D. A. Sannikov

Blue light emitting diode internal and injection efficiency

A simple experimental method of light emitting diode (LED) injection efficiency (IE) determination was suggested. IE and internal quantum efficiency (IQE) calculation is an actual and difficult problem in LED science. In this paper IE and IQE of blue LEDs were determined separately. The method is based on electroluminescence data fitting by the modified rate equation model. Efficiency droop caused by Auger recombination and poor injection were taken into account. Only one reasonable assumption was accepted during the calculations: IE tends to 1 at low current densities.

Self-consistent inhomogeneity of quantum wells in II–VI semiconductors

AbstractAn X-ray diffraction method that uses a slightly diverging (3′) beam and maximally attainable diffraction angles ϑB (as large as 77°) was developed to study quantum wells (QWs) with widths of 5–8 nm separated by wide (100–220 nm) barrier layers. The advantage of this method compared to the use of a parallel beam is an increase by two orders of magnitude in the intensity of the beam incident on the sample and an increase in the probability of diffraction for all QWs as a unified single crystal. It is found that the growth on GaAs substrates misoriented by 10° from the (001) plane in the [111]II direction brings about monoclinization of crystal lattices of the QW layers and barrier layers in opposite directions. Inhomogeneity of composition over the thickness of each well is observed. In the case of growth of a ZnSe/ZnMgSSe structure in which the layers have a crystal-lattice period close to the lattice period of the GaAs substrate, the QWs are inhomogeneously doped with elements from the composition of the barrier layers. The inhomogeneity of QW composition observed in the growth of mismatched layers in ZnCdSe/ZnSSe and ZnCdS/ZnSSe structures is caused by the fact that mismatch between the lattice parameters of QWs and barriers stimulates the growth of self-consistent compositions; this occurs due to a decrease in the Cd concentration in the Zn1−xCdxSe QW in the initial stages of growth compared to the Cd concentration in the flow of gases and an increase in the Zn concentration in the Cd1−xZnxS QW at small values of x up to the concentration matching GaAs (x = 0.4). The mismatch stresses are partially relaxed via dislocations with the (111)II glide planes, as a result of which is observed the combination of rotation of the crystal planes of the layers and QW around the [1

E-beam longitudinal pumped laser on MOVPE-grown hexagonal CdSSe/CdS MQW structure

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MOVPE growth and study of ZnCdSe/ZnSSe MQW structures for green VCSELs

0] axis and almost cylindrical bending of the entire sample around the perpendicular [110] axis. Mismatch between lattice parameters of the ZnMgSSe barrier layers and the substrate brings about decomposition of these layers into two phases; this decomposition is caused by thermodynamic instability of the alloy.

Scanning spreading resistance microscopy of undoped CdS/ZnSSe multiple quantum well heterostructure

The first electron-beam pumped VCSEL was fabricated on CdSSe/CdS MQW structure grown by metalorganic vapor phase epitaxy on CdS substrate misoriented by 12–16° from (0001) towards (1010). Substrate misorientation results in more perfect surface morphology and intense cathodoluminesence. Lasing in the 535–590 nm spectral range was achieved at room temperature with different VCSELs. The laser power maximum of one VCSEL was as high as 2 W at RT, with electron energy 50 keV and current 1.7 mA. The threshold current was lower than that for the bulk CdSSe laser although the heterostructure used in the VCSEL has the type-II band alignment.

Nanoscale ZnCdS/ZnSSe heterostructures for semiconductor lasers

En CdSSe/CdS multi quantum well structures were grown by metalorganic vapor phase epitaxy (MOVPE) on a CdS substrate misoriented by 12−15o from (0001) towards (1010). Microcavities with dielectric oxide mirrors were fabricated on the basis of these structures. Lasing in the 535−590 nm spectral range was achieved on different structures under longitudinal electron beam pumping at room temperature. The relatively high threshold of the laser and the blueshift from the spontaneous emission peak to lasing wavelength were explained by taking into account the type−II band alignment of the active region.