摘要:

The oxidation of polycrystallineSixGe1−xfilms with different compositions (i.e., different values ofx) is carried out in pyrogenic steam at 800 °C for various lengths of time. It is found that the oxidation is enhanced by the presence of germanium and that the enhancement effect is more pronounced for the films richer in germanium. A mixed oxide in the form of either(Si,Ge)O2orSiO2–GeO2is found at the sample surface if the initialSixGe1−xcontains more than 50&percent; of germanium. However, a surface silicon cap layer of about 14 nm is found to have a significant impact on the oxidation of theSi0.5Ge0.5films; it leads to the growth of about 115-nm-thickSiO2which is about four times that of theSiO2resulting from the oxidation of the cap layer itself. On theSixGe1−xfilms with only 30&percent; of germanium, theSiO2continues to grow after oxidation for 180 min resulting in 233-nm-thickSiO2which is about 2.4 times greater than theSiO2grown on ⟨100⟩ silicon substrates. Rejection of germanium results in piling up of germanium at the interface between the growingSiO2and the remainingSixGe1−x.Substantial interdiffusion of silicon and germanium takes place in the remainingSixGe1−x.The experimental results are discussed in terms of thermodynamics and kinetics. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366443

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A mathematical model of oxidation ofSixGe1−xalloys is presented. The growth ofSiO2is simulated in conjunction with the determination of silicon distribution inSixGe1−xusing numerical methods. The main feature of the model is the assumption of simultaneous oxidation of germanium and silicon when exposing theSixGe1−xto an oxidizing atmosphere. In accordance with thermodynamics, theGeO2formed is subsequently reduced by the (free) silicon available at the interface between the growingSiO2and the remainingSixGe1−xthrough a reduction reaction. Thus, the enhanced oxidation of silicon in the presence of germanium is modeled as a result of the rapid oxidation of germanium followed by the quick reduction ofGeO2by silicon. The growth of a mixed oxide in the form of either(Si,Ge)O2orSiO2–GeO2only occurs when the supply of silicon to theSiO2/SixGe1−xinterface is insufficient. A comparison is made between simulation and experiment for wet oxidation (in pyrogenic steam) of polycrystallineSixGe1−xfilms. It is found that the model gives a good account of the oxidation process. Kinetic parameters, i.e., interfacial reaction rate constant for oxidation of germanium and diffusion coefficient of silicon (germanium) inSixGe1−x,are extracted by fitting the simulation to the experiment. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366444

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This article demonstrates the growth of silicon dioxide(SiO2)on a gallium arsenide (GaAs) substrate by use of the liquid phase deposition (LPD) method at extremely low temperature(∼40 °C).This method cannot only growSiO2but it can also obtain good quality and reliability due to the suppression of interdiffusion in such a low temperature process. The deposition rate ofLPD-SiO2on GaAs is up to 1265 Å/h. The refractive index of theLPD-SiO2film on GaAs is about 1.42 with growth at 40 °C. When theLPD-SiO2film on the GaAs substrate is used to fabricate a metal–oxide–semiconductor capacitor with a device area of0.3 cm2,the surface charge density(Qss/q)is about3.7×1011 cm−2and the leakage current is 43.3 pA at−5 V.A proposed mechanism for the LPD ofSiO2on GaAs is also presented. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366445

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Nanostructured carbon thin films have been produced by deposition of supersonic cluster beams. The clusters are generated by a pulsed arc cluster ion source modified in order to achieve high fluxes and stability. Scanning electron microscopy, Raman, and optical spectroscopy show that the films are a low density network of nanometer-size particles. The nature of the films is essentially graphite-like with a large number of distorted bonds. The formation of structures based onsp3bondings is not observed. The use of cluster beam deposition for the synthesis of nanocrystalline thin films is discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366446

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Nanosecond KrF excimer laser ablation of benzyl chloride, benzyl alcohol, toluene, ethylbenzene, andn-propylbenzene diluted inn-hexane,n-heptane, dichloromethane, and 1,2-dichloroethane was investigated by time-resolved photographic, photoacoustic, and absorbance measurements. Ablation threshold values,Fth,for high concentration solutions (&agr;=250 cm−1,0.6–1 M) were confirmed to be correlated to photochemical reactivity (&bgr;-bond cleavage) of the solute molecules, whereas no distinct relation betweenFthand boiling point of solvents was observed. Time-resolved absorbance at the laser wavelength was almost constant during the excitation pulse, which means that the main light-absorbing molecules were fixed to the ground-state solutes. It is considered that this type of ablation is initiated by the photochemical fragmentation. On the contrary,Fthobserved in relatively low concentration solutions (&agr;=25 cm−1,0.06–0.1 M) were about twice higher than those for the high concentration solutions, and had no direct correlation with the photochemical reactivity of the solute molecules. The time-resolved absorbance increased during the excitation pulse, and was ascribed to the fact that benzyl radicals produced by the photodissociation of solute molecules absorbed the excitation photons and converted them into heat through “a cyclic multiphotonic absorption process.” Furthermore, morphological aspects observed in nanosecond photography exhibited appreciable differences by varying the solute concentrations. These results clearly mean a concentration-dependent ablation mechanism; the ablation mechanism of the benzene derivative solutions switches from photochemical to photothermal as the solute concentration decreases. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366447

