微波放电法生长GaS薄膜的性质

报道了微波放电法在GaAs表面与Al金属片上生长GaS薄膜．用俄歇电子能谱（AES）和卢瑟福背散射能谱（RBS）分析了薄膜的成分，X射线衍射测试了薄膜的结构．结果表明，微波放电法生长的GaS薄膜是属于六方晶系的多晶材料．此外，用椭圆偏振光谱测定了GaS薄膜的折射率以及由金属/绝缘体/金属（MIM）结构的电容值得到GaS薄膜的介电常数 关键词：     

Efficient band structure engineering and visible-light response in ZrS2/GaS heterobilayer by electrical field or external strains

Via first-principle methods, the electronic structures and optical properties of 2D ZrS₂/GaS van der Waals heterostructure (vdWH) are studied. It is found that the band alignment changes from type-II to type-I under negative electrical field, and compressive strains. The transition points are -0.2 V/Å and -1%, respectively. The band gap changes efficiently under positive electrical field and compressive strains. The tensile strains increase the optical adsorption coefficients in ultraviolet regions, while the compressive strains increase the optical adsorption coefficients in visible region significantly.     

Pulsed laser deposition of ZnO as conductive buffer layer of (001)-LiNbO3 thin films

1 (LO) mode peak at 579 cm^-1, indicating oxygen deficiency in the films. Significant dependence of the electrical property for the films on substrate temperature was shown. The I–V relation of the films exhibited non-ohmic behavior. Whereas the films deposited above 500 °C showed a metal-like property, at a lower substrate temperature semiconducting thin films were achieved. The (001)-oriented LiNbO₃/ZnO heterostructure was successfully prepared on quartz fused and (001) sapphire plates. Received: 6 April 1998/Accepted: 26 May 1998     

Optimization, design and fabrication of a non-cryogenic quantum infrared detector

A study of the optimization of the detectivity of a mid infrared double heterostructure photovoltaic detector is proposed. Simple approximate analytic expressions for the dark current are compared with full numerical calculations, and give physical insight on the mechanisms dominating the dark current. The analysis is performed step by step, from a simple p–n junction to the full double heterostructure. The influence of temperature, barrier band gap energy in a double heterostructure, doping density in the active region, on diffusion and generation–recombination mechanisms is analyzed. It is shown how the performances of a double heterostructure photovoltaic detector can be improved by a controlled doping the active region. Nevertheless, its development is still limited by the difficulties occurring during device processing. For example, the use of dry etching for the processing of InAs_0.91Sb_0.09 p–i–n photovoltaic detectors induces a strong leakage current along the mesa edge. In this letter, we show an improvement of the R₀A characteristic by several orders of magnitude at low temperature by using an Ion Beam Etching (IBE) followed by a wet chemical etching. This optimized and reliable device processing allows us to demonstrate that the detector performance is actually limited by the diffusion current of holes. Finally, we discuss the ability of an n-type barrier made of InAs/AlSb super-lattice to avoid hole diffusion and to improve the R₀A characteristic of these detectors. To cite this article: B. Vinter et al., C. R. Physique 4 (2003).     

GaS/GaAs界面电学性质研究

报道了微波放电法在GaAs表面生长GaS薄膜．用电容 电压法（C-V）、伏安法（I-V）以及深能级瞬态谱（DLTS）等测试手段对GaS/GaAs界面的电学性质进行了研究．GaS/GaAs界面的CV特性反映此处的界面特性比较好，界面态密度约为10¹²/（cm²·eV）．DLTS的测试得到了与其一致的结果．另外，从I-V曲线中漏电流的大小，估算出GaS的电阻率为10¹¹Ω·cm 关键词：     

X-ray rocking curves on inhomogeneous surface layers on Si single crystals

Two cases of inhomogeneous surface layers are considered — diffusion layers as well as implanted layers. The parameters of the layers are investigated by means of an X-ray rocking curve analysis. In this paper the concentration profile of a diffusion layer in Si is determined from X-ray rocking curves, the rocking curves on implanted layers will be discussed in the next paper. A graph is constructed for determining approximate values of surface concentrationC ₀ and diffusion lengthL from subsidiary maxima on the X-ray rocking curve. The dependence of the shape of the rocking curves on the type of the concentration profile and on the values ofC ₀ andL was shown. The influence of crystal thickness and curvature is studied theoretically and experimentally. As an example of using this method a rocking curve of a crystal with a boron diffusion layer is measured and the parameters of the concentration profile are determined. The parameters found are proved by multiplied measurement of rocking curves after anodic oxidation and by comparing these rocking curves with theoretical ones.     

