摘要:

GaxIn1−xAs quantum wire (QWR) arrays were grown on (100) on‐axis InP substrates by single‐step molecular‐beam epitaxy. The QWRs were formedinsituin (GaAs)2/(InAs)2.2short‐period‐superlattice (SPS) layers by the strain‐induced lateral‐layer ordering (SILO) process. An analysis of the cross‐sectional and plan‐view transmission electron microscopy images, photoluminescence peak energies, and polarization anisotropy has confirmed the QWR nature of these heterostructures. The SILO process occurs over a wide growth temperature range near 500 °C. However, both high and low growth temperatures result in a weaker lateral composition modulation. The strength of the lateral composition modulation is proportional to the total thickness of the SPS quantum‐well layers, regardless of the thickness of the individual quantum well. In other words, the magnitude of composition modulation accumulates when growth proceeds. A strain‐driven bulk solid‐state diffusion model has been proven to be part of the driving force of the SILO process, in addition to a dynamic surface diffusion during growth. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360507

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Understanding the coupling mechanism between SQUID (superconducting quantum interference device) loop and resonator in high‐frequency SQUIDs is essential for the application of these devices in sensitive magnetometers or controllable microwave devices. We have investigated, therefore, two kinds of planar microstrip tank circuit resonators: (1) S‐shaped &lgr;/2‐resonators with direct or indirect coupling to the SQUID loop with optional flux‐focussing pads and (2) conventional rf‐washer‐SQUID structures for which we have found resonant modes of the washer providing a coupling to the SQUID loop. A lumped element representation of SQUID loop and resonator is presented in order to describe the effective SQUID‐resonator coupling in case of direct or indirect coupling. According to this approach, the square of the effective coupling constantkin both cases is equal to the ratio of the magnetic energy stored in the SQUID loop to that stored in the resonator. For the indirect coupled S‐shaped &lgr;/2‐resonators,kcan be described in terms of a geometry‐defined mutual inductance. The predictions of the lumped element description are compared with simulations using a standard full‐wave analysis computer program in order to quantify the effect of the different layouts on microwave current distribution and onk. A method for the determination ofkby simulation is described, leading to useful design rules for the optimization of high‐frequency SQUIDs. The simulation results will also be compared with experimental data. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360508

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

This work deals with the study of the ‘‘trapping noise,’’ that is the low frequency noise caused by the random capture and release of carriers by localized traps. A numerical method, based on the linearization of the semiconductor device equations, is presented which allows one to determine the parameters of the Lorentzian noise spectrum due to a single trap inside a semiconductor device as a function of the position of the trap, of its activation energy and of the biasing conditions. The occupied trap is simulated by adding a single ionized shallow acceptor at the position of the trap. The method allows one to also determine the spectral density of the noise due to a general distribution of noninteracting traps inside the considered device. Numerical tests on elementary semiconductor devices are included to validate the proposed scheme and the trapping noise is then studied on a simple junction field effect transistor. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360509

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The most important mechanism of dark current inn‐doped quantum‐well infrared photodetectors (QWIPs) is due to interaction of electrons with longitudinal optical phonons. Theoretical expressions are derived for the carrier lifetime, and for generation currents originating from both photoexcitation as well as from thermal excitation in a single quantum well. Detector gain is discussed briefly. Calculated values of thermal generation currents and the ratio of photocurrent to thermal current are found to accord well with experimental data. Finally the conditions of background radiation limitation of QWIPs are investigated and the theory gives a temperature of background radiation limitationTBLIP=81 K for a 9 &mgr;m cutoff detector with a two‐dimensional grating and optical cavity, for 300 K background temperature, opticsfnumber=1 with 100% optical transmission, provided that a photocurrent to dark current ratio of 1 criterion is used. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360510

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Through the use of a novel vertically integrated resonant‐tunneling diode (RTD) heterostructure we have established experimentally the relationship between intentional variations in the structural parameters of the pseudomorphic In0.53Ga0.47As/AlAs resonant tunneling diode (i.e., barrier thickness, quantum‐well thickness, quantum‐well composition, and doping density) and the measured current–voltage characteristics of the device. Based upon the results of these experiments, we have determined that a 1 monolayer increase in AlAs barrier width, InGaAs quantum‐well width, or InAs subwell width results in a peak current reduction of 56%±7%, 19%±2%, and 18%±3%, respectively. Further, a 1% decrease in indium mole fraction of the InGaAs quantum well has been found to increase the peak current by 10%±1%. Sensitivity parameters have been tabulated for both the peak current and the peak voltage of the RTD. Through the use of these parameters, the maximum allowed fluctuation in the RTDs structural parameters has been estimated for a given tolerance in the RTDs electrical characteristics. Further, these data can also be used to evaluate the feasibility ofinsituepitaxial growth control of resonant tunneling devices. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360511

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A modified Fabry–Perot resonance technique using a single cavity was proposed to obtain the propagation loss of the optical waveguide. The propagation loss as well as the facet reflectance were measured without sequential cleavage for a GaAs/AlGaAs strip‐loaded waveguide based on the contrast ratios of the reflected and transmitted interference patterns. ©1995 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.360729

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Pb(Ti0.48Zr0.52)O3films produced by pulsed laser ablation deposition have been locally examined for their homogeneity and thickness through a comparative use of Raman and infrared spectroscopy. Raman scattering intensity appears to be an oscillating function of the position of the point under measurements. The observed oscillations were explained by light interference effects in the film and used to obtain the thickness profile and the refractive index dispersion of the film. The intensity distribution in Raman spectra across the film differs from that of the target. This difference is larger at the center than near the edge of the film. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360512

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have studied magnetic domain structure in (YSmLuCa)3(FeGe)5O12garnet thin film by using magnetic force microscopy (MFM). Domain wall contrast of bubble domains has been revealed using Permalloy–Fe double‐layer thin‐film tips. We have also observed that nanometer scale deformations of the surface disturb a magnetic bubble structure by introducing stripe domains. MFM images have shown that stripe domains pin their domain walls to surface scratches. The domains can change their location with respect to a scratch by switching a domain wall pinned to a scratch. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360513

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have measured the diamagnetic shift of band‐edge luminescence, no‐phonon peak, and phonon sideband from a pseudomorphic, undoped Si0.83Ge0.17/Si quantum well using high‐field magnetoluminescence spectroscopy. The quadratic dependence of the diamagnetic shift of the no‐phonon luminescence peak suggests that the luminescence originates from excitons. Using a variational calculation, we determine the effective heavy‐hole mass and the exciton binding energy to be 0.27m0and 14.8 meV, respectively, and compare these results with reported values obtained from other measurement techniques. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360514

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The index of refraction of Cd0.9Mn0.1Te was measured at a wavelength of 10.25 &mgr;m at room temperature on twinned unoriented monocrystal samples. The result wasn=2.57±0.01. Furthermore, the temperature dependence of the index of refraction was measured to be (1/n)dn/dt=5.0±0.1×10−5K−1. The optical absorption coefficient was &agr;=0.13 cm−1. Finally, the linear expansion coefficient in the range of 293–373 K was found to be &ggr;=−1±1×10−6K−1. ©1995 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.360515

出版商:AIP    

年代:1995

数据来源: AIP