Influence of low-temperature AlGaN intermediate multilayer structures on the growth mode and properties of GaN

GaN growth on the low-temperature (LT) AlGaN intermediate multilayer-coated GaN film was conducted using metal alkyls (trimethylgallium (TMG) and/or trimethylaluminum (TMA)) and ammonia in an inductively heated quartz reactor operated at atmospheric pressure. LT-AlGaN multilayers having certain Al contents and layer thicknesses were found to induce island growth of GaN based upon the observations of scanning electron microscopy (SEM). Cross-sectional transmission electron microscopic (TEM) studies show that the use of LT-AlGaN intermediate multilayers blocks threading dislocations (TDs) coming from the underlying GaN film very efficiently, and thereby results in great reduction of TD density in the GaN islands. The island growth nature of GaN is believed to originate from the lattice mismatch between GaN and LT-AlGaN multilayer structures. These nearly TD-free GaN islands exhibit enhanced room temperature (RT) near band-edge photoluminescence (PL) emissions.