Quantum well infrared photodetectors (QWIPs) have recently emerged as a potential alternative to the conventional detectors utilizing low bandgap semiconductors for infrared applications. There has been a considerable amount of experimental and theoretical work towards a better understanding of QWIP operation, whereas there is a lack of knowledge on the underlying physics. This work provides a better understanding of QWIP operation and underlying physics through particle simulations using the ensemble Monte Carlo method. The simulator incorporates Gamma, L, and X valleys of conduction band as well as the size quantization in the quantum wells. In the course of this work, the dependence of QWIP performance on different device parameters is investigated for the optimization of the QWIP structure.
The simulations on AlGaAs/GaAs QWIPs with the typical Al mole fraction of 0.3 have shown that the L valley of the conduction band plays an important role in the electron capture. A detailed investigation of the important scattering mechanisms indicates that the capture of the electrons through the L valley quantum well (L-QW) affects the device performance significantly when Gamma and L valley separation is small. The characteristics of electron capture have been further investigated by repeating the simulations on QWIPs for quantum well widths of 36 and 44 Å / . The results suggest that the gain in the shorter well width device is considerably higher, which is attributed to the much longer lifetime of the photoexcited electrons as a result of lower capture probability (pc) in the device.
The effects of the L-QW height on the QWIP characteristics have also been studied by artificially increasing this height from 63 to 95 meV in Al0.3Ga0.7As/GaAs QWIPs. The increase in the L valley (L-QW) height resulted in higher pc and lower gain due to high rate of capturing of these electrons when Gamma and L valley separation is small.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/2/12607291/index.pdf |
| Date | 01 March 2006 |
| Creators | Memis, Sema |
| Contributors | Tomak, Mehmet |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | Ph.D. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for METU campus |
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