Raman spectra of the laser-irradiated GaSe single crystals

The specific features of the crystal structure of the lamellar GaSe crystals of various polytypes are analyzed. The possibility of identifying the phase transitions, which occur as a result of variations in temperature, pressure, and composition, is considered from the standpoint of resonance Raman scattering. The effects of high-temperature thermal annealing and pulsed laser irradiation on Raman spectra is investigated. It is found that pulsed laser radiation gives rise to regions with different polytype composition and regions with residual stress.     

Er掺杂GaSe晶体特性的研究

对改进型布里奇曼方法生长的Er掺杂GaSe晶体的成 分、光学特性和倍频特性进行了测量和分 析。研究发现,掺杂晶体中Er的分布不均匀且浓度远低于装料浓度,高浓度掺杂使得晶体光 学质量下降。通 过对掺杂晶体光学特性测量发现,Er的掺杂没有明显改变晶体的光谱特性,掺杂浓度为0.07mass.%的 GaSe:Er晶体在可见光波段表现出了比较好的光学性质。通过对晶体拉曼光谱的测量发现, 在GaSe:Er (0.09 mass.%)和GaSe:Er (0.10mass.%)晶体中出现了新的拉曼散射带,它 是由Er³⁺的⁴F9/2→⁴I9/2跃迁产生的。 通过飞秒Ti:sapphire激光和CO₂激光泵浦下I类倍频实验发现,掺杂晶体相位匹配角与纯G aSe晶体相比没有明显变 化,实验结果与理论曲线符合得较好,最佳浓度掺杂晶体GaSe:Er(0.07mass.%)将CO₂倍 频转换效率提高了43%。     

Investigations on the nonlinear optical properties of glycinium oxalate single crystals

Single crystals of glycinium oxalate (GLO) are grown by solution growth technique. The Z scan technique is used to elucidate the third order nonlinearity in the material. The results indicate that the compound exhibits reverse saturable absorption (RSA) and self-defocusing performance. The second harmonic generation (SHG) efficiency of the crystal evaluated by Kurtz and Perry technique is compared with that of the standard KDP crystal. Attempt is made to correlate the SHG efficiency with the crystalline perfection in the material.     

Photoconductivity and luminescence in GaSe crystals at high levels of optical excitation

The photoconductivity and luminescence of GaSe layered crystals at high levels of optical excitation are studied experimentally. The specific features observed in the photoconductivity and photoluminescence spectra are controlled by the nonlinear optical absorption in the region of excitonic resonance.     

Specific features of the effect of irradiation with electrons and neutrons on photoelectric properties of CdS single crystals nominally undoped and doped with Cu

Electrical, photoelectric, and magnetic properties of CdS single crystals undoped and doped with copper (N _Cu ≈ 10¹⁸ cm^?3) and irradiated with electrons (E = 1.2 MeV, Φ = 2 × 10¹⁷ cm^?2) and neutrons (E = 2 MeV, Φ = 10¹⁸ cm^?2) are studied. It is shown that the donor-acceptor pairs are responsible for extrinsic photoconductivity and paramagnetic properties; in particular, these pairs are represented by Cu _Cd ^? -D ⁺ complexes that are destroyed during irradiation and are formed again with time (as secondary radiation defects) in irradiated samples. It is established that the majority of paramagnetic centers and donor-acceptor pairs are located in the near-surface region of the crystal. It is confirmed that large structural defects (defect clusters) formed by irradiation with neutrons are efficient sinks for copper atoms. Specific features of isochronous annealing of paramagnetic centers and donor-acceptor pairs responsible for the variation in magnetic parameters and in the photoconductivity spectra of irradiated undoped and Cu-doped CdS samples are studied.     

Properties of tellurium-doped gallium antimonide single crystals grown from nonstoichiometric melt

The electric and luminescence properties of tellurium-doped gallium antimonide single crystals grown from gallium-enriched melt by Czochralski’s method have been investigated. It was determined that the crystals possess n-type conductivity and are strongly compensated. It was found that toward the end of the ingot the concentration of the impurity tellurium increases more rapidly than that of the compensating acceptors. The possibilities of obtaining the properties of GaSb single crystals by growing the crystals from nonstoichiometric melts followed by heat treatment of the material are discussed. Fiz. Tekh. Poluprovodn. 31, 947–949 (August 1997)     

Specific features of Hall measurements in doped semiconductors

Semiconductors - The limits of applicability of the Hall method for separate determination of the impurity concentration are considered for the case of doping with only one main impurity. A diagram...     

非线性光学晶体材料GaSe激光参数的模拟计算

对红外非线性光学晶体GaSe的非线性性质进行了研究.计算模拟了1.064 μm、2.05 μm、2.79 μm泵浦情况下Ⅰ、Ⅱ类相位匹配情况下GaSe晶体的相位匹配角、有效非线性系数、走离角、允许角和泵浦波波长的关系.同时计算了晶体激光光参量震荡和倍频波波长和相位匹配角、有效非线性系数、走离角、允许角的关系.对计算结果进行了分析比较.所得结果对于GaSe晶体用于特定波长激光器设计新波段提供了理论依据.     

Special features of optical and photoelectric properties of nominally undoped and Cu-doped CdS single crystals

Experimental data on the effect of fast reactor neutrons on the absorption spectra, photoconductivity, and luminescence of nominally undoped and Cu-doped CdS single crystals are reported. It is shown that defect clusters formed as a result of neutron irradiation exhibit the properties of getters for easily migrating optically active impurities in the crystal lattice. In neutron-irradiated samples, the defects can be annealed in two stages. The first stage (100–150°C) involves the annealing of point defects, while the second stage (250–420°C) involves mainly the annealing of defect clusters. The degradation of the defect clusters is accompanied with the enrichment of the lattice with Cd and S vacancies.     

