Si-based normal incident mid-infrared photodetectors using Ge dots were investigated. P-I-P structures of boron-doped Ge dots embedded in the intrinsic region were grown using solid source molecular beam epitaxy. The dark current was strongly dependent on the doping level in Ge dot. The structure grown at 700 °C exhibited photoresponse peaking at 3.5 μm. FTIR measurements on identical structure showed an absorption band consistent with the photocurrent spectra. At lower temperatures, the response intensity decreased due to freeze-out of the holes. The devices also showed photovoltaic effect. The response increased with increasing bias.
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