S. V. Sorokin

Tunable laser spectroscopy of spin injection in ZnMnSe/ZnCdSe quantum structures

Magneto-optical spectroscopy in combination with tunable laser excitation is employed to study exciton spin alignment and injection in ZnMnSe/ZnCdSe quantum structures. This approach enables us to selectively create preferred spin orientation and to separately monitor subsequent spin injection from individual spin states, thus shedding light on a possible source of spin loss. It is shown that the limited spin polarization in a nonmagnetic quantum well due to spin injection from a ZnMnSe-based diluted magnetic semiconductor (DMS) is not caused by a limited degree of spin alignment in the DMS, which is in fact complete, but rather occurs during subsequent processes.

Efficient spin depolarization in ZnCdSe spin detector: an important factor limiting optical spin injection efficiency in ZnMnSe∕ZnCdSe spin light-emitting structures

Spin depolarization of a ZnCdSe quantum-well spin detector (SD) in ZnMnSe∕ZnCdSe light-emitting quantum structures is investigated by cw and time-resolved optical orientation spectroscopy. It is shown that spin depolarization is governed by three distinct spin relaxation processes with the corresponding polarization decay times of 850, 30, and <10ps. The dominant and the fastest process is attributed to spin relaxation accompanying energy relaxation of hot excitons (and hot carriers) within the SD, providing evidence that it can be an important source of spin loss, leading to the observed limited efficiency of optical spin injection in the structures.

Control of spin functionality in ZnMnSe-based structures: Spin switching versus spin alignment

The ability of attaining desired spin functionality by adjusting structural design is demonstrated in diluted magnetic semiconductor (DMS) quantum structures based on II–VI semiconductors. The following spin enabling functions are achieved by tuning the ratio between the rates of exciton spin relaxation within the DMS and exciton escape from it to an adjacent nonmagnetic spin detector. Spin switching is realized when using a thin layer of Zn0.95Mn0.05Se as a spin manipulator and is attributed to a fast exciton escape from the DMS preceding the spin relaxation. Spin alignment is accomplished in tunneling structures where the presence of an energy barrier inserted between a spin manipulator (a DMS-based superlattice) and a spin detector ensures a slow escape rate from the DMS layer.

Lasing in Cd(Zn)Se/ZnMgSSe heterostructures pumped by nitrogen and InGaN/GaN lasers

Photoluminescence and lasing at a wavelength of λ=510–530 nm (green spectral region) in Cd(Zn)Se/ZnMgSSe structures with a different design of the active region are studied in a wide range of temperatures and nitrogen laser pump intensities. A minimal lasing threshold of 10 kW/cm2, a maximal external quantum efficiency of 12%, and a maximal output power of 20 W were obtained for the structure with the active region composed of three ZnSe quantum wells with fractional-monolayer CdSe inserts. The lasers exhibited a high temperature stability of the lasing threshold (characteristic temperature T0=330 K up to 100°C). For the first time, an integrated converter composed of a green Cd(Zn)Se/ZnMgSSe laser optically pumped by a blue InGaN/GaN laser that is grown on a Si (111) substrate and incorporates multiple quantum wells is suggested and studied.

Green lasers based on CdSe/ZnSe nanostructures pumped by electron beams with energies below 10 keV

We have studied the output characteristics of pulsed electron-beam-pumped green lasers based on ZnSe-containing quantum-sized structures with thin (20 nm thick) external ZnMgSSe confinement layers. Room-temperature lasing has been observed for electron beam energies above 3.7 keV. At a beam energy of 8–9 keV, the minimum threshold beam current density was 0.4–0.5 A/cm2. The maximum laser output pulse energy was 2 W at a pumping electron beam energy of ∼5 kW.

Spectroscopic Evidence for the Exciton Percolation Threshold in Low‐Dimensional ZnCdSe Solutions with Nano‐Islands

We have studied photoluminescence (PL), PL excitation (PLE), and micro-PL spectra of single quantum wells (QWs) formed by CdSe insertions in ZnSe matrix with different nominal Cd thickness (1-3 monolayers (ML)). The PL spectra are considerably red-shifted with respect to the position expected for homogeneous Cd distribution over the QW and can be attributed to the luminescence of CdSe-rich islands. It has been found that PLE spectra of different points of the PL band show a characteristic divergence at excitation below some characteristic energy E ME . This energy is identified with the percolation threshold above which the exciton is able to move over the whole lateral plane of QW whereas below the E ME only a resonant excitation of island related states is possible.

Molecular-beam epitaxy of heterostructures of wide-gap II–VI compounds for low-threshold lasers with optical and electron pumping

The paper presents basic approaches in designing and growing by molecular beam epitaxy of (Zn,Mg)(S,Se)-based laser heterostructures with multiple CdSe quantum dot (QD) sheets or ZnCdSe quantum wells (QW). The method of calculation of compensating short-period ZnSSe/ZnSe superlattices (SLs) in both active and waveguide regions of laser heterostructures possessing the different waveguide thickness and different number of active regions is presented. The method allowing reduction of the density of nonequilibrium point defects in the active region of the II–VI laser structures has been proposed. It utilizes the migration enhanced epitaxy mode in growing the ZnSe QW confining the CdSe QD sheet. The threshold power density as low as Pthr ∼ 0.8 kW/cm2 at T = 300 K has been demonstrated for laser heterostructure with single CdSe QD sheet and asymmetric graded-index waveguide with strain-compensating SLs.

Midinfrared injection-pumped laser based on a III–V/II–VI hybrid heterostructure with submonolayer InSb insets

Lasing at 3.075 μm (T = 60 K) in a regime of pulsed injection pumping has been obtained in an AlGaAsSb/InAs/CdMgSe double hybrid heterostructure with the active region comprising an InAs layer with submonolayer InSb insets. The electroluminescence (EL) spectrum of the heterostructure has been studied for various values of the pumping current up to the stimulated emission threshold. An increase in the pumping current leads to a short-wavelength shift and a change in the EL band structure, which is explained by the occupation of higher states by the charge carriers in InSb quantum dots and/or in the adjacent InAsSb layer.

An efficient electron-beam-pumped semiconductor laser for the green spectral range based on II-VI multilayer nanostructures

Emission characteristics of an electron-beam-pumped Cd(Zn)Se/ZnMgSSe semiconductor laser are studied. The laser’s active region consists of a set of ten equidistant ZnSe quantum wells containing fractional-monolayer CdSe quantum-dot inserts and a waveguide formed by a short-period superlattice with the net thickness of ∼0.65 μm. Lasing occurs at room temperature at a wavelength of 542 nm. Pulsed power as high as 12 W per cavity face and an unprecedentedly high efficiency of ∼8.5% are attained for the electron-beam energy of 23 keV.

Molecular Beam Epitaxy of Low‐Strained CdSe/CdMgSe Heterostructures on InAs(001) Substrates

CdSe/CdMgSe quantum well heterostructures have been grown on InAs(001) substrates by molecular beam epitaxy. Their optical and structural properties are studied by photoluminescence, transmission electron microscopy (TEM), electron probe microanalysis and X-ray diffraction. A comparative analysis of two types of heterovalent III-V/II-VI interfaces (InAs/CdSe and InAs/ZnTe) and their effect on the structural properties of CdMgSe layers are discussed. Structures with the InAs/ZnTe interface exhibit a much lower stacking fault density (below the TEM detection limit of 10 6 cm -2 ) as compared to those with the InAs/CdSe interface, which is explained by the high probability of In 2 Se 3 nucleation at the latter interface. The CdMgSe energy gap versus composition dependence as well as the optical bowing parameter and the zinc-blende MgSe band-gap energy are determined.