A low growth temperature is essential to realize low-cost and large-area GaNbased lighting and display. In this work, through detailed investigation under plasma-assisted molecular beam epitaxy, a physical model for low-temperature growth of GaN under N-rich conditions is proposed based on the fact that the desorption process of Ga adatoms can be ignored and the energy for lattice incorporation of Ga adatoms comes only from active N species. A normalized diffusion length (NDL, a dimensionless parameter) is also introduced to provide further insight: the diffusion rate and diffusion time of Ga adatoms are determined by the growth temperature and N flux, respectively; meanwhile the average distance between Ga adatoms is affected by both Ga flux and N flux. Excellent agreement between theoretical predictions and experimental results validates this model and demonstrates the importance of NDL in optimizing the growth condition. The model and NDL could be applied in growing III-nitrides under N-rich conditions by various lowtemperature growth techniques where group-III adatoms are unable to incorporate into the lattice by their own kinetic energy.

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.

By introducing an aluminization process to achieve nucleation of nanowires (NWs), spontaneous growth of AlN NWs on Si substrates has been realized by plasma-assisted molecular beam epitaxy. The AlN NWs are grown from the nuclei formed by the aluminization process, and the NW density and diameter can be controlled by the aluminization parameters. The influence of growth conditions on the morphologies of AlN NWs is carefully investigated. Island-like films are found to grow between the NWs due to poor migration ability of Al adatoms. The films are proved to be Al-polar different from the N-polar AlN NWs, which can explain the absence of newly formed NWs. Increasing the V/III ratio can efficiently suppress the growth of Al-polar AlN films.

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.