Tensile strain engineering of germanium micro-disks on free-standing SiO2 beams

Abdelrahman Z Al-Attili,Satoshi Kako,Muhammad K Husain,Satoshi Iwamoto,Shinichi Saito,Yasuhiko Arakawa,Frederic Y Gardes

doi:10.7567/jjap.55.04eh02

Abdelrahman Z Al-Attili, Satoshi Kako + Show 5 more

Open Access

https://doi.org/10.7567/jjap.55.04eh02

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Abstract

Tensile strain is required to enhance light-emitting direct-gap recombinations in germanium (Ge), which is a promising group IV material for realizing a monolithic light source on Si. Ge micro-disks on free-standing SiO2 beams were fabricated using Ge-on-Insulator wafers for applying tensile strain to Ge in a structure compatible with an optical confinement. We have studied the nature of the strain by Raman spectroscopy in comparison with finite-element computer simulations. We show the impacts of the beam design on the corresponding strain value, orientation, and uniformity, which can be exploited for Ge light emission applications. It was found that the tensile strain values are larger if the length of the beam is smaller. We confirmed that both uniaxial and biaxial strain can be applied to Ge disks, and maximum strain values of 1.1 and 0.6% have been achieved, as confirmed by Raman spectroscopy. From the photoluminescence spectra of Ge micro-disks, we have also found a larger energy-splitting between the light-hole and the heavy-hole bands in shorter beams, indicating the impact of tensile strain.

Highlights

Engineering of energy-bands structures and carrier dynamics by lattice deformation is a promising pathway to revolutionize the performance of semiconductor devices.1–3) For example, strain application has been used to enhance channel mobility in complementary metal–oxide–semiconductor field-effect transistors (CMOSFETs).2) It was exploited to expand the detection wavelength of germanium (Ge) photo-detectors.4,5) Application of tensile strain is expected to play a key role in developing a Ge-based laser diode compatible with CMOS processes.6–10) Tensile strain is essential to transform Ge into an optical gain material.3,8,9,11) lasing of tensile-strained Ge Fabry–Perot (FP) structures was reported by optical12) and electrical13,14)pumping
We show the impacts of the beam design on the corresponding strain value, orientation, and uniformity, which can be exploited for Ge light emission applications
We have investigated the strain accumulated within Ge microdisks on free-standing SiO2 beams, using computer simulations and Raman spectroscopy

Summary

Introduction

Engineering of energy-bands structures and carrier dynamics by lattice deformation is a promising pathway to revolutionize the performance of semiconductor devices.1–3) For example, strain application has been used to enhance channel mobility in complementary metal–oxide–semiconductor field-effect transistors (CMOSFETs).2) It was exploited to expand the detection wavelength of germanium (Ge) photo-detectors.4,5) Application of tensile strain is expected to play a key role in developing a Ge-based laser diode compatible with CMOS processes.6–10) Tensile strain is essential to transform Ge into an optical gain material.3,8,9,11) lasing of tensile-strained Ge Fabry–Perot (FP) structures was reported by optical12) and electrical13,14)pumping. Increasing the probability of electrons injection in the Γ valley and enhancing the light-emitting direct-gap recombinations.9,10) besides the value of strain, uniformity of its distribution is crucial for light-emitting purposes.17–20) Non-uniformity of strain is translated into variations of Ge band-gap, eventually creating optical gain and loss regions within the same Ge structure.). Several approaches were proposed to enhance the tensile strain, which is limited to approximately 0.2% after the direct epitaxial growth of Ge layer on Si.10,24,25) The use of buffer layers, with lattice mismatch relative to Ge, is capable of delivering high and tuneable strain values on relatively thin. By using InxGa1−xAs layers, for example, the tensile strain was increased up to 1.37%, depending on the indium content (x).26) Such an approach might be suitable for quantum-well devices, yet requires the introduction of III–V materials in a CMOS line.

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