Fabrication by Electron-Beam Lithography and Analysis of Ultrafast Metal-Semiconductor-Metal Photodetectors

• Main Authors: Tang, Seng-Haung, 湯森煌
• Other Authors: Sheng-Fu Horng
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/49922596207431954004

碩士 === 國立清華大學 === 電機工程學系 === 85 === Abstract There are two major parts in this thesis. One is to calibrate the newly setup SEM lithography system and to apply it to the fabrication of submicron Metal-Semiconductor- Metal (MSM) photodetectors. The other is to setup a comprehensive model to analyze the photocurrent response of GaAs MSM schottky photodiodes. In the first part, the frame size was first calibrated, and the backlash of the motor stage, the dwell time, the step size, as well as the probe current were then optimized. Other factors such as the thickness of PMMA, the baking condition, the exposure procedure, the metal thickness, the proximity effects, and then the focusing were also investigated. With all these optimization procedure, we succeeded in fabricating MSM photodetector with submicron metal line width and various spacing. In the second part of this thesis , the photoresponse of the MSM photodetectors was analyzed with 2-D simulator. Our simulation of the carrier transport in these structures reveals the strong influence of distance between the finger electrodes, the external voltage, the GaAs layer thickness, the temperature and the excitation intensity on the intrinsic response time and the corresponding frequency bandwidth of these photo detectors.We also calculated the performance for intrinsic devices with 0.5um interdigital spacing with the corresponding equivalent circuit of the photodetector. It is pointed out that parasitic effects may induce a significant distortion and a delay of intrinsic response. These can be minimized by choosing the optimal photodetector capacitance. Our results are consistent with that reported in the literature.Finally, nonuniform illumination to generate electric pulses from the transmission lines was also studied and a 3THz bandwidth was found for the transmission lines with 20um linewidth and spacing.