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By using an alumination process of Si3N4 at high temperature with aluminum flux irradiation for sufficient time, homogeneously N-polar and atomically smooth AlN film has been realized on silicon substrate with inversion domain suppressed to less than 3.0 × 106 cm−2 and root mean square surface roughness of ∼0.4 nm. A general interface model is proposed to explain the mechanism of polarity determination. The sharp AlN(0001)/Si(111) interface exhibits 5:4 coincidence domain matching, resulting in an almost fully relaxed AlN film.

This paper reports on AlN epilayers with improved crystalline quality grown on silicon-on-insulators (SOIs) by plasma-assisted molecular beam epitaxy (PAMBE). The influences of the substrate on threading dislocation (TD) and surface morphology have been investigated. Two sets of wafers were grown on Si and SOI substrates with the same optimized growth parameters. An atomically smooth AlN epilayer was realized on an SOI substrate with reduced TD density compared to that on Si. This result is attributed to the stress release effect due to the lattice distortion in the top silicon layer of the SOI substrate.

This paper reports surface acoustic wave (SAW) devices fabricated on AlN epitaxial film grown on sapphire, aiming to avoid the detrimental polarization axis inconsistency and refrained crystalline quality of the normally used polycrystalline AlN films. Devices with center frequency of 357 MHz and 714 MHz have been fabricated. The stop band rejection ratio of the as-obtained device reaches 24.5 dB and the pass band ripple is profoundly smaller compared to most of the reported AlN SAW devices with the similar configuration. Judging from the rather high edge dislocation level of the film used in this study, the properties of the SAW devices have great potential to be improved by further improving the crystalline quality of the film. It is then concluded that the AlN epitaxial film is favorable for high quality SAW devices to meet the high frequency and low power consumption challenges facing the signal processing components.

The quantum-confined stark effect induced by polarization has significant effects on the optical properties of nitride heterostructures. In order to improve the emission efficiency of GaN/AlN quantum dots [QDs], a novel epitaxial structure is proposed: a partially relaxed GaN layer followed by an AlN spacer layer is inserted before the growth of GaN QDs. GaN/AlN QD samples with the proposed structure are grown by molecular beam epitaxy. The results show that by choosing a proper AlN spacer thickness to control the strain in GaN QDs, the internal quantum efficiencies have been improved from 30.7% to 66.5% and from 5.8% to 13.5% for QDs emitting violet and green lights, respectively.