Si/SiO2 Core/Shell Luminescent Silicon Nanocrystals and Porous Silicon Powders With High Quantum Yield, Long Lifetime, and Good Stability

Bernard Gelloz,Nobuyoshi Koshida,Lianhua Jin,Tomohiro Nozaki,Koji Asaka,Firman Bagja Juangsa

doi:10.3389/fphy.2019.00047

Abstract

Most of the highly efficient luminescent silicon nanocrystals (SiNCs) reported to date consists of organically capped silicon cores. Here, we report a method of obtaining Si/SiO2 core/shell nanoparticles emitting at a peak energy of 1.5 eV with very high quantum yields (53-61%). The same method led to quantum yields of ~ 30% for porous silicon powder emitting at 1.9 eV. The SiNCs were very stable under continuous excitation for several hours. The lifetime at 1.5 eV was over 232 μs, the longest ever reported for SiNCs, consistent with the very high luminescence efficiency. The SiNCs were first fabricated by non-thermal plasma synthesis or anodization in the case of porous silicon. Then, a thin oxide shell (~ 1 nm) was grown using high-pressure water vapor annealing. This oxidation process allows for the growth of very good quality oxide with low defect concentration and low stress, resulting in very good surface passivation, which explains the very high quantum yields obtained.

Highlights

Luminescent Si nanocrystals (SiNCs) are intensively studied for their potential applications in diverse fields, such as optoelectronics, sensing, and medicine [1–20]
absolute quantum yield (AQY) of 23% was reported with porous silicon (PSi) layers treated by high-pressure water vapor annealing (HWA) [26, 27] and with PSi powders modified by solution-based chemical oxidation [28]
The structures of the SiNCs and PSi powders were observed by transmission electron microscopy (TEM) using a JEOL JEM2010 microscope, performed at an acceleration voltage of 120 kV

Summary

Introduction

Luminescent Si nanocrystals (SiNCs) are intensively studied for their potential applications in diverse fields, such as optoelectronics, sensing, and medicine [1–20]. AQY of 23% was reported with PSi layers treated by high-pressure water vapor annealing (HWA) [26, 27] and with PSi powders modified by solution-based chemical oxidation [28]. The best results were obtained with the SiNCs, with very high AQYs, matching the highest values reported to date for organically terminated SiNCs, and very good stability.

Results

Conclusion