共查询到20条相似文献,搜索用时 15 毫秒
1.
T. H. Chen Y. S. Huang T. S. Shou K. K. Tiong D. Y. Lin F. H. Pollak M. S. Goorsky D. C. Streit M. Wojtowicz 《Physica E: Low-dimensional Systems and Nanostructures》2000,8(4)
We have characterized the properties of three AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor structures with two different well widths fabricated by molecular beam epitaxy on (0 0 1) GaAs substrates with different threading dislocation densities using room temperature photoreflectance (PR) and photoluminescence (PL). The samples were denoted as A, B and C with well widths of 140, 160 and 160 Å, respectively. Samples A and B were grown on substrates with lower threading dislocation densities. For samples B and C, the well width exceeds the pseudomorphic limit so that there is some strain relaxation and related misfit dislocations, as determined from X-ray measurements. In order to detect the anisotropic strain of the misfit dislocations related to strain relaxation, the PR measurements were performed for incident light polarized along [1 1 0] and
directions. Evidence for the influence of the strain relaxation upon the relaxed channel was provided by the observed anisotropy of the polarized PR features and reduction of the intensity of PL signals in the InGaAs channel layer. The lowest lying intersubband transition has been confirmed by a comparison of the PR and PL spectra. Signals have been observed from every region of the sample making it possible to evaluate the In and Al compositions, channel width and two-dimensional electron gas density as well as the properties of the GaAs/AlGaAs multiple quantum well buffer layer. 相似文献
2.
3.
Jia-Ren Lee Chien-Rong Lu Wei-I Lee Shih-Chang Lee 《Physica E: Low-dimensional Systems and Nanostructures》2005,25(4):562-568
We studied self-assembled InAs/GaAs quantum dots by contrasting photoluminescence and photoreflectance spectra from 10 K to room temperature. The photoluminescence spectral profiles comprise contributions from four equally separated energy levels of InAs quantum dots. The emission profiles involving ground state and excited states have different temperature evolution. Abnormal spectral narrowing occurred above 200 K. In the photoreflectance spectra, major features corresponding to the InAs wetting layer and GaAs layers were observed. Temperature dependences of spectral intensities of these spectral features indicate that they originate from different photon-induced modulation mechanisms. Considering interband transitions of quantum dots were observed in photoluminescence spectra and those of wetting layer were observed in photoreflectance profiles, we propose that quantum dot states of the system are occupied up to the fourth energy level which is below the wetting layer quantum state. 相似文献
4.
The artificial random Gaussian-type potential built in the GaAs/AlGaAs superlattices grown by molecular beam epitaxy was explored by various methods. The effect of the intentional disorder was shown to dominate intrinsic superlattice imperfections and its impact on the electronic properties was found to be in good agreement with the theoretical predictions. It was demonstrated that the modern state of the molecular beam epitaxy allows for a growth of the superstructured materials with well-defined disorder strength. 相似文献
5.
The photoluminescence (PL) at low temperature of three delta-doped AlGaAs/GaAs heterostructures is investigated under continuous and pulsed excitations. The PL under continuous excitations allows the identification of the trapping centres and probes the carrier's transfer to the GaAs channel. The time-resolved photoluminescence (TRPL) inquires about carrier dynamics and gives radiative lifetimes of different levels. The DX level shows two time constants of the intensity decay relating the splitting of the valence band under impurity strains which reduce the crystal symmetry. The two time constants evolve with temperature and exhibit an increase near T=50 K. 相似文献
6.
V. F. Sapega V. I. Perel’ A. Yu. Dobin D. N. Mirlin I. A. Akimov T. Ruf M. Cardona K. Eberl 《JETP Letters》1996,63(4):305-310
The polarization characteristics of hot photoluminescence in GaAs/AlAs superlattices are investigated experimentally and theoretically.
It is shown that the formation of an electronic miniband in the superlattice substantially changes the polarization characteristics
of the photoluminescence. As a result of the quasi-three-dimensional character of the motion of hot electrons in the superlattice,
the polarization depends on the ratio of the electron kinetic energies in the plane of the superlattice and along the axis
of the superlattice.
Pis’ma Zh. éksp. Teor. Fiz. 63, No. 4, 285–289 (25 February 1996) 相似文献
7.
《Current Applied Physics》2015,15(10):1226-1229
We propose optically biased photoreflectance (OBPR) spectroscopy, which is performed by continuous illumination of a secondary monochromatic light on a sample with conventional photoreflectance (PR), as a useful tool to investigate the internal electric fields dependence of the PR signals associated with band to band and quantum level transitions. Line shape of the PR signal has a strong dependence on the internal electric field. In OBPR, if a secondary incident light is absorbed, the internal electric field is suppressed by the photo-generated electron–hole pairs. On the other hand, if the secondary light is not absorbed, the internal electric field is not affected. Through the OBPR investigation of a GaAs epitaxial layer and an AlGaAs/GaAs quantum well, we are able to obtain an absorption like spectrum by performing a wavelength scan of a secondary monochromatic light. The results of OBPR measurements at each PR peak position show the contribution of the electric fields modification by the photo-generated carriers in each layers to the PR signals that are related to band gap and quantum level transitions. 相似文献
8.
