Measurement of ionization rate of charge carriers and breakdown characteristics of CVD-grown 4H-SiC diodes under steady magnetic field

Abstract

The impact ionization rate of electrons and holes in (0001)-oriented 4H-SiC has been measured under steady oblique magnetic field and hence, the influence of magnetic field on the breakdown characteristics of 4H-SiC diodes has been investigated. A set of three diodes having p+–n–n+ structure and another set of three diodes having n+–p–p+ structure have been grown on (0001)-oriented n+ and p+ 4H-SiC substrates using chemical vapor deposition (CVD) technique with different epitaxial layer thicknesses for carrying out the measurements within the electric field range of 2.5 × 108–4.0 × 108 V m−1. The ionization rate data are extracted from the photomultiplication measurements using ultra-violet light source of 260-nm wavelength. The ionization rates are found to be decreased with the increase of the magnetic field strength, especially at low electric fields; this decrement is found to be more pronounced in the ionization rate of electrons than the same of holes. A theoretical model developed by the authors is used to calculate the breakdown voltage of the 4H-SiC diodes. The numerical results are compared with the experimentally measured breakdown characteristics and those are found to be in good agreement within the externally applied magnetic field strengths of 0–1500 Gauss. Breakdown voltage of a diode is found to be increased due to the presence of magnetic field; the maximum values of these said increments are found to be around 5% and 2.6% in p+–n–n+ and n+–p–p+ diodes, respectively. Better magnetic field sensitivity is observed in the diodes having broader epitaxial layer widths.