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Since germanium(Ge)has a quasi-direct band gap of 0.8 eV,it is a promising material for fabricating on-chip optoelectronic devices.Although Ge based individual photo emitters and detectors have been studied in depth,high-performance Ge optoelectronics with CMOS-fi-iendly device structures are always desired for the purpose of large scale optoelectronics integration.Recently we achieved low electron barrier height(ΦBN)of 0.09 eV(TiN/Ge)and hole barrier height(ΦBP)of 0.06 eV(HfGe/Ge)[1,2].Based on these technologies,we demonstrate direct band gap(DBG)electroluminescence(EL)[3] as well as light detection [4] at room temperature using Ge diodes with a fin-type lateral HfGe/n-Ge/TiN structure,which was fabricated using a low temperature(<400 ℃)CMOS-friendly process.DBG EL spectrum peaked at 1.55 μm was clearly observed even at a small current density of 2.2 μ.A/μm,due to the small ΦBN and ΦBP.Superlinear increase in EL intensity was observed with increasing current density,due to superlinear increase in population of elections in direct conduction band.The DBG EL efficiency is also benefited from increasing doping level ofGe substrate.The efficiency of hole injection was clarified,implying that the number of injected holes is enough for EL generation.The integrated intensity of DBG EL spectrum is proportional to the area of active region,implying a good surface-uniformity of EL efficiency.Small dark current intensity was measured as 2.4× 10-7 A under a reverse bias voltage of-1 V,corresponding to a dark current density of 5.3 × 10-10 A/μm.At the wavelength of 1.55 nn,a linear dependence of photo current intensity on laser power was observed with a responsivity of 0.44 A/W at a reverse bias voltage of-1 V.