共查询到20条相似文献,搜索用时 15 毫秒
1.
Interband transitions in GaNyAs1−y/GaAs multi quantum well (MQW) samples with y=0.012 and 0.023 have been studied by contactless electroreflectance spectroscopy (CER). Optical transitions related to absorption in the GaAs barriers and in the GaNyAs1−y/GaAs QWs have been observed and analyzed. The GaAs related transition exhibits clear Franz-Keldysh oscillations with the period corresponding to the built-in electric field of 14 and 17 kV/cm for samples with y=0.012 and 0.023, respectively. The portion of the CER spectrum related to absorption in the GaNyAs1−y/GaAs QW exhibits two clear resonances which are attributed to optical transitions between the ground and excited states confined in the QWs. The resonance attributed to the ground state transition is associated with absorption between the first light- and heavy-hole subbands and the first electron subband (11L and 11H) while the resonance attributed to the excited state transition is associated with absorption between the second heavy-hole subband and the second electron subband (22H). The energies of the 11H and 22H transitions have been matched with those obtained from theoretical calculations performed within the effective mass approximation. Thus, the GaNyAs1−y/GaAs QWs are type-I structures with a conduction band offset, QC, between 70 and 80%. Moreover, the incorporation of N atoms into GaAs is found to cause a significant increase in the electron effective mass. The determined values of electron effective mass for GaNyAs1−y/GaAs QW with y=0.012 and 0.023 are 0.105m0 and 0.115m0, respectively. 相似文献
2.
S. Ben Bouzid W. Zaghdoudi N. Ben Sedrine J.C. Harmand 《Applied Surface Science》2008,254(22):7122-7126
We study the effect of the GaAsN narrow QWs on the optical properties of the GaInNAsSb/GaAs QWs using photoluminescence spectroscopy. A drastic effect of the N-rich layers on the QW photoluminesecnec (PL) intensity was observed with a strong influence of the spacer thickness. In the PL spectra a broad band caused by excitonic transitions related with N-related clusters in GaAs barriers is found. Based on calculations from experimental data, we have identified the low QW peak energy to the E1-H1 transition using the shear deformation potentials report Δp/p = 0.24. 相似文献
3.
D. S. Abramkin K. M. Rumynin A. K. Bakarov D. A. Kolotovkina A. K. Gutakovskii T. S. Shamirzaev 《JETP Letters》2016,103(11):692-698
The crystal structure of new self-assembled InSb/AlAs and AlSb/AlAs quantum dots grown by molecularbeam epitaxy has been investigated by transmission electron microscopy. The theoretical calculations of the energy spectrum of the quantum dots have been supplemented by the experimental data on the steady-state and time-resolved photoluminescence spectroscopy. Deposition of 1.5 ML of InSb or AlSb on the AlAs surface carried out in the regime of atomic-layer epitaxy leads to the formation of pseudomorphically strained quantum dots composed of InAlSbAs and AlSbAs alloys, respectively. The quantum dots can have the type-I and type-II energy spectra depending on the composition of the alloy. The ground hole state in the quantum dot belongs to the heavy-hole band and the localization energy of holes is much higher than that of electrons. The ground electron state in the type-I quantum dots belongs to the indirect XXY valley of the conduction band of the alloy. The ground electron state in the type-II quantum dots belongs to the indirect X valley of the conduction band of the AlAs matrix. 相似文献
4.
H. Momose N. Mori C. Hamaguchi T. Ikaida H. Arimoto N. Miura 《Physica E: Low-dimensional Systems and Nanostructures》1999,4(4):286
We present a review on recent study of the type I to type II transition in short-period superlattices (SLs) of GaAs/AlAs by means of cyclotron resonance (CR) in pulsed high magnetic fields. The behavior of CR varies depending on the thickness of the GaAs and AlAs layers. In CR of (GaAs)n/(AlAs)n, the resonance peak at the X minima was observed in the type II regime for n smaller than 14, whereas the resonance at the Γ point was observed for n>15. We estimated electron masses on X and Γ point in the SLs by using the empirical sp3 tight-binding method including second-nearest-neighbor interaction. These calculations have shown good agreement with the experimental results. Moreover, it was found that the angular dependence of the CR peak position does not obey the simple cosine dependence due to the subband mixing in high magnetic fields. From the angular dependence in the SLs, the longitudinal and transverses electron masses of AlAs at the X point were deduced to be mt=0.21m0 and ml=1.04m0, respectively. 相似文献
5.
