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An ensemble of InAs quantum dots with ground state transition energies centered at 1.216 eV and density 1011dots/cm2 has been studied by time-resolved photoluminescence (PL). The wavelength of the 100-fs excitation pulse was tuned through the ground (excited) state transitions, resulting in resonant (optical phonon sideband) PL. The decay of the PL was time resolved with a streak camera in the interval 1.5–3 ns to avoid scattered laser light. The intensity of the PL was recorded with its polarization both parallel with and perpendicular to the excitation polarization (along one of the crystal’s cleave axes); the ratio is 2.22 at low temperatures and low excitation. A phenomenological rate equation analysis is made, separating the excitations into two classes, one polarized along the excitation polarization and the other unpolarized (either that way immediately after the excitation pulse or scattered from the first class). Excellent fits to the data lead to the conclusion that both classes decay radiatively with a lifetime of 1 ns, and a transfer from the polarized to the unpolarized species takes place with a distribution time of 12 ns at low temperatures and low excitation, dropping rapidly toward zero for temperatures above 30 K and for intense excitation levels. The polarization of a coherently excited ground state exciton should dephase with a rate equal to the sum of the radiative rate plus the inverse of this distribution time.

The influence of an intra-cavity anti-reflection coating on the switch-on dynamics and the power input-output characteristic of a vertical-external-cavity surface-emitting laser (VECSEL) system are investigated. The experiments show a significantly higher threshold and slower switch-on dynamics for anti-reflection coated systems. These differences originate in the changes in the mode strength at the active medium due to the more or less pronounced sub-cavity. The presented simulations based on microscopic calculations are in good qualitatively agreement with the experiments. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We report a systematic study of the photoluminescence properties of ZnO nanostructures. In particular, mesoporous ZnO powders of varying surface-to-mass ratio are investigated and compared to a bulk reference. At low temperatures the emission from higher-energy states is very pronounced and even dominant for samples with high surface-to-mass ratio. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Formation of self-organized Ga(AsSb) quantum-islands during growth is shown to occur in a series of Ga(AsSb)/GaAs/(AlGa)As heterostructures, resulting in an in-plane hole confinement of several hundred meV. The shape of the in-plane confinement potential is nearly parabolic and thus yields almost equidistant hole energy levels. Transmission electronmicroscopy reveals that the quantum islands (QIs) are 100 nm in diameter and exhibit an inplane variation of the Sb concentration of more than 30%, which is the origin of the confinement. Up to seven bound hole states are observed in the photoluminescence spectra. Time-resolved photoluminescence data are shown as function of excitation density. The influence of size and density of such structures as well as the mechanisms of growth are discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

An overview of recent experimental and theoretical results on stationary and time-dependent photoluminescence spectra in disordered semiconductor heterostructures is presented. In particular, temperature-dependent peak position and linewidth of the luminescence spectra, as well as the luminescence intensity are considered along with the time evolution of the luminescence intensity after pulsed excitation. Emphasis is given on the comparison between experimental and theoretical results aiming at a characterization of disorder in the underlying structures.

We present results of experimental and theoretical studies of thermal quenching of the photoluminescence intensity in (GaIn)(NAs)/GaAs quantum wells after various postgrowth treatments. The experimental data are well described in the framework of a phenomenological model, if thermal emission of excitons out of localized states into delocalized states at the mobility edge prior to their non-radiative recombination is taken into account. Comparison between theoretical results and experimental data yields such material parameters as the energy scale of the band tail and the relative concentrations of non-radiative centers and traps. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We have grown In0.54Ga0.46As:Mn/MnAs granular paramagnetic–ferromagnetic hybrid structures by metal–organic vapor-phase epitaxy. The MnAs clusters have a Curie temperature of about 320 K. We have studied the optical activity of individual ferromagnetic MnAs clusters embedded in the paramagnetic In0.54Ga0.46As:Mn matrix at room temperature by far-field depolarization measurements. A scanning near-field optical microscopy set-up in constant height mode ( ≈ 100 nm above the sample surface) was used to achieve a high spatial resolution. Individual MnAs clusters rotate the linear polarization of the incoming light by almost 2 ∘ in this reflection geometry. This optical activity was analyzed in terms of birefringence and polar Kerr effect and correlated with the structural and magnetic properties of the MnAs clusters as determined by ferromagnetic resonance measurements. The optical activity of the MnAs clusters turns out to be dominated by linear birefringence caused by the uniaxial symmetry of the hexagonal crystal structure of MnAs. The polar Kerr effect plays a minor role in this experiment.

