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 degrees 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 degrees C. Secondary ion mass spectrometry (SIMS) showed a homogeneous Si depth profile up to a concentration of 7 x 10(20) cm(-3), but the Si doped layers remained highly resistive. Incorporation of Mg was observed only at a low growth temperature of 830 degrees 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.