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Details a study on band-gap renormalization and band filling in silicon- (Si) doped gallium-nitrogen (GaN) films with free-electron concentrations using temperature-dependent photoluminescence spectroscopy. Experimental details; Effect of n-type doping on the band-gap energy of highly Si-doped GaN; Results and discussion; Conclusions.

Studies the yellow GaN photoluminescence band in In[sub x]Ga[sub 1-x]N films grown pseudomorphically on GaN. Shift to the red of the peak energy E[sub p] of the band with the increase in x; Deep acceptor level's relationship with the valence band edge.

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 pseudodielectric function spectra <ε> of wurtzite GaN, AlGaN, and GaN/AlGaN heterostructures were determined for photon energies ranging from 2 to 5 eV, using variable angle spectroscopic ellipsometry (SE). Samples were grown by low-pressure metalorganic chemical vapor deposition on c-plane sapphire substrates. The experimental <ε> spectra were analyzed using a multilayer approach, describing the dielectric functions of the individual layers by a parametric oscillator model. In this way, parametric dielectric function spectra of GaN and Al[sub x]Ga[sub 1-x]N (x≤0.16) were derived, as well as the composition dependence of the Al[sub x]Ga[sub 1-x]N band gap energy. The SE band gap data were found to be consistent with a bowing parameter close to 1 eV. Finally, the GaN and Al[sub x]Ga[sub 1-x]N parametric dielectric functions were used to quantitatively analyze the pseudodielectric function spectrum of GaN/AlGaN modulation doped field effect transistor structures, demonstrating the potential of SE in combination with a multilayer parametric dielectric function model for nondestructive ex situ control of GaN/AlGaN device structures. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The blue Mg induced 2.8 eV photoluminescence (PL) band in metalorganic chemical vapor deposition grown GaN has been studied in a large number of samples with varying Mg content. It emerges near a Mg concentration of 1×10[sup 19] cm[sup -3] and at higher concentrations dominates the room temperature PL spectrum. The excitation power dependence of the 2.8 eV band provides convincing evidence for its donor–acceptor (D–A) pair recombination character. It is suggested that the acceptor A is isolated Mg[sub Ga] while the spatially separated, deep donor (430 meV) D is attributed to a nearest-neighbor associate of a Mg[sub Ga] acceptor with a nitrogen vacancy, formed by self-compensation. © 1998 American Institute of Physics. [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]

Compared to traditional light sources light emitting diodes (LEDs) provide an increased efficiency and long lifetime, making them the primary choice for many applications. However, these lifetimes are highly dependent on operational conditions like junction temperature, drive current and environmental conditions like the exposure to humidity or air pollutants. This work studies the effects of common air pollutants in different concentrations on the lifetime of commercial LEDs with different packages and analyses the observed degradation mechanisms on the AlGaInN LED chips, the metallization and the package components. A special focus is put on the effects of hydrogen sulfide. [ABSTRACT FROM AUTHOR]

Metamorphic (i.e., linear composition graded) GaInN buffer layers with an increased in-plane lattice parameter, grown by plasma-assisted molecular beam epitaxy, were used as templates for metal organic vapor phase epitaxy (MOVPE) grown GaInN/GaInN quantum wells (QWs), emitting in the green to red spectral region. A composition pulling effect was observed allowing considerable higher growth temperatures for the QWs for a given In composition. The internal quantum efficiency (IQE) of the QWs was determined by temperature and excitation power density dependent photoluminescence (PL) spectroscopy. An increase in IQE by a factor of two was found for green emitting QWs grown on metamorphic GaInN buffer compared to reference samples grown on standard GaN buffer layers. The ratio of room temperature to low temperature intensity PL of the red emitting QWs were found to be comparable to the PL efficiency of green emitting QWs, both grown on metamorphic GaInN buffers. The excitation density and well width dependence of the IQE indicate a reduction of the quantum confined Stark effect upon growth on GaInN buffer layers with increased in-plane lattice parameter. [ABSTRACT FROM AUTHOR]

This work investigates the extrinsic molecular doping of zinc oxide (ZnO) thin films grown by plasma enhanced molecular beam epitaxy (P-MBE). The dopant was thermally evaporated arsenic trioxide (formula: As2O3 in the solid state), which appears as As4O6 molecule in the gaseous phase. Cracking experiments of these As4O6 molecules were made using a radio frequency oxygen plasma. Structural, chemical and optical investigations were made with (High Resolution) X-ray diffraction (HRXRD), secondary ion mass spectroscopy (SIMS) and photoluminescence (PL). These results show high incorporation rates (about 2x1018 cm-3) and optical activity of the dopant. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

In[sub 0.13]Ga[sub 0.87]N/GaN double heterostructures and quantum wells (QWs) have been studied by room-temperature photoluminescence (PL) and spectroscopic ellipsometry (SE). PL revealed the presence of strong piezoelectric fields, which strongly influence the luminescence properties for InGaN QW widths in the 3-12 nm range. The pseudodielectric function spectrum derived from the SE measurements were analyzed using a multilayer approach, describing the dielectric function of the individual layers by a parametric oscillator model. The fundamental band-gap resonance in the InGaN dielectric-function spectrum was found to broaden for an InGaN layer width of 12 nm, as compared to bulk-like InGaN layers, due to piezoelectric field effects. For a much narrower QW width of 1.7 nm, however, quantum confinement was found to dominate over piezoelectric-field effects, resulting in a much sharper band-gap resonance shifted to higher energies and an increased oscillator strength. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

There is a high demand for compact low-cost ozone sensors. It has been shown recently that In2O3 nanolayers can act as ozone sensitive films activated at room temperature by ultraviolet light. In the present work, the authors integrate ultrathin layers of In2O3 nanoparticles and a GaInN/GaN based blue light emitting diode (LED) on a single sensor chip. The integrated sensor was found to be sensitive to O3 concentrations as low as ∼40 ppb. These results demonstrate that by integrating GaInN/GaN based blue LEDs and metal oxide sensing layers back to back on a single chip, compact and robust gas sensors can be realized. [ABSTRACT FROM AUTHOR]

Pseudodielectric function spectra of hexagonal (InGa)N epitaxial layers on GaN were obtained by spectroscopic ellipsometry and compared with photoreflection spectra. Composition and thickness of the In[sub x]Ga[sub 1-x]N layers grown by metalorganic chemical vapor deposition, were varied between 0.04≤x≤0.10 and 15–60 nm, respectively. The pseudodielectric function exhibits a clear maximum at the fundamental gap energy of the (InGa)N, which allows a determination of the In content via the composition dependence of that gap energy. The pseudodielectric function spectrum of a complete GaN/(InGa)N/(AlGa)N/GaN light-emitting diode structure shows maxima arising from fundamental gap interband transitions of all constituent layers including the (InGa)N active region. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]