共查询到20条相似文献,搜索用时 15 毫秒
1.
K. Ploog A. Fischer L. Tapfer B. F. Feuerbacher 《Applied Physics A: Materials Science & Processing》1991,52(2):135-137
We propose a new method to considerably reduce the overall growth interruption for high-quality GaAs single quantum wells during molecular beam epitaxy. The insertion of ultrathin AlAs smoothing layers at the constituent GaAs/Al
x
Ga1–x
As heterointerfaces and growth interruptions of not more than 15 s yields an improvement of the luminescence linewidth (FWHM) to 0.56 meV for a 13 nm wide GaAs well and to a value as low as 0.195 meV for a 27 nm wide GaAs well. In addition, no Stokes shift between absorption and emission and no line splitting due to monolayer fluctuations in the well width is observed. 相似文献
2.
3.
S. Balasubramanian I. Lahiri Y. Ding M.R. Melloch D.D. Nolte 《Applied physics. B, Lasers and optics》1999,68(5):863-869
The photorefractive response to an applied electric field is measured in a photorefractive quantum well, providing evidence
in favor of the nonlinear transport in the device due to the hot electrons. The reduced mobility of the hot electrons limits
the drift length, and thereby limits fringe overshoot. Thus the nonlinear transport prevents the slowing down of the grating
writing rate for increasing fields which is common in bulk photorefractives. The photorefractive phase shift in transverse-field
photorefractive quantum wells is measured as a function of the frequency offset between two laser writing beams that generate
moving gratings. The two-wave mixing passes through a maximum at an optimum frequency which depends on the magnitude and the
sign of the applied dc electric field. The phase shift associated with the moving grating adds or subtracts from the static
phase shift induced by hot-electron transport in the semiconductor quantum wells, depending on the sign of the field and the
sign of the dominant photocarriers. We observe a linear relationship between the roll-off frequency and the power of the writing
beams.
Received: 26 November 1998 / Revised version: 22 January 1999 / Published online: 12 April 1999 相似文献
4.
H. -J. Stock U. Kleineberg B. Heidemann K. Hilgers A. Kloidt B. Schmiedeskamp U. Heinzmann M. Krumrey P. Müller F. Scholze 《Applied Physics A: Materials Science & Processing》1994,58(4):371-376
Mo/Si multilayers are fabricated by electron-beam evaporation in UHV at different temperatures (30° C, 150° C, 200° C) during deposition. After completion their thermal stability is tested by baking them at temperatures (T
bak) between 200° C and 800° C in steps of 50° C or 100° C. After each baking step the multilayers are characterized by small angle CuK-X-ray diffraction. Additionally, the normal incidence soft-X-ray reflectivity for wavelengths between 11 nm and 19 nm is determined after baking at 500° C. Furthermore, the layer structure of the multilayers is investigated by means of Rutherford Backscattering Spectroscopy (RBS) and sputter/Auger Electron Spectroscopy (AES) technique. While the reflectivity turns out to be highest for a deposition temperature of 150° C, the thermal stability of the multilayer increases with deposition temperature. The multilayer deposited at 200° C stands even a 20 min 500° C baking without considerable changes in the reflectivity behaviour. 相似文献
5.
SiGe quantum dots (QDs) grown by ultra-high vacuum chemical vapor deposition using H2 and He carrier gases are investigated and compared. SiGe QDs using He carrier gas have smaller dot size with a better uniformity in terms of dot height and dot base as compared to the H2 carrier gas. There is a higher Ge composition and less compressive strain in the SiGe QDs grown in He than in H2 as measured by Raman spectroscopy. The Ge content is higher for He growth than H2 growth due to hydrogen induced Si segregation and the lower interdiffusivity caused by the more strain relaxation in the He-grown SiGe dots. The photoluminescence also confirms more compressive strain for H2 growth than He growth. Hydrogen passivation and Ge-H cluster formation play an important role in the QDs growth. 相似文献
6.
Structural, optical and electrical properties of ZnO and ZnO-Al2O3 films prepared by dc magnetron sputtering 总被引:1,自引:0,他引:1
X.Q. Meng W. Zhen J.P. Guo X.J. Fan 《Applied Physics A: Materials Science & Processing》2000,70(4):421-424
ZnO and ZnO-Al2O3 thin films were prepared by dc magnetron sputtering and their structural, optical and electrical properties were studied
comparatively. It is discovered that the ZnO-Al2O3 thin films remain transparent in a shorter wavelength range than the ZnO films, resulting from the increase of their band
gap. Their resistivity decreases by seven orders of magnitude, which is caused by doping of Al to ZnO grains in the film.
