Chemical Routes to the Growth of Crystalline Oxides Directly on Germanium for Applications in Future Generation Microelectronic Devices

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Presently, the majority of transistors that power microelectronic devices are based on silicon. While there have been significant increases in speed of silicon-based microelectronic devices in recent years, the speed at which silicon-based chips can operate is limited by the material itself, and in order to make faster devices a new semiconductor material is required. Germanium is one such promising material that can enable manufacturing of faster computer chips. One critical challenge in building transistors is the need for a good electrical semiconductor and a good insulator that is compatible with that semiconductor. To make germanium-based chips work, a good electrical insulator is needed. This award is to develop and understand a new type of electrical insulator that is compatible with germanium and which can allow for manufacturing of germanium-based microelectronics. The broader impact of the research will be in continued scaling of transistors to smaller sizes that will provide faster computer processor speeds, lower power consumption, and higher data storage capacities for microelectronic devices. This research examines perovskites for use as dielectric oxides in germanium transistors. Perovskites are selected for their ability to bond chemically to germanium and eliminate the electrical defects that affect device performance. This work will explore how to grow crystalline perovskite oxide films on germanium that meet the many performance requirements of modern microelectronic devices. The research explores an all-chemical growth process that should be scalable, is inherently less costly, and is based on current manufacturing tool infrastructure to promote easy adoption by industry. The research explores and describes the materials chemistry and the surface chemistry associated with growing crystalline SrHfO3 and SrZrO3 on germanium using atomic layer deposition processes. The overarching objectives are to understand and describe processes that lead to the formation of crystalline oxides on Ge (001) with requisite band offsets and interface trap densities in a chemical deposition process. The intellectual merits of the work stem from the specific focus areas of the fundamental studies which are: 1) elucidating the reactions and structural changes at the Ge (001) oxide interface that seed crystalline oxide formation; 2) understanding the evolution of structure in the perovskite layer leading to a crystalline film and how the structure depends on process conditions; and 3) establishing the structure-property-function relationships in the context of a gate oxide in a field effect transistor application.