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Physics and technology of the infrared detection systems based on heterojunctions

Aslan, Bülent
The physics and technology of the heterojunction infrared photodetectors having different material systems have been studied extensively. Devices used in this study have been characterized by using mainly optical methods, and electrical measurements have been used as an auxiliary method. The theory of internal photoemission in semiconductor heterojunctions has been investigated and the existing model has been extended by incorporating the effects of the difference in the effective masses in the active region and the substrate, nonspherical-nonparabolic bands, and the energy loss per collisions. The barrier heights (correspondingly the cut-off wavelengths) of SiGe/Si samples have been found from their internal photoemission spectrums by using the complete model which has the wavelength and doping concentration dependent free carrier absorption parameters. A qualitative model describing the mechanisms of photocurrent generation in SiGe/Si HIP devices has been presented. It has been shown that the performance of our devices depends significantly on the applied bias and the operating temperature. Properties of internal photoemission in a PtSi/Si Schottky type infrared detector have also been studied. InGaAs/InP quantum well photodetectors that covers both near and mid-infrared spectral regions by means of interband and intersubband transitions have been studied. To understand the high responsivity values observed at high biases, the gain and avalanche multiplication processes have been investigated. Finally, the results of a detailed characterization study on a systematic set of InAs/GaAs self-assembled quantum dot infrared photodetectors have been presented. A simple physical picture has also been discussed to account for the main observed features.