摘要:

We have measured the narrowest half‐width at half‐maximum photoluminescence linewidth of 2.8 meV, in 40‐period lattice‐matched In0.53Ga0.47As/In0.52Al0.48As multiple quantum wells, grown by molecular‐beam epitaxy with growth interruption. A simple analysis of the linewidth suggests that the structure has near perfect interfaces. Temperature‐dependent photoluminescence linewidth data indicate impurity incorporation due to the growth interruption. However, the high quality of the multiple quantum well is not impaired as is seen in the room‐temperature absorption data, where excitonic features up ton=3 sublevel are clearly seen. Carrier lifetime in this multiple‐quantum‐well system has been measured, we believe for the first time, using the picosecond photoluminescence correlation technique. A lifetime of 860 ps is obtained, which is similar to the value obtained for high‐quality GaAs/AlGaAs and In0.53Ga0.47As/InP quantum wells. This further confirms the high quality obtained in this ternary material system using growth interruption.

ISSN:0021-8979    

DOI:10.1063/1.348540

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

ZnS‐ZnxCd1−xS (x=0.56) superlattices with the same barrier (ZnS) thickness (47 A˚) and varied well (ZnxCd1−xS) thicknesses (23–80 A˚) were grown by molecular‐beam epitaxy. Reflection high‐energy electron diffraction patterns during the growth showed streaks, and superlattice structure was confirmed by the presence of satellites in the x‐ray diffraction profile. Low‐temperature photoluminescence (PL) peaks from near‐band‐edge emission shift to lower energy as the well thickness increases, suggesting that the emission is related to confinement in the wells. The full width at half maximum of PL lines increased with the increase in well thickness. A Raman spectrum from a single alloy layer showed two peaks (ZnS‐ and CdS‐like) which also appeared clearly in superlattice spectra. The positions of these two superlattice peaks shift from the single alloy value to higher energy as the well thickness decreases.

ISSN:0021-8979    

DOI:10.1063/1.348541

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Thin films of LixVO2(0≤x≲0.43) were made by reactive sputtering and annealing post‐treatment, followed by electrochemical cycling in an electrolyte containing LiClO4. The films showed electrochromism, and bleached under Li insertion. Weak thermochromism was observed with a drop of the transmittance, accompanied by a conductivity increase, at ∼60 °C.

ISSN:0021-8979    

DOI:10.1063/1.348542

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The optical properties of strained‐layer ZnSe/Zn0.86Cd0.14Se single quantum wells have been studied. The photoluminescence under direct and indirect excitation is investigated in detail. The temperature dependence of photoluminescence and resonant Raman scattering are investigated. Very strong 2LO‐phonon Raman scattering has been observed with Zn0.86Cd0.14Se quantum wells, where the scattered photon energy is in resonance with an exciton transition. Experimental exciton energies are compared with a finite‐square‐potential quantum‐well model including band nonparabolicity and the strain effect. Based on Hill’s theory [J. Phys. C7, 521 (1974)] we have computed the band gap of Zn1−xCdxSe as a function of compositionx.

ISSN:0021-8979    

DOI:10.1063/1.348543

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report room‐temperature measurements of the nonlinear absorption cross section, &sgr;eh, and the nonlinear refraction coefficient,neh, associated with saturation of excitonic absorption and bandfilling, for high‐quality multiple quantum well (MQW) structures in which each well consists of a highly strained, all binary (InAs)2(GaAs)5short‐period superlattice. The three samples studied, which have effective well thicknesses of 10.7, 14.8, and 18.8 nm, respectively, each display clearly resolved excitonic resonances at room temperature. Picosecond nonlinear transmission and transient grating measurements were performed on each sample in the spectral vicinity of then= 1 heavy‐hole excitonic resonance. The peak values ofnehand &sgr;ehextracted from these measurements are comparable to those measured in high‐quality GaAs/AlGaAs and unstrained InGaAs/InP MQWs. We determine the dependence of &sgr;ehandnehon the width of the quantum wells, and we discuss the fluence dependence of the nonlinearities. Consistency between the differential transmission and transient grating diffraction efficiency is demonstrated via a Kramers–Kronig analysis of the differential transmission spectra.

