摘要:

The formation of stable molecules such asNH3, NO,N2O, and HCN as well as reactive transient species, e.g., NH,NH2andN3, resulting from the reactions of energetic N atoms with a residual background ofH2Oand hydrogen in cryogenic solidN2matrices at temperatures of 12–27 K has been studied in situ by Fourier Transform Infrared spectroscopy (FTIR). Bombardment of the matrix by N andN2neutrals with estimated energies between 20 and 120 eV produces a concentration ofN3radicals linearly proportional to the beam flux. The lower limit concentration of active N atoms stored in a cryomatrix has been derived from FTIR spectroscopic measurements. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366271

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present the results of measurements of the noise temperature of a heterostructure field-effect transistor (HFET) low-noise amplifier operating at 683 MHz in high static magnetic fields. These measurements indicate that the amplifier noise temperature increases from 4.2 K in zero field to 7.0 K at 3.6 T. The effect is highly dependent on the orientation of the amplifier with respect to the magnetic field. We propose an explanation of this effect in which the paths of the electrons in the HFET channel are altered due to the Lorentz force from the applied field, affecting the HFET transconductance. Calculations based on this model are shown to be consistent with our measurements. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366000

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Interface traps created by amorphous silicon(a-Si)deposition using dc magnetron sputtering or a microwave plasma-enhanced chemical vapor deposition method ontop-type crystalline silicon(c-Si)substrates in solar cell structures were studied by thermally stimulated capacitance. The trap properties (type, energy, and concentration) have been estimated as a function of various cell fabrication conditions. Plasma deposition ofa-Siis seen to induce electron traps when thec-Sisubstrates are pretreated with hydrofluoric acid, and hole traps when a thin oxide layer is initially present on thec-Si.A strong correlation is observed between the trap activation energies when electron trapping centers are present and the corresponding photoresponse of these solar cells. Solar cells with 10&percent; efficiency fabricated bya-Sisputtered at 64 W of power, exhibit3×1014 cm−3trapping centers with an activation energy of 0.44 eV. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366001

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

This article investigates the effects of asymmetric Fabry–Perot (AFP) cavity structures on the switching dynamics of symmetric self-electro-optic effect devices (S-SEEDs) made ofAlxGa1−xAs/GaAs(x⩽0.05)extremely shallow quantum wells (ESQWs). We analyze the switching dynamics of AFP ESQW S-SEEDs (AE-SEEDs) by means of an impulse photocurrent response function and corresponding voltage transients of the two AFPp-i(ESQWs)-ndiodes connected in series. The photocurrent response function is obtained by using an appropriate electron-hole pair generation rate and the Green’s function method. The response function includes the LO phonon scattering from bound to continuum states and the carrier transit in the continuum states. Large internal optical fields and thin intrinsic region thicknesses of AFP SEEDs reduce the required incident switching energy and operating voltage, respectively. Our analyses show that the switching energy of an impedance-matched AE-SEED is about3.0 fJ/&mgr;m2,while that of a conventional antireflection coated ESQW S-SEED (E-SEED) is about4.1 fJ/&mgr;m2.Considering practicalRCtime constants and device sizes, the switching time of an impedance-matched AE-SEED is found to be as low as 10 ps while that of an E-SEED is about 18 ps for the same incident energy of4.1 fJ/&mgr;m2.©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366002

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A low-energy (550 eV) argon-ion beam was used to directly bombard the backsurface of nitridedn-channel metal-oxide-semiconductor field-effect transistors (n-MOSFETs) after the completion of all conventional processing steps. The interface and oxide-charge trapping characteristics of the bombarded MOSFETs were investigated as compared to nonbombarded and reoxidized-nitridedn-MOSFETs. It was found that after bombardment, interface state density decreases and interface hardness against hot-carrier bombardment enhances, and oxide charge trapping properties were also improved. The improvements exhibit a turnaround behavior depending on bombardment conditions and could be attributed to stress compensation in the vicinity of theSi/SiO2interface and an annealing effect. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366007

