PROJECTS

Ultrafast and efficient nanodevices for THz communications and spectroscopy based on narrow and wide bandgap semiconductors (ULTRADISPO)

 

This is an ambitious project aiming to the progress of a broad range of high-frequency semiconductor devices, which will be modelled, characterized and fabricated. The objectives of the research will be to improve the energy efficiency of the devices and to enlarge their functionalities by reaching the THz frequency range. The mid-term goal is to transfer the developments made on the different technologies targeted in this project to systems with practical applications in the fields of ultra-fast communications (for both transmitters and receptors) and sensors for THz spectroscopy. Both classical architectures, such as Schottky barrier diodes, Gunn diodes and HEMT transistors, and novel structures, such as selfswitching diodes (SSDs) and gated-SSDs (G-SSDs), will be addressed, with the common feature that all of them are based on III-V semiconductors, specifically InGaAs as narrow-bandgap semiconductor (oriented to low-power, ultrahigh-frequency applications, above 300 GHz) and GaN as wide bandgap one (oriented to high-power applications below 300 GHz). Two approaches for THz emitters will be studied. Gunn diodes (on both InGaAs and GaN) and frequency-multiplied sources based on Schottky barrier diodes. In the latter case, high-power GaN diodes will be used, so that one of the main issues will be the study of selfheating effects and the optimization of the breakdown voltage. Gated Gunn diodes with the G-SSDs architecture will straightforwardly allow for the modulation of the emitted signal (with simple on-off keying), so that their application to high-speed communications can be envisaged. Moreover, they would allow for wideband tunability; thus, THz spectroscopy is other important field of potential application of the outcomes of the project. The THz detection/receptor side will be tackled by means of the classic Schottky barrier diode technology (with the novelty of the high-power capability of GaN) and with the more innovative TERAFET concept (field effect transistors, FETs, employed as THz detectors), using HEMTs and G-SSDs.

Reference: PID2020-115842RB-I00
Funding entity:
Ministerio de Ciencia e Innovación
Period:
2021-2024
Improvement of GaN-based Schottky barrier diode technology for high-power efficient electronics

 

The use of wide bandgap semiconductors for the development of high-power (and high-frequency) applications may contribute to the challenge of reducing energy consumption from the side of electronics. The global objective of this project is to contribute to the enhancement of the efficiency of gallium nitride (GaN) Schottky-barrier diode (SBD) technology for such applications, in particular related to power conversion systems and wireless communications. GaN SBDs with several architectures and geometries will be analyzed in order to identify the influence of the different technological parameters on the performance of the devices. Additionally, the relatively novel gallium oxide (Ga2O3) SBD technology will be explored for high-power but lower-frequency applications. Optimized GaN SBD technologies can help reaching a dual aim: (i) boost the efficiency in the energy management of high-power circuits (like switched-mode power supplies and AC inverters for electric power generation) and (ii) the exploitation of the THz range of the electromagnetic spectrum.

The methodology is based on advanced simulation, fabrication and characterization techniques with permanent feedback among them. Modelling and design of the devices will be performed by means of Monte Carlo (MC) simulations. Special attention will be paid to the processes originating reverse leakage current, self-heating and, ultimately, the breakdown of the SBDs. In the field of fabrication, apart from SiC substrates for the growth of GaN layers on which SBDs are processed, high-quality native GaN substrates will also be used. The growth of the epilayers and the fabrication of the SBDs will be performed at NTU (Singapore) and IEMN (Lille, France), respectively, in the context of a common collaboration. Exploiting the advanced capabilities of radiofrequency (RF) laboratory at the USAL, partially funded by the JCyL, a detailed temperature-dependent characterization of the SBDs will be performed, including pulsed measurements, with the aim of determining the origin of leakage current and study self-heating of the devices. With this methodology, we will identify the origin of the issues limiting the performance of GaN SBDs and propose the design of optimized devices and new Ga2O3 architectures.

The collaborating company SENER AEROESPACIAL, which is currently developing strategic work lines for the inclusion of GaN devices in its RF systems and the fabrication of DC/DC converters, will contribute to the project by supervising the results and advising on the integration of the devices under study in systems for various applications.

The project results are expected to contribute to the development of essential electronic components with high impact in applications where improved efficiency is necessary, like power sources, energy converters, or communication networks, decisive aspects for the development of key industries for the Community of Castilla y León, such as those related to the electric vehicle or renewable energies.

Reference: SA136P23
Funding entity:
Junta de Castilla y León - Consejería de Educación
Period:
2024-2027
GaN planar Gunn diodes with substrate terminal for high power sub-THz generation (GaN-Gun-S)

 

Terahertz (THz) radiation, whose frequency range lies between microwaves and infrared in the electromagnetic spectrum, opens the possibility of new imaging and spectroscopy technology with a wide range of applications, from medical diagnosis, biotechnology (DNA or protein analysis), industrial quality control, artificial vision (ranging in robotics, landing systems in aeronautics, automotive radars) or security scanners (detection of drugs, explosives or hidden weapons). In the field of telecommunications, secure local communications (with a high level of attenuation outside the area of interest) at very high speeds (above 160 Gb/s) would be possible. However, the THz sources are at the limits of electronics on the one hand and optics on the other, resulting in low power sources with reduced efficiencies or not being operational at room temperature. Due to these limitations, the bottleneck for the broad development of practical applications exploiting the THz range of the electromagnetic spectrum is the lack of room-temperature, continuous-wave, compact, mass producible,
tuneable and powerful sources. In order to tackle this issue, this project aims to design, fabricate and characterize operational prototypes of high-frequency high-power fundamental oscillators based on Gunn effect in taking advantage of the GaN material properties. Indeed, high output power and frequencies (in excess of 300 GHz) are expected to be reached with GaN Gunn diodes due to its high saturation velocity and high breakdown field. However, in spite of large technological efforts, no direct evidence of Gunn oscillations in GaN has been observed up to now, even if simulations predict its appearance.
In previous projects we have proposed a planar fin-type Gunn diode topology based on tapered-channel geometry, which can be used to achieve THz sources by improving the efficiency of planar Gunn diodes due to a dual action: (i) The electrical field is well focused at the cathode side of the channel, so that the threshold voltage needed for the onset of the oscillations is reduced; the narrow part of the channel acts as a notch that also allows a better control of the oscillation frequency. And (ii) the heat dissipation can be efficiently
managed by an appropriate design of the channels and its separation. As a consequence of a lower applied voltage and weakened thermal effects, the device breakdown is avoided, so that continuous wave operation can be reached. However, the devices fabricated following such geometrically-shaped planar-Gunn-diode (GS-PGD) architecture show a catastrophic breakdown for applied voltages much lower than expected. This failure is not related to self-heating but due to an avalanche process initiated by the electrons passing below the isolation trenches.
Thus, in order to overcome this problem, in this project we propose the design and fabrication of GS-PGDs with a substrate terminal (introduced to mitigate the number of impact ionizations and avoid a premature breakdown), thus leading to a three terminal GS-PGD (3TGS-PGD). The final goal is to demonstrate for the first time the continuous wave operation of a GaN-based Gunn oscillator, at the mm/submm wave frontier, i. e. around 300 GHz, with output power of tens of mW.

Reference: PDC2023-145896-I00
Funding entity:
Ministerio de Ciencia e Innovación - Agencia Estatal de Investitgación
Period:
2024-2025


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