摘要:

An experimentally verified model for threshold current in GaAs/AlGaAs quantum well laser diodes has been extended to calculate for the first time the dependence of threshold current on stripe width. The lowest possible threshold is shown to occur when the lateral confinement factor is in the range of 55–60% for typical devices, a value that is not affected by mirror reflectivity or lateral index step. A simple, generalized optimization scheme for obtaining the unique width/length combination that results in lowest threshold is presented, and predicts potential as‐cleaved threshold currents as low as 0.5 mA.

ISSN:0003-6951    

DOI:10.1063/1.102887

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

New technique for optical generation of ultrashort electrical pulses in semiconductor heterostructures is proposed. It is shown that in asymmetric quantum well structures placed in a transverse magnetic field, optically excited carriers have an asymmetrical distribution ink‐vector space, and therefore, they have finite drift velocity in the direction perpendicular to both growth direction and field direction. It results in photogenerated voltage along the quantum well plane. The temporal response and sensitivity of the proposed scheme are evaluated, and possible applications are suggested in ultrafast detectors or as a tool for generation and study of hot carriers.

ISSN:0003-6951    

DOI:10.1063/1.102888

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Extremely high quality AlGaAs Bragg reflectors have been fabricated by molecular beam epitaxy using advanced growth techniques including phase‐locked epitaxy, short‐period superlattices, and growth interruptions. These techniques are used to control the layer periodicity, interface flatness, and producibility of the structures. The experimental reflectance spectrum shows an extremely square stop band and very regular side lobes closely matching the theoretical spectrum. A comparison of experimental to theoretical reflectance spectra is used to show that the layer periodicity is maintained within 1% and the interface flatness controls the optical loss per interface to less than 0.1%. Experimental results show a maximum reflectance of 98.5% for a (AlAs)6(GaAs)3/(AlAs)1(GaAs)435.5‐period Bragg reflector.

ISSN:0003-6951    

DOI:10.1063/1.102890

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Modifications to reduce the series resistance inp‐type semiconductor distributed Bragg reflectors (DBR) consisting of ten pairs of quarter‐wavelength GaAs (high refractive index)/Al0.7Ga0.3As (low index) layers were made by inserting an intermediate Al0.35Ga0.65As layer or a 200 A˚ superlattice of GaAs(10 A˚)/Al0.7Ga0.3As (10 A˚) at the GaAs/Al0.7Ga0.3As heterointerfaces. The specific DBR series resistance was reduced by two orders of magnitude to about 6.2×10−5&OHgr; cm2. These modifications did not alter the optical reflectivity and nearly identical reflection spectra were measured.

ISSN:0003-6951    

DOI:10.1063/1.102869

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Low‐threshold GaAs/AlGaAs lasers have, for the first time, been grown selectively on 10 &mgr;m stripe openings patterned in oxide on Si substrates. Lateral current confinement provided by side facets reduces edge leakage, and results in threshold currents as low as 75 mA for a 10 &mgr;m by 210 &mgr;m device, a nearly two‐fold improvement over comparable etched ridge waveguide lasers. Spectrum measurements show single longitudinal mode emission near 850 nm. This adaptation of selective heteroepitaxial growth for lateral current confinement of AlGaAs/GaAs lasers on Si substrates, adopted from similar work on GaAs substrates, offers potential for significant threshold current reductions of lasers integrable with Si.

ISSN:0003-6951    

DOI:10.1063/1.102870

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

An InGaAsP/InP superluminescent diode (SLD) emitting at 1.54 &mgr;m has been fabricated. The device uses a buried crescent structure on ap‐InP substrate. The parameters were optimized for high output power, small spectral modulation, and smooth far‐field operation. The coherence function of the SLD emission was studied systematically. An output power of 5 mW, a coherence length of 41 &mgr;m, and a second coherence peak suppression ratio of 22 dB were obtained.

ISSN:0003-6951    

DOI:10.1063/1.102871

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Slow compressional waves in fluid‐saturated porous solids offer a unique acoustical means to study certain material properties, such as tortuosity and permeability. We present a novel experimental technique based on the transmission of airborne ultrasound through air‐filled porous samples. The suggested method can be used to measure the velocity and attenuation of the slow compressional wave in a wide frequency range from 30 to 500 kHz. More important, the technique is so sensitive that it provides irrefutable evidence of slow wave propagation in air‐saturated natural rocks and lends itself quite easily to tortuosity measurements in such materials, too.

ISSN:0003-6951    

DOI:10.1063/1.102872

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

High resolution transmission electron microscopy and analytical electron microscopy show direct evidence for defect‐free interfaces produced byinsitucluster deposition of Au, Ag, and Ti onto ultrahigh vacuum‐cleavedn‐GaAs. In contrast to interfaces produced by atom‐by‐atom deposition, no specific interface reconstruction or orientation relationship and no change of stoichiometry of the GaAs near the interface was observed. Schottky barrier heights correspond to unusual Fermi level pinning positions in the upper half of the GaAs band gap, in clear contrast to values obtained for atom deposition and for diodes prepared by standard technology on GaAs (100). These results give clear evidence that Fermi level pinning for metal/GaAs interfaces formed without defects does not follow the predictions of current metal‐induced gap‐state models.

ISSN:0003-6951    

DOI:10.1063/1.102873

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

High‐resolution synchrotron radiation photoemission results for O2physisorbed on GaAs (110) show Ga‐O and As‐O formation that is a direct result of photon‐induced reaction at 20 K. Spatially resolved studies show that the thickness and chemical composition of the semiconductor oxides vary in proporition to total beam irradiation. The extent of reaction can be controlled by varying the amount of oxygen present on the surface, and As5+‐like bonding configurations can be formed. These results can only be understood when competition between thermodynamic, kinetic, photon‐ and electron‐mediated processes are considered.

ISSN:0003-6951    

DOI:10.1063/1.103259

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The emissivity of silicon wafers in a rapid thermal processing chamber has been measured as a function of the wafer temperature. Wafers with different surface roughness and layers have been studied. For transparent wafers, both sides of the wafer affect the emissivity. This emissivity is not only affected by surface roughness, but also by the layers deposited on the wafer. It has also been observed that while the emissivity increases rapidly as the temperature increases from its room value to 600 °C, the emissivity decreases with a slope of −8.89×10−5 °C−1for temperatures larger than 600 °C.

ISSN:0003-6951    

DOI:10.1063/1.102874

出版商:AIP    

年代:1990

数据来源: AIP