Effects of strain on the optical properties of aluminum indium gallium nitride quaternary alloys and their heterostructures

AlInGaN quaternary films were grown by atmospheric pressure metalorganic chemical vapor deposition at 875°C using trimethylgallium, trimethylaluminum, trimethylindium, and ammonia. The good optical quality of the quaternary films was revealed by low deep level emissions in the room temperature photoluminescence (PL) spectra for film compositions with up to 11% InN and 26% AlN, simultaneously. With the availability of the quaternary alloy as a barrier material, comprehensive investigations on the effects of strain on the optical properties of InGaN quantum wells are possible by independently varying the lattice constant and band gap of the barrier.; A test structure was designed to vary the lattice mismatch induced strain experienced by an AlInGaN/In_0.08Ga_0.92N/AlInGaN quantum well structure. Utilizing this test structure, the effects of tensile and compressive strain on the optical properties of InGaN quantum well layers were investigated for well widths of 3 nm and 9 nm. Time-resolved PL and temperature dependent PL from 10 K to 300 K was used to investigate recombination behavior.; It was found that the radiative recombination rate for unstrained wells much higher than that of strained wells due to the effects of the strain induced piezoelectric field. The rate difference results in higher emission intensity for unstrained 3 nm and 9 nm quantum wells than for their strained counterparts. It was found that the activation energy for non-radiative losses was a strong function of strain. For 3 nm wells, the activation energy was 37.7, 18, and 22.1 meV for wells under tensile, zero, and compressive strain respectively. A similar strain dependence trend was observed for the 9 nm wells.; Evidence that recombination is strongly influenced by transitions from localized states corresponding to compositional fluctuations is provided by the energy dependence of PL lifetime, the peak emission energy dependence on temperature, and temperature dependence of PL spectral shapes. Furthermore, the energetic depth of the localizing potentials, and hence the nature of the compositional fluctuations, are a strong function of strain. The potential fluctuations are smallest for the unstrained wells and increase as compressive or tensile strain increases.