Lattice thermal expansion for normal tetrahedral compound semiconductors

The cubic root of the deviation of the lattice thermal expansion from that of the expected value of diamond for group IV semiconductors, binary compounds of III-V and II-VI, as well as several ternary compounds from groups I-III-VI₂, II-IV-V₂ and I-IV₂V₃ semiconductors versus their bonding length are given straight lines. Their slopes were found to be 0.0256, 0.0210, 0.0170, 0.0259, 0.0196, and 0.02840 for the groups above, respectively. Depending on the valence electrons of the elements forming these groups, a formula was found to correlate all the values of the slopes mentioned above to that of group IV. This new formula which depends on the melting point and the bonding length as well as the number of valence electrons for the elements forming the compounds, will gives best calculated values for lattice thermal expansion for all compounds forming the groups mentioned above. An empirical relation is also found between the mean ionicity of the compounds forming the groups and their slopes mentioned above and that gave the mean ionicity for the compound CuGe₂P₃ in the range of 0.442.     

High ion density dry etching of compound semiconductors

The use of plasma sources that generate high ion densities (> 10¹¹ cm⁻³) enables dry etching of compound semiconductors at high rates with anisotropic sidewalls. In this paper we review the use of several types of electron cyclotron resonance (ECR) plasma sources and contrast the result with those obtained under reactive ion etching conditions. Various problems occurring in dry etching will be discussed, including aspect ratio dependent etch rates, mask erosion, sidewall roughening and damage introduction into the semiconductor. This damage may consist of point and line defect creation, non-stoichiometric surfaces, resputtering of mask materials or deposition of contaminating films. The use of low or high substrate temperatures to control the desorption kinetics of etch products is also discussed; at low temperatures problems can occur with condensation of the etch gases onto the substrate, while at elevated temperatures it is necessary to thermally bond the sample to the r.f. powered electrode to obtain reproducibility. Etch selectivity between the components of heterostructure systems such as GaAs/AlGaAs, GaAs/InGaP, InGaAs/AlInAs and GaN/AlN is usually much worse under high ion density conditions because of the high rates and large physical component.     

Makyoh topography for the morphological study of compound semiconductor wafers and structures

The application of Makyoh topography in the assessment of flatness and overall curvature of semiconductor wafers and layer structures is reviewed, with special emphasis on compound semiconductors. Application examples are shown as well.     

Laser processing of III–V compound semiconductors

Lasers have found an increasingly important role in semiconductor processing technology. While they are now widely used in some of the silicon-based device fabrication processes, their applications in III–V compound semiconductor processing are not equally well established. Considerable research work has been carried out to find ways to overcome some of the technical difficulties in their usage in technologies based mainly on GaAs. In this paper, we review these developments and mention possible future directions that will help establish the use of lasers in this very active field. Based on the talk given at the Winter School of Laser Material Processing, University of Poona, November 16–25, 1987.     

Scanning electron microscopy study of twins in ZnSe single crystals grown by solid-phase recrystallization

ZnSe single crystals were grown from n-type microcrystalline boules by a solid phase recrystallization (SPR) method. During SPR, twinned regions appear with different electronic recombination properties. The recrystallizations were performed under different atmospheres, Ar or Se, and pressures to investigate the influence of growth conditions on these structural features. Recombination properties were studied by means of cathodoluminescence (CL) and remote-electron beam induced current (REBIC). Wavelength dispersive X-ray (WDX) mappings were also performed to analyze possible differences in stoichiometry related to the presence of extended defects.     

Comparison of luminescence and physical morphologies of GaN epilayers

In this paper we examine a series of four GaN epilayers grown by MOVPE on sapphire substrates with different AlN buffer layer thicknesses. We examine the effect of the buffer layer thickness on the physical and optical properties of the samples via optical microscopy, cathodoluminescence imaging, photoluminescence, and cathodoluminescence spectroscopy. While the morphological and optical properties of all the films (excepting that with the thinnest buffer layer of 30 nm) are good, i.e. the films are smooth and the luminescence is dominated by excitonic luminescence, a number of circular island like features are observed in all the films whose density decrease with increasing buffer layer thickness. A large circular island present on the sample with the thinnest buffer layer and surrounded by cracks in the 11

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0 directions, displays some interesting acceptor related luminescence.     

Luminescence and Raman study of α-Bi2O3 ceramics

Cathodoluminescence in the scanning electron microscope and photoluminescence in a confocal microscope have been used to investigate the luminescence properties of the stable monoclinic α-phase of Bi₂O₃. Powders of this oxide have been sintered at temperatures of 500 °C and 750 °C in air or in nitrogen atmospheres. Spectra of the starting powder and of the samples treated at 500 °C show luminescence bands at 1.50 eV and 1.95 eV as well as a band at 2.1 eV, more prominent in nitrogen treated samples. Sintering at 750 °C leads to quenching of the 1.50 eV infrared emission and the formation of a broad band with emission above 3 eV. The evolution of Raman bands with the sintering treatments has also been investigated.     

