Effects of hydrogen on the properties of SiC crystals grown by physical vapor transport: Thermodynamic considerations and experimental results

Thermodynamic analysis of the effects of hydrogen addition to the growth ambient during physical vapor transport growth of SiC is presented. In the presence of hydrogen, the efficiency of carbon transport should greatly improve due to the interaction between hydrogen and graphite resulting in formation of hydrocarbons and due to more congruent evaporation of the SiC source material. The changes induced by hydrogen are more pronounced at lower growth temperatures and higher background pressures. A temperature range of 2000-2350 °C and total pressures of 10-100 Torr were considered. Among the consequences of the increased C/Si ratio in the vapor phase, the marked decrease of the nitrogen incorporation efficiency and the suppression of formation of deep traps related to Si-rich growth conditions are expected to be the most prominent. Growth experiments with hydrogen concentrations in the 0-50% range show that indeed the nitrogen concentration decreases by several times and the density of all electron traps in SiC becomes lower by about an order of magnitude with the addition of hydrogen.