h-BN Interlayer-Mediated Growth of AlN Thin Films on Sapphire for Optoelectronic Applications
摘要
The crystalline quality of sputtered AlN thin films on sapphire is often limited by high defect density and poor surface morphology, restricting their application in ultraviolet optoelectronic devices. This work involved optimization and use of a plasma-enhanced atomic layer deposition (PEALD)-grown hexagonal boron nitride (h-BN) buffer layer in enhancing the growth of AlN film grown by reactive radio-frequency (RF) magnetron sputtering. The effects of the buffer layer and post-deposition annealing were investigated in terms of the structural, morphological, and electrical properties of the film. From the X-ray diffraction and rocking curve analysis, it was observed that the optimized annealed AlN/h-BN/sapphire structure had the smallest full width at half maximum (FWHM) values of ~0.20° and ~0.25° in the AlN (002) and (102) planes, respectively. The screw and edge threading dislocation density were decreased to about 9.9 × 108 cm−2 and 4.52 × 109 cm−2, respectively. From the atomic force microscopy (AFM) analysis, there was significant reduction of surface root mean square (RMS) roughness from 5.4 nm for the as-deposited AlN/sapphire structure to 1.2 nm for the optimized AlN/h-BN/sapphire structure. The structural evolution of the AlN/h-BN heterostructure was supported by Raman spectroscopy, field-emission scanning electron microscopy (FESEM) cross-sectional imaging, and energy-dispersive spectroscopy (EDX) compositional analysis. The electrical characterization indicated that there was a marked decrease in the leakage current and increase in insulation after incorporating the layered h-BN buffer and high-temperature annealing. It is evident that the PEALD-formed h-BN layer and high-temperature annealing could be considered an effective technique for improving sputtered AlN thin film on sapphire substrates.