MOCVD growth and characterization of aluminum-rich aluminum nitride/aluminum gallium nitride epilayers and quantum wells

The correlation between polarity and material quality of un-doped Al 0.81Ga0.19N was studied. The overall material quality is significantly influenced by the growth polarity. The epilayers with aluminum-polarity have a much higher crystalline quality and better surface morphology than those of nitrogen-polarity. Nitrogen-polar growth more readily incorporates unintentional impurities.;A-plane AlN epilayers have been grown on r-plane sapphire substrates. The orientation and high crystalline quality were confirmed by x-ray diffraction (XRD) theta-2theta scan exhibiting a reflection peak at 2theta = 59.4° and rocking curve of the (110) reflection having a linewidth of 940 arcsec. Room temperature photoluminescence (PL) spectroscopy showed that the surface emission intensity of a-plane AlN epilayers is comparable to that of c-plane AlN. PL spectra of Mg-doped a- and c-plane AlN revealed that the Mg level in both a- and c-plane AlN is identical and is about ∼ 0.5 eV.;Identically designed a-plane and c-plane AlN/Al0.65Ga0.35N QWs have been grown on a- and c-plane AlN/Al2O3 templates respectively, and their PL emission properties were studied. Low temperature PL characteristics of a-plane QWs are primarily governed by the quantum size effect, whereas those of c-plane QWs are significantly affected by the polarization fields.;The growth of AlN epilayers on SiC substrates was investigated. A smooth, crack free AlN epilayer with high optical and crystalline quality was achieved. Because of its high quality, AlN was used as active layer in a hybrid Schottky photodetector.;Highly conductive Si-doped Al0.75Ga0.25N alloys were grown on AlN/SiC templates. The effects of using Indium as a surfactant during the growth of Si-doped Al0.75Ga0.25N epilayers at relatively high temperature 1050 °C were studied. Indium significantly increases the doping efficiency as shown by RT Hall measurements. RT PL measurements show a clear correlation between emission intensity of the defect related transition and indium flow rate.;P-type conductivity has been obtained in beryllium doped GaN by MOCVD. The activation energy of the beryllium acceptor was estimated to be 118 +/- 4 meV, which is about 40 meV less than the activation energy of the Mg acceptor in GaN.