MOCVD Growth and Electrical Characterization of AlInGaN Heterojunctions
III-N-based electronics and optoelectronics are reaching great levels of sophistication in the areas of power electronics, RF amplifiers, lighting, and display technologies. Much of the success of these technologies can be traced to superior or unique material properties that make III-N solid state devices the ideal choices for their applications. Consequently, state of the art devices are being pushed to the limit of what may be fabricated due to strain considerations in the AlGaN and InGaN systems. In order to continue the advancement of III-N based technologies toward greater performance, into new niches, and open up new markets, it is necessary to exploit the entire (Al,In,Ga)N system to its fullest potential.
The utility of AlInGaN is multifaceted. These materials can be used for strain management, fabrication of lattice-matched devices, and polarization engineering to manipulate electric fields within device active regions, or even create high-conductivity charge slabs. Unlike ternary alloys, there is no single unique combination of band gap, polarization charge, and lattice constant, which results in greater device design freedom. However, to effectively utilize these materials, reliable growth processes must be established, and the material parameters critical to device design must be characterized.
This thesis describes the progress in AlInGaN development at UCSB beginning with identification and exploration of the AlInGaN growth parameter space, using understanding from ternary alloys as a springboard into quaternary growth. From there, the thesis progresses to the establishment of a design toolbox for AlInGaN based devices via electrical characterization of these materials. Challenges associated with the AlInGaN system, coupled with sparse literature on the topic, necessitated the design of experiments to isolate and characterize the material parameters from measurements of solid-state devices. Electrical characterization focused on the net polarization charge at heterojunction interfaces, as well as the effects of Schottky barrier height inhomogeneity on both electrostatics and transport in diodes. The quantum mechanical scattering at the metal-semiconductor junction will be discussed, as will its physical origin and impact on diode current. A major goal of this thesis was to establish a device design toolbox populated with information of experimentally calculated net polarization charge at AlInGaN/GaN interfaces and Schottky barrier heights. This goal was accomplished and the information was established for future device designers in the field.
The thesis concludes with a discussion of the application and exploitation of the unique effects observed in AlInGaN materials to device design. Future outlook will be given on avenues for research in AlInGaN materials and AlInGaN-based devices, and direction will be provided to finish populating the (electrical) device design toolbox with conduction band offset measurements.