CAREER: Engineering point defect formation in UWBG-based optoelectronic devices

Many applications such as optoelectronics and power electronics rely on the functionality of ultra wide bandgap materials. But to reach their full potential, it is necessary to understand and realize novel processes to enhance their performance, either electrically or optically. The proposed processing framework has the opportunity of revolutionizing these family of materials, thus providing for the achievement of properties that otherwise will not be attainable. This is in addition to providing a unifying conceptual approach consistent with modern computational efforts that bring about a non-Edisonian approach to the design of materials and processes dealing with this class of materials. This research will directly lead to applications that deal with the preservation and extension of natural resources by allowing for: the availability of clean potable water through disinfection by the use of ultraviolet light emitting diodes, and the detection of pollutants and other effluents. The novel concepts developed within this project can also be implemented in the educational and outreach efforts (some specifically targeted at minority students), especially integrating materials characterization and control schemes to applications dealing with the need for the development of materials for sustainability purposes. This program will provide the opportunity to educate Ph.D. students on the growth, characterization and device fabrication of these materials while participating on an established international collaborators network. Furthermore, integration of these ideas into design of new courses broadens the community of students and experts related to the topic, especially those dealing with computational methods. From this, graduate students and group members will be able to effectively discuss their research for fruitful collaborations while accelerating their professional growth.

Charged point defects in compound semiconductors strongly determine electronic and optical properties. The energy of formation of a point defect is a function of the process conditions and the Fermi energy. In ultra wide bandgap materials or insulators, the contribution of the Fermi energy to the formation energy of charged point defects is significant. For the practical case of doping for n- or p-type conductivity, the larger the energy gap, the higher the concentration of compensating point defects that is at equilibrium with the system. This is a fundamental problem of these materials that will be directly addressed with these capabilities. In this approach, we will extend the concept of the quasi-Fermi level in an effort to quantify the impact of external excitation in the formation energy of the point defect. Increasing the formation energy of unwanted point defect through external excitation during a growth experiment leads to a reduction in compensating point defects and higher device efficiencies. The research objective of this proposal is to test the hypothesis that the energy of formation of charged point defects could be manipulated by an external excitation in a steady-state condition during growth. Approaches include the introduction of above-bandgap illumination or e-beam irradiation as excitation sources. This process is referred to as Fermi level control of point defects. Three main research tasks are designed to test the hypothesis: (1) demonstration of Fermi level control of technologically important point defects during the growth of III-nitrides based UV LED structures, (2) optical and electrical study of point defects and their influence on the device performance, (3) extension to other wide bandgap systems and alternative Fermi level management processes to show universality of the process. This research will extend these capabilities to AlGaN for the engineered reduction of compensating and non-radiative defects in deep UV LEDs. It is expected that this process is generally applicable to a broad class of wide bandgap materials, in particular, several oxide systems.