Abstract
ABSTRACT In order to resolve the trade-off between quantum efficiency and response speed in resonant cavity enhanced (RCE) photodiode, the scheme of the transparent and unique patter n ohmic contact (TUPOC) microstructure was proposed. This scheme can be used for improving devices response speed by reducing the diode capacitance without influencing quantum efficiency. Three kinds of the TUPOC microstructures were proposed and simulated, the first one was realized. The response speed of the finished device with mesa area of 50×50µm 2 is remarkably increased, 3dB bandwidth of 18GHz has been demonstrated, but the device without the TUPOC microstructure only have 3dB bandwidth of 9.47GHz. Keywords: RCE photodiode, TUPOC microstructure, diode capacitance, frequency response, quantum efficiency 1. INTRODUCTION With rapid development of optical communication network, the photodiodes with high speed, high quantum efficiency and wavelength selectivity has become the key devices of optical communication system and network. So RCE photodiode with good abovementioned properties is attractive for wavelength-demultiplex receiving application in optical fiber communication [1][2][3][4]. M.S.Unlu and S.Strite have analyses particularly about RCE photodiode and achieved many useful results[5]. The major response speed limitations in heterojunction photodiode are drift time across the depleted region, charging and discharging times of inherent and parasitic capacitances, the diffusion time for the carriers generated in the undepleted regions, and charge trapping at the heterojunctions. Proper design can minimizes the latter two by incorporating non-absorbing contact regions, grading the absorbing region heterojunctions, and placing the active layer in the depleted region. Therefore, intrinsic limitations imposed by the transit and capacitance charging times are the important limitations for photodiode. Moreover, RCE photodiode has the trade-off between quantum efficiency and response speed. Smaller mesa area make the RCE photodiode has high response speed, but quantum efficiency is low. So how to improving devices response speed without influencing quantum efficiency at the same time that has become the key to obtain higher quality RCE photodiode. The TUPOC microstructure can improve RCE photodiodes response speed without decreasing devices mesa area, so quantum efficiency is immovable. In this paper, three TUPOC microstructures, strip TUPOC microstructure, grid TUPOC microstructure and cirque TUPOC microstructure respectively, were proposed and analysed by finite difference method. Simulation results show that the TUPOC microstructure can improving devices response speed effectively. The RCE photodiode with strip TUPOC microstructure has been fabricated, and have 3dB bandwidth of 18GHz.
Published Version
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