「様式３」Project No.： 2004

Photocathodes based on CNT-yarn emitter and GaAs
photoswitch for new miniaturized terahertz vacuum tubes［１］Organization
Project Leader：Privatdozent (Senior Lecturer)
Dr.-Ing. Oktay Yilmazoglu
TechnicalUniversity
Darmstadt,
Merckstrasse 25, 64283 Darmstadt.
Germany
Representative at RIE： Prof. Hidenori Mimura
Research Institute of Electronics,
Shizuoka University, Hamamatsu［２］Research Progress
A high frequency photocathode based on a carbon
nanotube (CNT)-yarn and semi-insulating (s.i.)
GaAs was fabricated which allows an external
illumination with a low-cost laser. This hybrid twochip technology allowed the separate optimization of
the yarn emitter and the photoswitch. The device
capacitance was very small with a promising
application for miniaturized high-frequency vacuum
tubes. Hence, these systems can be compact, roomtemperature applicable to permit development into
a technology of interest for broader markets outsideof science.
A seminar was given on July 6th, 2018 in theShizuoka University in Hamamatsu. Title: “High‐frequency photocathodes based on CNT or graphene
emitters and ultrafast GaAs photoswitches.”
The visit was also used for the organization of thenew project. Initial photo-field emission results werediscussed.

［３］Results(３－１) Research results
New achievements in vacuum high frequency
sources have not only practical significance in thescientific context but also beyond, in fields such as
security screening of packages, remote radar-typesensing, pharmacy, biomedical engineering, andtomography.
A CNT yarn with 20 µm diameter was sandwitchedbetween the GaAs photoswitch and a quartz wafer
to achieve a stable low-resistive contact to the GaAs
photoswitch and allow an external illumination witha low-cost pulsed laser (Fig. 1). A 860 nm VCSEL
laser was used for pulse modulation of thephotocathode. The laser was coupled into a
multimode fiber and aligned close to the GaAs
photoswitch. A pulse width of 10 ns was used for thedevice characterization.

Fig. 1 Schematic of the photocathode based on CNTyarn emitter and GaAs photoswitch.
The used CNT yarn emitter with 20 µm diameterconsists of stacks of CNTs with few nanometer.
Relatively low turn-on and threshold electric fields of~0.8 V/µm (defined at 1µA/cm2) and ~1.8 V/µm
(defined at 1mA/cm2) were obtained for the yarn
emitter, respectively, with a stable field emittercurrent up to 400 µA. This simple external laser
illuminated the photoswitch and triggered the FEcurrent. Initial photo-field emission measurements
showed an on/off ratio > 500. The high-voltage
photomodulation was up to 100 MHz with highquantum efficiencies.

(３－２) Ripple effects and further developments
Up to now semi-insulating (s.i.) GaAs with higher
carrier lifetime was tested as photoswitch. Thehybrid integration of the ultrafast low-temperature(LT) GaAs photoswitch with the yarn emitter can
provide much shorter electron bunches in picosecond
range, which can be used for miniaturized terahertz
vacuum tubes. In particular, the integration of a lowcost pulsed VCSEL laser will result in a morecompact high-frequency photocathode and open theway even for the mass market.

［４］Achievements (List of Publications)（１） O. Yilmazoglu, S. Al-Daffaie, F. Küppers, Y.
Neo and H. Mimura, “High-frequency photocathodebased on CNT-yarn emitter and GaAs
photoswitch,“31stInternational
VacuumNanoelectronics Conference (IVNC 2018), Kyoto,Japan, 2018.
（ ２ ） O. Yilmazoglu, “High‐frequency
photocathodes based on CNT or graphene emittersand ultrafast GaAs photoswitches.” Seminar for2018 Cooperative Research Project by RIE,
Hamamatsu, July 6th, 2018.

Page 3：Travelling Report（Mention each travel by CRP budget.）Name： Senior Lecturer Dr.-Ing. Oktay Yilmazoglu
Affiliation： Technical University Darmstadt, Merckstrasse 25, 64283 Darmstadt. Germany
Period of time：5th to 14th of July, 2018
Destination：Research Institute of Electronics, Shizuoka University, Hamamatsu
Purpose： Seminar for 2018 Cooperative Research Project by RIE, Hamamatsu, July 6th, 2018. The visit
was also used for the organization of the new project. Initial photo-field emission results were discussed.
Name of receiver： Prof. Hidenori Mimura

Date: March 13th, 2019
Signature: