Wurtzite GaN films on AlN buffer layers were grown on Si (111) by electron cyclotron resonance microwave plasma assisted MBE (ECR-MBE). High resolution x-ray diffraction studies indicate that the mosaic disorder decreases with increasing growth temperature. The grain size is related to the growth temperature. The best (0002) diffraction peak full width at half maximum was 22 min. for a film 1.7 μm thick. Prominent exciton luminescence is observed at 3.46 eV at 10 K.
The plasma I-V characteristics were measured with a Langmuir probe near the growth position. The nitrogen ion density has been extracted from the data, and is a strong function of the N2 flow rate, the microwave power and the aperture size of the ECR source. The crystal quality of AlN is strongly affected by the plasma conditions.