Speaker
Description
Thin film technology, as used in LCD displays and photovoltaics, could enable the fabrication of large-area, low-mass tracking detectors on flexible substrates, ultimately building towards roll-to-roll printing. Thin film detectors may also potentially incorporate electronic elements into a monolithic design, or involve the deposition of active sensor material onto a readout ASIC. Physical and chemical vapor deposition methods allow the fabrication of tracking sensors from many other semiconductors besides Silicon. Potential new material candidates for charged particle tracking and photon detection are identified by properties such as band gap, resistivity, charge carrier mobility and charge collection efficiency.
This presentation focuses on Indium Phosphide (InP), which stands out as having a significantly higher electron mobility (>4500 cm$^2$/Vs) than Si and has found use in optoelectronics and high-frequency electronics. Single-pad sensors and 5x5 pad arrays have been fabricated at Argonne National Laboratory on commercially available 350-µm thick InP:Fe wafers.
For single-pad sensors, we will summarize the initial characterization in the laboratory (IV, CV with uniformity assessment over the wafer; red laser TCT), as well as the results of test beams conducted with 120 GeV protons and focused X-ray beams. The reconstruction of hit position in 5x5-pad arrays in red laser TCT utilizing inter-pad cross-talk in addition to the main channel, is discussed.
To study of the radiation hardness of InP sensors, which is practically unknown compared to e.g. Si and diamond, a set of InP single-pad devices was irradiated with 1 MeV reactor neutrons at JSI/Ljubljana to the fluences of 1e13, 1e14, 1e15 and 1e16 n/cm$^2$. The sensors irradiated to 1e13 and 1e14 n/cm$^2$, as well as a non-irradiated reference, were tested with a Sr-90 beta source using a silicon LGAD reference as a trigger at different temperatures. Operation at lower temperature improves CCE and provides timing resolution down to < 25 ps. We find that excellent timing resolution is retained at a fluence of 1e13 n/cm$^2$. At 1e14 n/cm$^2$, increased degradation in collected signal charge and pulse amplitudes is observed, and higher bias voltages and lower temperatures are needed to reach 40 ps timing resolution. Rise time (and FWHM) for irradiated sensors decreases to 200 ps and below, but with a lower signal-to-noise ratio.
Our future plans for material modeling and simulation, as well as the next steps towards fabricating InP sensors by thin-film deposition methods, will be described.
