Arsenic segregation and passivation in the heteroepitaxy of Ge/GaAs

Abstract

During the epitaxy of Ge, the arsenic introduced for doping is known to be partially incorporated into the layer and partially segregated at the Ge free surface. Arsenic at the (001) surface can saturate the Ge dangling bonds and the growth rate should decrease accordingly. An in situ monitoring of the chemical vapor deposition of Ge by laser reflectometry, and its theoretical simulation, give the morphology and the growth rate as a function of time (and thickness) and hence the segregation rate of As. The variation of the growth rate versus the AsH3/GeH4 flow rate ratio shows the formation of As2 dimers. Under constant temperature and constant AsH3/GeH4 flow rates, the growth rate first decreases, showing the segregation of As at the Ge(001) surface, then remains stable and finally increases, due to a change in the surface morphology exhibiting high order crystallographic planes on which no As2 dimers can stay.