Oxygen reduction through specific surface area control of AlN powder for AlN single-crystal growth by physical vapor transport

In the physical vapor transport (PVT) growth of AlN, re-oxidation of aluminum nitride (AlN) source powder happening in the process of setting seed crystal into crucible seems to be unavoidable. This process introduces oxygen just before AlN growth and has a significant impact on the crystal quality. In this paper, a high and low-temperature alternative sintering method (HLAS) is proposed based on the idea of specific surface area control to reduce the re-oxidation of AlN source powder. This method introduces cyclic sintering between 1500°C and 1900°C to the conventional three-step treatment repeatedly, which utilizes possible phase-transition along with the processes of powder sintering back and forth to increase the particle size and decrease the specific surface area significantly. The SEM (Scanning electron microscope) and BET (Brunauer, Emmett, and Teller) results showed that the specific surface area of AlN powder treated with the HLAS method can be reduced to one-third of that with the conventional method. Thus, the SIMS (secondary ion mass spectrometry) confirmed the reduction of oxygen impurity in AlN single-crystals to a good level of 1.5×1017cm-3. It is clear that this HLAS process is an effective way of controlling the specific surface area of AlN source powder, which contributes to the suppression of oxygen influence on PVT-AlN growth.