Preferential orientation of ZnO grains in the ZnO-Al2O3 thin films deteriorates because of the existence of Al2O3 impurity phase in the film.
Received: 5 January 1999 / Accepted: 11 October 1999 / Published online: 8 March 2000 相似文献
7.
W.H. Fan X. Hou W. Zhao X.J. Gao W. Zou Y. Liu 《Applied Physics A: Materials Science & Processing》2001,73(1):115-119
High-quality electron-trapping thin films CaS: Eu, Sm with red light output have been successfully deposited on quartz and
single-crystal silicon substrates by electron beam evaporation (EBE) and radio frequency (RF) magnetron sputtering in vacuum
and H2S partial pressures. Infrared upconversion efficiency of CaS: Eu, Sm thin films under different growth conditions has been
investigated by using ultrashort infrared (IR) laser pulse with 20 ps (full width at half-maximum (FWHM)). The results show
that upconversion efficiency of CaS: Eu, Sm thin films depends strongly on growth conditions in spite of the existence of
“exhaustion” phenomena. Microstructures identified by X-ray diffraction (XRD) indicate that crystallinity of CaS films relies
on both substrate materials and growth conditions. The stoichiometric composition of CaS films was measured by secondary-ion
mass spectrometry (SIMS). The post-annealing process was found to promote grain growth and activate strong luminescence so
that it could obviously improve upconversion efficiency of CaS: Eu, Sm films, even though it had negative influence on transmittance
and spatial resolution of these films.
Received: 5 June 2000 / Accepted: 7 June 2000 / Published online: 23 August 2000 相似文献
8.
Shape and stability of quantum dots 总被引:2,自引:0,他引:2
E. Pehlke N. Moll A. Kley M. Scheffler 《Applied Physics A: Materials Science & Processing》1997,65(6):525-534
} facets and a (001) surface on top. We compare to experiment and discuss the influence of growth kinetics on the shape.
Received: 21 March 1997/Accepted: 12 August 1997 相似文献
9.
W. Z. Shen W. G. Tang Z. Y. Li S. C. Shen T. Andersson 《Applied Physics A: Materials Science & Processing》1995,60(3):243-245
We report the first observation of well-resolved exciton peaks in the room-temperature absorption spectrum of the strained In0.20Ga0.80As/GaAs Single Quantum-Well (SQW) structure. The best fit of the exciton resonances gives the conduction-band offset ratioQ
c=0.70±0.05. The strength of the exciton-phonon coupling is determined from linewidth analysis and is found to be much larger than that of strained InGaAs/GaAs MQW structures. 相似文献
10.
N. Kalivas L. Costaridou I. Kandarakis D. Cavouras C.D. Nomicos G. Panayiotakis 《Applied Physics A: Materials Science & Processing》1999,69(3):337-341
The quality of a medical image depends, among other parameters, on quantum noise. Quantum noise is affected by the fluctuations
in the number of optical quanta produced within the phosphor, per absorbed X-ray (i.e. phosphor intrinsic-gain fluctuations).
This effect is considered by means of a factor, called in this study intrinsic-gain noise factor, IGNF(E). In existing theoretical
models of quantum noise, the corresponding factor is taken to be equal to one. In this paper, an expression that accounts
for the coefficient of variation of the phosphor intrinsic gain is introduced. This expression takes into account the process
of electron–hole pair conversion to optical photons and the frequency distribution function of the emitted optical photon
energy. Subsequently IGNF(E) is expressed in terms of this coefficient of variation. IGNF(E) has been calculated for several
phosphors and for various energies. For all medical X-ray energies studied, phosphors that exhibit a high relative fluctuation
of emitted optical photon energy, IGNF(E) exceeds by 2% to over 17% the corresponding factor of the existing theoretical models
of quantum noise.
Received: 25 March 1999 / Accepted: 29 March 1999 / Published online: 14 July 1999 相似文献
11.
Spatial arrangements of nano-islands (quantum dots) on the free surface of a composite two-layer substrate containing misfit
dislocations of edge type are theoretically examined. It is shown that the elastic interaction between misfit dislocations
and nano-islands is capable of causing coagulation of nano-islands. The coagulation of nano-islands is shown to be favourable
when the upper-layer thickness is smaller than a critical thickness, H0. An analytical form of H0 is presented for the partial case with four-to-one correspondence between nano-islands and cells of the misfit dislocation
network.
