Donor-Acceptor Pair Recombination in Size-Purified Silicon Quantum Dots

Area of Science:

• Materials Science
• Nanotechnology
• Quantum Physics

Background:

• Shallow impurity doping is crucial for tuning semiconductor quantum dot (QD) properties.
• Inhomogeneities in size, shape, and composition often obscure doping effects in QDs.

Purpose of the Study:

• Investigate optical properties of heavily boron (B) and phosphorus (P) doped, nearly monodispersed silicon quantum dots (Si QDs).
• Clarify doping-induced phenomena by minimizing size and shape variations.
• Determine the impact of doping on optical band gap and luminescence decay rates.

Main Methods:

• Utilized a size-separation process to achieve almost monodispersed spherical Si QDs.
• Studied optical properties, including optical band gap and luminescence decay rates.
• Compared experimental optical band gap data with theoretical calculations.

Main Results:

• Quantified doping-induced optical band gap shrinkage across a broad size range.
• Estimated the number of active donor-acceptor pairs within Si QDs.
• Observed a significant modification in luminescence decay rate dependence on size and detection energy below a critical diameter of approximately 5.5 nm.

Conclusions:

• Doping effects, such as band gap shrinkage, can be clearly observed in size-purified Si QDs.
• Below 5.5 nm, donor-acceptor distance becomes less critical for recombination rates, suggesting quantum confinement effects dominate.
• The study provides insights into controlling optical and electronic properties of doped Si QDs for advanced applications.