Effect of spiral-like islands on structural quality, optical and electrical performance of InGaN/GaN heterostructures grown by metal organic chemical vapour deposition

Abstract

InGaN layers were grown by metal organic chemical vapour deposition (MOCVD) technique on GaN/sapphire substrates by varying the growth time. The formation of spiral-like growth domains was observed using atomic force microscopy, revealed that the InGaN layer is atomically flat. In addition, the surface roughness was found to be dependent on the thickness of InGaN layer. The spiral-like islands was correlated with screw type threading dislocation density of InGaN. The thickness-dependent threading dislocation density was investigated using high-resolution x-ray diffraction. The Indium composition and thickness of InGaN were found to be 15–16% and 20–50 nm using the smooth fit software. The structural characteristics obtained using reciprocal space mapping indicate that the InGaN/GaN heterostructures are coherently strained. Photoluminescence (PL) spectra exhibit variations in the band-edge emissions between 437.0 and 443.5 nm peaks with varying temperature, showcasing a slight shift in all the InGaN samples. The low-temperature PL spectra revealed dominant emission mechanism. From the hall effect data it was observed that InGaN layer attained high mobility value close to that of the theoretical limit of GaN and/or InN at 300 K. It is worth to note that the compressive strain present in InGaN layer led to high sheet concentration when compared to that of the tensile strained InGaN layer. Hence, the spiral like islands entrenched InGaN layers which can be effectively utilized for optoelectronic applications.