Abstract
In recent years, III-N materials such as AlN, GaN, InN and their ternary compounds have attracted great interest in applications such as light-emitting diodes, laser diodes, and solar cells etc. AlxIn1-xN (AlInN) compounds are expected to have immense potential in this field of applications because they possess the widest spectral and lattice constant range in all III-N compounds. There were few reports on the growth of AlInN ternary films due to the large miscibility gap and difference in the thermal stability between AlN and InN. In this study, AlInN films were grown on glass substrates by pulsed-dc reactive sputtering. XRD analysis showed that the crystallinity of In-rich Al0.36In0.64N and Al-rich Al0.55In0.45N films directly deposited on glass improved as substrate temperature increased from 200 oC to 400 oC. However, for temperatures ≥300 oC, oxygen-diffusion was observed in the whole range from the glass substrate to the AlInN film by XPS analysis. After applying AlN buffer layer, the crystallinity of AlInN films was markedly improved and no oxygen contamination was observed. Highly c-axis-oriented AlInN films with very low FWHM of 2.9°~3.5° were obtained. The electron concentration of AlN-buffered AlInN films was obviously lower than that of oxygen contaminated films. In the study of optical bandgap, AlInN films with x = 0.12~0.87 grown on AlN/glass have highly c-axis preferred orientation and excellent crystal quality. The FWHM of (002) plane is between 2.6 o and 3.6 o. There is no oxygen detected in the bulk of AlInN films. The electron concentrations of sputtered In-rich AlInN films (x = 0.12~0.49) are in the range of 1×1016~3×1020 cm-3. The bandgaps of AlInN films are determined and compared with previous reports. The bandgap discrepancy of In-rich AlInN can be explained by the Burstein-Moss effect. The bowing parameter for bandgaps of AlInN alloys is 4.1 eV. Mechanical properties of AlInN films were characterized by nanoindentation. The film hardness was determined by the 10% rule and the elastic modulus was analyzed by a regression method using the exponential function. Elastic modulus of the AlInN films increases monotonously with the content of AlN ranging from 105 GPa to 300 GPa. The elastic modulus of the AlInN films with x = 0.82~0.84 which are lattice-matched with the GaN is found to be 275 GPa. After considering the effect of oxygen contamination and comparing with previous reports, the elastic modulus of the InN film is determined to be 130 GPa. A maximal hardness of 24.0 GPa occurs at x = 0.77. The maximum in hardness is considered to be caused by solid-solution hardening.