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Advances in OptoElectronics
Volume 2012, Article ID 916275, 4 pages
Research Article

Room Temperature Direct Band Gap Emission from Ge p-i-n Heterojunction Photodiodes

1Institut für Halbleitertechnik (IHT), University of Stuttgart, 70659 Stuttgart, Germany
2Leibniz-Institut für Innovative Mikroelektronik (IHP), 15236 Frankfurt (Oder), Germany
3Joint Lab IHP/BTU Cottbus, 03013 Cottbus, Germany

Received 18 October 2011; Accepted 12 December 2011

Academic Editor: Ram Gupta

Copyright © 2012 E. Kasper et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Room temperature direct band gap emission is observed for Si-substrate-based Ge p-i-n heterojunction photodiode structures operated under forward bias. Comparisons of electroluminescence with photoluminescence spectra allow separating emission from intrinsic Ge (0.8 eV) and highly doped Ge (0.73 eV). Electroluminescence stems from carrier injection into the intrinsic layer, whereas photoluminescence originates from the highly n-doped top layer because the exciting visible laser wavelength is strongly absorbed in Ge. High doping levels led to an apparent band gap narrowing from carrier-impurity interaction. The emission shifts to higher wavelengths with increasing current level which is explained by device heating. The heterostructure layer sequence and the light emitting device are similar to earlier presented photodetectors. This is an important aspect for monolithic integration of silicon microelectronics and silicon photonics.