Noise sources and improved performance of a mid-wave infrared uncooled silicon carbide optical photodetector

An uncooled photon detector is fabricated for the mid-wave infrared (MWIR) wavelength of 4.21 μm by doping an n-type 4H-SiC substrate with gallium using a laser doping technique. The dopant creates a p-type energy level of 0.3 eV, which is the energy of a photon corresponding to the MWIR wavelength 4.21 μm. This energy level was confirmed by optical absorption spectroscopy. The detection mechanism involves photoexcitation of carriers by the photons of this wavelength absorbed in the semiconductor. The resulting changes in the carrier densities at different energy levels modify the refractive index and, therefore, the reflectance of the semiconductor. This change in the reflectance constitutes the optical response of the detector, which can be probed remotely with a laser beam such as a He-Ne laser and the power of the reflected probe beam can be measured with a conventional laser power meter. The noise mechanisms in the probe laser, silicon carbide MWIR detector, and laser power meter affect the performance of the detector in regards to aspects such as the responsivity, noise equivalent temperature difference (NETD), and detectivity. For the MWIR wavelengths of 4.21 and 4.63 μm, the experimental detectivity of the optical photodetector of this study was found to be 1.07×10(10)  cm·Hz(1/2)/W, while the theoretical value was 1.11×10(10)  cm·Hz(1/2)/W. The values of NETD are 404 and 15.5 mK based on experimental data for an MWIR radiation source with a temperature of 25°C and theoretical calculations, respectively.