Raman scattering in PbTe and PbSnTe films: In situ phase transformations

The PbTe and Pb_{1 ? x} Sn _x Te films, both undoped and doped with indium, are studied by Raman spectroscopy. It is found that the film surface changes during spectra recording. From comparative analysis of the data obtained in the study and those reported in publications, it is inferred that the 90, 117, and 138 cm^?1 peaks correspond to the scattering of light at tellurium or tellurium-oxide precipitates. It is established that these peaks appear in the spectra of Pb_{1 ? x} Sn _x Te films and epitaxial PbTe films only when doped with indium. The 180-cm^?1 peak is observed in the spectra of all of the samples and not attributed to the plasmon-phonon mode. The nature of the 180-cm^?1 peak is still not completely understood.     

Photoconductivity of pyrolytic CdS films alloyed with Cs

The investigation of the influence of Cs alloy on recombination processes has been carried out for the pyrolytic CdS films. The effect of photomemory has been observed for such structures, both pure and alloyed. Cs impurity introduction leads to a five- to tenfold photocurrent increase in comparison with pure samples. It also leads to increase of the nonequilibrium conductivity relaxation time from 300 to 10⁴ s. The stored conductivity is due to the present of the internal potential barriers between the different conductivity areas, which are related with the heterogeneity of the investigated polycrystalline structures. Here, the non-equilibrium conductivity relaxation kinetic of alloyed CdS films corresponds to the case of square-law recombination. It is determined that the potential barrier increases from 0.33 to 0.44 eV along the nonequilibrium conductivity relaxation.     

Photoconductivity in evaporated CdSe films

Evaporated semiconductor films are used in many applications. Physical properties of such films are dependent on the deposition conditions. The present article describes the influence of the source and substrate temperature on the photoresistance of CdSe films. The results are explained by stoichiometric changes in the CdSe vapours.     

Photoconductivity of two-phase hydrogenated silicon films

Electrical, photoelectric, and optical properties of hydrogenated amorphous silicon films with various ratios between the nanocrystalline and amorphous phases in the structure of the material have been studied. On passing from an amorphous to a nanocrystalline structure, the room-temperature conductivity of the films increases by more than five orders of magnitude. With increasing fraction of the nanocrystalline component in the film structure, the steady-state photoconductivity varies nonmonotonically and is determined by the variation in the carrier mobility and lifetime. Introduction of a small fraction of nanocrystals into the amorphous matrix leads to a decrease in the absorption in the defect-related part of the spectrum and, accordingly, to a lower concentration of dangling bonds, which are the main recombination centers in amorphous hydrogenated silicon. At the same time, the photoconductivity in these films becomes lower, which may be due to appearance of new centers that are related to nanocrystals and reduce the lifetime of nonequilibrium carriers.     

Photoconductivity of nanostructured hydrogenated silicon films

The photoconductivity of nanostructured hydrogenated silicon films prepared by different techniques was studied in relation to the Fermi level position, the density of defects, and the type of Si-H bonding. The influence of Si⁺ ion implantation on the photoconductivity and other parameters of a-Si:H films was determined.     

Effect of oxidation on the conductivity of nanocrystalline PbTe:In films in an alternating electric field

Temperature and frequency dependences of components of complex impedance for nanocrystalline PbTe:In films in the temperature range of 4.2–300 K and the frequency range from 20 Hz to 1 MHz have been studied. The films were deposited onto a cooled glass substrate and then annealed in an oxygen atmosphere at temperatures of 300 and 350°C. The charge-carrier transport in the studied films is controlled by charge transport over inversion channels at the surface of grains and by transitions through barriers at the grain boundaries. Parameters (resistance and capacitance) corresponding to each of above-mentioned mechanisms were determined. Dominant contribution to conductance of the film annealed at 350°C is made by inversion channels. It is shown that the transport of charge carriers over inversion channels in the region of low temperatures is realized by hopping conductivity.

