Surface Studies by the Traveling Wave Method

In this part we briefly mention a new experimental tool that may become useful for analyzing conduction processes near surfaces and interfaces because it measures only these, even when the total dc conductance is dominated by the bulk. This technique was pioneered by Adler et a/. (1981) and further developed by Fritzsche and Chen (1983) and Chen and Fritzsche (1983). 

Consider a semiconductor film placed in the fringe field that exists above a piezoelectric crystal such as LiNbOj, which carries a surface acoustic Rayleigh wave. The geometry is shown in Fig. 16. One can use the quasistatic approximation for the traveling wave because the wave travels with the sound velocity which is nearly static when compared with the light veloc- 

Moreover, when the diffusion term is small compared to trE, no space-charge wave is produced and 

The complex coefficients A and B are determined by the boundary conditions at the interfaces (Chen and Fritzsche, 1983 Fritzsche and Chen, 1983), and h is the separation between the free surface of the film (at y — h) and the piezoelectric crystal. The potential 0o at the crystal surface (y = 0) is determined by the acoustic wave power (Auld, 1973). 

The electric field Ey = — /dy produces a current aEy in the film. This leads to two surface-charge waves of opposite phase aty = h (surface 1) and y= h + d (surface 2)  

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