Surface morphology ofCr:Ga2Se3heteroepitaxy on Si(001)

Abstract

Addition of the transition-metal dopant Cr to ${\text{Ga}}_{2}{\text{Se}}_{3}$ 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 ${\text{Ga}}_{2}{\text{Se}}_{3}$ 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 ${\text{Ga}}_{2}{\text{Se}}_{3}$ 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 ${\text{Ga}}_{2}{\text{Se}}_{3}$. Growth of Cr-doped ${\text{Ga}}_{2}{\text{Se}}_{3}$ directly on Si(001):As is qualitatively similar to growth on a pure ${\text{Ga}}_{2}{\text{Se}}_{3}$ buffer layer; however, the island structure changes dramatically upon coverage of a highly doped layer with undoped ${\text{Ga}}_{2}{\text{Se}}_{3}$. Addition of Cr stabilizes cubic overlayer growth under Se-poor growth conditions beyond that of pure ${\text{Ga}}_{2}{\text{Se}}_{3}$; no growth of the hexagonal layered structure characteristic of bulk GaSe was observed.