I. V. Sedova

Growth and excitonic properties of single fractional monolayer CdSe/ZnSe structures

Single fractional monolayer (FM) CdSe/ZnSe structures have been grown by molecular beam epitaxy (MBE), employing both conventional MBE and migration-enhanced epitaxy (MEE). A precise calibration of the FM mean thickness in the range of 0.15–3.0 ML has been performed for both techniques, revealing more than a 3.5 times lower Cd incorporation ability for the MEE mode at the same Cd and Se incident fluxes. Steady-state and time-resolved photoluminescence spectroscopy is used to characterize the intrinsic morphology of the CdSe FMs, with a special emphasis on the submonolayer thickness range. Both MBE and MEE grown samples exhibit inhomogeneity of the excitonic system, which can be explained by coexistence of a homogeneous alloylike layer and relatively large CdSe 2D clusters. The MEE samples display smaller fluctuations of the layer thickness and island sizes.

CdSe fractional-monolayer active region of molecular beam epitaxy grown green ZnSe-based lasers

This letter reports on the self-organized growth of nanoscale dot-like CdSe-based islands during molecular beam epitaxy of CdSe/ZnSe nanostructures with a CdSe thickness between 0.75 and 3.0 monolayers. An increase in the nominal CdSe thickness results in a higher density of islands (up to 2×1010 cm−2) and is accompanied by dramatic enhancement of the photoluminescence efficiency. The density of large relaxed islands appears to saturate at a value of (3–4)×109 cm−2. Room temperature (Zn, Mg)(S, Se)-based optically pumped lasers with an extremely low threshold (less than 4 kW/cm2), as well as (Be, Mg, Zn)Se-based injection laser diodes using a single (2.5–2.8) monolayer thick CdSe active region, both demonstrating significantly enhanced degradation stability, have been fabricated and studied.

Molecular-beam epitaxy of (Cd,Mn)Se on InAs, a promising material system for spintronics

We describe the growth characteristics of a type of II–VI/III–V heterostructure, (Cd,Mn)Se/InAs, which shows promise for application in spintronics. We used a variety of approaches for growing the heterostructure, and found that a high epilayer quality could be obtained by incorporation of a thin ZnTe buffer layer between the two materials.

Room-temperature midinfrared electroluminescence from asymmetric AlSbAs/InAs/CdMgSe heterostructures grown by molecular beam epitaxy

A hybrid double heterostructure with large asymmetric band offsets, combining AlAsSb/InAs (as a III–V part) and CdMgSe/CdSe (as a II–VI part), has been proposed as a basic element of a midinfrared laser structure design. The p-i-n diode structure has been successfully grown by molecular beam epitaxy and has exhibited an intense long-wavelength electroluminescence at 3.12 μm (300 K). A less than 10 times reduction of electroluminescence intensity from 77 to 300 K indicates an efficient carrier confinement in the InAs active layer due to high potential barriers in conduction and valence bands, estimated as ΔEC=1.28 eV and ΔEV∼1.6 eV. The type of band lineups at a coherent InAs/Cd1−xMgxSe interface is discussed for 0⩽x⩽0.15.

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.

Resonant spin-dependent electron coupling in a III-V/II-VI heterovalent double quantum well

We report on design, fabrication, and magnetooptical studies of a III-V/II-VI hybrid structure containing a GaAs/AlGaAs/ZnSe/ZnCdMnSe double quantum well (QW). The structure design allows one to tune the QW levels into the resonance, thus facilitating penetration of the electron wave function from the diluted magnetic semiconductor ZnCdMnSe QW into the nonmagnetic GaAs QW and vice versa. Magneto-photoluminescence studies demonstrate level anticrossing and strong intermixing resulting in a drastic renormalization of the electron effective g factor, in perfect agreement with the energy level calculations.

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.

Asymmetric AlAsSb/InAs/CdMgSe quantum wells grown by molecular-beam epitaxy

Asymmetric (6.7–300)-nm-thick InAs quantum wells (QWs) confined between AlAsSb and CdMgSe barriers have been fabricated by molecular-beam epitaxy. A special procedure of the CdMgSe-on-InAs growth initiation, exploiting an ex situ S passivation of InAs and in situ deposition of an ultrathin ZnTe buffer layer, results in the fabrication of high quality structures with a density of extended defects below 106 cm2. QW photoluminescence studies demonstrate a confinement effect and confirm the type I band alignment at the heterovalent InAs/CdMgSe interface mediated by the ZnTe interlayer. Observation of Shubnikov de Haas oscillations of magnetoresistance for an asymmetric 19-nm-thick InAs QW indicates an existence of the two-dimensional electron gas with the low-temperature sheet electron density of 1.3×1012 cm−2 and the mobility as high as ∼10 000 cm2/V s.

Low-threshold green laser heterostructures with Zn(Mg)SSe/ZnSe graded-index superlattice waveguide: Structural and optical properties

We report on structural and optical properties of green (λ∼520 nm) ZnCdSe/ZnMgSSe optically pumped laser heterostructures with a Zn(Mg)SSe/ZnSe graded-index superlattice (SL) waveguide, grown by molecular beam epitaxy. The pseudomorphic 400 nm thick waveguide comprising a set of strained ZnMgSSe/ZnSe and ZnSSe/ZnSe SLs of different periods and barrier-to-well thickness ratios at each side of a ZnCdSe quantum well (QW) active region provides efficient transport of nonequilibrium carriers to the QW. This results in reduction in laser threshold down to the extremely low value of 1.5 kW/cm2 at 300 K and increasing the external quantum efficiency above 44%.