COUPLING OF SURFACE ACOUSTIC-WAVES TO A 2-DIMENSIONAL ELECTRON-GAS

When a surface acoustic wave (SAW) is coupled piezoelectrically to a t wo-dimensional electron gas (2DEG), a velocity shift and attenuation o f the SAW are induced that reflect the conductivity of the 2DEG. This paper considers the case of an AlxGa1-xAs heterostructure with a 2DEG a distance d from a (100) surface of the crystal where the SAW's are p ropagated in the [011] direction at wave vector q. It is found that th e velocity shift Delta upsilon(s) and the attenuation coefficient kapp a satisfy the well known equation (Delta upsilon(s)/upsilon(s)) - (i k appa/q) = (alpha(2)/2)/[1 + i sigma(xx)(q,omega)/sigma(m)], where sigm a(xx)(q,omega) is the complex conductivity at wave vector q and freque ncy omega = upsilon(s)q with upsilon(s) the velocity of the SAW. The c oefficients alpha and sigma(m) are calculated and it is found that alp ha has a nontrivial dependence on the product qd.