S. S. Shirokov

Electroreflectance spectra of InGaN/AlGaN/GaN quantum-well heterostructures

Abstractp−n InGaN/AlGaN/GaN heterostructures with InGaN/AlGaN multiple quantum wells are studied by electroreflectance spectroscopy. The structures are grown by metal—organic epitaxy and arranged with the p region in contact with the heat sink. Light is incident on and reflected from the structures through the sapphire substrate. To modulate the reflectivity, rectangular voltage pulses and a dc reverse bias are applied to the p−n junction. A line corresponding to interband transitions in the region of InGaN/AlGaN multiple quantum wells is observed in the electroreflectance spectra. The peak of this line is shifted to shorter wavelengths from the peak of injection luminescence of the light-emitting diode structures. The low-field model developed by Aspnes is used to describe the electroreflectance spectra. By choosing the parameters of the model to fit the experimental data, the effective band gap of the active region of the structure, Eg*, is determined at 2.76–2.78 eV. The experimental dependence of Eg* on the applied voltage is attributed to the effect of piezoelectric fields in the InGaN quantum wells. In the electroreflectance spectra, an interference pattern is observed in the wide spectral range from 1.4 to 3.2 eV. The interference is due to the dependence of the effective refractive index on the electric field.

Uniaxial compression influence on valence sub-bands energy spectrum and electroluminescence in n-AlGaAs/GaAsP/p-AlGaAs diode structures

Numerical calculations of the valence band and conduction band size quantized levels in a strained p-AlxGa1-xAs/GaAs1-yPy/n-AlxGa1-xAs (y = 0.16) double heterostructure were performed for different values of the external uniaxial compression along [110] direction. They indicate that the two upper levels in the valence band merge at pressure about 4 kbar and a strong state mixing develops around the merging point. The results of calculations explain the nonlinear character of the photon energy shift and electroluminescence intensity increase that were experimentally observed in these structures under uniaxial compression up to 5 kbar.

Electroluminescence and band structure in p-Al x Ga1−x As/GaAs1−y P y /n-Al x Ga1−x As under uniaxial compression

Band structure calculations in p-Al x Ga1−x As/GaAs1−y P y /n-Al x Ga1−x As heterostructure under uni-axial compression in the 1 1 0 direction indicates an increase in the optical energy gap with dE ph/dP ≈ 85 meV GPa−1, a decrease in the quantum well barriers and light hole–heavy hole crossover at uniaxial stress P ≈ 450–500 MPa. The observed increase in electroluminescence intensity and photon energy shift under uni-axial compression are explained by numerical calculation data.

Simple apparatus for moderate wave length tuning by means of uniaxial stress

We describe a simple cryostat combined with a device for uniaxial compression up to 4 kbar that permits optical measurements and a moderate electroluminescence wave length tuning at liquid nitrogen temperatures.

The emission spectrum of p-AlGaAs/GaAsP/n-AlGaAs diodes under uniaxial compression

AbstractNew experimental data are presented on the effects of uniaxial compression of up to 4 kbar along the [110] and [1

Size quatized levels of the valence band and the optical gain in strained p-AlGaAs/GaAsP/n-AlGaAs structures under uniaxial compression

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A Role of the Built-in Piezoelectric Field in InGaN/AlGaN/GaN Multiple Quantum Wells in the Electroferlectance Experiments

0] crystallographic directions on the spectra of electroluminescence and the current-voltage characteristics of diodes based on n-AlxGa1 − xAs/GaAsyP1 − y/p-AlxGa1 − xAs (y = 0.84) heterostructures that were designed for injection lasers. With increasing pressure, the spectra show a shift to shorter wavelengths, reaching 25 meV at 3 kbar; the intensity increases 2–3 times as well. Numerical calculations were carried out on the band structure of the investigated heterostructures under compression along the [110] axis, which indicate the increase in the effective band gap in the quantum well (QW) GaAsyP1 − y, with a pressure coefficient of about 8.5 meV/kbar and reduction of the barrier height at the boundaries of the QW. The calculations predict the possibility that light and heavy holes crossover at pressures above 4.5–5 kbar. The increase in the effective band gap completely describes the experimental data on the shift of the electroluminescence spectra. The mixing of light and heavy holes when approaching the band crosspoint is the probable cause of an increase in the intensity of radiation under uniaxial compression.

Electroreflectance spectra of InGaN/AlGaN/GaN p-n-heterostructures

Electroluminescence spectra and color characteristics of light-emitting diodes of white luminescence based on p-n heterostructures of the InGaN/AlGaN/GaN type with blue emission (λmax ≈ 455 nm) coated with phosphors of the type of aluminum-yttrium-gadolinium garnets activated with the Ce3+ ions are studied. The maximum in the excitation spectra of phosphors varies in the range 460–470 nm. The luminescence spectra of phosphors have the peaks from 530 to 590 nm and a width at half-maximum of intensity from 120 to 135 nm depending of the compound composition. The selection of intensities of blue and yellow-orange bands allows one to shift the coordinates of chromaticity of white light-emitting diodes to the region of “warm” luminescence with a correlated color temperature to TCC = 3000 K and maximum luminous efficiency up to 50 lm/W.