D. Yang J. W. Garland P. M. Raccah C. Coluzza P. Frankl M. Capizzi F. Chambers G. Devane 《Physica B: Condensed Matter》1991,170(1-4):557-560
We have studied by electrolyte electroreflectance and photoluminescence a GaAs/AlGaAs resonant tunneling structure (RTS) with a highly n-doped GaAs cap, before and after hydrogenation. We measured the amount of passivation of shallow donor states and of deep traps in the cap and found the approximate pinning levels and interace charges of the RTS. 相似文献
9.
《Superlattices and Microstructures》2005,37(2):139-150
Self-sustained oscillations of the current with a frequency ranging from 0.7 to 3.6 MHz have been detected in weakly coupled GaAs/AlGaAs superlattice at 4.2 K. A study of the static and dynamic characteristics of the structure showed that the spontaneous oscillations arise in the local region of the superlattice, restricted by a size of the domain boundary expansion. The oscillations arise in the negative differential conductivity regions due to the periodic coupling and decoupling of subbands in adjacent quantum wells, forming the expanded domain boundary. We suggest that the spatio-temporal oscillations of the domain boundary should be considered as oscillations of an ensemble of several strongly phase-coupled oscillators. Each oscillator is a couple of two adjacent quantum wells, which operates as a single resonant tunneling diode. 相似文献
10.
K.I. Lin K.C. Chen T.S. Wang Y.T. Lu J.S. Hwang 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):211
Photoreflectance (PR) and photoluminescence (PL) spectra are measured for a series of In0.54Ga0.46P1−yNy/GaAs heterostructures at temperatures ranging from 25 to 300 K. The redshifts of the PR and PL peaks indicate that the band gap of InGaPN is dramatically reduced as nitrogen is incorporated. The transition energies of the band edge at various temperatures are measured and least-squares fitted to the Varshni equation. With N incorporation, the PL peak energy exhibits a particular behavior with temperature, which is not observed in PR spectra. This is attributed to carrier localization at low temperatures resulting from N clusters in the samples. In addition, the emergence of additional peaks in PR spectra as N is incorporated implies that the band alignment switches from type I to type II, due to the lowering of the conduction band, thus forming a two-dimensional electron gas (2DEG) in the interface region between InGaPN and GaAs. The number of confined levels in the 2DEG is found to increase with N concentrations. 相似文献
11.
Conclusions The studies performed here have shown that the superlattice samples studied exhibit photoluminescence spectra which agree
with the Kronig-Penney model, although in calculating the energies of the radiative transitions it is necessary to take into
account the binding energy of the excitons,E
B. Due to the exciton—phonon interaction, the 1HH peak breaks up on the long wavelength side into a Poisson distribution. The
energy of the LO phonon so determined is 34 meV. Bands due toD
0-A
0 andD
0X transitions, caused by remaining low-level impurities in the GaAs crystals are also observed.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 61, Nos. 3–4, pp. 241–245, September–October, 1994. 相似文献
12.
《Superlattices and Microstructures》1999,25(1-2):47-51
The mean free path of ballistic electrons in GaAs/AlGaAs superlattices was measured using the technique of hot electron spectroscopy in magnetic fields perpendicular to the growth direction. We utilize the fact that the total effective path of an injected hot electron is a function of the applied magnetic field. For a superlattice with 6.5 nm GaAs wells and 2.5 nm GaAlAs barriers we measure a mean free path of 80 nm. The experimental results of a ten-period SL sample are compared to a fully three-dimensional calculation of the transmission including interface roughness with island sizes of 10 nm. We demonstrate that the observed mfp is limited due to interface roughness scattering for temperatures up to 50 K. 相似文献
13.
14.
The ratio of the densities of intra-and interwell excitons in a symmetric system of coupled quantum wells — a superlattice
based on a GaAs/AlGaAs heterostructure — is investigated over a wide range of optical excitation power densities. Conversion
of interwell excitons into intrawell excitons as a result of exciton-exciton collisions is observed at high exciton densities.
Direct evidence for such a conversion mechanism is the square-root dependence of the interwell exciton density on the optical
excitation level. The decrease in the lifetime of interwell excitons with increasing excitation density, as measured directly
by time-resolved spectroscopy methods, confirms the explanation proposed for the effect.
Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 623–628 (25 April 1997) 相似文献
15.
