摘要:

Time resolved spectroscopy and electron concentration measurements were performed on an Ar–He–F2mixture excited by an external rf antenna creating a plasma with features of a plasma source generated by a Helicon reactor commonly used in materials processing. The low pressure range and the simplified chemistry allow an appropriate modelling of some processes and lead to the determination of some fundamental data concerning atomic and molecular fluorine. We give a F2direct dissociation coefficient by electron impact of about 2.0×10−9cm3 s−1for an electron temperature of 5 eV. Excitation rate coefficients of some fluorine levels (3p 2P3/2, 3p 4D7/2, and 3p′ 2F7/2) are given as well as rate coefficients of line emissions following F2dissociation by electron impact. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360743

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Shoulders have been observed in the measured semilogarithmic current‐voltage (I–V) characteristics of high‐efficiency passivated emitter and rear locally diffused silicon (Si) solar cells. An improved understanding is given of the mechanism proposed to cause these nonidealI–Vcurves. It is shown that this mechanism is due to the electrostatic behavior of free carriers at the Si/SiO2interface of oxidized Si devices in which the Si adjacent to the oxide is depleted (or in some cases, inverted) at equilibrium, and results in saturation of the surface recombination rate. Two‐dimensional numerical computer simulations are used to investigate this mechanism and its effect on cell performance. In addition, the simulations provide a means of estimating the extent to which lateral conduction in the rear surface channel also contributes to the observed recombination saturation in these cells. It is shown that ohmic limitation of lateral conduction occurs, however, the lateral current flows are negligible in comparison to the recombination currents due to the former mechanism. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359821

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Certain aspects of the blocking layer behavior in semiconductor heterojunction lasers can be modeled as a thin resistive film overlaying a semiconductor forward biased junction. The dc behavior of such a model has been studied previously by W. B. Joyce and S. H. Wemple [J. Appl. Phys.41, 3818 (1970)]. This paper studies the ac aspects of that model, and also makes some of the dc results of Joyce and Wemple more immediately accessible. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359822

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The electric‐field distribution in a ferroelectric capacitor often is treated as a uniform effective field for circuit‐level modeling. By solving Poisson’s equation and treating the ferroelectric capacitor as a back‐to‐back Schottky‐barrier system, the nonuniform electric‐field distribution is calculated inside a ferroelectric thin film, assuming that the thin‐film capacitor is completely depleted and has a constant doping concentration. It is found that the departure of the local field from the uniform effective field increases with an increase in the doping concentration of the film. Within this model, the uniform field approach to extraction of microscopic ferroelectric parameters is inaccurate for doping levels great enough that the surface field exceeds the coercive field even at zero bias. Based on this criterion, the critical doping concentration for parameter extraction using the uniform field approximation is found to be about 5×1017cm−3. That is, according to the assumed model, for the high doping concentrations reported for typical lead‐zirconate‐titanate thin films (1018–1019cm−3), the extraction of microscopic film properties based on a uniform electric field approximation is inaccurate. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359823

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A series of non‐converging frequency‐dependent Mott–Schottky straight lines can lead to significant errors in the calculation of the device‐related parameters (such as; built‐in‐potential, barrier height, carrier concentration, etc.) for the ZnO‐Bi2O3based varistors. These errors are illustrated using the frequency‐dependent slope of these straight lines. To avoid this problem, a method of obtaining the frequency‐independent Mott‐Schottky response has been devised for these devices. This method employs the well‐known lumped parameter/complex plane analysis technique, and thereby resolves the complexity of the frequency‐dependent Mott–Schottky response. Using this technique, it is possible to characterize the Mott–Schottky behavior of varistor materials without incorporating frequency‐dependent phenomenon in the analysis. These parameters are self‐consistent, and satisfy the basic/classical Mott‐Schottky equation. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359824