Raman scattering from GaSxSe1-x

The non resonant Raman scattering spectra of GaSe, GaS and of eight different mixed crystals GaS_xSe_1-x are presented. The frequencies of some vibrational modes shift continuosly from GaSe to GaS indicating that the mixed crystals are homogeneous. The discontinuous shift of some other modes is explained either by the change of the stacking of the layers, or by a ‘two mode’ behaviour as previously observed in other types of mixed crystals. Moreover, local vibrational modes are observed.     

Influence of Al-concentration on the current density in GaAs/Al<Subscript><Emphasis Type="Italic">c</Emphasis></Subscript>Ga<Subscript>1-</Subscript><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript>As generalized Thue-Morse superlattices

The influence of Al concentration on the current density in GaAs-Al _c Ga_{1- c} As heterostructure is studied for two different classes of the Generalized Thue-Morse superlattice (GTS): (i) width-barrier GTS and (ii) height-barrier GTS. The occurrence of resonances in the transmission is found to be highly dependent on the Al concentration as well as on the degree of quasi-periodicity of the system. Interesting features are noted for the current density profile with the increase in the Al content for the width-barrier case. The use of the height-barrier GTS with small Al content could be suggested to achieve the negative differential conducting regimes at comparatively low applied bias. The effects of the applied field as well as of the quasi-periodicity on the carrier localization are also studied.     

GaS multi-walled nanotubes from the lamellar precursor

Inorganic fullerene-like (IF) nanotubes constructed from layered metal chalcogenides are of particular significance because of their excellent physical properties and potential application in wide fields. But very few previous studies were focused on the IF nanotubes of layered III-VI semiconductor. Therefore we investigate the preparation, structure and photoluminescence (PL) properties of GaS nanotube (an important III-VI semiconductor IF nanotube). A simple method is introduced to prepare GaS multi-walled nanotubes for the first time by annealing the natural lamellar precursor in Ar. The reaction temperature is crucial for the formation of nanotube. A suitable temperature range is 500–850 °C. Bulk quantities of GaS nanotubes with diameters of 30–150 nm and lengths up to ten micrometers were produced. Some of these nanotubes show corrugated and interlinked structure and form many segments, demonstrating a bamboo-like structure. As compared to bulk materials, the obvious distinction of the products in PL spectra at liquid nitrogen temperature of 77 K was due to the structure variety. PACS 61.46.+w; 81.07.De; 81.16.Be     

CH3CSNH2钝化对铁磁金属与GaAs界面扩散的影响

通过实验对比,研究了CH₃CSNH₂钝化对铁磁金属与GaAs界面处As扩散行为的影响.发现S钝化处理改变了表面As元素的化学环境,减弱了As元素向铁磁金属外延层中的扩散现象,削弱了As与铁磁金属的反应,形成了较窄的反应层,并且改善了界面磁性.初步探讨了S钝化影响As扩散的原因. 关键词： S钝化 半导体界面 电子结构 磁性     

Tunable electronic properties of GaS-SnS2 heterostructure by strain and electric field

Vertically stacked heterostructures have received extensive attention because of their tunable electronic structures and outstanding optical properties. In this work, we study the structural, electronic, and optical properties of vertically stacked GaS-SnS₂ heterostructure under the frame of density functional theory. We find that the stacked GaS-SnS₂ heterostructure is a semiconductor with a suitable indirect band gap of 1.82 eV, exhibiting a type-II band alignment for easily separating the photo-generated carriers. The electronic properties of GaS-SnS₂ heterostructure can be effectively tuned by an external strain and electric field. The optical absorption of GaS-SnS₂ heterostructure is more enhanced than those of the GaS monolayer and SnS₂ monolayer in the visible light region. Our results suggest that the GaS-SnS₂ heterostructure is a promising candidate for the photocatalyst and photoelectronic devices in the visible light region.     

