Nature of optical properties of GdFe3(BO3)4 and GdFe2.1Ga0.9(BO3)4 crystals and other 3d5 antiferromagnets

Influence of the partial substitution of paramagnetic Fe³⁺ ions by diamagnetic Ga³⁺ ions in the trigonal crystal GdFe₃ (BO₃)₄ on its optical and magnetic properties is studied and discussed in connection with problems common for all antiferromagnets containing 3d ⁵ ions. Polarized optical absorption spectra and linear birefringence of GdFe₃ (BO₃)₄ and GdFe_2.1Ga_0.9 (BO₃)₄ single crystals have been measured in the temperature range 85–293 K. Specific heat temperature dependence (2–300 K) and structure of GdFe_2.1Ga_0.9 (BO₃)₄ crystal have been also studied. As a result of substitution of 30% Fe to Ga the Neel temperature diminishes from 38 till 16 K, the strong absorption band edge shifts on 860 cm^-1 (0.11 eV) to higher energy and the d-d transitions intensity decreases substantially larger than the Fe concentration does. Strong absorption band edge is shown to be due to Mott-Hubbard transitions. Correlation between position of the strong absorption band edge and the Neel temperature of antiferromagnets has been revealed. Properties of the doubly forbidden d-d transitions in the studied crystals and in other antiferromagnets are explained within the framework of the model of the exchange-vibronic pair absorption, which is theoretically analyzed in detail. The model permitted us to determine the connection between parameters of d-d absorption bands (intensity, width and their temperature dependences), on the one hand, and the exchange, spin-orbit and electron-lattice interactions, on the other hand.     

Photoelectric Phenomena in Au3In5Se9 and Au3Ga5Se9 Compounds

The anisotropy of photoconductivity in Au₃In₅Se₉ and Au₃Ga₅Se₉ crystals grown by the Bridgman method have been investigated as a function of temperature in the temperature range of 100 - 420 K. It is shown that the crystals have a wide range of spectral sensitivity of 0.9 - 1.8 eV. The width of the band gaps and their temperature coefficient are determined. The life time of the current carriers are determined at different levels of excitations.     

Piezobirefringence in γ1-(GaxIn1−x )2Se3 single crystals

The piezobirefringence of uniaxial γ₁-(Ga_xIn_1−x )₂Se₃ crystals (x=0.3, 0.4) was investigated in the spectral range 0.6–1.1 μm at temperatures from 77 to 295 K. It is shown that uniaxial compression leads to a linear decrease in the birefringence, whereas a decrease in temperature reduces the effect of piezobirefringence. The baric changes in the birefringence are attributed to the baric changes in the contribution of the edge transitions to the total birefringence. __________ Translated from Optika i Spektroskopiya, Vol. 95, No. 3, 2003, pp. 458–461. Original Russian Text Copyright ? 2003 by Studenyak, Kran’chets, Suslikov, Kovach.     

等离子体活化硒对电沉积Cu-In-Ga金属预制层硒化的影响

使用等离子体活化硒源对电沉积制备的Cu-In-Ga金属预制层进行了硒化处理时, 发现等离子体功率对Cu(In_1-xGa_x)Se₂(CIGS)晶粒的生长有重要影响, 当等离子体功率为75 W时, 制备出单一Cu(In_0.7Ga_0.3)Se₂相的CIGS薄膜. 通过对不同衬底温度的等离子体活化硒源硒化的CIGS 薄膜进行了研究与分析, 并与普通硒化后的薄膜进行对比, 发现高活性硒在低温下会促进Ga-Se二元相的生成, 从而有利于Cu(In_0.7Ga_0.3)Se₂单相的生长. 对等离子体硒化后的CIGS薄膜进行了电池制备, 发现单相CIGS薄膜没有显著提高电池性能. 通过优化工艺, 所制备的CIGS电池效率达到了9.4%. 关键词： 0.7Ga_0.3)Se₂')" href="#">Cu(In_0.7Ga_0.3)Se₂ 电沉积 Cu-In-Ga金属预制层 等离子体活化硒     

