Engineering of InN epilayers by repeated deposition of ultrathin layers in pulsed MOCVD growth

Highlights: • Roles of timing parameters and temperature in shaping ultrathin InN layers are shown. • Better structural quality can be achieved by using thicker ultrathin layers. • PL intensity correlates with the ratio of the timing parameters. • Growth temperature ramping decreased the Burstein-Moss shift of PL band. • The domain-like pattern of InN epilayers determines the PL properties. Capabilities of repeated deposition of ultrathin layers by pulsed metalorganic chemical vapor deposition (MOCVD) for improvement of structural and luminescence properties of InN thin films on GaN/sapphire templates were studied by varying the growth temperature and the durations of pulse and pause in the delivery of In precursor. X-ray diffraction, atomic force microscopy, and spatially-resolved photoluminescence (PL) spectroscopy were exploited to characterize the structural quality, surface morphology and luminescence properties. Better structural quality is achieved by using longer trimethylindium pulses. However, it is shown that the luminescence properties of InN epilayers correlate with the pause and pulse ratio rather than with their absolute lengths, and the deposition of 1.5–2 monolayers of InN during one growth cycle is optimal to achieve the highest PL intensity. Moreover, the use of temperature ramping enabled achieving the highest PL intensity and the smallest blue shift of the PL band. The luminescence parameters are linked with the structural properties, and domain-like patterns of InN layers are revealed.