P.H. Fuoss

Gallium arsenide surface reconstructions during organometallic vapor‐phase epitaxy

In situ surface x‐ray scattering studies of the GaAs(001) surface were used to determine whether specific surface reconstructions occur during organometallic vapor‐phase epitaxy. Prior to growth, we find that surfaces heated in the presence of As form a c(4×4) structure, while those heated in the absence of organometallics or in Ga form two similar fourfold reconstructions. We find no evidence for the presence of any surface reconstruction during the actual layer‐by‐layer growth process.

Structure of GaAs=GaSb incoherent interface after epitaxial growth

The structure of GaAs=GaSb(001) incoherent interface has been studied by grazing incidence x‐ray scattering. The interface is periodic with a square array of edge dislocations. It is shown that the interface is nonplanar with 2–4 GaAs monolayers protruding in the GaSb epilayer at the dislocation core. This corrugated interface does not increase the strain energy by a large factor. Two possible mechanisms are suggested for the interface formation of large misfit epitactic growth: a stress induced mechanism or the presence of an ordered intermediate 2D layer.

Experimental considerations for in situ X-ray scattering analysis of OMVPE growth

Abstract We have recently performed a set of experiments using a chamber for growth of semiconductor single crystal films via organometallic vapor phase epitaxy (OMVPE) while simultaneously scattering X-rays from the growing crystal surface. Due to the special complications of OMVPE growth, such as near-atmospheric pressures, toxic and flammable gases, and high substrate temperatures, the chamber design includes many novel features. In this paper we will discuss the advantages of the z -axis diffractometer for such a chamber and the specific solutions to problems such as convective flow near the sample and film growth on the Be windows attached to the growth chamber. The X-rays enter the chamber through a 35-mm-diameter Be window mounted on a 2.75 in. UHV flange; they exit through a separate window which allows detection of X-rays from −5° to 125° in 2θ and take-off angles from the surface from −5° to 45°. Results from our experimental run on the PEP storage ring studying the growth of ZnSe on GaAs will be discussed.

X‐ray analysis of GaAs surface reconstructions in H2 and N2 atmospheres

In this work, we demonstrate the first in situ study of GaAs using grazing incidence x‐ray scattering during processing at 100 Torr prior to epitaxial film growth. Our results indicate that the native oxide is removed and a well‐ordered surface reconstruction is established at temperatures as low as 500 °C in hydrogen. In contrast, no surface reconstruction is observed when the substrate is heated in nitrogen at temperatures as high as 585 °C while comparable heating in hydrogen causes surface degradation in the form of liquid Ga droplets. These results suggest that a chemically induced surface transformation occurs rather than oxide evaporation during thermal treatment.

Atomic scale studies of epitaxial growth processes using X-ray techniques

In this work we have applied grazing incidence X-ray scattering to the study of nucleation and growth of GaAs by organometallic vapor phase epitaxy. Using the sensitivity of scattering at the 110 crystal truncation rod (CTR) position to the smoothness of the surface, we are able to monitor the crossover from layer-by-layer to step-flow growth. More detailed information about the nucleation process was determined by using diffuse scattering near the CTR position to measure the spacing of two-dimensional islands during growth as a function of flux and deposition temperature. Application of standard nucleation theory to the analysis of this data suggests that the critical island size during OMVPE growth is likely to be much larger than a single adatom, in contrast with what is usually assumed for semiconductor systems.

Characterization of vapor phase growth using X-ray techniques

Abstract Chemical vapor deposition environments, while technologically quite important, are difficult to study using traditional analytical probes, such as electron-based techniques and optical tools. In this work, we will describe some of the ways in which X-rays can be applied to understand not only the gas phase composition through fluorescence, but also surface processes such as nucleation and diffusion.

In situ characterization of organometallic growth of ZnSe using grazing incidence X-ray scattering

Abstract We have used in situ grazing incidence x-ray scattering to probe the near atmospheric pressure (100 Torr) OMVPE growth of ZnSe on GaAs. For the first time, we have directly observed the establishment of a clean GaAs surface in a hydrogen ambient with a characteristic (2×4) reconstruction and followed the development of the ZnSe epitaxial film during the initial stages of growth. Our results indicate the presence of a very stable and well-ordered p(2×1) reconstruction during growth, despite the presence of the ambient carrier gas and organic reaction by-products. In addition, by observing the changes in X-ray reflectivity due to the introduction of source compounds, we have also been able to investigate kinetic effects during alternating source growth.

In-situ X-ray studies of organometallic vapor phase epitaxy growth

Abstract In this paper we present an overview of the use of X-ray measurements to determine the atomic mechanisms of organometallic vapor phase epitaxy (OMVPE). Detailed information about OMVPE processes has been difficult to obtain because of the high pressure, chemically reactive environment present during growth. X-ray scattering measurements using very intense synchrotron X-ray sources have been uniquely productive in determining the structure of surfaces during OMVPE growth. For example, surface smoothness, step ordering, growth modes, growth rates and surface reconstructions have been determined. In addition, X-ray spectroscopy measurements have revealed much about the complicated gas phase behavior in the OMVPE reactor. From these scattering and spectroscopy measurements, a more complete model of OMVPE growth is being developed.

Thermal stability of GaAs (C)/InAs superlattices grown by metalorganic molecular beam epitaxy

The thermal stability of GaAs(C)/InAs superlattices grown by metalorganic molecular beam epitaxy on InP substrates has been examined by Hall measurements, transmission electron microscopy, and high resolution x‐ray diffraction. These structures provide an ordered counterpart to a random In0.53Ga0.47As alloy, in which high concentration carbon doping is generally difficult to achieve. In a 43 period (23 A GaAs/26 A InAs) superlattice in which the GaAs was C‐doped and the InAs undoped an average hole concentration of 7×1019 cm−3 and hole mobility of 20 cm2 V−1 s−1 was achieved. Such structures are stable against rapid thermal annealing (10 s) up to 750 °C. An 850 °C/10 s anneal reduced the hole concentration to 1.5×1019 cm−3, accompanied by the onset of intermixing of the superlattice. The surface morphology of all but very thick (36 A GaAs/40 A InAs) period superlattice structures remained specular, even after 850 °C, 10 s annealing. These superlattices show properties suitable for use in a range of electr...

Developing models of OMVPE growth from in situ X-ray measurements

This paper summarizes our recent X-ray scattering and X-ray spectroscopy experiments looking at the organometallic vapor phase homoepitaxial growth of GaAs. The measured composition profiles and growth rates agree well with predictions by Jensen and coworkers for our reactor. Evidence for the presence of a partially decomposed trimethylgallium layer on the surface during growth at 500/spl deg/C is presented. A schematic model of growth which includes the presence of this structurally ordered adsorbed layer is presented.