R. Cingolani K. Ploog L. Baldassarre M. Ferrara M. Lugarà C. Moro 《Applied Physics A: Materials Science & Processing》1990,50(2):189-196
The band structure and the optical transitions of symmetric ultra-short period (GaAs)
m
/(AlAs)
n
superlattices (n=m is the number of monolayers) have been studied using different spectroscopic techniques, namely photoacoustic spectroscopy, reflectivity and luminescence, photoluminescence excitation and high excitation intensity time-resolved luminescence. Direct observation of the transition from type I to type II energy band alignment is reported for superlattices whose configuration consists of more than 12 monolayers (i.e. m=n>12). The radiative recombination processes associated with the real space indirect transitions have been investigated as a function of the density of photogenerated electron-hole pairs, revealing an unusual density-dependent behaviour. A tentative interpretation in terms of a condensed electron-hole state at the indirect gap is given, which accounts for the long decay time of the type II luminescence at high excitation rate. 相似文献
6.
The secondary ion mass spectrum of silicon sputtered by high energy C60+ ions in sputter equilibrium is found to be dominated by Si clusters and we report the relative yields of Sim+ (1 ≤ m ≤ 15) and various SimCn+ clusters (1 ≤ m ≤ 11 for n = 1; 1 ≤ m ≤ 6 for n = 2; 1 ≤ m ≤ 4 for n = 3). The yields of Sim+ clusters up to Si7+ are significant (between 0.1 and 0.6 of the Si+ yield) with even numbered clusters Si4+ and Si6+ having the highest probability of formation. The abundances of cluster ions between Si8+ and Si11+ are still significant (>1% relative to Si+) but drop by a factor of ∼100 between Si11+ and Si13+. The probability of formation of clusters Si13+-Si15+ is approximately constant at ∼5 × 10−4 relative to Si+ and rising a little for Si15+, but clusters beyond Si15 are not detected (Sim≥16+/Si+ < 1 × 10−4). The probability of formation of Sim+ and SimCn+ clusters depends only very weakly on the C60+ primary ion energy between 13.5 keV and 37.5 keV. The behaviour of Sim+ and SimCn+ cluster ions was also investigated for impacts onto a fresh Si surface to study the effects that saturation of the surface with C60+ in reaching sputter equilibrium may have had on the measured abundances. By comparison, there are very minor amounts of pure Sim+ clusters produced during C60+ sputtering of silica (SiO2) and various silicate minerals. The abundances for clusters heavier than Si2+ are very small compared to the case where Si is the target.The data reported here suggest that Sim+ and SimCn+ cluster abundances may be consistent in a qualitative way with theoretical modelling by others which predicts each carbon atom to bind with 3-4 Si atoms in the sample. This experimental data may now be used to improve theoretical modelling. 相似文献
7.
L. V. Butov A. Imamoglu K. L. Campman A. C. Gossard 《Journal of Experimental and Theoretical Physics》2001,92(2):260-266
We report on the (magneto-) optical study of many-body effects in spatially separated electron and hole layers in GaAs/AlxGa1?x As coupled quantum wells (CQWs) at low temperatures (T = 1.4 K) for a broad range of electron-hole (e-h) densities. Coulomb effects were found to result in an enhancement of the indirect (interwell) photoluminescence (PL) energy with increasing the e-h density both for a zero magnetic field and at high fields for all Landau level transitions; this is in contrast to the electron-hole systems in single QWs where the main features are explained by the band-gap renormalization resulting in a reduction of the PL energy. The observed enhancement of the ground state energy of the system of the spatially separated electron and hole layers with increasing the e-h density indicates that the real space condensation to droplets is energetically unfavorable. At high densities of separated electrons and holes, a new direct (intrawell) PL line has been observed: its relative intensity increased both in PL and in absorption (measured by indirect PL excitation) with increasing density; its energy separation from the direct exciton line fits well to the X ? and X + binding energies previously measured in single QWs. The line is therefore attributed to direct multiparticle complexes. 相似文献
8.