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This work reports an investigation of the effect of excitons on carrier recombination and solar energy conversion processes. The probabilities of exciton-stimulated modulation of the occupancy ofrcenters in CdS as well as the binding coefficient of free electrons and holes into excitons are estimated. Carrier recombination and transport theories are presented. The theories are applied toCu2S/CdSsolar cells for AM1 illumination at a temperature of 300 K. It has been shown by numerical estimation that exciton-stimulated modulation of the occupancy of deep impurities does give a significant reduction of carrier recombination losses and efficiency improvements forCu2S/CdSsolar cells. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366448

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Transmission electron microscopy (TEM) image contrast was used to characterize doping-dependent etching ofn+/pjunctions in silicon. The local variations in crystal thickness give rise to the appearance of thickness fringes which may be interpreted as two-dimensional iso-concentration contours that map the dopant distribution. The etchant solution used for selective chemical etching of TEM samples prepared using wedge technique was modified to reduce the etch rate and maintain high selectivity to then+doped region. The two-dimensional dopant profiles were quantified by calibrating against one-dimensional secondary ion mass spectroscopy data and also compared with one-dimensional spreading resistance analysis data. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366449

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report characteristics and degradation of an InGaN/AlGaN double-heterostructure light-emitting diode (LED) grown by metalorganic chemical vapor deposition on a sapphire substrate. The InGaN/AlGaN LED exhibited an optical output power of 0.17 mW, an external quantum efficiency of 0.2&percent;, a peak emission wavelength at 440 nm with a full width at half-maximum of 63 nm, and a stable operation up to 3000 h under 30 mA dc operation at 30 °C. However, the InGaN/AlGaN LED showed electrical and optical degradations under high injected current density and high ambient temperature. Electroluminescence, electron-beam-induced current and cathodoluminescence observations showed that the degraded InGaN/AlGaN LED exhibited formation and propagation of dark regions, which act as nonradiative recombination centers. The values of the degradation rate were determined to be1.1×10−3,1.9×10−3,and3.9×10−3 h−1under the injected current density of100 A/cm2,and1.6×10−2,3.6×10−2,and8×10−2 h−1under200 A/cm2at ambient temperatures of 30, 50, and 80 °C, respectively. The activation energy of degradation was also determined to be 0.23–0.25 eV. The degradation of electrical and optical characteristics was caused by the growth of dark regions. It was also observed that GaN-based LEDs on sapphire substrates have longer lifetime than the ZnSe-based LED, but shorter than the AlGaAs and InGaAsP LEDs. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366450

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The multipeak current–voltage(I–V)characteristic and hysteresis phenomena based on a series combination of several resonant tunneling diodes (RTDs) are analyzed and simulated. Our analytic model is based on a load-line technique with a piecewise-linear approximation for theI–Vcurve of RTD. The peak-to-valley current ratio ofNRTDs in series and the effects of series resistance on the combinedI–Vcharacteristic are investigated. The results provide a useful design and estimation for the multipeakI–Vcharacteristic with series-connected several RTDs before circuit accomplishment. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366397

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Superconductors can in theory be used to detect rotation by Josephson interference or by detection of the London field, a magnetic induction that fills the interior of any rotating bulk superconductor. One might hope to use these properties of superconductors to build a practical inertial guidance gyroscope. A problem arises from the necessity of surrounding the device with superconducting magnetic shielding: the London field generated by a co-rotating shield eliminates the response of the superconducting device within the shield. The present article demonstrates this point more rigorously than has been done before, discussing solutions of Ampe`re’s law for rotating and nonrotating superconductors and paying careful attention to boundary conditions. Beginning with a supercurrent density derivable from either the Ginzburg-Landau or the London theory of superconductivity, the article shows: 1) that a superconducting device cannot distinguish between rotation and an applied magnetic field: 2) that a superconducting device surrounded by a co-rotating superconducting shield cannot detect rotation. The term “superconducting gyroscope” in this article refers only to a device whose working principle is the response of the superconductor itself to rotation, not to any device in which superconducting electronic components are used to detect some other effect. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366451

出版商:AIP    

年代:1997

数据来源: AIP