Band Gap-Engineered Group-IV Optoelectronic Semiconductors, Photodiodes and Prototype Photovoltaic Devices

Si-Ge-Sn alloys have emerged as promising group IV semiconductors for the direct integration of optical designs on Si platforms, thus representing an entirely group IV approach to advance IR technologies. In this paper we discuss new developments in materials and devices that have led to the demonstration of photodiodes with enhanced performance relative to Ge reference systems as well as light-emitting semiconductors on silicon that exhibit strong direct-gap photoluminescence obtained via simultaneous n-type heavy doping and Sn alloying. With regard to detectors we present new results for Ge0.98Sn0.02 diodes with IR coverage extended down to 1800 nm and exhibiting enhanced optical and electrical response relative to initial prototypes grown directly on Si substrates. We also review the fabrication of SiGeSn/Ge(100) diodes with tunable absorption edges and very low dark current densities superior to those of Ge and GeSn counterparts. Particular emphasis is placed on devices exhibiting highly desirable 1 eV direct gaps and specific p-n heterostructure designs that are suitable for PV applications. These provide a starting point for the development of an entirely group-IV-based 1 eV junction that is proposed to enhance the efficiency of conventional III-V devices grown on Ge.