Luis F. Sanz

Optically induced recovery by near band gap photons (1.4 eV<hν<1.5 eV) of EL2 level from its metastable state in semi‐insulating GaAs

The study of the recovery of the EL2 related photocurrent by photons of the near‐band gap spectral range (1.4–1.51 eV), after photoquenching reveals that the amount of EL2 levels that can be quenched depends on the excitation conditions. In particular light of the 1.44 eV, photocurrent band, produces an increase in the amount of EL2 quenchable levels. This is discussed in terms of an actuator level, whose charge state controls the transition to the metastable state and on the other hand ensures the electrical compensation when EL2 is in the metastable configuration, for which it is in its neutral charge state, and hence unable to compensate the ionized shallow acceptors.

Stress distribution mapping of GaAs on Si conformal layers

Cathodoluminescence and micro-Raman studies of GaAs on Si layers grown by the conformal method show a characteristic quasiperiodic modulation of the stress distribution perpendicular to the growth direction. Using the capability of the spectral imaging in the cathodoluminescence technique, the stress distribution has been directly mapped. The Raman data give accurate information of the stress level variations in the upper part of the samples, which compare well with the luminescence data. The origin of the quasiperiodic stress variations are discussed in terms of the growth geometry, taking account of the presence of a compliant thin SiO2 layer in between the Si substrate and the ⟨110⟩ growing GaAs layer.

Characterization of the homogeneity of semi-insulating InP by the spatially resolved photocurrent

Abstract Semi-insulating Fe-doped InP wafers have been studied by a spatially resolved photocurrent technique. The photocurrent fluctuations are interpreted on the basis of either N D −N A or [ Fe +3 ] variations, resulting in non-homogeneous electric local compensation, owing to local variations in either the total electrically active Fe concentration or the net donor concentration. Growth striations are revealed, showing differences in the local photocurrent fluctuation at different parts of the wafers, these being barely observable in the wafer edge.

Photocurrent study of Fe-doped semi-insulating InP

Abstract Fe distribution is studied in semi-insulating liquid-encapsulated Czochralski (LEC) Fe-doped InP, by means of spatially resolved photocurrent measurements. Local fluctuations of the extrinsic photocurrent are related to Fe distribution inhomogeneities, which are related to the dislocation atmospheres. The electronic transitions involved are modelled by a set of rate equations. The theoretical model gives an excellent fit of the experimental data, thus allowing us to obtain an estimation of the local Fe3+ concentration, which can fluctuate by up to 15% of the average concentration.

Study of defects in conformal GaAs/Si layers by optical techniques and photoetching

We present the characterization of crystal defects in GaAs layers grown on silicon substrates by the conformal growth method. This technique consists of GaAs lateral growth from GaAs seeds confined in between the Si substrate and an overhanging dielectric cap layer. These conformal layers grow with a reduced density of crystal defects, e.g. dislocations, which are effectively filtered by the particular geometrical configuration. The samples were analyzed by micro-Raman spectroscopy, cathodoluminescence, phase stepping microscopy and were etched by diluted stirl solution applied with light (DSL). Several structures were revealed and analyzed, e.g. a quasi-periodic array of hillocks and valleys that are spatially correlated with fluctuations of the luminescence intensity. Other revealed crystal defects were grooves, hillocks and cracks. The main properties of these defects and their possible origin are studied.

A Study of Conformal GaAs on Si Layers by Micro-Raman and Spectral Imaging Cathodoluminescence

Spectral imaging cathodoluminescence and micro-Raman spectroscopy studies of GaAs layers grown on Si substrates by the conformal method allow to reveal a great variety of physical features of the layers, such as the complete stress distribution, self-doping effects, or the incorporation of dopants. We present herein the characterization of GaAs conformal layers grown by hydride vapor phase epitaxy, where the main issues concerning the distribution of defects and stresses are revealed. Also, intentionally doped layers were analyzed, revealing the main aspects of the incorporation of dopant impurities during growth.

Study of doping in GaAs layers by local probe techniques: micro-Raman, micro-photoluminescence and cathodoluminescence

The free carrier concentration of GaAs layers grown by MOCVD either on GaAs or Si substrates, by the conformal method in the last case, was obtained from the micro-Raman spectra using the hydrodynamic approach to fit the LO phonon-plasmon coupled Raman modes. The results on homoepitaxial layers were used as a calibration of the fitting method. The measurements in the selectively doped conformal layers were then compared with data obtained by micro-photoluminescence and cathodoluminescence spectroscopy and imaging. The doping data are compared with those deduced from the room temperature micro-photoluminescence and cathodolumiescence spectra.

Bulk Homogeneity of Iron Doped InP

Fe- doped InP is studied by a spatially resolved photocurrent technique, probing electronic transitions related to the iron impurity levels. This scanning technique allows to get information on bulk homogeneity regarding to the electrically active iron impurity distribution. The presence of doping growth striations is revealed with a high sensitivity. Also results about the local photocurrent at the Cottrell atmospheres of the dislocations are shown. The role played by other defect levels in the photocurrent contrast is also discussed.