| Summary: | 碩士 === 臺灣大學 === 電子工程學研究所 === 95 === The infrared photodetectors are important in many civilian, military and scientific applications. Some of them, for example temperature sensing and target discrimination, require the infrared photodetectors to be equipped with the ability of multicolor detection. In the thesis, a new structure of superlattices bounded by two thick barrier was investigated. The detection range of this infrared photodetector was 7~16μm, and the detector showed the voltage-tunable characteristic.
Due to dopant migration, build-in electric field exists in the device. There is open-circuit photoresponse, the detector can operate in photovoltaic mode. Under ultra low bias, build-in electric field dominates the energy band. There are two peaks in the open-circuit photoresponse. Photoelectrons in the two energy states which corresponding to the two peaks move to different direction. Therefore, response is different under same amplitude but different bias polarity. We presented the energy band diagram affected by build-in electric field.
Under high bias, applied electric field dominates energy band. Voltage drops not only on the barrier but also in the superlattice region. Transition energy changes because of band-bending. We observed five peaks in the response as applied bias increased. These five peaks are different from four peaks calculated by flat-band. We presented the energy band diagram under high bias. Recalculated the energy level, we concluded the ground states of each transition energy.
Response is also affected by temperature. Under low bias, electrons follow Fermi-Dirac distribution. Whole response increases as temperature increases. While bias increase, electrons is affect by tunneling and scattering effect. There is a crossing point in the response. The crossing point jumps to next long wavelength peak as bias increases, and the crossing points become two.
With this structure, our detector has broad-band response.
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