Current Transport Mechanisms for MSM-Photodetectors on ZnO:N Thin Films
- PDF / 171,654 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 45 Downloads / 186 Views
1201-H05-41
Current Transport Mechanisms for MSM-Photodetectors on ZnO:N Thin Films Tingfang Yen, Alan Haungs, Sung Jin Kim, Alexander Cartwright, and Wayne A. Anderson Electrical Engineering Department, 332 Bonner Hall, University at Buffalo, State University of New York, Buffalo, NY 14260 ABSTRACT Metal-semiconductor-metal photodetectors (MSM-PDs) on ZnO:N thin films deposited by radiofrequency (RF) sputtering and with post N+ ion implantation processing were fabricated using a ZnO/Si structure. A 10 times reduction in dark current was observed compared to the devices on an as-deposited ZnO thin film without ion implantation. These MSM-PDs gave performances of a photo-to-dark current ratio of 2030 and responsivity (R) = 2.7 A/W; the pulse response was a 12.3 ns rise time and 15.1 ns fall time using a femto-second pulse. Temperature-dependent current -voltage (I-V-T) characteristics of the MSM-PDs were observed and the space charge limited current (SCLC) theory was applied to determine the current transport mechanisms. In the SCLC region, J~Vm gave m to determine the current transport mechanism and the value of m changes with temperatures and applied voltages. Current transport is governed by the ZnO structure rather than the electrodes. . INTRODUCTION Ultraviolet photodetectors (UV-PDs) operating in the short wavelength are important devices in various commercial and military applications. Most UV-PDs have been silicon-based. However, due to the indirect bandgap of 1.2 eV for Si, it requires bulky band filters to block solar radiation background and it is intolerant of high temperature and caustic environments[1]. ZnO is one of the potential materials to eliminate those disadvantages, and has been of interest in optical electronics applications for a few years due to its large exciton binding energy, wide bandgap, and some advantages over GaN, such as low cost of bulk single crystals, lower growth temperature, tolerance to high energy radiation, and ease of etching in most acids and alkalis. In this paper, we report MSM-PDs on ZnO thin films. There are many advantages of using a MSM structure for photodetectors, such as simplicity of fabrication, low capacitance, low dark currents, good noise suppression, high speed, and high sensitivity. However, the main drawback of the MSM-PD is high dark current due to the Schottky barrier junction. In this paper, we have reached lower dark current of MSM-PDs by adopting various post-processing steps to modify the properties of ZnO thin films [2, 3] and in addition, have investigated the current transport mechanisms of MSM-PDs. EXPERIMENT ZnO thin films were deposited by RF sputtering using an unheated substrate with ratio of oxygen to argon of 1 to 3 and nitrogen partial pressure of 0.4 mT. A ZnO target with purity of
99.98% was utilized and placed 12 cm from the substrate. Before deposition, a Ti pump was applied to decrease the moisture and contamination in the vacuum system. After sputtering, the samples were implanted by 50 keV N+ ions with implantation dose of 1x1012
Data Loading...
