J.H. Neave

Arsenic incorporation kinetics in GaAs(001) homoepitaxy revisited

Abstract Reflection high-energy electron diffraction (RHEED) intensity oscillations have been used to obtain the arsenic incorporation coefficients for the homoepitaxial growth of GaAs on the (001) surface at different substrate temperatures. The incorporation coefficients of As 2 and As 4 are both temperature-dependent and saturate at maximum values of 1.0 and 0.5 at low temperatures. The results have been modelled using a kinetic scheme which assumes that the incorporation process using either As 2 or As 4 occurs via the formation of a molecularly adsorbed As∗ 2 precursor. The variation of the incorporation coefficients with temperature can be attributed to the fraction of As∗ 2 which does not participate in the incorporation process as the temperature is increased. The final step leading to growth and the formation of GaAs depends only on the incorporation of arsenic from this intermediate, and the implication is that the final incorporation step is independent of the arsenic species used in growth.

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.

The morphology and asymmetric strain relief behaviour of InAs films on GaAs (110) grown by molecular beam epitaxy

Abstract 30, 60 and 400 A thick InAs layers on GaAs (110) grown by MBE were studied using both TEM and X-ray diffraction techniques. Two different strain relief mechanisms, directly associated with (110) surface geometry, were observed in the two orthogonal directions [1 1 0] and [001]. In the [1 1 0] direction, the strain relief was via the nucleation of a regular array of Lomer type dislocations which have line direction u = [001] and Burgers vector b = 1 2 a [1 1 0] , whereas the relief in the [100] direction was via the generation of 60° type dislocations with u = [1 1 0] and b = 1 2 a 〈101〉 and 1 2 〈011〉 . The density of the latter was film thickness dependent. As a consequence, the overall strain relief of the InAs layers was thickness dependent and asymmetric in the thinner layers. The 60° type dislocations also give rise to local tilt about the [1 1 0] direction with large overall tilt in the thicker layer (400 A).

Is the arsenic incorporation kinetics important when growing GaAs(001), (110), and (111)A films?

The incorporation coefficients of As2 and As4, obtained from reflection high-energy electron diffraction intensity oscillations in the As-limited growth regime, are compared for the growth of GaAs on (001), (110), and (111)A surfaces by molecular beam epitaxy. The kinetic results are remarkably similar for (110) and (111)A, but very different from those obtained on (001). The incorporation coefficients decrease with increasing temperature for all three surfaces, with the effect being much more dramatic on (110) and (111) A. The low- and temperature-dependent incorporation coefficients on (110) and (111)A explain the need for high As:Ga flux ratios and low substrate temperatures in the preparation of high-quality GaAs epitaxial layers.

Incorporation kinetics of As2 and As4 on GaAs(110)

Abstract Reflection high energy electron diffraction (RHEED) intensity oscillations have been used to obtain the arsenic incorporation coefficient for the growth of GaAs on GaAs(110) by molecular beam epitaxy (MBE) using either As 2 or As 4 as the source of arsenic. In both cases, the incorporation coefficients decrease with increasing growth temperature, with the values obtained for As 2 being approximately twice those of As 4 . The results are modelled within a kinetic scheme based on the assumption that the incorporation processes are precursor mediated and in both cases involve a molecularly adsorbed As 2 intermediate. The difference in the activation energies for the desorption and incorporation of the As 2 intermediate is the same when using either As 2 or As 4 . The implication is that the final incorporation step in the growth of GaAs(110) is independent of the arsenic species used.

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.

Growth of III-V compounds on vicinal planes by molecular beam epitaxy

The dynamics of growth of III-V compounds by molecular beam epitaxy can be evaluated experimentally using the temporal variation of the intensity of reflection high-energy electron diffraction patterns. The use of substrate surfaces which are slightly misoriented from an exact low-index plane (vicinal planes) enables direct measurements to be made of cation migration parameters, but a correct analysis requires both step anisotropy and nucleation on the terraces to be taken into account. The experimental results are strongly supported by Monte Carlo simulations of growth, especially with regard to growth mode changes and the anisotropy of cation incorporation at steps. The direct growth of quantum wires (structures giving quantum confinement of carriers in two dimensions) on vicinal planes has been achieved experimentally and it is shown here how the wire quality, as determined by its compositional integrity, can be obtained by the simulation technique. The effects of flux, temperature, misorientation direction and interruptions of growth on quality are demonstrated.

A transmission electron microscopy (TEM) study of a wedge-shaped InAs epitaxial layer on GaAs (001) grown by molecular beam epitaxy (MBE)

Abstract InAs layers with a gradual increasing thickness from 0 to 300 A were grown on GaAs (001) by molecular beam epitaxy (MBE). Transmission electron microscopy (TEM) was carried out on both (001) plan-view and {110} cross-sections to investigate the development of the InAs layer morphology and the roughness of the InAs/GaAs interface. The observation shows that the initial InAs strained layer disintegrates at the stage when three-dimensional island nucleation begins. This is followed by simultaneous island growth and dissociation of the exposed GaAs substrate. The excess Ga atoms are then incorporated into the growing islands to form (In,Ga)As, leaving craters on the GaAs surface. The interfacial roughness originates from the in-fill of such craters, and results in the formation of the previously reported protrusions.

Growth of Si-doped GaAs(110) thin films by molecular beam epitaxy; Si site occupation and the role of arsenic

We have studied the relationship between the surface morphology, Si doping behavior, and arsenic incorporation kinetics for GaAs(110) thin films grown on singular substrates by molecular beam epitaxy. To obtain films with good surface morphology, homoepitaxial growth requires low substrate temperatures and high As:Ga flux ratios. Under these conditions, the Si-doped layers exhibit n-type behavior. Growth at higher temperatures and lower As:Ga flux ratios produces films with a poorer morphology, the n-type layers become increasingly compensated, and p-type layers are eventually formed. This growth-related site switching behavior and corresponding variation in surface morphology can be attributed to a low arsenic surface population, a consequence of the small and temperature-dependent arsenic incorporation coefficient for growth on GaAs(110).