Caracterización por difracción de rayos X de heteroestructuras de semiconductores III-V : aplicación al diseño de superredes tensadas para epitaxias de GaAs-Si

217 páginas, 89 figuras, 7 tablas.-- Tesis para optar al grado de Doctor en Ciencias Físicas presentada el 17-12-1992 por Ángel Mazuelas Esteban.Esta tesis doctoral presenta resultados experimentales de caracterización de heteroestructuras de semiconductores III-v crecidos sobre substratos de gaas por mbe. Se presenta una descripción completa de la difracción de rayos x como herramienta de caracterización de materiales. Se ha aplicado a diversas estructuras tanto sin tensiones como pensionadas. Se han determinado los espesores críticos de diversos semiconductores III-v. Se han estudiado diversos tipos de superredes tensadas. Por ultimo, los estudios anteriores se sintetizan en una propuesta de superred tensada para epitaxias de gaas/si.Peer reviewe

Folded acoustic phonons in InAs-AlAs strained-layer superlattices

Raman spectroscopy is used to characterize highly mismatched (7%) InAs-AlAs superlattices grown by atomic layer molecular beam epitaxy. In particular, folded acoustic modes are presented and compared with two different theoretical models (Rytov and linear chain). We find good agreement between theory and experiments. We estimate, with a simple model, the magnitude of the effect of the strain on the phonon frequency shifts.Peer Reviewe

Structural characterization of GaAs/GaP superlattices.

Powder and double-crystal X-ray diffraction were used to study the structural properties of highly strained (GaAs)N/(GaP)M short-period superlattices grown on GaAs (001) substrates. In spite of the large lattice mismatch (f=3.6%) between GaAs and GaP and the competition for incorporation between As and P, high-quality short-period superlattices of GaAs/GaP have been grown by a development of conventional molecular beam epitaxy named atomic layer molecular beam epitaxy. The in-plane lattice parameter (a/sub ///) of the different superlattices was measured and studied as a function of the GaP content. The authors found that, for a given total superlattice thickness of 4000 AA, the critical lattice mismatch is fc approximately=0.5% (corresponding to an average GaP content of 13.6% in the superlattice). This means that for an average misfit or lattice mismatch above fc the superlattice starts to relax. This experimental result is compared with predictions of critical thickness theories based on energy criteria. A clear relation of the degree of relaxation with peak width of the superlattice zeroth-order diffraction peak is found. High-resolution transmission electron microscopy has been performed to analyse the type of dislocations that relax the mismatched layers.Peer Reviewe

X-ray diffraction determination of critical thickness of InAs and InP on GaAs grown by atomic layer molecular beam epitaxy

6 páginas.-- Comunicación oral presentada al Symposium F – Mechanisms of Heteroepitaxial Growth - Materials Research Society Spring Meeting celebrado en San Francisco (USA/1992).Peer reviewe

Atomic layer molecular beam epitaxy growth of InAs on GaAs substrates

3 páginas, 3 figuras, 1 tabla.-- PACS: 68.55.+bInAs layers with thickness ranging from 0.1 to 2.5 μm have been grown directly on highly mismatched (7.4%) (001) GaAs substrates by atomic layer molecular beam epitaxy (ALMBE). This growth method, based on the modulated deposition of one or both component species, provides InAs layers with excellent flat morphology, independently of the total thickness. A detailed study of the evolution of the electron diffraction (RHEED) pattern indicates that a complete decoupling between the InAs epitaxial layer and the GaAs substrate is reached in less that 10 monolayers. Evidence is obtained that layer-by-layer nucleation takes place from the beginning of the growth.Peer reviewe

Growth and characterization of ultrathin GaP layer in a GaAs matrix by X-ray interference effect

