Photoconductivity Dependence on the background oxygen pressure in Nanostructured ZnO UV Sensor
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1178-AA09-28
Photoconductivity Dependence on the background oxygen pressure in Nanostructured ZnO UV Sensor Nilima V. Hullavarad and Shiva S. Hullavarad Office of Electronic Miniaturization, University of Alaska Fairbanks, Fairbanks, AK 99701
ABSTRACT The present work describes the photoconductivity dependence on ZnO nanostructure UV sensor. ZnO nanostructures were synthesized by direct vapor phase (DVP) technique. ZnO nanowires are of dimensions 30-65 nm in diameter and 5 µm in length. The role of oxygen in deciding the optoelectronic properties of nanostructured ZnO UV sensors was studied. INTRODUCTION The miniaturization of future electronic platforms demands the high density integration in order to achieve high speed, low power consumption and less space. This endeavor demands a new outlook in realizing the devices by employing the techniques of nanoscale electronics at the basic atom or cluster of atoms scale as building blocks. Semiconducting sensors offer an inexpensive and simple method for monitoring UV radiation. Due to large exciton binding energy of 60 meV and the accessibility of large-area single crystal, ZnO has become a prominent material in fabrication of UV detectors. ZnO is a versatile semiconductor material, which has attracted attention for its wide range of applications, such as solar cells, luminescent, acoustic devices and chemical sensors. ZnO is known to be one of the earliest discovered and the most widely applied sensing material. The sensitivity of ZnO surface to oxygen leads to interesting phenomena that are crucial to realization of ZnO based sensors. In this work, we present how change in oxygen pressure affects the opto-electronic properties of nanostructured ZnO UV sensors. EXPERIMENTAL ZnO nanostructures and nanowires were synthesized using direct vapor phase deposition method in which a programmable horizontal tube furnace was used, details are explained elsewhere1. In brief, the processing temperature of 800o C was selected. The source material, Zn granules (99.9%) were placed at the center of the furnace. In the initial stage, the furnace was flushed by Ar gas. When the furnace reached 420oC, the Zn metal evaporated and O2 gas was introduced with a combined Ar/O2 gas mixture. The evaporated Zn metal formed ZnO nanostructures when the reactants achieved supersaturation and got deposited onto substrates and also on the walls of the tube furnace. Thus obtained ZnO nanostructures were characterized using Scanning Electron Microscopy (SEM), and Photoluminescence (PL, PerkinElmer LS 55B) measurements. ZnO nanowire based UV sensors are fabricated on a glass plate with silver electrodes with gap size of 80µm. The UV light of wavelength
380 nm using Ocean Optics Mini2G lamp was incident on the UV sensor during current voltage measurements. The current-voltage characteristics were carried with and without UV illumination under oxygen levels of atmospheric pressure and under vacuum.
PL Intensity (arb.units)
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