ISSN:0021-8979    

DOI:10.1063/1.348544

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The linear and nonlinear optical‐absorption coefficients and changes in refractive indices due to intersubband optical transitions in a modulation‐doped quantum well with an applied electric field are derived theoretically based on the density‐matrix formalism. The calculations of electron energy levels and envelope wave functions in a double‐confinement quantum‐well structure are discussed with electric‐field and screening effects. The electric‐field, screening, and tunneling effects on the electronic properties (electron energy levels and envelope wave functions) and optical properties (linear and nonlinear optical‐absorption coefficients and changes in refractive indices) are discussed with detailed numerical results. The comparisons between theoretical results and the corresponding experimental data show good agreement. The results presented here will be useful for high‐speed intersubband infrared photodetectors and electro‐optical modulators.

ISSN:0021-8979    

DOI:10.1063/1.348545

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Thin films of LiyV2O5(0<y<1) were made by reactive dc magnetron sputtering of V followed by electrochemical treatment in LiClO4. X‐ray diffractometry showed an orthorhombic structure that varied from nanocrystalline (n‐X ) for unheated substrates to polycrystalline (p‐X ) for substrates at 180 °C. Optical absorption was measured at 0.3<&lgr;<2.5 &mgr;m. The semiconductor bandgap lay fixed at ∼0.5 &mgr;m forp‐X  LiyV2O5and appeared blue‐shifted in proportion withyforn‐XLiyV2O5. At &lgr;>0.5 &mgr;m there are absorption peaks associated with V4+ions both forp‐Xandn‐Xmaterials, and a broad absorption feature forp‐XLiyV2O5that is tentatively ascribed to electron hopping in the crystallographicbdirection. The absorption goes up for increasedy, as expected from the higher V4+density.

ISSN:0021-8979    

DOI:10.1063/1.348546

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Deep‐level photoluminescence (PL) studies were performed on Si‐doped, metal organic chemical vapor deposition grown AlxGa1−xAs as a function of the most important growth parameters. The SiH4input mole fraction, the V/III ratio, and the Al fraction were varied over a wide range, resulting in net charge carrier concentrationsnranging between 1.8×1016and 4.5×1018cm−3, Hall mobilities &mgr;Hbetween 220 and 2400 cm2/V s, and a solid Al fractionxbetween 0 and 0.72. Two novel PL emissions for AlxGa1−xAs in the energy range of 1.05–1.35 eV were recorded. By a systematic analysis of the growth conditions these emissions were attributed to SiGa–SiAsand SiGa–VGacomplexes. The behavior of the broad PL emission at 0.8 eV as a function of the growth parameters was studied systematically. It was demonstrated that this emission is not related to the DX center. Instead, there are strong indications that it should be attributed to an internal transition within a native, or oxygen‐related defect.

ISSN:0021-8979    

DOI:10.1063/1.348547

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The photoluminescence and electrical behavior of Si‐doped AlxGa1−xAs has been investigated on various GaAs substrate orientations viz. (100)2°(110), (111)Ga, and (110). The growth has been performed by metalorganic chemical vapor deposition with a systematic variation of the silane input mole fraction, the V/III ratio and the aluminum fraction. It is found that the (110) layers show an abnormal electrical behavior especially in carrier concentration and mobility. On these layers also two new PL peaks have been found. By correlating all possible pair defects with the peaks as a function of the experimental conditions, these two peaks could be assigned to originate from aVAs‐AsGacomplex and aVAs‐SiAsorVAs‐SiGacomplex. The abnormal electrical results for (110) can be explained by the presence of these complexes.

ISSN:0021-8979    

DOI:10.1063/1.348548

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A method is presented which, through the simultaneous analysis of the photothermal deflection spectroscopy (PDS) signal amplitude and phase spectra, enables to detect surface states and buried interface states and to measure their absorption. A theoretical model for the PDS signal suitable for the present approach has been developed and the measurements were performed on single crystalline GaAs wafers with ion‐implanted layers on the front surface or buried beneath the front surface.

ISSN:0021-8979    

DOI:10.1063/1.348549

出版商:AIP    

年代:1991

数据来源: AIP