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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$30~\mu $ </tex-math></inline-formula>m. The detector exhibited a low dark current of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim ~0.12$ </tex-math></inline-formula> nA<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula>cm<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{2}}$ </tex-math></inline-formula> with a fully depleted sensitive region at 200 V. The sensitivity of unit area of the detector achieved <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$36.67~\mu $ </tex-math></inline-formula>C<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula>Gy<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{1}} \cdot $ </tex-math></inline-formula>cm<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{2}}$ </tex-math></inline-formula> (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$28.09~\mu $ </tex-math></inline-formula>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.