Room temperature direct band-gap emission from an unstrained Ge p-i-n LED on Si Tzanimir Arguirov 1,2,a , Martin Kittler 1,2,b , Michael Oehme 3 , Nikolay V. Abrosimov 4 , Erich Kasper 3 and Jörg Schulze 3 1 IHP GmbH, Im Technologiepark 25, 15236 Frankfurt (Oder), Germany 2 Joint Lab IHP/BTU, BTU Cottbus, Postfach 101344, 03013 Cottbus, Germany 3 Institut für Halbleitertechnik, Pfaffenwaldring 47, 70569 Stuttgart, Germany 4 Leibniz-Institut für Kristallzüchtung, Max-Born-Str. 2, 12489 Berlin, Germany a Arguirov@tu-cottbus.de, b Kittler@ihp-microelectronics.com Keywords: Ge, dislocations, light emitter, luminescence Abstract We present a novel Ge on Si based LED with unstrained i-Ge active region. The device operates at room temperature and emits photons with energy of 0.8 eV. It basically resembles a p-i-n structure formed on a sub-micrometer thin Ge layer. The Ge layer has been grown on Si substrate by utilizing thin virtual buffer, so it becomes stress free but with high threading dislocation density. We show that such forward biased diode generates strong emission, caused by direct band to band transition in Ge. Using an InSb based detector we were able to analyze the emission spectrum in a broad energy range. We show that at low and moderate currents, features belonging to the direct and the indirect band to band electronic transitions are present which are characteristic for Ge. Clearly dominating is the direct transition related peak. Due to the missing stress-related red shift this peak appears close to the desired communication wave length of 1.55 µm. The dependence of radiation intensity on the excitation current follows a power low with exponent of 1.7, indicating that the recombination rate of the competitive non-radiative processes is relatively low. At high excitation currents features appear in the low energetic part of the spectrum. All results presented here are discussed in view of the outcome from measurements on Ge high quality bulk material. The role of the dislocation in the Ge films is discussed. Introduction The photonic application of Si based devices attracts attention of the researchers worldwide. Currently, a technological implementation of such devices is basically hampered by the low light emission capabilities of the Si. Indeed, the indirect character of the band to band transition in Si renders its radiative recombination a low probability process. Materials, compatible with the CMOS technology, but capable of efficient radiative recombination are looked for to create on-chip based light sources. Additionally, to the CMOS compatibility requirement a special wavelength of the emission is needed. The energy of the generated photons by the emitters should be below the band gap of Si in order to use Si based optics. For compatibility with the current discrete optoelectronics a wavelength of 1.55 µm is desired. A variety of approaches have been suggested and studied, such as a MOS-LED using the D1-radiation of a dislocation network in Si [1]. However a concept of choice is still to be found. Devices build on Ge/Si heterostructures with remarkable emission properties has been newly demonstrated [2-345]. They use the direct band gap transition in Ge which corresponds to the required communication wavelength of 1.55 µm. The light emitting devices (LEDs) are usually fabricated on tensile strained (0.2-0.25 %) a few µm thick Ge layers with low dislocation density, grown by chemical vapor deposition (CVD) on Si substrates. Solid State Phenomena Vols. 178-179 (2011) pp 25-30 Online available since 2011/Aug/16 at www.scientific.net © (2011) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/SSP.178-179.25 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 141.43.75.139-18/08/11,10:14:20)