Optical phonon instability induced by high-speed electron transport in nanoscale semiconductor structures

Abstract

We analyze the interaction of high-speed electrons and polar optical phonons in nanoscale semiconductor structures. Under the velocity overshoot regime, it is found that electrons can induce optical phonon instability (i.e., the lattice optical vibrations grow in time when the electric current exceeds a threshold value). For nanoscale diodes based on III-V compounds, the threshold current density is estimated to be of the order of $100\phantom{\rule{0.3em}{0ex}}\mathrm{kA}∕{\mathrm{cm}}^{2}$ and the corresponding bias $0.5--1.5\phantom{\rule{0.3em}{0ex}}\mathrm{V}$ for the diode lengths of $50--100\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The wavelengths of unstable phonons are about $10\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ with the characteristic time for instability development in the $10\phantom{\rule{0.3em}{0ex}}\mathrm{ps}$ range. We suggest that this phenomenon can lead to efficient generation of coherent optical phonons with a number of potential applications.