     

Photoconductivity and surface chemical analysis of ZnO thin films deposited by solution-processing techniques for nano and microstructure fabrication

The fabrication of zinc oxide(ZnO) from inexpensive solution-processing techniques,namely,electrochemical deposition and electrospinning were explored on various conducting and mesoporous semiconducting surfaces.Optimised conditions were derived for template- and self-assisted nano/micro structures and composites. ZnO thin films were annealed at a fixed temperature under ambient conditions and characterised using physical and optical techniques.The photocurrent response in the UV region shows a fast rise and double decay behaviour with a fast component followed by a slow oscillatory decay.Photocurrent results were correlated with surface chemical analysis from X-ray photoelectron spectroscopy.Various characterisation details reveal the importance of fabrication parameter optimisation for useful low-cost optoelectronic applications.     

Photoconductivity of CdS films,undoped and doped with alkali-metal impurity ions

The nonequilibrium electron processes that occur during photoconductivity increase and relaxation in pyrolytic CdS films, both nominally undoped and doped with alkali metals, are studied. The photocurrent increase and relaxation are slow. In some cases, the experimental curve describing the photoconductivity increase is S-shaped or exhibits several thresholds. The dependence of the steady-state photocurrent on the excitation intensity is superlinear. The introduction of alkali-metal impurities increases the photocurrent in the CdS films by up to an order of magnitude compared to the photocurrent in the undoped films. The experimentally observed features of the photoconductivity kinetics of the structures under study are attributed to the profound effect of trapping centers of several types on the behavior of nonequilibrium charge carriers.     

Photoconductivity of organic polymer films doped with porous silicon nanoparticles and ionic polymethine dyes

Features of electrical conductivity and photoconductivity of polyvinylbutyral films containing porous silicon nanoparticles and similar films doped with cationic and anionic polymethine dyes are studied. Sensitization of the photoelectric effect by dyes with different ionicities in films is explained by the possible photogeneration of holes and electrons from dye molecules and the intrinsic bipolar conductivity of porous silicon nanoparticles. It is assumed that the electronic conductivity in porous silicon nanoparticles is higher in comparison with p-type conductivity.     

The In/PbTe barrier structures with a thin intermediate insulating layer

Epitaxial n-PbTe layers were grown on BaF₂ {111} single-crystal substrates by hot-wall epitaxy from the gaseous phase. These layers were kept in atmospheric air for 15–30 days, after which In and protective BaF₂ layers were deposited. Current-voltage characteristics and photoelectric sensitivity spectra of the In/n-PbTe barrier structures were measured in the temperature range T=80–300 K. Based on the experimental results, a model of charge transport is suggested and the effective barrier height ? _b ^eff , the insulator layer thickness δ, and the surface-state density D _S are determined.     

Sign-Alternating Photoconductivity in PbSnTe:In Films in the Space-Charge-Limited Current Regime

Semiconductors - The dependence of the photoconductivity sign on the bias voltage, intensity, and duration of illumination is studied for PbSnTe:In films in the space-charge-limited current regime....     

Intrinsic defect states in PbTe single-crystal films grown by laser-modulated epitaxy

The electrical properties of PbTe/KCl(KBr) layers grown by infrared-laser-modulated epitaxy and their dependences on conditions of fabrication (power density of the laser beam W, substrate temperature T _s ) have been investigated. It is established that the R _H (T) dependences can be explained within the framework of a two-level model in which one of the levels (E _d1) is in the conduction band and the second level E _d2 is in the band gap. The positions of the energy levels and their density of states depend on the conditions of growth. Fiz. Tekh. Poluprovodn. 32, 47–49 (January 1998)     

Nonstoichiometry and solubility of impurity in In-doped PbTe films on Si substrates

The chemical quantitative composition, phase constitution, and crystal structure of doped with In lead telluride films on Si (1 0 0) or SiO₂/Si (1 0 0) substrates have been studied in this work. By EPMA and atomic absorption measurements, it has been found that the concentration of In atoms y_In varied from 0.0011 to 0.045 in these deposited Pb_1−yIn_yTe films. The results of EPMA, SEM, and X-ray diffraction (XRD) measurements show that formation of In solid solutions in lead telluride matrix revealed not only in PbTe–InTe cross-section, but in PbTe–In₂Te₃ pseudobinary system also. The results of XRD show that the lattice parameter a_PbTe of PbTeIn/Si and PbTeIn/SiO₂/Si heterostructures is described by nonmonotone function and does not obey the Vegard's law within concentration interval 0.0011y_In0.045.     

