Coupling of Surface Acoustic Waves to a Two Dimensional Electron Gas

Abstract

When a surface acoustic wave (SAW) is coupled piezoelectrically to a two dimensional electron gas (2DEG), a velocity shift and attenuation of the SAW are induced that reflect the conductivity of the 2DEG. This paper considers the case of a AlGaAs heterostructure with a 2DEG a distance $d$ from a (100) surface of the crystal where the SAWs are propagated in the [011] direction at wavevector $q$. It is found that the velocity shift $\Delta v_s$ and the attenuation coefficient $\kappa$ satisfy the well known equation $(\Delta v_s/v_s)-(i\kappa /q)=({\alpha }^2/2)/\left(1+\frac{i{\sigma }_{xx}(q,\omega )}{{\sigma }_m}\right)$ where ${\sigma }_{xx}(q,\omega )$ is the complex conductivity at wavevector $q$ and frequency $\omega =v_{s}q$ with $v_s$ the velocity of the SAW. The coefficients $\alpha$ and ${\sigma }_m$ are calculated and it is found that $\alpha$ has a nontrivial dependence on the product $qd$.

7 pages, RevTeX, 2 figures