Yu. A. Nitsuk

Optical absorption and chromium diffusion in ZnSe single crystals

ZnSe:Cr single crystals were obtained using diffusion-related doping with chromium. The diffusion of chromium was performed in an atmosphere of saturated zinc vapors, and the metallic Cr layer deposited on the crystal surface was used as the source. Lines corresponding to chromium absorption at 2.766, 2.717, and 2.406 eV were observed in the optical-density spectrum at 77 K. The highest chromium concentration in the crystals was determined from infrared absorptance in the region of 0.72 eV and was found to be equal to 8 × 1019 cm−3. It is shown that the diffusion profile of the chromium impurity can be determined by measuring the optical density of the crystals in the visible region of the spectrum. The diffusion coefficients D of chromium in ZnSe crystals at temperatures of 1073–1273 K are calculated. An analysis of the temperature dependence D(T) made it possible to determine the coefficients in the Arrhenius equation: D0 = 4.7 × 1010 cm2/s and E = 4.45 eV.

Optical absorption and diffusion of iron in ZnSe single crystals

ZnSe:Fe single crystals obtained by the diffusion doping are studied. The spectra of optical density in the range of energies of 0.4–3 eV are studied. The iron concentration in the studied crystals is determined using the magnitude of the shift of the absorption edge. The nature of the optical transitions determining the optical properties of ZnSe:Fe single crystals in the visible and IR regions of the spectrum is identified. The diffusion profile of Fe impurity is determined by measuring the relative optical density of crystals in the visible spectral region. The diffusivities of Fe in the ZnSe crystals are calculated for temperatures of 1120–1320 K. At 1270 K, the diffusivity of Fe is 3 × 10−10 cm2/s.

Native and impurity defects in ZnSe:In single crystals prepared by free growth

The optical absorption and photoluminescence spectra and the Hall effect were studied in ZnSe:In single crystals. The presence of electrically active InZn+ donor centers responsible for the impurity absorption and electrical conduction of crystals is established. It is shown that the conduction compensation in the ZnSe:In crystals is effected by cationic vacancies. The InZn+ donors and cationic vacancies form associative defects responsible for long-wavelength ZnSe:In luminescence. A high crystal conductivity (∼5 Ω−1 cm−1) is achieved as a result of ZnSe:In annealing in the zinc melt, which results in the extraction of cationic vacancies. The electron mobility in high-conductivity crystals is limited by scattering at the LO phonons and macrodefects formed due to the reduction of In solubility in crystals by their annealing in zinc.

Preparation and optical properties of ZnSe:Ni crystals

The ZnSe:Ni single crystals doped by diffusion are investigated. The diffusion is carried out from metallic nickel in helium and argon atmosphere. The optical-density spectra are investigated in the wave-length range of 0.4–3 μm. From the value of the absorption-edge shift, the nickel concentration in crystals under investigation is determined. The optical-density and luminescence spectra of ZnSe:Ni are identified. The nickel-impurity diffusion profile is determined by measuring the relative optical density of crystals in the visible spectral region. The diffusivities of nickel in ZnSe crystals are calculated at temperatures of 1073–1273 K.

Energy states of a Cr2+ ion in ZnSe crystals

ZnSe:Cr single crystals fabricated by diffusion doping are studied. The optical density spectra in the energy range 0.4–3 eV are investigated. The chromium concentration in the investigated crystals is determined by the absorption-edge shift. The energy states of the Cr2+ ion in ZnSe crystals are calculated. The nature of optical transitions determining the optical properties of ZnSe:Cr single crystals in the visible and IR spectral regions is established. It is shown that effective excitation of the IR luminescence of ZnSe:Cr crystals is implemented by light from the fundamental absorption region of Cr2+ ions.

Effect of iron impurities on the photoluminescence and photoconductivity of ZnSe crystals in the visible spectral region

The photoconductivity and photoluminescence of ZnSe:Fe crystals in the visible spectra region are studied. The scheme of optical transitions within Fe2+ impurity centers is established. It is shown that the high-temperature photoconductivity of ZnSe:Fe crystals is controlled by optical transitions of electrons from the 5E(F) ground state to the higher levels of excited states of Fe2+ ions, with subsequent thermal activation of the electrons to the conduction band. Efficient excitation of intracenter luminescence of ZnSe:Fe crystals is attained with light corresponding to the region of intrinsic absorption in Fe2+ ions.

Preparation and optical properties of Co-doped ZnSe single crystals

ZnSe single crystals doped via Co diffusion are investigated. The diffusion was carried out from metal Co in He or Ar atmosphere. The spectra of optical density in the wavelength range 0.4–2 μm are investigated. It is found that the absorption edge shifts as the concentration of doping impurities increases. This shift is caused by the formation of the Zn1 − xCoxSe alloy. The diffusion profile of the Co dopant is determined via measurement of the relative optical density of the crystals in the visible spectral region. The Co diffusivities (D) in the ZnSe crystals at T = 1103–1273 K are calculated. The analysis of the temperature dependence D(T) made it possible to determine the coefficients in the Arrhenius equation, namely, D0 = 3.4 × 106 cm2/s and E0 = 3.8 eV.

Optical absorption of vanadium in ZnSe single crystals

The study is concerned with ZnSe:V single crystals produced by diffusion doping. The optical density spectra are recorded in the photon energy range from 0.4 to 3 eV. From the shift of the absorption edge, the vanadium concentration in the crystals is determined. The nature of optical transitions controlling the optical properties of the ZnSe:V single crystals in the visible and infrared spectral regions is identified. The diffusion profile of the vanadium impurity is established from measurements of the relative optical density of the crystals in the visible spectral region. The vanadium diffusion coefficients in ZnSe crystals at temperatures of 1120–1320 K are calculated; at 1320 K, the vanadium diffusion coefficient is 10−9 cm2 s−1.

Study of the impurity photoconductivity and luminescence in ZnSe:Ni crystals in the visible spectral region

The photoconductivity and photoluminescence spectra of ZnSe:Ni crystals in the visible spectral region are studied. It is established that the high-temperature impurity photoconductivity of ZnSe:Ni crystals is controlled by the optical transitions of electrons from the ground state 3T1(F) to high-energy excited states, with subsequent thermally activated transitions of electrons to the conduction band. A photoconductivity band associated with the photoionization of Ni impurities is revealed. The intracenter luminescence of ZnSe:Ni crystals is efficiently excited with light corresponding to the intrinsic absorption region of Ni2+ ions.

Indium doping of ZnSe single crystals during vapor phase growth

A process for indium doping of ZnSe single crystals during vapor phase growth is described. The solubility limit of indium in ZnSe is determined as a function of temperature and zinc selenide stoichiometry. The conclusion is drawn that the entire homogeneity range of ZnSe in the equilibrium phase diagram lies at selenium-enriched compositions.