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

摘要

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 ×10~8 -4.0×10~8 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.