13C Isotopic Labeling Studies of Growth Mechanisms in the Metalorganic Vapor Phase Epitaxy of GaAs.

Isotope tracer techniques using 13C are employed to obtain information on how the alkyl reactants used in MOVPE affect heterogeneous growth processes and impurity incorporation reactions. GaAs growth was performed using trimethylgallium, 13C-enriched (50%) trimethylarsine and 13C-enriched (99%) methane. Data were obtained on isotope-labeled effects resulting from substrate crystallographic orientation, gas phase composition and growth temperature. Secondary ion mass spectrometry (SIMS) was used to detect the level of 13C in the deposited films. SIMS sensitivity for carbon species was improved by as much as a factor of 50 by use of the 75As13C- ion at m/e=88, rather than standard detection at m/e=13 which is subject to interference from 12CH- ions. Similarly, a factor of 10 increase in 12C sensitivity was achieved by detection at m/e=87 rather than m/e=12. The 13C experiments provide the first direct evidence that methyl groups from metalorganic reactants are a major source of carbon in MOVPE grown GaAs films. The measured 13C concentration was as high as 1017 cm-3. Carbon incorporation increased with growth temperature, but was independent of the V/III molar ratio. Films deposited on misoriented substrates exhibited a monotonic increase in carbon content as the misorientation angle from the {001} crystal plane was decreased from 6o to 0o. For substrates with different crystallographic orientations the carbon level was highest for {001} and {011} surfaces, and least for the {111}As face. Addition of 13C-methane to the reactants had no effect on either the growth process or carbon incorporation level. The implications of these results for MOVPE growth models are discussed in detail.