Electrical and materials characterization of GSMBE grown Si1−x−yGexCy layers for heterojunction bipolar transistor applications

Abstract

This paper reports on detailed materials and electrical characterization of strain-compensated Si1−x−yGexCy (x ⩽ 11%, y ⩽ 1%) layers synthesized by gas source molecular beam epitaxy (GSMBE). Materials assessment included the application of spectroscopic ellipsometry (SE), x-ray diffraction (XRD) and high-resolution cross-section transmission electron microscopy (HRXTEM). An almost fully strain-compensated Si0.88Ge0.11C0.01 alloy with high substitutional carbon incorporation (XRD) and well-defined structure with coherent interfaces (HRXTEM) was produced. An increase of C content (up to 1.6%) resulted in a tensile strained SiGeC alloy and degraded electrical characteristics. The minority-carrier lifetime is a parameter strongly dependent on mid-gap energy band levels, which determine the leakage currents in heterojunction bipolar transistors, and it was assessed here using the capacitance-transient technique. Metal–oxide–semiconductor (MOS) test capacitors were fabricated on Si/SiGe/Si and Si/SiGeC/Si structures using low-temperature plasma oxidation for dielectric growth. The strain-free Si0.88Ge0.11C0.01 layers exhibit a minority-carrier lifetime, τg, of ∼0.1–0.2 µs which constitutes degradation of the carrier lifetime by two orders of magnitude compared to control SiGe layers. The obtained range of τg is nevertheless sufficient for the successful application of epitaxial strain-compensated SiGeC layers in high performance heterojunction bipolar transistors (HBTs).