Temperature- and Al/N ratio-dependent AlN seed layer formation on (110) Si substrates by using plasma-assisted molecular beam epitaxy

AlN seed layers with a thickness of 50 nm were grown by using nitrogen plasma-assisted molecular beam epitaxy on (110) Si substrates with different V/III ratios in the temperature range from 850 .deg. C to 940 .deg. C. In varying the Al/N ratio and the growth temperature, distinct surface morphologies emerge, which are quite different from those observed in AlN growth on (111) Si substrates. Under N-rich conditions, AlN films exhibits randomly distributed islands with different sizes ranging from 10 nm to 1 m. In Al-rich conditions, two distinct surface morphologies, (1) closely-packed islands preferentially aligned along the [1120]AIN /[110]Si azimuth and (2) smooth flat surfaces, are observed at various growth temperatures. The observed morphology transition is attributed to the asymmetric strain distribution between hexagonal symmetric AlN layers and rectangular (110) Si substrates and to varying surface adatom migration rates present at different growth temperatures.