摘要:

Surface morphological changes in ZnSe-related II–VI epitaxial films grown by molecular beam epitaxy have been investigated by atomic force microscopy and transmission electron microscopy. We found that under group-II-rich conditions withc(2×2)surface reconstruction, the process of roughening gives rise to periodic elongated corrugations aligned in the [11¯0] direction. Under group-VI-rich conditions with(2×1)surface reconstruction, rounded grains form instead of corrugated structures. The surface morphology is dependent on the VI/II ratio and growth temperature, but is independent of the film strain. The observed morphological changes are mainly due to growth kinetics and are not stress driven. We propose a model to explain the changes in surface morphology under group-II-rich conditions and group-VI-rich conditions. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366128

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We compare measurements of the roughness of silicon(001) wafers cleaned by several methods. The roughness values were obtained using crystal truncation rod (CTR) scattering and atomic force microscopy. Although they do not yield identical results, both methods show the same relative roughness for the different cleans. CTR scattering is sensitive to roughness on lateral length scales down to atomic dimensions. The quantitative differences in roughness can be explained by the different wavelength spectrum of roughness probed by the two techniques. CTR measurements were also performed after a 60 Å thermal oxide was grown on the wafers. The roughness trends are the same after oxidation, but we also find that the oxidation process has significantly reduced the interfacial roughness. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366129

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have observed images and local electron spectra of an oxide pattern on Si(100) using metastable electron emission microscopy (MEEM) recently developed at our laboratory. Low-energy electron microscopy (LEEM) was also used. For both MEEM and LEEM, the energy-filtered images were obtained for the first time. It was shown that MEEM gives the information on the outermost surface layer selectively, while LEEM provides averaged information on several surface layers. The intensity of the band in the local electron spectrum of MEEM can be related to the distribution of the relevant orbitals exposed outside the surface, with which metastable atoms interact effectively. Thus, using energy-filtered MEEM, we can observe the map reflecting the distribution of individual orbitals at the outermost surface layer. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366130

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The wave-vector dependent, electron initiated, impact ionization transition rates for the cubic and hexagonal phases of ZnS have been numerically determined using a pseudopotential calculated band-structure and wave-vector dependent dielectric function. The rates for both phases show a strong dependence on the relative band structures. A detailed band-by-band analysis of the transition rate in the first Brillouin zone has been performed to determine the wave-vector dependence of the rate. The energy dependent rates have also been computed by averaging the transition rate over energy. It is found that the hexagonal phase of ZnS exhibits a higher ionization transition rate than the cubic phase. A preliminary estimation of the nature of the threshold has been made using a previously published phonon scattering rate. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366131

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The selectivity and sensitivity of deep level transient spectroscopy (DLTS) depend significantly on the choice of the correlation function. In this article, the factors limiting the resolution of correlation DLTS are discussed. It is argued that the weighting functions reported to date provide asymmetrical rate windows, being effective filters only for slow transients. To overcome this limit, a correlation procedure, based on the Gaver–Stehfest algorithm for the inverse Laplace transformation, is proposed. Using this procedure one can obtain a temperature scanned DLTS mode resolution comparable to the resolution of sophisticated methods of inversion of the Laplace integral equation. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366269

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The properties of electron traps in nominally undopedIn1−xGaxAsyP1−ylayers grown onGaAs0.61P0.39substrates by liquid phase epitaxy were investigated by deep level transient spectroscopy measurements. Only one kind of electron trap with the activation energy of 0.38 eV was observed inIn0.32Ga0.68P. A new kind of electron trap with the activation energy of 0.15 eV began to appear and its concentration increased as the As composition was increased. But this trap was not detected inGaAs0.61P0.39.This 0.15 eV trap was found to have a capture barrier causing the persistent photoconductivity phenomenon inIn1−xGaxAsyP1−yat low temperatures. This defect was also found to have acharge-state controlled stability. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366132

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This paper presents results from the calculation of the high-energy electron–electron scattering rate in silicon based on a full energy-band structure obtained by the pseudopotential technique. The effects on the scattering rate of the overlap integrals, wave-vector-dependent dielectric function and umklapp processes are described and the transition rate is compared with that obtained using a semiclassical analysis based on a parabolic energy dispersion. A hybrid Monte Carlo/iterative technique for solving the Boltzmann transport equation is used to obtain the electron energy distribution function generated by binary particle interactions in a one-dimensional system. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366133

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Current–voltage characteristics measured in triple barrier resonant tunneling diodes reveal new features about energy level alignment in a superlattice. Our data indicate that energy levels in the two quantum wells are not aligned at current peaks. Current peaks are observed when one of the energy levels in the two wells becomes resonant with the emitter level. One of the current peak was thermally activated, and showed inverted bistability at 77 K temperature. We explain that this is due toXstate assisted tunneling. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366134

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The tunability of band offsets in ZnSe/GaAs(001) heterovalent heterostructures is investigated. The interface composition, Ga/As, is controlled by means of Zn or Se treatment or by thermal etching of the GaAs surfaces before the growth of ZnSe. Consequently, it is revealed by X-ray photoemission spectroscopy that artificial control of Ga/As from 1.0 to 2.8 leads to variation of the valence band offsets from 0.6 to 1.1 eV. Based on the electron counting model and the layer-attenuation model, a structural model which is responsible for the Ga-rich interface and for the increase of valence band offset is proposed, in which the As plane just below the interface consists of As, anti-site Ga and As vacancies. The electronic properties of then-ZnSe/p+-GaAs heterojunction diodes (HDs) provide further evidence of the tunability of the band offsets at the interface, that is, the diffusion potentials in the HDs are modified according to the interface compositions. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366135

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Undoped single crystalline aluminum nitride films were grown on 4H and 6H SiC substrates using metal–organic chemical-vapor deposition at 1200 °C. Fromin situreflection high-energy electron diffraction, x-ray diffraction rocking curves, and cathodoluminescence spectra, the crystallinity of the films was confirmed. Atomic force microscopy showed that some films were substantially dominated by island growth, rather than step flow growth. Aluminum was evaporated to form metal–insulator–semiconductor (MIS) capacitors for high-frequency capacitance voltage measurements carried out at room temperature. Low leakage made it possible to measure the structures and characterize accumulation, depletion, deep depletion, and, in some cases, inversion. From independent optical thickness measurements, the relative dielectric constant of aluminum nitride was confirmed at 8.4. The flatband voltage of the AlN MIS capacitors onp-type SiC was close to the theoretical value expected. The films were stressed up to 60 V (3 MV/cm) without breakdown, but excessive leakage currents(>0.1 A/cm2),probably dominated by grain-boundary conduction, shifted the flatband voltage of the capacitors. These results indicate the possibility of replacing silicon dioxide with aluminum nitride in SiC field effect transistors using insulated gates. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366136

出版商:AIP    

年代:1997

数据来源: AIP