共查询到20条相似文献,搜索用时 0 毫秒
1.
M. Meléndez-Lira I. Hernández-Calderón D. W. Niles H. Höchst 《Applied Physics A: Materials Science & Processing》1994,58(3):219-222
CdTe films have been grown on top of GaAs(100) by means of Molecular Beam Epitaxy (MBE) at 300 °C substrate temperature. Different procedures for the CdTe growth and for the preparation of the GaAs substrates resulted in diverse crystalline qualities of the CdTe films. We present the results obtained from PhotoReflectance (PR) measurements of these films employing HeNe and Ar-ion lasers as modulating excitation. For Ar excitation, the ratio of CdTe to GaAs signal strength for the E
0 transition is enhanced, allowing a differentiation of the contributions from film and substrate. Both the PR line shape and intensity are correlated to the structural quality of the CdTe films. One of the samples presented a below-band-gap transition of the GaAs substrate around 30±5 meV from E
0 which is attributed to donor states produced by Te atoms diffused in the interface; this result demonstrates the high sensitivity of the photoreflectance technique to the structural properties of interfaces. 相似文献
2.
J. Humliček F. Lukeš K. Navrátil M. Garriga K. Ploog 《Applied Physics A: Materials Science & Processing》1989,49(4):407-412
Multiple-angle-of-incidence ellipsometry at 632.8 nm and optical reflectance spectra are used to study GaAs/AlAs superlattices on GaAs substrates. The diagnostic potential of the two methods are compared to each other. Precise values of the total film thicknesses are obtained from the ellipsometric data. Significant disagreement between the measured and nominal thicknesses based on RHEED controlled MBE growth conditions is observed. Nonuniformity of a superlattice film is identified with the spatial resolution of about 1 mm2. The thickness variations are accompanied by pronounced variations of the optical constants. 相似文献
3.
Y. -H. Zhang N. N. Ledentsov K. Ploog 《Applied Physics A: Materials Science & Processing》1991,53(5):437-441
Two Mn-related luminescence peaks have been observed in a series of nominally undoped Ga0.47In0.53As/Al0.48In0.52As multiple quantum wells (MQW) grown lattice-matched on InP substrates by molecular beam epitaxy. These two peaks correspond to on-center and on-edge impurity states, respectively. The origin of the Mn impurities is outdiffusion from the Fe-doped semiinsulating InP substrate into the epitaxial layer. The binding energy of Mn acceptors, determined to be 53±3 meV in bulk-like Ga0.47In0.53As, increases to 80±5 meV for the on-center Mn state in a 58 Å MQW. The strong well-width dependence of the binding energy is explained in terms of the unique behavior of the Mn impurity in III–V semiconductors. The Mn in Ga0.47In0.53As and Ga0.47In0.53As/Al0.48In0.52As MQWs behaves predominantly as a deep impurity.On leave from: A. F. Ioffe Physicotechnical Institute, Leningrad, USSR 相似文献
4.
S. Kalem T. Curtis W.B. de Boer G.E. Stillman 《Applied Physics A: Materials Science & Processing》1998,66(1):23-28
1-x Gex single quantum wells (x=0.19) grown by rapid thermal chemical vapor deposition at 625 °C. A well-resolved strong excitonic
luminescence with TO-phonon and no-phonon transitions with a full width at half-maximum as low as 6 meV is observed for a quantum
well of 98 Å. The photoluminescence emission shows a significant blue shift and a broadening with excitation intensity. The
results are analysed in terms of localization of photoinduced charge carriers at the heterointerfaces.
Received: 11 September 1996/Accepted: 15 August 1997 相似文献
5.
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
6.
N. N. Ledentsov R. Nötzel P. S. Kop'ev K. Ploog 《Applied Physics A: Materials Science & Processing》1992,55(6):533-536
Hot exciton relaxation is observed in GaAs/Al
x
Ga1–x
As multiple quantum wells. The photolumnescence excitation spectra of the localized exciton emission at low temperatures and excitation densities are composed of narrow equidistant peaks exactly separated by the GaAs LO-phonon energy (36 meV). The relaxation mechanism via LO-phonons is found to be important for localized excitons in multiple quantum wells with GaAs layer thicknesses of about 50 Å, where pronounced alloy fluctuations in the barriers provide a strong additional lateral potential which suppresses the dissociation of hot excitons. 相似文献
7.
