摘要:

Both 1→2 and 1→3 intersubband transitions have been observed in a step quantum well structure consisting of 60 A˚ GaAs wells, 90 A˚ Al0.18Ga0.82As steps, and 280 A˚ Al0.44Ga0.56As barriers. The transition energy and oscillator strength are 112 meV and 0.23 for the 1→2 transition and 150 meV and 0.15 for the 1→3 transition, respectively. The asymmetric property of a step quantum well allows the normally forbidden 1→3 transition to occur. The relaxation of the selection rule suggests a possibility of using optical pumping for infrared laser applications.

ISSN:0003-6951    

DOI:10.1063/1.102610

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Spatially resolved Raman scattering measurements (<1 &mgr;m) have been performed to determine the surface temperature distribution on coated and uncoated facets of ridge‐waveguided GaAs/AlGaAs single quantum well graded‐index separate‐confinement heterostructure lasers. A strong nonlinear temperature versus output‐power dependence is observed for cleaved, uncoated mirrors (&Dgr;T>100 K forP>1 MW/cm2). Raman line scans show hot spot regions at the facets. Degradation strength correlates with facet heating. Disorder‐activated Raman phonon modes indicate strong crystal damage. Laser mirrors with &lgr;/2‐Al2O3coatings withstand up to 4–5 times the power density without significant heating and degradation. Local electroluminescence measurements along the cavity confirm increasing temperatures when approaching the facets and show that the resonator bulk material remains cold (&Dgr;T<5 K).

ISSN:0003-6951    

DOI:10.1063/1.102611

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The ionizing radiation dose rate response of GaAs junction field‐effect transistors (JFETs) cannot be explained by the usual photocurrent model. A model is proposed in which superhot electrons from a region of many tens of microns are collected ballistically over the repulsive built‐inP+gate barrier of irradiatedn‐JFETs providing a gate current of polarity opposite to that of the ordinary junction photocurrent. Steady state is established by inflow of thermal electrons from the source which increases the bulk electron concentration and causes a drift velocity saturated drain current through the substrate at positive drain voltages. Since collection range of holes is much shorter than of electrons,p‐JFETs do not exhibit this effect.

ISSN:0003-6951    

DOI:10.1063/1.102612

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Resonant Raman scattering with photon energies between 2.35 and 2.7 eV has been used to study both the alloy composition and local structural order in Hg1−xCdxTe forxvalues near 0.25 and for samples prepared by bulk growth, liquid phase epitaxy, molecular beam epitaxy, and metalorganic chemical vapor deposition. The resonance behavior of the HgTe‐like transverse optical and longitudinal optical (LO) modes, the CdTe‐like LO mode, and that of an additional mode probably due to preferential clustering of three Hg and one Cd about the Te sites, all indicate strong enhancement at theE1edge. However, surfaces annealed with a Nd:yttrium‐aluminum‐garnet‐pumped dye laser show strong suppression of the cluster mode (but not the LO mode) in all samples, which suggests that extremely rapid epitaxial regrowth may inhibit the 3:1 cluster formation.

ISSN:0003-6951    

DOI:10.1063/1.102613

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We experimentally demonstrate the firstp‐channel negative resistance field‐effect transistor. Low‐temperature current‐voltage characteristics exhibit negative differential resistance in the drain circuit which is controlled by the substrate voltage. The negative differential resistance is attributed to the real‐space transfer of holes.

ISSN:0003-6951    

DOI:10.1063/1.102564

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A SiGe three‐terminal hot‐hole transistor using a double‐barrier resonant tunneling structure as an emitter is fabricated. Injected carriers from the emitter are transferred near‐ballistically into the collector through a thin base. The demonstrated main feature of the device is a controllable negative differential resistance in the collector current. Utilizing the high‐speed characteristics of the tunneling process and negative differential resistance, integration of the device into Si technology could find applications in the areas of high‐speed digital circuits, frequency multipliers, and tunable oscillators/amplifiers.

ISSN:0003-6951    

DOI:10.1063/1.102565

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The application of ammonium sulfide chemical treatments for molecular beam epitaxy regrowth is examined. Reflection high‐energy electron diffraction, transmission electron microscopy, and capacitance‐voltage profiling techniques are used to investigate the regrown interface. A slight enhancement of the electron concentration is seen at the regrown interface due to the incorporation of residual sulfur atoms as donors. The amount of residual sulfur donors is a strong function of the substrate temperature at which regrowth is initiated.

ISSN:0003-6951    

DOI:10.1063/1.102566

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have fabricated a metal‐semiconductor‐metal Schottky photodetector on a semi‐insulating InP substrate using a nominally lattice‐matched In0.52Al0.48As/In0.53(GaxAl1−x)0.47As (graded)/In0.53Ga0.47As structure grown by molecular beam epitaxy. On average the graded quaternary layer enhanced the responsivity by about 35% compared to an identical device without the graded region, reaching a maximum of 0.45 A/W at 10 V applied bias. The associated dark current was 95 nA; the dark capacitance was 90 fF. High‐speed measurements with a gain‐switched 1.3 &mgr;m laser diode demonstrated an instrumentation‐limited impulse response of 50 ps.

ISSN:0003-6951    

DOI:10.1063/1.102567

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Magneto‐optical media using ultrathin Co/Pt and Co/Pd films were prepared on 2P (photopolymer) glass substrates with a double‐layer disk structure. Thermomagnetic writing was successfully made in the magneto‐optical disks by the relatively low laser power above 3 mW. The values of the C/N ratio were 50 dB for the Co/Pt disk and 45 dB for the Co/Pd disk at a bit length of 5 &mgr;m. Clear and regular bit domains were observed even in the shorter recorded bit length.

ISSN:0003-6951    

DOI:10.1063/1.102568

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A reaction, based on tungsten hexafluoride chemically reduced by silicon hydride vapors, has been developed for low‐temperature laser deposition of high‐purity tungsten. Compared to previous tungsten deposition methods, the new (pyrolytic) process requires very little thermal energy for initiation and propagation of the scanned reaction. WF6and SiH4(or Si2H6) mixtures have been optimized to yield tungsten interconnect lines with abrupt square cross section and conductivities of 12–25 &mgr;&OHgr; cm. Impurity levels are below the detection limits of Auger spectroscopy. Lines 3–20 &mgr;m in width and 0.1–4 &mgr;m in thickness are written at scan speeds of ∼100 &mgr;m/s. Argon‐ion laser powers (488 nm) are typically 30–60 mW, corresponding to reaction temperatures sufficiently low for direct writing on polyimide dielectrics.

ISSN:0003-6951    

DOI:10.1063/1.102569

出版商:AIP    

年代:1990

数据来源: AIP