Functional Devices Based Space Transfer in Si/SiGe on Real Structure

A charge injection transistor, which operates as an exclusive-OR logic gate, and a monolithic multiterminal de- vice, electrically reprogrammable between OR and NAND logic function, have been successfully implemented in a Si/Sio 7Geo 3 heterostructure grown by rapid thermal epitaxy on a Si substrate. Room temperature operation of the charge injection transistor is demonstrated, with 10 dB odoff ratio for the excluAive-OR logic function. Microwave measurements indicate a short circuit current gain cutoff of 6 GHz, for a device with a source-drain dis- tance of 0.5 wm. Device simulations were used to identify primary dependencies of the device performance on the parameters used in the design of the structure. Further structural improvements are suggested. I. INTRODUCTION N important direction in microelectronics research is A the development of new functional devices, which can perform logic tasks that would normally require an assembly of several transistors ( 11. The physical operation of these new functional devices is generally different from the field-effect principle, that CMOS logic devices use, or from the potential- effect principle of bipolar transistors. The phenomenon of real-space transfer' (RST) offers interesting opportunities for building functional devices. The concept of RST describes the process in which carriers in a narrow semiconductor layer, accelerated by an electric field parallel to the layer, acquire high-average energy and then spill over an energy barrier into the adjacent layer. This principle underlies the operation of a three terminal heterojunction device, called the charge injection transistor (CHINT) (3). A generic CHINT structure is illustrated in Fig. 1. One of the two conducting layers, the emitter, plays the role of a hot- cathode, with the heating voltage applied between the contacts S and D. The other conducting layer, the collector, is separated by a heterostructure barrier. The RST manifests itself with the increase of the collector current IC, at constant collector bias Vc, when a sufficient high-heating bias Vo is applied. A fundamental property of the CHINT is the symmetry equivalence (4) between the internal states S(VD, VC) of the