T. Shitara

Ga adatom incorporation kinetics at steps on vicinal GaAs (001) surfaces during growth of GaAs by molecular beam epitaxy

We have systematically examined the transition from two‐dimensional nucleation to step‐flow growth on variously misoriented vicinal GaAs (001) surfaces during molecular beam epitaxy using reflection high‐energy electron diffraction (RHEED). The time to the first maximum of the RHEED intensity oscillations is gradually delayed as the growth mode transition temperature is approached from below as the result of an increasing number of adatoms being incorporated at steps. Detailed analysis of this delay has shown that the incorporation rate is independent of the Ga flux, but it is strongly dependent on the direction of misorientation. This means that step edges do not act as perfect sinks for adatoms, but that detachment can occur relatively easily. The energy barrier for incorporation is considerably higher for Ga‐ than As‐terminated steps, which strongly suggests that the anisotropic growth mode transition on GaAs (001) stems mainly from the different step structures rather than anisotropic Ga adatom migration.

Morphological model of reflection high‐energy electron‐diffraction intensity oscillations during epitaxial growth on GaAs(001)

Reflection high‐energy electron diffraction (RHEED) measurements have been carried out on vicinal GaAs(001) surfaces which are misoriented by 2° and 3° toward the [010] direction. The misorientation‐angle dependence and the Ga‐flux dependence of the growth‐mode transitions for a fixed As/Ga ratio of approximately 2.5 have been reproduced by Monte Carlo simulations of a solid‐on‐solid model. The surface step‐density evolutions generated by the simulations are remarkably similar in profile to the measured RHEED oscillations, and show approximately the same relative change of amplitude with temperature for the chosen diffraction conditions.

Reflection high‐energy electron diffraction intensity oscillations and anisotropy on vicinal AlAs(001) during molecular‐beam epitaxy

We have examined the reflection high‐energy electron diffraction (RHEED) specular beam intensity oscillations on vicinal AlAs(001) which was grown on GaAs(001) substrates misoriented by 2° or 3° toward [110], [010], and [110]. The temperature dependence of the RHEED oscillation behavior on vicinal surfaces is similar to that on GaAs(001) and InAs(001). The cation flux and misorientation angle dependencies of Tc on AlAs(001) also followed the same pattern as on GaAs(001), as expected. Similarly, the same anisotropic behavior was also obtained, in that Tc[110]≳Tc[110]. Unlike GaAs(001), however, the surface reconstruction could not be kept constant during the growth mode transition and it is therefore very difficult to analyze AlAs(001) data in as much detail as that for GaAs(001), but from the similarity between them we have qualitatively estimated the effective surface migration barrier for Al adatoms on AlAs(001) as ∼1.74 eV.

In adatom migration studies by reflection high‐energy electron diffraction oscillations on vicinal InAs(001) surfaces

The transition from growth by the formation and coalescence of two‐dimensional clusters to the growth by step advancement on vicinal InAs(001) surfaces has been examined during molecular‐beam epitaxy by the measurements of reflection high‐energy electron diffraction oscillations. The growth mode transition is compared with results from vicinal GaAs(001) surfaces and qualitatively analyzed on the basis of the surface migration and attachment kinetics of In adatoms.

As/Ga ratio dependence of Ga adatom incorporation kinetics at steps on vicinal GaAs(001) surfaces

Abstract Systematic measurement of the growth kinetics on the transition from growth by cluster formation and coalescence to growth by step advancement on vicinal surfaces during MBE growth of GaAs(001) films has revealed that the first maximum of the RHEED intensity oscillation is gradually delayed (the period increases) as the growth mode transition temperature is approached from below. This is a direct consequence of the gradual change of the growth mode with temperature; as more atoms are involved in the step propagation mode, the number available for island nucleation decreases, with a resultant increase in the period. We have reported that detailed analysis of this delay allows us to investigate the incorporation kinetics of Ga adatoms into step edges and that the energy barrier for incorporation is considerably higher for Ga- than for As-terminated steps. Here we have examined the As/Ga ratio dependence of the Ga incorporation mechanisms using this technique and have found that the incorporation rate for Ga-terminated steps is enhanced while that for As-terminated steps is reduced as the As/Ga ratio is increased near transition temperatures. It suggests that additional arsenic enhances incorporation kinetics into the Ga-terminated steps via As-As dimers but blocks the sites on the As-terminated steps.

