CONTACTLESS SEMICONDUCTOR SURFACE CHARACTERIZATION USING SURFACE ACOUSTIC-WAVES

The electric field which accompanies a surface acoustic wave (SAW) propagating on a piezoelectric substrate can interact with the free charge carriers near the surface of an adjacent semi-conductor. This interaction produces a measurable DC acoustoelectric voltage across the semi-conductor and attenuates the SAW. The magnitude of these effects are dependent on the semi-conductor conductivity. Monitoring the acoustoelectric voltage or SAW attenuation while varying the conductivity by external means can yield information about the density and the dynamics of the surface and impurity states in the semiconductor. By observing the optical wavelength dependence of the acoustoelectric voltage developed across the semiconductor, the energy profile of the states in the bandgap can also be determined. Experimental results will be presented for several semiconductor samples. These include GaAs and GaP with or without added impurities and silicon. Tlie results show that the use of the SAW convolver provides a simple sensitive contactless and nondestructive means of evaluating the electrical properties of the semiconductor surface. © 1979.