摘要:

We study how hydrogen‐induced quantum confinement in hydrogenated amorphous silicon influences the distribution of tail states. To do this, the potential structure of this semiconductor is treated as being comprised of an ensemble of potential wells, these wells corresponding to unhydrogenated regions enveloped by hydrogenated regions. To evaluate the distribution of states, we determine the ground state associated with each well, and then average over the distribution of wells. We find that our calculated distribution of tail states exhibits an essentially exponential functional dependence, over several decades, and that this tail of states shifts toward the band edge as the hydrogen content is increased. This shift toward the band edge is suggested to be one of the factors responsible for the observed increase in energy gap with higher hydrogen content. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359828

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Photoreflectance spectra have been obtained from single strained Si1−xGexepilayers (0.12<x<0.24) buried under a silicon cap. Despite dramatic changes in the shape of photoreflectance spectra obtained at different positions on a sample wafer, which are explained in terms of a strong interference effect as the Si cap thickness varied, spectra were fitted adequately using three Lorentzian oscillators. Critical point transition energies calculated in this way were consistent withE1andE1+&Dgr;1in Si1−xGexandE′0in silicon and allowed for determination of composition to withinx±1.5%. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359829

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Femtosecond pulses were used to study the photoexcitation dynamics and transient photoinduced dichroism in polydiacetylene 4BCMU film. Ultrafast photoinduced dichroism and optical Kerr gate response were observed. These measurements allowed estimation of the diffusion constant (D∼0.1 cm2/s), nonlinear index of refraction (n2∼10−8esu), and third‐order susceptibility (&Dgr;&khgr;(3)∼6 × 10−10esu), in the film. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360702

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Vacancy‐ordered Sr2Ti2O5(110) epitaxial filmsinsitudeposited on YBa2CU3O7−&dgr;(YBCO) (103) epitaxial films are studied for insulating layers in high‐Tcsuperconducting heterostructures. The ordered structure is interpreted by a 2×2×2 superstructure with a long‐range ordered arrangement of oxygen vacancies in the film and a 2×1 surface superstructure with an ordered arrangement of surface oxygen vacancies on it. The resistivity of the Sr2Ti2O5film sandwiched between Au and YBCO films is measured as a function of the thickness and temperature, and discussed with respect to electron scattering induced by a deficiency of oxygen in the film and at the film boundary. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359830

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report experimental results on monolithic stable‐resonator semiconductor lasers. Curved end mirrors defining a near‐concentric stable resonator were fabricated on wide‐stripe GaAs/AlGaAs GRINSCH‐SQW lasers using reactive‐ion‐etching. These lasers oscillate in close to the expected lowest‐order Gaussian stable‐resonator modes at threshold, evolving into a coherent superposition of higher‐order modes as the pump current is increased up to two to three times threshold. At higher pump currents nonlinear defocusing effects cause the resonators to become geometrically unstable so that the lateral modes are determined by both the resonator geometry and the saturated gain and index profile. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359831

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Published experimental data on silicon oxide precipitate growth kinetics are interpreted in the framework of the theory of Ham for diffusion limited precipitation. A growth law for plate‐like, octahedral and spherical precipitates is derived showing a size dependence which varies as the square root of time. Using well accepted data for the solubility and the diffusion constant of oxygen in silicon, the calculations suggest that the precipitated phase is closer to SiO than toSiO2. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359832

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Oh and Persson [J. Appl. Phys.65, 3852 (1989)] proposed an equation of state to extrapolate high‐pressure shock Hugoniot data to other high‐pressure and high‐temperature states and compared it to data. The requirement thatF=−(∂E/∂V)P/(∂E/∂V)H≊1 (E is specific internal energy, V is specific volume, P is the constant pressure path and H is the constant Hugoniot path) needed to establish the equation of state appears to be in error. I have foundFto vary from 0.16 to 3.59 for fifteen common materials of interest to shock physicists. Oh and Persson’s [J. Appl. Phys.65, 3852 (1989)] comparison of their equation of state to data gives the impression of a better agreement than actually occurs because of possible errors in the transcription of data, and the use of an inappropriate Hugoniot for water. When data are correctly plotted and an appropriate water Hugoniot is used, the comparison of data to theory indicates that the equation of state loses accuracy with increasing pressure or decreasing porous initial density.

ISSN:0021-8979    

DOI:10.1063/1.359833

出版商:AIP    

年代:1995

数据来源: AIP