Silicon-Based Long Wavelength Infrared Detectors Fabricated by Molecular Beam Epitaxy

ABSTRACTSiGe/Si heterojunction internal photoemission (HIP) long wavelength infrared (LWIR) detectors have been fabricated by molecular beam epitaxial (MBE) growth of p+ SiGe layers on p-type Si substrates. The SiGe/Si HIP detector offers a tailorable spectral response in the long wavelength infrared regime by varying the SiGe/Si heterojunction barrier. Degenerately doped p+ SiGe layers were grown by MBE using either HBO2 or elemental boron as the dopant source. Improved crystalline quality and lower growth temperatures were achieved for boron-doped SiGe layers as compared with the HBO2-doped layers. The dark current density of the boron-doped HIP detectors was found to be thermionic emission limited and was drastically reduced as compared with that of HBO2-doped HIP detectors. The heterojunction barrier was determined to be 0.066 eV from activation energy analysis of the HIP detectors, corresponding to a 18 μm cutoff wavelength. Photoresponse of the detectors at wavelengths ranging from 2 to 12 μm has been characterized with corresponding quantum efficiencies of 5 – 0.1%.