| Deep UV emitters are essential for a number of applications that involve the detection of organic molecules such as dyes, biological or chemical agents. Nitride semiconductors are one of the most promising materials for the development of efficient UV emitters due to their large electronic bandgaps. More specifically, heterostructures of the binaries GaN/AlN are ideal candidates for deep UV emitters due to the high bandgap offset between these two semiconductors.; The objectives of the present thesis are time-resolved photoluminescence (TRPL) studies of GaN/AIN multiple quantum well heterostructures as well as Si-doped high Al mole fraction AlGaN epilayers grown by molecular beam epitaxy. These studies have shown that GaN/AIN quantum well structures exhibit strong room-temperature photoluminescence in the UV, despite the considerable lattice mismatch between the barrier and well materials. The photoluminescence (PL) peak positions are in good agreement with the values predicted by a calculation which takes into account the piezoelectric fields and the spontaneous polarization existing inside the wells. Furthermore, the temperature dependence of the photoluminescence intensity, full width at half maximum of the PL feature and carrier radiative lifetimes suggests the emission is associated with excitonic recombination as well as transitions involving free carriers and localized states.; TRPL studies of the Si-doped AlGaN epilayers, previously characterized by another group using temperature-independent electrical conductivity, can be useful in determining the donor and acceptor energies in these epilayers. Specifically, a component-resolved temperature study of the PL spectra and carrier lifetimes in such samples reveals the presence of a very shallow donor state (binding energy equal to only a few meV) associated with silicon. The presence of donor-bound excitons at low temperatures is observed in samples with Al concentration as high as 33%. A simple rate equation model is proposed to explain the slow PL decay times measured at early delay times in some AlGaN epilayers.; In summary, this work provides a detailed analysis of the photoluminescence properties of GaN/AlN heterostructures and Si-doped AlGaN epilayers with emphasis on the impurity states and the nature of recombination mechanisms in these materials. |