《Superlattices and Microstructures》2000,27(1):39-51
GaAs/AlAs single quantum well structures designed with well thickness near the type-I/type-II crossover show distinctive photoluminescence peaks corresponding to both type-I and type-II recombinations. Photoluminescence measurements as a function of applied electric field and temperature ranging from 23 to 180 K and current–voltage measurements are presented for two MBE-grown structures clad with Si-doped Al0.45Ga0.55As layers onn + -GaAs [100] substrates. The large and field-dependent energy separation between type-I and type-II luminescence peaks is understood to arise from the build-up of electrons at the X point in the AlAs barrier. 相似文献
9.
K. S. Zhuravlev A. M. Gilinskii T. S. Shamirzaev V. V. Preobrazhenskii B. R. Semyagin M. A. Putyato S. S. Chipkin 《Physics of the Solid State》1998,40(9):1577-1581
A study is reported of steady-and nonsteady-state photoluminescence of intentionally undoped and uniformly silicon-doped type-II
(GaAs)7(AlAs)9 superlattices grown by MBE simultaneously on (311)A-and (100)-oriented GaAs substrates. It has been established that at elevated temperatures (160>T>30 K) the superlattice spectra are dominated by the line due to the donor-acceptor recombination between donors in the AlAs
layers and acceptors located in the GaAs layers. The total carrier binding energy to the donor and acceptor in a pair has
been determined.
Fiz. Tverd. Tela (St. Petersburg) 40, 1734–1739 (September 1998) 相似文献
10.
Binding energies of the ground state and of four excited states of a hydrogenic impurity in quantum well structures consisting of a single slab of GaAs sandwiched between two semi-infinite slabs of Ga1?xAlxAs are calculated using a variational approach. The ground-state binding energy is calculated as a function of the barrier potential for a given size of the GaAs quantum well and is found to be linearly dependent on the inverse of the square root of the barrier potential except for very small potentials. The variation of the binding energies of all five states as a function of the size of the GaAs quantum well are also calculated and their behavior is discussed. 相似文献
11.
M.A. AliA.K.M.A. Islam 《Physica B: Condensed Matter》2012,407(6):1020-1026
The structural, elastic, electronic and optical (x=0) properties of doped Sn1−xBixO2 and Sn1−xTaxO2 (0≤x≤0.75) are studied using the first-principles pseudopotential plane-wave method within the local density approximation. The independent elastic constants Cij and other elastic parameters of these compounds have been calculated for the first time. The mechanical stability of the compounds with different doping concentrations has also been studied. The electronic band structure and density of states are calculated and the effect of doping on these properties is also analyzed. It is seen that the band gap of the undoped compound narrowed with dopant concentration, which disappeared for x=0.26 for Bi doping and 0.36 for Ta doping. The materials thus become conductive oxides through the change in the electronic properties of the compound for x≤0.75, which may be useful for potential application. The calculated optical properties, e.g. dielectric function, refractive index, absorption spectrum, loss-function, reflectivity and conductivity of the undoped SnO2 in two polarization directions are compared with both previous calculations and measurements. 相似文献
12.
K. Shinohara Y. Shimizu S. Shimomura Y. Okamoto N. Sano S. Hiyamizu 《Physica E: Low-dimensional Systems and Nanostructures》1998,2(1-4)
Effectively atomically flat GaAs/AlAs interfaces over a macroscopic area (“super-flat interfaces”) have been realized in GaAs/AlAs and GaAs/(GaAs)
(AlAs)
quantum wells (QWs) grown on (4 1 1)A GaAs substrates by molecular beam epitaxy (MBE). A single and very sharp photoluminescence (PL) peak was observed at 4.2 K from each GaAs/AlAs or GaAs/(GaAs)
(AlAs)
QW grown on (4 1 1)A GaAs substrate. The full-width at half-maximum (FWHM) of a PL peak for GaAs/AlAs QW with a well width (
) of 4.2 nm was 4.7 meV and that for GaAs/(GaAs)
(AlAs)
QW with a smaller well width of 2.8 nm (3.9 nm) was 7.6 meV (4.6 meV), which are as narrow as that for an individual splitted peak for conventional GaAs/AlAs QWs grown on (1 0 0) GaAs substrates with growth interruption. Furthermore, only one sharp peak was observed for each GaAs/(GaAs)
(AlAs)
QW on the (4 1 1)A GaAs substrate over the whole area of the wafer (7
7 mm
), in contrast with two- or three-splitted peaks reported for each GaAs/AlAs QW grown on the (1 0 0) GaAs substrate with growth interruption. These results indicate that GaAs/AlAs super-flat interfaces have been realized in GaAs/AlAs and GaAs/(GaAs)
(AlAs)
QWs grown on the (4 1 1)A GaAs substrates. 相似文献
13.
