Modeling Quantum Efficiency of Ultraviolet 6H–SiC Photodiodes

The quantum efficiency of p-n junction 6H-SiC ultraviolet (UV) photodiodes has been theoretically modeled for the doping concentration range of 10¹⁴ -10²⁰cm^-3. The calculations take into account the contribution from the depletion region and the doping dependence of charge carrier transport characteristics. Data on optical and physical properties of 6H-SiC that determine the charge carrier transport and bandgap energy are collected and analyzed. The highest average external efficiency of up to 76%, through a working wavelength range of 200-400 nm, can be achieved at lower dopings that result in a fully depleted top active photoabsorbing layer. This is different from the current technology of commercial higher doped SiC UV photodetectors. The detectivity is shown to be conformal to the quantum efficiency in response to the design variations. The temperature dependence of the device does not change the design tradeoffs that depend on the electrical characteristics. The model presented can be extended to elevated temperatures when optical data become available at these temperatures.