MOCVD-GaN on sapphire +c
97 Weyher [32]

(bulk GaN)

- Smooth side Chemical stability (alkali solution) inert
Rough side etched
97 Seelmann-Eggebert [6]

(bulk GaN)


Smooth (inert) HSXPD

(photoelectron)

+c
Rough (etched) -c
98 Sumiya [36]

(MOCVD)

GaN at 600°C on non-nitrided sapphire Smooth CAICISS

(2keV He+ beam)

+c
GaN at 600°C on nitrided sapphire Hexagonal -c
98 Shimizu [38]

(MBE)

Nitrided sapphire 600°C for 5min

(20nm GaN at 500°C)

N-rich (spotty RHEED)

CAICISS -c
Ga-rich (streak RHEED)

-c

Table Ib

 Methods for detecting relative differences depending on the polarity of the GaN.
Year Who [Ref.]

(growth)

Substrate or buffer layer Process or Feature of HT-GaN How Remarks
01 Jones [42]

(MBE)

Sapphire

(AlN, none)

Ga-rich growth

+c, -c on a divided substrate

Kelvin probe force microscope +c domain +25mV

-c domain -30mV

02 Jiang [25]

(MOCVD)

Sapphire

(none mentioned)

+c confirmed by CBED atomic location by channeling-enhanced microanalysis

(e-beam)

consistent with the results by CBED
02 Koukitu [17]

(MOHVPE)

GaAs (111) A-face +c Gravimetric monitoring of decomposition

(heat)

low temp: +c > -c

GaAs (111) B-face -c high temp: -c > +c
02 Jang [44]

(MOCVD)

30nm GaN on nitrided-sapphire Smooth (+c) SBH measured by I-V with Ti/Al contact high
Ga pulse injection on
nitrided-sapphire
 Hexagonal (-c) low
02 Rodriguez [43]

(MBE)

GaN on sapphire Rough (rms. 5nm) -c Piezoresponse force microscopy -c
4-10nm AlN on sapphire
 Smooth (0.6nm) +c +c
03 Cros [41]

(MBE)

GaN on sapphire Rough (rms. 5nm) Raman Strong A1(TO) 534cm-1
4-10nm AlN on sapphire
 Smooth (0.6nm) Strong A1(LO) 739cm-1

Table IIa

 Relationship between the growth condition and the polarity of GaN deposited on sapphire substrates by MBE. The table shows the list of research groups, each of which has their own know-how on regarding growth.
Group [Ref.] (polarity) Nitridation source Nitridation temperature
 Phenomena Buffer layer condition Epi-layer polarity
Crete Univ. [54]

(RHEED)

N-radical for 100min 500W plasma

(N exist from AES)

 at 750°C
Roughened, increase of lattice by 6%
16nm GaN at 350°C

+c
16nm GaN at 350°C and then, annealed at 700°C -c
at 200°C Smoothing, increase of lattice by 9% 16nm AlN +c
Georgia Inst. of Tech. [62]

(SP-EFM, RHEED))

N-radical for 1h at 700°C
 6 Å AlN [55]
30nm GaN at 500°C 0.9µm/h 615°C
-c
12nm AlN -c (IDs)
30nm AlN +c
at 200°C
23Å AlN+NO
30nm GaN at 500°C +c(IDs)
2-67nm AlN at 700-850°C +c
Virginia Commonwealth Univ. [65] (H3PO4, RHEED)
N-radical

at 890-985°C, and 500°C
 No effect of the nitridation temperature on polarity
 30-40nm GaN (0.6µm/h at 500°C Ga-rich 0.3-1µm/h720-850°C
-c
60-150nm GaN (0.6µm/h at 500°C +c
110-220nm GaN (0.22µm/h at 500°C) -c
GaN at 800°C -c
20nm AlN at 500°C 20-30nm/h -c
20nm AlN at 500°C
60nm/h 		+c
20nmAlN at 890-930°C +c
Walter Schottky Inst, and Cornell Univ. [60]

(KOH)

Non-nitridation






15nm GaN at 800°C at 800°C
-c
0-5nm AlN at 800 °C -c
5-15nm AlN at 800 °C +c
Cal. Inst. of Tech. [61]

(KOH)

N-radical for 30min at 800°C
 formation of AlN 5-8nm GaN N-rich -c

V/III=1
Ga-rich
5-8nm AlN under Al-rich Slightly Ga-rich

+c

5-8nm AlN under V/III=1
5-8nm AlN under N-rich
AIST

(RHEED, CAICISS)

N-radical 350W plasma for 5min at 700°C [59]








