Neueste Forschungsergebnisse

Room-Temperature Electroluminescence From GeSn Light-Emitting Pin Diodes on Si

In this paper a GeSn light emitting pin diode integrated on Si via a Ge buffer is demonstrated and it is compared with a light emitting pin diode made from pure, unstrained Ge on Si.
The diode layer structures are grown with a special low temperature molecular beam epitaxy process. The pseudomorphic GeSn layers (1.1 % Sn content) on the Ge buffer are compressively strained. Both light emitting pin diodes clearly show direct bandgap electroluminescence emission at room temperature. The electroluminescence peak of the GeSn light emitting pin diode is shifted by 20 meV into the infrared region compared to the electroluminescence peak of the unstrained Ge light emitting pin diode. The shift is due to the lower bandgap of GeSn and the influence of strain.

Picture (top): Room-temperature EL spectra of a GeSn-LED (mesa radius 80 m) for different injection currents. The inset shows the forward current - voltage characteristic of the GeSn - LED.
Picture (bottom):Comparison of the EL spectra of GeSn LED with Ge LED. A clear infrared shift of 40 nmor 20 meV for theGeSn LED in comparison to Ge LED is observed.


Authors: M. Oehme, J. Werner, M. Gollhofer, M. Schmid, M. Kaschel, E. Kasper, J. Schulze
Source: IEEE Phot. Techn. Lett. 23, 2011

Germanium-Tin p-i-n photodetectors integrated on Silicium grown by Molecular Beam Epitaxy

GeSn heterojunction p-i-n diodes with a Sn content of 0.5% are grown with a special low temperature molecular beam epitaxy.
The Sn incorporation in Ge is facilitated by a very low temperature growth step in order to suppress Sn surface segregation. The diodes with sharp doping transistions are realized as double mesa structures with diameter from 1.5µm up to 80µm. An optical responsivity of these GeSn diodes of 0.1A/W at a wavelength of λ = 1.55 µm is measured.
In comparison with a pure Ge detector the optical responsivity is increased by factor of three as a result of Sn caused band gap reduction.

Picture: Optical responsivity from λ = 1230nm up to λ =1700nm for the GeSn p-i-n detector and for comparision a similar fabricated 40GHz Ge-p-i-n detector without Sn. The inset shows the optical output for the same wavelength range from the broadband super continuum laser.

Authors: J. Werner, M. Oehme, M. Schmid, M. Kaschel, A. Schirmer, E. Kasper, J. Schulze
Source: Applied Physics Letter 98, 2011

Germanium photodetectors on Silicon-on-insulator grown with differential molecular beam epitaxy in silicon wells

In this paper a method for growing fast Germanium pin photodetectors in pre-patterned areas on a Silicon-on-insulator substrate is proposed. The layers are deposited by means of molecular beam epitaxy and structured by chemical mechanical polishing.
These photodetectors have a performance comparable to the reference sample on a plane wafer. As the electrical properties indicate, the layers of both samples have the same crystal quality as well as the top contact layer has to be protected as the CMP and cleaning steps could damage the surface. RF measurements yield external cutoff frequencies of over 20 GHz showing even more potential for detectors with smaller active areas. The energy of the direct band edge is also the same as well as the spectral range leading to the conclusion that the dMBE does not increase the strain in the active Germanium absorption layer.
These results show that dMBE is a valid method for processing waveguide-coupled detectors in future applications and enables the integration of optical circuits in microelectronics.

Authors: M. Kaschel, M. Schmid, M. Oehme, J. Werner, J. Schulze
Source: Solid State Electronics 60, pp.105-111, 2011

Electrical spin injection and transport in germanium

We report the first experimental demonstration of electrical spin injection, transport, and detection in bulk germanium (Ge). The nonlocal magnetoresistance (MR) in n-type Ge is observable up to 225 K. Our results indicate that the spin relaxation rate in the n-type Ge is closely related to the momentum scattering rate, which is consistent with the predicted Elliot-Yafet spin relaxation mechanism for Ge. The bias dependence of the nonlocal MR and the spin lifetime in n-type Ge is also investigated.

Picture: Device structure (left) and measurement results for nonlocal magnetoresistance (right).

Authors:Y. Zhou, W. Han, L.-T. Chang, F. Xiu, M. Wang, M. Oehme, I. Fischer, J. Schulze, R.K. Kawakami, K.L. Wang
Source: Phys. Rev. B 84, 125323, 2011