On the optical properties and micro structures of GaN films inserted with low-temperature Al_(0.8)Ga_(0.2)N interlayers

摘要

High-temperature (HT)-GaN films having low-temperature (LT)-Al_(0.8)Ga_(0.2)N interlayers were prepared on (0001) sapphire substrates. The insertion of a LT-Al_(0.8)Ga_(0.2)N 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-Al_(0.8)Ga_(0.2)N 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 ～10nm was determined for the LT-Al_(0.8)Ga_(0.2)N interlayers. The LT-Al_(0.8)Ga_(0.2)N 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).