Giuseppe Di Gioia's thesis "GaN Schottky diodes for THz generation".

Oral defence on 13 December at 10.30 a.m.
The defence will take place in videoconferencing

Jury :

- Rachid DRIAD, IAF Research Engineer, Rapporteur
- Frédéric ANIEL, Professor, Université Paris Sud, Rapporteur
- Tiphaine CERBA, Research Engineer III-V Lab, Examiner
- Guillaume DUCOURNAU, Professor, University of Lille, Examiner
- Yannick ROELENS, Professor, University of Lille, Co-supervisor
- Mohammed ZAKNOUNE, CNRS Research Director, Director

Summary:

Terahertz science has many areas of application, such as astronomy, security, biomedical analysis and wireless telecommunications. However, the application of THz technology has been hampered by the lack of suitable, reliable, compact and cost-effective terahertz sources. Although there are many ways to generate a signal at THz frequencies, many of these sources suffer from several drawbacks and limitations, such as limited output power, the need for cryogenic temperatures to operate, excessive size, complexity and prohibitive cost. Among current THz sources, one type of solid-state technology stands out: the frequency multiplier.
The current state of the art in frequency multiplier technology is held by GaAs Schottky diode frequency multipliers. This is a well-known technology that has been used successfully, but as output frequency requirements become increasingly demanding, it is now facing a bottleneck due to the intrinsic physical limitations of GaAs in terms of breakdown voltage and thermal conductivity, which affect the output power of the frequency multiplier. GaN, due to its higher breakdown field and higher thermal conductivity, can theoretically offer higher pump power holding capabilities for frequency multipliers compared to GaAs. These capabilities can lead to simplified frequency multiplier designs, compared to the state of the art of GaAs frequency multipliers. In theory, eight GaAs diodes are required for a 200 GHz doubler with an input power of 150 mW, while one GaN diode with a similar anode area is capable of handling this input pump power.
In this thesis, quasi-vertical GaN Schottky diodes are fabricated and characterised, in order to study their parameters and performance for frequency multiplication applications. The fabrication process is carried out on three different types of GaN epitaxy: GaN on sapphire, GaN on Si and GaN on SiC. The diodes are manufactured with an air-bridge structure to reduce high-frequency parasitic components.

Abstract:

Terahertz science has many application areas, such as astronomy, security, biomedical analysis, and wireless telecommunications. However, the application of THz technology has been hampered by the lack of suitable, reliable, compact and cost-effective terahertz sources. Although there are many ways to generate a signal at THz frequencies, many of these sources suffer from several drawbacks and limitations, such as limited output power, the need for cryogenic temperatures to operate, excessive size, complexity and prohibitive cost. Among current THz sources, one type of solid-state technology stands out: the frequency multiplier.
The current state of the art in frequency multiplier technology is held by GaAs Schottky diode frequency multipliers. This is a well known technology that has been used successfully, but as the output frequency requirements become higher and higher, it is now facing a bottleneck due to the intrinsic physical limitations of GaAs in terms of breakdown voltage and thermal conductivity, which affect the output power of the frequency multiplier. GaN, due to its higher breakdown field and higher thermal conductivity, can theoretically offer higher pump power holding capabilities for frequency multipliers compared to GaAs. These capabilities can lead to simplified frequency multiplier designs compared to the state of the art GaAs frequency multipliers. Theoretically, eight GaAs diodes are required for a 200 GHz doubler with an input power of 150 mW, while a GaN diode with similar anode area is capable of handling this input pump power.
In this thesis, quasi-vertical GaN Schottky diodes are fabricated and characterized, in order to study their parameters and performance for frequency multiplication applications. The fabrication process is performed on three different types of GaN epitaxy: GaN on sapphire, GaN on Si and GaN on SiC. The diodes are fabricated with an air-bridge structure to reduce high frequency spurious components.