Growth of α ‐ SiC Single Crystals from Chromium Solution

Abstract

The travelling solvent method of crystal growth has been successfully adapted to the growth of single crystals, using pure chromium as the solvent. Since molten chromium does not wet chemically cleaned in a uniform and reproducible manner, a prewetting procedure was developed which involves a heat treatment of the at 1200°–1300°C in vacua at 10−9–10−10 Torr, followed immediately by the evaporation of a thin (104Aå) film of pure chromium onto the clean surfaces. The chromium solvent zones were passed under the influence of a temperature gradient in a simple r. f. furnace; the average specimen temperature was 1750°C. Subsequent metallographic and x‐ray examination revealed that good crystal growth had occurred. Growth rates of the order of 0.75 mm hr−1 were obtained under the above conditions, p‐n junctions prepared by deposition, from chromium solution, of one conductivity type onto the opposite type were assembled into diode structures. Junction capacitance varies with bias in accordance with a law, indicating an abrupt (step) junction. The forward I–V characteristics are unique for SiC devices in that the forward voltage drop is 1.2–1.5v compared to 2–5v reported for previous diodes at comparable current densities. The slope of the forward biased characteristics was found to be e/2.4kT. Considerable leakage is observed (under reverse bias); the peak inverse voltage, which ranges from 6–15v, is much lower than expected from the resistivity of the bulk material. This low voltage breakdown is tentatively discussed in terms of a peculiar dislocation structure in the region of the p‐n junction. The over‐all rectifying properties of the devices prepared by TSM persist up to at least 540°C.