Photoluminescence enhancement by deterministically site-controlled, vertically stacked SiGe quantum dots

Area of Science:

• Materials Science
• Optoelectronics
• Semiconductor Physics

Background:

• Silicon-germanium (SiGe) heterosystems are promising for integrated light sources but face challenges due to indirect band gaps and type-II band offsets.
• Efficient light emission in Si/SiGe is hindered by poor wave function overlap between electrons and holes.

Purpose of the Study:

• To overcome the limitations of SiGe for light emission by employing strain engineering in vertically stacked quantum dot (QD) pairs.
• To enhance radiative recombination efficiency and improve the performance of SiGe-based light sources.

Main Methods:

• Design and strain engineering of SiGe QD pairs using strain-dependent Schrödinger-Poisson simulations.
• Implementation of stacked QD structures via molecular beam epitaxy.
• Comprehensive characterization of structural and optical properties, including photoluminescence measurements.

Main Results:

• Strain engineering in double SiGe QDs creates strain pockets in the Si cap, confining electrons and enhancing wave function overlap with holes.
• Separation of QD functions, with the lower QD acting as a stressor and the upper QD facilitating radiative recombination.
• Observed shift in thermal quenching of photoluminescence to higher temperatures and suppression of light emission from wetting layers.

Conclusions:

• Vertically stacked SiGe QD pairs with optimized strain engineering enable efficient light emission, overcoming intrinsic material limitations.
• The double QD configuration enhances thermal stability and reduces parasitic light emission, crucial for CMOS-compatible integrated photonics.
• This approach offers a viable pathway for developing efficient light sources based on SiGe quantum dots.