A. Zakrzewski

Structural properties of cubic MnTe layers grown by MBE

Abstract We report on the growth of zinc-blende MnTe on (001) GaAs substrates by MBE. Layers with thickness up to 8 μm were grown. The growth was performed for various ratios of Mn and Te fluxes. For high values of the Te Mn flux ratio, Raman scattering spectra showed a presence of tellurium lines corresponding to crystalline tellurium. For low flux ratios the presence of Te precipitates was less evident. These results were confirmed by X-ray diffraction studies. The lattice parameter of cubic MnTe and its temperature dependence were determined by X-ray diffraction. From the analysis of the rocking curves, for various Bragg reflections, the fluctuations of the lattice parameter and mosaicity were separated out.

Properties of epitaxially grown CdTe layers doped with indium

Abstract We report on the growth and characterization of n-type indium-doped CdTe films grown by molecular beam epitaxy on GaAs substrates. By varying the In flux we are able to control the carrier concentration in the range from 8 × 1014 to 1.5 × 1018 cm−3. The samples have been investigated by photoluminescence, transport, and deep level transient spectroscopy (DLTS) measurements. By DLTS we established that the concentration of the dominant electron trap, located at 0.45 eV below the edge of the conduction band, is proportional to the net donor concentration. This result indicates that the trap may be related to the presence of indium dopants.

Spatial correlations of In-donor charges in CdTe layers

Abstract We present experimental evidence that indium donors in CdTe localize electrons in a spatially correlated manner. We have studied the Hall mobility, μ H , as a function of the electron concentration, n H , at T = 77 K. Three methods leading to changes of n H have been used (i) high pressure freeze-out of electrons onto localized states of In-donors, (ii) the persistent photoconductivity effect, and (iii) a subsequent annealing of the sample. Each method causes a related modification in a degree of spatial correlations in the arrangement of donor charges. As a consequence, different values of μ H correspond to the same value of n H .

The effect of pressure on the luminescence of CdTe/CdMnTe quantum wells

Abstract We have studied photoluminescence in two CdTe / Cd 1− x Mn x Te multiple quantum-well samples with well thicknesses from 9.7 A to 100 A and with barrier compositions x = 0.5 and x = 0.68. The following effects have been observed after hydrostatic pressure up to 3 GPa was applied: (i) decrease of the luminescence intensity from wider wells, which can be related to the stress-induced deterioration of initially strained CdTe layers; (ii) transfer of photoexcited electrons from thinner wells into the barriers where Mn-related recombination occurs; (iii) large negative pressure coefficient (≈ −80 meV/GPa) of the Mn-related photoluminescence; (iv) positive pressure coefficients for CdTe well luminescence, which do not practically depend on the well thickness, while their magnitude decreases with increasing Mn concentration in the barriers (75 meV/GPa for Cd 0.50 Mn 0.50 Te and 60 meV/GPa for Cd 0.32 Mn 0.68 Te).

Photo-ESR characterization of donor and acceptor impurities in ZnS

Abstract The electron spin resonance (ESR) technique is used to study the dynamical parameters of main ZnS donors and acceptors. By studying light or/and temperature induced changes of the ESR signal intensity of a deep trap center (chromium) we can estimate, and in some cases determine ionization energies, effective capture cross sections and average donor-acceptor (DAP) recombination rates for a range of donors and acceptors. We conclude also on the role of deep trap centers in reducing the DAP recombination rate in ZnS.

Spatial Correlations of Donor Charges in MBE CdTe

We present experimental evidence that at high pressures indium donors in CdTe localize electrons in spatially correlated manner. We have studied Hall mobility, μH , as a function of electron concentration, n H , at T 77 K. Changes of nH have been achieved by two methods. High pressure freeze-out of electrons onto localized states of In-donors leads to the mobility enhancement with respect to the situation when nH has been modified by means of a subsequent annealing of the sample. As a result, depending on the degree of spatial correlations in the impurity charges arrangement, different values of μH correspond to the same value of nH. The variation of mobility with electron concentration suggests that the localized state of In-donor represents likely negatively charged DX state.