Exciton photoluminescence (PL) in a GaInNAs/GaNAs quantum well was measured in the temperature range from 15 K to 300 K. Two striking features of the PL were observed: the nonmonotoneous temperature dependence of the Stokes shift and the abrupt increase of the PL linewidth in a rather narrow temperature range. These features are known to be strong indications of the hopping relaxation of excitons via localized states distributed in space and energy. Computer simulations of the hopping relaxation of excitons were carried out. Comparison between the simulation results and the experimental data provides an important and reliable information on the energy shape of the density of states and also on the energy range, in which localized states for excitons are distributed. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ballistic currents of spin-polarized carriers are generated by quantum interference of one and two photon absorption. Polarization and relative phase of the exciting femtosecond laser fields control the magnitude and direction of the currents as well as the electron spin orientation. These spin-polarized currents are experimentally detected by a phase-dependent spatial shift of the circularly analyzed photoluminescence in cubic ZnSe.

Signatures of exciton and two-exciton states in semiconductor systems are investigated experimentally and theoretically. A set of quantum well samples with different well widths is studied using coherent excitation spectroscopy. The experimental results are analyzed using a microscopic model demonstrating the importance of biexciton correlations and disorder effects. Additional numerical investigations of absorption changes in small nanorings are employed to analyze optical transitions from two-exciton to three-exciton resonances.

The influence of coupling, correlation, and disorder on exciton and biexciton signatures is investigated using coherent excitation spectroscopy. Different biexciton-induced transitions of a single biexciton state are spectrally resolved. One of the transitions is found to be particularly sensitive to disorder. Mixed biexciton resonances, resulting from attractively interacting heavy and light hole exciton states, are identified. The observations are analyzed on the basis of microscopic model calculations.

We discuss advances, advantages and problems of spintronics through the example of a semiconductor laser whose emission intensity and polarization are modulated by the spin orientation of electrons. We show that spin transport should be feasible at room temperature and present possible concepts and first results concerning spin injection at high temperatures. Finally, we describe the coherent dynamics of coupled electron and hole spins in a quantum mechanical picture and measure the magnetic field-induced dynamics of localized excitons in a 3 nm GaAs quantum well. The system is capable of performing a quantum controlled not operation (CNOT), which realizes a basic two-qubit operation of quantum information processing in a semiconductor nanostructure.

The ultrafast emission dynamics of a 1.3-/spl mu/m (GaIn)(NAs)/GaAs vertical-cavity surface-emitting laser is studied by femtosecond luminescence upconversion. We obtain a minimum peak delay of 15.5 ps and a minimum pulse width of 10.5 ps. Laser operation with picosecond emission dynamics is demonstrated over a temperature range from 30 to 388 K. The bandgap shift with temperature of (GaIn)(NAs)/GaAs is determined to be about -2.9/spl middot/10/sup -4/ eV/K, which is smaller than for GaAs. Our measurements of the optical gain provide gain spectra similar to those of commercial (GaIn)(PAs)/InP-structures at moderate densities but broaden considerably for elevated carrier densities due to the stronger carrier confinement. We compare our experimental results with gain spectra calculated from a microscopic model and confirm the predictive capability of the model. The theoretical gain spectra are used as the input for a calculation of the temperature dependence of the (GaIn)(NAs)/GaAs surface-emitter emission which results in very good agreement with experiment.

Wide band-gap (Zn,Cd,Mn)Se/ZnSe quantum well structures were grown by MBE. Q-discs have been prepared of these parent structures by electron beam lithography followed by dry and wet-chemical etching. With increasing magnetic field a decrease of the energy transfer from excitonic states into the localised internal Mn 2+ (3d 5 ) states has been observed. The effect is caused by the spin dependence of the energy transfer. The underlying mechanism is discussed, highlighting the importance of bound exciton states for fulfilling the spin selection rule.

Summary form only given. Over the last two years much effort has been devoted to experimentally explore spin electronics in semiconductors. These experiments also support the hope of implementing quantum information devices based on spins using the mature technology of semiconductors. A basic requirement for quantum information processing with spins is the control of the mutual interaction between single spins. We extend here the investigation of spin coherence to the case of exchange coupled electron hole spins within a single exciton. The sample under investigation is an intrinsic 3 nm GaAs/(AlGa)As multiple quantum well (MQW) with a large Stokes shift of 9 meV.