Optical constants of Cu(In0.7Ga0.3)5Se8 and Cu(In0.4Ga0.6)5Se8 crystals

Variable angle spectroscopic ellipsometry has been applied to characterize the optical constants of bulk Cu(In_0.7Ga_0.3)₅Se₈ and Cu(In_0.4Ga_0.6)₅Se₈ crystals grown by the Bridgman method. The spectra were measured at room temperature over the energy range 0.8-4.4 eV. Adachi’s model was used to calculate the dielectric functions as well as the spectral dependence of complex refractive index, absorption coefficient, and normal-incidence reflectivity. The calculated data are in good agreement with the experimental ones over the entire range of photon energies. The parameters such as strength, threshold energy, and broadening, corresponding to the E₀, E_1A, and E_1B interband transitions, have been determined using the simulated annealing algorithm.     

Highly strained InxGa(1−x)As−InyAl(1−y)As (x>0.8,y<0.3) layers for short wavelength QWIP and QCL structures grown by MBE

Highly strained quantum cascade laser (QCL) and quantum well infrared photodetector (QWIPs) structures based on In_xGa_(1−x)As−In_yAl_(1−y)As (x>0.8,y<0.3) layers have been grown by molecular beam epitaxy. Conditions of exact stoichiometric growth were used at a temperature of 420°C to produce structures that are suitable for both emission and detection in the 2–5 μm mid-infrared regime. High structural integrity, as assessed by double crystal X-ray diffraction, room temperature photoluminescence and electrical characteristics were observed. Strong room temperature intersubband absorption in highly tensile strained and strain-compensated In_0.84Ga_0.16As/AlAs/In_0.52Al_0.48As double barrier quantum wells grown on InP substrates is demonstrated. Γ–Γ intersubband transitions have been observed across a wide range of the mid-infrared spectrum (2–7 μm) in three structures of differing In_0.84Ga_0.16As well width (30, 45, and 80 Å). We demonstrate short-wavelength IR, intersubband operation in both detection and emission for application in QC and QWIP structures. By pushing the InGaAs–InAlAs system to its ultimate limit, we have obtained the highest band offsets that are theoretically possible in this system both for the Γ–Γ bands and the Γ–X bands, thereby opening up the way for both high power and high efficiency coupled with short-wavelength operation at room temperature. The versatility of this material system and technique in covering a wide range of the infrared spectrum is thus demonstrated.     

(Al0.1Ga0.9)0.5In0.5P材料的MOCVD生长温度窗口研究

用来制作光电子器件的(Al0.1Ga0.9)0.5 In0.5P为直接带隙的四元合金材料,对应的发光波长为630 nm,在其LP-MOCVD (low press-metalorganic chemical vapor deposition)外延生长过程中温度的高低成为影响其质量的关键,找到合适的生长温度窗口很有必要.实验中分别在700℃,680℃,670℃和660℃的条件下生长出作为发光二极管有源区的(Al0.1Ga0.9)0.5 In0.5P多量子阱结构,通过PL谱的测试对比分析,找出最佳生长温度在670℃附近.之后对比各外延片的PL谱、表面形貌,并对反应室的气流场进行了模拟,对各温度下生长状况的原因作出了深入分析.分析得到,高温下In组分的再蒸发会引起晶格失配并导致位错;低温下O杂质的并入会形成大量非辐射复合中心影响晶体质量,因此导致了(Al0.1Ga0.9)0.5In0.5P生长温度窗口较窄,文章最后提出In源有效浓度的提高是解决高温生长的一条有效途径.     

Synthesis and Growth of New Compounds Au3In5Se9 and Au3Ga5Se9

The phase analysis was performed and a character of interaction in AuInSe₂ - In₂Se₃ and AuGaSe₂ -Ga₂Se₃ quasi-binary systems were considered. The technology of synthesis and growth of single crystals of new semiconducting compounds Au₃In₅Se₉ and Au₃Ga₅Se₉ were developed. The materials for ohmic contacts were chosen and the electrical, optical and thermal properties of obtained compounds have been investigated. The forbidden band gap, its temperature coefficient, the type of the optical transitions and heat capacity of Au₃In₅Se₉ and Au₃Ga₅Se₉ compounds were determined. The charge of entropy and enthalpy has been estimated by numerical integration.     