Texture and microstructure of thin copper films

Microstructure is an important factor influencing the reliability of thin film interconnects. The microstructure of copper films is of particular interest because of its use in numerous electronic applications. Pole figure x-ray diffraction and transmission electron microcopy were conducted on copper films deposited by several techniques: sputtering, partially ionized beam deposition, chemical vapor deposition, evaporation, and electroplating. Quantitative texture data are determined from fiber texture plots. A typical copper film consists of three texture components: (111), (200), and random. (220) and (511) texture components are possible under some deposition conditions. Compared to aluminum films, the fraction of the random texture component and the distribution of the (hkl) components in copper films are relatively large. Bimodal grain size distributions are observed in some films.     

Electrical properties of uncontaminated PbTe films on mica substrates prepared by molecular beam deposition

Uncontaminated PbTe films were prepared by molecular beam deposition under clean conditions in a uhv environment and the film properties were measured in situ. The carrier concentration was found to be determined by source conditions and values between 10¹⁶ cm^?3 (intrinsic level) and n = 5 × 10¹⁸cm^?3 could be obtained in a controllable manner. A low temperature anneal enabled bulk value Hall mobilities (1750 cm² V^?1 sec^?1 at 300 K) to be obtained at room temperature and above which indicated that surface scattering in the films was predominantly specular. The mobility at low temperatures (down to 100 K) was limited by small potential barriers located at the double-positioned grain boundaries which were present in the film. Field effect measurements indicated the potential barriers arose from a continuous distribution of band gap states situated in the grain boundaries. These states had a fairly uniform density (? 10¹²cm^?2 (kT)^?1) but there was some increase towards the conduction band edge. They also limited the field effect mobility (μ_FE) to ?0.5 bulk value, giving μ_FE ? 800cm² (volt sec)^?1 for films with carr concentrations above 5 × 10¹⁷ cm^?3. By exposure to low pressures of oxygen the carrier concentrations in annealed n-type films could be reduced to near intrinsic values with no associated degradation in the electrical properties. This indicated that the films were not compensated with the native p-type defect.     

光学薄膜微结构的透射电镜测试

本文论述了应用透射电子显微镜技术对光学薄膜的微结构进行测试,并详细叙述了透射电镜的样品制备技术。     

Photoconductivity of silicon with nanoclusters of manganese atoms

In this work, specific features of photoconductivity of silicon with multicharge nanoclusters of manganese atoms are investigated. It is shown that for such samples, anomalously high impurity photoconductivity is observed in the spectral region λ = 1.8–3 μm. It is also shown that such samples possess giant residual photoconductivity.     

Photoconductivity spectra of CdHgTe crystals with photoactive inclusions

This paper analyzes how both wide-and narrow-band-gap inclusions in CdHgTe host material affect the generation-recombination behavior of the latter. It is found that the shape of the photoconductivity (PC) spectral characteristic is sensitive to the type of inclusion present in the host: wide-band-gap inclusions lead to additional maxima in the spectral region near the fundamental absorption edge, while narrow-band-gap inclusions wash out the edge at long wavelengths. It is found that the shape of the PC spectra of these nonuniform crystals depends on the magnitude and polarity of the applied bias voltage. A photovoltage which alternates in sign as a function of wavelength and which is similar to the photosensitivity spectra of opposing barriers in graded-gap layers, is observed. Fiz. Tekh. Poluprovodn. 33, 47–51 (January 1999)     

Ti—Si—N纳米晶复合膜微结构的TEM观察

2000年，Veprek等报道了在Ti-Si-N复合膜中获得了80-150GPa的超高硬度，这一超过金刚石薄膜硬度（70-90GPa）的结果令人惊讶并引起竞相研究。对于Ti-Si-N纳米晶复合膜的微结构，目前仅有的Veprek模型认为：不容于TiN的Si3N4相以非晶态形式“润湿”于生长中的TiN晶体表面并阻止其长大，因而复合膜形成厚度小于1mm的非晶Si3N4界面相分隔并包裹直径小于10mm的三维TiN纳米晶的微结构，