Enhanced photo-sensitivity in a Si photodetector using a near-field assisted excitation

Silicon is an indispensable material in electric device technology. However, Si is an indirect bandgap material; therefore, its excitation efficiency, which requires phonon assistance, is low under propagating far-field light. To improve the excitation efficiency, herein we performed optical near-field excitation, which is confined in a nano-scale, where the interband transitions between different wave numbers are excited according to the uncertainty principle; thus, optical near-field can directly excite the carrier in the indirect bandgap. To evaluate the effect of optical near-field confined in a nano-scale, we fabricate the lateral Si p–n junction with Au nanoparticles as sources to generate the field confinement. We observed a 47.0% increase in the photo-sensitivity rate. In addition, by using the thin lateral p–n junction, which eliminates the far-field excitation, we confirmed a 42.3% increase in the photo-sensitivity rate. The technological importance of silicon is unquestionable; however the indirect bandgap of this semiconductor results in low excitation efficiency in the far field region of the electromagnetic spectrum. Here, the authors adopt optical near field excitation to improve the efficiency of Si, also paving the way for photodector applications based on other indirect band gap materials.