ADVANCED CMOS AND QUANTUM TUNNELING DIODES: MATERIALS, EXPERIMENT AND MODELING

With the current CMOS technology reaching its physical scaling limits, new device topologies and materials are being explored to continue its advancement in performance and power consumption for microelectronic chips now found in most consumer products. And with the advent of artificial intelligence (AI), the need for new advanced computing technologies is ever more important nowadays. This puts challenges upon the semiconductor materials therein, and the advanced devices derived from these materials.Germanium, as an alternative to the silicon semiconductor, has garnered much interest in recent years as a high mobility channel replacement material in p-MOS. However, the epitaxial growth of germanium atop a silicon substrate is non-trivial due to the ~4% lattice mismatch between the two crystals. There are multiple avenues to growing low defect density Ge layers on Si; such as growing thick buffer layers, graded buffers, low-temperature growth, and surfactant mediated growth. Various techniques are explored in this dissertation to reduce the density of a specific type of defect (threading dislocation defect) caused by the relaxing of grown Ge layer on Si after the critical thickness limit is passed. Advanced tunneling-based devices offer the highest room temperature oscillation (~2 THz) to date, far beyond any transistors. These tunneling devices are being reported in a wide variety of topics: memory, logic, optoelectronics, high-speed switching, etc. Monolithic integration of tunneling devices with the Si-based technology platform is a challenge. SiGe-based resonant interband tunneling diodes (RITD), incorporating Ge for judicious band offsets, overcome this challenge, and therefore have an advantage over other device topologies. Theoretical simulations are performed to gain a better understanding of the design issues affecting the performance of such devices and a very interrelated device, backwards diodes. Further, InGaAs/AlAs, a semiconductor material combination for very high electron mobility, was investigated as unipolar-doped resonant tunneling diodes (RTDs) that were also fabricated and analyzed for their application for high-speed switching. The phenomena of electroluminescence in InGaAs/AlAs unipolar-doped RTDs is reported for the first time and its dependence on temperature is analyzed. An external quantum efficiency of 0.44% is reported for the first time in these type of devices.