Post on 31-Jan-2016
description
Growth and impurity doping of compound semiconductor nanowires
Solid State Physics, Lund University, Lund
E. Norberg, P. Wickert, H. Nilsson, J. Trägårdh, P. Ramvall,
G. Statkute, K. Dick, K. Deppert, L. Samuelson
Philips Research laboratories, Eindhoven
H -Y. Li, O. Wunnicke, G. Immink, M van Weert, M. A. Verheijen, L-F. Feiner, R. Algra, E. P. A. M. Bakkers
1. Introduction2. Nanowire impurity
doping3. InP pn junctions
M.T. Borgströmmagnus.borgstrom@ftf.lth.se
Energy (transformed from one form to another)
• 50 times increase in energy consumption since pre industrial era (15 terawatt-years per year)
• US, 300 million, 5 % of world population > 21 % world energy consumption
• India, 1000 million, 16 % worlds population 3.4 % world energy consumptionMrs Bulletin, 2008. 33
Power to the people(renewable energy)
Mrs Bulletin, 2008. 33
Off-Grid solar cells: Nasa ISS
Metalparticle
liquidAu-IIIeutect
vapor
III-
V n
anow
iretime
VLS (Vapor-Liquid-Solid) Crystal Growth
Wagner and Ellis, APL, 1964
Small lateral dimensions:
Elastic strain relaxation via surface
Single nucleation event (III/V on Si)
Nanowires
Impurity doping in nanowiresParticle assisted growth:• Low temperature (400-500ºC) MOVPE 600-700ºC• Via catalyst particle ?• Complex growth dynamics• [111] growth direction• crystal structure
Large surface/bulk ratio: Surface states
Characterisation:• Chemically (EDX)• Electrically (Field effect)• Optically (PL)•Atom probe
Deliberate NW doping in literature
• Hiruma (GaAs p-n junction, APL 1992)• Meyyappan (p and n-type ZnO, Nano letters 2004)• H-M. Kim (GaN p-n junction, Nano letters 2004)• Appenzeller (Ge p-n junction, Nano letters 2006)• Bakkers (p and n –type InP, InAs, Nano letters 2007)• Lieber (p and n-type InP, GaN, Si p-n junction, dopant modulation)
Lieber, Nano Letters 2008
Evaluate doping – nw-FET
• Drude model, nq • Carrier concentration, n = doping concentration• Mobility (µ) extracted from gate-sweep measurements• Conductivity (σ) extracted from I-V
-0.1 -0.05 0 0.05 0.1-2
-1.5
-1
-0.5
0
0.5
1
1.5
2x 10
-6
SD-voltage [V]
SD
-cu
rre
nt [
A]
D D D
LV RI I
A
n-type
TESn for n-doping(Sn:InP ionization energy 5.9 meV)
• Gate voltage dependent action - n-type• transconductance + IV (ohmic contacts) threshold voltage (non ohmic contacts)
TESn for n-doping(Sn:InP ionization energy 5.9 meV)
• Gate voltage dependent action - n-type• transconductance + IV (ohmic contacts)• threshold voltage (non ohmic contacts)• TESn: excellent n type InP dopant
precursor
ox thqnV Q C V
Dimethylzinc for p-doping(Zn:InP ionization energy 35 meV)
• DMZn enhances the nanowire growth rate and suppresses side wall growth
• Nucleation problems for high dopant precursor molar fraction
XDMZn=1e-6, 20min XDMZn=1e-5, 20min XDMZn=5e-5, 20min1E-7 1E-6 1E-50
2
4
6
8
10
DMZn TESn
Leng
th (µm
)
Dopant precursor molar fraction
Evaluate doping – Results DMZn
• p -type PL behaviour • P-type gate voltage dependent behaviour• Normally turned off at zero gate voltage: low doping• Incomplete DMZn pyrolysis
Van Weert el al, APL, 2006
DiEthylZinc for p doping
• DEZn more effective dopant precursor than DMZn
• InP :DEZn Vth=10V (~1018 cm-3)Minot et al, Nano Letters, 2007
n+p junctions
• XTESn=1E-5, XDMZn=5.5 E-5
• ND=6E18 cm-3, NA= xE17
• 80 nm Au catalyst
order is important
n- InP (111)B
n-In
Pp
-InP
-3 -2 -1 0 1 20
5
10
15
20
25
30
I (nA
)
U (V)
Gate -10V Gate 0 Gate +10 V
0 1 2
1
10
100
1000
I (nA
)
U (V)
Gate -10V Gate 0 Gate +10 V
n=2.97
n=10.1
n=15,6
n+p junction- IV
• pn junction behaviour• Reverse breakdown voltage about 20V• Ideality factor around 3Do they shine?
Electroluminescence
• Light emitting diode• Quantum efficiency ~10-5 at 300K
Photo current measurements
• Voc (707 W/cm2) = 0.97V
Summary
InP• TESn – n type dopant with excellent
controllability• H2S – n type dopant (high doping levels shown)• DMZn- affects nanowire growth rate - low doping levels• DEZn – versatile p-dopant precursor• InAs/InP Core-Shell modulation doping• pn-junctions