Eriko KagiNobuyuki Yamamoto Hisashi FujiwaraMasaru Fukushima Takashi Ishiwata 《Journal of Molecular Spectroscopy》2002,216(1):48-51
Optical-optical double resonance spectroscopy was used to study the 1g(3P1) ion-pair state of I2 correlating to I−(1S)+I+3P1) at the dissociation limit. We gained access to the 1g(3P1) state though the A3Π (1u) state in the (1+1) photon-excitation scheme. The pump laser excited the A3Π (1u)-X1Σg+ transition at a fixed frequency for state selection. The probe laser was scanned to detect the 1g(3P1)-A3Π (1u) resonance by monitoring the ultraviolet emission from the 1g(3P1) state at 278 nm. The 1g(3P1) state was observed in a vibrational progression consisting of P and R doublets. An energy level analysis was carried out for the 1g(3P1) state in the 0≤ v ≤ 14 and 12≤J≤135 range, which led to a set of molecular parameters including the Ω-doubling constant. The Ω-doubling of the 1g(3P1) state was discussed by the pure precession model and interpreted to occur through the heterogeneous coupling with the 0g−(3P1) state correlating to the same ionic asymptote. 相似文献
14.
The optical and electronic properties of (GaAs)n/(InAs)n superlattices are calculated by means of LMTO-ASA method. The too small band gap problem of bulk material and superlattices is corrected by adding to the effective potentials an additional external potential that is sharply peaked at the atomic sites. The results show that the optical properties of GaAs/InAs(001) superlattices are about average of that of two bulks of GaAs and InAs. 相似文献
15.
《Superlattices and Microstructures》1994,15(4):405-407
We have theoretically investigated the valence-band discontinuity (ΔEv) at the (100) GaAs/AlAs interface with the InAs strained insertion-layer. The theoretical calculation is carried out by the self-consistent tight-binding method with the sp3s* basis in the (GaAs)5/(InAs)1/(AlAs)5/(InAs)1 [100] superlattice. ΔEv at the GaAs/InAs(1ML)/AlAs interface is calculated to be 0.50 eV, which is practically equal to ΔEv = 0.51 eV at the GaAs/AlAs interface with no InAs layers. The insertion of the InAs monolayer changes the detail of valence charge density at the GaAs/AlAs interface but does not change ΔEv. The result of calculation is in consistent with our experimental measurement by using the x-ray photoelectron spectroscopy. 相似文献
16.
Sun-Ho Kang Jeong-Doo YiHan-Ill Yoo Si-Hyung KimYoung Woo Lee 《Journal of Physics and Chemistry of Solids》2002,63(5):773-780
The electrical conductivity (σ) of (EryU1−y)O2+x (y=0.06, 0.20) and (CeyU1−y)O2+x (y=0.05, 0.15, 0.25) has been measured as a function of oxygen partial pressure in the temperature range of 1100≤T/°C≤1300 by a d.c. 4-probe method. Both of the oxides exhibited Po2-regions where the electrical conductivity is independent of oxygen partial pressure, which indicates that doped Er and Ce exist as trivalent cations on uranium sites and fix the hole concentration by acting as electron acceptors, i.e. [h]=[Er′U] and [h]=[Ce′U], respectively. It is considered that strong oxidization tendency of uranium and reduction tendency of cerium simultaneously render the cerium ions exist exclusively as Ce3+ in the uranium dioxide. The electron-hole mobility of (EryU1−y)O2+x and (CeyU1−y)O2+x in the Po2 region where σ is constant has been calculated by the combination of the electrical conductivity and charge carrier concentration; the activation energy (EH) of each oxide has been obtained from the temperature dependence of the mobility. Small polaron hopping conduction mechanism was confirmed by small magnitude of the mobility (0.018-0.052 cm2 V−1 s−1) and the activation energy (0.12-0.22 eV). 相似文献
17.
