Quantifying the barrier lowering of ZnO Schottky nanodevices under UV light.

Ming-Yen Lu,Shuen-Jium You,Ming-Pei Lu,Ying-Jhe Wang,Chieh-Wei Chen

doi:10.1038/srep15123

Abstract

In this study we measured the degrees to which the Schottky barrier heights (SBHs) are lowered in ZnO nanowire (NW) devices under illumination with UV light. We measured the I–V characteristics of ZnO nanowire devices to confirm that ZnO is an n-type semiconductor and that the on/off ratio is approximately 104. From temperature-dependent I–V measurements we obtained a SBH of 0.661 eV for a ZnO NW Schottky device in the dark. The photosensitivity of Schottky devices under UV illumination at a power density of 3 μW/cm2 was 9186%. Variations in the SBH account for the superior characteristics of n-type Schottky devices under illumination with UV light. The SBH variations were due to the coupled mechanism of adsorption and desorption of O2 and the increase in the carrier density. Furthermore, through temperature-dependent I–V measurements, we determined the SBHs in the dark and under illumination with UV light at power densities of 0.5, 1, 2, and 3 μW/cm2 to be 0.661, 0.216, 0.178, 0.125, and 0.068 eV, respectively. These findings should be applicable in the design of highly sensitive nanoscale optoelectronic devices.

Highlights

In our modern societies we are often exposed to ultraviolet (UV) radiation, from sunlight, artificial light sources, and electrical appliances
We report our study into the mechanism of the photoresponse of ZnO NW Schottky devices
For an n-type ohmic device, the desorption and adsorption of O2 on the NW surface have a major effect on its response; in contrast, variations in the Schottky barrier heights (SBHs) are responsible for the superior characteristics of an n-type Schottky device

Summary

Introduction

In our modern societies we are often exposed to ultraviolet (UV) radiation, from sunlight, artificial light sources, and electrical appliances. Nanodevices that can vary their electrical signals under illumination have attracted much attention because of their high sensitivity and ease of signal reading[9,10,11] Such detectors can be categorized as either Schottky or ohmic nanodevices. Schottky nanodevices can display outstanding photon detection ability[12,13] when the Schottky barrier height (SBH) is lowered after irradiating with light from an external source. This detection concept can be adopted for the detection of molecules[14] and gases[15]. We used temperature-dependent I–V measurements to extract the SBHs of Schottky devices, as well as the variations in SBHs under different UV illumination power densities

Methods

Results

Conclusion