Reduced dislocation density and residual tension in AlN grown on SiC by metalorganic chemical vapor deposition

Crack-free AlN films with threading dislocation density (TDD) below 10(9) cm(-2) are needed for deep-UV optoelectronics. This is typically achieved using pulsed lateral overgrowth or very thick buffer layers (>10 mu m), a costly and time-consuming approach. A method for conventional metalorganic chemical vapor deposition growth of AlN/SiC films below 3 mu m with greatly improved quality is presented. Focusing on substrate pretreatment before growth, we reduce average film stress from 0.9GPa (tension) to -1.1GPa (compression) and eliminate cracking. Next, with optimized growth conditions during initial deposition, AlN films with x-ray rocking curve widths of 123 arc-sec (0002) and 304 arc-sec (20 (2) over bar1) are developed, and TDD is confirmed via plan view transmission electron microscopy (TEM) to be 2 x 10(8) cm(-2). Film stress measurements including x-ray 2 theta-omega, reciprocal space mapping, and curvature depict compressively stressed growth of AlN on 4H-SiC due to lattice mismatch. The thermal expansion coefficient mismatch between AlN and SiC is measured to be Delta alpha = alpha(AlN) = alpha(SiC) = 1.13 x 10(-6) degrees C-1 and is found to be constant between room temperature and 1400 degrees C. TEM confirms the existence of dense misfit dislocation (MD) networks consistent with MD formation near SiC step edges and low MD density regions attributed to nearly coherent AlN growth on SiC terraces. These low-TDD, crack-free AlN/SiC buffers provide a platform for deep-UV optoelectronics and ultrawide bandgap electronics. Published under license by AIP Publishing.