Observation of negative photoconductivity at bandgap and super bandgap excitations in GaN nanorods

Kaushik, S and Kapoor, AK and Pant, RK and Krupanidhi, SB and Singh, R (2021) Observation of negative photoconductivity at bandgap and super bandgap excitations in GaN nanorods. In: Optical Materials, 121 .

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Abstract

We report on the surprising observation of negative photoconductivity (NPC) in GaN nanorods (NRs) by bandgap and super bandgap excitations. A metal-semiconductor-metal (MSM) type of device configuration using Ni/Au as an electrode at both ends, has been used to study the NPC phenomenon. On exposing the device to the light sources with 363 nm (bandgap excitation) and 250 nm (super bandgap excitation) wavelengths, NPC with a drop of approximately 50 and 60 was observed, respectively. To explain this phenomenon, a model of trapping of photogenerated electrons by the trap states is proposed. Interestingly, a significant drop in the illumination current is observed at low values of power density (up to 3 μW/mm2) of the incident light. It has been interpreted that on increasing the power density, the density of trapped electrons starts approaching the density of available trap states. The de-trapping process is observed to be very slow as the illumination current reached the dark current value in nearly 2 h after switching off the incident light. The observation of NPC and saturation of trap states with high intensity of incident light are also validated by Kelvin Probe Force Microscopy (KPFM) characterization performed in the dark and on illumination with varying intensity of the incident light. Furthermore, on increasing the temperature from room temperature (RT) to 300 °C, the NPC was found to reduce to almost zero, which indicates the de-trapping of trapped electrons on increasing the temperature. © 2021 Elsevier B.V.

Item Type:	Journal Article
Publication:	Optical Materials
Publisher:	Elsevier B.V.
Additional Information:	The copyright for this article belongs to Elsevier B.V.
Keywords:	Energy gap; Gallium nitride; Incident light; Light sources; Nanorods; Photoconductivity; Wide band gap semiconductors, 'current; Band-gap excitation; De-trapping; GaN nanorods; Incident light; Negative photoconductivity; Trap; Trap state; Trapping and de-trapping time; Trapping time, III-V semiconductors
Department/Centre:	Division of Chemical Sciences > Materials Research Centre
Date Deposited:	03 Dec 2021 08:25
Last Modified:	03 Dec 2021 08:25
URI:	http://eprints.iisc.ac.in/id/eprint/70193

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