摘要:

Surface emitting laser operation at room temperature at &lgr;=496 nm by ps pulsed optical injection has been demonstrated in a II–VI separate confinement heterostructure containing three 80 A˚ thick (Zn,Cd)Se quantum wells (QW). The vertical cavity was formed by low loss, dielectric, distributed Bragg mirrors, yielding a quality factor for the structure of approximatelyQ≊2000. The room‐temperature threshold excitation corresponds to an absorbed optical energy density of 1.4 &mgr;J/cm2or, equivalently, to an estimated electron‐hole pair density of 1×1012cm−2. AtT=200 K, quasicontinuous wave operation was obtained at an average output power of up to 1 mW and an output/input conversion efficiency of 20%. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115051

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Thin films of infinite layer compounds were prepared by molecular beam epitaxy. Defect layers were incorporated into the structure in order to dope the infinite layer phase. Hole type doping is usually observed. Resistivity measurements show that the conduction mechanisms change gradually with increasing doping level, from activational type to variable range hopping (or a mechanism governed by the Coulomb interaction between localized electrons) and then further to a mechanism related to weak localization which can be described by &Dgr;&rgr;=T−S, where the exponentSranges from 0.5 to 1.5. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115052

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present a study of the effective piezoelectric activity of thin ZnO films produced by radio‐frequency (rf) planar magnetron sputtering. The energetic plasma particles which bombard the substrate in the above deposition system increase the substrate temperature, thus causing a gradual variation in film structure during the beginning of the film growth. As a result, a precursor layer is formed which consists of small randomly oriented crystallites, exhibiting poor piezoelectric activity. Hence, the film thickness responsible for piezoelectric activity is generally less than the physical thickness of the film and is adjacent to a layer having different acoustic impedance. This leads to an increase in the resonant frequency of the film. For example, a film designed to have a half‐wave resonance at 288 MHz, was found to be resonant at 332 MHz. The poorly structured initial layer meant in this typical case that only 87% of this film volume exhibited piezoelectric activity. Investigations based on the substrate temperature, the optical losses, scanning electron microscope imaging, and rf electrical behavior are presented in this letter. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115053

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Highly conductive ruthenium oxide (RuO2) has been epitaxially grown on LaAlO3substrates by pulsed laser deposition. The RuO2film is (h00) oriented normal to the substrate surface. The heteroepitaxial growth of RuO2on LaAlO3is demonstrated by the strong in‐plane orientation of thin films with respect to the major axes of the substrate. High crystallinity of RuO2thin films is also determined from Rutherford backscattering channeling measurements. Electrical measurements on the RuO2thin films demonstrate a quite low room‐temperature resistivity of 35±2 &mgr;&OHgr; cm at deposition temperatures of above 500 °C. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115054

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Atomic resolution scanning tunneling microscope images of the (2×1) andc(2×2) reconstructions of CdTe(001) are presented. Both reconstructions can be described by a structural model in which the surface is terminated with 0.5 ML twofold‐coordinated Cd atoms. Step edges, domain boundaries and various types of point defects are characterized. The measurements indicate that the surface atoms are highly mobile at room temperature. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115055

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Heterojunctions of solid C70 andn‐ orp‐type crystalline Si have been made. Current–voltage measurements show that both C70/n‐Si and C70/p‐Si contacts are rectifying but their directions of rectification are opposite to each other. Thermal activation measurements at a fixed forward bias show an exponential dependence of current on the reciprocal of temperature, from which we determine the effective barrier height as 0.23 eV for C70/n‐Si and 0.27 eV for C70/p‐Si. Relative dielectric constant of solid C70 was determined to be 4.96 through the study of high‐frequency capacitance–voltage characteristics for Ti/C70/p‐Si structures. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115056

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The 9.5 eV bond energy of the nitrogen molecule makes it very difficult to break it up into atoms and incorporate in III–V nitride compounds grown by molecular beam epitaxy (MBE). By comparison, it is relatively easy to dissociate ammonia due to the existence of a catalytic effect on the GaN surface when there is Ga present. Using ammonia as the nitrogen source, we have achieved high quality GaN by MBE at a growth rate as high as 1 &mgr;m/h. This is an order‐of‐magnitude faster than previously reported using electron‐cyclotron resonance plasma‐assisted growth. Most importantly, our results indicate that there is no intrinsic limit to the growth rate of GaN using ammonia, a situation similar to that of conventional III–V MBE using gas sources. The unintentionaln‐type doping as low as 2×1017cm−3at room temperature. In addition, room‐temperature hole densities of 4×1017cm−3in Mg‐doped GaN films have been achieved without postgrowth annealing. Low‐temperature photoluminescence for both undoped and Mg‐doped GaN are dominated by near band‐edge emissions without deep‐level related luminescence, indicative of high quality materials. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115057

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Using electron paramagnetic resonance (EPR), we show the alignment of defect dipoles along the direction of the spontaneous polarization in polycrystallineBaTiO3ceramics by subjecting the capacitors to a dc bias at elevated temperatures. The alignment is demonstrated to occur via orientation dependent EPR signals in the polycrystalline perovskite lattice. The alignment of the defect dipoles is found to strongly enhance the light sensitivity of the defects. This observation may have important implications for photorefractive applications. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115058

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A sol‐gel spin‐coating procedure was established to prepare La0.5Sr0.5CoO3/ PbZr0.56Ti0.44O3/La0.5Sr0.5CoO3multilayer structure on SrTiO3(100) and LaAlO3(100) substrates. The films were characterized by means of x‐ray diffraction, scanning electron microscopy, and electrical measurements. The results showed the advantages of the sol‐gel processing in compositional control as well as in oriented growth of films. A high remnant polarization was obtained in the films prepared with this procedure. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.115059

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Molecular beam epitaxial growth of CaF2on Si(110) was studied using reflection high‐energy electron diffraction (RHEED) and scanning electron microscopy (SEM). An optimum substrate temperature range exists between 800 and 900 °C within which (110)‐oriented epitaxy can be sustained. At the initial growth stage, long strips of CaF2parallel to the [1¯10] direction are formed due to the growth anisotropy on the (110) surface. This is followed by the development of low‐energy {111} facets, producing a ridged and grooved surface morphology. Growth then proceeds via the stacking of {111} planes on the sidewalls of the ridges. This surface morphology is believed to result from the combination of favorable energetics in exposing the low‐energy {111} facets and the presence of twinned crystallographic domains. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.115060

出版商:AIP    

年代:1995

数据来源: AIP