• pixel detectors
• graphene
• mos2
• radiation detector
• mip
• 2d materials
• tmd
• semiconductor
• simulation

Pixels detectors are widely used ionizing radiation detection devices in high-energy physics experiments. Segmented detectors have been employed for many years due to the need to simultaneously track the thousands of particles emerging from modern colliders. These devices are based on a matrix of sensing elements made of semiconducting materials, which are designed to detect incoming particles by the ionization charges produced inside each pixel. For more precise and accurate measurements one would like to have faster, less noisy and smaller pixels, but current technology imposes several limits on these characteristics.

The aim of this thesis is to explore the possible applications of bi-dimensional materials such as graphene or transition metal dichalcogenide monolayers (TMDs) to address these problems. In particular, one wants to determine whether nanoelectronic devices based on 2D materials could be used to obtain built-in preamplification of the pixel signal, thus achieving better detection performance. The thesis work was mostly done at INFN-PI (Pisa), INFN-LNF (Frascati) and CNR-IFN (Rome).

In the first part of the thesis, a review of the relevant physics and recent results is given, in order to highlight the current technological limits of pixel devices, and the properties of the materials that will be used. A summary of other proposed next-generation pixel detectors is also presented to give an idea of the work being done in this field.

The following part is a feasibility study of some prototype pixel sensors (50x50$\upmu$m) based on graphene or MoS$_2$, where by means of numerical simulations the possible performance of the devices is assessed. The working principle is the field-effect modulation of the channel conductivity in a 2D material-based transistor, due to the presence of ionization charges in a silicon absorber. Several architectures are tested, and a final device of choice is presented, with a sketch of a realistic readout system and its noise figure. The conductance modulation due to incoming particles is found to be more than $30\%$, resulting in a strong current signal.

Finally, the thesis describes the laboratory work done in parallel to the simulations. In particular, CVD graphene growth and characterization, as well as graphene-based device fabrication were performed at INFN-LNF and CNR-IFN laboratories, in order to highlight the most critical aspects for a future realization of prototype devices. The fabricated devices were then tested for their electrical transport properties (resistivity, gate capacitance, field-effect).

At the end of the work, several interesting aspects emerge: 2D materials-based pixels show built-in pre-amplification, and thus better signal quality if compared to standard hybrid pixels. Moreover, their fabrication would be in principle very simple, if 2D materials fabrication technology continues to improve. More specifically, these devices would be much less complex than other proposed integrated amplification systems such as SOI or DEPFET pixels. These aspects allow to conclude that it would be highly desirable to further study the subject, to perfect the device design, as well as to build some prototype devices to be tested with a radiation source.