Simple theory of buried channel acoustic charge transport in GaAs

Abstract

A theory is developed which describes the fundamental charge transfer characteristics of basic buried channel GaAs structures which are illuminated by large amplitude surface acoustic waves. Several approximations which simplify the analysis are shown to be valid in this channel structure. The theoretical approach treats carrier diffusion as a perturbation on the diffusionless two-dimensional electrostatic problem. Simple closed form expressions are obtained for packet charge density and boundary shape in terms of the channel parameters. It is shown that four sets of numerically generated and normalized curves are sufficient for the determination of the transport characteristics of a wide range of channel potential geometries. The dependence of diffusion induced transfer inefficiency on charge load and wave potential is investigated. The results indicate that high speed acoustic charge transport is capable of supporting typical buried channel charge loads at very high transfer efficiency.

Experimental performance of the buried-channel acoustic charge transport device

“…1. A more detailed circuit is given elsewhere [ 3 ] . The TRAPATT diode [2] ~ mounted in a coaxial line with no tuning slugs, is biased from the variable dc pedestal voltage Vo together with a pulsed output from the pulser.…”

“…2(a). When the injection level is increased beyond the charge handling capacity of the wave, signal dispersion due to diffusion-induced transfer inefficiency [3] occurs, as shown in Fig. 2…”

“…5 , The burst measurement is also shown for comparison. Finally, the diffusion-limited inefficiency as predicted by the theory of [3] is also presented. The SAW potential in the channel is determined from the acoustic intensity and the piezoelectric properties of GaAs.…”

“…are eliminated in the present device by using the substrate backgating effect [8] to achieve the necessaryinterface barrier. Adjustment of the backgating voltage applied to the substrate permits an optimized bias condition to be achieved, whereby the transported charge is confined to the region of the channel which has a maximum in the SAW potential magnitude [3].…”

“…In this device, buried-channel electron transport is accomplished at the sound velocity using the traveling-wave electric field of a SAW generated directly in the GaAs. Several attractive features associated with the acoustic charge transport (ACT) concept have been discussed [ l ] , [ 2 ] , and a theoretical investigation of transport performance indicates that the ACT device is fundamentally capable of high-speed operation and very high transfer efficiency [ 3 ] , This is primarily because traveling-wave excitation provides a nearly uniform drift field within the transported charge packets for all space and time, so that carrier transfer occurs continuously and entirely under the influence of an electric field.…”