Supervisors: E. Giulio Villani (RAL/PPD) & Daniel Hynds (University of Oxford)
Planned HEP experiments over the coming decade present formidable technical challenges, including extreme radiation hardness, pileup rejection, higher levels of detector segmentation and time-resolving capabilities of the order of ps.
Gallium nitride (GaN) semiconductors are now commonly found in optoelectronic and high-power devices, e.g. , light-emitting diodes (LEDs), lasers and high electron mobility transistors (HEMT). GaN can also be used for detecting ionizing radiation under extreme radiation conditions due to its properties such as a wide bandgap (3.39 eV), large displacement energy (theoretical values averaging 109 eV for N and 45 eV for Ga), and high thermal stability (melting point around 2500 0C). A comparison with other wide band-gap semiconductors, such as SiC, demonstrates GaN's higher electron mobility and potential for better carrier transport properties, which translate to fast operating devices.
This jointly supervised project aims to assess the potential of GaN as a material for the fabrication of fast and radiation-hard devices for HEP applications, including particle detection and read out electronics for current and future colliders.
The first phase of the project will focus on confirming that GaN is indeed a radiation-hard material and that it can be successfully used for HEP experiments. The student will characterise already available GaN test structures (Schottky diodes) and will take active part in the irradiation campaign of the devices. He will also liaise with the devices manufacturers (NRC /University of Carleton, Canada, and CNM, Spain) to gain the necessary knowledge on the GaN-based devices characteristics and fabrication process. A crucial aspect of the investigation will be on the potential timing applications of GaN devices. This will require an ad-hoc modification, studied and implemented by the student, of some of the RAL PPD Laser test facility, for the generation of UV (355 nm wavelength) fast (< 35 ps) and low jitter (< 1 ps) pulses using the already existing 1064 nm wavelength fast pulses TCT laser.
The second phase of the project will focus on detailed device simulation using leading-edge TCAD software available from RAL/Oxford and GEANT4 to improve the modelling of radiation interaction with GaN and of charge transport mechanisms. The final, and ambitious, goal of this phase will be the design of a novel GaN sensor array consisting of a matrix of pixels and to evaluate its tracking and timing performance using custom ASIC fabricated in 28 nm CMOS technology.
For more details, contact E. Giulio Villani giulio.villani@stfc.ac.uk) or Daniel Hynds (daniel.hynds@physics.ox.ac.uk).
