摘要:

The intermixing (and associated interdiffusion) resulting from ion implantation of argon ions into Cd1−xMnxTe quantum‐well structures has been investigated. The experimental value of the mixing parameter of 1.5×103A˚/eV is large compared with the values reported for this parameter in metallic superlattices, and is consistent with an appreciable degree of inter diffusion accompanying the implantation process. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361093

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The spin lattice relaxation rates and the absorption spectra of7Li in both LiB3O5crystal and glass samples were measured from room temperature up to 800 K. At low temperatures the dominant contribution to the relaxation rates was due to the spin–phonon interaction in both samples. For the crystal the relaxation caused by the diffusion of Li ions became significant above 580 K, and the narrowing of the absorption line started at about 540 K. For the glass the narrowing of the line started at room temperature and the effect of the diffusion of Li ions on the relaxation rate appeared above 400 K. From these results the correlation time &tgr;cof the fluctuating field at Li nuclei was obtained. Each value of the activation energy of &tgr;cdeduced from the relaxation rate and the narrowing of the line, respectively, agreed well. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361094

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Very thin diamond films (thickness ∼0.1 &mgr;m) have been investigated by x‐ray diffraction pole figure measurements using synchrotron radiation in order to understand the mechanism of heteroepitaxial diamond nucleation and the first steps of film growth on silicon(001) substrates. The diamond layers consist of an epitaxially aligned component with a crystallographic orientation identical to the substrate. The initial orientational spread of the grains around the perfect epitaxial orientation prior to any modification by a subsequent textured growth step has been determined. In the studied temperature range for the nucleation step the misalignment decreases slightly with increasing temperature. Besides the epitaxial crystallites their corresponding twins of first and second order have been found. The intensity distribution of the pole figures indicates that the process of twinning plays a dominating role in the initial growth stage which shows a tendency to become even more pronounced for higher substrate temperatures. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361080

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Epitaxial growth of PbSe on (111)‐ and (100)‐oriented Si substrates without an intermediate buffer layer is studied. It is found that on Si(111) the orientation of the IV‐VI layer can by varied from (100) at 200 °C to (111) at 400 °C substrate temperature. On Si(100), only (100)‐oriented layers were obtained for the whole temperature range. (100)‐oriented layers with thicknesses above 0.5 &mgr;m were cracked due to thermally induced mechanical strain on cooldown to room temperature. This strain cannot be relaxed by dislocation glide in the first glide systems as it is the case for (111)‐oriented layers. The structural quality of (100)‐oriented PbSe layers on Si(100) and Si(111) is inferior compared to layers grown with an intermediate BaF2/CaF2or CaF2buffer layer. This implies that the covalent/ionic PbSe/Si interface seems to impede high‐quality epitaxy, contrary to the well known ionic/ionic IV‐VI/IIa‐fluoride interface. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361076

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Nonhydrogenated diamondlike carbon films prepared at a substrate temperature (ST) of 100, 300, and 500 °C by the laser ablation of graphite on a single‐crystal silicon substrate have been characterized by scanning tunneling microscopy for the surface structure and Raman spectroscopy for the microstructure. Distorted pentagonal and hexagonal rings are observed on the surface of the film grown at 100 °C while only hexagonal rings are observable for the one grown at 500 °C. The rise in ST is found to increase the surface roughness. To assign the various coexisting carbonaceous species formed at different growth temperatures and to check their thermal stability, heat treatment was performed at up to 1300 °C in vacuum and 600 °C in air. The changes occurring on heat treatment in vacuum in these films around 600 °C have been correlated with the release of defects from the threefold network. Likewise, 950 °C temperature has been associated with the conversion of disordered tetrahedral bonding to a distorted trigonal one. The heat treatment in air shows that the microstructure induced due to lower ST is thermally more stable. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361081

