Mutlicolor electroluminescent Si quantum dots embedded in SiO_x thin film MOSLED with 24% external quantum efficiency

Abstract

The enhanced recombination and external quantum efficiency (EQE) of the multi-color metal-oxide-semiconductor light-emitting diodes (MOSLEDs) made on the SiOx film with buried Si quantum dots (Si-QDs) grown by plasma-enhanced chemical vapor deposition are demonstrated. By shrinking Si-QD size from 4.2 to 1.8 nm with increasing RF plasma power from 20 to 50 W, these MOSLEDs enhance the maximal electroluminescent (EL) power from 0.1 to 0.7 μW. This is mainly attributed to the enhanced recombination rate by enlarging the overlap between electron and hole wave-functions. As evidence, the photoluminescent lifetime is significantly shortened from 5 µs to 0.31µs due to the enhanced direct recombination in smaller Si-QDs. The corresponding power-current slope and EQE are observed to increase from 0.09 to 5.7 mW/A and from 1.9 × 10(-5) to 2.4%, respectively. The EL enhancement originates from shorter wavelength and stronger carrier confinement within Si-QDs with smaller size, as confirmed by the increased barrier height at the ITO/SiOx:Si-QD interface from 1.05 to 3.62 eV. The smaller and denser Si-QDs result in a current endurance to operate the MOSLED at breakdown edge with highest power conversion efficiency, thus providing a maximal blue-light EL power at 0.7 μW with the highest EQE of 2.4%.