Characteristics of silicon solar cell emitter with a reduced diffused phosphorus inactive layer

The diffusion of phosphorus using a phosphorous oxychloride (POCl₃) source in silicon has been used widely in crystalline silicon solar cells. The thermal diffusion process in the furnace consists of two steps: pre-deposition and drive-in. The phosphorous doping profile via thermal diffusion often exhibits high concentrations in the surface-near emitter, which result in a recombination increase. This layer, called the dead layer, should be inhibited in order to fabricate high efficiency silicon solar cells. In this paper, the amount of the POCl₃ flow rate was varied during the pre-deposition process in order to minimize the dead layer, and the characteristics of the phosphosilicate glass (PSG) and emitter were analyzed. From the secondary ion mass spectroscopy (SIMS) and electrochemical capacitance–voltage profiler (ECV) measurements, the emitter formed using a POCl₃ flow rate of 1000 sccm contained the least amount of inactive dopant and resulted in reasonable performance in the silicon solar cell. As the POCl₃ flow rate increased, the doped silicon wafer included electrically inactive P near the surface, which functions as a defect degrading the electrical performance of the emitter. As a result of this, the removal of the dead layer containing the inactive P was attempted through dipping the doped wafer in a HF solution. After this process, the emitter saturation current density and implied V_oc were improved. The completed solar cells and their external quantum efficiencies at a short wavelength also demonstrated improved performance. A quantitative analysis of the emitter can provide a deeper understanding of methods to improve the electrical characteristics of the silicon solar cell.     

Dopant diffusion and segregation in semiconductor heterostructures: Part III, diffusion of Si into GaAs

We have mentioned previously that in the third part of the present series of papers, a variety of n-doping associated phenomena will be treated. Instead, we have decided that this paper, in which the subject treated is diffusion of Si into GaAs, shall be the third paper of the series. This choice is arrived at because this subject is a most relevent heterostructure problem, and also because of space and timing considerations. The main n-type dopant Si in GaAs is amphoteric which may be incorporated as shallow donor species Si_Ga ⁺ and as shallow acceptor species Si_As ^-. The solubility of Si_As ^- is much lower than that of Si_Ga ⁺ except at very high Si concentration levels. Hence, a severe electrical self-compensation occurs at very high Si concentrations. In this study we have modeled the Si distribution process in GaAs by assuming that the diffusing species is Si_Ga ⁺ which will convert into Si_As ^- in accordance with their solubilities and that the point defect species governing the diffusion of Si_Ga ⁺ are triply-negatively-charged Ga vacancies V_Ga ^3-. The outstanding features of the Si indiffusion profiles near the Si/GaAs interface have been quantitatively explained for the first time. Deposited on the GaAs crystal surface, the Si source material is a polycrystalline Si layer which may be undoped or n⁺-doped using As or P. Without the use of an As vapor phase in the ambient, the As- and P-doped source materials effectively render the GaAs crystals into an As-rich composition, which leads to a much more efficient Si indiffusion process than for the case of using undoped source materials which maintains the GaAs crystals in a relatively As-poor condition. The source material and the GaAs crystal together form a heterostructure with its junction influencing the electron distribution in the region, which, in turn, affects the Si indiffusion process prominently. Received: 19 April 1999 / Accepted: 3 May 1999 / Published online: 4 August 1999     

Nanoporous carbon microspheres as matrix of sulfur to prepare sulfur/carbon cathode material for lithium–sulfur battery

A high specific surface area (2798.8 m² g^?1) of nanoporous carbon microsphere (NPCM) is prepared by activated carbon microsphere in hot CO₂ atmosphere, which is used as matrix material of sulfur to prepare NPCM/sulfur composite cathode material by a melt-diffusion method. The NPCM/sulfur composite cathode material with the sulfur content of 53.5% shows high discharge capacity; the initial discharge capacity is 1274 mAh g^?1 which maintains as high as 776.4 mAh g^?1 after 50 cycles at 0.1 C current. At high current density of 1 C, the NPCM/sulfur cathode material still shows initial discharge capacity of 830.3 mAh g^?1, and the reversible capacity retention is 78% after 50 cycles. To study the influence of different sulfur content of NPCM/sulfur cathode material to the performance of Li–S battery, the different sulfur content of NPCM/sulfur composite cathode materials is prepared by changing the thermal diffusion time and the ratio of sulfur powder to NPCM. The performance of NPCM/sulfur cathode material with different sulfur content is studied at a current of 0.1 C, which will be very important to the preparation of high-performance sulfur/carbon cathode material with appropriate sulfur content.     