Received: 5 December 2000 / Accepted: 29 March 2001 / Published online: 20 June 2001 相似文献
12.
D. He W. Cheng H. Jia E. Xie X. Chen G. Wu 《Applied Physics A: Materials Science & Processing》2001,72(4):499-501
Silicon grain arrays were prepared using a pattern crystallization technique of pulsed KrF excimer laser irradiation. The
precursor material was hydrogenated amorphous silicon (a-Si:H) thin films deposited on single crystal Si wafers by plasma-enhanced
chemical vapor deposition. It was shown that Si grains with a uniform size and a well-defined periodicity embedded in the
a-Si:H matrix were obtained by this simple technique. The grain size was less than 2 μm. Relativly strong photo-luminescence
with two peaks at 720 and 750 nm was observed at room temperature. We expect to reduce Si grain sizes by optimizing the growth
conditions of a-Si:H thin films and controlling the temperature distribution in the film during laser irradiation.
Received: 21 November 2000 / Accepted: 12 December 2000 / Published online: 9 February 2001 相似文献
13.
M.K. Lee J.D. Song J.S. Yu T.W. Kim H. Lim Y.T. Lee 《Applied Physics A: Materials Science & Processing》2001,72(3):357-360
The influence of the InGaAs capping layer on the intermixing behavior of dielectric-capped In0.53Ga0.47 As/In0.81Ga0.19As0.37P0.63 multiple quantum wells (MQWs) was investigated by measuring the change in the photoluminescence spectra after rapid thermal
annealing. The magnitude of the energy shift in the transition energy from the first electronic sub-band to the first heavy-
and light-hole sub-bands of the MQWs is large when SiO2 and InGaAs hybrid capping layers are employed, but it is rather small when Si3N4 and InGaAs hybrid capping layers are employed. This result indicates that the InGaAs capping layer holds promise for applications
involved in the fabrication of integrated photonic devices, but only when it is incorporated with the SiO2 capping layer. The reason why the InGaAs capping layer behaves differently under the SiO2 and Si3N4 capping layers is also discussed.
Received: 4 December 1999 / Accepted: 26 September 2000 / Published online: 10 January 2001 相似文献
14.
M. Carrascosa F. Agulló-Rueda F. Agulló-López 《Applied Physics A: Materials Science & Processing》1992,55(1):25-29
A theoretical model based on the Dember mechanism is proposed to describe the steady state photorefractive gratings generated in semiconductor multiple quantum wells (MQW). It has been applied to an GaAs/AlGaAs MQW in parallel configuration (external electric field applied parallel to the MQW layers) for which recent experimental data are available. The model predicts a dependence of the first-order diffraction efficiency on the applied field in qualitative accordance with experiments, including the occurrence of saturation at high field values. Absolute values of the efficiencies are in good agreement with the experimental ones. Finally, high second-order diffraction efficiencies, associated with the development of a perpendicular space charge field, are also predicted by the model. 相似文献
15.
H. Hobert H.H. Dunken G. Peiter W. Stier M. Diegel H. Stafast 《Applied Physics A: Materials Science & Processing》1999,69(1):69-76
A large number of thin SiC films, prepared at different conditions by KrF excimer laser ablation of solid SiC targets and
deposition onto Si substrates (some onto quartz glass (QG) and yttrium-stabilized zirconia (YSZ)) were characterized by infrared
and Raman spectroscopy. The films consisted of nano- and microcrystalline SiC and contained nanocrystalline carbon in the
case of QG or YSZ substrates. Raman spectra of nanocrystalline SiC (grains <30 nm) reflect the phonon density-of-state function
of SiC by broad scattering effects at 220–600 and 650–950 cm−1. Medium-size crystallites are represented by a relatively narrow asymmetric band at 790 cm−1 and crystallites >200 nm by an additional asymmetric band at 960 cm−1. Small satellite bands at 760 and 940 cm−1, attributed to SiC surface layers, were resolved in some well-ordered samples. Optical modelling was needed to interpret
the IR spectra. SiC films could be represented by an effective medium model containing a SiC host phase and embedded particles
with free charge carriers. The crystalline order of SiC films can be estimated from the parameters of the SiC oscillators.
Received: 5 October 1998 / Accepted: 8 January 1999 / Published online: 5 May 1999 相似文献
16.
