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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.
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