Correlation of early-stage growth process conditions with dislocation evolution in MOCVD-based GaP/Si heteroepitaxy

Abstract

To identify the complex relationships between early-stage growth processes and the resultant defect microstructure in GaP/Si heteroepitaxy, a holistic study of several key metal–organic chemical vapor deposition (MOCVD) parameters was conducted, focusing on Si surface preparation and GaP atomic layer epitaxy (ALE) based nucleation processes. Crystalline defects related to the lattice mismatch and/or interfacial heterovalency, namely misfit dislocations (MD), threading dislocations (TD), and stacking fault pyramids (SFP), were quantitatively characterized via electron channeling contrast imaging (ECCI) and correlated against the different process variations. Choice of Si surface preparation method between the two examined (dilute SiH4 annealing versus Si2H6 based homoepitaxy) had little impact on resultant GaP film morphology and defect content, whereas differing GaP ALE nucleation conditions produced much more substantial changes. In particular, the initial precursor species (tert-butylphosphine versus triethygallium) and ALE cycle purge times both yielded significant influence over threading dislocation densities (TDD) in thin (100 nm), post-critical thickness GaP/Si films, with TDD spanning two orders of magnitude, from 6.7 × 107 cm−2 to 7.1 × 105 cm−2, depending on the specific process conditions employed. SFP densities were also found to follow a similar trend, ranging from 2.0 × 107 cm−2 to 1.8 × 105 cm−2, but with no apparent causal relationship between SFP density and TDD. To help explain the dramatic differences observed, detailed, large-area MD network characterization was used to provide statistically-relevant quantitative analyses of the critical dislocation dynamics (introduction rates and glide velocities) associated with the different process variants. These extracted values are then correlated against the ALE process variants to provide insight into the potential mechanistic roles of the different growth processes.