摘要:

The resonant tunneling effect is optically enhanced in a GaAs/GaAlAs double‐barrier structure that has partial lateral current confinement. The peak current increases and the valley current decreases simultaneously when the device surface is illuminated, due to the increased conductivity of the top layer of the structure. The effect of the lateral current confinement on the current‐voltage characteristic of a double‐barrier resonant tunneling structure was also studied. With increased lateral current confinement, the peak and valley current decrease at a different rate such that the current peak‐to‐valley ratio increases up to three times. The experimental results are explained by solving the electrostatic potential distribution in the structure using a simple three‐layer model.

ISSN:0021-8979    

DOI:10.1063/1.348515

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The spatial variation of stress and crystal orientation in laser‐crystallized silicon‐on‐insulator films has been determined using the Raman‐microprobe technique. The spatial resolution achieved is better than 1 &mgr;m. The phonon shift relative to unstressed silicon is in the range of −1.5 cm−1which corresponds to a tensile stress of 380 MPa and is in good agreement with theoretical analysis. Using a laser plasma line as an online reference, the peak position of the phonon signal has been measured with a resolution better than ±0.02 cm−1. Our results also show a 4°‐backward tilt of the crystal orientation along a crystallization path length of 90 &mgr;m. This has been determined using a new polarization sensitive intensity‐monitoring method on cross‐cut specimens which features an angular resolution of ±1° independent of surface roughness.

ISSN:0021-8979    

DOI:10.1063/1.348516

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

It is shown thatinsituHeNe laser ellipsometric measurements performed during and after rf plasma exposure of a Si wafer with or without oxide can be used to obtain the wafer temperature during plasma exposure. The method utilizes either the temperature coefficient &dgr;n/&dgr;Tof the refractive index of Si or the linear thermal expansion coefficient &dgr;l/l&dgr;Tof SiO2. The values of these parameters have been redetermined in this work.

ISSN:0021-8979    

DOI:10.1063/1.348517

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

p‐type doping of molecular beam epitaxy grown GaSb by Ge and Sn has been demonstrated. Both impurities are well behaved with demonstrated free acceptor concentrations as high as 2×1019cm−3for Ge and 5×1018cm−3for Sn. In addition reflection high‐energy electron diffraction measurements during growth indicate that Sn segregation which is common in GaAs does not occur in GaSb. The absence of Sn segregation as well as thep‐type nature of Ge and Sn dopants is attributed to the large covalent bond radius of Sb. These dopants are important since they provide an excellent alternative to Be forp‐type doping of Sb based materials.

ISSN:0021-8979    

DOI:10.1063/1.348518

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We suggest that annealing GaAs samples at high temperatures encourages the relatively rapid in‐diffusion of divacancies which either are acceptors themselves or quickly dissociate into acceptors. Rapid quenching to room temperature freezes in these defects and results in altered electrical properties for the samples. A simple model, fit to some sparse existing data, yields a 950 °C estimate of (3–5)×10−7cm2/s for the diffusivity of the divacancy. When combined with other existing data, obtained at lower temperatures, on the in‐diffusion of a defect with a level atEc‐0.23 eV and tentatively identified as the divacancy, we find the diffusivity of the divacancy to be given by (3×10−3)exp(−0.94 eV/kT) cm2/s over the temperature range 250–950 °C.

ISSN:0021-8979    

DOI:10.1063/1.348519

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

As‐grown superconducting YBa2Cu3O7−ythin films with various thicknesses were successfully grown on lattice‐matched NdGaO3substrates by ArF laser ablation deposition. An as‐grown 2000‐A˚‐thick film has a zero‐resistance temperature (Tc) at 90 K and a 170‐A˚‐thick film has aTcat 88 K. The existence of a thin interfacial diffusion layer between a 170‐A˚‐thick film and the substrate was observed by Auger electron spectroscopy. Rutherford backscattering spectroscopy suggest that as‐grown YBa2Cu3O7−yfilms on NdGaO3substrates are high‐quality crystals. It is demonstrated that the NdGaO3has considerable potential as an electronic substrate material by less interfacial diffusion layer and good crystallinity of grown thin films.

ISSN:0021-8979    

DOI:10.1063/1.348520

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Thin films of iodinated nickel phthalocyanine were made by double‐source evaporation of nickel phthalocyanine and iodine in vacuum. They were obtained by keeping the substrate temperature at about −90 °C. Thecaxes of crystallites composing the film were almost perpendicular to the quartz glass substrate. The conductivities of the films were 0.1–1 S/cm at room temperature which decreased slightly as the measuring temperature wasloweredto−170 °C.

ISSN:0021-8979    

DOI:10.1063/1.348521

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Superconducting YBa2Cu3O7−xthick films have been growninsituon polycrystalline CaO stabilized ZrO2substrates by radio frequency thermal plasma chemical vapor deposition at ∼0.1 &mgr;m/min. Mixed aqueous nitrate solutions of yttrium, barium, and copper were used as precursors. Different substrate temperatures of 450, 500, and 600 °C were used for deposition. The as‐deposited films were black, dense, smooth, and superconducting with onsetTc’s higher than 80 K. X‐ray diffraction shows that the films were highly textured with thecaxis normal to the substrate. Energy dispersive x‐ray spectroscopy was used to analyze the film composition. From direct current magnetization measurements, the critical current density was found to be 1 × 106A/cm2at 10 K and zero field for a film deposited at 450 °C.

ISSN:0021-8979    

DOI:10.1063/1.348522

出版商:AIP    

年代:1991

数据来源: AIP