Growth of aluminum nitride on (111) silicon: Microstructure and interface structure

The growth of hexagonal aluminum nitride directly on (111) silicon has been studied by grazing incidence x-ray diffraction and high resolution electron microscopy as a function of film thickness. Two epitaxial relationships were observed: (1) AlN (0001) $\text{[2}\overline{11}\text{0]//}\mathrm{Si}\text{(111)}$ [022̄], which prevails at deposition temperatures larger than 650 °C, and (2) AlN (0001) [101̄0]//Si(111) [022̄]. For a 40 Å thick layer, the average in-plane crystallite size is 162 Å, the in-plane rotation is $\text{∼2°}$ and the dislocations induce an average strain distribution of 0.8%. The Si/AlN interface is very sharp and complete relaxation (down to $\text{∼0.2\%}$ ) occurs within one bilayer. No long range order was observed at the interface. This implies a low mobility of the AlN species on Si, inhibiting any structural rearrangement. In particular the in-plane rotations originate from the early stage of the layer growth and decrease with the layer thickness, especially for thicknesses larger than 250 Å.