The development and characterization of nitride QW structures grown by atomic layer epitaxy (ALEp) for device applications are discussed. We have grown epitaxial thin films (4-10nm) covering the full range of binary and ternary III-N compositions by ALEp. In this work, ALEp-grown QW structures are presented. Optical characteristics are discussed. Characterization of layer interfaces and composition are critical to the development of this growth technique for quantum-based devices. Structures to study this by atom probe tomography have been created. By understanding the structure of crystalline ALEp films with nanometer-scale thickness, the unique properties of these materials can be advanced for quantum-scale applications.
Mg-doped AlN epilayers grown by metalorganic chemical vapor deposition have been studied by deep UV time-resolved photoluminescence (PL) spectroscopy. A PL emission line at 6.02 eV has been observed at 10 K in Mgdoped AlN, which is about 40 meV below the free-exciton (FX) transition in undoped AlN epilayer. Temperature dependent measurement of the PL intensity of this emission line also reveals a binding energy of 40 meV. This transition line is believed to be due to the recombination of an exciton bound to neutral Mg acceptor (I1) with a binding energy, Ebx of 40 meV. The recombination lifetime of the I1 transition in Mg doped AlN have been measured to be 130 ps, which is close to the expected value. Excitation intensity dependence of time-resolved PL for Mg-doped AlN epilayer is also measured to understand carrier and exciton dynamics.
Deep ultraviolet (UV) photoluminescence (PL) spectroscopy has been employed to study the optical properties and carrier dynamics in AlN and GaN epilayers at temperatures from 10 to 800 K. The parameters that describe the temperature variation of the energy bandgap (α and β, or aB and θ) and linewidth broadening have been obtained and are compared with the previously reported values in AlN and GaN obtained by different measurement methods in narrower temperature ranges. Our experimental results demonstrate that the broader temperature range of measurements is necessary to obtain accurate values of these parameters, particularly for AlN. The phonon-carrier interactions were also investigated in both AlN and GaN epilayers. At low temperatures, the linewidth of PL emission lines increases with temperature due to the electron-acoustic phonon interaction. The electron-LO phonon interaction becomes important above 200 K and eventually dominant at high temperatures in both AlN and GaN. The temperature dependencies of the decay lifetimes were investigated up to 500 K, from which free excitons and free carriers interactions are discussed for AlN and GaN epilayers. The implications of our findings to the optoelectronic and electronic device applications at elevated temperatures are discussed.