THEORETICAL CALCULATIONS OF CHARGE CONFINEMENT IN A PN(-)NP HETEROJUNCTION ACOUSTIC CHARGE-TRANSPORT DEVICE

An alternative structure for heterojunction acoustic charge transport (HACT) devices has been devised and analyzed. The structure uses a pn( -)np doping profile near the surface of the device to create a charge transport layer and provide top vertical confinement. This is contrary to previous n-type HACT structures which rely on residual surface sta tes and a heterojunction discontinuity for the same functions. The use of the pn(-)np doping as the channel depletion mechanism makese insen sitive to the residual surface state density, thus providing a more ro bust design. In addition, the use of the bark np junction enables wide ning of the transport layer thereby increasing the amount of charge th at fan be transported by the acoustic wave. As a result of the increas ed charge capacity it is expected that the pn(-)np ACT device will exh ibit a greater dynamic range and current than previous HACT designs. T he analysis of the device structure is accomplished herein using a two dimensional hydrodynamic simulation code, Semiconductor Total Energy Balance Simulator in two Dimensions (STEBS-2D), which has been modifie d to account for the potential created by the surface acoustic wave. T he calculated results indicate that an order of magnitude enhancement in charge capacity is possible using the new structure. Transfer effic iency calculations for several different lifetimes in the transport la yer show high efficiency values, greater than 7 9's efficient with a S hockley Read Hall lifetime of 10 nsec.