In summary, quantum size effects in SiGe/Si heterostructures are discussed. A detailed discussion on infrared absorption between different subbands of Si1-xGex/Si multiple quantum wells and δ-doped structures is presented. The origins of different transitions were identified using the polarization-dependence measurements. The importance of many-body effects in determining transition energy is also demonstrated. Infrared detectors based on intersubband and intervalence band transitions have been demonstrated. The photoresponse was shown to cover both the 3-5-and 8-14-μm atmospheric windows. A possible avenue for improvement of the responsivity as well as the detectivity of the device was outlined. The continued progress in the study of SiGe intersubband transitions indicates that monolithic integration of SiGe/Si multiple quantum well infrared detectors with Si signal processing circuits should be realizable for focal plane applications.
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