Strong ultraviolet and violet photoluminescence from Si-based anodic porous alumina films 总被引:5,自引:0,他引:5
J.H. Wu X.L. Wu N. Tang Y.F. Mei X.M. Bao 《Applied Physics A: Materials Science & Processing》2001,72(6):735-737
We have investigated photoluminescence (PL) from Si-based anodic porous alumina films formed by real-time controlled anodization
of electron-beam evaporated Al films. As-anodized samples show three strong PL bands at 295, 340, and 395 nm. These bands
blueshift and their intensities decrease after the samples are annealed. When the annealing temperature increases to 1000 °C,
the blueshift becomes specially pronounced and meanwhile the structures of the films develop toward crystalline Al2O3. Based on discussions on the thermal annealing behaviors of the PL and PL excitation spectra, we suggest that optical transitions
in oxygen-related defects, F+ (oxygen vacancy with one electron) centers, are responsible for the observed ultraviolet and violet PL.
Received: 24 July 2000 / Accepted: 24 February 2001 / Published online: 3 May 2001 相似文献
17.
Room-temperature direct-bandgap photoluminescence from strain-compensated Ge/SiGe multiple quantum wells on silicon 下载免费PDF全文
Strain-compensated Ge/Si0.15Ge0.85 multiple quantum wells were grown on an Si0.1Ge0.9 virtual substrate using ultrahigh vacuum chemical vapor deposition technology on an n +-Si(001) substrate.Photoluminescence measurements were performed at room temperature,and the quantum confinement effect of the direct-bandgap transitions of a Ge quantum well was observed,which is in good agreement with the calculated results.The luminescence mechanism was discussed by recombination rate analysis and the temperature dependence of the luminescence spectrum. 相似文献
18.
Room-temperature direct-bandgap photoluminescence from strain-compensated Ge/SiGe multiple quantum wells on silicon 下载免费PDF全文
Strain-compensated Ge/Si0.15Ge0.85 multiple quantum wells were grown on an Si0.1>Ge0.9 virtual substrate using ultrahigh vacuum chemical vapor deposition technology on an n+-Si(001) substrate. Photoluminescence measurements were performed at room temperature, and the quantum confinement effect of the direct-bandgap transitions of a Ge quantum well was observed, which is in good agreement with the calculated results. The luminescence mechanism was discussed by recombination rate analysis and the temperature dependence of the luminescence spectrum. 相似文献
19.
O.M. Hussain K. Srinivasa Rao K.V. Madhuri C.V. Ramana B.S. Naidu S. Pai J. John R. Pinto 《Applied Physics A: Materials Science & Processing》2002,75(3):417-422
Molybdenum trioxide thin films were prepared by reactive pulsed laser deposition on Corning 7059 glass substrates. The influence
of oxygen partial pressure and deposition temperature on the structure, surface morphology and optical properties of these
films was studied to understand the growth mechanism of MoO3 thin films. The films formed at 473 K in an oxygen partial pressure of 100 mTorr exhibited predominantly a (0k0) orientation,
corresponding to an orthorhombic layered structure of α-MoO3. The evaluated optical band gap of the films was 3.24 eV. The crystallite size increased with increase of deposition temperature.
The films formed at an oxygen partial pressure of pO2=100 mTorr and at a deposition temperature greater than 700 K exhibited both (0k0) and (0kl) orientations, representing α-β
mixed phases of MoO3. The films formed at an oxygen partial pressure less than 100 mTorr were found to be sub-stoichiometric with α-β mixed phases.
The investigation revealed the growth of polycrystalline and single-phase orthorhombic-layered-structure α-MoO3 thin films with composition nearly approaching the nominal stoichiometry at moderate substrate temperatures in an oxygen
partial pressure of 100 mTorr.
Received: 9 April 2001 / Accepted: 6 August 2001 / Published online: 17 October 2001 相似文献
20.
V.M. Farztdinov S.A. Kovalenko Y.A. Matveets N.F. Starodubtsev G. Marowsky 《Applied physics. B, Lasers and optics》1998,66(2):225-230
60 thin film was investigated in the energy range between 1.6 eV and 3.4 eV by a pump-supercontinuum probe (PSCP) technique
with a 40 fs time resolution. The relaxation rate showed pronounced spectral dependence, with a maximum at 2 eV in the region
of photo-induced darkening and at 2.4 eV in the region of photo-induced bleaching. The ultrafast relaxation rate decreased
with increasing pump-pulse intensity. We suggest that the observed decrease results from extraheating of the carriers in the
hu and t1u bands due to internal conversion from higher excited states, which are populated by two-step photon absorption of the intense
pump pulse.
Received: 2 May 1997/Revised version: 4 August 1997 相似文献