J2&!J __ __ 8B +: .:::. :.:::. .-.:.:-.:::: :x:‘::::l:.:; . . . . : .:. :,~:~::,; :,:,:, ...._: .. . . ..:: applied zyxwvutsrqpon surface science ELSEVIER Applied Surface Science lOO/lOl (1996) 493-497 Routine measurement of the absolute As, flux in a molecular beam epitaxy system with conventional RHEED equipment Ch. Heyn, M. Harsdorff * Received 15 August 1995; accepted 26 September 1995 zyxwvutsrqponmlkjihgfedcbaZYXWVUTS Abstract The Ga/As flux ratio during epitaxial growth of GaAs is a very important parameter for the quality of the deposit. A low As, flux leads to formation of nonstoichiometric films with a rough surface structure. On the other hand, excessive As, flux is the reason for incorporation of As at Ga-sites (antisite defects). In addition, a high As population reduces the Ga surface migration and increases the surface roughness. In this work, a method was shown for an accurate measurement of the actual As, flux during molecular beam epitaxy (MBE) growth of GaAs using the sharp cut-off of the RHEED oscillations at flux ratios zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA J&J,,, higher than 1 S3. In order to calculate the absolute As, flux. the ratio of incorporated Ga-atoms per As-atom was determined from the decreasing growth rate under the condition of As deficiency. The reproducability of the As, flux measurements was found to be better than +4% and the data were in good agreement with quadrupole mass spectroscopy measurements of the As, flux. 1. Introduction The crystal quality and surface smoothness of molecular beam epitaxy (MBE) grown GaAs films is strongly determined by the process parameters such as growth temperature, growth rate and III-to-V flux ratio [l]. Most of these parameters can easily be determined except that measuring the absolute value of the As, flux requires more effort. This is due to the uncertainty regarding the sticking coefficient of As,, which may vary from zero up to a maximum value of 0.5 during MBE growth on (001) GaAs [2]. Neave et al. [3] used the frequency of As-con- trolled reflection high energy electron diffraction * Corresponding author. Tel.: + 49-40-31232030: fax: +49-W 41236368. (RHEED) oscillations for the determination of the As, flux. This method relies on a value of 0.5 for the sticking coefficient for condensation of As,- molecules on a Ga-terminated surface. One disadvan- tage of the procedure is that only a few oscillations with a small amplitude will appear and an exact determination of the oscillation frequency and, hence, of the As, flux is difficult. We present here an alternative way for routinely calibrating the As, flux by using the reproducible break-off of RHEED oscil- lations during continuous increase of the flux ratio zyxwvutsrq JdJ/,\; 2. Experimental setup The MBE system was described in detail in an earlier paper [4]. As an additional feature in compari- 0169.4332/96/$15.00 Copyright 0 1996 Elsevier Science B.V. All rights reserved. PII SO169-4332(96)00326-l