Effect of laser irradiation passes for fabricating mid-wave infrared silicon carbide detectors

A Mid-Wave Infra-Red (MWIR) detector is developed by doping an n-type 4H-SiC with Ga using a laser doping technique. Doping is one of the challenges for silicon carbide (SiC) device fabrication due to its hardness, chemical inertness and the low diffusion coefficient of most impurities. A laser doping technique is chosen to dope 4H-SiC by gallium which is incorporated into the semiconductor as p-type dopants. The substrate is simultaneously heated with a continuous wave Nd:YAG laser of wavelength 1064 nm under the laser power, focal length, laser beam diameter and micro-stage speed were 10.5 W, 150 mm, 200 µm and 0.8 mm/sec respectively using metal-organic dopant precursor. The gallium dopant profile in the laser-doped SiC wafer is obtained by secondary ion mass spectroscopy and the maximum concentration of Ga in SiC wafer surface with 4 time of laser irradiation passes is found to be 6.251×10²⁰ cm⁻³, which is two orders of magnitude higher than the reported value (6.0×10¹⁸ cm⁻³) and the dopant depth is approximately 360 nm. The data revealed enhanced solid solubility exceeding the equilibrium solubility limit. The detection mechanism is based on the photoexcitation of electrons by the photons of this wavelength absorbed in the doped SiC. This process modifies the electron density, which changes the refractive index and, therefore, the reflectance of the semiconductor is also changed. The change in the reflectance, which is the optical response of the detector, can be measured remotely with a laser beam such as a He-Ne laser. The variation of refractive index was calculated as a function of absorbed irradiance based on the reflectance data for the as- received and doped samples. A distinct change was observed for the refractive index of the doped sample, indicating that the detector is suitable for applications at 4.21 µm wavelength.