Máximo López

Surface diffusion length of Ga adatoms in molecular-beam epitaxy on GaAs(100)–(110) facet structures

Abstract By the molecular-beam epitaxial (MBE) growth of GaAs on [001]-mesa stripes patterned on GaAs(100) substrates, (110) facets were formed on the mesa edges defining (100)–(110) facet structures. The surface diffusion length of Ga adatoms along the [010] direction on the mesa stripes was obtained for a variety of growth conditions by in-situ scanning microprobe reflection high-energy electron diffraction (μ-RHEED). Using these values and the corresponding growth rate on the GaAs(110) facets, the diffusion length on the (110) plane was estimated. We found that the Ga diffusion length on the (110) plane is longer than that on the (100) and (111)B planes. The long diffusion length on the (110) plane is discussed in terms of the particular surface reconstruction on this plane.

Molecular Beam Epitaxy of GaAs/AlAs on Mesa Stripes along the [001] Direction for Quantum-Wire Fabrication

We report on the growth of GaAs/AlAs layers by molecular beam epitaxy on GaAs (100) substrates patterned with mesa stripes oriented along the [001] direction. The GaAs growth led to the formation of {110} facets which were smoother than the facets formed on [01]- and [0]-oriented mesa stripes. It was also found that the GaAs growth rate on the {110} facets is extremely low. We fabricated quantum wire-like structures by narrowing the width of the mesa-top (100) facet, which is limited by the (10) and (110) facets, to the nanometer scale, and then growing an AlAs/GaAs quantum well. The resulting structure was as narrow as ~30 nm with a thickness of ~30 nm at its center.

Realization of mirror surface in (111)- and (110)-oriented GaAs by migration-enhanced epitaxy

The layer-by-layer growth mode was readily realized on exactly oriented GaAs(111)B and GaAs(110) substrates by migration-enhanced epitaxy. This growth mode results in a mirror surface with low hillock density of ∼103 cm−2 which is 3 orders of magnitude lower than the density obtained by conventional MBE growth.

Initial Growth Mechanism of GaAs on Si(110)

We report the initial growth mechanism of GaAs on Si(110) by molecular beam epitaxy. From in-situ reflection high-energy electron diffraction (RHEED) measurements we infer an initial two-dimensional growth mode. Streak RHEED patterns were observed up to about 20 Athickness of GaAs epitaxial growth. With further deposition, extra spots appeared due to twins. We propose a model in which the twins are formed from antiphase domain boundaries.

Initial growth process of GaAs on Ge substrate and pseudomorphic Si interlayer

Abstract The initial growth process of GaAs on Ge and Si was investigated relating to the segregation of Ge and Si atoms in the hetero-systems with small lattice mismatch and no anti-phase domain. It was clarified that the initial growth process is distorted by the segregation of Ge and Si, changing the surface reconstruction. The segregated atoms disturb the surface migration of Ga. It was estimated that little segregation of Ge atoms appears even in the AlAs initial layer, which effectively suppresses the segregation.

Realization of low facet density and the growth mechanism of GaAs on GaAs(110) by migration‐enhanced epitaxy

Smooth GaAs layers were successfully grown by migration‐enhanced epitaxy on exactly (110) oriented substrates. The surface of layers grown by conventional molecular beam epitaxy was completely covered with facets, whose density was higher than 106 cm−2. The facet density was reduced remarkably by three orders of magnitude using the migration‐enhanced epitaxy method. Observing the intensity oscillations of the specular spot of reflection high‐energy electron diffraction patterns, the growth mode and the migration characteristics of surface adatoms have been investigated.

Etching temperature dependence of the surface composition and reconstruction for Cl2‐etched GaAs layers

In order to understand the mechanism of the Cl2‐etching reaction with GaAs, the composition and reconstruction of in situ Cl2‐etched GaAs surfaces were studied as functions of the etching temperature. From an Auger electron spectroscopy analysis and reflection high‐energy electron‐diffraction observations, it was shown that the GaAs surface changed from As stabilized to Ga stabilized during low‐temperature (∼50 °C) etching, while it remained As stabilized during high‐temperature (150–250 °C) etching. This result can be understood by considering the temperature dependence of the desorption rate of chloride compounds. At low temperature, the desorption of Ga chlorides is more suppressed than that of As chlorides, resulting in rough Ga‐stabilized surfaces. At high temperature, the desorption of any chlorides is not suppressed. Thus, stoichiometric etching is realized, resulting in smooth As‐stabilized surfaces, which are advantageous for high‐performance microdevice fabrication.

AlGaAs/GaAs wire and box structures prepared by molecular‐beam epitaxial regrowth on in situ patterned GaAs substrates

We have developed a processing technique which is conducted entirely under an ultrahigh vacuum environment, called in situ electron‐beam (EB) lithography, to pattern GaAs substrates on which AlGaAs/GaAs wire and box structures are subsequently regrown. In this technique a thin GaAs oxide layer is selectively formed by EB‐stimulated oxidation under a controlled oxygen atmosphere, and is then used as a mask material to define mesa stripes and mesa squares by Cl2 gas etching. Subsequently, the initial mesa size is reduced by the regrowth of a GaAs layer. Finally, AlGaAs/GaAs wire and box structures are fabricated on the top of the mesas by the growth of a quantum well. These structures were characterized by cathodoluminescence measurements at 77 K.

Nanometer‐scale pattern formation of GaAs by in situ electron‐beam lithography using surface oxide layer as a resist film

We have studied the effects of the microscopic roughness of a GaAs epitaxial surface on the oxide layer, which is used as a resist‐mask material in in situ electron‐beam lithography. When electron beam patterning, followed by Cl2 gas etching, was carried out for an oxide‐mask layer formed on a rough surface, an indented pattern edge elongated along the [110] direction, typically having a size of several tens of nm, was formed. On the other hand, when we used a misoriented substrate in order to obtain a smooth epitaxial surface by introducing the so‐called step‐flow growth mode, the resulting pattern exhibited a sufficiently sharp edge. Based on this improvement, together with the optimized electron‐beam patterning system, we successfully fabricated an ultrafine trench structure with a width as small as 20 nm.

Molecular‐beam epitaxy and migration‐enhanced epitaxy growth modes of GaAs on pseudomorphic Si films grown on GaAs(100) substrates

GaAs layers were grown by molecular‐beam epitaxy and by migration‐enhanced epitaxy (MEE) on pseudomorphic Si films grown on GaAs(100) substrates. The Si interlayer thickness (tSi) was varied from 0 to 3 monolayers (ML), and the effect on the GaAs growth mode was investigated by observing the behavior of the intensity of the specular spot of reflection high‐energy electron diffraction patterns. From these measurements it was concluded that the surface migration of Ga atoms is disturbed by the Si atoms on the growing surface. The disturbance increased, at the growth temperature of 520 °C, with increasing the Si interlayer thickness to the point that for tSi≥0.4 ML, the two‐dimensional (2D) growth changed to a three‐dimensional one. By increasing the growth temperature, the growth mode improved but the Si surface segregation increased, as detected by secondary ion mass spectrometry. The effect of the thermally activated Si segregation process on the GaAs growth mode is discussed. Using MEE at a growth temper...