Demonstration of lateral epitaxial growth of AlN on Si (1 1 1) at low temperatures by pulsed reactive sputter epitaxy

We present a pulsed reactive magnetron sputter process for high quality AlN on Si (1 1 1) beneficially avoiding any high-temperature growth. Initially, metallic aluminium with a nominal thickness of about one monolayer is deposited at a substrate temperature around 850 °C in an Ar plasma followed by sputtering in an Ar/N plasma. For 250 nm thick AlN layers a surface roughness below 0.2 nm rms is obtained as determined by atomic force microscopy (AFM). Using an Al nucleation step prior to AlN growth substantially improves the crystalline properties of AlN. The FWHM values of the AlN (0 0 0 2) and the AlN (1 0 1 0) diffraction peaks with 0.45° and 0.86°, respectively, are comparable to state-of-the-art AlN on Si layers grown by metalorganic vapour phase epitaxy (MOVPE). Two different N-precursor gases, namely N2 and NH3, lead to distinct layer qualities as revealed by atomic force microscopy and transmission electron microscopy. Only with NH3 substantial lateral growth can be achieved at T = 850 °C which is mandatory to obtain smooth surface morphologies. In MOVPE such lateral AlN growth is typically only achieved at high growth temperatures (T > 1000 °C).