Determination of as Sticking Coefficients Using Reflection high Energy Electron Diffraction Intensity Oscillations on Ga
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DETERMINATION OF As STICKING COEFFICIENTS USING REFLECTION HIGH ENERGY ELECTRON DIFFRACTION INTENSITY OSCILLATIONS ON GaAs
ROBERT CHOW AND ROUEL FERNANDEZ Varian Associates, Thin Film Technology Division, 3550 Bassett Street, Santa Clara, California 95054 ABSTRACT RHEED intensity oscillations were used to investigate As-controlled incorporation rates. The measurements were made under Ga accumulation at the surface of the substrate, and at fluxes and substrate temperatures common for 1.0 micron/hr GaAs growth. The results between the dimer and tetramer As species were compared. The transition between Ga and As controlled incorporation rates was constant within 2.50C for a constant As flux and was independent of the substrate temperature. Also, the As-controlled incorporation rate curves shows two regions as the substrate temperature increases. At low substrate temperatures, the As incorporation rate is substrate temperature independent. Then at higher substrate temperatures, the As incorporation rate has an arrhenius dependence with a positive activation energy. An interpretation of these results is possible by assigning the maximum sticking coefficient of the tetramer to the region where the As incorporation rate is independent of substrate temperature. This assignment allows one to derive the As (dimers and tetramers) sticking coefficient dependence with substrate temperature. The dimer sticking coefficients are greater that the tetramer sticking coefficients for a given substrate temperature and As flux, and the maximum sticking coefficient of the As dimer was determined to be 0.8 in these experiments.
INTRODUCTION Application of RHEED intensity oscillations in detailing the MBE kinetic growth process is increasing [1-3]. Oscillations can be observed readily for both group III and group V species controlled conditions. Neave et al. [4] observed RHEED intensity oscillations under excess Ga conditions on the growth surface. They explained these oscillations as GaAs epitaxial growth, where the incorporation rate is determined by the availability of the As species. Lewis et al. [5] studied As controlled incorporation rates as a function of substrate temperature, and proposed this measurement technique as a quantitative method of setting up comparable As/Ga flux ratios between MBE system. Fernandez [6] examined the transition between Ga and As controlled incorporation rates on GaAs (001), which showed the existence of an atomic As surface concentration in excess of the available As surface sites. This conclusion is based on the observations that at a Ga flux below the transition point and at high substrate temperatures, the Ga controlled incorporation rates are greater than the As controlled incorporation rates; and at the transition point, there were a few monolayers of growth which were Ga controlled, prior to becoming As controlled. Evidence of this As layer was also observed by C. W. Farley et al [3]. This paper presents the results of substrate temperature effects on the transition point between Ga and As contr
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