M. Aguilar

Observation of non-trigonal lattice distortion in pseudomorphic InGaAs/GaAs superlattices grown on misoriented (111)B GaAs

We demonstrate the asymmetric lattice distortion of pseudomorphic superlattices grown on misoriented substrates. High-resolution x-ray diffractometry has been employed to study InGaAs/GaAs superlattices grown by molecular beam epitaxy on (111)B GaAs with a miscut angle of 1°. We observe the nontrigonal deformation of the InGaAs unit cells, while the GaAs cells retain the cubic symmetry. This result is in accord with the behavior predicted by the anisotropic elasticity theory. Consequently, the threefold symmetry of the [111] axis is lost and, therefore, the interpretation of the diffraction profiles must take account of the actual Miller indices of the substrate surface and reflecting planes used during each measurement. Otherwise, a non-negligible error in the determination of the period thickness and indium fraction could be introduced.

High‐resolution x‐ray diffraction study of piezoelectric InGaAs/GaAs multiquantum well p‐i‐n photodiodes grown on (111)B GaAs

High‐resolution x‐ray diffractometry has been applied to the structural characterization of piezoelectric strained InGaAs/GaAs multiquantum well p‐i‐n diodes grown by molecular beam epitaxy on (111)B GaAs substrates. Reference samples simultaneously grown on (001) GaAs have been also characterized. Diodes with 3, 7, and 10 periods and different well to barrier thickness ratio have been studied. Symmetric and asymmetric reflections at various azimuths were measured and the scans were fitted with theoretical curves obtained through a dynamical simulation program developed in our lab. The comparison between experimental and simulated profiles has enabled us to determine the main structural parameters of the samples. High‐resolution x‐ray diffractometry provided accurate data about period and capping layer thicknesses, indium content in the wells and state of relaxation, information which cannot be always obtained in (111)B samples from other characterization techniques such as photoluminescence or photocurre...

Direct determination of the piezoelectric field in (111) strained InGaAs/GaAs multiple quantum well p-i-n structures by photoreflectance

Abstract The photoreflectance (PR) technique has been applied to a p-i-n structure at room temperature containing InGaAs/GaAs multiple quantum wells to directly obtain the strain induced piezoelectric field and other critical parameters of the structure which was grown by molecular beam epitaxy on a (111)B GaAs substrate. It is shown that by this technique it is possible to measure the barrier field in the intrinsic regions of the diode through the Franz–Keldysh effect as well as the optical transition energies between all the confined electron and hole states in the wells. Structural parameters such as the well and barrier widths, length of the intrinsic region and InGaAs composition were determined from high-resolution X-ray diffractometry. As the p-i-n diode has a well defined built-in potential, by using this value in conjunction with a comprehensive characterization of the sample it is then possible to determine accurately the piezoelectric field in the wells. The measured value is compared to previously reported values.

Indium Isoelectronic Doping Influence on Etch Pit Density in GaAs Layers Grown by Vapour Phase Epitaxy

In this letter we report the In doping of GaAs layers grown by VPE (chloride method) using a Ga/In alloyed source. This work also aims to contribute to an understanding of the influence of isoelectronic doping on etch pit density (EPD) reduction. With a 4.5×1019 at.cm-3 optimum doping and a 8 µm optimum thickness, a 50-fold EPD reduction has been obtained. Buffer layers assure considerable EPD reductions to In concentration values of 4.5×1020 at.cm-3.

Design and characterization of (111)B InGaAs/GaAs piezoelectric superlattices

Expressions for the field distribution in novel clamped or free-standing piezoelectric strained InGaAs/GaAs superlattices are given. The voltage for miniband formation can be selected by incorporating these structures into p-i-n diodes, without requiring strain compensation between wells and barriers. This feature is evidenced by the photocurrent spectra and photocapacitance versus voltage characteristics obtained from high quality 40-period (111)-oriented superlattices. Wannier-Stark localization and resonant transport of carriers have been observed in the piezoelectric superlattices. The In concentration, thickness of the superlattice period and strain relaxation are deduced from X-ray measurements.

Trichloride Vapour Phase Epitaxial Growth of In1-xGaxAs on InP Using an In/Ga Alloy Source

In this paper, we report on the In1-xGaxAs epitaxial layer growth on InP using a Ga/In alloyed source. Lattice-matched In1-xGaxAs can be grown using an In/Ga alloy for 5–9% at. Ga. The influence of different parameters (source and deposition temperatures, the source stoichiometry and the input AsCl3 mole fraction) on the In stoichiometry has been studied in order to obtain the desired stoichiometry within a certain range.

Influence of Strain Compensation on Structural and Electrical Properties of InAlAs/InGaAs HEMT Structures Grown on InP

Strain-compensated InAlAs/lnGaAs HEMT structures, grown on InP substrate, have been investigated in terms of structural and electrical properties. From detailed x-ray diffraction (XRD) investigations the compensation index and the evolution of the strain state were measured. We show that a partial and controlled strain compensation significantly improves the structural quality and the thermal stability of HEMT structures as well as their electrical properties.

Temporization of a scanning ion gun for the in-depth measurement of the erosion rate compatible with SIMS data acquisition: a recursive method

Abstract In-depth high resolution erosion rate measurement is very important when looking for the best results in profiling thin, gradual atomic concentration films with SIMS, AES, or other techniques of surface analysis based on sputtering. We have developed an improved procedure to obtain the erosion rate, following the classic method using sputtered crater wall profile derivatives, fully compatible with SIMS data acquisition, adapted to digital raster scan primary ion beams, and independent of the nature of the materials to be studied. As derivatives introduce much noise and the measurement of changing slopes by conventional mechanical profilometers often carries several systematic errors, we pattern the crater shape to minimize these problems. With the proper timing, we reduce the sputtered area step-by-step, so that the final crater has straight-line shaped walls when the analyzed material is homogeneous. In the case of heterogeneous materials, we sputtered a series of craters, each made using the time calculated from the erosion rate obtained from the previous one, such that the profiles of the walls of each new crater took the aspect of straight lines. This iterative method ended when a crater looked like one made on a homogeneous material using the first temporization. So, we check the quality of the achieved erosion rate in a self-consistent way.

Charge accumulation effects in InGaAs/GaAs [111]-oriented piezoelectric multiple quantum wells

Abstract We show that charge accumulation in piezoelectric [111]-oriented multiple quantum wells (MQWs), with average electric fields opposing the field in the barriers, inhibits the shift of optical transitions by externally applied electric fields. This effect is due to the screening of the average electric field as photogenerated electrons and holes drift towards the opposite edges in the MQW region due to this average field. The resulting dipole flattens the envelope potential and hence precludes the change of energy levels with variations of external voltage. This behavior has been observed in different device configurations employing InGaAs/GaAs MQW embedded in a p-i-n diode by low temperature photoluminescence (PL) and photocapacitance spectroscopies under different bias conditions. In addition to these ‘self-locked’ transitions we also observed other peaks in the PL spectra related to the charge accumulation effect and that are qualitatively explained using Hartree calculations.

Growth and characterization of (InSb)m(InP)n short period superlattices

Short period superlattices of (InSb)m(InP)n were grown on semi-insulating (001) InP substrates by atomic layer molecular beam epitaxy. High resolution x-ray diffractometry was used to study the structural quality of the superlattices. Raman spectroscopy, in conjunction with theoretical calculations, provided information about intermixing at the interfaces.