摘要:

A modified epitaxial design leads to straightforward implementation of short (1&lgr;) optical cavities and the use of C as the solep‐type dopant in AlGaInP/AlGaAs red vertical‐cavity surface‐emitting lasers (VCSELs). Red VCSELs fabricated into simple etched air posts operate continuous wave at room temperature at wavelengths between 670 and 690 nm, with a peak output power as high as 2.4 mW at 690 nm, threshold voltage of 2.2 V, and peak wallplug efficiency of 9%. These values are all significant improvements over previous results achieved in the same geometry with an extended optical cavity epitaxial design. The improved performance is due primarily to reduced optical losses and improved current constriction and dopant stability. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115434

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Strained quantum‐well diode lasers emitting at 3.9 &mgr;m have been fabricated. The laser structure, grown on a GaSb substrate by molecular beam epitaxy, consists of compressively strained InAsSb active layers and tensile‐strained InAlAsSb barrier layers, surrounded by AlAsSb cladding layers. Broad‐stripe lasers have exhibited pulsed operation up to 165 K, with threshold current density of 78 A/cm2at 80 K. The characteristic temperature is 30 K up to 120 K. The devices operated cw up to 123 K, and the maximum cw power at 80 K is 30 mW/facet. Ridge‐waveguide lasers have operated cw up to 128 K, with cw threshold current at 80 K of 35 mA. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115435

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An innovative family of thin‐film photodetectors optimized for the ultraviolet (UV) spectrum is presented here. The devices are made of hydrogenated amorphous silicon (a‐Si:H) and silicon carbide (a‐SiC:H) on glass substrates. At room temperature, the photodetectors exhibit values of quantum efficiency of 21% in the vacuum UV and 0.08% at 750 nm, without external voltage. The great advantage of this technology lies in the possibility to produce low‐cost, large‐area arrays of photodetectors on glass or flexible substrates. All these features candidate thea‐Si/SiC:H photodetectors as possible, concurrent to specialized commercial devices. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115436

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Ablation of diamond by short UV pulses is reported. The ablation threshold for 500 fs pulses at 248 nm was found to be 0.6 J/cm2(equal to a peak intensity of 1.1 TW/cm2). Intensity‐dependent transmission measurements from low intensities to 100 GW/cm2showed that two‐photon absorption is the dominant nonlinearity in this range and the two‐photon absorption coefficient was measured to be (1.6±0.3) cm/GW. In the intensity regime above threshold (≳1 TW/cm2), however, low ablation rates indicate strong absorption by laser induced free carriers. The dynamics of diamond ablation was investigated time‐resolved using pump probe transmission and pulse pair ablation measurements. Ablation with short pulses at 248 nm is also compared to ablation with 15 ns pulses at 193 nm. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115437

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The possibility of hypersound generation by means of a double‐barrier resonant‐tunneling structure is suggested. The intensity of the generated sound is estimated. Prospects for phonon spectroscopy and acoustoelectronics based on the resonant‐tunneling devices are suggested. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.115438

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have investigated the effects of substrate misorientation towards (111)A, (111)B, and (011) on asymmetries in the strain relaxation of InxGa1−xAs, grown on (001) GaAs substrates by molecular beam epitaxy. For epilayers grown under conditions of two‐dimensional growth, we find large anisotropies in bulk strain relaxation and epilayer rotation about an in‐plane axis (epilayer tilt) in proportion to the degree of (111)A misorientation. The residual strain asymmetry is largest for the (111)A misoriented substrate (≳50%) and smallest for the (111)B misoriented substrate (<15%). At higher growth temperatures, the bulk strain relaxation becomes isotropic while the epilayer tilt remains sensitive to the offcut direction. At all temperatures, a preference for epilayer tilt toward the [110] direction for (011) misorientations is observed. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115439

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Various layered transition metal dichalcogenides were scanned with an optical‐lever atomic force microscope (AFM). The microscopic images indicate the occurrence of strong lateral stick–slip effects. In this letter, two models are presented to describe the observations due to stick–slip, i.e., either as a static or as a dynamic phenomenon. Although both models describe correctly the observed shapes of the unit cell, details in the observed and simulated images point at dynamic nonequilibrium effects. This exact shape of the unit cell depends on cantilever stiffness, scan direction, and detector direction. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115440

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Experimental determination of the free energy barrier to nucleation of amorphous‐to‐crystalline transformation reveals a selection principle for the average scale of crystalline microstructure of partially or fully crystallized materials prepared by crystallization of the amorphous precursors: it is determined by the free energy barrier to nucleation, and minimization of the free energy barrier leads to the formation of the finest crystalline microstructure. It is found that the nucleation at the temperature at which an amorphous alloy is crystallized with the finest crystalline microstructure is an isoenergetic process, the free energy barrier to the nucleation of crystallites at that temperature is contributed only by the entropic change. A model is developed to explain these observations that may provide a unified principle for designing materials with desirable scale of microstructure. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115441

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A chemical vapor deposition apparatus enhanced by electron cyclotron resonance plasma was employed to deposit nitrogen containing carbon films. In the apparatus, negative dc bias voltage was applied to the substrate for acceleration of positive ions toward the substrate. The deposition rate and nitrogen content of the film was found to be mainly dependent upon the deposition conditions. Although a large N2flow rate and bias voltage contribute to inhibit film growth through surface sputtering of the substrate, an optimum [N2]/([CH4]+[N2]) flow rate of 0.67 and a bias voltage of 50 V promote nitrogen implantation into the growing films through possible nitrogen ion bombardment. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.115442

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A model for the annealing of implantation‐induced structural disorder is proposed. The phenomenon is treated on the basis of a physical analogy between point defect cluster formation/dissolution in a crystal and droplet condensation/evaporation in a saturated vapor. Explicit relationships are obtained for diffusion broadening and drift of the dopant profile upon disorder annealing. The predictions of the droplet model are compared with experimental data on boron in silicon and are found to be accurate better than within a factor of 2 in the temperature range 800–1050 °C. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114627

出版商:AIP    

年代:1995

数据来源: AIP