Absorption and fluorescence were investigated for liquid-crystalline discotics, which are characterized by the spontaneous formation of one-dimensional columnar structures in the fluid phase. Such materials have been considered for applications in organic light-emitting diodes and as photoconductors. We investigated materials based on asymmetrically substituted triphenylenes displaying a novel highly ordered plastic columnar state. These materials show an unexpected time dependence of the fluorescence spectrum during irradiation apparently because of their specific spatial structure. Transfer of energy from a high-energy excited state to a newly developing lower-energy state takes place. We attribute the evolution of this state to the particular spatial arrangement of the molecules within the columns in the plastic columnar state. This causes the photoinduced formation of dimers, a process that is absent in solutions and in polymer-dispersed systems of discotic materials and that has, so far, not been doc...

We study semiconductor quantum-well samples with different disorder strengths by coherent excitation spectroscopy with particular emphasis on disorder-mediated couplings of exciton subensembles. Our experiments show that there is no coherent coupling of excitons in different quantum islands and in a strongly inhomogeneously broadened sample. Latest results with polarization-resolved coherent excitation spectroscopy indicate a disorder-induced dephasing of biexcitons in the inhomogeneously broadened sample.

We measured time and spectrally resolved, resonantly and nonresonantly excited photoluminescence of self-assembled vertically aligned InP/(GaIn)P quantum dots on GaAs substrates with various spacer thicknesses (2, 4, 8, and 16 nm) between the dot layers. The different interdot coupling in the various structures leads to considerable differences in the electron relaxation process. Carriers tunnel in the vertically aligned dot stacks to the lowest energy state when the spacer thickness is small, resulting in a pronounced red shift and slowing down of the photoluminescence decay. We present simple models to explain the results of our measurements.

We demonstrate the mutual influence of the dynamics in the real-space and the spin parts of the exciton wavefunction evoked by the exchange interaction. In the regime of high exciton density, the exciton–exciton interaction in ZnSe/ZnMgSSe quantum wells is found to be strongly affected by the exciton spin orientation and the longitudinal spin relaxation via single-fermion spin flips. The exciton's homogeneous linewidth as deduced from degenerate four-wave mixing with prepulse is significantly enhanced in spin-pure exciton populations by scattering including fermionic exchange. The transverse spin relaxation in the low-density limit is deduced from the decay of spin quantum-beats in photoluminescence experiments. We find an anti-proportionality between the spin relaxation and the optical dephasing times. The temperature dependence of both relaxation times is determined by the exciton–phonon interaction. The latter gradually reduces the electron–hole exchange coupling which is the dominating term in the exciton's transverse spin relaxation.

Microscopic calculations including energetic disorder and Coulomb correlations up to third order in the laser field are performed. The resulting four-wave-mixing signals show polarization-dependent dephasing induced by diagonal disorder. The correct modeling of this disorder-induced dephasing requires the proper inclusion of Coulomb correlations. The theoretical results are in good qualitative agreement with measurements performed on a variety of quantum-well samples.

We study the population of excitons in GaAs/AlGaAs quantum wells in the time span between optical excitation and optical recombination. We distinguish between 1s excitons and free electrons and holes by tracing the electron–hole exchange energy and thereby the overlap of electron and hole. The experiments prove that at many experimental conditions rather electrons and holes than 1s excitons are present during this time span although recombination takes place at the 1s exciton energy of free or localized excitons. The 1s exciton states are only populated under stringent experimental conditions.

First, we study coupling of excitons in different quantum-well islands by coherent excitation spectroscopy and find that excitons in different islands are not coherently coupled. Second, we investigate exciton and biexciton binding energies in inhomogeneously broadened (GaIn)As/Ga(PAs) multi quantum wells. A strong increase of the 1s–2s-splitting with increasing exciton localization is found, whereas the biexciton binding energy shows a very weak decrease with increasing localization.

