AVS 46th International Symposium
    Nanometer-scale Science and Technology Division Tuesday Sessions
       Session NS-TuA

Paper NS-TuA2
Cross-Sectional Scanning Tunneling Microscopy as a Probe of Atomic-Scale Order in MOVPE Grown GaInP@footnote 1@

Tuesday, October 26, 1999, 2:20 pm, Room 612

Session: Innovative Nanoscale Measurements
Presenter: J. Steinshnider, Texas A&M University
Authors: J. Steinshnider, Texas A&M University
M. Weimer, Texas A&M University
M. Hanna, National Renewable Energy Laboratory
Correspondent: Click to Email
III@sub a@-III@sub b@-V alloys grown by metal-organic vapor phase epitaxy (MOVPE) exhibit varying degrees of CuPt-B order in which III@sub a@ and III@sub b@ atoms preferentially enrich alternating <111>-B planes during growth to form a monolayer superlattice. We have used cross-sectional scanning tunneling microscopy (STM) to examine and characterize spontaneous ordering in MOVPE-grown GaInP films lattice-matched to GaAs. We show how cross-sectional STM permits the direct, real-space visualization of CuPt order based on III@sub a@-III@sub b@ site discrimination, and indicate how the degree of local order in selected regions of a sample may be quantitatively assessed through the In-In pair correlation function constructed from atomic-resolution data. We introduce a local order parameter, based on the pair correlation function, that is identified with the Bragg-Williams parameter in the case of long range order and which allows a direct comparison of the STM results with optical or x-ray measurements. We have examined the spatial evolution of the local order parameter in the vicinity of the alloy / buffer interface, where the STM images show evidence for atomically-abrupt antiphase boundaries, and find that the onset of recognizable group-III sublattice order requires approximately twenty monolayers. The ability of cross-sectional STM to probe the development of local order on these length scales suggests it will be a powerful tool for studying the mechanism of atomic ordering as well as optimizing the growth of ordered films. @FootnoteText@ @footnote 1@Work supported in part by a grant from the National Science Foundation, Division of Materials Research.