Space charge limited conduction mechanism in GaAsSb nanowires and the effect of in situ annealing in ultra-high vacuum

Abstract

In this work, the first observation of the space charge limited conduction mechanism (SCLC) in GaAsSb nanowires (NWs) grown by Ga-assisted molecular beam epitaxial technique, and the effect of ultra-high vacuum in situ annealing have been investigated. The low onset voltage of the SCLC in the NW configuration has been advantageously exploited to extract trap density and trap distribution in the bandgap of this material system, using simple temperature dependent current–voltage measurements in both the ensemble and single nanowires. In situ annealing in ultra-high vacuum revealed significant reduction in the trap density from 1016 cm−3 in as-grown NWs to a low level of 7 × 1014 cm−3 and confining wider trap distribution to a single trap depth at 0.12 eV. A comparison of current conduction mechanism in the respective single nanowires using conductive atomic force microscopy (C-AFM) further confirms the SCLC mechanism identified in GaAsSb ensemble device to be intrinsic. Higher current observed in current mapping by C-AFM, increased 4 K photoluminescence (PL) intensity along with reduced full-width half maxima and more symmetric PL spectra, and reduced asymmetrical broadening with increased TO/LO mode in room temperature Raman spectra for in situ annealed NWs again attest to effective annihilation of traps leading to the improved optical quality of NWs compared to as-grown NWs. Hence, the I–V–T analysis of the SCLC mechanism has been demonstrated as a simple approach to obtain information on growth induced traps in the NWs.

Hybrid GaAsSb/GaAs Heterostructure Core–Shell Nanowire/Graphene and Photodetector Applications

“…A closed-cycle optical cryostat from Montana Cryostation with the sample chamber interfaced with a fiber-coupled confocal microscope was used for μ-PL measurements at 4 K. For ensemble devices NW/graphene samples were spin-coated with insulating and transparent poly­(methyl methacrylate) (PMMA), which served as both a protective layer and filler for NWs. Oxygen plasma treatment followed by chemical etching was used to expose the NW core tips for contact. , Metal contacts for the NW device consisted of Au/Ti (200/20 nm) and Au (200 nm) depositions for top contacts and graphene, respectively. The photoresponse of the PD device was performed using two-probe electrical measurements under optical illumination using a HORIBA microHR (LSH-T250) spectrometer for wavelength dispersion with a tungsten–halogen lamp as the excitation source and a Keithley-4200 electrical source meter.…”

“…The photoresponse of the PD device was performed using two-probe electrical measurements under optical illumination using a HORIBA microHR (LSH-T250) spectrometer for wavelength dispersion with a tungsten–halogen lamp as the excitation source and a Keithley-4200 electrical source meter. The detector is illuminated through a monochromator on the tip of the NWs. , The illuminated beam spot size (20 mm 2 ) is larger than the active area of the sample, so light can transmit to the NW through the sidewalls. Low-frequency noise (LFN) measurements were conducted by dc-biasing of the metal electrodes of the ensemble device and using a fast Fourier transform dynamic signal analyzer.…”

“…Oxygen plasma treatment followed by chemical etching was used to expose the NW core tips for contact. 4,35 Metal contacts for the NW device consisted of Au/Ti (200/20 nm) and Au (200 nm) depositions for top contacts and graphene, respectively. The photoresponse of the PD device was performed using two-probe electrical measurements under optical illumination using a HORIBA microHR (LSH-T250) spectrometer for wavelength dispersion with a tungsten−halogen lamp as the excitation source and a Keithley-4200 electrical source meter.…”

“…The detector is illuminated through a monochromator on the tip of the NWs. 4,35 The illuminated beam spot size (20 mm 2 ) is larger than the active area of the sample, so light can transmit to the NW through the sidewalls. Low-frequency noise (LFN) measurements were conducted by dc-biasing of the metal electrodes of the ensemble device and using a fast Fourier transform dynamic signal analyzer.…”

“…One-dimensional (1D) semiconductor nanowires (NWs) have been identified as potential building blocks for nanophotonic integrated devices because of their superior light trapping characteristics, high crystal quality, and heterogeneous integration of diverse NW materials and substrate combination caused by the relaxed lattice matching condition. − Similarly, 2D materials have also emerged as an excellent platform for flexible device growth because of their weak van der Waals interaction, which similarly leads to relaxed lattice matching conditions. , Hence, heterogeneous integration of NWs with a 2D material offers opportunities for a broad range of advanced generation flexible optoelectronic device applications, namely, aerial infrared tracking, night vision, wearable devices, mobile applications, medical detection, and petroleum exploration by taking advantage of distinct properties exclusive to the 1D architecture and 2D platform. − Moreover, an NW/2D integrated device may also prove to be very cost-effective. , …”