20nm GaN at 700°C 700°C

(0.6µm/h)

-c
20nm GaN at 500°C -c
20nm AlN at 700°C -c
20nm AlN at 500°C +c
No-cracking NH3 5sccm for 30min at 910°C [56]

20nm GaN at 500°C 100nm at 820°C +c

(-c without NH3 treatment)

Univ. of Minnesota [29]

(RHEED)

NH3 flow (1x10-5Torr)  for 15min from 500 to 1000°C



GaN at 700°C


-c
for 3min 25nm AlN at 1000°C
+c
for 15min mixed

Table IIb

 List of reports claiming polarity conversion from -c to +c MBE-GaN by insertion of a metal layer.
Group [Ref.]

(polarity)

Nitridation condition Buffer layer condition Epi-layer polarity
Chiba Univ. [66]

(CAICISS)

N-radical at 200°C for 40min
20nm GaN at 650°C at 820°C
-c
Al thin layer after 100nm epi-GaN +c
Dongguk Univ. [68]

(RHEED)

N-radical at 500°C for 10min, 250W plasma
AlN at 850°C 800°C 0.9µm/h
-c
Al metal (~6 layers) +AlN +c when Al 2 layers
Sophia Univ. [69]

(KOH)

Non-nitrided 10nm AlN at 750°C

(alternative supply of Al, N source, MEE)

MEE of Ga, N at 750°C
+c
Nitridation non -c
Furukawa Elcetric Co. Ltd. [70] Non-nitridation Ga metal (2 layers) + 50nm GaN at 700°C 850°C

1.5µm/h

+c

Table III

 GaN samples grown on sapphire substrates by HVPE. Relationship between surface morphology and the initial growth on the substrate is summarized.
Year Who [Ref.] Initial growth condition Morphology
90
Naniwae [95]
Ga+HCl treatment of sapphire sub. at 1030°C <70 ml/min for 10min rough + pit
Ga+HCl treatment of sapphire sub. at 1030°C >70 ml/min for 20min smooth
92
Detchprochm [96]
Sputtered ZnO buffer smooth + transparent
Direct growth granular
97
Molnar [97]
Direct growth hexagonal facet
ZnO or GaCl treatment smooth
97
Lee [98]
Sputtered 50nm AlN at <960°C rough
Sputtered 50nm AlN at 980-1020°C Relatively smooth
99

Paskova [99]

Nitrided a-plane sapphire hillocks
GaCl treatment hillocks
Magnetron-sputtered 50nm AlN at 1000°C on a-plane sapphire Smooth with pits
99



Wagner [100]



Direct growth hillock
GaN (<10nm) buffer layer by MOCVD at 600°C  hexagonal facets
GaN (>10nm) buffer layer by MOCVD at 600°C  smoothest
AlN buffer layer by MOCVD at 600°C smooth
GaN (20 to 200nm) buffer layer by HVPE at 650°C truncated pyramids
00 Tavernier [101] 0.1µm GaN buffer by HVPE at 550°C on sapphire, and then two-step growth at 1050-1100°C. smooth
02

Zhang [106]

HT-GaN buffer on c-sapphire treated by GaCl at 800-1050°C without HT-GaN TD(cm-2):109, rms:4.1
HT-GaN buffer on c-sapphire treated by GaCl at 800-1050°C with HT-GaN TD(cm-2):108, rms:0.5
HT-GaN buffer on c-sapphire treated by GaCl at 800-1050°C with + flow modulation TD(cm-2):107, rms:1.4

Table IV

 Growth conditions for our sample preparation. Numbers in () are optimized values.
H2 cleaning Nitridation (in case) LT-buffer layer Annealing of LT-buffer Deposition of HT-GaN
600-1080°C

(1080°C)

H2 1slm

10min




600-1080°C

NH3 1 slm + H2 1 slm

0-20min (5min)




AlN Up to 1040°C

Increasing rate: 60°C /min

NH3:H2:N2= 750:750:500 (sccm)

0~40min (10min for GaN, 20min for AlN)




1040°C

V/III ratio:

15 000

NH3:H2:N2= 750:750:500

Growth rate; 1.2 µm/h




500-1040°C

TMA: 2.45-4.9µmol/min

V/III ratio 600-13700

NH3: H2 =60- 1500: 1000sccm

Thickness: 10-80nm (20nm)

GaN
600°C

TMG: 0.56-5.6µmol/min

NH3: H2 = 250: 750sccm

V/III ratio: 2000 - 20 000

Thickness: 0-210nm (20nm) 

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