MBE Growth Of GaAs Research Articles

A RHEED and reflectance anisotropy study of the MBE growth of GaAs, AlAs and InAs on GaAs(001)

MBE growth of GaAs, AlAs and InAs on GaAs(001) has been monitored in real time, using simultaneous reflection high-energy electron diffraction (RHEED) and reflection anisotropy (RA) measurements, the RA measurements all being made with a fixed wavelength laser source operating at 647 nm. For the growth of GaAs and AlAs on GaAs(100), RA oscillations which occurred during the bilayer growth are explained in terms of the variation in the anisotropic distribution of surface “dimer” bonds during the growth process. RA data obtained during the growth of InAs/GaAs heterostructures are presented and discussed in relation to the influence of surface roughening upon both the RA and RHEED measurements.

Dopant patterning of MBE GaAs during growth by very low energy focussed tin ion beam deposition

For the first time a focussed ion beam has been used to successfully dope MBE GaAs during growth. GaAs with a mobility of 73 000 cm 2 V −1 s −1 at a carrier concentration of 1 × 10 14 cm −3 has been attained which is the highest mobility MBE GaAs achieved by the technique of ionised beam doping. The use of a tin focussed ion beam as an MBE dopant source has also allowed the three-dimensional patterning of the dopant concentration in GaAs, for the first time. The focussed ion beam apparatus did not interfere with or affect the conventional MBE growth of GaAs and AlGaAs in the chamber.

Comparative study of amorphous and crystalline buffer layers in MBE growth of GaAs on Si

The crystal quality and the annealing effect of the GaAs buffer layers grown on a (111)Si substrate were studied to find the best growth condition for two-step heteroepitaxial growth of GaAs on Si. Two kinds of buffer layers, one amorphous and the other crystalline, were grown at 100 and 350°C, respectively. The thickness of both kinds of buffer layers were varied from 25 to 200 Å. The difference in annealing behavior was studied by an in-situ RHEED technique. The amorphous buffer layer showed the presence of a much smaller number of plane defects than the crystalline buffer layer. It was found that there is a fundamental difference in the entering process of the dislocation between these two buffer layers. An X-ray diffraction study shows that the optimum thickness of the buffer layer resulting in the best epitaxial growth quality was 50–150 Å.

Si doping and MBE growth of GaAs on tilted (111)A substrates

Molecular beam epitaxy of GaAs doped with Si on a vicinal surface of (111)A, (211)A and (311)A have been examined. The variations of the impurity concentrations are dependent on the growth conditions and are affected by the angle of the substrates. The impurity concentrations are compared with a model calculation which is based on microscopic surface structures and kinematical surface reactions. Growth modes are monitored by reflection high-energy electron diffraction intensity oscillations. A doping mechanism of Si atoms into GaAs films is proposed.

Electrical properties and dopant incorporation mechanisms of Si doped GaAs and (AlGa)As grown on (111)A GaAs surfaces by MBE

The relation of Si incorporation site and the growth parameters in MBE growth of GaAs and (AlGa)As on (111)A surface is systematically investigated. Both n- and p-type GaAs and (AlGa)As layers with reasonably low compensation are achieved, and the dependencies of Si incorporation on the parameters can be qualitatively understood by the change of the population of As atoms at the surface. Two-dimensional electron and hole gas (2DEG, 2DHG) structures are successfully grown on (111)A substrates.

In-situ monitoring of antiphase domain evolution during atomic layer MBE (ALMBE) and MBE growth of GaAs/Si(001) by reflectance difference

Reflectance difference technique is used to in-situ monitor the antiphase domain (APD) annihilation process during atomic layer MBE and MBE growth of GaAs on Si 2° and 4° off (001) towards <110>. We show that this technique is able to provide quantitative information on the domain evolution. Experimental data obtained with reflectance difference show that thin GaAs layers (typically 50–100 nm) are enough for achieving a single domain growth front. APD evolution is characterized by a process which starts at the onset of growth and is thickness dependent. We observe a fast APD evolution during growth of the first 500 Å thick layer followed by a slow step in case a single domain growth front has not yet been achieved. We find that the rate of the APD annihilation process depends on growth conditions, although the GaAs thickness (∼500 Å) at which kinetics changes is dependent both on growth conditions and on density of steps in the starting surface (2° and 4° off (001) Si substrate). A possible relation between APD annihilation and lattice mismatch relaxation process is proposed based on these observations.

