G. G. Yakushcheva

Hexagonal ZnCdS epilayers and CdSSe/ZnCdS QW structures on CdS(0001) and ZnCdS(0001) substrates grown by MOVPE

Abstract Optimization of growth conditions allows us to grow mirror-like hexagonal ZnCdS layers and CdSSe/ZnCdS quantum well (QW) structures on CdS(0001) and ZnCdS(0001) substrates by MOVPE. ZnCdS epilayers with high cathodoluminescence (CL) intensity at room temperature (RT) have also been obtained. An intense QW emission line has been observed in CdS/ZnCdS QW structures. With increasing excitation intensity the line shifted to shorter wavelength, which is a manifestation of an internal piezoelectric effect. An additional short-wavelength line appears in low-temperature CL spectra of CdSSe/ZnCdS QW structures due to localization of charge carriers by nonuniformity of alloy composition or QW thickness.

SPECTRAL ELLIPSOMETRY OF MULTILAYER ZnS/ZnSe HETEROSTRUCTURES

By the method of spectral ellipsometry with binary modulation of the polarization state the dispersions of the refractive index n, absorption coefficient k, and layer thickness in ZnS/ZnSe multilayer structures grown by the chemical gas‐phase deposition method from heteroorganic compounds on GaGaAs‐substrates with ZnSe buffer layers have been determined. The efficiency of local ellipsometric measurements (with a light beam size less than 150 × 500 μm) permitting mapping of the parameters of structures with A2B6 layers up to a few microns thick has been demonstrated. The optical properties of oxide layers formed on the zinc selenide surface have been investigated. Multilayer structures (ZnSe/ZnS)n/ZnSe/GaAs with a pronounced exciton absorption and specific features in the reflection spectra coinciding in energy with exciton transitions, as well as Bragg mirrors with a reflection coefficient up to 99% in the blue region of the spectrum, have been studied.

Ultrafast nonlinear response of heterostructures based on zinc chalcogenides

Nonlinear optical response of periodic structures based on ZnSe/ZnS heterostructures using interband excitation of a ZnSe sublattice by 1 50 fs laser pulses is reported. A considerable shift of reflection spectrum and large relative reflection changes were observed in a wide spectral range corresponding to the transparency region of ZnSe far from the intrinsic absorption onset. Evaluated refraction index change is about -0.02 with the relaxation time being about 3 picoseconds. The nonlinear refraction is supposed to be controlled by population induced absorption changes in ZnSe single crystals and relevant refraction index modification via Kramers-Kronig relations. The nonlinearity relaxation time is supposed to trace a transition from non-equilibrium to quasi-equilibrium distribution of electrons and holes within ZnSe conduction and valence bands, respectively, rather than electron-hole recombination time. The nonlinearity mechanism does not reduce to just population dependent absorption saturation but essentially results from the specific distribution function in the first instance after excitation.

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

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.

Photo-MOVPE growth and characterization of ZnSeZnxCd1 − xSe heterostructures

Abstract We have studied the growth of ZnCdSe layers on (1 0 0) GaAs substrates using atmospheric metalorganic vapor phase epitaxy (MOVPE). It was found that surface fluctuations of temperature were the main reason for compositional non-uniformity. The photo-assisted technique and a mechanism for rotational and back and forth movement of the substrates have been used for the growth of the Zn 0.45 Cd 0.55 Se- and CdSe-based heterostructures giving good homogeneity of the width and composition on a 12 cm 2 area at growth temperatures as low as 400–425°C. Strained single Zn 0.45 Cd 0.55 Se layers embedded in a ZnSe matrix were pseudomorphic up to the thickness of 4.5 nm. Strong green emission from a single well and 50 periodic Zn 0.45 Cd 0.55 Se ZnSe superlattices (SL) are observed under 441.6 nm HeCd laser excitation at 77 K.

Excitons in ZnSe1 − xSxZnSe1 − ySy superlattices grown by photomodulated MOCVD

Abstract The superlattices ZnSe 1 − x S x ZnSe 1 − x S y of alternating layers of solid solutions differing in composition were grown by photomodulated MOCVD method. A high quality of our samples was evidenced by the sharp exciton spectra and high intensity of exciton luminescence. The analysis of the band shapes of 1LO and 2LO exciton replica shows that the excitons in our SLs can be considered as free particles with the equilibrium kinetic energy distribution. The exciton motion in the studied SLs has essentially three-dimensional character due to the small height of the barriers. However, the periodic potential of SL perturbs the exciton wave vector, introducing additional elastic exciton scattering which can be detected through the band-shapes of phonon-assisted exciton luminescence.