A systematic RHEED study of regular and random steps on GaAs(001) surfaces

Abstract A detailed understanding of step structures is becoming increasingly important in the growth of low-dimensional semiconductor structures such as quantum wells and quantum wires and also in the study of thin-film growth dynamics. One of the main techniques to have been employed is reflection high-energy electron diffraction (RHEED), mostly within the framework of a kinematic treatment of the observed diffraction effects. In this paper we report the results of a systematic study of diffracted intensity distribution along and perpendicular to reciprocal lattice rods from both the regular step structures present on a vicinal GaAs(001) surface and the irregular structures resulting from submonolayer film deposition. The validity of using a kinematic treatment is examined critically and an alternative model which includes various forms of incoherent scattering is proposed.

Elementary processes in the MBE growth of GaAs

Abstract The application of surface science and computer simulation techniques to stusies of surface reaction kinetics and growth dynamics has enabled significant advances to be made in our understanding of thin film growth by molecular beam epitaxy (MBE). In this paper we will discuss surface migration and incorporation processes of adatoms during the growth of GaAs from elemental sources and also surface relaxation which follows the termination of growth. Experimental measurements have been based on the application of reflection high-energy electron diffraction (RHEED) measurements to growth on vicinal surface for adatom migration studies and singular surfaces for relaxation effects. These have been complemented by theoretical treatments using principally Monte Carlo simulations and nucleation kinetics.

Applications of RHEED to the study of growth dynamics and surface chemistry during MBE

Abstract We discuss three applications of RHEED to the study of semiconductor film growth by MBE. In the first we discuss the extension of the vicinal plane method to the in-situ measurement of step propagation rates and show how they vary with growth parameters. The second concerns some apparent anomalies in the RHEED response to the growth of GaAs on GaAs(110) surfaces. Finally we consider surface chemical processes (reaction and segregation) in the growth of Si and SiGe alloys from molecular beams of Si 2 H 6 and GeH 4 . We demonstrate that the in-situ measurement of the growth rate on a monolayer-by-mono-layer basis can provide quite detailed chemical information.

Common Features of Epitaxial Growth on Vicinal GaAs(001), AlAs(001) and InAs(001) Surfaces

We have carried out RHEED measurements and Monte Carlo simulations of the growth on GaAs(001), AlAs(001) grown on GaAs(001), and InAs(001) to address the common features of the growth near the transition to step flow. For a fixed V/IIl ratio, the cation flux and misorientation-angle dependencies of the transition temperature on AlAs(001) and InAs(001) follow the same pattern as on GaAs(001). The same anisotropic behavior was also obtained, in that the transition temperature on a surface misoriented toward [110] is higher than that on a surface misoriented toward [110]. Unlike the case of GaAs(001), however, the surface reconstruction could not be kept constant near the growth mode transition for AlAs(001) and InAs(001). Therefore, we cannot compare simulations with experiments in as much detail as we have done for GaAs(001). Nevertheless, we can still estimate the effective surface migration barrier for Al adatoms on AlAs(001) as approximately 1.74eV and for In adatoms on InAs(001) as at most 1.23eV. This value should be compared with the value of 1.58eV obtained for GaAs(001).

Precursor‐mediated epitaxial growth of GaAs(001) from triethylgallium: Where is the gallium released?

A model is described for the morphological evolution of GaAs(001) during metalorganic molecular‐beam epitaxy (MOMBE) with triethylgallium (TEG) and solid‐As sources. The model includes the migration and attachment/detachment kinetics of atomic Ga and the migration and decomposition kinetics of a more mobile precursor (not necessarily TEG). By biasing the decomposition of the precursor to sites with low coordination, we are able to account for two important observations concerning MOMBE and molecular‐beam epitaxy under nominally the same growth conditions: the reflection high‐energy electron diffraction (RHEED) specular intensity oscillations on a singular surface show higher amplitude and are less damped during MOMBE, but on a vicinal surface, there is no discernible difference in the RHEED measurements for the two techniques.