Production and Laser Characteristics of Fe<Superscript>2+</Superscript>:ZnS<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> Polycrystals

A method is developed for producing active laser elements (spectrum range 4 to 5 μm) based on polycrystalline solid solutions ZnS_xSe_x-1 doped with iron ions. Bilateral diffusion doping of the elements by Fe²⁺ ions is performed during hot isostatic pressing. Spectral and energy characteristics of the laser are investigated with the Fe²⁺:ZnS_0.1Se_0.9 active element kept at room temperature. It is found that the absorption band of the Fe²⁺:ZnS_0.1Se_0.9 crystal is blueshifted with respect to the Fe²⁺:ZnSe absorption band, while the lasing spectra of the Fe²⁺:ZnSe and Fe²⁺:ZnS_0.1Se_0.9 lasers and their energy parameters are almost identical. The lasing energy of 580 mJ is obtained at the slope efficiency with respect to the absorbed energy of 46%. Further increase in the lasing energy is limited by development of transversal parasitic oscillation at a large size of the pump beam spot.     

Optical absorption edge of Cd1−x Mn x Ga2Se4 crystals

Summary We report the absorption edge spectra of the new family of diluted magnetic semiconductors Cd_1−x Mn _x Ga₂Se₄ (0≤x≤1), grown from the vapour phase by chemical transport. Absorption bands observed under the gap of CdGa₂Se₄ are attributed to intra-Mn²⁺ transitions involving excited states of the 3d ⁵ electrons, split by the crystal field. The authors of this paper have agreed to not receive the proofs for correction.     

Effect of barrier configuration on excitonic recombination in Ga.47In.53As/Al.48In.52As multi quantum well structures

Photoluminescence and photoluminescence excitation spectroscopy on Ga_.47In_.53As multi quantum wells confined either by homogenous ternary Al_.48In_.52As barriers or by Ga_.47In_.53As/Al_.48In_.52As short-period superlattice (SPS) barriers show that the confinement by SPS barriers improves the edge luminescence significantly. The spectral width of the free-exciton absorption and the low-temperature emission peak as well as the Stokes-shift between emission and excitation spectra are reduced as compared to samples clad by homogenous ternary Al_.48In_.52As barriers. Based on temperature-dependent emission and excitation measurements, the dominant low-temperature emission line in the SPS-clad Ga_.47In_.53As multi quantum wells is assigned to intrinsic excitonic recombination.     

低温超薄高效Cu(In,Ga)Se2太阳电池的实现

衬底温度保持恒定, 在Se气氛下按照一定的元素配比顺序蒸发Ga, In, Cu制备厚度约为0.7 μrm的Cu(In_0.7Ga_0.3)Se₂ (CIGS)薄膜. 利用X射线衍射仪分析薄膜的晶体结构及物相组成, 扫描电子显微镜表征薄膜形貌及结晶质量, 二次离子质谱仪测试薄膜内部元素分布, 拉曼散射谱 分析薄膜表面构成, 带积分球附件的分光光度计测量薄膜光学性能. 研究发现在Ga-In-Se预制层内, In主要通过晶界扩散引起Ga/(Ga+In)分布均匀化. 衬底温度高于450 ℃时, 薄膜呈现单一的Cu(In_0.7Ga_0.3)Se₂相; 低于400℃, 薄膜存在严重的Ga的两相分离现象, 且高含Ga相主要存在于薄膜的上下表面; 低于300 ℃, 薄膜结晶质量进一步恶化. 薄膜表层的高含Ga相Cu(In_0.5Ga_0.5)Se₂以小晶粒形式均匀分布于薄膜表面, 增加了薄膜的粗糙度, 在电池内形成陷光结构, 提高了超薄电池对光的吸收. 加上带隙值较小的低含Ga相的存在, 使电池短路电流密度得到较大改善. 衬底温度在550 ℃–350 ℃变化时, 短路电流密度J_SC是影响超薄电池转换效率的主要因素; 而衬底温度T_sub低于300 ℃时, 开路电压V_OC和填充因子FF降低已成为电池性能减退的主要原因. T_sub为350 ℃时制备的0.7 μm左右的超薄CIGS电池转换效率达到了10.3%. 关键词： 2薄膜')" href="#">Cu(In,Ga)Se₂薄膜 衬底温度 超薄 太阳电池     

