Alexandria Digital Research Library

Contributions to the Understanding of (Al,Ga)N - Silicon Nitride Interfaces

Swenson, Brian
Degree Grantor:
University of California, Santa Barbara.Electrical & Computer Engineering
Degree Supervisor:
Mishra Umesh K
Place of Publication:
[Santa Barbara, Calif.]
University of California, Santa Barbara
Creation Date:
Issued Date:
Electrical engineering
Interface State Density
Electron Injection

For the last decade Gallium Nitride and its alloys have been a popular topic in high power and high frequency transistors. GaN's main enabling material properties are its high breakdown voltage, high electron mobility combined with its high electron density (when combined with AlGaN), and its high temperature stability. In the early years of GaN development, a major breakthrough has been identified to be the introduction of SiN<sub>X</sub> passivation, which considerably reduced dispersion caused by surface states and led to a significant increase in output power density. The use of a gate insulator is also crucial in power electronics to minimize the leakage current through the gate. Understanding and optimizing these passivation and gate insulators are crucial steps along with optimizing the device design and structure in order to achieve greater performance and higher power densities.

This thesis focuses on minimizing the interface state density of the SiN<sub>X</sub> / GaN interface by exploring the growth parameter space of the SiN<sub>X</sub> grown in situ by MOCVD. The SiN<sub>X</sub> interface state density is studied on Ga-polar (0001), N-polar (000-1), and M-plane (10-10) GaN material. The interface state density is measured by a Photo-assisted CV technique developed in this thesis that takes advantage of the type-II band alignment in the SiN<sub>X</sub> / GaN system. It was found that growth temperature had the largest impact on interface states for all crystal planes tested, where the highest growth temperature measured (&sim;1200 &deg;C) also had the lowest interface state density. On the other hand, defect density (from 1e7 to 1e9 cm<super>-2</super>) had almost no impact on interface state density.

The effect of introducing a thin AlGaN or AlN interlayer between the SiN<sub>X</sub> and GaN is also studied in an effort to separate the interface states from Fermi level of the device. It is found that, while the interface states still exist, it is possible to use the polarization of the Al(Ga)N on Ga-polar GaN to raise the energy level of the interface states with respect to the bulk GaN so that they are not able to interact with the Fermi level. The opposite effect is shown for N-polar GaN, where the interface states are pushed into the midgap of GaN.

Finally, the charge injection phenomenon, widely observed in SiN<sub>X</sub>, is preliminarily investigated. The emission and extraction of the injected charge is also studied. Additionally, field enhanced trap ionization was observed and briefly studied.

UCSB electronic theses and dissertations
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