Study And Improvement Of Novel GaAs/AlGaAs Quantum Well Middle And Long Wavelength Infrared Photodetectors

GaAs/AlGaAs quantum well photodetectors (QWIPs) are new type devices and progressed rapidly in recent 20 years. QWIPs utilizing intersubband absorption between gallium arsenide (GaAs) well and aluminum gallium arsenide (AlxGa1_xAs) barriers were perfected. Therefore, the ability to accurately control the band structure and hence the spectral response, as well as both established technology for growing and processing GaAs optical devices and commercially available large area VLSI GaAs IC's, makes GaAs/AlGaAs QWIPs attractive devices for use in very large focal plane arrays (FPAs), especially available in the range of long wavelength 8-12 urn.In order to overcome the three main limitations of the conventional GaAs/AlGaAs QWIPs, small photocurrent, high dark current and hence high noise, and low response speed, the novel mechanism of QWIPs that photocurrent increases step by step with the well number's increasing was proposed by Professor Shen. In this thesis, to overcome the difficulty in controling material growth, the detector's structure was improved, and the improved novel GaAs/AlGaAs QWIPs were fabricated. The improved mechanism was analyzed theoretically in detail, and to verify the feasibility of the improved structure, many experiments were attempted. The main contents are following:1. The basic infrared knowledge and the applications of the infrared technology are stated. The academic background of this research is introduced. For the related research area of photodetectors in the country and overseas, the progress, the status quo and the room for improvement are granted. The significance of the novel GaAs/AlGaAs QWIPs research is proposed.2. The mechanism of conventional GaAs/AlGaAs QWIPs is introduced, including the property of the intersubband absorption between bound states, three kinds of QWIPs that are different in the first excited-state position, and the comparison of these different QWIPs. The inherent defects and limitations of the conventional GaAs/AlGaAs QWIPs, which are lead by the structure, were analyzed.3. The principle of the novel GaAs/AlGaAs QWIPs and the strongpoints of the new structure were elucidated in detail. For the novel GaAs/AlGaAs QWIPs, The influence of several important structure parameters on the device was analyzed. Based on the established experiment data, the feasibility and superiority of the novel mechanism was verified. At last, the specific difficulty met in the research was discussed.4. The novel structure was improved. The experiments on each part of the separated structure were carefully made. All the experiments are attempted to verify the feasibility of this improvement on the device structure. Because a conventional quantum well is needed to add in the novel structure, many experiments were madeon conventional GaAs/AlGaAs QWIPs. The experiment results based on various test methods were well analyzed. The detectivity of conventional GaAs/AlGaAs QWIPs can be comparable to the current level gradually.5. According to the problems in practice, the calculation on several performance parameters of the quantum well was done, and the related conclusions were made out of these results. The device processing was introduced in detail, and the flow chart of processing was protracted. The device performance can be influenced by some specific processing steps, and the influence was carefully analyzed. At last, the test methods and system were explicated.