A new GaAs double triangular barrier (DTB) switch, prepared by molecular-beam epitaxy (MBE), using p+-n-6(p+)-n-8(p+)-n n + structure was fabricated and demonstrated. A tristate switching behaviour due to the sequential collapse of internal barriers was clearly observed for the first time. This phenomenon introduced triple stable regions into the device operation. Based on a proper circuit design, the structure studied has good potential for tristate-logic applications.
Introd uction
Considerable interest has been shown in the development of GaAs switching devices using the p+ n-6(p+)-n-n + structure where the 6(p+) denotes an ultrathin layer with a high doping level, for example, 10.0 nm with a doping level of 5 x 10 ~s cm -3 [I-5]. These devices are characterized by high-and low-impedance states, separated by a negative differential resistance (NDR). The S-shaped NDR characteristic is mainly attributed to the collapse of the internal barrier which is dominated by the injection of holes from the p+ n junction. The accumulated holes at the internal barrier effectively lower the barrier height, which increases the electrons thermionically emitted over the barrier. Finally, the large flow of current due to the establishment of positive feedback makes the device change from a high-impedance offstate to a low-impedance on-state I-1].
Recently, much attention has been given to the development of heterostructure switching devices [6] and their possible applications. However, detailed investigation of sequential switching behaviour using double triangular barrier (DTB) structures are still rare and limited. The purpose of this work is to present experimental two-terminal tristate switching evidence of a GaAs p+-n-6(p+)-n-6(p+)-n-n + structure. In the experimental results, an interesting sequential double S-shaped NDR phenomenon is presented. Based on the idea of modulating the internal barrier heights by the external voltage, a conceptual understanding of such a set of results would enhance understanding of the physics of DTB devices in general.