Abstract
Since the BGaN alloy is considered a promising material in the wide range of optoelectronic applications, a detailed study of its band structure and optical properties is highly demanded. Here, BxGa1-xN layers with 0.5%, 1.1%, and 1.2% B were grown by metalorganic vapor-phase epitaxy on AlN/sapphire templates and investigated by structural and optical methods. The bandgaps of the investigated alloys were examined by contactless electroreflectance (CER) spectroscopy. Because no GaN layer is present in the investigated samples, the detected CER resonances do not overlap with the GaN-related signal, which is typical for BGaN layers grown on GaN templates. Thus, the energy of the bandgap-related transition in BGaN samples can be unambiguously determined from the resonances observed in the CER spectra. The boron-induced redshift of the bandgap was determined to be about 60 meV/% B for the studied samples. By means of photoluminescence measurements, the deteriorating optical quality of samples with increasing boron content is shown as the decreasing bandgap- to defect-related emission intensity ratio. What is more, the defect-related emission is shifted from typical for GaN yellow range to the red and is located at 1.9 eV for all BGaN samples.