SiGe/Si heterojunction internal photoemission long-wavelength infrared detectors fabricated by molecular beam epitaxy

A new SiGe/Si heterojunction internal photoemission (HIP) long-wavelength infrared (LWIR) detector has been fabricated by molecular beam epitaxy (MBE). The detection mechanism of the SiGe/Si HIP detector is infrared absorption in the degenerately doped p⁺-SiGe layer followed by internal photoemission of photoexcited holes over a heterojunction barrier. By adjusting the Ge concentration in the SiGe layer, and, consequently, the valence band offset between SiGe and Si, the cutoff wavelength of SiGe HIP detectors can be extended into the LWIR (8-17-μm) regime. Detectors were fabricated by growing p⁺-SiGe layers using MBE on patterned p-type Si substrates. The SiGe layers were boron-doped, with concentrations ranging from 10¹⁹ cm^-3 to 4×10²⁰ cm^-3. Infrared absorption of 5-25% in a 30-nm-thick p⁺-SiGe layer was measured in the 3-20-μm range using a Fourier transform infrared spectrometer. Quantum efficiencies of 3-5% have been obtained from test devices in the 8-12-μm range