X-Ray Detector With Internal Gain Based on a SiC npn Structure

A two-terminal npn device based on 4H-SiC has been employed as a radiation detector for the first time. This device was designed as a vertical npn structure with a sensitive area of up to 1 cm2, and the thickness of the sensitive layer was about $30~\mu $ m. The detector exhibited a low dark current of $\sim ~0.12$ nA $\cdot $ cm $^{-{2}}$ with a fully depleted sensitive region at 200 V. The sensitivity of unit area of the detector achieved $36.67~\mu $ C $\cdot $ Gy $^{-{1}} \cdot $ cm $^{-{2}}$ ( $28.09~\mu $ A @ 0.766 Gy/s) to X-ray illumination (generated by bremsstrahlung with a tungsten target with tube voltage 30 kV) at 200 V, which was attributed to the amplification mechanism of the npn structure. Compared with the response characteristics of a SiC-PiN detector with the same sensitive volume, the gain of the two-terminal SiC npn detector was estimated to be 11.46 at 200 V. Specifically, the internal gain of the detector increased with the X-ray dose rate, where the X-ray photocurrent worked as the base current in the BJT devices. The internal gain also increased with the bias voltage due to the Early effect. Moreover, the two-terminal SiC npn detectors had a good switching response to X-rays and showed great potential in the applications of radiation detection.