Growth and impurity doping of compound semiconductor nanowires

1. M.T. Borgström magnus.borgstrom@ftf.lth.se 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. Introduction 2. Nanowire impurity doping 3. InP pn junctions

2. Energy (transformed from one form to another) • 50times 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 consumption Mrs Bulletin, 2008. 33

3. Energy availability

4. Power to the people(renewable energy) Off-Grid solar cells: Nasa ISS Mrs Bulletin, 2008. 33

5. liquid Au-III eutect vapor Metal particle III-V nanowire time VLS (Vapor-Liquid-Solid) Crystal Growth Small lateral dimensions: Elastic strain relaxation via surface Single nucleation event (III/V on Si) Nanowires Wagner and Ellis, APL, 1964

6. Impurity doping in nanowires • Particle 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

7. 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

8. 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 n-type

9. 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)

10. 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

11. 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, 20min

12. 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

13. DiEthylZinc for p doping • DEZn more effective dopant precursor than DMZn • InP :DEZn Vth=10V (~1018 cm-3) Minot et al, Nano Letters, 2007

14. n+p junctions • XTESn=1E-5, XDMZn=5.5 E-5 • ND=6E18 cm-3, NA= xE17 • 80 nm Au catalyst p-InP n-InP n- InP (111)B order is important

15. n+p junction- IV • pn junction behaviour • Reverse breakdown voltage about 20V • Ideality factor around 3 Do they shine?

16. Electroluminescence • Light emitting diode • Quantum efficiency ~10-5 at 300K

17. Photo current measurements • Voc (707 W/cm2) = 0.97V

18. 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