Observation of the Coulomb Blockade at 77 K in a Lattice-Mismatched GaAs/Si Heterojunction

Abstract

Fabrication of GaAs-based structures on Si substrates gives possibilities of easy integration of silicon electronics with optical devices. A major obstacle for a success of such technology are lattice defects, e.g. antiphase boundaries, twins, and dislocations, which are generated in GaAs by the 1attice mismatch to Si [1]. A substantial contribution of charged misfit dislocations to electronic vertical transport in those structures is then expected. In this work we investigated a system consisting of GaAs layer grown by molecular beam epitaxy on p+-type Si (for growth details see Ref. [2]). Formation of antiphase domains in that polar-on-nonpolar system was suppressed by simple misorienting the Si (001)-oriented substrate slightly toward the [011] direction. The nominally undoped GaAs epitaxial layer of 2 m thickness was n-type with Si concentration of 10 15 -10 16 cm-3 . Typically, as verified by secondary ίon mass spectroscopy (SIMS), the Si atoms move into the GaAs layer, and Ga atoms diffuse into the Si substrate. Moreover, a site exchange mechanism can occur by which Si donors on Ga sites move to As vacancies, thereby creating acceptor sites. This process is tremendously enhanced near the interface by the high density of lattice defects in heteroepitaxial layer. As a result the p-n junction is shifted to GaAs side with respect to the Si/GaAs interface [3]. The lattice constant of GaAs is about 4% larger than that of Si. This mismatch leads to the formation of a twodimensional network of misfit dislocations at