Candi S. Cook

Versatile buffer layer architectures based on Ge1−xSnx alloys

We describe methodologies for integration of compound semiconductors with Si via buffer layers and templates based on the GeSn system. These layers exhibit atomically flat surface morphologies, low defect densities, tunable thermal expansion coefficients, and unique ductile properties, which enable them to readily absorb differential stresses produced by mismatched overlayers. They also provide a continuous selection of lattice parameters higher than that of Ge, which allows lattice matching with technologically useful III-V compounds. Using this approach we have demonstrated growth of GaAs, GeSiSn, and pure Ge layers at low temperatures on Si(100). These materials display extremely high-quality structural, morphological, and optical properties opening the possibility of versatile integration schemes directly on silicon.

SnGe superstructure materials for Si-based infrared optoelectronics

We report growth of device-quality, single-crystal SnxGe1−x alloys (with x=0.02–0.2) directly on Si via chemical vapor deposition with deuterium-stabilized Sn hydrides. The high Sn-content materials are stabilized with ordered superstructures that gives rise to a layered structure adjacent to the Si substrate. Density functional theory simulations were used to elucidate the structural and bonding behavior of this material. Optical determinations show a Ge-like band structure that is substantially redshifted compared to that of elemental Ge. Thus, these systems are excellent candidates for a new generation of infrared devices, with the critical advantage that they can be grown directly on Si.

Compositional Dependence of Critical Point Transitions in Ge1−xSnx alloys

The compositional dependence of the E1, E1+Δ1, E0′, and E2 optical transition energies in Ge1−xSnx alloys has been measured in the 0 < x < 0.18 range. Deviations from linearity are clearly observed and characterized by a bowing parameter b. The value of this parameter is much larger in Ge1−xSnx alloys than in the isoelectronic Si1−xGex system.

Characterization techniques for high-mobility strained Si CMOS

This paper discusses critical characterization techniques for strained Si technology, especially to determine the strain state, thickness, and Ge content in the underlying Si/sub 1-x/Ge/sub x/ alloy pseudosubstrate.