Persistent Photoconductivity Studies in Nanostructured ZnO UV Sensors

Shiva Hullavarad,David Look,Nilima Hullavarad,Bruce Claflin

doi:10.1007/s11671-009-9414-7

Shiva Hullavarad, David Look + Show 2 more

Open Access

https://doi.org/10.1007/s11671-009-9414-7

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Abstract

The phenomenon of persistent photoconductivity is elusive and has not been addressed to an extent to attract attention both in micro and nanoscale devices due to unavailability of clear material systems and device configurations capable of providing comprehensive information. In this work, we have employed a nanostructured (nanowire diameter 30–65 nm and 5 μm in length) ZnO-based metal–semiconductor–metal photoconductor device in order to study the origin of persistent photoconductivity. The current–voltage measurements were carried with and without UV illumination under different oxygen levels. The photoresponse measurements indicated a persistent conductivity trend for depleted oxygen conditions. The persistent conductivity phenomenon is explained on the theoretical model that proposes the change of a neutral anion vacancy to a charged state.

Highlights

The synthesis methods and the use of nanostructures for various applications have been a very lucrative topic in the last decade [1]
Unknown phenomena and/or new approaches to explain with precision the observed experimental and theoretical facts from the macro/micro world [2]
When all is said and done, the issues in nano-sized devices and basic impediments in device operation have not been addressed largely due to not having a perception of enduser requirements, leaving the device’s operational bottlenecks unaddressed [3]. This is true for two well-researched opto-electronic materials GaN- [4] and ZnO-based [5] devices like light-emitting diodes and photodetectors

Summary

Introduction

The synthesis methods and the use of nanostructures for various applications have been a very lucrative topic in the last decade [1]. When all is said and done, the issues in nano-sized devices (individual or arrays) and basic impediments in device operation have not been addressed largely due to not having a perception of enduser requirements, leaving the device’s operational bottlenecks unaddressed [3] This is true for two well-researched opto-electronic materials GaN- [4] and ZnO-based [5] devices like light-emitting diodes and photodetectors. PPC is very difficult to observe in bulk materials and needs to be measured at very low temperature, which in turn complicates the carrier transport mechanisms, limiting the ability to extract and interpret the exact cause of the problem [18] This phenomenon is observable in both macro and nanostructured films; the effects are more prominent in nanostructured materials due to singularity in their joint density of states, allowing a bulk phenomenon to be observable clearly even at room temperature. ZnO nanostructures were characterized by environmental scanning electron microscope (E-SEM) (Electro Scan) and photo-luminescence (PL) at room temperature

Results and Discussion

X 10-1 Torr - under UV 8 X 10-2 Torr - under UV

X 10-2 Torr