Molecular beam epitaxy and characterization of gallium arsenic nitride and its application to quantum dot cascade light sources

Recent advances in material quality of the Ga(As,N) alloy have provided engineers with a unique material that is tensile-strained with a negative conduction band offset to GaAs. This work has studied the defects present in molecular beam epitaxy (MBE) grown, lattice-matched (In,Ga)(As,N) alloys on the GaAs substrate. A dominant electronic trap, similar to a known oxygen trap in GaAs, was observed by deep-level transient spectroscopy (DLTS) with energy and capture cross-section of 0.44 eV and 1.5 x 10 -14 cm-2 respectively and concentrations which vary linearly with nitrogen content. These characteristics suggest that the trap results from oxygen impurities in the nitrogen source gas. Photoluminescence (PL) measurements on the same samples have suggested the trap is responsible for reduced PL intensity in GaAsN material.; A method for quasi-independent tuning of the confined states in self-organized quantum dots (QDs) based on differences between the electron wave functions of each state has been proposed. By capping InAs quantum dots with 4 nm of GaAsN, the excited electron state can be shifted by nearly 36 meV with less than 5 meV change to the ground state. These shifts are believed to arise from changes to strain in the quantum dot and selectively reduced confining potential for the electron quantum states. This technique is particularly important for quantum dot cascade sources, wherein the energy separation between ground and excited states determines emission wavelength, but lower ground state energy can prevent successful QC design.; By incorporating quantum dots instead of quantum wells in the active region of a quantum cascade structure, improved threshold current and vertical emission are possible. The unique properties of the GaAsN material have been successfully exploited in the design of a strain-compensated quantum dot cascade heterostructure. Successful strain compensation has permitted the epitaxial growth of several successive quantum-cascade periods. Devices fabricated from these samples exhibited the first observed electroluminescence from a quantum dot cascade light source. Total output power of a device is estimated at 90 nW per facet under pulsed operation at 18 K.