Intersubband light emission and electrical bistability in SiGe/Si quantum structures

This dissertation deals with band engineering in Si/SiGe structures and its possible applications to light emission and static random access memory (SRAM). It consists of two main parts. The first part deals with band engineering using hetero-structures and its possible application to light emission. The second part deals with band engineering using doping modulation and its possible application to SRAM cells.; Part I. Light emission from Si/SiGe based structures has received considerable interest due to its possible applications in optoelectronics and more importantly, its compatibility with the current mainstream Si technology. The integration of optical components onto a Si-based chip allows further functional integration and consequently the realization of new concepts. On the other hand, Si/SiGe based materials have indirect bandgaps, which yields interband radiative recombination that is very slow compared to other non-radiative interband recombination mechanisms, such as Auger recombination. In this dissertation, a new method of light emission based on Si/SiGe quantum well structures is proposed. The relaxation times are calculated and the threshold current is estimated.; Part II. The bistability in delta-doped Si diodes is very attractive for SRAM applications. This is because, in conventional SRAMs, a circuit is built to achieve the bistability in its logic operations. This usually takes six transistors for one cell. Therefore, packing is limited. To circumvent this problem, new cell topologies were recently {dollar}rm proposedsp{lcub}1,2{rcub}.{dollar} The basic idea involves the use of a device with built-in bistability in its I-V characteristics and therefore, the SRAM cell can be greatly simplified. In fact, only three devices are needed, namely, a bistable diode, a control transistor and a load. This essentially reduces the device count by half and if we stack the load resistor on top of the transistor, the cell area can be reduced even further. In this dissertation, novel Si based bistable diodes are studied. The bistability is achieved through the quantum effect of doping modulation.