F. Höhnsdorf

From N isoelectronic impurities to N-induced bands in the GaNxAs1−x alloy

GaNxAs1−x samples with x<3% grown by metalorganic vapor phase epitaxy were studied by low-temperature photoluminescence under hydrostatic pressure and photomodulated reflectance spectroscopy. The transformation from N acting as an isoelectronic impurity to N-induced band formation takes place at x≈0.2%. The N level does not shift with respect to the valence band edge of GaNxAs1−x. Concentration as well as hydrostatic-pressure dependence of the GaNxAs1−x bands can be described by a three band kp description of the conduction band state E− and E+ and the valence band at k=0. The model parameters for T<20 and T=300 K were determined by fitting the model to the experimental data. Modeling the linewidth of the E− transition by combining the kp model and ion statistics leads to the conclusion that the electron-hole pairs are strongly localized.

Optical Spectroscopic Studies of N‐Related Bands in Ga(N, As)

We have investigated the unusual band formation at the Γ-point and in the vicinity of the L-point in the alloy system Ga(N, As) by various spectroscopic methods. A series of GaNxAs1—x epitaxial layers with x varying from 0.05 to 2.8% was grown on (100) GaAs by metal-organic vapour phase epitaxy. The samples were studied by photoluminescence (PL) as well as photoluminescence excitation (PLE) spectroscopy, photomodulated reflectance (PR), and conventional reflectance (R) spectroscopy at room temperature and liquid helium temperature. The low-temperature PL and PLE spectra in the spectral region of the E0 band gap show clear evidence for in-gap nitrogen-pair and cluster states at low concentrations (x < 0.1%), and for higher nitrogen concentrations the formation of a new band. The dependence of the E0 band gap on N-content for x < 1% at 8 K is considerably stronger than at 300 K. Furthermore, R spectra of the E1 and E1 + Δ1 transitions show an uncommonly strong disorder-induced broadening with increasing N-content.

(GaIn)(NAs)/GaAs vertical-cavity surface-emitting laser with ultrabroad temperature operation range

The temperature dependence of the emission of a (GaIn)(NAs)/GaAs vertical-cavity surface-emitting laser is investigated. We find laser emission over an extremely broad temperature range from 30 K up to 388 K. The laser threshold varies from 5 kW/cm2 at 373 K down to a minimum of 1 kW/cm2 at 180 K and increases again to 4 kW/cm2 at 30 K. Picosecond emission dynamics after femtosecond optical excitation is obtained with peak delays below 33 ps and pulse widths below 20 ps over the entire operation range.

Emission dynamics and optical gain of 1.3-/spl mu/m (GaIn)(NAs)/GaAs lasers

The ultrafast emission dynamics of a 1.3-/spl mu/m (GaIn)(NAs)/GaAs vertical-cavity surface-emitting laser is studied by femtosecond luminescence upconversion. We obtain a minimum peak delay of 15.5 ps and a minimum pulse width of 10.5 ps. Laser operation with picosecond emission dynamics is demonstrated over a temperature range from 30 to 388 K. The bandgap shift with temperature of (GaIn)(NAs)/GaAs is determined to be about -2.9/spl middot/10/sup -4/ eV/K, which is smaller than for GaAs. Our measurements of the optical gain provide gain spectra similar to those of commercial (GaIn)(PAs)/InP-structures at moderate densities but broaden considerably for elevated carrier densities due to the stronger carrier confinement. We compare our experimental results with gain spectra calculated from a microscopic model and confirm the predictive capability of the model. The theoretical gain spectra are used as the input for a calculation of the temperature dependence of the (GaIn)(NAs)/GaAs surface-emitter emission which results in very good agreement with experiment.

TEM investigations of (GaIn)(NAs)/GaAs multi-quantum wells grown by MOVPE

Quantum wells of the quaternary (GaIn)(NAs) alloy are grown compressively strained on GaAs by metal-organic vapor phase epitaxy (MOVPE) at low temperatures under non-equilibrium conditions. Growth experiments of particular heteroepitaxial multilayer systems are reported and the influence of varying conditions, namely of the arsenic source partial pressure and of the growth rate on the structural quality of the quantum wells is studied. Up to a critical amount of incorporated nitrogen, high perfection layers can be obtained which show a roughness of the interfaces between the wells and the barriers in the range of only a few monolayers. Any phase separation effects have been excluded by exact control of the particular growth conditions. For the structural characterization of the layer systems, conventional and high resolution transmission electron microscopy have been applied.

Structural properties of (GaIn) (NAs)/GaAs MQW structures grown by MOVPE

Abstract The structural properties of (GaIn)(NAs)/GaAs multiple quantum well structures (MQW) have been evaluated by means of high-resolution X-ray diffraction (XRD) in combination with simulation using dynamic modelling and TEM studies. This metastable material system has been grown successfully by non-equilibrium MOVPE at low substrate temperatures using the efficient group V precursors 1,1-dimethylhydrazine (UDMHy) and tertiarybutylarsine (TBAs). High structural quality of the quaternary material has been achieved for both lattice matched and strained layers for In and N concentrations up to 30% and 4%, respectively. Due to the extreme non-equilibrium growth conditions there is no indication of phase separation effects. A novel morphology transition presumably caused by a microscopic strain effect has been established experimentally in compressive-strained quaternary (GaIn)(NAs) when exceeding a critical N-content of about 4.5%. Possible explanations for this effect are discussed.