Broadening of terahertz spectrum due to Zener tunnelling in superlattices

The resonant interminiband Zener tunnelling rates between two minibands in the process of terahertz (THz) radiation have been calculated for three structures of GaAs/Al0.3Ga0.7As superlattices with high electric field in this work by using the Kane model. It is found that Zener tunnelling rate, which corresponds to the broadening of line-width of spectrum, not only increases with the applied electric field F but also is very dependent on the width of the minibands and that of the gap between minibands. Without any fitting parameter, the calculated results agree with the experimental data reported by Prof. Hirakawa and his co-workers. The results we obtained in this work demonstrate that the measured broadening in the spectra of terahertz emission in the high electric field region is indeed due to the resonant interminiband Zener tunnelling.