Examination of multiply reflected surface acoustic waves by observing acoustoelectric current generation under pulse modulation

We investigate multiply reflected surface acoustic waves (SAWs) by using SAW acoustic-charge-transport devices. The acoustoelectric current generated by a SAW passing through a one-dimensional constriction is highly sensitive to the electric potential in the electron-capture region. This means that the effect of reflected SAWs can be observed in the structure of the frequency dependence of the acoustoelectric current. By pulse modulating the microwave power on the transducer, we are able to resolve reflected SAWs, mostly by the transducers, with various time delays. We find that the reflected SAWs produce a complex pattern, and we estimate the reflection power coefficient of the transducers to be as high as 97%. We have observed reflected SAWs persisting for over $400\mu \mathrm{s}$.

Figure 1

Schematic of the device.

Figure 2

Acoustoelectric current frequency dependence for a pulse width $w$ ranging from $0.5\mu \mathrm{s}$ (bottom trace) to $50\mu \mathrm{s}$ (top trace) step $0.5\mu \mathrm{s}$. The ratio $\frac{\tau }{w}=10$, where $\tau$ is the period—traces are offset for clarity. (Data are taken from sample B.)

Figure 3

Fourier transform of Fig. 2. Inset: detail of upper ten traces—traces are offset for clarity.

Figure 4

Fourier transform of frequency dependence for a pulse width of $0.5\mu \mathrm{s}$, pulse period increased from $10\mu \mathrm{s}$ (bottom trace) to $30\mu \mathrm{s}$ (top trace) at $0.1\text{−}\mu \mathrm{s}$ intervals—traces are offset for clarity. (Data are taken from sample B.)

Figure 5

(a) Peak positions (open circles) and amplitudes (solid line) from Fig. 4 (b) The equivalent data are taken from sample A.

Figure 6

Fourier transform of frequency dependence for a pulse width of $5\mu \mathrm{s}$, pulse period increased from $25\mu \mathrm{s}$ (bottom trace) to $475\mu \mathrm{s}$ (top trace) at $25\text{−}\mu \mathrm{s}$ intervals—traces are offset for clarity. (Data are taken from sample A.)

Figure 7

Upper trace: the first peak from subsequent time delays in Fig. 6. Lower trace: result for $25\text{−}\mu \mathrm{s}$ pulse period from Fig. 6. The solid line shows Fourier-transform data, circles show peak maxima, the dashed line shows exponential decay fitted to the peak maxima, the dotted line on the lower graph shows exponential decay from upper graph for comparison.