The notorious implication of integrated optics in the nowadays communication systems makes more interesting the development of optical integrated devices and circuits. The evolution of the communication systems was sustained by the integrated optics and it is obvious that the actual interests in the optical communications are also transferred and adapted to integrated optics. The presentation of actual state-of-the-art in this field is a good opportunity both for an evaluation on the above mentioned evolution and for discerning the actual trends and their perspectives. These trends, guided by applicative goals, have to be discussed not only from the theoretical point of view but also from a practical one.

Optical integrated circuits

In this Letter we present the electrical and electro-optical characterization of single crystalline germanium nanowires (NWs) under tensile strain conditions. The measurements were performed on vapor–liquid–solid (VLS) grown germanium (Ge) NWs, monolithically integrated into a micromechanical 3-point strain module. Uniaxial stress is applied along the ⟨111⟩ growth direction of individual, 100 nm thick Ge NWs while at the same time performing electrical and optical characterization at room temperature. Compared to bulk germanium, an anomalously high and negative-signed piezoresistive coefficient has been found. Spectrally resolved photocurrent characterization on strained NWs gives experimental evidence on the strain-induced modifications of the band structure. Particularly we are revealing a rapid decrease in resistivity and a red-shift in photocurrent spectra under high strain conditions. For a tensile strain of 1.8%, resistivity decreased by a factor of 30, and the photocurrent spectra shifted by 88 meV...

Tuning the Electro-optical Properties of Germanium Nanowires by Tensile Strain

R. R. Lieten,1,2,3,* K. Bustillo,4 T. Smets,1 E. Simoen,3 J. W. Ager III,2 E. E. Haller,2,4 and J.-P. Locquet1 1Department of Physics and Astronomy, K.U. Leuven, 3001 Leuven, Belgium 2Division of Materials Sciences, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 3IMEC, 3001 Leuven, Belgium 4Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA (Received 25 April 2012; published 9 July 2012)

Photoluminescence of bulk germanium

The paper presents progress in infrared (IR) detector technologies during 200 history of their development. Classification of two types of IR detectors (photon detectors and thermal detectors) is done on the basis of their principle of operation. The overview of IR systems and detectors is presented. Also recent progress in different IR technologies is described. Discussion is focused mainly on current and the most rapidly developing detectors: HgCdTe heterostructure photodiodes, quantum well AlGaAs/GaAs photoresistors, and thermal detectors. The outlook for near-future trends in IR technologies is also presented.

Infrared detectors: an overview

In the past decades, group IV nanowires and nanoparticles have been the subject of extensive research. Beside tremendous progress in morphological control and integration in advanced device archite...

Metastable Group IV Allotropes and Solid Solutions: Nanoparticles and Nanowires

Group IV semiconductor-based alloy Ge1−xSnx can be grown on Si platform and a crossover from indirect (L valleys) to direct gap (Γ valley) occurs for x > 0.08. The direct gap alloy shows promise for use in high-speed electronic and photonic devices. An earlier study predicted that the electron mobility in the alloy would increase by a few orders of magnitude above the value for pure Ge. In that work, however, electrons were assumed to occupy only the low effective mass Γ valley and only the deformation potential acoustic phonon and alloy scatterings were considered. In the present work, we give a more realistic estimate of the values of electron mobility in direct gap GeSn alloy, considering the Γ and L valleys and the phonon (deformation potential acoustic, optical and intervalley), alloy, and impurity scatterings. The effect of strain, both tensile and compressive, on the mobility is also studied. It is found that for higher alloy composition and suitable strain, mobility values ∼2 × 105 cm−2/V · s, more than 50 times higher than the value in pure Ge (3900 cm2/V · s) may be achieved. This is attributed to increased separation between Γ and L valleys and consequent reduction in intervalley scattering.

Prediction of Large Enhancement of Electron Mobility in Direct Gap Ge1−xSnx Alloy

This work presents a theoretical analysis of a GeSn/SiGeSn Quantum Well Infrared Photodetector (QWIP). The absorption coefficient is obtained by inter subband transition of the carriers inside the well. Main analysis is concentrated on finding the quantum efficiency, responsivity of QWIP. The responsivity of the detector is studied as a function of capture probability, carrier lifetime and well number. The result shows that an acceptable responsivity is obtained in mid infrared terahertz region for a particular choice of material and well number. Finally the photo generated current is estimated and compared with previously reported data.

Performance analysis of GeSn/SiGeSn quantum well infrared photodetector in terahertz wavelength region

Photodetecctors using Si, Ge and other group IV alloys are of current interest for use at telecommunication wavelength 1550 nm We have presented in this paper our work on resonant cavity enhanced (RCE) Si/SiGe multiple Quantum Well (MQW) and Ge Schottky photodetectors Tensile strained Ge layers grown with suitable barriers show direct gap type I band alignment Predicted performance of photodetectors using strong Quantum Confined Stark Effect and Franz-Keldysh effects in these structures and properties related to photodetection using these new materials are also described

Ge/Si photodetectors and group IV alloy based photodetector materials

Dark current and responsivity are two important parameters of quantum well infrared photodetectors (QWIPs). An optimization approach is applied herein to achieve low dark current along with high responsivity for a GeSn/SiGeSn QWIP. The dark current is reduced by varying different physical parameters of well and barrier, operating temperature and bias voltage of the QWIP. To optimize the QWIP, the detectivity is calculated. The results show that the optimally designed GeSn/SiGeSn QWIP can achieve a low dark current of 2.35 pA at 2 V with a peak responsivity of 1.24 A/W at 4.3 µm and a high detectivity of 3.47 × 1012 cm · Hz1/2 W−1 at 2 V and 77 K. Finally, the frequency response of the optimally designed GeSn/SiGeSn QWIP device is estimated. The theoretically predicted higher detectivity with respect to previously reported SiGe/Si QWIPs and GeSn/SiGeSn interband QWIPs indicates a promising future for GeSn/SiGeSn intersubband QWIPs.

Gopa Sen

Papers

Prediction of Large Enhancement of Electron Mobility in Direct Gap Ge1−xSnx Alloy

Performance analysis of GeSn/SiGeSn quantum well infrared photodetector in terahertz wavelength region

Ge/Si photodetectors and group IV alloy based photodetector materials

Optimization of different structural parameters of GeSn/SiGeSn Quantum Well Infrared Photodetectors (QWIPs) for low dark current and high responsivity

An analytical approach of elimination of ambipolarity of DPDG- TFET using strained type II staggered SiGeSn heterostructure