assivation and Doping due to Hydrogen in IIINitrides

1
assivation and Doping due to Hydrogen in
III-Nitrides
Sukit Limpijumnong and Chris G. Van de
Walle Xerox Palo Alto Research Center, Palo Alto,
CA 94304
Jörg Neugebauer Fritz-Haber-Institut, Faradayweg
4-6, D-14195 Berlin, Germany
Acknowledgements J. Northrup, N. Johnson, and M.
McCluskey
Supported by ONR AFOSR
2
otivation and outline

• Role of hydrogen in III-N
• Electrically active
• Incorporates during growth
• MOCVD, HVPE, MBE with NH3
• passivates acceptors during p-type growth
• Monitor acceptor activation
• Vibrational spectroscopy
• Comparison with first-principles calculations
• New results on microscopic structure of Mg-H
• Studies so far limited to GaN
• Device structures involve InGaN or AlGaN
• Systematic study of H in AlN, InN

3
omputational methods

• First principles calculations
• density functional theory in local density
  approximation
• pseudopotentials with a plane-wave basis set
• super cell sizes
• Up to 64 atoms for zinc blende
• Up to 96 atoms for wurtzite

4
g-H complex in GaN
H passivates Mg microscopic structure?
5
degree structure
Polarized IR Spectroscopy
RECENT
B. Clerjaud et al., PRB 61, 8238 (2000).
Electric dipole induced by N-H vibration forms
1305o with c-axis.
6
ydrogen in AlN and InN

• Eform formation energy
• impurity concentration Nsite exp(- Eform/kT)
• Example H in GaN
• Eform(H) Etot(H) - Etot(GaN) - mH EF
• mH energy of H in reservoir, i.e., H chemical
  potential
• EF energy of electron in its reservoir, i.e.,
  the Fermi level

• Calculations for zinc-blende
• OK for systematic comparison
• Only small differences with wurtzite

7
ossible sites and charge states
1 Å
N
H
Ga
Bond center (BC)
Anti-bonding N (ABN)
Anti-bonding Ga (ABGa)
8
ydrogen in GaN
e(0/-)
e(/0)

• H amphoteric
• H in p-type
• H- in n-type
• always counteracts prevailing conductivity

5
4
0
H
(ABGa)
3
Formation Energy (eV)
2

-
1
H
(ABGa)
H
(ABN)
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
E
(eV)
F
J. Neugebauer and C. G. Van de Walle, PRL 75,
4452 (1995).
9
ydrogen in AlN
e(/0)
e(0/-)

4

• Similar to GaN
• H lower energy in p-type
• H- lower energy in n-type more important than in
  GaN
• Negative U
• U -2.6 eV

0
H
(ABAl)
3
2
Formation Energy (eV)
1

0
-

H
(ABN)
H
(ABAl)
-1
0
1
2
3
4
E
(eV)
F
10
ydrogen in InN
4
3
2
Formation Energy (eV)
1
0
-1
0
1
2
3
4
5
0
1
2
3
0
1
AlN
GaN
InN
11
ydrogen in InN

3
0
H
(ABIn)

• H lowest energy for all EF positions!
• H0, H- never stable
• Hydrogen is a donor in InN!

2
-
H
(ABIn)
1
Formation Energy (eV)

0

H
-1
(ABN)
0.0
0.5
1.0
1.5
E
(eV)
F
12
nintentional doping of InN
C. Stampfl et al., PRB 61, R7846 (2000).
3

• Nitrogen vacancies unimportant
• Oxygen
• Silicon

2
V
N
1
Si
Formation Energy (eV)
Ga
O
0
N
-1
0.0
0.5
1.0
1.5
E
(eV)
F
13
ummary

• Microscopic structure of Mg-H complex
• New model, agrees with experimental frequency and
  with N-H bond angle of 134o (from polarized IR
  spectroscopy)
• Hydrogen in AlN, GaN and InN
• Stable sites for each charge state are similar
  for H in AlN, GaN and InN
• In GaN and AlN, H acts as amphoteric impurity
• H in p-type
• H- in n-type
• In InN H always act as a donor