摘要:

We analyze the threshold properties of small area selectively oxidized vertical cavity lasers. Agreement for threshold gain versus laser size is found using the experimental intrinsic threshold voltage matched with a gain theory, as compared to a two-dimensional optical cavity simulation. Our analysis indicates the increasing threshold current density of small area lasers arises from both increasing threshold gain and the concomitant increasing leakage current. We further show that the optical loss can be reduced for lasers with areas as small as 0.25&mgr;m2while maintaining sufficient transverse optical confinement by displacing the apertures longitudinally away from the cavity and reducing the oxide thickness. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118234

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An amorphous silicon–germanium alloy (&agr;-SiGe:H) infrared photosensor with a Bragg reflector to obtain high optical gain and responsivity is demonstrated. The Bragg reflector containing &agr;-Si:H and &agr;-SiGe:H layers was grown on the top ofp-i-nstructure with an amorphous silicon/germanium alloy. All of the amorphous silicon and amorphous silicon–germanium layers were deposited by a low-temperature plasma enhanced chemical vapor phase deposition system. The experimental results of the new structures exhibit a much superior performance to that of conventionalp-i-navalanche photosensor structures. That is, the structure with a Bragg reflector shows a significant improvement in optical gain from 80 to 328 under the incident optical power of 1 &mgr;W, and the full width at half maximum can be reduced from 250 to 150 nm. ©1997 American Institute of Physics.   

ISSN:0003-6951    

DOI:10.1063/1.119070

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An increment of the x-ray flux in crystal Bragg–Fresnel lens (BFL) focus in backscattering geometry obtained by means of acoustic excitation of the BFL crystal substrate has been investigated. The dependence of the x ray’s total reflected power versus ultrasound parameters has been studied in a low frequency range (10–50 MHz). The proposed technique allows an increase in the flux in a BFL focus by a factor of 2 which almost achieves the kinematic limit. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118240

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present the design, analysis, and results of the high brightness electron beam experiments currently under investigation at Sandia National Laboratories. The anticipated beam parameters are the following: energy 12 MeV, current 35–40 kA, rms radius 0.5 mm, and pulse duration 40 ns full width at half-maximum. The accelerator is SABRE, a pulsed linear inductive voltage adder modified to higher impedance, and the electron source is a magnetically immersed foilless electron diode. 20–30 T solenoidal magnets are required to insulate the diode and contain the beam to its extremely small-sized (1 mm) envelope. These experiments are designed to push the technology to produce the highest possible electron current in a submillimeter radius beam. Design, numerical simulations, and experimental results are presented. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118217

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The first direct observation of the velocity distribution of the metastableAr+*(2G9/2)ions in the presheath of an inductively coupled plasma has been achieved by using the Doppler shifted laser induced fluorescence technique. Drift of the ions along the electric field in the presheath is observed and distribution functions of the velocity in both parallel and perpendicular directions, relative to the E field, are deduced at 5 and 40 mTorr. Present results show that in high density plasmas the velocity distribution of the metastable ions is directly related to that of the ground state argon ions. Neutral gas temperature of around 600 K is also measured from the absorption profile of a diode laser beam, set on one of the 772.4 nm argon lines. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118218

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Structural properties of alternating nanocrystalline silicon/amorphous silicon multilayers with visible light emission at room temperature were examined by means of x-ray diffraction. According to the linewidths and intensities of the diffraction peaks in the low- and high-angle ranges, we have determined the effective interface thickness, the mean crystallite sizes, and the internal strains, which are closely related to the photoluminescence in this material. In addition, the existence of the voids or holes was also observed, indicating that the improved electrical properties of this kind of hydrogenated nanocrystalline materials are due to the inhomogeneous structure of the material. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118219

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The dependence of the degree of supercooling(&Dgr;T−)of melts preceding the onset of solidification on the level of melt overheating(&Dgr;T+)above the equilibrium liquidus or melting temperature, is investigated on Sn and SnPb. We demonstrate the dependence of&Dgr;T−on&Dgr;T+can be either abrupt or continuous, depending on the length of holding time. In particular, the dependence is bounded by two discontinuous limits, and the known continuous linear relationship between&Dgr;T−and&Dgr;T+is only a special possibility. Our observations can be tentatively linked to the transient structural evolution of melts, and are probably general, occurring also for element Bi and SnSb. Our results may have important consequences for any thermal modeling of electronics manufacturing involving soldering operations. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118220

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

High resolution (“atomic”) images of clinochlore and muscovite have been obtained in aqueous solution by inducing an electric double layer between the atomic force microscope tip and the sample surface. The electric double layer is created by the addition of a surfactant to water and greatly improves image resolution. A theoretical model is proposed to explain the improved resolution. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118221

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The radiation damage introduced inn-GaAs by 4-MeV N+implantation at a dose of1×1015cm−2has been analyzed using micro-Raman spectroscopy. Implantation followed by annealing at 600 °C was found to produce a strongly compensated near-surface layer possessing a high crystalline quality. At the same time a pronounced disorder was found underneath the high-resistance layer which enables the fabrication of 2.5-&mgr;m thick free-standing membranes using selective electrochemical etching techniques.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118222

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have demonstrated a room-temperature silicon single-electron transistor memory that consists of (i) a narrow channel metal-oxide–semiconductor field-effect transistor with a width (∼10 nm) smaller than the Debye screening length of single electron; and (ii) a nanoscale polysilicon dot (∼7×7 nm) as the floating gate embedded between the channel and the control gate. We have observed that storingoneelectron on the floating gate can significantly screen the channel from the potential on the control gate, leading to a discrete shift in the threshold voltage, a staircase relationship between the charging voltage and the threshold shift, and a self-limiting charging process. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118236

出版商:AIP    

年代:1997

数据来源: AIP