Lasing is demonstrated for a Ga(NAsP) multi quantumwell structure grown pseudomorphically on GaP using metal-organic vapour-phase epitaxy. For a series of temperatures ranging from 8 K to 290 K, the sample emission characteristics are determined. With increasing pump power, a spectral narrowing of the emitted light along with a blue-shift is observed as the lasing threshold is approached. Above the threshold, the emission splits up spectrally into a pattern of clearly distinguishable modes. In addition, the potential of this material concerning roomtemperature lasing is investigated by means of a variable stripe-length experiment, where a modal gain of 10 cm–1 is observed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A new spectroscopic technique is demonstrated on three characteristically different semiconductor quantum-well samples. Coherent excitation spectroscopy reveals coherent coupling and effectively suppresses the signatures of inhomogeneous broadening and incoherent transfer between various excitonic states in quantum wells. Coherently coupled homogeneous subsystems are analyzed in an inhomogeneously broadened excitonic ensemble.

We present an investigation of the excitonic resonances in wurtzite GaN by ultrafast linear, and nonlinear optical spectroscopy. The exciton lifetime and the cooling of the exciton distribution are investigated by time-resolved photoluminescence (PL) studies of the LO-phonon replicas. We obtain a biexponential decay of the exciton number with time and find that excitons cool mainly by scattering with acoustic phonons via deformation potential interaction. Transient four-wave-mixing (FWM) studies yield the homogeneous broadening of the A-exciton and the strengths of exciton–exciton and exciton–phonon interactions. These values are comparable to other direct gap semiconductors. The biexciton binding-energy is (5.7±0.3) meV. The energy splitting between A- and B-exciton is obtained with very high accuracy from quantum-beat spectroscopy.

Pump-probe measurements were performed with a subwavelength spatial resolution of 355 nm and a temporal resolution of 130 fs in a multiple quantum well sample at T= 8 K. A solid immersion lens was used to increase the spatial resolution to 0.41 lambda, demonstrating that the limit of conventional microscopy was surpassed.

GaAs-based vertical cavity surface emitting laser structures (VCSEL) with strain-compensated (GaIn)As/Ga(PAs) multiple quantum well heterostructures (MQWH) active regions have been deposited using the less hazardous, liquid group-V-sources tertiarybutyl arsine (TBAs) and tertiary butyl phosphine (TBP) in metal organic vapour phase epitaxy (MOVPE). We report on growth optimization, characterization of the VCSEL structures, and ultrafast emission dynamics after femtosecond optical excitation. The improved decomposition characteristics of the alternative compounds yield a small variation in the cavity thickness of only ±0.35% across the 2″ wafer. The high quality of the VCSEL structures having a 2 λ cavity with 4 stacks of 3 (GaIn)As/Ga(PAs)-MQWH and AlAs/GaAs-Bragg mirrors is revealed by the large normal mode splitting of 10.6 meV. Excellent pulse response with a pulse width of 3.2 ps and a peak delay of 4.8 ps at 30 K is obtained after femtosecond optical excitation. The high crystalline perfection with respect to layer homogeneity, optical properties as well as ultrafast emission dynamics demonstrate the advantages of the strain-compensated material system for VCSEL structures grown by MOVPE using TBAs and TBP.

A new experimental method is presented to determine the sign of the electron Land' g factor in semiconductors by time-resolved magneto photoluminescence. This technique is used to demonstrate the reversal of the electron g factor for different material compositions. Measurements and theoretical estimates for the spin dynamics in quantum well systems are compared.

A new method using the broad spectrum of a 10 fs Ti:sapphire laser is demonstrated for measuring the gain spectra of semiconductor lasers with high and quantitative accuracy. Results are shown for an edge-emitting ridge-waveguide In0.05Ga0.95As single quantum well (SQW) laser. The device is studied from the absorption regime up to the strong gain regime recording both, TE and TM polarizations. The experiments are compared to the predictions of a microscopic model based on the semiconductor Bloch equations including microscopic scattering and dephasing terms. A very good quantitative agreement is obtained.

We investigate the influence of carrier relaxation on the emission dynamics of a semiconductor microcavity laser. The structure is optically excited with energies of 1.477 down to 1.346 eV (resonant excitation). The stimulated emission dynamics clearly becomes faster for decreasing excitation energy and the influence of the light hole on the emission dynamics is demonstrated. Theoretical calculations reproduce the results only if the nonequilibrium carrier dynamics is treated on the basis of a microscopic model.

