Molecular beam epitaxy and doping of AlN at high growth temperatures

The growth of AlN on c-plane sapphire substrates is reported for a growth temperature of 1100 °C in a radio frequency plasma assisted molecular beam epitaxy system. The high growth temperature in combination with Al-rich growth conditions resulted in a high crystalline quality (FWHM of the 0002 x-ray reflection of 650?) and low O incorporation. Furthermore, the incorporation of Si and Mg as n- and p-type dopants, respectively, has been studied for these growth conditions. For Si doping the corresponding cell temperature was varied between 1300 and 1350 °C. Secondary ion mass spectrometry (SIMS) showed a homogeneous Si depth profile up to a concentration of 7 x 10(exp 20) cm-3, but the Si doped layers remained highly resistive. Incorporation of Mg was observed only at a low growth temperature of 830 °C; at higher growth temperatures SIMS revealed a strong surface segregation effect while the amount of Mg incorporated into the AlN layer remained below the detection limit. The build-up of a Mg accumulation layer at the growth surface due to segregation was found to cause a significant reduction in growth rate.