摘要:

We study the evolution of AlGaAs/GaAs growth during organometallic chemical vapor deposition on pyramidal recess patterns etched into GaAs{111}Bsubstrates. Cross-sectional atomic force microscopy clearly demonstrates the self-organized growth behavior in the inverted pyramid structures. During AlGaAs deposition, the side corners and the tip of the pyramid sharpen up to a self-limited radius of curvature of less than 10 nm. In addition, vertical Ga-rich AlGaAs quantum wells are formed at these corners. Subsequent GaAs growth results in the formation of GaAs quantum wires along the corners of the pyramid. These wires meet at the tip of the pyramid, forming a quantum dot structure at this point. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119882

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We investigate why high levels of hydrogen dilution of the process gas lead to enhanced light soaking stability of amorphous silicon(a-Si) alloy solar cells by studying the microstructural properties of the material using high-resolution transmission electron microscopy (TEM) and Raman spectroscopy. The TEM results show thata-Sialloy (with or without hydrogen dilution) is a heterogeneous mixture of amorphous network and linear-like objects that show evidence of order along their length. The volume fraction of these ordered regions increases with increasing hydrogen dilution. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119928

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Electron field emission from allotropes of carbon (graphite, diamondlike carbon, and diamond) have been reported many times in the literature. This work explores the use of ion irradiation for improving electron field emission from carbon fibers. Carbon fibers have been irradiated with H, C, Ar, and Xe ions. Field emission characteristics have been measured as a function of ion dose. A reversible reduction in the required field for a fixed current level has been observed. The critical dose,Dc,defines the dose corresponding to the lowest field necessary to emit a fixed current (5 &mgr;A). The critical dose appears to correlate with the nuclear energy loss (collisions with atoms) of the ion in the carbon fiber. Transmission electron microscopy and parallel electron energy loss spectroscopy analysis indicate an amorphous surface, and an increase in thesp3content of the fiber surface to 20&percent;–30&percent;. A corresponding decrease in the work function is expected and may account for the improvement in electron emission. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119883

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Fast proton-conductingP2O5–ZrO2–2SiO2glasses were successfully prepared by the hydrolysis of metal alkoxides. The glasses obtained by heating at 150 to 400 °C are chemically stable and exhibit high conductivities of∼104 S/cmat room temperature, conductivities that are higher by∼4order than that of glasses containing noP2O5.These high conductivities were regarded as the fast proton transfer accelerated by molecular water bonded with POH groups. These glasses have a high potential for practical applications. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119884

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Amorphous-hydrogenated boron (a-B:H) and carbon (a-C:H) thin films were prepared by radio-frequency plasma deposition using(B2H6+H2)orCH4as a precursor gas. The film composition and density were investigated by ion-beam analysis. The films were eroded by hydrogen electron cyclotron resonance plasmas at floating potential and by atomic hydrogen dissociated by a hot filament. The temperature of the substrates was increased during the erosion process from 330 to 680 K. Erosion rates were measuredin situby ellipsometry.a-B:Hfilms are shown to be much more resistant to erosion by hydrogen ions(H+)and atomic hydrogen(H0)thana-C:H films. In contrast toa-C:Hfilms, no chemical erosion ofa-B:Hfilms byH0was observed at temperatures below 600 K. Ion energies lower than the threshold energy for physical sputtering cause measurable erosion rates fora-B:Hfilms. It is concluded that this is a synergistic effect of simultaneousH0andH+bombardment and it is designated as ion-induced chemical erosion. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119885

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Highly oriented and columnar grained diamond layers only a few microns thick, deposited at different substrate temperatures (500, 550, and 800 °C) on silicon using microwave-plasma-assisted chemical vapor deposition, are investigated by special photothermal techniques and high-resolution transmission electron microscopy (HRTEM). Small effective diamond–silicon boundary resistances of<4×10−9 m2 K/Ware determined for thermal conduction normal to the interface. Thermal conductivities normal to the interface,k⊥,are found to be about an order of magnitude greater than the conductivities parallel to the interface,k∥(k⊥/k∥=9–18).The boundary resistances measured are in good agreement with limits estimated from the interface structure observed by HRTEM, which indicate a low near-interfacial disorder for the layers. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119886

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Charge carrier transport in vapor-deposited films of 1,6,7,12-tetraphenoxy-N,N′-bis-(2,6-diisopropylphenyl)-perylene-3,4,9,10-bis(dicarboximide) was investigated using two different methods, the time-of-flight (TOF) technique and time-resolved electroluminescence. Electron mobilities of10−5 cm2/V swere measured in the bulk using a time-of-flight technique. Hole transport was found to be dispersive and, thus, a transit time for holes could not be obtained. The above dye was also used to fabricate single layer light emitting diodes showing clearly visible red electroluminescence under ambient conditions. Our experiments on transit electroluminescence confirmed the measured electron mobility and ruled out the possibility that the transit time of holes is shorter than the time range investigated in our time-of-flight experiments. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119929

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We study ionic conductivity of the model composites, copper(I) bromide-titanium dioxyde, in a large domain of composition. The experimentally observed enhancement of conductivity is interpreted by a numerical model taking into account grain size effects and interactions between ionic conductor and insulator grains. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120418

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have observed optical scintillations and corresponding electric current pulses when uniformly heating potassium titanyl phosphate (KTP) crystals at 0.1–0.4 K/s over the temperature range 8–300 K. The scintillations correspond to molecular nitrogen emission occurring during the electrical breakdown of air near the crystal surface, and imply the existence of pyroelectrically induced peak electric fields at the crystal surface exceeding 30 kV/cm, which is ten times larger than dc electric fields reported to induce electrochromic (EC) damage in this material. Recent optical damage studies on KTP under high repetition rate, high average-power laser irradiation reveal an EC-like damage, implying the existence of an internal electric field arising during laser irradiation. Our observation of a sizable total pyroelectric response suggests one possible mechanism for the origin of these internal fields in KTP and other nonlinear optical materials. ©1997 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.119887

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Polycrystalline(1−x)Ta2O5–xAl2O3thin films were fabricated by metalorganic solution deposition technique on Pt-coated Si substrate at a temperature of 750 °C. Thin films with0.9Ta2O5–0.1Al2O3composition exhibited improved dielectric and insulating properties compared toTa2O5thin films. The measured small signal dielectric constant and dissipation factor at 100 kHz were 42.8 and 0.005, respectively. The temperature coefficient of capacitance was 20 ppm/°C in the measured temperature range of 25–125 °C. The leakage current density was lower than6×10−8 A/cm2up to an applied electric field of 1 MV/cm. A charge storage density of18.9 fC/&mgr;m2was obtained at an applied electric field of 0.5 MV/cm. The high dielectric constant, low dielectric loss, low leakage current density, and good temperature and bias stability suggest(1−x)Ta2O5–xAl2O3thin films to be a suitable dielectric layer in integrated electronic devices in place of conventional dielectrics such asSiO2orSi3N4.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119888

出版商:AIP    

年代:1997

数据来源: AIP