An ultrathin two monolayers thick layer of GaP sandwiched within a GaAs matrix was grown by atomic layer molecular beam epitaxy (ALMBE). The X-ray interference effect (Pendellösung) was used to determine the structural parameters such as thickness, lattice parameter, chemical composition, and strain. Excellent agreement between the experimental rocking curve and the simulation using the dynamical theory of X-ray diffraction was found indicating the high quality of the sample. Analysis of the scans in symmetrical (004) and asymmetrical (224) reflections, sensitive to both perpendicular and parallel strain, shows that the GaP layer is coherent with the substrate, i.e., it is below the critical thickness in agreement with critical thickness theories. Despite the competition for incorporation between arsenic and phosphorus the experimental GaP thickness is found to be identical to the nominal growth value, demonstrating full incorporation of phosphorus when growing by ALMBE. No significant out-diffusion or segregation of P is observed. © 1992 Springer-Verlag.Peer Reviewe

X-ray characterization of InAs laser structures grown by molecular beam epitaxy

An x-ray interference effect was used to characterize a set of strained layer laser structures containing N monolayers of InAs (N=1, 3, 5, 7) conveniently distributed in the quantum well active region. A sample containing 100 Å of Ga0.8In0.2As in the quantum well was also grown and characterized for comparison. Structural parameters such as thickness, chemical composition, and strain status of the different layers (cladding, waveguide, and quantum well layers) as well as the relaxation process and critical thickness due to increasing InAs content in the active region were studied. It was found that indium content was very close to the design values and that the whole structure is coherent with the substrate for 1 and 3 monolayers of InAs (and 100 Å of Ga0.8In0.2As) while the structure starts to relax by dislocation formation for 5 monolayers of InAs and is clearly relaxed for 7 monolayers of InAs. These x-ray results are in full agreement with transmission electron microscopy and characterization of the structures as laser devices.Peer Reviewe

High-resolution electron microscopy and X-ray diffraction characterization of alternately strained (GaAs)n(GaP)m(GaAs)n(InP)m superlattices grown by Atomic Layer Molecular Beam Epitaxy.

Alternately-strained-layer of (GaAs)n(GaP)m(GaAs)n(InP)m, superlattices with n = 10, 90 and m = 2 monolayers, have been characterized by X-ray diffraction and high-resolution transmission electron microscopy. The heterostructures were grown by atomic layer molecular beam epitaxy on GaAs semi-insulating substrates at a substrate temperature of 710K. All the structures were coherent with the substrate and there is an effective compensation of the strains due to GaP and InP layers. X-ray diffraction and high-resolution electron microscopy analysis indicate a high crystalline quality with layers thickness deviations of ± 1 monolayer from the designed value.Peer Reviewe

SnTe-doping of GaAs grown by atomic layer molecular beam epitaxy

Using x-ray diffraction and ellipsometry we have studied the incorporation process of SnTe in GaAs for n-type doping. Combining these two techniques allows us to decide whether SnTe is incorporated pairwise, as has been proposed in the literature. We found SnTe doping to change the E1 and E 1+Δ1 critical point parameters in a way similar to that previously reported for n-type Si-doped GaAs. X-ray diffraction and Hall measurements show that the free carrier concentration is more than 1/2 of the [Sn]+[Te] concentration. We thus conclude that a large proportion of SnTe is incorporated as independent Sn and Te dopant atoms. © 1995 American Institute of Physics.Ministerio de Educación y Ciencia de EspañaPeer Reviewe

Strain determination in MBE-grown InAs quantum wires on InP

6 páginas, 10 figuras.-- PACS number(s): 68.65.La, 68.60.Bs, 81.07.Vb, 81.05.Ea.-- Comunicación presentada al E-MRS 2002 Spring Meeting celebrado en Estrasburgo (Francia) del 18 al 21 de Junio de 2002.We have determined the strain in the three crystallographic directions in InAs quantum wires (QWr) grown by molecular beam epitaxy on (001)InP substrate. We used triple crystal x-ray diffraction to make scans along and perpendicular to the QWr direction in reciprocal space, around InP(220) reflections. We use the shape and strain sensitivity of the different scans to deconvolute both contributions. We used the f scan analysis in grazing incidence diffraction to measure the strain relaxation perpendicular to the QWr as a function of height in the wire. We finally compare these results with finite elements calculations of the strain tensor in InAs QWr on InP.This work was partially financed by Spanish MCyT under NANOSELF Project No. (TIC2002-04096) and by the SANDiE Network of excellence (Contract No. NMP4-CT-2004-500101 group TEP-0120).Peer reviewe