Showing papers by "E. Muñoz published in 1994"

Dependence on the In concentration of the piezoelectric field in (111)B InGaAs/GaAs strained heterostructures

Abstract: A series of (111)B InxGa1−xAs/GaAs multiple quantum well p‐i‐n structures have been investigated via low temperature photocurrent and photoluminescence spectroscopies. The indium mole fraction was in the range of 0.07–0.23. Evolution of the experimental blueshifts of the transition energies, with the external bias, agreed very well with the theoretical calculations. This allowed us to obtain precise information about the piezoelectric constant, e14, for the various In compositions. For the range of x investigated, we have found e14(x) to be linear with x but significantly lower than predicted by a simple linear interpolation of the accepted values for GaAs and InAs.

Conduction‐band engineering in piezoelectric [111] multiple quantum well p‐i‐n photodiodes

Abstract: The influence of the design parameters on the conduction‐band profile and optoelectronic properties of [111]‐oriented InGaAs/GaAs p‐i(MQW)‐n diodes is presented. An analytical expression for the average electric field (AEF) in the p‐i‐n active region (MQWs within the intrinsic region) is obtained. The existence of two different potential envelopes, corresponding to a positive or to a negative sign of the AEF, and giving rise to clearly different optical and electronic properties, is demonstrated. In samples with negative AEF, as compared to structures with positive AEF, larger reverse voltages are needed to quench the photoluminescence and to enhance the p‐i‐n photocurrent. An analysis of both transition energies and intensities, versus bias, clearly indicates that in samples with a negative AEF carriers accumulate at the extremes of the active region, giving rise to a long‐range screening effect of the field in the wells.

Room‐ and low‐temperature assessment of pseudomorphic AlGaAs/InGaAs/GaAs high‐electron‐mobility transistor structures by photoluminescence spectroscopy

Abstract: The use of room‐ and low‐temperature photoluminescence (PL) spectroscopy for the assessment of n‐type pseudomorphic AlGaAs/InGaAs/GaAs high‐electron‐mobility transistor structures is reported. We describe a method to determine the InAs mole fraction x, the channel layer thickness L, and the confined two‐dimensional electron gas density (ns), based on the comparison between the PL transitions and the recombination energies derived from self‐consistent calculations of the subband structure. A detailed analysis of the optical transitions and their dependence on the Fermi level position and temperature is performed. It is shown that, in real devices, the high sensitivity of the recombination energies and intensities on small changes of the parameters x, L, and ns allows us to detect deviations from their nominal structural parameters within the uncertainty of the molecular beam epitaxy growth technique. The present assessment procedure has been applied to a significant number of samples, and it has been backe...

Relaxation of InGaAs layers grown on (111)B GaAs

Abstract: The relaxation behavior of InGaAs layers grown by molecular beam epitaxy on (111)B GaAs is investigated and compared with simultaneously grown (100) reference samples. Surface morphology, defect microstructure, and optical quality of the layers during the relaxation process are studied by Nomarski interference contrast, transmission electron microscopy, low‐temperature photoluminescence, and Raman spectroscopy. These techniques reveal an inhomogeneous and anisotropic relaxation in (111) samples. In (111) samples, the increase of critical thickness and the slower relaxation dependence on thickness, as compared with the (100) reference samples, is discussed

Nonlinear optical response, screening, and distribution of strain in piezoelectric multiple quantum wells

Abstract: By embedding piezoelectric InGaAs/GaAs multiple quantum wells (MQWs) in specifically designed p‐i‐n structures, we demonstrate that the nonlinear optical response can be used to identify the dominant screening mechanisms and simultaneously to determine the strain distribution Furthermore, we show that a knowledge of the screening mechanisms and spatial band structure, in turn, can be used to control the nonlinear optical response For this demonstration, we fabricate two p‐i(MQW)‐n samples on [111]‐oriented GaAs substrates The samples are designed such that, if the dominant screening is associated with photogenerated carriers that remain in the wells, a blue shift of the exciton would be expected in each By contrast, if the screening is associated with carriers that have escaped the wells and moved to screen the entire MQW, one will shift to the blue and the other to the red if the lattice is mechanically clamped, but both will shift to the red if the lattice is mechanically free The observation of a