Two-dimensional nucleation in MBE growth of GaAs

The form and the energy of a two-dimensional critical nucleus (CN), arising on the As-stabilized (001) surface of GaAs, are discussed. It is shown that the CN, which consists of Ga and As consecutive layers, is strongly stretched along the [110] direction and the free energy of the CN is much less compared with the free energy of an isotropic nucleus.

Surface characterization by RHEED techniques during MBE growth of GaAs and Al xGa 1−xAs

The structure of GaAs(001) and AlGaAs(001) surfaces has been studied by RHEED over a wide range of growth conditions. Insight into the different dependence of surface order on stoichiometry for singular and vicinal surfaces is obtained via spot profile measurements and the time-dependent recording of the RHEED intensity. The behaviour of the singular surface is explained by a model that includes the terrace-step structure of the surface as well as a reconstruction induced roughness.

7280. GaAs MBE growth under Ga-rich conditions studied by RHEED intensity oscillations: A Bosacchi et al,Vacuum, 41, 1990, 919–922

7280. GaAs MBE growth under Ga-rich conditions studied by RHEED intensity oscillations: A Bosacchi et al,Vacuum, 41, 1990, 919–922

Substrate Misorientation Effect on Be Transport during MBE Growth of GaAs

The Be transport during MBE growth of GaAs has been studied. The Be surface segregation was clearly separated from the Be diffusion by using misoriented as well as nominal (100) substrates. The Be profiles measured by SIMS showed that the surface segregation was suppressed by the substrate misorientation even when the anomalous diffusion took place. The CAT observation revealed that the Be-induced disordering of superlattices occurred for 6×1019 cm-3 doping. The width of the disordered region was found to depend on the substrate misorientation, which was due to the misorientation dependence of the surface segregation. The step exchange model has been successfully employed to account for these results.

On the RHEED specular beam and its intensity oscillation during MBE growth of GaAs

The importance of the often neglected reflection of electrons in RHEED is established through examination of measurements of the specular beam intensity under different diffraction conditions from various surfaces. These results, together with rocking curve measurements provide an insight into ways in which the specular beam intensity is affected by changes on the surface. The necessary condition for the existence of intensity oscillations is identified and its diffraction basis is discussed. The model is subsequently applied to the study of the formation of the “inverted” interface during interrupted growth of GaAs/(Al,Ga)As heterojunctions.

GaAs MBE growth under Ga-rich conditions studied by RHEED intensity oscillations

We report on the study of RHEED intensity oscillations observed during the MBE growth of GaAs performed under different conditions. We experimentally show that under Ga-rich, As-limited conditions the growth rate does not depend only on the As beam equivalent pressure, but it is determined also by the As availability on the surface and that it has different values when a Ga-rich surface liquid phase is being formed or exhausted on the solid GaAs. Under the assumption that the surface liquid phase may also incorporate As, we deduce that the surface liquid phase may act as a sink or a reservoir of As, thus affecting the growth rate. We develop a quantitative model which: (1) explains the experimental data, and (2) allows for the evaluation of the Ga mole fraction in the surface liquid phase. We conclude that the liquidus temperature of the surface liquid phase is approximately 2/3 of that of the bulk GaAs system. This result points to a relevant contribution of the surface energy to the free energy of the surface liquid phase.

Periodic flux interruption and sustained two-dimensional growth for molecular beam epitaxy

Periodic interruption of Ga flux during MBE growth of GaAs has been used to achieve sustained two-dimensional layer-by-layer growth. RHEED intensity oscillation for extended growth shows no degradation in the oscillation amplitude, indicating an atomically smooth growth front throughout the growth.

