[Show abstract][Hide abstract] ABSTRACT: We present a systematic study of the transport properties of n- and p-type Ge0.98Sn0.02 alloys using infrared spectroscopic ellipsometry and electrical measurements. We measure the dielectric function of our samples in the infrared range where the response is mainly due to free carrier absorption. In the case of p-type material, we observe, in addition to the free carrier response, optical transitions between split-off (SO), light (LH), and heavy-hole (HH) bands. The electron and hole mobilities for Ge0.98Sn0.02 alloys with carrier concentrations >1018 cm-3 are comparable to those found in Ge samples with similar doping concentrations. The electron and hole effective masses of Ge0.98Sn0.02 alloys are close to that of n-doped and p-doped Ge respectively.
[Show abstract][Hide abstract] ABSTRACT: The application of silicon photonic technologies to optical telecommunications requires the development of near-infrared detectors monolithically integrated to the Si platform. Recently, new low-temperature CVD techniques have been developed for growth of high-quality epitaxial films of Ge, Ge1-ySny, and SixGe1-x-ySny directly on Si. In this poster, we present details on the growth of these films, optimization of processes for the fabrication of photonic devices, and results from some prototype p-i-n heterostructure devices.
Bulletin of the American Physical Society. 01/2009; 54.
[Show abstract][Hide abstract] ABSTRACT: Prototype detector structures were fabricated on Si substrates using Ge1−ySny as active material for the first time. This alloy system covers the entire near-IR telecommunication spectrum and grows at a low temperature of 350 °C, compatible with complementary metal-oxide-semiconductor CMOS Si technology. Processing protocols were developed for photolithography-based patterning and subsequent etching, CMOS compatible metallization, and for the formation of low-resistivity Ohmic contacts. A first generation of devices based on as-grown Ge1−ySny layers was followed by a second generation incorporating ex situ rapid thermal annealing for defect reduction, as well as additional growth and processing improvements, leading to enhanced mobilities and simultaneous reduction in intrinsic carrier concentrations. While both device generations show a significant photoconductive response at 1.55 um, the thicker second-generation samples yield improved performance due to better confinement of deleterious defects near the interface, which increases the optically active fraction of the film.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 01/2008; 26:1952. · 1.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Si-Ge-Sn alloys represent an emerging class of IR semiconductors offering the potential for independent variation of band structure and lattice dimension, making them the first practical group-IV ternary system. Here we present the development and application of new and commercially viable protocols to fabricate Ge 1-x-y Si x Sn y semiconductors on Ge buffered Si (100) exhibiting tunable direct band gaps (E o) ranging from 0.8-1.4 eV at a fixed lattice constant perfectly identical to that of Ge. This is a behavior typical in III-V quaternaries that was not previously observed in group IV elements, thereby making it possible to envision entirely new families of devices, from conduction band quantum cascade lasers to high efficiency solar cells. For the latter application these alloys may serve as the long-sought, ~ 1eV gap active component in Ge/InGaAs/InGaP multijunctions. As a proof-of-concept demonstration we deposited lattice-matched Si(100)/Ge/SiGeSn/InGaAs architectures on Si(100) platforms en route to a four-junction device structure. In the context of Si-Ge-Sn optoelectronic applications the ternary alloys may serve as higher-gap barrier layers for the design of optical modulators based on strain-free Ge/SiGeSn quantum well stacks operating at 1.55 m.