Modulation of the absorption coefficient at 1.3 μm in Ge/SiGe multiple quantum well heterostructures on silicon

Area of Science:

• Materials Science
• Optoelectronics
• Semiconductor Physics

Background:

• Germanium/silicon-germanium (Ge/SiGe) multiple quantum wells (MQWs) are promising for optoelectronic devices.
• Modulating optical properties is crucial for integrated photonic circuits.
• The quantum-confined Stark effect (QCSE) offers a method for tuning electronic and optical properties in quantum wells.

Purpose of the Study:

• To investigate the modulation of the absorption coefficient in Ge/SiGe MQWs at 1.3 μm.
• To utilize strain engineering to enhance the direct optical bandgap of Ge quantum wells.
• To demonstrate the effectiveness of the quantum-confined Stark effect (QCSE) for optical modulation.

Main Methods:

• Fabrication of Ge/SiGe MQWs on a silicon substrate using epitaxy.
• Growth of 9 nm-thick Ge quantum wells on a relaxed Si0.22Ge0.78 buffer layer.
• Application of electric fields to induce the quantum-confined Stark effect and measure absorption coefficient changes.

Main Results:

• Achieved significant modulation of the absorption coefficient at 1.3 μm.
• Strain engineering increased the direct optical bandgap in the Ge quantum wells.
• Demonstrated a contrast in the absorption coefficient greater than 3.2 in the 1290-1315 nm spectral range.

Conclusions:

• The QCSE effectively modulates the absorption coefficient in Ge/SiGe MQWs on silicon.
• Strain engineering is a viable strategy to optimize bandgap properties for specific wavelengths.
• These findings support the development of Ge/SiGe-based modulators for silicon photonics.