摘要:

Auger electron spectroscopy (AES), x‐ray photoelectron spectroscopy (XPS), and electron microprobe analysis (EMA) were applied to investigate the chemical composition, impurities, and the homogeneity of thin para‐ and ferroelectric epitaxial KTa1−xNbxO3(KTN) layers grown by liquid‐phase epitaxy using a KTN‐KF flux. AES indicated no Ta/Nb fluctuations within the layer plane and in the growth direction. XPS and EMA determined a F incorporation of 0.8–0.9 mol % for as‐grown and 0.6 mol % for annealed samples. Valence analyses with XPS and electron paramagnetic resonance (EPR) revealed only the regular valence state for the B atoms of a (I,V)ABO3perovskite lattice. An unexpected splitting of the K 2pdoublet peak was found for as‐grown layers. Structural defects observed by optical microscopy and x‐ray topography were attributed to lattice relaxation effects. Optical waveguiding could be achieved for para‐ and ferroelectric layers.

ISSN:0021-8979    

DOI:10.1063/1.349378

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

As part of our effort to control the growth of diamond films by chemical vapor deposition, we are studying the chemical mechanism for conversion of gas phase hydrocarbons into diamond. In this work we analyze the thermochemistry of a number of structures on the hydrogenated diamond (111) surface. We use the MM2 molecular mechanics force field to calculate strain energies, which are due to crowding of adsorbed species on the surface, and we use a group additivity scheme to estimate bond enthalpies and entropies. These data allow calculation of equilibrium structures on the surface and, together with estimates for rate constants, will permit a prediction for the kinetics of diamond formation as a function of growth conditions. We find that a straightforward abstraction/addition mechanism using either CH3or C2H2to grow on a hydrogenated (111) surface cannot account for experimentally measured growth rates. We suggest that experimental measurements of growth rates on (111) surfaces are strongly influenced by growth at steps, kinks, and edges on those surfaces.

ISSN:0021-8979    

DOI:10.1063/1.349379

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The transformation of C49 phase TiSi2to the low resistivity C54 phase is necessary for many microelectronic applications. Here, we report on attempts to decrease this transformation temperature by low‐energy ion bombardment at elevated temperature. Ion irradiation was performed using a broad beam Kaufman ion source operated in N2or Ar gas between 0.1 and 2 keV beam energy, with ion doses ranging from 2.0×1016to 1.9×1018ions/cm2, and sample temperatures from 480 °C to 735 °C. For comparison, room‐temperature Ar+implantation at higher energy (105–210 keV) was performed with a dose of 1016ions/cm2with projected ranges within and beyond the TiSi2layer thickness. Resistivity measurements as a function of temperature, x‐ray diffraction, and Rutherford backscattering spectrometry were used to determine the composition and phases. Results show that low‐energy ion bombardment does not promote the C49‐C54 transformation at the temperatures studied, while ion implantation actually raises the temperature for the transformation. In addition, bombardment of C54 TiSi2does not cause it to revert to the C49 phase, indicating that both phases appear to be surprisingly stable under ion bombardment. Simulations of defect production using thetrimcode indicate the formation of a higher number of displaced atoms than are usually required to initiate a transformation. We conclude that the defects introduced into C49 TiSi2by ion bombardment at energies up to 2 keV are either not sufficient to nucleate the C54 phase or they are annealed out too quickly at the temperature needed for C54 phase growth.

ISSN:0021-8979    

DOI:10.1063/1.349380

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A detailed study of the electrical and defect properties of ion‐implanted erbium in silicon shows that erbium doping introduces donor states. The concentration of erbium related donors as a function of implant dose saturates at 4×1016cm−3at a peak implanted Er‐ion concentration of (4–7)×1017cm−3. The defect levels related to erbium in silicon are characterized by deep level transient spectroscopy and identified asE(0.09),E(0.06),E(0.14),E(0.18),E(0.27),E(0.31),E(0.32), andE(0.48). The dependence of the photoluminescence on annealing temperature for float zone and for Czochralski‐grown silicon show that oxygen and lattice defects can enhance the luminescence at 1.54 &mgr;m from the erbium. Temperature‐dependent capacitance‐voltage profiling shows donor emission steps when the Fermi level crossesEC−ET= 0.06 eV andEC−ET= 0.16 eV.

ISSN:0021-8979    

DOI:10.1063/1.349381

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The effect of impurity coimplantation in MeV erbium‐implanted silicon is studied. A significant increase in the intensity of the 1.54‐&mgr;m Er3+emission was observed for different coimplants. This study shows that the Er3+emission is observed if erbium can form an impurity complex in silicon. The influence of these impurities on the Er3+photoluminescence spectrum is demonstrated. Furthermore we show the first room‐temperature photoluminescence spectrum of erbium in crystalline silicon.

ISSN:0021-8979    

DOI:10.1063/1.349382

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We present an experimental study of the EL2‐defect thermal recovery inn‐type GaAs under hydrostatic pressure up to 1.2 GPa. The most characteristic experimental result is the nonmonotonous pressure dependence of the temperature at which the EL2 defect thermally recovers. We solve numerically the equations describing the recovery process, and we prove that in order to explain our experimental data it is absolutely necessary to take into account the existence of the recently discovered acceptorlike level of the metastable EL2. Moreover, we show that the most straightforward explanation of all our experimental results should assume that inn‐type GaAs the recovery process always proceeds via the negative‐charge state of the metastable EL2. Since our explanation of the recovery process does not require the recovery rate to be directly proportional to the free‐electron concentration, the problem of the so‐called Auger‐like thermal recovery of the EL2 defect inn‐type GaAs seems to be finally gone.