Characterisation of vacancy-like defects in III–V compound semiconductors using positron annihilation technique

Single crystals of GaP and InSb were irradiated by 3 MeV electrons at 20 K to a total dose of 4 × 10¹⁸ e ⁻/cm². Isochronal annealing in the temperature region 77–650 K followed the irradiation. In GaP, the positron lifetime measurement indicated the presence of irradiation-induced vacancies in the Ga-sublattice. The vacancies disappeared at two stages observed in temperature ranges 200–300 and 450–550 K. In InSb the positron lifetime was found to increase by 8 ps compared to that in as-grown crystals (i.e. 282±2 ps) after irradiation. The increase indicated the presence of irradiation-induced defects; the crystal was found to recover until 350 K with a sharp annealing stage at 250–350 K.     

Ternary GeSiSn alloys: New opportunities for strain and band gap engineering using group-IV semiconductors

Ternary GeSiSn alloys have been recently demonstrated on Ge- and GeSn-buffered Si substrates. These alloys, with a two-dimensional compositional space, make it possible to decouple lattice constant and electronic structure for the first time in a group-IV system. This paper reviews the basic properties of the GeSiSn alloy, presents some new results on its optical properties, and discusses the approach that has been followed to model heterostructures containing GeSiSn layers for applications in modulators, quantum cascade lasers, and photovoltaics.     

Fiber Raman background study and its application in setting up optical fiber Raman probes

Fiber Raman background spectra of different types of fused-silica fibers are studied and compared. The results show the following: (a) all the background spectra are very similar and comparable with Raman spectra of fused silica, regardless of the difference in the cladding and buffer materials; (b) the overall background intensity increases with the fiber numerical aperture but has no obvious relation with the core diameter. Both experimental evidence and theoretical explanation have been provided for these views. A simple and unfiltered fiber probe for surface-enhanced Raman scattering detection with low fiber Raman background interference is constructed, and the optimum configuration of the probe is suggested and discussed based on the results of the background study.     

非晶半导体的研究与应用

1968年Ovshinsky在多元硫系薄膜中观察到电的开关与存贮效应以来,特别是1975年氢化非晶Si的p型与n型掺杂控制的实现,非晶半导体作为一个重要的电子材料,在过去的30多年中吸引了大量的基础研究并得到了广泛的应用。本文综述了至今为止非晶半导体重要的研究与应用进展,并探讨非晶半导体今后主要的发展趋势。     

Modulation of luminescence emission spectra of N-doped ß-Ga2O3 nanowires by thermal evaporation

In this study, we have synthesized N-doped ß-Ga₂O₃ nanowires on a p-type Si (100) substrate at the temperature of 850 °C through evaporation to modulate the spectra of the luminescence emission. Both TEM and XRD analyses confirmed that N-doped ß-Ga₂O₃ is monoclinic with a uniform mean diameter of 30 nm and a length up to several tens of micrometers. As determined by selected area diffraction (SAD), the growth direction of N-doped ß-Ga₂O₃ nanowires is [002]. The optical properties of the N-doped ß-Ga₂O₃ nanowires were studied by cathodoluminescence (CL) at the 10 and 300 K, exhibiting a UV and red light emission as a function of the nitrogen dopant. The results serve to reinforce the potential of N-doped ß-Ga₂O₃ nanowires for optoelectronic device applications.     

Fractal properties of gold, palladium and gold-palladium thin films on InP

Thermal interaction of indium phosphide (InP) bulk compound semiconductor with thin gold metal films was investigated in the course of the present work. The interaction of the InP/Au system resulted in a pattern showing fractal dimensions. The temperature dependence of the fractal parameters was investigated in a broad temperature range from 200 to 600 °C. No significant temperature dependence of the fractal dimension was observed.The same calculations will be presented for Au/InP and AuPd/InP systems. Our calculations show that the Pd-based contacts have a different behaviour than AuGe metallization where a strong temperature dependence of the fractal number was observed earlier.Another topology measure, the structural entropy is also calculated for the samples. The structural entropy is usually applied for determining the type of the localization of charge distributions, but it can also be used for generalized charges, such as the lightness of the pixels of an electron microscopy picture.     

Organic semiconductors for organic field-effect transistors

Abstract

The advantages of organic field-effect transistors (OFETs), such as low cost, flexibility and large-area fabrication, have recently attracted much attention due to their electronic applications. Practical transistors require high mobility, large on/off ratio, low threshold voltage and high stability. Development of new organic semiconductors is key to achieving these parameters. Recently, organic semiconductors have been synthesized showing comparable mobilities to amorphous-silicon-based FETs. These materials make OFETs more attractive and their applications have been attempted. New organic semiconductors resulting in high-performance FET devices are described here and the relationship between transistor characteristics and chemical structure is discussed.     

