Growth And Optical Properties Of Cubic Ain Films Deposited By Laser Molecular Beam Epitaxy

The Ⅲ-Ⅴ semiconductor cubic AIN film is becoming a promising optoelectronic and microelectronic material for its excellent properties. However, cubic AlN film exhibits poor quality due to its metastable nature, and thus the energy band structure, optical and electrical properties, and other basic physical properties are seldom reported. In this paper, cubic AlN films were prepared on MgO (100) substrates by laser molecular beam epitaxy technique. The crystal structure, surface morphology, interfacial structure and optical properties of cubic AlN films deposited at different process parameters were analyzed systematically. Meanwhile, the energy band structure and density of states of cubic AlN were simulated using the first principles. The results are as follows:1. Cubic rock-salt AlN films with the single preferred orientation were deposited on MgO (100) substrates by laser molecular beam epitaxy technique. The orientation relationship of cubic AIN film and MgO substrate is AIN (100)[100]//MgO (100)[100]. Cubic AIN films show the excellent crystallinity and surface morphology at the substrate temperature of700℃, the pulsed laser energy of125mJ·p-1, the nitrogen partial pressure of0.8Pa, and the annealing temperature of700℃. For the lattice mismatch between MgO substrate and cubic AIN films, there exists certain misfit stress in the cubic AlN films.2. The interface between cubic AIN film and MgO substrate is clear and smooth. Adjacent to the MgO substrate, a thin strain layer caused by the strain relaxation of lattice mismatch is observed. A coherent interface is formed at the interface between cubic AIN film and MgO substrate. However, lattice defects, such as misfit dislocation and disordered structure, are also found in the film and at the interface as a result of the misfit stress, and the defect density is extremely high in the interface region.3. Cubic AIN films exhibit high transmittance in the visible region. Near the absorption edge, the absorption curves show an obvious shoulder shape structure, indicating the indirect band gap semiconductor of cubic rock-salt AIN film. Based on the transmittance spectra of cubic AIN films, the phonon energy which was calculated by BCC method for the films deposited under different process parameters lies in0.120-0.125eV, corresponding to its transverse optical phonon energy. The bandgaps of cubic AIN films are in the region of4.3-4.5eV, which decrease as the increasing of lattice distortion.4. According to the first principle, the energy band structure and density of states of cubic AIN are simulated using MS software. The results show that the bottom of conduction band and the valence band maximum of cubic AIN are not in the same K point, which confirms that cubic AIN is an indirect band gap semiconductor. The calculated bandgap of cubic AIN is4.392eV, which is consistent with the experimental value.