Normal incidence infrared detector using intervalence-subband transitions in Si1−xGex/Si quantum wells

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Abstract
Normal incidence infrared detection due to intervalence band transitions of holes is demonstrated using Si1−xGex/Si multiple quantum‐well structures. Two samples with Ge composition (x) of 30% and 60% are used in this study and broad photoresponse peaks (∼100 meV) at near 3 and 2 μm, respectively, are observed. The peak positions of the photoresponse are in close agreement with those observed in the absorption measurement using a waveguide geometry. The low‐temperature photocurrent spectrum for each sample shows that the broad absorption peak at room temperature consists of many peaks due to several transitions. From the calculated energy levels due to different hole bands, we conclude that the transitions are from the heavy‐hole ground state to the split‐off and continuum states. This principle of normal incidence detection can be readily implemented for focal plane infrared detection in the 3–5 μm (and 8–12 μm) range with potential for monolithic integration with Si signal processing circuits.