摘要:

1H nuclear magnetic resonance measurements in proton‐exchanged LiNbO3were employed to determine structural positions of sites believed to be responsible for the desirable optical properties of this material. Contributions from other proton sites were first subtracted from the line shape which was subsequently analyzed by Van Vleck’s second moment method using a spin‐echo technique to separate like‐spin from unlike‐spin contributions. Among various models examined, only one in which protons are located on oxygen planes nearest to normal lithium sites, midway between two oxygen anions in an oxygen triangle, was found to be consistent with the data. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114628

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An x‐ray scattering study of electroclinic layer constriction verifies the interpretation of the electroclinic effect as field‐induced molecular tilt. The tilt angles deduced from the layer spacing changes are in close agreement with those from optical measurements. Layer buckling, a consequence of the layer constriction, is also observed and may be the cause of the loss of optical contrast observed in electroclinic devices. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114629

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Epitaxial potassium niobate thin films were depositedinsituby low pressure metalorganic chemical vapor deposition (MOCVD) at a growth temperature of 800 °C using niobium pentaethoxide and potassium tert‐butoxide as volatile metalorganic precursors. Growth on single crystal (100) lanthanum aluminate substrates produced [110]‐oriented potassium niobate films. The films have a smooth, featureless morphology. Atomic force microscopy of the MOCVD‐derived films surface indicates a root‐mean‐square roughness of less than 2 nm. Second‐harmonic generation of 1.064 &mgr;m incident light is observed from the potassium niobate thin films, and the effective second order nonlinear susceptibilitydof the as‐deposited film is as high as 13 pm/V. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114630

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Dry etching‐induced surface damage and contamination on SiC have been investigated for electron cyclotron resonance (ECR) plasma etching and conventional reactive ion etching (RIE) using a CF4/O2gas mixture. Auger electron spectroscopy shows that there is no residue on the ECR etched surfaces and sidewalls of the etched structures. In contrast, the conventional RIE process leaves residues containing large amounts of Al, F, and O impurities on the surfaces and the etched sidewalls. Pd Schottky diodes on the ECR etched surface show a near‐ideal diode characteristics with ideality factor of 1.06, indicating a good surface quality. Pd Schottky diodes on the conventional RIE etched surface, however, have a substantially reduced barrier height from 1.05 eV for the as‐grown sample to 0.64 eV and a high ideality factor of 1.27, indicating a substantially damaged surface. Significant free‐carrier reduction is observed in the RIE etched sample. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114631

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Surface photovoltage spectroscopy (SPS) is used to determine the position of the deep defect state levels in undoped hydrogenated amorphous silicon (a‐Si:H). The occupied and the empty levels, and their nature, are identified with a clear advantage over existing methods. The identification of the levels and the effect of light soaking on their concentration provides direct experimental confirmation of the main features predicted by thermal equilibrium models. The finding of other levels ina‐Si:H materials of larger disorder further supports the recently proposed potential fluctuations model. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114632

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The incorporation of nitrogen in oxides has been studied after furnace oxidation inN2O at 900 °C. We observe that nitrogen isremovedfrom the oxide bulk during oxidation inN2O, while simultaneously nitrogen is incorporated at the growingSi–SiO2interface. This results suggests that nitrogen incorporation involves a dynamic equilibrium between competing processes which causes both nitrogen incorporation and depletion. A chemical model for nitrogen removal is proposed based on a reaction with NO. Reaction energies, estimated from semiempirical quantum‐mechanical calculations, support the proposed model. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114633

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The time evolution of the 1.54 &mgr;m Er3+photoluminescence intensity of Er‐doped silicon following a 30 &mgr;s excitation pulse is investigated. It is found that at 9 K, the 1.54 &mgr;m luminescence from Er3+continues to increase up to 50 &mgr;s after the pulse is terminated, when excess photocarriers no longer exist. This provides the first direct experimental evidence that a state in the forbidden gap of silicon acts as the gateway to the excitation of Er3+. Further analysis indicates recombination of bound excitons to be the most likely excitation mechanism. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114634

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The photoluminescence spectrum of undoped epitaxial wurtzite GaN layers on sapphire was measured for applied hydrostatic pressures up to 73 kbar at 9 K and up to 62 kbar at 300 K. The pressure dependences of theI2exciton recombination line and the ‘‘yellow’’ band (2.2 eV band at ambient pressure) were examined at 9 and 300 K, and the series of donor‐acceptor‐pair emission lines was analyzed at 9 K. From theI2lines, it was found that the band gap increases with pressure by 4.4±0.1 meV/kbar at 9 K and 4.7±0.1 meV/kbar at 300 K. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114635

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have investigated the atomic structure and chemical bonding present at sulfur exposed GaAs(111)B‐(2×2) surfaces using both scanning tunneling microscopy (STM) and synchrotron radiation core‐level photoemission. Exposure of the (2×2) surface to a molecular beam of sulfur leads to the appearance of a (1×1) low‐energy electron diffraction pattern which becomes increasingly well defined as the sample is annealed. However, at no stage of the annealing process does the surface display an ordered (1×1) ideal termination. Both the photoemission data and STM images show that a large proportion of the As trimer units of the clean (2×2) surface remain after sulfur exposure and annealing to 450 °C with strong evidence of sulfur substituting for As in atomic layers below the surface. The effect of these reactions is to increase the surface band‐bending from that of the clean (2×2) surface. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114636

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have studied electric field heating of low‐dimensional electrons in GaAs/AlGaAs heterostructures at 4.2 K using thermal noise measurements. For the two‐dimensional (2D) wire, the increase in electron temperature, &Dgr;Te, extracted from noise measurements is in agreement with previous measurements of &Dgr;Teand is explained by emission of acoustic and optical phonons. Measurements are extended to quasi‐one‐dimensional (Q1D) wires which are shorter than the 2D wires. In these Q1D wires, we find that for small &Dgr;Te, power dissipation is more effective than in the 2D wires, due to additional energy relaxation through the contacts. This effect is most pronounced in the highest mobility wire where the energy relaxation length is the longest. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114637

出版商:AIP    

年代:1995

数据来源: AIP