Effects of indium flow rate on the structural, morphological, optical and electrical properties of InGaN layers grown by metal organic chemical vapour deposition

Abstract

InGaN/GaN heterostructures were grown on c-plane sapphire substrates using metal organic chemical vapour deposition by varying the trimethylindium flow rate as 7, 10 and 14 μmol/min. The structural, morphological, optical and electrical properties of InGaN layers were investigated. Crystalline quality, dislocation densities comprising of screw and edge types in InGaN and GaN layer have been analyzed using High-Resolution X-ray Diffractometer (HRXRD). The composition of Indium (In) in the InGaN layers was estimated around 8–10% which was found to be dependent on the In flow rate. The strain between InGaN and underlying GaN layer have been analyzed through reciprocal space mapping studies along the (1 0–1 5) plane in InGaN/GaN heterostructures. The features of V and trench defects were observed using scanning electron microscopy and atomic force microscopy, respectively. The V and trench defect density has been correlated with the pre-existing threading dislocation density estimated using HRXRD measurements. Also the trench defects were observed to be a coalescence of V defects in InGaN layers. The photoluminescence results showcased the band edge emission peaks at three different points (primary flat, centre, and Edge) on InGaN/GaN heterostructures. These peak variations were found to be red shifted in all three points. This may be due to the fluctuations in the Indium composition and its corresponding V and trench defects, respectively. The Hall measurements exhibit an alteration in the semiconducting behavior with respect to V and trench defect surrounded InGaN layers. And, it also emphasizes that the compressive strain in underlying GaN can lead to the high sheet concentration than that of the tensile strain in the underlying GaN layer. It clearly suggests that the V and trench defect surrounded InGaN layers are the suitable material for next generation optoelectronics applications.