摘要:

Green light emission at room temperature was achieved from nonhydrogenated amorphous silicon–nitrogen (a-SiN) thin films. The films were deposited by cosputtering a silicon target covered with metallic erbium platelets in anAr+N2atmosphere. According to the deposition conditions, the nitrogen concentration [N] reached∼40 at. &percent;rendering an optical gap of approximately 3.5 eV while the Er concentration [Er] was estimated to be∼10 at. &percent;in the present films. The high [Er] associated to the optical band gap allows the direct excitation ofEr3+ions. This optical excitation is more efficient at low temperatures as a consequence of the reduction in nonradiative processes, and when exciting the samples with the 488.0 nm line of anAr+laser which is in resonance with the4F7/2Er3+energy level. In addition to light emission at∼520and∼545 nm,transitions in the infrared energy region could be easily verified in as-deposited samples. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121568

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Quantum cascade (QC) lasers emitting at&lgr;≈8 &mgr;mwith a power performance equal to short-wavelength(&lgr;≈5 &mgr;m)QC lasers are reported. The device improvement is mainly achieved by a design of the injector/relaxation region, which at laser threshold allows resonant carrier injection between the ground state of the preceding and the upper laser level of the subsequent active region. In pulsed operation a peak output power of 1.3 W per facet has been measured at 100 K. At room temperature a record peak power of 325 mW and a record slope efficiency of 180 mW/A have been measured. In continuous-wave operation the maximum power at 30 K was 510 mW per facet and still 200 mW per facet at 80 K. The high values of the output power and slope efficiency demonstrate the validity of the cascading scheme, in which electrons above threshold generate one photon per each active region they successively traverse. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121569

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We present a focused ion-beam (FIB) fabrication method for very clean and well-defined subwavelength fiber probes with metallic apertures of a desired diameter for use in near-field scanning optical microscopy. Such probes exhibit improved features compared to probes coated with metal by the conventional angled evaporation technique. Examples of FIB fabricated fiber probes are shown and images of a test sample are presented using one of the probes in a near-field microscope. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121570

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Room-temperature optical pumped lasing emission in the red, green, and blue has been obtained from ZnCdMgSe/ZnCdSe quantum well (QW) laser structures grown on InP substrates. The structures are nearly identical, except for variations in the thickness and/or composition of the QW layer. No other single set of semiconductor materials has been demonstrated whose structures are pseudomorphic on one single substrate, and produces light emitters throughout the entire visible range. Our results demonstrate the potential for these materials as integrated full color display devices. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121571

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A unidirectional electro-optic modulator based on an asymmetrical highly multimode waveguide coupler is proposed. To achieve high switching performance in a guided-wave coupler, a grating-based dumping wall is placed on the larger waveguide. This dumping effect makes the asymmetric highly multimode waveguide coupler possess a highly efficient unidirectional coupling process. A high modulation depth of 99&percent; is experimentally achieved at 633 nm wavelength with an index modulation of3.0×10−4.This device can be used for multimode optical interconnection systems such as data communications and fiber sensor networks. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121572

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In exploiting tribological applications of diamondlike carbons (DLC,a-C:H), both elastic and plastic properties must be optimized. We use tight-binding molecular dynamics to generate realization of DLC, from which can be obtained properties and their dependence on the precursors used, and on the H/C ratio. Here we analyze the elastic properties and especially the rebonding events which occur under strain. Rebonding occurs only at rather large strains; in some cases, it is reversible. Hydrogen has a key role in determining the number of carbons with less than four carbon neighbors, since it is mainly these carbons which participate in the major plastic (rebonding) events. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121573

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The atomic structure of ordered domains inBa(Mg1/3Nb2/3)O3and La-doped and undopedPb(Mg1/3Nb2/3)O3is studied by high-resolution Z-contrast imaging. The ordered domain structure in both doped and undopedPb(Mg1/3Nb2/3)O3is determined to be in agreement with the charge balanced random-layer model and inconsistent with the space-charge model. It is shown that La doping inPb(Mg1/3Nb2/3)O3enhances not only the domain size but also the degree of ordering. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121574

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Synchrotron-based x-ray topography (XRT) measurements have been used to study the initial stages of relaxation in ZnSe layers grown by molecular beam epitaxy on vertical gradient freeze Bridgman GaAs substrates. The formation of the very first strain-relieving misfit dislocations in the grown ZnSe layers has been detected in a layer of thickness 100 nm. No such dislocations have been observed in a corresponding layer of 95 nm thickness. The critical thickness for this material system is therefore estimated to be 97.5±2.5 nm, which is markedly lower than the widely accepted value of 150 nm. In contrast to the InGaAs/GaAs system, combined XRT and transmission electron microscopy studies indicate that the initial misfit dislocations observed for ZnSe/GaAs are not, in general, formed by the bending over of pre-existing threading dislocations into the interface, but by other mechanisms such as stacking fault decomposition. The critical thickness data obtained have been used to infer the maximum critical thickness of CdZnSe quantum wells possible in II–VI laser diodes. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121575

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report on a self-regulated method for the growth of tilted superlattices. It relies on the reconstructed surfaces alternatively stabilized during the atomic layer epitaxy (ALE) of compound semiconductors. Thec(2×2)+(2×1)Cd-stabilized and the(2×1)Te-stabilized surfaces alternatively formed during the ALE of CdTe and CdMn(Mg)Te ensure a self-regulation of the growth at 0.5 monolayer deposited per ALE cycle forbothCdTe and CdMn(Mg)Te. We are thus able to overcome the problem of precise flux control inherent to tilted superlattices. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121576

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

An ultrahigh vacuum scanning Kelvin probe force microscope (UHV SKPM) utilizing the gradient of electrostatic force, was developed based on an ultrahigh vacuum noncontact atomic force microscope (NC-AFM) capable of atomic level imaging, and used for simultaneous observation of contact potential difference (CPD) and NC-AFM images. CPD images of a Si(111) surface with Au deposited, clearly showed the potential difference in phases between7×7and5×2structures. When Ag was deposited as a submonolayer on the Si(111)7×7reconstructed surface, the atomic level lateral resolution was observed in CPD images as well as in NC-AFM topographic images. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121577

出版商:AIP    

年代:1998

数据来源: AIP