E.A MahmoudM.M El-Samanoudy A.S Abd Rabo 《Journal of Physics and Chemistry of Solids》2002,63(11):2003-2010
Optical absorption at room temperature and electrical conductivity at temperatures between 283 and 333 K of vacuum evaporated GexFexSe100−2x (0≤x≤15) amorphous thin films have been studied as a function of composition and film thickness. It was found that the optical absorption is due to indirect transition and the energy gap increases with increasing both Ge and Fe content; on the other hand, the width of the band tail exhibits the opposite behavior. The optical band gap Eopt was found to be almost thickness independent. The electrical conductivity show two types of conduction, at higher temperature the conduction is due to extended states, while the conduction at low temperature is due to variable range hopping in the localized states near Fermi level. Increasing Ge and Fe contents were found to decrease the localized state density N(EF), electrical conductivity and increase the activation energy for conduction, which is nearly thickness independent. Variation of the atomic densities ρ, molar volume V, glass transition temperature Tg cohesive energy C.E and number of constraints NCo with average coordination number Z was investigated. The relationship between the optical gap and chemical composition is discussed in terms of the cohesive energy C.E, average heat of atomization and coordination numbers. 相似文献
18.
Ferromagnetic ordering of silver impurities in the AlN semiconductor is predicted by plane-wave ultrasoft pseudopotential and spin-polarized calculations based on density functional theory (DFT). It was found that an Ag impurity atom led to a ferromagnetic ground state in Ag0.0625Al0.9375N, with a net magnetic moment of 1.95 μB per supercell. The nitrogen neighbors at the basal plane in the AgN4 tetrahedron are found to be the main contributors to the magnetization. This magnetic behavior is different from the ones previously reported on transition metal (TM) based dilute magnetic semiconductor (DMS), where the magnetic moment of the TM atom impurity is higher than those of the anions bonded to it. The calculated electronic structure band reveals that the Ag-doped AlN is p-type ferromagnetic semiconductor with a spin-polarized impurity band in the AlN band gap. In addition, the calculated density of states reveals that the ferromagnetic ground state originates from the strong hybridization between 4d-Ag and 2p-N states. This study shows that 4d transition metals such as silver may also be considered as candidates for ferromagnetic dopants in semiconductors. 相似文献
19.
Reflection high-energy electron diffraction, atomic force microscopy, transmission electron microscopy, and double-crystal X-ray curves showed that high-quality InAs quantum dot (QD) arrays inserted into GaAs barriers were embedded in an Al0.3Ga0.7As/GaAs heterostructure. The temperature-dependent photoluminescence (PL) spectra of the InAs/GaAs QDs showed that the exciton peak corresponding interband transition from the ground electronic subband to the ground heavy-hole subband (E1-HH1) was dominantly observed and that the peak position and the full width at half maximum corresponding to the interband transitions of the PL spectrum were dependent on the temperature. The activation energy of the electrons confined in the InAs/GaAs QDs was 115 meV. The electronic subband energy and the energy wave function of the Al0.3Ga0.7As/GaAs heterostructures were calculated by using a self-consistent method. The electronic subband energies in the InAs/GaAs QDs were calculated by using a three-dimensional spatial plane wave method, and the value of the calculated (E1-HH1) transition in the InAs/GaAs QDs was in reasonable agreement with that obtained from the PL measurement. 相似文献
20.
L. Shi 《Solid State Communications》2011,151(24):1907-1911
In the framework of perturbation theory, a variational method is used to study the ground state of a donor bound exciton in a weakly prolate GaAs/Ga1−xAlxAs ellipsoidal finite-potential quantum dot under hydrostatic pressure. The analytic expressions for the Hamiltonian of the system have been obtained and the binding energy of the bound exciton is calculated. The results show that the binding energy decreases as the symmetry of the dot shape reduces. The pressure and Al concentration have a considerable influence on the bound exciton. The binding energy increases monotonically as the pressure or Al concentration increases, and the influence of pressure or Al concentration is more pronounced for small quantum dot size. 相似文献