Modeling of microwave diode on diamond like coating Si cathode

• Published in: Journal of vacuum science and technology. B, Nanotechnology & microelectronics Nanotechnology & microelectronics, 2015-05, Vol.33 (3)
• Main Authors: Goncharuk, N. M., Karushkin, N. F.
• Format: Article
• Language: English
• ISSN: 2166-2746; 2166-2754
• DOI: 10.1116/1.4906821

Microwave diode structures were applied to the base of a silicon cathode with diamond like coating (DLC) to theoretically investigate resonant and nonresonant electron emission in the framework of small-signal theory. Negative conductance of the diode with resonant electron emission is caused at first by negative conductivity of the cathode due to resonant electron tunneling and at second an electron delay due to the finite time of an electron dwelling in a quantum well of DLC and its transit in the vacuum transit layer. Thus, its origin is the same as for a semiconductor resonant-tunneling diode and a negative conductivity takes place on a falling part of a resonant dependence of a direct emission current on an electric field. Owing to the sufficiently small electron mass of DLC, the duration of resonant electron emission for the studied diodes is considerably less than the optimal transit time, which is determined by the negative emission conductivity value. Therefore, resonant emission frequency of the diodes noticeably exceeds the optimal transit frequency, and, thus, the diode's frequency spectrum of negative conductance consists of a single band. Maximum negative conductance in the spectrum occurs at a few tenths or a few units of terahertz depending on the values of electric-field and parameters of the cathode coating and transit layer. These values determine the character of electron emission (resonant or nonresonant), negative conductivity, and delays in electron emission and transit. Negative conductance of the diodes with nonresonant emission results from combined delays of electron emission and transit. The delay in electron emission is caused a finite duration of electron tunneling under the vacuum potential barrier of electron affinity in DLC. The barrier is situated in the vacuum layer that is adjoined to the DLC and adjacent to the vacuum layer of electron transit. The delay in electron tunneling is comparable with transit delay for the studied diodes due to the great electron mass in vacuum that results in the multiband spectra of the diodes with nonresonant emission.