Biaxial tensile strain effects on photoluminescence of different orientated Ge wafers

Abstract

The enhanced photoluminescence of direct transition is observed on (100), (110), and (111) Ge under biaxial tensile strain. The enhancement is caused by the increase in electron population in the Γ valley. The shrinkage of energy difference between the lowest L valleys and the Γ valley is responsible to the population increase on (100) and (110) Ge. For (111) Ge, the energy difference increases under biaxial tensile strain but the strain decreases energy difference between the electron quasi-Fermi level and the Γ valley due to the small density of state of the lowest L valleys, and thus enhances direct recombination.

Optical Emission of a Strained Direct-Band-Gap Ge Quantum Well Embedded Inside InGaAs Alloy Layers

“…This successful method led to the realization of light emitting sources [6][7][8] and optically pumped lasers [9] operating at 1:55 m. Similarly, direct-band-gap photoluminescence (PL) was obtained from other tensile-strained n-type Ge structures, where the strain was applied to the material using external mechanical methods [10][11][12][13].…”

The effects of tensile-strain conditions on doping density requirements for Ge-based injection lasers

“…The behaviour of different conduction band valleys depends on the type of strain and its orientation. In a recent study Lan et al have observed an enhancement of direct photoluminescence transitions in ntype (100), (110), and p-type (111) Ge under 0.315 % biaxial tensile strain [6].…”

Optimum strain configurations for carrier injection in near infrared Ge lasers

“…However, the band structure of Ge can be engineered by tensile strain: the direct bandgap decreases, the degenerate equivalent indirect valleys (X and L) shift in energy and might split, and the degeneracy of the heavy hole (HH) and light hole (LH) valence bands is lifted, depending on the type of the applied strain and its direction, as well as the substrate orientation. 1,4 Under the conventional biaxial tensile strain, Ge grown in [001] direction becomes a direct bandgap material at 1.7% strain, with about 0.2 eV reduction in energy due to the conduction band minima at Cand L-points moving downwards with respect to the vacuum level, 5 the former doing so faster. On the practical side, a moderate ($0.25%) tensile strain has been obtained in Ge grown on Si due to the difference of thermal dilatation coefficients between the two materials.…”