《Superlattices and Microstructures》1986,2(4):303-307
Compositional disordering of AlGaAs superlattices induced by Si ion implantation and subsequent annealing has been studied by secondary ion mass spectrometry (SIMS). Distinct correlation is found between the induced disordering and the rapid Si diffusion which occurs above the critical concentration of about 3×1018 cm−3. The annealing-condition dependence of the disordering suggests that AlGa intermixing is induced by the vacancy flow enhanced by the SiIIISiV pair movement which causes the rapid Si diffusion. SIMS depth profiles of the heat treated superlattices co-doped with Si and Be do not show any appreciable Si diffusion and induced disordering. This is well-explained by the formation of SiBe pairs which prevents that of SiIIISiV pairs. 相似文献
16.
Koichi Sato Tadashi Takamasu Giyuu Kido 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):305
On AlAs:Yb/GaAs superlattice samples, we measured photoluminescence (PL) spectra including their temperature dependence, magnetic field dependence and resistance up to 25 T. In case of selective excitation of well layers, two broad band PLs were observed in additional to the exception of intra-4f PL from Yb. These peaks show oscillatory behavior similar to that of two-dimensional electron system. From the periods of the oscillation, the electron densities are estimated of the order of which are cannot be archived by usual photoexcitation. It was found that the electron density shows a linear dependence on the excitation energy. To explain such distinctive phenomena, we proposed a new model where Yb ions form hole traps in AlAs. 相似文献
17.
E. L. Ivchenko V. P. Kochereshko A. Yu. Naumov I. N. Uraltsev P. Lavallard 《Superlattices and Microstructures》1991,10(4)
Optical orientation and alignment in the presence of a magnetic field have been applied to study the fine structure of excitons in type II GaAs/AlAs superlattices. We have developed a theory of polarized photoluminescence taking into account the anisotropic exchange splitting of the radiative excitonic doublet. The observed effects of the longitudinal and transverse magnetic fields on the polarization of the exciton emission unambiguously confirm that the actual symmetry of the exciton is lower that D2d and that there exist two classes of excitons with opposite signs of the anisotropic exchange splitting. 相似文献
18.
G. K. Rasulova P. N. Brunkov I. V. Pentin V. V. Kovalyuk K. N. Gorshkov A. Yu. Kazakov S. Yu. Ivanov A. Yu. Egorov D. A. Sakseev S. G. Konnikov 《Technical Physics》2011,56(6):826-830
The interaction of self-oscillators based on 30-period weakly coupled GaAs/AlGaAs superlattices is studied. The action of
one self-oscillator on the other was observed for a constant bias voltage in the absence of generation of self-sustained oscillations
in one of the oscillators. It is shown that induced oscillations in a forced oscillator appear due to excitation of oscillations
in the system of coupled oscillators forming the electric-field domain wall at the frequency of one of the higher harmonics
of a forcing oscillation. 相似文献
19.
A. I. Tartakovskii V. B. Timofeev V. G. Lysenko D. Birkedal J. Hvam 《Journal of Experimental and Theoretical Physics》1997,85(3):601-608
Luminescence and luminescence excitation spectra are used to study the energy spectrum and binding energies of direct and
spatially indirect excitons in GaAs/AlaAs superlattices, with different widths of the electron and hole minibands, located
in a high magnetic field perpendicular to the heterolayers. It is found that the ground state of the indirect excitons formed
by electrons and holes and spatially separated between neighboring quantum wells lies between the ls ground state of the direct excitons and the continuum threshold for dissociated exciton states in the minibands. Indirect
excitons in superlattices have a significant oscillator strength when the binding energy of the exciton exceeds the order
of the width of the resulting miniband. The behavior of the binding energy of direct and indirect heavy hole excitons during
changes in the tunneling coupling between the quantum wells is established. It is shown that a strong magnetic field, which
intensifies the Coulomb interaction between the electron and hole in an exciton, weakens the bond in a system of symmetrically
bound quantum wells. The spatially indirect excitons studied here are analogous to first order Wannier-Stark localized excitons
in superlattices with inclined bands (when an electrical bias is applied), but in the present case the localization is of
purely Coulomb origin.
Zh. éksp. Teor. Fiz. 112, 1106–1118 (September 1997) 相似文献
20.
V. B. Timofeev A. I. Tartakovskii A. I. Filin D. Birkedal J. Hvam 《Physics of the Solid State》1998,40(5):767-769
Luminescence and luminescence excitation spectra are used to study the energy spectrum and binding energies of direct and
spatially indirect excitons in GaAs/AlGaAs superlattices having different electron and hole miniband widths in high magnetic
fields perpendicular to the heterolayers. The ground state of the indirect excitons formed by electrons and holes which are
spatially distributed among neighboring quantum wells is found to lie between the ground 1s state of the direct excitons and the threshold of the continuum of dissociated exciton states in the minibands. The indirect
excitons have a substantial oscillator strength when the binding energy of the exciton exceeds the scale of the width of the
resulting miniband. It is shown that a high magnetic field shifts a system of symmetrically bound quantum wells toward weaker
bonding. At high exciton concentrations, spatially indirect excitons are converted into direct excitons through exciton-exciton
collisions.
Fiz. Tverd. Tela (St. Petersburg) 40, 833–836 (May 1998) 相似文献