Performance Analysis of a 4H-SiC n-p-n Phototransistor With Floating Base for Ultraviolet Light Detection

A 4H-SiC n-p-n bipolar phototransistor detector (PTD) with a floating-base configuration is fabricated and studied in this work. The PTD exhibits low dark current and high responsivity in the ultraviolet (UV) wavelength band, which results in a large photo-to-dark current ratio (PDCR). The optical gain of the PTD is found highly dependent on the incident light intensity, which is larger at high light levels. Nevertheless, at low light levels, a unity gain is obtained, which is limited by the recombination current within the emitter–base (E–B) junction. The PTD further exhibits high-temperature operation potential and a detectivity of <inline-formula> <tex-math notation="LaTeX">$7.06\times 10^{{12}}$ </tex-math></inline-formula> cm<inline-formula> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula>Hz<inline-formula> <tex-math notation="LaTeX">$^{\text {1/2}}$ </tex-math></inline-formula>/W can be achieved at 150 °C. The transient response characteristics of the PTD are characterized as a function of incident power density and temperatures. It is found that optical gain and junction capacitance are both important for explaining the variation trends of response time. Finally, a demonstration board is designed and fabricated to test the potential of the SiC PTD for UV radiometer applications. When operating in active mode, the PTD circuit could exhibit reasonable linear response to incident UV power density.