Normal incidence mid- and far-infrared photodetectors based on phosphorus δ -doped Ge dots were achieved on Si (100) substrates. Ge dots embedded in Si spacer layers were grown by molecular-beam epitaxy in the Stranski-Krastanov mode. The heavily doped (5× 1019 cm-3) Ge dot in the intrinsic Si matrix forms self-consistent potential wells in the conduction band for the ionized electrons. Photoresponse was demonstrated for an n-i-n structure in both the mid- and far-infrared wavelength ranges. The nonvanishing normal incidence response was due to the presence of nonzero off-diagonal terms for the electron mass tensor in Ge.
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