Improved device performances based on Si quantum dot/Si nanowire hetero-structures by inserting an Al₂O₃ thin layer

Si quantum dot-based light emitting devices were fabricated on Si nanowire arrays in order to improve light extraction efficiency. However, the device performance is deteriorated by using Si nanowires with a depth of 1.2 μm due to serious surface recombination. By introducing an Al₂O₃ thin layer between the Si quantum dots and Si nanowires, significantly enhanced electroluminescence (∼8.5 fold) has been demonstrated. Based on electron spin resonance, capacitance-voltage and conductance-voltage measurements, the effect of the Al₂O₃ thin layer on the improvement of device performance is quantitatively evaluated. Our results demonstrate that besides the chemical passivation to reduce the surface defect states of Si nanowires, the Al₂O₃ thin layer can act as a barrier layer to confine the injected carriers in the active Si quantum dot layer due to the existence of negatively fixed charges and a potential barrier. As a consequence, radiative recombination is promoted which contributes to the enhanced light emission from devices based on Si quantum dot/Si nanowire hetero-structures.