Ge_1-x-ySi_xSn_y light emitting diodes on silicon for mid-infrared photonic applications

This paper reports initial the demonstration of prototype Ge_1-x-ySi_xSn_y light emitting diodes with distinct direct and indirect edges and high quality I-V characteristics. The devices are fabricated on Si (100) wafers in heterostructure pin geometry [n-Ge/i-Ge_1-x-ySi_xSn_y/p-Ge(Sn/Si)] using ultra low-temperature (T < 300 °C) depositions of the highly reactive chemical sources Si₄H₁₀, Ge₄H₁₀, Ge₃H₈, and SnD₄. The Sn content in the i-Ge_1-x-ySi_xSn_y layer was varied from ∼3.5% to 11%, while the Si content was kept constant near 3%. The Si/Sn amounts in the p-layer were selected to mitigate the lattice mismatch so that the top interface grows defect-free, thereby reducing the deleterious effects of mismatch-induced dislocations on the optical/electrical properties. The spectral responsivity plots of the devices reveal sharp and well-defined absorption edges that systematically red-shift in the mid-IR from 1750 to 2100 nm with increasing Sn content from 3.5% to 11%. The electroluminescence spectra reveal strong direct-gap emission peaks and weak lower energy shoulders attributed to indirect gaps. Both peaks in a given spectrum red-shift with increasing Sn content and their separation decreases as the material approaches direct gap conditions in analogy with binary Ge_1-ySn_y counterparts. These findings-combined with the enhanced thermal stability of Ge_1-x-ySi_xSn_y relative to Ge_1-ySn_y and the observation that ternary alloy disorder does not adversely affect the emission properties - indicate that Ge_1-x-ySi_xSn_y may represent a practical target system for future generations of group-IV light sources on Si.