Heavy Ga Doping of Ge and Ge1-xSix Semiconductors by CVD Using GaH3·N(CH3)3
Abstract
We describe a new chemical method for doping and hyper-doping Ge and Ge1-xSix with Ga acceptors for potential applications in high-speed transistors. We employ the volatile GaH3·N(CH3)3 Ga source as a better alternative to metalorganic precursors for low temperature deposition of epitaxial layers grown directly on Si and Ge-buffered Si substrates. Proof-of-concept samples were initially produced at 380-400 °C using a single-wafer epitaxy reactor operating at 10-5 Torr and designed for small substrates to test GaH3·N(CH3)3 as a dopant and demonstrate feasibility. The process was subsequently transitioned to a multiwafer UHV CVD system which supports larger substrates suitable for device fabrication. This system enabled depositions at lower-temperature (<360 °C) and higher-pressure for better tuning of Ga substitution, improved film homogeneity, and enhanced stoichiometric control. We found that in both cases GaH3·N(CH3)3 reacts cleanly with Ge4H10 and Si4H10 sources to deliver pure Ga atoms without carbon contaminants and preventing Ga surface segregation issues. Epitaxial growth of p-type Ge and Ge1-xSix layers is achieved, resulting in optimal crystal quality and minimal defect levels, as evidenced by Rutherford backscattering (RBS), X-ray diffraction, (XRD) and cross-sectional transmission electron microscopy (XTEM). The Si contents in the Ge1-xSix films range from x = 0.06 to 0.22, as determined by RBS and XRD. The Ga concentrations are measured by secondary ion mass…
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