P. Motisuke

Deep center characterization by photo‐induced transient spectroscopy

We show that photo‐induced current transients in semi‐insulating GaAs are well fitted by a unique sum of exponentials including the anomalous case, in which one of the exponentials has a negative amplitude. This fitting procedure is proposed as a more reliable method to be used in obtaining the trap emission constant. We also present an analytic solution for the kinetic equations of carriers taking into account the background current and the carrier recapture processes, which have been neglected in the previous approaches. This solution contains a very simple and physically coherent explanation for the appearance of negative peaks in the spectra of photo‐induced transient current spectroscopy.

Optical and structural properties of polycrystalline CdSe deposited on titanium substrates

We report studies of photoluminescence, Raman scattering and x-ray diffraction performed on CdSe polycrystalline films deposited on titanium substrates by two different methods: chemical deposition and electroplating. We discuss the changes observed in these films as they are subjected to heat treatments. The differences observed in the energy gap of both types of film and their evolution as a function of annealing temperature are tentatively explained in terms of quantum confinement produced by the small grain size of the films.

Raman scattering from InGaAs/GaAs strained-layer superlattices

Abstract We report the results of room temperature Raman scattering experiments on a series of In0.12Ga0.88As/GaAs strained-layer superlattices. From these measurements the amount of strain present in each type of layer is determined quantitatively. This information is used to discuss the question of critical thicknesses for this type of superlattice.

Effect of excited electron states lifetime on gain spectra of EHL in CdS

Abstract Gain spectra in highly photoexcited CdS have been studied. The results are compatible with the assumption of condensation of the photoexcited carriers into a strongly interacting electron-hole liquid (EHL). A gain tail, which extends well below the renormalized band gap energy, is observed. We show that carrier lifetime accounts for this tail, with the EHL not having achieved equilibrium with the thermal bath during the time it is probed.

Photoreflectance measurements on Si δ‐doped GaAs samples grown by molecular‐beam epitaxy

We investigate δ‐doped GaAs samples grown by molecular‐beam epitaxy with different silicon areal concentration and cap layer thickness, using photoreflectance spectroscopy. The features observed on the high‐energy side of the fundamental gap are attributed to transitions involving electronic sub‐bands in the δ‐doped potential well that take into account the diffusion of the dopants.

Thermally induced In/Ga interdiffusion in InxGa1−xAs/GaAs strained single quantum well grown by LPMOVPE

Abstract A strained single quantum well of GaAs/In x Ga 1− x Ga/GaAs ( x =0.23) has been grown by low pressure MOVPE on a (100) GaAs substrate at 625° C. Samples were annealed under AsH 3 /H 2 at different temperatures in the range 750 to 900° C. Since the quantum well thickness (∼80 A) is below the critical value for this lattice mismatched system, we assume that the InGaAs layer is commensurate with the GaAs substrate. We analyse the low temperature (2 K) photoluminescence of the electron to heavy hole transition in the quantum well of these samples to study the In/Ga interdiffusion at the InGaAs/GaAs interfaces. The position in energy of the photoluminescence peaks shift to higher energies when annealing. The shifts are quantitatively interpreted in terms of changes in the quantum well profile due to the In and Ga interdiffusion. We determined the interdiffusion coefficient at 850° C to be 3×10 −17 cm 2 /s, with an activation energy 2.07 eV. The values obtained for the In/Ga interdiffusion coefficient are larger than those published for the Al and Ga interdiffusion in AlGaAs/GaAs heterojunctions.

On the origin of Franz–Keldysh oscillations in AlGaAs/GaAs modulation‐doped heterojunctions

We have performed a series of photoreflectance measurements in a modulation‐doped AlGaAs/GaAs heterojunction containing a high mobility two‐dimensional electron gas. Measurements were performed as a function of temperature in the range 2 K≤T≤300 K. We studied the Franz–Keldysh oscillations associated with the E0 transition of both the GaAs and AlGaAs. The fields obtained from these oscillations for both sides of the heterojunction are quite different. Also, the temperature dependence of these fields are radically different. In fact, the temperature dependence of the field in the GaAs side of the modulation‐doped heterojunction sample is very similar to that of the field in a single undoped GaAs film deposited on a GaAs substrate, where no two‐dimensional electron gas is present. This shows that the field producing the observed oscillations on the GaAs side of the modulation‐doped heterojunction sample is not related to the field that confines the two‐dimensional electron gas.

Electroluminescence of III–V single‐crystal semiconducting electrodes

The luminescence generated by hole injection from an aqueous electrolyte into GaAs and InP has been investigated. Solid‐state properties are responsible for the variations encountered in different samples and for most differences observed between photoluminescence and electroluminescence.

Direct analysis of the photocurrent transient in semi-insulating GaAs

Abstract We report the results of a detailed analysis of digitally recorded photocurrent transients in semi-insulating GaAs. These generally consist of a sum of exponentials with decay time constants that can be uniquely determined from the fitting procedure. The obtained values for these time constants are more reliable than those determined from the conventional double gate method, where some questionable approximations are always included. At high temperatures and under a strong background illumination, we observed photocurrent transients with an inverted derivative signal. This signal inversion can be understood if we take into account the background current.

Hot electron and hot phonon contributions to radiative emission spectra in CdS at high excitation intensities

Abstract The dependence of excitation frequency of photoluminescence spectral shape of CdS at high excitation intensities allowed discrimination between hot phonon and hot electron contributions to the broadening of the emission band on one side and the broadening due to many body effects on the other. It was found that the shift towards lower energies of the emission peak is mainly due to induced high carrier density and that the broadening is related to the presence of high densities of optical phonons and hot carriers.