Highly uniform sheet resistance of the double-channel AlInN/GaN heterostructure

A high uniformity of sheet resistance was achieved in the double-channel (DC) Al_0.82In_0.18N/GaN heterostructure by lowering the interface roughness scattering effect. The variation of the AlInN/GaN interface roughness as a key factor influenced the uniformity of the sheet resistance. In the DC heterostructure, the distribution of the two dimension electron gas (2DEG) was modified to reduce interface roughness scattering effect. As a result, the uniformity of the sheet resistance was enhanced, and the nonuniformity of the sheet resistance in the DC Al_0.82In_0.18N/GaN could be reduced to 0.7% after structure optimization.     

An X-ray diffraction study of the interdiffusion in a KCl:PbCl2 solid solution system

Broadening of X-ray diffraction line profile due to compositional variations can be used as a powerful, non-destructive toll to study the interdiffusion in metallic alloys, binary solid solutions and alloy catalysts. Since powder samples are easy to prepare and have technological importance and KCl, PbCl₂ form solid solution, high purity Aldrich chemicals of KCl and PbCl₂ (-325 mesh, 50 μm) were mixed at a ratio 1:0.1963 by weight. After diffusion anneals at different temperatures, X-ray diffractograms show the shift in KCl and PbCl₂ peaks. The powder becomes amorphous at and above 550°C. Interdiffusion was found to be very fast at the beginning and wask limited to the surface only. The activation energy for such diffusion was found out to be 0.0012 eV. Such a low activation energy has been explained on the basis of surface diffusion mechanism. The degree of interdiffusion (F) as well as diffusion coefficient (D) were also calculated from the concentric sphere model.     

Diffusion and ballistic contributions of electron-electron interaction to the conductivity in an Al0.26Ga0.74N/AlN/GaN heterostructure

The results of an experimental study of quantum correction of electron-electron interaction (EEI) to the conductivity of two-dimensional electron gas (2DEG) in an undoped heterostructure are reported. A small but significant decrease of the Hall slope with the increase of temperature was discovered. This is not due to the increase of electron concentration as temperature increases but to the EEI effect. Both diffusion and ballistic contributions of EEI to the conductivity of 2DEG were observed. As the temperature increases, the negative diffusion EEI correction to the conductivity increases in an absolute value while the ballistic EEI correction reduces to a renormalization of the transport mobility.     

Generalized Wagner’s diffusion model of surface modification of materials by plasma diffusion treatment

0 f^-1(t/t₀), where g(t) is the sub-layer thickness at time t, g₀ and t₀ are parameters that depend on the treated material and plasma characteristics, and f^-1 is the inverse function of f(x)=-(ln(1-x)+x), where x=g(t)/g₀, 0≤x≤1. Under negligible erosion effects, the model becomes of Wagner’s diffusion model type and the expression for g(t) reduces to the parabolic law. The model can be simplified by considering the compound layer as a united one. The general and simplified models can be used as a method for the experimental determining of the effective diffusion coefficients and the erosion rate during plasma treatment of material surfaces. Received: 26 February 1998/Accepted: 15 March 1998     

赝形InGaAs/InAlAs渐变异质结中的零磁场自旋分裂

在赝形渐变InGaAs/In_0.52Al_0.48As异质结的二维电子气中,发现了自旋方向向上的电子和自旋向下的电子在零磁场下存在着自旋分裂.利用Shubnikov-de Haas振荡研究了异质结中的自旋分裂行为,通过振荡中的拍频现象,发现了零磁场下的自旋分裂量为8.76meV. 关键词：     

硫偏析在钼(111)表面上的有序结构

用AES和LEFD在700—800℃温度范围内研究了硫在钼(111)表面上的偏析动力学和表面结构。样品加热到800℃硫迅速地偏析到表面上并逐步地取代了表面上的碳。加热到700℃硫没有明显的表面偏析。硫的偏析主要受它的体扩散速率的控制,表面碳的存在也抑制了硫的表面偏析。不同温度下的偏析动力学实验后,分别进行了低能电子衍射实验,观察到钼(111)(3^1/2×3^1/2)R30°-硫和1/3(⁴⁴_-99)-硫两种表面结构的低能 关键词：