P. V. Shapkin

Nonlinear transmittance of ZnSe :Fe2+ crystal at a wavelength of 2.92 μm

ZnSe crystals doped with Fe2+ ions are produced with the diffusion method under the conditions for thermodynamic equilibrium of solid ZnSe, solid Fe, and vapors (SZnSe-SFe-V). The transmittance of the samples is varied from 7 to 50% (in the absence of the antireflection coating) for a wavelength of about 3 μm. It is demonstrated that the transmittance of the ZnSe:Fe2+ crystals increases with an increase in the energy density of the high-power laser radiation with a wavelength of 2.92 μm. An equation that describes the propagation of the resonant radiation in a medium with saturable absorption at an arbitrary ratio of the radiation pulse duration to the relaxation time of the medium is introduced for the analysis of the experimental dependence of the transmittance on the energy density.

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.

EPR diagnostics of laser materials based on ZnSe crystals doped with transition elements

The electron paramagnetic resonance (EPR) spectra observed in laser materials based on zinc selenide (ZnSe) crystals doped with transition elements have been analyzed and identified. It has been shown that, in addition to working impurities (Cr2+, Co2+, or Fe2+), the diffusion layer exhibits EPR spectra of accompanying impurities due to the diffusion of transition elements (chromium, cobalt, or iron) used in the preparation of active materials for quantum electronics (lasers, switches) operating in the mid-infrared range. EPR diagnostics of these impurities can be used in the development of appropriate regimes for minimizing concentrations of accompanying impurities that adversely affect the performance characteristics of laser materials. It has been found that, during the diffusion of transition metals, ions of the accompanying impurity Mn2+, which is characterized by extremely informative EPR spectra, are embedded in the crystal lattice. It has been proposed to use these ions as ideal markers to control, on the electronic level, the crystal structure of the active diffusion layer.

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.

Explosive boiling in water exposed to q-switched erbium laser pulses

Pressure signals generated in water under the action of erbium laser pulses (100–200 ns, 2.94 μm) are investigated with lithium niobate piezoelectric transducer. For the first time multiply short (subnanosecond) pressure pulses standing against smooth pressure background are observed when the laser intensity exceeds explosive boiling threshold.

Cobalt diffusion during doping of ZnSe single crystals

Cobalt diffusion into single crystals of the compound semiconductor ZnSe has been studied under the conditions of the SZnSe-SCoSe-LZn-V phase equilibrium at temperatures from 700 to 970°C, and the diffusion coefficients of cobalt in (100)-and (111)-oriented single-crystal samples of zinc selenide have been determined as functions of temperature. The diffusion rate of cobalt along the [111] direction is shown to exceed that along [100].

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.

Effective 2.5-μm ZnSe:Cr2+ laser with transverse laser pumping

Effective lasing is obtained in the transversely pumped ZnSe single crystals that are doped with Cr2+ ions using diffusion methods. A Q-switched Er3+-doped glass laser with a radiation wavelength of 1.54 μm is used for pumping. The resulting laser energy is 150 μJ at an absorbed pump energy of 600 μJ, so that the efficiency is 25% and the slope efficiency is 29%. An increase in the gain (up to the superluminescence level) due to the application of the transverse pumping of the active element with a substantially non-uniform distribution of the dopant is discussed.