Study of GaAs MBE growth under Ga-rich conditions by RHEED intensity oscillations

We report on the study of RHEED intensity oscillations observed during the MBE growth of GaAs performed under various conditions. We experimentally show that under Ga-rich conditions, the growth rate has different values when a Ga-rich surface liquid phase is being formed or exhausted on the GaAs solid phase. Under the assumption that the surface liquid phase may also incorporate As, we develop a quantitative model which (1) explains the experimental data and (2) allows for the evaluation of the Ga mole fraction in the surface liquid phase. From these data, we conclude that the liquidus temperature of the surface liquid phase is approximately 2 3 of that of the bulk GaAs system. This result points to a relevant contribution of the surface energy to the free energy of the liquid phase.

μm-Scale Lateral Growth of Ga-Monolayers Observed In-Situ by Electron Microscopy

ABSTRACTAn ultra high vacuum scanning electron microscope equipped to an MBE system is utilized to study a transient of a surface atomic structure during MBE growth of GaAs and AlGaAs by the alternate supply method. Lateral growth of a Ga-monolayer over microns is realized utilizing Ga droplets. This is confirmed by discriminating the Ga and As top layer by using the secondary electron intensity difference between the Ga and As top layer. The growth mechanism of the Ga monolayer is discussed based on the results.

The application of RHEED intensity effects to interrupted growth and interface formation during MBE growth of GaAs/(Al, Ga)As structures

There is a diffraction-induced phase effect in the RHEED intensity oscillation technique used in MBE, whereby intensity maxima only correspond to monolayer completion for very restricted conditions. In particular, the angle of incidence of the primary beam is extremely critical. The effect occurs because the total intensity at the measured position of the specular beam is always derived from at least two different diffraction processes, which do not have the same phase relation to monolayer formation. It can be accomodated either by a systematic series of measurements to establish an empirical relationship between incidence angle and phase, or by Fourier transform techniques. Unless full account is taken of this purely diffraction-induced effect, very misleading results can be obtained for the time constants of the recovery period following cessation of growth and this is illustrated for GaAs. The effect also has important implications for the growth-interrupt technique. In addition, it is shown that for heterojunction formation in the GaAs/(Al, Ga)As system, adatom (Ga and Al) migration lengths are of greater importance than the position in the monolayer at which the composition is changed, and that RHEED can provide only limited information on the interface structure.

Properties of Patterned Gallium Arsenide on Silicon

AbstractThe growth of GaAs on Si by MBE through openings in an oxide or nitride represents a convenient means for achieving monolithic GaAs/Si integration. We have examined a number of the materials growth and processing issues that must be resolved in order to achieve this goal. Some of the specific areas that have been investigated are (a) the effect of trench etching on the morphology of the patterned GaAs; (b) the dependence of patterned feature size on Hall mobility in both as-grown and postgrowth annealed samples; (c) the effect of annealing on the defect structure in the transition region from single crystal GaAs to polycrystalline growth; (d) the dependence of GaAs MESFET performance on proximity to the polycrystal transition; and (e) the performance of Si MOS devices following the GaAs MBE growth. Specific growth and processing issues concerning the integration of GaAs and Si device functions have also been examined.

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.

Phase-locked RHEED oscillations during MBE growth of GaAs and Al xGa 1−xAs

RHEED oscillations of the specular beam intensity have been analyzed during growth of GaAs and Al xGa 1−xAs on (001) GaAs. We found that it is possible to sustain RHEED oscillations indefinitely by a periodic phase locked perturbation of the growth front. This perturbation is provided by short interruptions of the impinging As 4 flux. A simple model is proposed to explain these results and the damping mechanism of RHEED oscillations.

MBE Growth of GaAs on Porous Silicon

ABSTRACTGaAs layers have been grown on porous silicon (PS) substrates by molecular beam epitaxyNo surface morphology deterioration was observed onGaAs-on-PS layers in spite of the roughness of PS. A 10% Rutherford backscattering spectroscopy (RBS) channeling minimum yield for GaAs-on-PS layers as compared to 16% for GaAs-on-Si layers grown under the same condition indicates a possible improvement of crystallinity when GaAs is grown on PS. Transmission electron microscopy (TEM) reveals that the dominant defects in the GaAs-on-PS layers are microtwins and stacking faults, which originate from the GaAs/PS interface. GaAs is found to penetrate into the PS layers.