摘要:

We have calculated a new stable structure and the electronic structure of boron clusters in silicon crystal. According to our calculation, which was based on the first-principles local density functional approach forSi54B12H60clusters, the cubo-octahedralB12cluster was found to be more stable than the icosahedral one proposed previously. The total energy difference was about 4.6 eV. The analysis of the partial density of states showed that the cubo-octahedralB12cluster should act as a double acceptor. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118454

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Structural analysis was performed on a purple laser diode composed of In0.20Ga0.80N (3 nm)/ In0.05Ga0.95N (6 nm) multiple quantum wells, by employing transmission electron microscopy and energy-dispersive x-ray microanalysis, both of which are assessed from the cross-sectional direction. It was found that the contrast of light and shade in the well layers corresponds to the difference in In composition. The main radiative recombination was attributed to excitons localized at deep traps which probably originate from the In-rich region in the wells acting as quantum dots. Photopumped lasing was observed at the high energy side of the main spontaneous emission bands. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118455

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Effects of strong optical excitation on the properties of surface emission from an InGaN/GaN heterostructure grown by metal-organic chemical-vapor deposition have been investigated. An intriguing feature observed was that as the excitation intensity increased the surface emission spectrum evolved abruptly from a single dominating band to two dominating bands at a critical intensity. This phenomenon has a sharp phase transition or a switching character and can be accounted for by (i) the formation of an electron–hole plasma state in the InGaN vertical cavity under strong optical excitation, (ii) the photoreflectance effect (variation of index of refraction with excitation intensity), and (c) the Fabry–Pe´rot interference effect in the InGaN vertical cavity. These findings are expected to have impact on the design of the laser structures, in particular on the design of the vertical-cavity surface-emitting laser diodes based on III-nitride wide-band-gap semiconductors. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118456

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We calculated band structures of (11¯00)-oriented GaN with various strains. We found that introducing anisotropic strain in thecplane separates heavy- and light-hole bands. We also found that a tensile strain in the (11¯00) plane makes the light-hole band topmost. These two effects result in a reduction in the density of states at the valence-band edge. In this way we can significantly reduce the transparent carrier density to generate gain. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118457

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Epitaxy of Al films deposited on GaN has been studied using reflection high-energy electron diffraction (RHEED), atomic force microscopy (AFM), x-ray diffraction, and ion channeling techniques. Al (111) films have been found to grow epitaxially on GaN (0001) surfaces with Al ⟨21¯1¯⟩‖GaN⟨21¯1¯0⟩. For growth at 15 and 150 °C with a deposition rate of 0.26 Å/s, the epitaxial quality of the film was poor initially, as evidenced by the observation of diffuse RHEED patterns. After a few monolayers, a sharp and streaky RHEED pattern develops and is maintained during subsequent deposition, indicating an improvement in epitaxial quality with a two-dimensional growth mode. AFM studies indicate that the initial GaN surface quality is a significant factor in achieving epitaxial growth, and that the size of Al epitaxial islands increases substantially for higher growth temperatures. X-ray diffraction and ion channeling results confirm the epitaxial nature of the Al films in spite of a significant lattice mismatch of 10.2&percent;. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118458

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present a study of emission mechanisms and band filling effects in GaAs–AlGaAs V-groove quantum wires. A comparison of surface emitted photoluminescence (PL) and electroluminescence (EL) spectra from ap-i-njunction structure shows enhanced quantum wire emission in EL compared to PL. This behavior is discussed in terms of enhanced carrier capture by the quantum wire for electrical injection into the structure. With increasing forward bias current the quantum wire EL spectra exhibit subband filling and saturation effects. In addition to the ground state transition, at least three excited state related transitions are observed. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118459

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Quality of low-pressure chemical-vapor-deposited (LPCVD) oxide andN2O-nitrided LPCVD (LN2ON) oxide is investigated under high-field stress conditions as compared to thermal oxide. It is found that LPCVD oxide has lower midgap interface-state densityDit-mand smaller stress-inducedDit-mincrease than thermal oxide, but exhibits enhanced electron trapping rate and degraded charge-to-breakdown characteristics, which, however, are significantly suppressed in LN2ON oxide, suggesting effective elimination of hydrogen-related species. Moreover, LN2ON oxide shows further improvedSi/SiO2interface due to interfacial nitrogen incorporation. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118460

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The response of B-ion-implanted type-IIa diamond to light ion (H, He) irradiation is investigated by monitoring the sample resistance as a function of dose. It is found that the resistivity of the layer increases rapidly with increasing dose, and reaches the resistivity of the undoped diamond for irradiation doses much less than those required for the onset of damage related electrical conductivity in pristine diamond. It is shown that defects created by the nuclear stopping process act as compensating centers for the B acceptors. The present findings are of importance for the design of radiation hard diamond based electronic devices and suggests a method for the isolation of B-doped devices on a diamond chip. The results of the present work also explain why the collection distance in intrinsic nondoped diamond radiation detectors actually increases with increasing ion dose. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118461

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Three-terminal GaAs/InGaAs/GaAs pseudomorphic real-space transfer heterostructure employing graded channel as the emitter layer grown by low-pressure metal-organic chemical-vapor deposition has been fabricated. We observe controllable drain cut-in voltage characteristics with strong negative differential resistance. The largest peak-to-valley current ratio of the proposed device is about 33 000 at room temperature. Moreover, we observe an energy exchange effect between electrons. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118465

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The Te donor concentration has been used as a probe to infer the surface carrier concentration during growth by organometallic vapor phase epitaxy. With the partial pressure of Te held constant during the growth of annpnstructure, the Te concentration is found to remain nearly unchanged across thep-njunctions. This result is used to show that the carrier concentration at the growing surface shifts by a negligible amount as the growth is switched betweenn- andp-type GaAs. When combined with previous results forp-type GaAs, we conclude that the Fermi energy at the (100)-oriented surface remains pinned between 100 and 200 meV below the intrinsic Fermi energy, independent of the type or the concentration of dopant used. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118474

出版商:AIP    

年代:1997

数据来源: AIP