B.A. Joyce

Dynamics of film growth of GaAs by MBE from Rheed observations

Detailed observations have been made of the intensity oscillations in the specularly reflected and various diffracted beams in the RHEED pattern during MBE growth of GaAs, GaxAl1−xAs and Ge. The results indicate that growth occurs predominantly in a two-dimensional layer-by-layer mode, but there is some roughening, which is enhanced by deviations from stoichiometry and the presence of impurities. In the case of the GaAs (001) −2×4 reconstructed surface a combination of dynamic and static RHEED measurements has provided firm evidence for the presence of one-dimensional disorder features as well as surface steps.

Oscillations in the surface structure of Sn-doped GaAs during growth by MBE

Abstract The presence of predeposited or surface-accumulated Sn during MBE growth modifies the reconstruction of the (001)GaAs surface, as observed by RHEED, at coverages as low as 0.025 monolayer. If growth is initiated on such a surface, oscillation in the intensity modulation of some of the RHEED streaks occurs, with a period equal to the monolayer deposition time of the GaAs. This oscillation decays away at a rate determined by the substrate temperature and Ga flux.

Structure and stoichiometry of {100} GaAs surfaces during molecular beam epitaxy

Abstract Relationships between surface structures on {100} GaAs substrates and incident fluxes of Ga and As 4 have been examined in detail over the temperature range 300–950 K. Surface reconstruction effects observed by RHEED have been related to surface stoichiometry, and the stability criteria for several reconstructed surfaces determined. Reconstruction observed during autoepitaxial growth of GaAs from beams of As 4 and Ga is not a simple function of the incident fluxes, since effects associated with the thermal stability of the substrate can have important consequences. The results are discussed in relation to surface kinetic information obtained from modulated beam measurements, and to some current theories of surface reconstruction and growth step behaviour. Results on surface topography are used to illustrate the ambiguities of streaked RHEED patterns. It is shown that streaks of constant intensity normal to the shadow edge cannot be used as the sole criterion by which to define the presence of a flat surface.

Dynamic RHEED observations of the MBE growth of GaAs

Detailed measurements have been made of the specular beam intensity in RHEED patterns from static and growing GaAs surfaces. The basic parameters investigated were substrate temperature and electron beam azimuth. The results have provided further understanding of growth dynamics and surface disorder, respectively. There is a significant trend away from two-dimensional growth at the higher temperatures, which also correspond to more Ga-rich surface structures. Conversely, surface disorder is apparently greater during growth at the lower temperatures, where the structure is As-rich. The static As-stable 2×4 surface is, however, the most ordered and the most closely two-dimensional. It has also been shown that ordered, two-dimensional growth can be initiated from excess Ga adatom populations.

Rheed studies of heterojunction and quantum well formation during MBE growth-from multiple scattering to band offsets

Abstract The basic concepts and first-order growth model derived from the RHEED intensity oscillation technique are described and the limitations imposed by the experimentally demonstrated multiple-scattering nature of the diffraction process are indicated. Despite these restrictions the value of the technique is illustrated in relation to growth mechanism studies, heterojunction and quantum well interface formation and as a process control monitor.

Current understanding and applications of the RHEED intensity oscillation technique

Abstract The problem of reflection high energy electron diffraction (RHEED) and electron scattering from smooth and growing surface is briefly reviewed. Evidence is given that strong electron beam penetration and multiple scattering effects are present under the conditions used to observe intensity oscillations in RHEED during growth by molecular beam epitaxy (MBE). A survey is made of the predominant RHEED oscillation features, i.e. damping, increases in amplitude, transient behaviour, phase differences and the appearance of harmonics. These features can be related to growth and diffraction processes.

Effects of diffraction conditions and processes on rheed intensity oscillations during the MBE growth of GaAs

The RHEED intensity oscillation technique has received wide-spread attention for the study of MBE growth dynamics, but insufficient consideration has been given to the diffraction conditions and processes involved. We report here a systematic investigation of the intensity oscillation behaviour as a function of diffraction parameters (azimuth, incidence angle, specular and non-specular beams), with constant growth conditions for GaAs films on GaAs (001) substrates.We show that many reported anomalies attributed to growth effects, such as phase differences and periodicity variations, can be accounted for entirely by diffraction events, provided it is realised that multiple scattering processes are the dominant cause of RHEED intensity variations during growth.The technique can provide valuable information on growth behaviour, but only if diffraction-dependent effects are first eliminated.

Kinetic limitations to surface segregation during MBE growth of III–V compounds: Sn in GaAs

The incorporation of Sn as a dopant in GaAs has been studied in the temperature range of 500°–650° C, over a wide range of Ga and As fluxes, the latter being incident as either As4 or As2 molecules. The results are explained in terms of a surface segregation model in which the behaviour at high growth temperatures (above ∼600 °C) approaches thermal equilibrium, but growth at lower temperatures involves a kinetic limitation to the segregation process.

Surface processes controlling the growth of GaxIn1−xAs and GaxIn1−xP alloy films by MBE

Abstract The kinetics of surface processes involved in the growth of certain III-III-V alloy films from beams of their constituent elements has been investigated by modulated beam techniques in combination with RHEED and AES. It has been shown that the principle limitation to the growth of these alloy films by MBE is the thermal stability of the lasser stable of the two III–V compounds of which the alloy may be considered to be composed. This leads to the preferential desorption of the Gp V element (as a dimer), leaving an excess surface population of the Gp III elements. At somewhat higher temperatures the situation is further complicated by the preferential desorption of the more volatile Gp III element. Surface segregation effects as such appear to be minimal.

Composition effects in the growth of Ga(In)AsyP1-y alloys by MBE

Abstract Factors controlling the overall composition of films of GaAs y P 1- y and InAs y P 1- y grown by MBE on [100]GaAs substrates have been investigated by direct measurement of the sticking coefficients and surface lifetimes of As 4 and P 4 molecules using modulated beam techniques. A simple model for the basic growth process is presented in which it is shown that the Ga(In) to As 4 flux ratio is the critical parameter in the control of composition. Additional results based on TEM and SIMS investigation of the films show that complex local distribution effects can occur resulting in both phosphorus incorporation in the substrate and specific anion clustering in the film.