Significance of This Article
The main contribution of this paper theoretically demonstrates that an optical near field (ONF) induces an indirect interband transition due to the Fourier components of the ONF with large wavenumbers. Time-dependent dynamics calculations of a one-dimensional potential model with an indirect band-gap structure reveal that electronic transitions definitely occur between Bloch states having different wavenumbers without an electron–phonon coupling. The calculated absorption spectra for the conventional laser-field and the ONF excitations exhibit completely different absorption edges and spectral patterns from each other. This difference indicates that the ONF opens optical transition pathways between Bloch states with different wavenumbers. Although the physical mechanism and the calculation method of the ONF excitation have been presented for a simple potential model in this study, they can be straightforwardly extended to realistic crystal systems. Silicon is commonly known as its low optical, absorption and emission, efficiency, which entirely originates from its indirect band-gap structure. Our theoretical idea is expected to overcome this serious drawback and pave the way for developing optoelectronic functional materials based on indirect band-gap semiconductors.