摘要:

Strain-compensated InGaAsP/InGaP superlattices are studied in cross section by atomic force microscopy and scanning tunneling microscopy. Undulations in the morphology of the {110} cross-sectional faces are observed, and are attributed to elastic relaxation of this surface due to underlying strain arising from thickness and compositional variations of the superlattice layers. Finite element computations are used to extract a quantitative measure of the strain variation. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121165

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Evidence is presented for phase separation inIn0.27Ga0.73N/GaNmultiple quantum wells. After annealing for 40 h at a temperature of 950 °C, the absorption threshold at 2.95 eV is replaced by a broad peak at 2.65 eV. This peak is attributed to the formation of In-rich InGaN phases in the active region. X-ray diffraction measurements show a shift in the diffraction peaks toward GaN, consistent with the formation of an In-poor phase. A diffraction peak corresponding to an In-rich phase is also present in the annealed material. Nanoscale In-rich InGaN precipitates are observed by transmission electron microscopy and energy dispersive x-ray chemical analysis. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121166

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The exciton lifetime has been found to be repeatedly tuned by a MHz frequency acoustic driving without degradation of the optical properties of CdS crystals. The increase in the lifetime, up to 5&percent;, followed by its ∼20&percent; decrease has been detected with increasing driving amplitude. The lifetime increase can now be understood as due to reduction in the electron-hole wave function overlap in electric fields generated by the driving. The decrease in the recombination lifetime is ascribed to a widening of the potential well trapping the exciton due to variations in the local-crystal environment at acoustic driving. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121167

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We demonstrate photoluminescence (PL) from self-assembling InGaN quantum dots (QDs), which are artificially fabricated on AlGaN surfaces via metalorganic chemical vapor deposition. InGaN QDs are successfully fabricated by the growth mode transition to three-dimensional nanoscale island formation by using “antisurfactant” silicon on AlGaN surface. The diameter and height of the fabricated InGaN QDs are estimated to be∼10 nmand∼5 nm,respectively, by an atomic-force microscope (AFM). Indium mole fraction ofInxGa1−xNQDs is controlled fromx=∼0.22to∼0.52by varying the growth temperature of QDs. Intense photoluminescence is observed even at room temperature from InGaN QDs embedded with the GaN capping layers. In addition, from the temperature dependence of the PL-peak energy, we convincingly show that the PL emission actually comes from the InGaN QDs. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121168

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Resonant tunneling measurements are used to probe the inhomogeneous strain in individual SiGe quantum dots. Current–voltage characteristics of strained Si/SiGe resonant tunneling diodes of diameterD⩽0.25 &mgr;mexhibit additional fine quasi-periodic structure in the resonant peaks. The fine structure is consistent with lateral quantization in the SiGe quantum well due to in-plane confining potentials arising from inhomogeneous strain, which we calculate by finite element techniques for variousD. Quenching of the fine structure by a magnetic field is consistent with the effective length scale of the strain-induced potential. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121169

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

A diffraction analysis in the transmission electron microscope was carried out onInxGa1−xNlayers grown on (0001) sapphire by metalorganic vapor phase epitaxy on top of thick GaN buffer layers. It is found that the ternaryInxGa1−xNlayers can be chemically ordered. The In and Ga atoms occupy, respectively, the two simple hexagonal sublattice sites related by the glide mirrors and helicoidal axes of theP63mc symmetry group of the wurtzite GaN. The symmetry of the ordered ternary is subsequently lowered by the disappearance of these operations, and it is shown to agree with the P3ml space group. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121170

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

By using a back-gate operation, a high-quality two-dimensional electron gas (2DEG) is formed in an undoped GaAs/AlGaAs inverted heterostructure. A high mobility of around3×106 cm2/V sat 1.6 K is obtained for the structure without any compensating surface doping. The electron density is controllable down to7×109 cm−2.The relation between electron density and mobility is studied for samples both with and without a surface gate. The obtained results indicate that background impurities and an inhomogeneity of the electric field coming from the surface govern the mobility in a low-electron-density region and that the interface inhomogeneity becomes important at a high electron density. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121171

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We have clarified the effect ofH2andNH3on the passivation of Mg acceptor inp-type GaN films grown by metalorganic chemical vapor deposition. It has been found that the small amount ofH2carrier gas strongly influences the electrical property of the Mg-doped GaN films. Low-resistivityp-type GaN has been obtained byH2-free growth without any post-treatments. Its acceptor concentration is as high as that obtained by conventionalH2-rich growth with subsequent thermal annealing. It has also been clarified that hydrogen produced byNH3dissociation does not prevent Mg from electrically activating inH2-free growth. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121172

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We present a theoretical study on the angular and frequency distributions of the acoustic and optic-phonon generation by hot electrons during the terahertz-driven transport in a GaAs-based quantum well. Based on the detailed solution of the nonlinear balance equations in the presence of an oscillating electric field of arbitrary strength, we find that, when the system is exposed to an intense terahertz radiation, emissions of acoustic and optic phonons are significantly enhanced, especially along the polarized direction of the electric field. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121173

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Spectral shifts associated with ⟨100⟩ dark line defects of degraded II-VI laser diodes based on ZnCdSe/ZnSSe/MgZnSSe separate confinement heterostructures have been studied by spatially resolved cathodoluminescence at room temperature. Dark line defects were induced by electron-beam bombardment. Peak shifts as large as 2 nm were observed towards the blue or the red depending on the local circumstances. Peak widths usually became narrower after degradation. Redshifts and blueshifts are explained in terms of strain relaxation and Cd out-diffusion associated locally with degradation, as well as the kinetic energy dependence of the degradation-related carrier capture cross section. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.121174

出版商:AIP    

年代:1998

数据来源: AIP