The GeSn Alloy and its Optoelectronic Properties: A Critical Review of the Current Understanding

GeSn is nowadays recognized as a promising candidate to enable monolithic on-chip Si photonics operating in the near-infrared (NIR) and short-wave infrared (SWIR) wavelengths. The addition of Sn to the Ge lattice induces a red-shift in the material bandgap, extending the absorption cut-off wavelength towards the infrared. In addition, above 7-9 at.% Sn, the GeSn alloy acquires a direct bandgap, enabling its use as active material in SWIR light-emitting devices. Ge-rich GeSn alloys have been demonstrated in a plethora of optoelectronic devices including photodetectors, lasers and light emitting diodes (LEDs). Furthermore, the high theoretical mobility of GeSn motivated research for GeSn high-mobility field-effect transistors (FETs), while the possibility of monolithic integration on Si platforms has also pushed the investigation of GeSn for on-chip thermoelectric applications. However, despite more than 15 years of intensive research in the field, there exists no commercial device to date based on GeSn. In fact, there are numerous challenges hindering the rise of this material for the next-generation (opto)electronics. Here, we give a concise review of the historical achievements in GeSn research and the withstanding challenges. This is followed by a detailed description of the GeSn physical properties relevant for its use in optoelectronic devices. We conclude with a discussion of the open questions in the field.Comment: Draft versio

Fundamental limits in the external quantum efficiency of single nanowire solar cells

The fundamental limits for the measurement of the efficiency of single nanowire solar cell devices are presented. We evaluate the effect of the substrate, light polarization, and existence of Mie resonances in the absorption of the solar spectrum for nanowires with diameters from 10 to 300 nm. We find that the efficiency measured under such configuration can be underestimated between a factor 1.6 and 7.0 for GaAs nanowires and between 6.7 and 15.9 for silicon nanowires. These results constitute a reference for understanding the limits in the measurement of single nanowire devices. (C) 2011 American Institute of Physics. [doi:10.1063/1.3672168

Phonon confinement and plasmon-phonon interaction in nanowire based quantum wells

Resonant Raman spectroscopy is realized on closely spaced nanowire based quantum wells. Phonon quantization consistent with 2.4 nm thick quantum wells is observed, in agreement with cross-section transmission electron microscopy measurements and photoluminescence experiments. The creation of a high density plasma within the quantized structures is demonstrated by the observation of coupled plasmon-phonon modes. The density of the plasma and thereby the plasmon-phonon interaction is controlled with the excitation power. This work represents a base for further studies on confined high density charge systems in nanowires

Wafer bonded virtual substrate and method for forming the same

A method of forming a virtual substrate comprised of an optoelectronic device substrate and handle substrate comprises the steps of initiating bonding of the device substrate to the handle substrate, improving or increasing the mechanical strength of the device and handle substrates, and thinning the device substrate to leave a single-crystal film on the virtual substrate such as by exfoliation of a device film from the device substrate. The handle substrate is typically Si or other inexpensive common substrate material, while the optoelectronic device substrate is formed of more expensive and specialized electro-optic material. Using the methodology of the invention a wide variety of thin film electro-optic materials of high quality can be bonded to inexpensive substrates which serve as the mechanical support for an optoelectronic device layer fabricated in the thin film electro-optic material