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Ferroelectric Pb(Zr0.52Ti0.48)O3(PZT) (001) thin films, integrated to highTcsuperconducting YBa2Cu3O7−x(YBCO) films used as electrodes, have been studied for their photocurrent response and permittivity as a function of temperature. A stable photocurrent was observed to increase with increasing the temperature over the range of 25–350 °C. This increase was found to be strongly polarization dependent and due to the change of the pyroelectric coefficient of PZT thin film with temperature. The pyroelectric coefficient for a PZT sample was measured as ∼30 nC/cm2 K at room temperature, and ∼80 nC/cm2 K at 320 °C. The YBCO electrode showed a stable metallic resistance behavior in this temperature range. There was no detectable photocurrent from YBCO layer. No poling is required until 350 °C for the PZT/YBCO heterostructure detector because the PZT film is oriented when grown onc‐axis oriented YBCO. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359825

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have fabricated a SiO2/TiO2high‐reflectivity dielectric multilayer mirror specifically suitable for ZnSe‐based vertical cavity surface‐emitting lasers operating in the green‐to‐blue spectral region. In the fabrication process, the thickness of each layer has been precisely controlled by using aninsituoptical monitoring system. A photo‐pumped ZnCdSe/ZnSe/ZnSSe surface‐emitting laser has also been demonstrated using the SiO2/TiO2dielectric multilayer mirrors stacked with the ZnCdSe/ZnSe/ZnSSe structures. Cavity mode emission with a linear polarization has been observed in the direction normal to the surface at 20 K. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359758

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Two‐color photoconductive detectors in the 3–5 &mgr;m wavelength range using multilayer undopedn‐type Hg1−xCdxTe heterostructures have been demonstrated at room temperature. These heterostructures, consisting of three or four Hg1−xCdxTe layers separated with CdTe layers, were grown by the metal‐organic chemical‐vapor‐deposition (MOCVD) technique. The quality of MOCVD films was verified by near‐theoretical values of the minority‐carrier lifetime at 300 K, ranging from 0.8 to 4.7 &mgr;s depending on thexvalue. The Hg1−xCdxTe layers are either detectors or filters, and the CdTe layers serve as insulating separators. The concept of using the exponential absorption tails of two Hg1−xCdxTe layers with different band gaps to form an absorption band was verified by the difference in the photoconductive spectral responses between backside and frontside illumination. Two different multilayer heterostructures with two‐color peaks at 3.2/3.8 &mgr;m and 3.7/4.6 &mgr;m, respectively, were studied. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359759

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The mass and velocity distributions of neutral species, ejected from a laser‐ablated 6H‐SiC target, are measured by time‐of‐flight mass spectroscopy. The laser‐generated plume is shown to consist of atomic silicon and carbon and small neutral clusters. Measured values of the mean kinetic energies of neutral Si and SiC2species are 1.1 and 1.5 eV, respectively, when a 6H‐SiC target is irradiated with 248 nm radiation at a power density of 1×108W/cm2. The kinetic energy distribution of Si+ions is also measured for comparison with the neutral species, and shows a peak in the distribution at 38 eV. These data illustrate that an electronic, and not a thermal, mechanism for particle emission is active during the ablation of a 6H‐SiC target. The relationship between the dynamics of the photoablation process and the properties of pulsed‐laser‐deposited films is also briefly discussed. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359760

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Absorption, photocurrent, and infrared reflectivity spectra of the polycrystalline &bgr;‐FeSi2thin films in relation to the Si substrate temperature are presented. The photocurrent spectra involving both the fundamental interband, extrinsic defect transitions of &bgr;‐FeSi2and the intrinsic transitions of Si substrates are observed. Both the absorption and photocurrent measurements show the direct gap nature. A simple recombination model is proposed to account for the photocurrent results. We show that better quality &bgr;‐FeSi2films can be achieved at higher substrate temperature. The simplicity, sensitivity, and reliability of the photocurrent measurements for studying &bgr;‐FeSi2are well demonstrated. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.359761

出版商:AIP    

年代:1995

数据来源: AIP