On the optical properties and microstructures of GaN films inserted with low-temperature Al0.8Ga0.2N interlayers

High-temperature (HT)-GaN films having low-temperature (LT)-Al0.8Ga0.2N interlayers were prepared on (0 0 0 1) sapphire substrates. The insertion of a LT-Al0.8Ga0.2N interlayer in a HT-GaN film was found to influence the optical and morphological properties of the film. Room temperature (RT) photoluminescence (PL) spectra of the HT-GaN films show strong and narrow near-band edge emissions when the films are inserted by LT-Al0.8Ga0.2N interlayers with thicknesses being less than critical layer thickness (CLT). Based on a plot of the line widths of RT near-band edge PL emissions of HT-GaN films versus the interlayer thicknesses, a CLT value of ∼10 nm was determined for the LT-Al0.8Ga0.2N interlayers. The LT-Al0.8Ga0.2N interlayer was observed to efficiently block threading dislocations (TDs) originated from the underlying GaN layer according to the studies of cross-sectional transmission electron microscopy (XTEM).