Mid-wave infrared (MWIR) detection has been a topic of interest because of its applications in imaging, security, military, and medical diagnostics. The challenge for the MWIR imaging system has been reducing the system size, weight, power consumption, and cost (SWaP-C) while maintaining range and resolution. To help improve SWaP-C, a novel Cadmium Selenide (CdSe) on Lead Selenide (PbSe) type-II heterojunction photovoltaic detector has been demonstrated by epitaxial growth of n-type CdSe on p-type PbSe single crystal film. The I-V measurements show a p-n junction diode with a rectifying factor over 50 at room temperature. The detector structure is characterized by radiometric measurement at room temperature. 30μm × 30μm pixel achieved a D* of 6.5×10^8 Jones under zero bias photovoltaic operation. With decreasing temperature to 230K (thermoelectric cooling), we achieved a D* of 4.4×10^9 Jones.
In-situ surface treatment of vicinal Ge substrates provide a modified surface kinetic regime in which PbSe thin films form highly ordered 3D nanoparticles that coalesce to form bulk monocrystalline PbSe films. Doping of PbSe films forms a strong p-n heterojunction with the p-Ge substrates, resulting in a natural dual-band photovoltaic detector structure with low measured reverse bias current density. In-situ RHEED measurements show the growth evolution of PbSe films under varying conditions, with the ability to form high quality bulk monocrystalline PbSe films >1µm directly on mismatched Ge(100) & (111) substrates. While PbSe and Ge showcase a large lattice mismatch (8.2%) and thermal expansion coefficient mismatch (328%), the resulting structure is a crack-free monocrystalline PbSe film with low x-ray diffraction (XRD) full-width half maximum (FWHM) and strong Photoluminescence (PL) spectra.