N. B. Gruzdev

Inhomogeneous lattice distortions in a Zn1 − xCrxSe crystal

The structure of a Zn1−xCrxSe semiconductor crystal with x = 0.0029 was studied using thermal neutron diffraction. It was detected that the diffraction patterns of the crystal contain regions of diffuse scattering concentrated in the vicinity of the strong Bragg reflections. It was shown that the diffuse scattering was caused by transverse displacements of lattice atoms induced by chromium impurities, which undergo static tetragonal Jahn-Teller distortions in ZnSe.

Nanoscale distortions of the lattice of a ZnSe crystal doped with 3d elements

The structure of semiconductor crystals Zn1−xVx2+Se (x = 0.0018) and Zn1−xCrx2+Se (x = 0.0006) was studied for the first time using thermal neutron diffraction at 300 and 120 K. The diffraction patterns of the crystals were revealed to contain diffuse scattering regions near the Bragg reflections of the initial cubic lattice. The experimental results are discussed in combination with earlier obtained data on neutron diffraction and propagation of ultrasonic waves in Zn1−xNix2+Se (x = 0.0025) and Zn1−xCrx2+Se (x = 0.0029). The diffuse scattering is shown to be due to nanoscale shear strains of the ZnSe lattice. The character of these strains is determined by Jahn-Teller 3d ions.

Magnetic state of a Zn1 −xCrxSe bulk crystal

The spin system of a Zn1 −xCrxSe bulk crystal (x = 0.045) was studied using thermal-neutron diffraction and magnetic measurements. Previously, it was reported in the literature that thin films (∼200 nm thick) of this type of semiconductors exhibit a ferromagnetic order. In this study, the ferromagnetic order is found to be absent in the bulk crystal.

Lattice Instability Induced by 3d Impurities in II–VI Compound Semiconductors

Nickel-impurity-induced transverse displacements of ions in a Zn1−xNixSe lattice (x = 0.0025) were detected. This type of displacement correlates with macroscopic distortions of a crystal associated with transverse ultrasonic waves that are propagated along the 〈110〉 direction. The shear instability is assumed to be due to the hybridization of the sp3 bonds with the 3d states of the impurity centers.

Effect of doping with nickel ions on the structural state of a zinc oxide crystal

The fine structure of a hexagonal zinc oxide crystal doped with nickel ions of the composition Zn1 − xNixO has been studied using neutron diffraction and magnetic measurements. It is established that even at very low doping levels (x = 0.0004), the crystal undergoes local distortions in basal planes of the initial hexagonal lattice. The local distortions are assumed to be sources of the formation of ferromagnetism in compounds of this class.

Low-energy charge transfer excitations in NiO

Comparative analysis of photoluminescence (PL) and photoluminescence excitation (PLE) spectra of NiO poly- and nanocrystals in the spectral range 2-5.5 eV reveals two PLE bands peaked near 3.7 and 4.6 eV with a dramatic rise in the low-temperature PLE spectral weight of the 3.7 eV PLE band in the nanocrystalline NiO as compared with its polycrystalline counterpart. In frames of a cluster model approach we assign the 3.7 eV PLE band to the low-energy bulk-forbidden p-d (t1g(π)-eg) charge transfer (CT) transition which becomes the allowed one in the nanocrystalline state while the 4.6 eV PLE band is related to a bulk allowed d-d (eg-eg) CT transition scarcely susceptible to the nanocrystallization. The PLE spectroscopy of the nanocrystalline materials appears to be a novel informative technique for inspection of different CT transitions.

Local vibrational mode in zinc telluride associated with a charged nickel impurity

Field exciton-vibration spectroscopy of the ZnTe: Ni semiconductor has revealed a local lattice vibrational mode due to the nickel impurity, which is negatively charged relative to the lattice. The electroabsorption spectrum of ZnTe: Ni contains equidistant vibrational replicas of the zero-phonon line of frequency 13±1 THz, which exceeds the limiting phonon frequency in ZnTe by more than twofold. Possible reasons for the formation of the local mode in ZnTe: Ni are analyzed within the concept of ionic-covalent character of ZnTe bonding, and the large width of the local mode resulting from its anharmonicity is discussed.

Ultrasonic investigation of a phase transition in ZnSe:Ni

Ultrasonic experiments on ZnSe and ZnSe:Ni crystals with impurity concentrations of 5.5×1019 cm−3 have revealed precursor phenomena at temperatures much higher than the temperature of the structural transition (Tc=14.5 K). It is found that the elastic constant C44 softens while C11 and C12 become stiffer as Tc is approached from above; the strains associated with the order parameter are transverse deformations of the e4 type. A brief symmetry analysis of the possibilities of formation of a tetragonal phase is given. The Jahn–Teller effect and displacement of the charge density on the chemical bonds are discussed as probable causes of the low-temperature phase transition.

A Raman Study of Lattice Vibrations in II–VI Semiconductors Doped with 3d Elements

Room-temperature Raman spectra were obtained for powder samples of Zn1−xNixSe and Zn1−yCrySe compounds and for a single-crystal Zn1−xNixSe (x = 0.0025) sample in the temperature range 5–140 K. The results obtained are interpreted in terms of large-scale lattice shear strains induced by 3d elements in these solid solutions.

Low-energy excited states of 3d transition metal ions in zinc selenide

The results of studying the impurity heat capacity of Zn1−xMxSe (M = Cr2+, Fe2+, Ni2+, Mn2+) solid solutions in the temperature range 1.8–20.0 K are presented. A heat-capacity method is described and applied for the measurement of the intracenter-transition energy in these systems. The role of the Jahn-Teller effect in the formation of low-energy excited states of 3d ions in ZnSe is discussed.