Specific features of anisotropic optical thermoelements

The effect of different temperature distributions on the main parameters of anisotropic optical thermoelements are studied in the optical transmission mode. It is shown that such devices implementing the ingenious “transparent wall” method are promising for recording radiation fluxes of different densities in wide spectral and power ranges.     

Optical spectra of Eu2+ ion doped KMgF3 single crystals grown by Bridgman method

High-quality KMgF3 single crystal containing 0.5 mol% europium (Eu) was prepared by an improved Bridgman method. X-ray diffraction (XRD), photoluminescence spectra and fluorescence lifetime were measured. The results indicate the reduction of Eu3+ to Eu2+ in the KMgF3 single crystal. Under the excitation of 259 nm, 370 nm and 394 nm, the sample has two distinct emissions of Eu2+:4f7→4f7(~363 nm) and 4f65d1→4f7 (~440 nm). The substitution site for Eu ion is confirmed. The optical property investigation result shows that the Eu2+ doped KMgF3 single crystal may be used as potential laser media and related materials for optical devices.     

Servo tuning and stabilization of nonlinear optical crystals

A new optical technique for servo tuning and stabilization of angle tuned nonlinear optical crystals is described. This technique has zero insertion loss and works equally well with collimated, focused, or noncollinear fundamental beams. Servo tuning of a Type I KDP nonlinear crystal for summing the output of a tunable dye laser with the Nd:YAG second harmonic and servo stabilization of the production of the Nd:YAG fourth harmonic in Type I KDP are demonstrated.     

Reflection spectra of doped bismuth-antimony crystals in the far-infrared region of the spectrum

The plasma reflection spectra of the doped bismuth and bismuth-antimony alloyed crystals were studied experimentally at liquid-nitrogen temperature within a range of 30–600 cm^?1. Specificities in the optical functions of the samples are revealed within the infrared range that lies on the low-frequency side of the plasma edge and coincides with the optical-phonon frequencies in bismuth. When the plasma frequency is approached, the character of the interaction of radiation with anisotropic electron-hole plasma changes considerably.     

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.     

Diffusion of nonstoichiometric defects in n-GaP crystals

Diffusion of nonstoichiometry-related point defects from a LEC-grown GaP substrate to a Te-doped GaP n-type epitaxial layer was investigated by means of photocapacitance. It was revealed that deep donor level at E_C−2.1 eV was introduced into GaP substrate with annealing under phosphorus vapor pressure. Thus, the 2.1 eV deep level is thought to be involved with excess P atoms such as interstitial phosphorus atoms. In Te-doped crystal, 2.1 eV level was detected and the density increased as the time of substrate annealing increased. By measuring PHCAP spectra of samples with different thickness of epitaxial layer, diffusion profile of the defects from the substrate interface was obtained. From this, the diffusion coefficient at 850°C is estimated to be 8×10^–11 cm²/s.     

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.     

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.     

Conductivity anisotropy in the doped Bi2Te3 single crystals

Temperature dependences (temperature range T = 0.5?300 K) of resistivity in the plane of layers and in the direction perpendicular to the layers, and the galvanomagnetic effects in undoped and doped Bi₂Te₃ single crystals are studied (magnetic field H < 80 kOe, T = 0.5?4.2 K). It is shown that upon doping of Bi₂Te₃ with the Group III atoms (In and B), conductivity anisotropy increases mainly due to an increase in resistivity in the direction perpendicular to the layers. This fact makes it possible to assume that the atoms of these impurities are incorporated mainly into the van der Waal gaps between the layers upon doping. It is also revealed that, upon doping of Bi₂Te₃ with In and B, the temperature dependence of conductivity becomes weaker, which indicates an increase in the role of scattering by defects in scattering mechanisms. The concentrations and mobilities of charge carriers, values of the Hall factor conditioned by the anisotropy of effective masses and orientation of ellipsoids with respect to crystallographic axes, areas of the extreme section of the Fermi surface by the plane perpendicular to the direction of the magnetic field, and the Fermi energy are evaluated.     

Effect of electron and neutron bombardment on the orange luminescence spectra of not specially doped and copper-doped cadmium sulfide single crystals

CdS single crystals which were not specially doped and which were doped with copper (N _Cu=10¹⁸ cm⁻³) have been investigated. It is concluded on the basis of an analysis of the dose dependences of the orange luminescence intensity (λ _M=605 nm) of “pure” and doped samples upon bombardment by electrons with E=1.2 MeV and by fast reactor neutrons that the centers responsible for this luminescence are complex in nature. They consist of interstitial cadmium atoms and oxygen atoms. Electron bombardment of CdS:Cu single crystals results in the formation of new centers which are responsible for luminescence with λ _M=570 and 545 nm. Fiz. Tekh. Poluprovodn. 31, 390–392 (April 1997)     

Interrelation of pyroelectric and nonlinear optical coefficients in ferroelectric crystals

An experimental relation is found between the pyroelectric and electrooptic coefficients of several ferroelectric materials. The physical basis of this relation is explained using Garrett's anharmonic oscillator model, and the pyroelectric coefficients of Sr0.25Ba0.75Nb2O6, Sr2NaNb5O15,Ba2NaNb5O15, KSr2Nb5O15, K3Li2- Nb5O15, and Ag3AsS3are predicted from the known electrooptic coefficients.