E. Tournie O. Brandt K. H. Ploog 《Applied Physics A: Materials Science & Processing》1993,56(2):109-112
We study the low-temperature photoluminescence (PL) of strained InAs single quantum wells (SQWs) embedded in a Ga0.47In0.53As matrix grown on InP substrates by modified solid-source molecular beam epitaxy. The spectra are interpreted in the frame of a two-level rate equation model describing the carrier dynamics in the structures. We show that band-filling occurs in these QWs for an excitation power as low as 30 Wcm–2. Moreover, the spectra reveal that the band-filling results from the rapid population of the hole subband. This observation highlights the low in-plane heavy-hole mass in the compressively strained film. Our results therefore demonstrate the high potential of InAs/Ga0.47In0.53As QW nonlinear optical devices operating in the mid-IR wavelength range. 相似文献
8.
This paper describes measurements of exciton relaxation in GaAs/AlGaAs quantum well structures based on high resolution nonlinear laser spectroscopy. The nonlinear optical measurements show that low energy excitons can be localized by monolayer disorder of the quantum well interface. We show that these excitons migrate between localization sites by phonon assisted migration, leading to spectral diffusion of the excitons. The frequency domain measurements give a direct measure of the quasi-equilibrium exciton spectral redistribution due to exciton energy relaxation, and the temperature dependence of the measured migration rates confirms recent theoretical predictions. The observed line shapes are interpreted based on solutions we obtain to modified Bloch equations which include the effects of spectral diffusion. 相似文献
9.
The microstructural and the optical properties of multiple closely stacked InAs/GaAs quantum dot (QD) arrays were investigated by using atomic force microscopy (AFM), transmission electron microscopy (TEM), and photoluminescence (PL) measurements. The AFM and the TEM images showed that high-quality vertically stacked InAs QD self-assembled arrays were embedded in the GaAs barriers. The PL peak position corresponding to the interband transitions from the ground electronic subband to the ground heavy-hole band (E1-HH1) of the InAs/GaAs QDs shifted to higher energy with increasing GaAs spacer thickness. The activation energy of the electrons confined in the InAs QDs increased with decreasing with GaAs spacer thickness due to the coupling effect. The present results can help to improve the understanding of the microstructural and the optical in multiple closely stafcked InAs/GaAs QD arrays. 相似文献
10.
We report a reflectance study on series of shallow quantum wells GaAs/AlxGa1−xAs types with different aluminium concentration. The observed barrier exciton reflectance line shape depends strongly on the shift in aluminium concentration in the two barriers, with the appropriate choice of the cap layer thickness. This observation was based on the reflectivity line shape analysis of anti-Bragg structures. 相似文献
11.
N. N. Ledentsov N. Tsukada K. Ploog 《Applied Physics A: Materials Science & Processing》1992,54(3):261-264
The luminescence associated with residual carbon acceptors in type-I (direct-gap) ultrathin-layer superlattices (UTLS) with well and barrier widths of 22.7<L
z<25.2 Å and 11.5<L
b<14.0 Å, respectively, is composed two lines reflecting the on-center and on-edge state of the impurities. In these narrow wells the on-center acceptor binding energy increases to 60 meV in agreement with theoretical calculations for GaAs single quantum wells using a valence band offset of 500 meV. While the binding energy of the on-center state does not vary significantly within the studied L
z and L
b range, the on-edge state shows a strong dependence on the very narrow barrier width. This increase of the acceptor binding energy makes the energy position of the impurity-related luminescence in UTLS very sensitive to the actual barrier height. Investigation of the impurity-related luminescence thus provides a versatile tool to determine the band offset ratio at the heterojunction. 相似文献
12.
R. Germar W. Dürr J. W. Krewer D. Pescia W. Gudat 《Applied Physics A: Materials Science & Processing》1988,47(4):393-398
We have used plots of the Auger amplitudes versus deposition time to investigate the growth mode of 3d-transition metals on
noble metal (100) surfaces. The systems considered are Fe/Cu(100), Fe/Au(100), Co/Cu(100), and Cr/Ag(100). We find that: 1.
The Auger plots consist of a succession of straight lines of constant length with sharp breaks in between, i.e. the growth
mode is essentially layer-by-layer. 2. From the experimental data points a slight rounding off in the vicinity of the break
points cannot be excluded, although a numerical analysis shows that the deviation from perfect layer-by-layer growth is less
than 10% of a monolayer for all systems considered. 相似文献
13.