InGaN薄膜中电子自旋偏振弛豫的时间分辨吸收光谱研究

采用飞秒时间分辨圆偏振光抽运-探测光谱对In_01Ga_09N薄膜的电子自旋注入和弛豫进行了研究.获得初始自旋偏振度约为02,此结果支持在圆偏振光激发下,重、轻空穴带的跃迁强度比为3∶1,而不支持1∶1或1∶094的观点同时获得自旋偏振弛豫时间为490±70ps,定性分析了自旋弛豫机理,认为BAP机理是电子自旋弛豫的主要机理. 关键词： 电子自旋 InGaN 自旋极化 自旋弛豫     

Optical activity of γ<Subscript>1</Subscript>-(Ga<Subscript>x</Subscript>In<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>Se<Subscript>3</Subscript> crystals

The optical activity of uniaxial γ₁-(Ga_xIn_1?x )₂Se₃ crystals (x=0.1, 0.2, 0.3, 0.4) is studied at T=295 and 77 K in the spectral range 0.5–0.8 πm. It is found that the cationic substitution In → Ga leads to a nonlinear increase in the specific rotation of the plane of polarization ρ and the component g ₃₃ of the gyration tensor. It is shown that the gyrotropy of the crystals studied is determined by high-energy transitions whose energy exceeds the energy of the edge transitions and that the gyrotropy observed has a molecular origin.     

Gamma-ray irradiation effect on the absorption and luminescence spectra of Nd:GGG and Nd:GSGG laser crystals

Laser crystals Nd³⁺:Gd₃Ga₅O₁₂ (Nd:GGG) and Nd³⁺:Gd₃Sc₂Ga₃O₁₂ (Nd:GSGG) were grown by Czochralski method. The influence of gamma-ray irradiation on their absorption and luminescence spectra has been investigated. Two additional absorption (AA) bands induced by gamma-ray irradiation appear in the spectra of Nd:GGG crystal while only a very weak AA band appears for the Nd:GSGG crystal. This indicated that Nd:GSGG crystal has stronger ability to resist the color center formation by irradiation. The intensity of the excitation and emission spectra of Nd:GGG crystal decrease after the irradiation of 100 Mrad gamma-ray. In contrast, a luminescence strengthening effect was observed in Nd:GSGG crystal after exposure to the same irradiation dose. The results showed that the Nd:GSGG crystal is a promising candidate used under radiation environments such as in outer space.     

Band alignments in the Cu(In,Ga)(S,Se)2 alloy system determined from deep-level defect energies

The composition dependence of defect energies in polycrystalline Cu(In_1-xGa_x)(Se_1-yS_y)₂ chalcopyrite semiconductor thin films is investigated by admittance spectroscopy. Alloying CuInSe₂ with S increases the energy of the dominant acceptor from 300 meV to approximately 380 meV in CuIn(Se_0.4S_0.6)₂, whereas in the alloy system Cu(In_1-xGa_x)Se₂, the acceptor energy remains unchanged over the whole composition range 0≤x≤1. Using the acceptor energy as a reference, we extrapolate the valence-band offsets ΔE_V=-0.23 eV for the combination CuInSe₂/CuInS₂ and ΔE_V=-0.04 eV for CuInSe₂/CuGaSe₂. Received: 19 July 2001 / Accepted: 27 July 2001 / Published online: 2 October 2001     

Optical properties of TlGaxIn1-xSe2-layered mixed crystals (0.5 ≤ x ≤ 1) by spectroscopic ellipsometry,transmission, and reflection measurements

