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Hexagonal (AIGa)N heterostructures were characterized by variable angle spectroscopic ellipsometry, to determine the resulting spectra.

Optical excitation was used to study resonant Raman scattering from A1xGa1-xN (x

Research was conducted to examine Si-doped n-type GaN with free-electron concentrations up to 1.7 x 10(to the 19th power) cm-3 using temperature-dependent photoluminescence (PL) spectroscopy. Results reveal that band-filling effects dominate the PL line broadening and that dopant-induced changes in residual strain generate line shifts that are small in comparison to those that arise from band-gap renormalization.

We show that the conduction band structure of dilute AlxGa1-xAs1-yNy with x<=0.37 and y<=0.04 can be described consistently by the experimentally motivated band anticrossing model. The interband transition energies E-, E-+Δ0, and E+ have been derived from a full line shape fit to photomodulated reflectance (PR) spectra recorded at room temperature. The PR data were taken (a) from a series of Al0.06Ga0.94As1-yNy samples with y<=0.04 and (b) from a set of AlxGa1-xAs0.99N0.01 layers with x<=0.37. The latter series covers the range of Al concentrations where the AlxGa1-xAs band gap energy EM is expected to cross the nitrogen-induced energy level EN. The resulting nitrogen- and Al-concentration dependent interband transition energies are described by the band anticrossing model using a matrix element for the coupling between the nitrogen-induced states and the extend lowest conduction band states of CMN=2.32 eV and a nitrogen level energy EN=(1.625+0.069x) eV, the latter measured with respect to the GaAs valence band edge. [ABSTRACT FROM AUTHOR]

The influence of the Mg doping profile on the electroluminescence (EL) efficiency of (AlGaIn)N quantum well (QW) light-emitting diodes, grown by low-pressure metal-organic vapor-phase epitaxy on sapphire, has been investigated. The actual Mg profile close to the active region was found to be influenced by segregation as well as by diffusion during growth. In a first experiment, diffusion of the Mg dopants towards the QW region through a not intentionally doped narrow GaN spacer layer, separating the topmost GaInN quantum well from the AlGaN:Mg electron-blocking barrier, was controlled by the growth temperature of the AlGaN:Mg barrier and GaN:Mg contact layer. Starting from low growth temperatures, an increase in Mg concentration close to the active region results in an improved hole injection and thus increased EL efficiency. However, for a too high growth temperature, an excessive spread of the Mg atoms into the active region leads to nonradiative recombination in the QW active region and thus a reduction in EL output. In a second experiment, identical structures were prepared with the Mg-doped sAldGaN layers grown at lower temperature to minimize Mg diffusion. Instead, the nominal Mg doping level in the GaN spacer layer was varied systematically. Secondary-ion-mass spectrometry revealed that almost identical Mg doping profiles close the QW active region, and in turn very similar EL efficiencies, can be achieved by both approaches when appropriate growth parameters are used. [ABSTRACT FROM AUTHOR]

The band anticrossing (BAC) model is used for describing the conduction band structure of dilute [Al.sub.x][Ga.sub.1-x][As.sub.1-y][N.sub.y] (x