M. Pérez Méndez J. Fayos F. Briones 《Applied Physics A: Materials Science & Processing》1989,48(5):471-473
A determination of the lattice parametersa
andb
of InAs/AlAs short-period strained-layer superlattices grown by Atomic Layer Molecular Beam Epitaxy (ALMBE) on GaAs(001) substrates has been performed by means of an X-ray precession camera using copper radiation. Spots belonging to the superlattice are clearly differentiated from those of the substrate, which confirms that they are partly decoupled from each other. It was also possible to resolve the lattice spots of InAs or In0.8Ga0.2 As decoupling buffer layers grown between the substrate and the superlattice. This technique proves to be very useful to characterize, in a very short time and with a reasonable resolution, highly mismatched epitaxial systems in which lattice parameters parallel to the interface play a crucial role in the understanding of the growing behaviour. 相似文献
14.
《Superlattices and Microstructures》1994,16(4):327-329
We have studied theoretically the electron-phonon scattering rates in GaAs/AlAs quantum wells which have additional thin AlAs layers in them using the dielectric continuum approach for the phonons. The confined and interface phonon modes and the intersubband electron phonon scattering rates of these structures have been calculated. The system with an additional AlAs layer is found to have intersubband electron scattering rates which are increased modestly as compared to those for the corresponding quantum well. These results show that scattering rates in general are expected to depend only weakly on the effects of system structure on the optical phonon spectra. 相似文献
15.
K. Fujiwara J. L. de Miguel L. Tapfer K. Ploog 《Applied Physics A: Materials Science & Processing》1987,44(4):323-328
Excitonic resonance structures in GaAs/AlAs multiple quantum well heterostructures with varying barrier-layer thicknessesL
B
down to 1.3 nm are investigated for two sets of samples with the nominal well widths ofL
Z
=9.2 and 6.4 nm, by 2K photoluminescence excitation spectroscopy. The observed resonance energies of then=1 heavyhole (1 hh) and light-hole (1 lh) free excitons imply that quantum confinement effects persist at least down to the decreased barrier-layer thickness ofL
B
=1.3 nm. This result is inconsistent with the red shifts expected from the simple well-coupling theory within the one-band Kronig-Penney model at the point. Instead, blue shifts of 6–8 meV (8–17 meV) are observed for the 1 hh (1 lh) excitonic resonance peaks whenL
B
is decreased from 10 to 2 nm. A relative decrease of the oscillator strength of the 1 lh transition compared to the 1 hh transition is also observed asL
B
is decreased. These results manifest important effects of the indirect-gap barrier material for the actual wavefunction matching across the interface and the breakdown of the envelope function approach to GaAs/AlAs quantum well heterostructures with ultrathin barriers. 相似文献
16.
J. Windscheif W. Wettling W. Jantz 《Applied Physics A: Materials Science & Processing》1988,47(2):115-118
It is demonstrated that ion implanted layers can be analysed prior to annealing by measuring the sub-bandgap optical absorption of the damaged lattice. The absolute value and lateral homogeneity of the implantation dose can be measured. The method is fast, nondestructive and compares favorably with existing measurement techniques. 相似文献
17.
18.
The effect of the surface preparation of the GaAs(110) substrate on the ZnSe epitaxial layer grown by molecular beam epitaxy
(MBE) was investigated by means of etch-pit density (EPD) measurements, surface morphology observation, and reflection high-energy
electron diffraction (RHEED) analysis. The ZnSe epitaxial layer grown on a GaAs(110) surface prepared by cleaving the (001)-oriented
wafer in ultrahigh vacuum (UHV) showed about 5×104 cm-2 of EPD. This value is much lower than that observed from both the samples grown on the mechanically polished surface with
and without a GaAs buffer layer. Due to the non-stoichiometric surface after thermal evaporation of the surface oxide, three-dimensional
growth can easily occur on the mechanically polished GaAs(110) substrate. These results suggest that the stoichiometric and
atomically flat substrate surface is essential for the growth of low-defect ZnSe epitaxial layers on the GaAs(110) non-polar
surface.
Received: 21 August 1998 / Accepted: 19 October 1998 / Published online: 28 April 1999 相似文献
19.
We have determined the minority carrier diffusion length in n-type and p-type GaAs epitaxial layers grown on GaAs substrates as well as on intentionally misoriented Si substrates by photocurrent spectroscopy. It is found that for heteroepitaxial GaAs-on-Si, the minority carrier diffusion length is limited by the amount of dislocation density irrespective of the doping level. The value of dislocation density obtained from diffusion length measurements agrees well with that obtained from the double-crystal x-ray diffraction measurements. 相似文献
20.
V. Demuth H.P. Strunk D. Wörle C. Kumpf E. Burkel M. Schulz 《Applied Physics A: Materials Science & Processing》1999,68(4):451-455
Received: 18 November 1997 / Accepted: 16 October 1998 / Published online: 24 February 1999 相似文献