Bas-relief InAlN films: growth, structure, and quantum properties Yu.V. Danylyuk, D.A. Romanov, and G.W. Auner Department of Electrical and Computer Engineering, Wayne State University, Detroit, MI 48202, U.S.A. Abstract. We report a systematic investigation of thick (~ 100 ÷ 500 nm) InAlN films on sapphire substrate. The films have been grown by plasma source molecular beam epitaxy on c-plane sapphire (0001) substrates with thin (about 100 Å) buffer layers of AlN and without such layers. Throughout the whole range of In concentration (from 0 to 1), the obtained films exhibited wurtzite crystal structure with no alloy segregation. On the surface of the films, peculiar bas-relief structures emerge, with large number of bulges. The typical size of a bulge is 50 ÷ 80 nm, varying appreciably with the growth temperature and composition. This bas-relief structure correlates with additional absorption peaks below the fundamental threshold. These peaks are ascribed to electrons trapped and quantized near the bulge tops by a strong built-in electric field. Thus, the bulges act as specific quantum dots with soft localization. The calculated structure of the electron states in a bulge is in a good agreement with the spectroscopic data. 1. Introduction Due to their wide direct band gaps, tuneable by composition and ranging from 1.5 eV for InN to 6.2 eV for AlN, ternary alloys of AlN and InN have receive much attention in the regard of their potential application in light-emitting and laser diodes [1,2]. These devices, based on quantum wells or on self-assembled arrays of quantum dots, would operate in the ultraviolet to visible wavelength region and be indispensable in space and medical applications, supported by excellent radiation and thermal stability of the materials. The development of these promising devices is impeded by technological difficulties associated with the Al 1-x In x N film growth [3-6]. These difficulties stem mainly in the thermal instability due to spinodal phase separation that frustrates solubility between AlN and InN [7]. Responding the challenge, the growth of Al 1-x In x N thin films has been attempted using various substrates and various growth techniques such as metal- organic vapor phase epitaxy [2], magnetron reactive sputtering [3,6], metal-organic chemical-vapor deposition [4], and microwave-excited metalorganic vapor phase epitaxy [5]. Depending on the growth conditions and techniques, the films obtained varied from spontaneously segregated polycrystalline to highly oriented epitaxial. It is highly desirable to achieve control of the crystal structure and morphology of the films, thereby controlling their optical and electrophysical properties.