Electron Emission from Diamond (111) p + -i-n + Junction Diode
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1203-J14-05
Electron Emission from Diamond (111) p+-i-n+ Junction Diode D. Takeuchi 1, T. Makino 1, H. Kato 1, M. Ogura 1, N. Tokuda 2, K. Oyama 1,3, T. Matusmoto 1,3, I. Hirabayashi 1, H. Okushi 1, S. Yamasaki 1,3 1 Energy Technology Research Center, AIST, AIST-TC2-13, Umezono 1-1-1, Tsukuba, 305-8568, Japan 2 Institute of Science and Engineering, Kanazawa University, Kakuma-machi, Kanazawa 920-1192, Japan 3 Graduate School of Pure and Applied Science, University of Tsukuba, Tennodai 1-1-1, Tsukuba, 305-8577, Japan ABSTRACT We successfully observed electron emission from hydrogenated diamond (111) p+-i-n+ junction diodes. Here, p+- and n+-layers mean that the boron and phosphorous impurity concentrations in these layers are around 1020 cm-3. The heavily doped layers play an important role to obtain high diode and emission currents. The emission started when the applying bias voltage was equal to the built-in potential, and the emission current reached to over 1 µA at room temperature operation. With taking into account our previous photoemission yield spectroscopy results and with the very high binding energy of free excitons of 80 meV in diamond, we suggested that the electron emission was derived from free excitons generated in the i-layer of the diodes. INTRODUCTION Electron emission from solid state devices is utilized in a variety of practical applications. Especially, electron emission devices with negative electron affinity (NEA) have been attracted a lot of researchers since high efficiency and unique properties of electron emission can be expected. We have investigated detailed photoelectron emission yield spectra from hydrogenterminated (H-terminated) diamond surfaces with NEA, and concluded that useful electron emission from the bulk could not be obtained with a combination of n-type diamond and NEA. [1-3] Recently Koizumi et al. successfully demonstrated electron emission from (111) p–n junctions with NEA. [4] The efficiency was recorded by more than 10% even though the device structure remained with enough room to develop. The device performances were mainly reported at higher temperatures of 200–300 °C to reduce resistance of n-type layer. The emission current of 1 µA at 200 °C was achieved with 100 V. He suggested that n-type layer behaved electron source, and the surface of p-type layer acted as NEA cathode. However, the electron emission mechanism, which gives ideas for optimization of the device structures, has not clearly been understood. According to our previous works on photoelectron emission yield spectroscopy, we suggested that the electron emission from these diodes was derived from free excitons generated in the diodes, with taking into account the results of the photoemission yield experiments, [1,2] electron emission from a (001) diode with NEA, [5] and very high binding energy of free
excitons of 80 meV. In addition, we aimed high-current at room temperature (RT) operation to develop diamond p-n diode based electron emitter with NEA surfaces for various applications. To demonstrate o
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