Synthesis and characterization of molecular semiconductors based on aromatic diamines with various electron acceptors

The synthesis, spectral, electrical and magnetic properties of charge transfer materials of aromatic diamines namely benzidine (BEN) andρ-toluidine (O.TOL) with various acceptors such as iodine, 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), tetracyanoquinodimethane (TCNQ), andp-chloranil (p-CA) have been reported. These materials excepto-toluidine-chloranil complex have been found to be typical molecular semiconductors on the basis of temperature dependence on their electrical conductivity. They have low electrical conductivities and two thermal activation energies indicating mixed conductivity mechanism in which both the electrons and holes are charge carriers, one dominating over the other at different temperatures. The observation of the metal like electrical conductivity i.e. the increase of electrical conductivity with decreasing temperature in theo-toluidine-chloranil system is unique for this class of molecular electronic materials.     

Dielectric behaviour of ZnO-based ceramic semiconductors

The effect of composition, sintering parameters, frequency and temperature on the dielectric parameters of ZnO-based ceramic semiconductors (cersems) having small amounts of Bi₂O₃, Sb₂O₃, CoO, MnO₂, La₂O₃ and/or Cr₂O₃ has been investigated. The unusually high dielectric constant of these composites, arising due to a two-phase microstructure has been explained on the basis of a depletion layer model. The agreement in values of barrier height and donor concentration calculated fromC ⁻² −V plot, Hall measurement and I-V characteristics of these cersems supports the validity of barrier and depletion layer models. The depletion and inter-granular layers are estimated to be nearly 10² nm and 1–2 nm respectively. The observed variation of dielectric constant/capacitance with sintering parameters and temperature of measurement has also been explained on the basis of simplified microstructure and depletion layers. The loss peak (f _max) observed at 300 kHz remains practically unaltered with change in composition and sintering parameters. The observed dielectric dispersion in the range 10²−10⁶ Hz, exhibiting multiple relaxation times and activation energy of relaxation process as 0·36 eV, has been explained on the basis of Debye-type relaxation process originating due to trapping/detrapping and possibly due to scattering of carriers in the depletion regions.     

Correlation between the defect structure and the residual stress distribution in ZnO visualized by TEM and Raman microscopy

A deep understanding of the appearance and distribution of residual stresses in ZnO is of high importance as mechanical stresses directly influence its electrical and optical properties. In this paper we investigate the correlation between residual stresses and the plastic deformation below a micro indent placed on a prism plane of a ZnO single crystal. The residual stress field was mapped by means of confocal Raman microscopy. A cross section was studied by transmission electron microscopy and cathodoluminescence to visualize defect structures. In the Raman measurement bands of residual stresses were observed. The analysis of the defect structure showed that the residual stress distribution corresponds to crystallographic directions which are known to be the preferred directions for plastic deformation. The preparation of lamellae by FIB strongly alters both the residual stress state as well as the defect density caused by plastic deformation.     

基于PCA-SVMR快速测定复方氯丙那林和对乙酰氨基酚

基于主成分分析-支持向量机回归(PCA-SVMR)方法,利用近红外光谱技术研究了复方氯丙那林和复方对乙酰氨基酚两种模型制剂有效组分的快速同时测定,建立了它们的多元校正模型,并以传统的稳健方法偏最小二乘回归(PLSR)为基础考察了PCA-SVMR方法对于小样本药物体系的拟合能力、预测能力和模型稳定性。研究表明,PLSR的预测能力必须以强拟合能力为前提,PCA-SVMR则没有这样的要求,使前者对校正样本的依赖性远强于后者,从而在小样本药物体系中前者的稳定性大大弱于后者,该两种药物制剂的PCA-SVMR多元校正模型的测定准确度总体上优于PLSR。     

Application of combined experimental and numerical techniques in determining the temperature dependence of reflectivity of semiconductors

Combined experimental and numerical techniques for determining the temperature dependence of reflectivity of basic semiconductors are analyzed. The method for determination of the reflectivity dependence of liquid semiconductors under pulsed laser irradiation on temperature developed earlier by the authors is modified for the case of solid semiconductors. The results obtained by the time-resolved reflectivity measurement technique together with the known temperature dependencies of the refraction index and the extinction coefficient for the cw probe laser and the room-temperature data for the reflectivity at the frequency of the primary pulsed laser beam are the input parameters of this method. The method itself consists in matching the experimental and computed values of the maximum reflectivity of cw probe laser in dependence on the energy density of the laser pulse and a least-squares fitting procedure. The method is verified on experimental data for the XeCl excimer laser irradiation of Si( 100), givingR _s=0.590±0.005+(4.5±0.5)× 10^–5(T–293) for the reflectivity of crystalline silicon, which is in good agreement with experimental measurements done by other investigators. In addition, numerical test and error analyses of both the method presented here and the previous method proposed for liquid semiconductors are described and the accuracy and error limits of both methods are discussed.     

Electrical properties of polycrystalline silicon and zinc oxide semiconductors

Polycrystalline silicon and zinc oxide ceramic are important electronic materials. The electrical properties which determine the applications of polycrystalline silicon in integrated circuits and solar cells and that of ZnO ceramic in varistors are due primarily to grain boundary effects in them. A large amount of information in this area has already been gathered in literature but the quantitative understanding of grain boundary effects in these materials is not yet complete. In this review the important aspects of grain boundaries and their effects on transport and photoelectric properties of polycrystalline silicon and on the I–V characteristic of ZnO varistors are discussed. An erratum to this article is available at .