Influence of TMIn flow rate on structural and optical quality of AlInGaN/GaN epilayers grown by MOCVD

•Nearly lattice-matched AlInGaN grown on (0001) Al2O3 substrate by MOCVD at 750 °C.•TMIn flow has a strong influence on the structural and optical quality of AlInGaN.•High TMIn flow (200 sccm) could be decrease the threading dislocation density.•Tunable optical bandgap from 3.69 to 3.78 eV was obtained.•The existence A1(LO) mode of In(Ga)N clusters has been verified by Raman spectra.

In this paper, nearly lattice-matched AlInGaN/GaN epilayers grown on sapphire substrate by metal organic chemical vapor deposition have been studied. The structural and optical properties of these epilayers have been investigated and compared. The TMIn flow is believed to have a direct influence on the quality of the AlInGaN epilayer. By increasing indium composition in AlInGaN epilayer, dislocations have been found to decrease, indicating lower threading dislocation density confirmed by HRXRD. Reciprocal space mapping analysis has confirmed that the growth of AlInGaN on GaN buffer is a fully strained growth. Room temperature photoluminescence from AlInGaN exhibits two emissions originating from In(Ga)N clusters and the AlInGaN random matrix, respectively. Upon increasing the TMIn flow, red shift has been observed in the photoluminescence peak confirming the decrease in bandgap of AlInGaN epilayers. In the Raman spectra, the mode at 751 cm−1 is attributed to the A1 (LO) mode of AlInGaN. The mode at 632 cm−1 is attributed to In(Ga)N clustering and assigned as A1 (LO) mode. V-shaped defect pits with different density and size have been observed on the surface of AlInGaN epilayers.

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