Effects of ionizing radiation on nanomaterials and III-V semiconductor devices.

Kate Gleason College of Engineering Rochester Institute of Technology Degree Doctor of Philosophy Program Microsystems Engineering__ Name of Candidate Cory D. Cress ` Title: Effects of ionizing radiation on nanomaterials and III-V semiconductor devices__ Devices based on III-V semiconductors and nanomaterials are expected to be critical components of future microsystems as the demand for greater functionality, range of application, and robustness continue to increase. There currently is a need for small-scale power supplies which can be used to power microsystems thereby enabling autonomous functionalities. The use of III-V semiconductor-based solid state devices and nanomaterials to convert the radiant energy of a radioisotope source into electricity has been investigated as a viable option to fulfill this demand. The energy imparted to a material by incident alpha-particles, resulting in electron-hole pair formation and ionization, may be converted into usable electrical power by a radioisotope microbattery (RIMB). A model describing the spatially varying rate of ionizing energy deposited in an absorber material held in close proximity to an isotropic alpha-emitting radioisotope source has been developed. The alpha-particle energy deposition model (ADEP) allows the total energy exciting the RIMB devices to be calculated and thereby provides a means to determine the efficiency of the experimentally measured devices. Two RIMB designs are investigated including a direct conversion microbattery based on a nipi-diode structure and an indirect conversion microbattery employing radioluminescent nanophosphors. The multi-functional nature of microsystems may best be exploited by deploying them in extreme environments, such as space, where a low power consumption, small volume, and superior functionality are required. Expanding microsystems into such environments requires a full understanding of the effects that ionizing radiation will have on the optoelectronic properties of the devices and the materials which they are composed of. Irradiating devices with an isotropic alpha-particle flux is a good method for simulating the radiation damage encountered by III-V devices or nanomaterials employed in space. The large mass of alpha particles, in comparison to beta particles, leads to higher momentum transfers in nuclear interactions corresponding to a larger displacement damage dose near the surface of a material for comparably lower fluences. The effects of such irradiation on the optoelectronic properties of III-V semiconductor devices and epitaxially grown InAs quantum dots arrays are investigated. A crystal binding model based on the Tersoff interatomic potentials is developed and used to explain the increased radiation tolerance observed in the InAs quantum dot material system. Abstract Approval: Committee Chair _______________________________________ Program Director _______________________________________ Dean KGCOE _______________________________________Approval: Committee Chair _______________________________________ Program Director _______________________________________ Dean KGCOE _______________________________________