Effect of indium accumulation on the growth and properties of ultrathin In(Ga)N/GaN quantum wells

In this work, we present the investigation of InN/GaN multiple-quantum-well (MQW) growth by plasma-assisted molecular beam epitaxy using in-situ reflection high-energy electron diffraction (RHEED) to monitor the growth process. The analysis of the RHEED intensity and pattern transitions identified an indium surface accumulation even with a nominal thickness of InN as small as 0.5 monolayer (ML). This result explicitly shows that, even at low growth temperatures of ~550 °C, not all of the supplied indium is incorporated into the quantum well (QW). Moreover, the residual indium can become incorporated into the GaN matrix on either side of the QW. Both QW thickness and the photoluminescence (PL) emission energy showed a self-regulating behavior. The apparent thickness did not exceed 2 MLs even when the deposited InN thickness is as large as 5 MLs. The PL emission shows a continuous redshift with the deposited InN from ~370 nm for 0.5 ML until it saturates at ~423 nm for >2 ML. Based on the observed growth phenomena, a qualitative growth model was developed to explain the self-limited epitaxial growth of ultrathin In(Ga)N/GaN QWs. Keywords: InN, MQW, PAMBE, RHEED, Epitaxy, Growth model