The layered semiconducting TlGa_xIn_1-xSe₂-mixed crystals (0.5?≤?x?≤?1) were studied for the first time by spectroscopic ellipsometry measurements in the 1.2–6.2?eV spectral range at room temperature. The spectral dependence of the components of the complex dielectric function, refractive index, and extinction coefficient were revealed using an optical model. The interband transition energies in the studied samples were found from the analysis of the second-energy derivative spectra of the complex dielectric function. The effect of the isomorphic cation substitution (indium for gallium) on critical point energies in TlGa_xIn_1-xSe₂ crystals was established. Moreover, the absorption edge of TlGa_xIn_1-xSe₂ crystals have been studied through the transmission and reflection measurements in the wavelength range of 500–1100?nm. The analysis of absorption data revealed the presence of both optical indirect and direct transitions. It was found that the energy band gaps decrease with the increase of indium content in the studied crystals.     

Exciton absorption,photoluminescence and band structure of N-Free and N-DOPED In1−xGaxP

Optical absorption data on In_1?xGa_xP are reported showing the first observation of the exciton absorption peak in a III-V ternary alloy. This allows the most accurate determination to date of both the composition dependence of the Γ band gap and the position of the Γ ? X crossover (x_c = 0.72, 77°K; x_c = 0.73, 300°K). Absorptio and photoluminescence spectra are compared for both direct and indirect In_1?xGa_xP. In addition, absorption, photoluminescence, and luminescence lifetimes of In_1?xGa_xP:N are examined. These data suggest that the A-line is perturbed by alloy disorder and forms a broad luminescence band for x ? 0.94. The observed Stokes shift for the N-trap in the alloy is characteristic of an impurity strongly coupled to the lattice. The temperature dependence of the N luminescence band is found to be well described by the conventional configuration-coordinate model for phonon-coupled impurity luminescence. Implications of these results for light emitting devices are mentioned.     

Flexible Cu（In,Ga）Se2 Thin-Film Solar Cells on Polyimide Substrate by Low-Temperature Deposition Process

The electrical and structural properties of polycrystalline Cu（In, Ga）Se2 films grown on polyimide （PI） substrates below 400℃ via one-stage and three-stage co-evaporation process have been investigated by x-ray diffraction spectra （XRD）, scanning electron microscopy （SEM） and Hall effect measurement. As shown by XRD spectra, the stoichiometric CIGS films obtained by one-stage process exhibit the characteristic diffraction peaks of the （In0.68Ga0.32）2Se3 and Cu（In0.7Ga0.3）2Se. It is also found that the film structures indicate more columnar and compact than the three-stage process films from SEM images. The stoichiometric CIGS films obtained by three-stage process exhibit the coexistence of the secondary phase of （In0.68Ga0.32）2Se3, Cu2-xSe and Cu（In0.7Ga0.3）2Se. High net carrier concentration and sheet conductivity are also observed for this kind of film, related to the presence of Cu2-xSe phase. As a result, when the CIGS film growth temperature is below 400℃, the three-stage process is inefficient for solar cells. By using the one-stage co-evaporation process, the flexible CIGS solar cell on a PI substrate with the best conversion efficiency of 6.38% is demonstrated （active area 0.16cm^2）.     

Local atomic structure of Cu(In x Ga1−x )Se2 (x = 0.25, 0.5, and 0.75) systems for solar cells

The local atomic structure of thin surface layers of crystalline quasi-binary Cu(In _x Ga_1?x )Se₂ solid solutions was studied by SIMS and EXAFS techniques. The SIMS method showed that the elemental composition of the sample changes most significantly in thin layers at a depth of 5–10 nm; in deeper layers, the component concentrations correspond to the bulk values. The EXAFS method in the x-ray fluorescence mode showed that the results obtained are in agreement with the assumption that quaternary crystalline quasi-binary Cu(In _x Ga_1?x )Se₂ solid solutions exhibit local disorder while average long-range order is detected from x-ray diffraction data.