Strain Engineering of Germanium Nanobeams by Electrostatic Actuation

Abstract

Germanium (Ge) is a promising material for the development of a light source compatible with the silicon microfabrication technology, even though it is an indirect-bandgap material in its bulk form. Among various techniques suggested to boost the light emission efficiency of Ge, the strain induction is capable of providing the wavelength tunability if the strain is applied via an external force. Here, we introduce a method to control the amount of the axial strain, and therefore the emission wavelength, on a suspended Ge nanobeam by an applied voltage. We demonstrate, based on mechanical and electrical simulations, that axial strains over 4% can be achieved without experiencing any mechanical and/or electrical failure. We also show that the non-uniform strain distribution on the Ge nanobeam as a result of the applied voltage enhances light emission over 6 folds as compared to a Ge nanobeam with a uniform strain distribution. We anticipate that electrostatic actuation of Ge nanobeams provides a suitable platform for the realization of the on-chip tunable-wavelength infrared light sources that can be monolithically integrated on Si chips.

Simultaneous Crystallization and Strain Induction Enable Light-Emitting Germanium Nano/Microbridges for Infrared Lasers

“…While the realization of GeSn with such a high Sn concentration is a challenging task due to the low solid solubility of Sn in Ge, the introduction of the required high tensile strain levels in Ge is a well-resolved technique studied and established by several research groups. To this end, a variety of methods have been utilized, including the external application of strain into Ge through electrical or mechanical force, , heteroepitaxial growth of Ge on a buffer layer with a larger lattice constant, ,− redistribution of an intrinsically introduced small amount of strain in the Ge-on-Si film into suspended Ge microstructures, ,, and strain transfer from a stressor layer to Ge. ,,,, In these studies, an important observation was that tensile strain induction in Ge can only yield a reliable light emitter platform if the crystalline quality of Ge is high enough to endure the introduced amount of strain levels. It has also been well established that the Ge-on-insulator (GOI) substrates are preferable as compared to the Ge films deposited directly on the Si platform to avoid the defective Si–Ge interfaces, which would overshadow the strain-induced light emission efficiency of Ge. − To emphasize the latter point further, Sukhdeo et al hypothesized that the key reason for achieving higher tensile strain levels in their work as compared to a similar work done by Süess et al is the high crystalline quality of GOI wafers with defect-free interfaces that they fabricated via the metal organic chemical vapor deposition technique.…”

Verifying the band gap narrowing in tensile strained Ge nanowires by electrical means

“…To overcome the indirect behavior of Ge and thus inefficient photon emission, several approaches have been explored such as modifying the band structure by quantum confinement [6], alloying [7], or strain engineering. Regarding the latter approach, the predicted transformation of Ge to a direct semiconductor [8,9] at an uniaxial strain of about 5.3% along the á ñ 111 direction or biaxial strain of 2.0% triggered a lot of theoretical [8][9][10][11][12] and experimental [5,[13][14][15][16][17][18][19][20] works. Among the manifold techniques, applying uniaxial strain to a quasi-1D Ge nanowires (NW) presents itself as an approach of high potential.…”