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Please use this identifier to cite or link to this item: http://hdl.handle.net/1860/1232

Title: Carrier transport in high-speed photodetectors based on two-dimensional-gas
Authors: Zhao, Xia
Keywords: Electric engineering;Optoelectronics;Optical detectors
Issue Date: 19-Jan-2007
Abstract: Monolithically integrated high-speed photodetectors are important components in fiber communications and optoelectronic integrated circuits (OEIC) with metal-semiconductor-metal (MSM) photodetectors (PD) being the device of choice due to the its high overall performance and technology compatibility with integrated circuits (IC). The speed of conventional top illuminated MSM-PD is limited by the transit time of photogenerated carriers. The concept of internal vertical field, developed in the MSM intrinsic absorption region by the two-dimensional-gas along the heterojunction, is proposed and implemented for the purpose of facilitating carrier transport, hence improving the transit time limitations. The time response of a two-dimensional-electron-gas (2-DEG) based photodetector suggests an enhanced electron transport but a long tail due to the slow holes. We have designed and fabricated two-dimensional-hole-gas (2-DHG) based MSM photodetector to investigate hole transport in the vertical field MSM photodetector. Simulation of charge carrier transport, verifies experimentally observed behavior, which manifests the enhanced hole transport benefit from the vertical field. In addition, the 2-DHG based MSM structure device shows excellent capacitance-voltage (C-V) characteristic making it an excellent candidate for applications in odd-order high frequency multipliers. The high Cmax/Cmin ratio of 113 and high sensitivity of 35 are one of the best results reported. In addition, optoelectronic measurements demonstrate the slope of the C-V relationship can be modulated by the intensity of the incident optical power. A model describing the source of the C-V results is proposed along with the simulation results verifying the observed C-V behavior. In order to produce a complete picture of charge transport and collection, we developed a program using Ensemble-Monte-Carlo (EMC) method incorporating the electron-electron scattering in the 2-DEG confined by AlGaAs/GaAs heterojunction. The result reveals an energy thermalization time of tens of femto-second in the 2-DEG, which suggest the 2D gas has the potential to collect the photogenerated carriers. Based on all previous experimental results and analysis, a 2-DEG/2-DHG combined structure has been proposed on GaAs substrate. The design, taking advantage of the vertical field and fast thermalization time in the confined 2D gas, results in a wide bandwidth, high external quantum efficiency for vertically illuminated MSM device.
URI: http://hdl.handle.net/1860/1232
Appears in Collections:Drexel Theses and Dissertations

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