Electron dynamics for uncooled MWIR SiC detector for digital imaging

Abstract

An uncooled mid-wave infrared (MWIR) detector is developed by doping n-type 4H-SiC with Ga using a laser doping technique. Crystalline silicon carbide (SiC) is a wide bandgap covalent semiconductor material with excellent thermomechanical and optical properties. While the covalent bonding between the Si and C atoms allows n-type or p-type doping by incorporating dopant atoms into both the Si and C sites, the wide bandgap enables fabrication of optical detectors over a wide range of wavelengths. Doping SiC with Ga creates an acceptor energy level of 0.30 eV, corresponding to the MWIR wavelength of 4.21 μm. To fabricate the MWIR detector, an n-type 4H-SiC substrate is doped with Ga using a laser doping technique. Photons of wavelength ~4.21 μm excite electrons from the valence band to the acceptor level, altering the electron density, refractive index, and therefore the reflectance of the substrate. This change in reflectance constitutes the detector optical response. To understand the dynamic response of the detector, the photoexcited electron density and lifetime in the acceptor level is theoretically analyzed. This response is experimentally measured by projecting 633 nm radiation from a laser or high power light-emitting diode (LED) array off the detector at an angle towards a CMOS camera, and examining the digital output of the captured images pixel by pixel to determine the relative intensity of the reflected radiation across the detector. Through digital image processing, a distinct difference is observed in the measured intensity of light reflected off the as-received (undoped) detector sample over infrared temperatures ranging from 100°C to 600°C compared to that of the doped sample comprising quadrants characterized by different doping concentrations, evidencing a change in reflectance from MWIR exposure and thus detector response for the Ga doped SiC detector device.