J. C. Bezerra

Field-enhanced trapping in deep levels by multiple phonon emission in semi-insulating GaAs

We have carried out the time, temperature, and illumination dependencies of the current density in a semi-insulating GaAs sample grown at 300 °C under strong electric field. Standard ohmic behavior was observed at room temperature. A negative differential behavior as a function of the applied electric field was observed by lowering the temperature and increasing the photon flux, and this phenomenon was associated to the field-enhanced trapping effect. We have fit our data with a model for enhanced capture by a multiple-phonon emission capture process assisted by the applied electrical field.

Broadening of the Si doping layer in planar-doped GaAs in the limit of high concentrations

Abstract A series of samples of GaAs planar doped with Si, grown by MBE at low substrate temperatures and with different doping concentrations, is investigated. A comparison of Shubnikov-de Haas measurements and self-consistent numerical calculations shows that a broadening of the doped region occurs in spite of the low growth temperature. The broadening occurs via segregation of the Si impurities with the growth surface when the solid solubility limit of Si in GaAs is exceeded. For the growth conditions used this limit is determined to be (2.1 ± 0.2) × 1019 cm−3. At high doping densities an intrinsic compensation mechanism becomes active, limiting the concentration of conduction electrons.

Observation of the negative and positive persistent photoconductivity phenomena in silicon planar-doped GaAs

Abstract Photo-Hall free electron concentrations were measured on MBE-grown silicon planar-doped GaAs samples, for silicon nominal concentration in the range of (1.4 to 88)×1012 cm-2. We found both positive and negative persistent photoconductivities (PPPC and NPPC), which were discussed based on the growth parameters. Time resolved PPC measurements show some evidence that the positive and negative PPC effects are related to different physical processes. The PPPC effect seems to be related to the spatial charge separation and to the EL2 center and the NPPC effect to the DX center.

Evidence for negatively charged DX-center in Si-doped AlGaAs from persistent photoconductivity measurements

Abstract Persistent photoconductivity experiments were carried out in Si-doped AlxGa1-xAs at 77 K. The density of persistent free electrons was changed by a factor of 4 to 8. The electron mobilities micro were observed to increase for increasing electron densities n and from the behavior of micro(n) the variation of the ionized scattering impurity densities Ni with n was evaluated. The densities Ni show little change as compared to n. It is concluded that negatively charged centers are the only or at the least the dominant deep centers related to silicon impurities in AlGaAs.

Impurity breakdown in GaAs samples grown by molecular beam Epitaxy

In this work we present studies for the behavior of impurity breakdown of two GaAs samples grown by Molecular Beam Epitaxy at 200°C and 300°C. We vary the temperature and the illumination intensity. For the sample grown at 200°C, the transport mechanism after the breakdown is of the same type of the main free carriers at low electric fields. Below 100K, a clear dependence of the threshold electric field with temperature was observed. The sample grown at 300°C shows a breakdown due to an acceptor level at 41meV from the valence band. The threshold electric field increases with illumination due to the generation of free electrons by deep levels. A similar behavior was also observed for a Cr doped GaAs sample.

Use of the DX center as a probe to study the profile of Si impurities in planar‐doped GaAs

Photo Hall concentration and mobility were measured for two molecular beam epitaxy‐grown samples having a silicon planar‐doped structure in the GaAs layer of a GaAs/AlGaAs heterojunction. The nominal silicon concentration for both samples was 1.5×1013 cm−2 and the distance between the ideal localization of the doped plane and the interface was adjusted to be 15 A. The difference between the two samples is the growth direction. The Hall measurements were carried out at 77 K both in darkness and under illumination using an infrared light emitting diode as light source. Photoexcited effects indicate the presence of silicon atoms inside the undoped AlGaAs layer and that the silicon profile spreads mainly in the growth direction. Self‐consistent electronic structure calculations, in the effective‐mass approximations, were performed assuming doping profiles that simulate both samples. The calculations show that parallel conduction occurs when the growth direction is from GaAs to AlGaAs. This is consistent with ...

Hot electrons in delta-doped GaAs(Si) layers

Abstract Low temperature (2K) photoluminescence measurements have been performed in delta-doped GaAs(Si) layers, with carrier sheet concentrations Ns ranging from 1012 to 1013cm−2. Under the same excitation intensity, the luminescence spectra of all samples show a high energy tail which becomes more pronounced as Ns increases. Well defined electron temperatures, higher than the lattice temperature, are obtained, characterizing the electron heating effect in this system. The architecture of the delta-doping allows to observe hot electrons even at relatively low laser pumping intensities.

EPITAXIA DE COMPOSTOS III—V SOBRE SUBSTRATOS DE SILÍCIO

Pelicula heteroepitaxiais do Arseneto de Galio sobre Silicio sao obtidas por Epitaxia por Feixes Moleculares (MBE). As amostras sao analisadas atraves das tecnicas de Retrodifusao de Rutherford, Fotoluminescencia e Espalhamento Raman.