We study the dependence of the biexciton binding energy on confinement in semiconductor quantum wells. A set of symmetrically strained (GaIn)As/Ga(PAs) quantum wells with different well depths and equal well widths is investigated by quantum beat spectroscopy based on transient degenerate four-wave mixing. The ratio of biexcitonic to excitonic binding energy increases with stronger confinement. This new experimental result is discussed in the framework of recent theoretical predictions and experimental results.

We study the dependence of the binding energies of excitonic molecules on the confinement in semiconductor quantum wells. A set of symmetrically strained (GaIn)As/Ga(PAs) quantum wells with different well depths and equal well widths is investigated with transient degenerate four-wave mixing. The ratio of biexcitonic to excitonic binding energy increases with stronger confinement. This experimental result is discussed in detail in the framework of recent theoretical predictions and experimental results.

Circularly polarized optical excitation of a semiconductor microcavity in a transverse magnetic field leads to pulsed laser emission with alternating circular polarization synchronized to the electron Larmor precession. The synchronization originates from the transfer of electron-spin coherence to the dynamics of the optical field. A microscopic theory is developed to analyze the coupled carrier--light-field dynamics.

We investigate epitaxial layers of GaN on c-plane sapphire by photoluminescence, optical density and x-ray diffraction. Besides the well known luminescence from hexagonal GaN we have identified two emission bands from cubic GaN. We observe the emission of the donor bound exciton in cubic GaN at 3.279 eV. The luminescence at 3.15 - 3.21 eV is explained as the cubic donor - acceptor recombination. The corresponding acceptor binding energy is found to be low as . For layers of 400 nm thickness, the optical density yield values for the average contents of cubic GaN between 10 and 25%. Proper growth conditions minimize the cubic contents in the upper regions of such layers.

Magnetic circular dichroism and time-resolved photoluminescence spectra were measured for cubic GaN epitaxial layers grown by gas source molecular beam epitaxy using NH3 plasma. Pronounced spectral features were observed in the magnetic circular dichroism spectra at the same energy position as the highest energy signals in reflection and photoluminescence spectra of the epilayers. The time-resolved photoluminescence measurement showed that the corresponding transition has a lifetime of around 15 ps. Considering these results, the exciton bandgap of cubic GaN is estimated to be 3.27 ± 0.01 eV at 4.2 K.

We present a study of tunnelling processes between CdTe CdMnTe quantum wells by means of steady-state and time-resolved spectroscopy. The energy difference of the involved states and the barrier height can be controlled by an external magnetic field and resonances of the heavy-hole and exciton levels can be achieved. The heavy-hole (hh) resonance is essential for the type and direction of the transfer process. An efficient transfer of excitons is possible even without emission of LO phonons.

Spin quantum-beat spectroscopy is presented as a powerful tool for the investigation of the electron Lande g factor and the spin dynamics in bulk and low-dimensional semiconductors. The technique has several advantages including high sensitivity, broad applicability, and ease of implementation and, therefore, proves to be superior to other techniques as, e.g., the Hanle-effect, spin-flip Raman scattering, and conduction band spin-resonance. We demonstrate the utility of this technique by the study of the temperature dependence of the electron Lande g factor g* in GaAs up to room temperature. We present as well results on the temperature dependence of g* in InP, the dependence of g* on quantum film thickness in GaAs-AlGaAs heterostructures, and the anisotropy of g* in quantum films and wires. A modification of this technique yields the direction of the spin rotation, i.e., the sign of g*. Finally, recent results on spin quantum beats in microcavities will be presented.

Steady-state and picosecond photoluminescence experiments on CdTe/CdZnTe and CdTe/CdMnTe asymmetric double quantum wells are presented. An external magnetic field is used to tune the coupling between the two QWs by allowing resonances to occur between excitonic states. Very efficient tunnelling is found when an exciton from the high-energy QW can transfer either with the emission of an LO phonon or via the resonance with the 2s state of the low-energy QW.

We report on the resonantly ground-state excited, time-resolved photoluminescence of self assembled InP dots embedded in In 0.48 Ga 0.52 P grown by molecular beam epitaxy. Measurements dependent on excitation power and temperature show that the resonant luminescence is sensitive neither to exciton-exciton scattering nor phonon scattering, demonstrating the quantum dot nature of the InP islands. The measured decay times yield the intrinsic radiative lifetimes of excitons, typically 400 ps and one order of magnitude larger than that found in quantum wells.