ISSN:0021-8979    

DOI:10.1063/1.349383

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Cadmium sulfide (CdS) and zinc sulfide (ZnS), direct gap semiconductors with room temperature band‐gap energy of 2.42 and 3.66 eV, respectively, form a continuous series of solid solutions (Cd1−xZnxS). The band‐gap energy of Cd1−xZnxS can be tailored in the range of the binary band gaps. In this work, polycrystalline films of Cd1−xZnxS have been deposited on glass, SnO2:F/glass, and ZnO:F/glass substrates by the reaction of dimethylcadmium (DMCd), diethlyzinc (DEZn), and propyl mercaptan (PM) in a hydrogen atmosphere. The deposition rate and properties of Cd1−xZnxS films depend on the substrate temperature and the composition and flow rate of the reaction mixture. The deposition rate of Cd1−xZnxS films has been measured at 375 and 425 °C as a function of the DMCd/DEZn molar ratio in the reaction mixture. Without intentional doping, the deposited films are of high lateral resistivity, and the resistivity increases with increasing ZnS concentration. The electrical resistivity of the deposited films can be reduced by using octyl chloride or trimethylaluminum as a dopant. The effects of DMCd/DEZn and (DMCd+DEZn)/PM molar ratios on the optical and electrical properties of Cd1−xZnxTe films have been investigated. Thin film heterojunctions have been prepared by the successiveinsitumetal organic chemical vapor deposition of Cd0.7Zn0.3S (Eg∼2.8 eV), an absorber, and the ohmic contact on a ZnO:F/glass substrate, and their electrical and photovoltaic properties characterized.

ISSN:0021-8979    

DOI:10.1063/1.349384

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The thermoelectric properties ofN‐type andP‐type Si‐Ge alloys have been reviewed and detailed calculations for the efficiency of a thermoelectric generator made from a 70% Si‐30% Ge alloy have been made over the temperature range from 300 to 1300 K. A model employing one valence band and two conduction bands has been used. A generator of standard material, optimally doped, and infinitely segmented will have an efficiency of 12.1% operating over this range. If the lattice thermal conductivity can be reduced to its minimum value without upsetting the electrical properties, then the efficiency can be raised to an ultimate maximum of 23.3%. A more modest increase in efficiency to 14.7% could be obtained by a 2.4 volume percent of finely dispersed second‐phase precipitates which would act as phonon scatterers. The utility/futility of GaP additions and grain‐boundary scattering as methods to increase the efficiency is discussed.

ISSN:0021-8979    

DOI:10.1063/1.349385

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Monte Carlo calculation has been applied to investigate the temperature and compensation dependence of steady‐state electron transport inn‐type GaAs over a wide range of applied field strengths. It is found that doping compensation has stronger effect on the transport properties at low temperatures than at high temperatures. Compensation‐enhanced impurity scattering is responsible for the reduction not only in low‐field mobilities and peak velocities but also in the negative differential mobilities and the high‐field velocities. The two‐maxima behavior in the velocity‐field characteristics persists at low temperatures through room temperatures for high doping compensation then it starts to diminish at 450 K except for compensation ratio of 0.9. The physical origin of this unique two maxima feature in the velocity‐field relation has been discussed in comparison with other compensated semiconductors.

ISSN:0021-8979    

DOI:10.1063/1.349386

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

In this paper we describe a variant of the scanning capacitance microscope (SCaM) which is based on the atomic force microscope. Our SCaM involves a cantilever beam that is used to press a conducting tip against a conducting substrate coated with a dielectric film. A capacitance sensor is then used to measure the tip‐sample capacitance as a function of lateral position. The deflection of the cantilever can also be used to measure independently the surface topography. This microscope can be used to measure electrical properties of dielectric films and their underlying substrates. We have applied this microscope to the study of the nitride‐oxide‐silicon (NOS) system. This system has been studied extensively because of its ability to store information by trapping charge in the silicon nitride. Commercial semiconductor nonvolatile memories have been designed using this NOS technology. We have used the SCaM tip to apply a localized bias to the NOS sample, causing charge to tunnel through the oxide layer and to be trapped in the nitride film. This trapped charge induces a depletion region in the silicon substrate, which can be detected by the resulting depletion capacitance between the tip and sample. The stored charge can be interpreted as a digital memory. Bit sizes as small as 750 A˚ full width at half maximum have been stored using this technique. The stored charge has been observed to be stable over a period of seven days. The stored charge can be removed by applying a reverse bias to the region, and the bit can be subsequently rewritten. By simultaneously measuring capacitance and topography images, we have demonstrated that the stored information is not the result of any topographic change to the surface. Simulations of the potential distributions resulting from this trapped charge have been performed and are compared with the experiments. Finally, a discussion is presented on the ultimate density and speed limits of such a storage technology.

ISSN:0021-8979    

DOI:10.1063/1.349388

出版商:AIP    

年代:1991

数据来源: AIP