Influence of delta‐doping profile and interface roughness on the transport properties of pseudomorphic heterostructures

Abstract: Thickness effects of the InGaAs channel on photoluminescence and transport properties of δ‐doped Al0.3Ga0.7As/In0.3Ga0.7As heterostructures are investigated. The spreading of the Si δ‐doping layer is deduced from a comparison of the measured charge with self‐consistent calculations assuming a Gaussian Si distribution profile and a definite ionization probability of the Si‐related DX centers. With decreasing channel thickness below 80 A, the effect of the spreading on the sheet carrier concentration increases and the low temperature mobility decreases due to roughness scattering at the In0.3Ga0.7As/GaAs interface. In channels thicker than 80 A the thickness‐independent alloy scattering process dominates.

Surface photovoltages due to pulsed sources: Implications for photoemission spectroscopy

Abstract: Photoemission spectroscopy experiments have shown that photons used to determine semiconductor band bending can induce measurable photovoltages. Because of the pulsed-photon source, the charging and discharging processes taking place at the semiconductor surface have been proposed as seriously affecting synchrotron-radiation photoemission measurements [M. H. Hecht, Phys. Rev. B 43, 12102 (1991)].In this paper we present some illustrative experiments showing the effects of using a pulsed-photon source on the surface potential of n-type GaAs with a semitransparent Schottky diode. Implications for synchrotron-radiation photoemission results are discussed. We conclude that in these experiments the originated photovoltages are practically flat, and that they can be calculated from average photocurrent data, taken as effective restoring currents. Photoelectron spectroscopy has been routinely used to study surface-semiconductor band bending during adsorption and interface formation. It is now well established that photovoltages present during photoemission experiments are responsible for a nonequilibrium contribution that directly affects band-bending measurements. Indeed, experimental studies corroborated that photon fluxes used in Schottkybarrier formation studies can induce measurable photovoltages. Incident photons produce electron-hole pairs that are separated by the electric field of the depletion region

Influence of In on Si local vibrational modes in InxGa1−xAs (0≤x≤0.12)

Abstract: Local vibrational modes (LVM) of Si in substitutional sites have been observed by resonant Raman spectroscopy in highly doped (≥8×1018 cm−3) InxGa1−xAs layers, either relaxed or under strain, on [100] GaAs substrates. The peak frequency ωLVM of the Si on Ga site (SiGa) LVM in unstrained samples shifts to lower values with increasing In content. For x≤0.10 this shift is clearly higher than expected from a linear interpolation between the measured values in the binaries. The comparison between the SiGa peak frequency measured in both a full strained layer and a relaxed layer with similar composition provides a rough determination of the deformation potentials for the SiGaLVM in these layers: q/ω2LVM=−2.7±1 and p/ω2LVM=−2.5±1. As the In content becomes higher the width of the SiGa peak increases much more than that of the GaAs‐like longitudinal optical‐phonon peak, revealing the splitting due to the loss of local symmetry introduced by the In. New calibration factors for the Si‐defect concentrations have bee...

Time-resolved piezoelectric nonlinearities and exciton dynamics in strained [111] p-i-n multiple quantum well structures

Abstract: Solid-state laser systems capable of delivering both moderate average power and high peak power are of interest to the scientific and industrial communities, especially in applications requiring efficient harmonic wavelength conversion. We have developed a regeneratively amplified, mode-locked diode-pumped, Nd: YAG system presently capable of delivering 1 mJ in a 20 ps FWHM pulse at a repetition rate of 2 kHz. Our system, shown in Fig. 1, consists of a diode-pumped, cw mode-locked oscillator and a diode-pumped regenerative amplifier separated by an optical isolator. The oscillator is a standard astigmatically compensated resonator pumped by a single 3 W laser diode and mode-locked by a L i m o 3 phase modulator. It produces 12 ps FWHM pulses at a repetition rate of 200 MHz with 700 mW of average power. The regenerative amplifier is based on a pump head consisting of a 1 .1%-doped, 2-mm diameter, 40-mmlong, anti-reflection coated Nd:YAG rod side-pumped by six 10 W linear diode arrays. The diodes are focused in pairs into the center of the rod by three elliptical copper mirrors arranged symmetri-