Observation of impact ionization in 4H-SiC radiation detectors

Nonequilibrium charge transport has been studied in a structure with a Schottky barrier fabricated on a CVD-grown n-4H-SiC film. The charge introduced by single α-particles was recorded by nuclear spectrometric techniques. The maximum electric field strength in the structure was 1.1 MV/cm. The recorded charge as a function of the reverse bias applied to the structure shows a superlinear rise. Simultaneously, the width of the amplitude spectrum increases superlinearly, too. The observed effect is attributed to the initial stage of impact ionization. The manifestation of the process at unusually low fields (∼1.0 MV/cm) is accounted for by specific features of the charge generation process. The carriers generated by an α-particle are found to be originally 'heated'. The results obtained allow prognostication of the appearance of silicon carbide (SiC) detectors of the 'proportional counter' type in the near future. This is enabled by the advances made in the field of high-voltage electronics in obtaining in practice the required electric field strengths.