Surface morphology of Cr:Ga₂Se₃ heteroepitaxy on Si(001)

Addition of the transition-metal dopant Cr to Ga₂Se₃ during heteroepitaxial growth on Si(001), a system of interest as a prototype silicon-compatible, dilute magnetic semiconductor, has been studied with scanning-tunneling microscopy and scanning Auger microscopy as a function of Cr concentration and the presence or absence of an undoped buffer or capping layer. Chromium incorporates into laminar Ga₂Se₃ films up to a solubility limit of several atomic percent, after which Cr-rich islands nucleate. At low Cr concentrations, the vacancy-ordered nanoridge structure characteristic of pure Ga₂Se₃ remains but nanoridge aspect ratios decrease with Cr concentration; this is likely associated with Cr removing intrinsic vacancies. At higher Cr concentrations, faceted, Cr-rich islands nucleate, often surrounded by trenches, and the terrace morphology no longer resembles pure Ga₂Se₃. Growth of Cr-doped Ga₂Se₃ directly on Si(001):As is qualitatively similar to growth on a pure Ga₂Se₃ buffer layer; however, the island structure changes dramatically upon coverage of a highly doped layer with undoped Ga₂Se₃. Addition of Cr stabilizes cubic overlayer growth under Se-poor growth conditions beyond that of pure Ga₂Se₃; no growth of the hexagonal layered structure characteristic of bulk GaSe was observed.