SWIR and MWIR photodetector technologies are mainly served by III-V and II-VI materials such as InSb, InGaAs, and HgCdTe which are costly, require cooling, and face manufacturing and scalability challenges. GeSn is an attractive group IV material that is Si-compatible with the potential to circumvent these challenges by enabling the fabrication of SWIR and MWIR detectors on a scalable and cost-effective Si platform. In this work, material development and optoelectrical properties of a set of heterostructures made of Si/Ge/GeSn are presented. The material properties and its potential application in photodetectors are discussed. For instance, at a low Sn content (below 5 at.%), we found that GeSn-based photoconductive devices display unexpectedly a low dark current and exhibit a room-temperature cutoff wavelength of 1.75 um and a responsivity of 0.52 A/W at 1.55 um. Results from microscopic and spectroscopic studies are also presented. Finally, capacitance devices are fabricated to extract unintentional doping concentrations from CV measurements.
KEYWORDS: Short wave infrared radiation, Nanowires, Silicon, Heterojunctions, Silicon photonics, Tin, Chemical species, Transmission electron microscopy, Compound semiconductors, Control systems
Sn-containing group IV semiconductors (Si)GeSn represent a versatile platform to implement a variety of Si-compatible photonic, optoelectronic, and photovoltaic devices. This class of semiconductors provides two degrees of freedom, strain and composition, to tailor the band structure and lattice parameter thus laying the groundwork to implement novel heterostructures and low-dimensional systems on a Si substrate. In this presentation, we will discuss the recent progress in controlling and understanding the opto-electronic properties of metastable (Si)GeSn semiconductor nanowires and heterostructures. We will shed new light on the basic mechanisms governing their epitaxial growth and thermal stability. We will also discuss the opto-electronic properties and present strategies to integrate these material systems in the fabrication of short wavelength infrared (SWIR) and mid-infrared (MIR) detectors and light emitting devices.
Hexagonal SiGe has been theoretically shown to feature a tunable direct bandgap in the range 0.4-0.8eV. We study arrays of site-selectively grown Si_(1-x)-Ge_x nanowires (NWs) grown using the crystal transfer method in which wurtzite GaP core NWs are used as template for SiGe growth. Our approach opens up routes towards photonic band-edge lasers using group-IV NWs. Low-temperature µPL studies of arrays of SiGe NW-arrays reveal strong emission at 0.395eV and linear power dependence for weak excitation levels (P_ex~0.01-1kW/cm^2). For P_ex>4kW/cm^2, a new peak emerges at 0.37eV with an intensity that increases according to ~(P_ex)^5, indicative of stimulated emission close to the photonic band-edge.
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