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Measurements of defect density, photoconductivity, and dark conductivity are used to obtain information about the values of the electron capture cross sections of charged and neutral metastable dangling‐bond defects in high‐quality, undoped, hydrogenated amorphous silicon at room temperature. Sixty measurements, obtained in the process of optical degradation experiments as a function of time at four different temperatures, have been analyzed using photoconductivity models corresponding to either one or two types of discrete‐level, multivalent defects. A model with two types of defects is able to accurately describe both dark conductivity and photoconductivity results, and gives the following average values: an electron capture cross section of about 1×10−16cm2for neutral centers of both higher‐lying (density not increased by light) and lower‐lying (density increased by light) defects, of about 2×10−16cm2for positively charged higher‐lying defects, and of about 20×10−16cm2for positively charged lower‐lying defects. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361082

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report a study of the steady‐state photoconducting properties in the conjugated polymer poly(2,5‐dimethoxy‐p‐phenylene vinylene) using the sandwich and surface cell configurations. The photocurrent spectral response in both the configurations is nearly identical with the onset of the photocurrent around the band edge. The rise in the photocurrent is more gradual than the increase in absorption with respect to the photon energy and the peaks in the photocurrent responses are separated from the absorption maxima by nearly 1 eV. The chopper frequency, electric field, and the intensity dependence of the photocurrent are remarkably different for the two configurations. We speculate on the mechanisms leading to such differences. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361083

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We solve a pair of Boltzmann transport equations based on an interacting two‐isotropic‐band model in a general way first to get transport parameters corresponding to the relaxation time. We present a simple method to calculate effective relaxation times, separately for each band, which compensate for the inherent deficiencies in using the relaxation time concept for polar optical–phonon scattering. Formulas for calculating momentum relaxation times in the two‐band model are presented for all the major scattering mechanisms ofp‐type GaAs for simple, practical mobility calculations. In the newly proposed theoretical framework, first‐principles calculations for the Hall mobility and Hall factor ofp‐type GaAs at room temperature are carried out with no adjustable parameters in order to obtain direct comparisons between the theory and recently available experimental results. In the calculations, the light‐hole‐band nonparabolicity is taken into account on the average by the use of energy‐dependent effective mass obtained from thek⋅pmethod and valence‐band anisotropy is taken partly into account by the use the Wiley’s overlap function.. The calculated Hall mobilities show a good agreement with our experimental data for carbon‐dopedp‐GaAs samples in the range of degenerate hole densities. The calculated Hall factors showrH=1.25–1.75 over hole densities of 2×1017–1×1020cm−3. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361084

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present a generalized Ramo–Shockley theorem to evaluate particle currents and energy currents at device contacts, in classical drift‐diffusion or hydrodynamic simulation techniques as well as for semiclassical Monte Carlo and quantum mechanical transport simulation. In contrast to the Ramo–Shockley theorem, our technique (1) is derived for conditions of extreme time dependence in the charge carriers and forces (including particle‐induced radiation), (2) explicitly accounts for particle generation and recombination processes such as photoexcitation, forward and inverse Auger processes, or Shockley–Read–Hall recombination, and (3) distinguishes clearly between the contributions of electrons, holes, and the displacement current. The resulting simple new formalism reduces to the standard Ramo–Shockley theorem as a special case. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361074

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A model is proposed for the description of the current instabilities in GaAs‐AlGaAs heterojunctions. It consists of three parts: the injection of electrons via the contact into the AlGaAs layer, the partial capture of these electrons in deep centers, and the change with time of the band structure. This last ingredient is crucial, since due to the increase of the total number of electrons in the AlGaAs layer the band bending decreases making real‐space transfer from the AlGaAs layer to the two‐dimensional electron gas possible. We have performed quasistationary simulations of the time dependence of the current. The velocities, average energies, capture rates, etc. were taken from Monte Carlo simulations. It turned out, that the parameters for the modeling of the contact, which are to a high degree unknown, play an essential role. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361045

出版商:AIP    

年代:1996

数据来源: AIP