摘要:

Transmission electron energy loss spectra were obtained from small (approximately 100‐A˚ diam) regions of a series of single‐phase silicon‐containing specimens at 100‐keV incident beam energy, using a field emission source transmission electron microscope fitted with a magnetic sector spectrometer. The specimen foils were diamond cubic silicon, &agr;‐silicon carbide, &agr;‐silicon nitride, and amorphous silica. The SiLnear‐edge structure depends markedly upon the chemical environment of the silicon. In this paper we show that the changes in near‐L‐edge structure, including threshold onset energy shift and edge profile, result from bond‐induced changes in the valence shell electronic structure of the specimen materials. Extended Hu¨ckel molecular orbital theory was used to calculate the valence shell electronic structure of five‐atom tetrahedral clusters, with silicon as the central atom and the other atoms noted above in corner positions. Inelastic electron scattering cross sections for silicon 2pand 2score shell transitions to valence shell excited states were then calculated using the first Born approximation.

ISSN:0021-8979    

DOI:10.1063/1.335768

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A relationship has been derived between Hall constant and carrier densities in terms of two experimentally accessible quantities, the grain size and the intergrain barrier height. It is found that the carrier density as measured by the Hall effect can underestimate the average carrier density in the grain by up to an order of magnitude or more in some cases. These predictions are compared with experimental results.

ISSN:0021-8979    

DOI:10.1063/1.335769

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The open‐circuit voltage‐decay of a highly forward biasedp‐njunction diode switched off abruptly after reaching steady state is studied theoretically for high‐level injection. The present theory takes into account the terminal voltage instead of junction voltage as the open‐circuit voltage, and is based on ambipolar diffusion phenomenon. The results are in qualitative agreement with the available experimental results for the entire range of decay characteristics.

ISSN:0021-8979    

DOI:10.1063/1.335770

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The first direct effective mass measurements of electrons in metalorganic vapor phase epitaxy (MOVPE) Sn‐doped Ga1−xAlxAs (x<0.33) epilayers from Shubnikov–de Haas (SdH) oscillations are reported. Them@B|e&Ggr;values of the conduction band were obtained up tox=0.3. These data, corrected for nonparabolicity, were compared to values calculated by thek ⋅ pmodel, taking into account the disorder bowing.

ISSN:0021-8979    

DOI:10.1063/1.335771

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A new type of slow‐relaxation phenomena is reported together with the conventional fatigue phenomenon in photoconductivity for undoped semi‐insulating liquid‐encapsulated Czochralski GaAs. First, conventional fatigue is induced by the ∼1.1‐eV light irradiation (primary light). Secondary‐light irradiation (∼0.8 eV) subsequently carried out is found to generate a rapid increase followed by a gradual exponential decrease in photoconductivity. The latter phenomenon shows very different characteristics from those of conventional fatigue, though the two phenomena are similar to each other. Through the detailed experimental studies, a configuration‐coordinate model is presented, involving a main deep levelXand its metastable excited stateX* with large lattice relaxation. This phenomenon is explained by the transition of electrons which occurs in part from levelX* excited by the preceding primary‐light irradiation, via levelX, to the conduction band as a result of secondary‐light irradiation.

ISSN:0021-8979    

DOI:10.1063/1.335772

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

We report a study ofa‐Si:H films deposited in a hot‐wall glow‐discharge machine. Optical and transport properties were studied as a function of frequency (400 kHz and 13.56 MHz) and power of the radio frequency (rf), temperature and pressure during deposition, and they were found very similar to those of films deposited by other glow‐discharge techniques. Thin films (<1 &mgr;m) have a higher defect density than thicker films. The lowest defect density and disorder are achieved in the 200–250 °C temperature range. Pressure and rf frequency have no effect on defect density and disorder but control the position of the Fermi level. Reversible defect creation is induced by long and intense light irradiation but this induces no shift of the Fermi level.

ISSN:0021-8979    

DOI:10.1063/1.335773

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

By computer simulation we have been studying the relation between the effective conductivity and the geometrical configuration of two‐dimensional composite or inhomogeneous materials consisting of a metal and an insulator, considering the problem as a continuum percolation problem. Following our previous paper [J. Appl. Phys.56, 806 (1984)], we further simulate two new types of continuum percolation models, and compute the effective conductivities by the finite element method. We compare the calculated conductivities with previous results, theoretical formulas, and experimental data. We clearly show that the critical volume fractions for the metal‐insulator transition and the conductivities of the continuum percolation problem greatly depend on the geometrical configuration of the metal areas of the formed patterns. The extended Watson–Leath equation is a good approximation to the conductivity of the two‐dimensional continuum percolation problem.

ISSN:0021-8979    

DOI:10.1063/1.335774

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The rf power dependence of structural, optical, electrical, and optoelectronic properties of hydrogenated amorphous silicon carbon alloy films prepared by magnetron sputtering of silicon in methane‐argon gas mixtures has been investigated. With increasing rf power, the optical band gap and the activation energy of dark conductivity decrease, accompanied by a decrease in the concentration of Si‐C bonds. The dark conductivity and the photoconductivity increase with increasing rf power. These results are discussed in terms of the compositional and structural change of the films with rf power, such as the factor of preferential attachment of hydrogen to carbon deduced from IR measurements, and the conduction‐band tail width deduced from optical absorption spectra or from temperature dependence of photoconductivity.

ISSN:0021-8979    

DOI:10.1063/1.335775

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Implantation of 100‐eV hydrogen ions on the (0001¯) face of ZnO produces extremely strong electron accumulation layers on the surface. Calibrated argon‐ion sputtering measurements indicate that the implanted ions (consisting mostly of protons) penetrate to a depth of 10–20 A˚ beneath the surface. They act as fully ionized donors giving rise to a free electron layer of comparable depth and of surface electron densities up to 2×1014cm−2. The narrow width, combined with detailed transport measurements, show that the implanted accumulation layers closely resemble ordinary accumulation layers on ZnO surfaces obtained, for example, by exposing the surface to atomic hydrogen. Thus the implanted layers, just as the ordinary accumulation layers, constitute a quantized, two‐dimensional electron gas system. The important advantage of the implanted over the ordinary accumulation layers, however, is that they are completely inert to oxygen or even to room air. Annealing experiments provide estimates for the activation energies for release of the hydrogen ions from the surface layer. The results indicate the presence of several different types of lattice sites for the implanted ions.

ISSN:0021-8979    

DOI:10.1063/1.335776

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The simulation of a superconducting flux counting analog‐to‐digital (A/D) converter for advanced high‐speed signal processing systems is performed to investigate its performance and sensitivity. This report describes the algorithms and the results associated with simulating the whole sequence (count‐store‐readout‐reset‐count). Parameter sensitivities are also checked and optimized.

ISSN:0021-8979    

DOI:10.1063/1.335777

出版商:AIP    

年代:1985

数据来源: AIP