Band engineering in silicon/silicon(1-y)carbon(y) and silicon/silicon(1-x-y)germanium(x)carbon(y) heterostructures and application to PNP heterojunction bipolar transistors (Silicon carbide, Silicon germanium carbide)

The incorporation of substitutional C in epitaxial Si and Si_1−x Ge_x is of considerable interest, since it is expected to provide additional flexibility in engineering the strain and the bandstructure of Column IV-based heterostructures, enabling new device applications. The effects of strain in conjunction with the chemical effect of carbon, is expected to produce a sizable conduction band offset at the Si/Si_1−yC _y interface. This is significant because pseudomorphic, strained Si _1−xGe_x on Si lacks a conduction band offset. Another alloy of interest is Si_1−x−yGe_xC_y. Addition of carbon to Si_1−xGe_x compensates some of the biaxial compressive strain. This relaxes the film thickness constraints for pseudomorphic growth, enabling the growth of thicker layers, which provides greater flexibility to device designers. In preliminary studies of the effect of C incorporation on the band lineup in Si/Si_1−yC_y and Si/Si_1−x−yGe_xC_y heterojunctions, the data has been scant and inconsistencies exist in the literature, particularly concerning the conduction band offsets. In this work, the conduction band offsets in these two systems are examined in detail. Given this information, a novel P-n-P heterojunction bipolar transistor (HBT) is designed and demonstrated for the first time.; In this work the conduction band offsets in Si/Si_1−yC _y and Si/Si_1−x−yGe_xC_y have been investigated using metal-oxide-semiconductor capacitance-voltage (MOS C-V) characteristics and Schottky barrier admittance spectroscopy. Based on the ΔE_c measurements in this work and past determination of a negligible valence band offset, the band lineup at the Si/Si_1−yC_y interface is believed to be ideally suited to P-n-P HBT operation. The first Si_1−y C_y base P-n-P HBTs were thus designed, fabricated, and characterized. Temperature dependent measurements of the collector intercept current have been used to extract the Si/Si_1−yC_y bandgap difference, ΔE_g as a function of substitutional carbon fraction. For a given amount of strain, it is found that the extracted bandgap difference is comparable to that in the Si/Si _1−xGe_x system. However, the advantage of Si_1−y C_y/Si compared to Si_1−xGe_x/Si is a band alignment (ΔE_g ∼ Δ E_c) that is better suited to P-n-P HBTs. It has also been found in this work that carbon suppresses phosphorus autodoping, enabling the growth of very abrupt, thin n + base layers.