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

Energy availability

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