The electron affinity of a semiconductor defines the relationship of the vacuum level and the semiconductor band structure. It is dependent on the atomic orbitals of the material and the surface termination. We report experimental and theoretical results that support the presence of a negative electron affinity on AlN and the Al rich AlGaN alloys. The GaN surface is found to exhibit a (positive) electron affinity of 3.3eV. The experimental measurements employ UV-photoemission spectroscopy on in situ gas-source MBE samples and on CVD samples. Theoretical results indicate that the (negative) electron affinity of AlN depends sensitively on the surface reconstruction and adatom termination. The experimental dependence of the electron affinity on alloy concentration is presented. The results indicate that AlGaN alloys with band gap similar or greater than that of diamond will exhibit a negative electron affinity. Field emission results are reported, and the characteristics are similar to those obtained from a diamond film. Issues related to cold cathode electronic devices based on NEA surfaces are noted.

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The emitter turn-off thyristor (ETO) is a new emerging high power semiconductor switch which combines the advantages of thyristor's high voltage/current capability and MOS easy gate control. Due to very high silicon utilization and use of conventional thyristor technology, it has much lower cost compared with other competing technologies. Furthermore, it has significantly improved performance in current conduction, turn-off speed, and snubberless turn-off current capability. Future ETO switches under development will also pack with additional features that no-competing technologies offer, including built-in voltage, current and temperature sensing capability, control-power self-generation capability and high-voltage current saturation capability. These capabilities make ETO a very promising power semiconductor device to reduce the cost of converter-based transmission controllers while improving the controller output power, dynamic performance, and operating reliability.

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