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Detailed investigations of the device characteristics of poly-p-phenylene-vinylene (PPV) light-emitting diodes are reported. We analyze the influence of various hole- and electron-injecting electrodes on the current–voltage (I–V) characteristics and electroluminescence behavior. Our studies reveal that thermal conversion of the prepolymer on indium–tin–oxide (ITO) substrates leads—in contrast to conversion on Au and other high-work-function metals—to ap-type doping of PPV and, additionally, to the formation of an ohmic hole-injecting contact at the ITO/PPV interface. Hence, devices fabricated with low-work-function metals acting as the electron injecting contact (for example, Al and Ca) display Schottky behavior. These Schottky diodes are distinguished by a high rectification ratio&rgr;rof about106and display electroluminescence at bias voltages as low as 1.5 V for ITO/PPV/Ca light-emitting diodes. TheI–Vcharacteristics can be quantitatively described within the modified Shockley equation, taking into account the voltage drop on a serial resistance, yielding ideality factorsnranging from 1.6 to 2.4 for different devices. At high current densities, space-charge-limited currents determine the device characteristics. The hole mobility&mgr;his found to be of the order of10−5 cm2/V s. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366003

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Electrical impedance measurements on poly-p-phenylene-vinylene (PPV) light-emitting diodes in the frequency range between 100 Hz and 10 MHz are reported. A significant difference can be revealed between the device characteristics of light-emitting diodes eliminated on indium-tin-oxide (ITO) and those of other high-work-function metals (e.g., Au). Thermal conversion of the precursor polymer on ITO substrates results in ap-type doping of the conjugated polymer PPV. Hence, devices in the configuration ITO/PPV/Al display Schottky behavior, which can be modeled by a simple equivalent circuit of two RC elements in series, representing a bulk and a junction region. The low-frequency device capacitance displays a pronounced voltage dependence and, from a detailed analysis, the ionized acceptor concentrationNA,the diffusion potentialVD,and the width of the space charge regionwcan be obtained. Typical values forNAare1016–1017cm−3, and forVDwithin the range 1–1.5 V, resulting in a widthwof the space charge region at zero bias of about 50–150 nm. Via temperature-dependent investigations a transition from ap-type semiconductor Schottky diode at room temperature to a metal/insulator(polymer)/metal structure at lower temperatures is revealed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366004

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

DXcenters were investigated in Si dopedGa0.4Al0.6Asby capacitance-voltage(C-V)characterization, by deep level transient spectroscopy (DLTS), and by fast defect transient (FDT) measurements. Since the last method is capable of measuring transients in micro- and nanosecond ranges, it allowed us to measure transients ofDXcenters up to room temperature. The investigated samples were laser structures where only the cladding layer is doped by Si, so theDXcenters are localized within a few Debye lengths in the vicinity of the depleted layer edge. The capture and emission activation energies determined by capacitance DLTS and by FDT measurements are in agreement with the values reported in the literature, in contrast to our previous FDT measurements in bulk GaAlAs samples. The results suggest that the DLTS signal is dominated by transients in the vicinity of the depleted layer edge even in bulk samples. The differences between FDT measurements in bulk and laser structure samples are explained by the recently proposed Auger capture model of theDXshallow–deep transition. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365945

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Powder sample electron paramagnetic resonance (EPR) spectrum ofCr3+ions inYAlO3crystals contains off-axis extra lines, which do not belong to the principalX, Y,andZcomponents of the fine structure. Orientation dependence of the EPR spectrum ofCr3+dopedYAlO3single crystal confirms the existence of extra turning points corresponding to directions lying off theX, Y,andZaxes, consistent with theoretical predictions. This results in five EPR lines due to the transition between the central Kramers doublet in the powder system. The observed powder pattern EPR has been used in identification ofCr3+as an impurity ion in undopedYAlO3crystals. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366005

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Through the use of relations analogous to that of the Rayleigh law, it is demonstrated that the ac electric field dependence of the permittivity of ferroelectric thin films can be described. It is further shown that both reversible and irreversible components of the permittivity decrease linearly with the logarithm of the frequency of the ac field. The results demonstrate that the models describing the interaction of domain walls and randomly distributed pinning centers in magnetic materials can be extended to the displacement of domain walls in ferroelectric thin films. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366006

出版商:AIP    

年代:1997

数据来源: AIP