Optical properties of aluminum gallium nitride alloys and aluminum nitride epilayers

AlxGa1-xN (0 < X < 1) epilayers, particularly AlN, have been grown by MOCVD on sapphire substrates. Deep ultraviolet picosecond time-resolved photoluminescence (PL) spectroscopy has been employed to study the optical properties of these epilayers.;For AlGaN alloys, we investigated the growth and optical and electrical properties of AlxGa1- xN alloys with x between 0 and 1. Our results have revealed that the PL emission intensity decreases with an increase of the Al content. The activation energy of the impurity level in Al xGa1-xN alloys was found to increase sharply at x = 0.4. We have also investigated the polarization properties of AlxGa1- xN epilayers between x = 0 and 1. The emission intensity with the E⊥c polarization as well as the degree of polarization decreases with increasing x. Impurity transitions in AlGaN alloys have been investigated. The YL in GaN and VL in AlN have been observed and discussed as special cases of a group of impurity transitions in AlGaN alloys.;Fundamental optical transitions in AlN epilayers have been observed and discussed for the first time. Two band edge emission lines were observed at 10 K and were assigned to the donor bound exciton and free exciton transitions, respectively. The recombination lifetimes were also measured for the I 2 and FX transitions at different temperatures; from which the binding energies associated with the donor bound excitons and free excitons in AlN epilayers have been deduced. The temperature dependence of fundamental optical transitions in AlN will be discussed in the temperature range from 10 to 800 K, from which the parameters that describe the temperature variation of the bandgap and line width broadening have been obtained and compared with the previously reported values.;AlN/GaN multiple quantum wells have been studied by time-resolved PL spectroscopy. PL emission lines from the interband recombination between electrons and holes in the n = 1 and n = 2 subbands in the wells were observed. The carrier transfer between different subbands as well as the decay lifetimes of the interband transitions have been measured and compared with the calculations. Five samples of Al0.5Ga 0.5N/GaN heterostructures were also grown and investigated.