Reflectance-Difference Spectroscopy: A New Look At Semiconductor Crystal Growth By MBE And OMCVD

Publisher Website
Google Scholar
Abstract
Reflectance-difference spectroscopy (RDS) is a recently developed normal-incidence optical probe that uses symmetry to enhance the typically low sensitivity of reflectance measurements to surface phenomena. In RDS, the difference between reflectances parallel and perpendicular to the two principal optic axes in the plane of the surface are determined experimentally by modulation techniques. Contributions from the bulk and randomly oriented surface species largely cancel in subtraction, leaving those from the lower-symmetry surface. Sensitivities of 0.01 monolayer to surface species have been demonstrated with averaging times of 100 ms. Being an optical probe, RDS is well suited either to the reactive, relatively high pressure sample environments in organometallic chemical vapor deposition (OMCVD) reactors or to the ultrahigh-vacuum environment of molecular beam epitaxy (MBE) chambers. This allows comparisons of various growth chemistries to be made. Our MBE results for the (001) AlGaAs system show that reflectance-difference (RD) signals respond to either surface chemistry or surface structure depending on photon energy, and can distinguish Al- from Ga-terminated surfaces. Our OMCVD results for the (001) GaAs-trimethylgallium-arsine system follow submonolayer coverage of reacted species and provide the first microscopic information about crystal growth by OMCVD. The time, temperature, and pressure dependences of this coverage show OMCVD growth to be kinetically limited by a combination of reversible excluded-volume chemisorption (at 26 kcal/mole) and subsequent irreversible decomposition (at 39 kcal/mole) of trimethylgallium at surface lattice sites. Further work, especially in combination with a probe such as spectroellipsometry that can detect optically isotropic species, is expected to lead to new understanding of crystal growth and better control of growth processes.

This publication has 0 references indexed in Scilit: