Steady-state and transient photoconductivity in c-axis GaN nanowires grown by nitrogen-plasma-assisted molecular beam epitaxy

Journal Article · Mon Feb 15 00:00:00 EST 2010 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.3275888· OSTI ID:21476133

Sanford, N A; Blanchard, P T; Bertness, K A; Mansfield, L; Schlager, J B; Sanders, A W; Roshko, A ^[1]; Burton, B B; George, S M ^[2]

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1. Optoelectronics Division 815, National Institute of Standards and Technology, Boulder, Colorado 80305 (United States)
2. Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309 (United States)

Analysis of steady-state and transient photoconductivity measurements at room temperature performed on c-axis oriented GaN nanowires yielded estimates of free carrier concentration, drift mobility, surface band bending, and surface capture coefficient for electrons. Samples grown (unintentionally n-type) by nitrogen-plasma-assisted molecular beam epitaxy primarily from two separate growth runs were examined. The results revealed carrier concentration in the range of (3-6)x10{sup 16} cm{sup -3} for one growth run, roughly 5x10{sup 14}-1x10{sup 15} cm{sup -3} for the second, and drift mobility in the range of 500-700 cm{sup 2}/(V s) for both. Nanowires were dispersed onto insulating substrates and contacted forming single-wire, two-terminal structures with typical electrode gaps of {approx_equal}3-5 {mu}m. When biased at 1 V bias and illuminated at 360 nm (3.6 mW/cm{sup 2}) the thinner ({approx_equal}100 nm diameter) nanowires with the higher background doping showed an abrupt increase in photocurrent from 5 pA (noise level) to 0.1-1 {mu}A. Under the same conditions, thicker (151-320 nm) nanowires showed roughly ten times more photocurrent, with dark currents ranging from 2 nA to 1 {mu}A. With the light blocked, the dark current was restored in a few minutes for the thinner samples and an hour or more for the thicker ones. The samples with lower carrier concentration showed similar trends. Excitation in the 360-550 nm range produced substantially weaker photocurrent with comparable decay rates. Nanowire photoconductivity arises from a reduction in the depletion layer via photogenerated holes drifting to the surface and compensating ionized surface acceptors. Simulations yielded (dark) surface band bending in the vicinity of 0.2-0.3 V and capture coefficient in the range of 10{sup -23}-10{sup -19} cm{sup 2}. Atomic layer deposition (ALD) was used to conformally deposit {approx_equal}10 nm of Al{sub 2}O{sub 3} on several devices. Photoconductivity, persistent photoconductivity, and subgap photoconductivity of the coated nanowires were increased in all cases. TaN ALD coatings showed a reduced effect compared to the Al{sub 2}O{sub 3} coated samples.

• OSTI ID: 21476133
• Journal Information: Journal of Applied Physics, Vol. 107, Issue 3; Other Information: DOI: 10.1063/1.3275888; (c) 2010 American Institute of Physics; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

77 NANOSCIENCE AND NANOTECHNOLOGY
36 MATERIALS SCIENCE
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALUMINIUM OXIDES
CARRIER DENSITY
CARRIER MOBILITY
COATINGS
DEPLETION LAYER
DEPOSITION
ELECTRONS
GALLIUM NITRIDES
HOLES
MOLECULAR BEAM EPITAXY
PHOTOCONDUCTIVITY
PLASMA
QUANTUM WIRES
SEMICONDUCTOR MATERIALS
SUBSTRATES
TANTALUM NITRIDES
ALUMINIUM COMPOUNDS
CHALCOGENIDES
CRYSTAL GROWTH METHODS
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELEMENTARY PARTICLES
EPITAXY
FERMIONS
GALLIUM COMPOUNDS
LAYERS
LEPTONS
MATERIALS
MOBILITY
NANOSTRUCTURES
NITRIDES
NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
PNICTIDES
REFRACTORY METAL COMPOUNDS
TANTALUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS