Studies of photoconductivity and field effect transistor behavior in examining drift mobility, surface depletion, and transient effects in Si-doped GaN nanowires in vacuum and air
- NIST, Physical Measurement Laboratory, Division 686, 325 Broadway, Boulder, Colorado 80305 (United States)
- School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States)
- Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States)
Variable intensity photoconductivity (PC) performed under vacuum at 325 nm was used to estimate drift mobility ({mu}) and density ({sigma}{sub s}) of negative surface charge for c-axis oriented Si-doped GaN nanowires (NWs). In this approach, we assumed that {sigma}{sub s} was responsible for the equilibrium surface band bending ( Empty-Set ) and surface depletion in the absence of illumination. The NWs were grown by molecular beam epitaxy to a length of approximately 10 {mu}m and exhibited negligible taper. The free carrier concentration (N) was separately measured using Raman scattering which yielded N = (2.5 {+-} 0.3) Multiplication-Sign 10{sup 17} cm{sup -3} for the growth batch studied under 325 nm excitation. Saturation of the PC was interpreted as a flatband condition whereby Empty-Set was eliminated via the injection of photogenerated holes. Measurements of dark and saturated photocurrents, N, NW dimensions, and dimensional uncertainties, were used as input to a temperature-dependent cylindrical Poisson equation based model, yielding {sigma}{sub s} in the range of (3.5 to 7.5) Multiplication-Sign 10{sup 11} cm{sup -2} and {mu} in the range of (850 to 2100) cm{sup 2}/(V s) across the (75 to 194) nm span of individual NW diameters examined. Data illustrating the spectral dependence and polarization dependence of the PC are also presented. Back-gating these devices, and devices from other growth batches, as field effect transistors (FETs) was found to not be a reliable means to estimate transport parameters (e.g., {mu} and {sigma}{sub s}) due to long-term current drift. The current drift was ascribed to screening of the FET back gate by injected positive charge. We describe how these gate charging effects can be exploited as a means to hasten the otherwise long recovery time of NW devices used as photoconductive detectors. Additionally, we present data illustrating comparative drift effects under vacuum, room air, and dry air for both back-gated NW FETs and top-gated NW MESFETs.
- OSTI ID:
- 22102378
- Journal Information:
- Journal of Applied Physics, Vol. 113, Issue 17; Other Information: (c) 2013 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
77 NANOSCIENCE AND NANOTECHNOLOGY
CARRIER DENSITY
DOPED MATERIALS
FIELD EFFECT TRANSISTORS
GALLIUM NITRIDES
ILLUMINANCE
MOBILITY
MOLECULAR BEAM EPITAXY
PHOTOCONDUCTIVITY
PHOTOCURRENTS
PHOTOEMISSION
POISSON EQUATION
POLARIZATION
QUANTUM WIRES
RAMAN EFFECT
RAMAN SPECTRA
SEMICONDUCTOR MATERIALS
SILICON ADDITIONS
SURFACES
TEMPERATURE DEPENDENCE