We report on the intrinsic radiative lifetime of excitons in InP quantum dots embedded in an In0.48Ga0.52 P matrix. This lifetime is about 400 ps as measured by time-resolved photoluminescence with resonant excitation of the ground states. It is independent of excitation density and temperature demonstrating the quantum dot nature of the InP islands and the strong localization of the excitons. Similar experiments on excitons localized by well width fluctuations in a GaAs quantum well reveal distinct differences: weakly localized excitons disappear with increasing density or temperature.

The origins and structure of molecular and solid-state fullerenes are reviewed. Comparison of the optical properties of solution and solid state indicates strongly that the molecular nature is preserved in the solid state. Picosecond time resolved photoluminescence, photoconductivity and resonant Raman measurements are performed to investigate the influence of high-intensity illumination on the properties of Fullerene single crystals. A highly non-linear dependence of the luminescence emission efficiency and lifetime is observed on increasing the intensity. This non-linear increase is associated with a dramatic shift to the red of the emission maximum. Under similar conditions, the photoconductive response of the fullerenes is also seen to increase non-linearly with input intensity. Temperature-dependent measurements indicate that the non-linear processes are associated with an insulator-metal phase transition in the material. The transition is reversible and the observed photophysical changes coincide with a reversible shifting of the characteristic fullerene Raman lines to lower energies. At room temperature, in many samples, the shifting becomes irreversible, and a high molecular weight, insoluble material is formed. The photochemical process is proposed to be a polymerisation-like reaction of the fullerene molecules in the triplet excited state. This is supported by the observation that the rate of the reaction is reduced greatly in the presence of oxygen, an efficient triplet quencher. In conclusion, the response of Fullerene crystals to light is divided into three categories. At low intensities the photophysical processes are characteristic of those of a molecular insulator, the electronic wavefunctions being molecularly localised. At higher intensities, the material undergoes an optically-induced Mott-like transition to a semiconductor/metal, in which the electrons become delocalised in three dimensions. Thirdly, the material is found to be photochemically unstable under some conditions but analysis of the temperature and intensity dependence of Raman spectroscopy shows that the photodegradation process can be predicted and therefore controlled.

Spin quantum beats of free-electron Larmor precession are measured by time-resolved photoluminescence spectroscopy and yield an extreme anisotropy of the electron Lande g-factor in quantum wires. The g-factor changes from 0.56 along the wires to approximately 0 perpendicular to the wires. The experimental results are in good agreement with an estimate according to k p theory.

The aim of the present study was to determine the correlation of cotinine levels in amniotic fluid and in fetal and corresponding maternal blood samples. Amniotic fluid samples (N = 130) were taken during second trimester amniocentesis, umbilical artery blood samples (N = 75) at birth, both together with corresponding maternal blood samples. Self-reported smokers showed maternal serum cotinine levels > 15 ng/ml in 93%, self-reported nonsmokers levels < 15 ng/ml in 89%. Correlation of corresponding values for cotinine was 0.81 - 0.92. Cotinine values were increased in fetal blood and amniotic fluid in comparison to maternal serum levels. Despite the fact that pathophysiology is not fully understood, an accumulation of nicotine and its metabolites both in the fetus and in the amniotic fluid appears to be evident

We report on time-resolved luminescence in GaAs quantum wells in high magnetic fields up to 21 T. Results on resonant tunneling and exciton relaxation including spin flip are presented

The initial nonthermal electron distribution at densities \ensuremath{\le}${10}^{14}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ is studied in GaAs:Be by investigating the band-to-acceptor luminescence after excitation by picosecond laser pulses. Two peaks are observed originating from electrons generated out of the heavy- and light-hole valence bands, respectively. This assignment is confirmed by polarization dependence. Variation of excitation energy yields the valence-band dispersions for wave vectors 0.04(\ensuremath{\pi}/a), where purely parabolic terms dominate. The light- and heavy-hole masses relevant for optical interband excitation of a 100 GaAs surface close to the band edge are determined to be ${\mathit{m}}_{\mathrm{lh}}$=0.093${\mathit{m}}_{0}$\ifmmode\pm\else\textpm\fi{}0.007${\mathit{m}}_{0}$ and ${\mathit{m}}_{\mathrm{hh}}$=0.54${\mathit{m}}_{0}$\ifmmode\pm\else\textpm\fi{}0.05${\mathit{m}}_{0}$.