Sergiy G. Krylyuk

Enhancement of the photoluminescence intensity in short-period GaAs/AlAs superlattices with different well and barrier thickness

The transition from an indirect to a direct energy band structure has been induced in short-period GaAs/AlAs superlattices by going from a symmetric to an asymmetric distribution of the well and the barrier thickness within the unit cell of the superlattice. Reducing the barrier thickness dB to half the well thickness dW moves the lowest state in the conduction band from the X point in the AlAs barrier to the Γ point in the GaAs well. For dW=2dB, the band structure becomes therefore direct for all values of dW. This change in the type of energy gap is accompanied by a significant enhancement of the integrated photoluminescence intensity for asymmetric superlattices.

Observation of stimulated emission in an ultrashort-period nonsymmetric GaAs/AlAs superlattice

Nonsymmetric short-period GaAs/AlAs superlattices, for which the well thickness is at least a factor of 2 larger than the barrier thickness, have been shown to exhibit a direct band gap for any well thickness. These superlattices are characterized by an enhanced intensity of the luminescence as compared to their symmetric indirect-gap counterparts with the same well width, and, thus, may be used as light-emitting devices, in particular, as low-threshold lasers in the red visible spectrum. This conjecture is supported by the observation of stimulated emission at T=80 K for a GaAs/AlAs superlattice with six monolayers well and three monolayers barrier width.

Characterization of ultrashort-period GaAs/AlAs superlattices by exciton photoluminescence

Abstract Ultrashort-period GaAs/AlAs superlattices of type-II were investigated by low-temperature photoluminescence spectroscopy. The photoluminescence spectra consisting of many lines were carefully analyzed to obtain energy position, full width at half maximum and relative intensity for each individual line. Influence of the energy band structure, layer thickness and interface disorder on the radiative electron-hole transitions in these structures is discussed.

Asymmetric short-period GaAs/AlAs superlattices for light-emitting devices

Photoluminescence properties of short-period asymmetric GaAs/AlAs superlattices with the well and barrier thickness varied from 10 to 3 monolayers were studied at high optical excitation. It was shown that an asymmetric structure of the superlattice, in which the well layers are at least twice wider than the barrier ones, allows us to maintain the direct band gap and, hence, to improve emission properties for any well width. This is important for utilization of such structures in light-emitting devices. The stimulated emission at 80 K was observed for a GaAs/AsAs superlattice with the well and barrier thickness of 6 and 3 monolayers, respectively. At the same time, investigations of the dependences of the emission intensity on the pump intensity for different superlattices revealed an enhancement of nonradiative recombination with decreasing the well thickness due to an enhanced influence of interface roughness.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Gamma-ray CdTe and CdZnTe detectors: investigations and applications in radiation control devices

In this paper we present results of our investigations on the technology improvement for high-grade CdTe and CdZnTe single-crystals growth as well as results of the obtained materials testing by photoluminescence method. Perspectives for the materials utilization in detectors and devices of radiation control are discussed. Design features and characteristics of the developed personal (gamma) - and X-radiation dosimeters on the base of CdTe detectors and (gamma) -radiation spectrometers on the base of CdZnTe detectors are presented and discussed as well.

Identification of electron-hole transitions in short-period GaAs/AlAs superlattices by time-resolved photoluminescence

Temporal characteristics of the carriers recombination were investigated in different types of GaAs/AlAs superlattices by the time-resolved photoluminescence spectroscopy. The peculiarities of the electron-hole transitions were established for the superlattices studied in the dependence of the superlattice type and the width of quantum well and barrier layers. In particular, the conditions of existence of free and localized on the interface roughness excitons were found.