  The Cherenkov Telescope Array (CTA) is the the next generation facility of
imaging atmospheric Cherenkov telescopes; two sites will cover both
hemispheres. CTA will reach unprecedented sensitivity, energy and angular
resolution in very-high-energy gamma-ray astronomy. Each CTA array will include
four Large Size Telescopes (LSTs), designed to cover the low-energy range of
the CTA sensitivity ($\sim$20 GeV to 200 GeV). In the baseline LST design, the
focal-plane camera will be instrumented with 265 photodetector clusters; each
will include seven photomultiplier tubes (PMTs), with an entrance window of 1.5
inches in diameter. The PMT design is based on mature and reliable technology.
Recently, silicon photomultipliers (SiPMs) are emerging as a competitor.
Currently, SiPMs have advantages (e.g. lower operating voltage and tolerance to
high illumination levels) and disadvantages (e.g. higher capacitance and cross
talk rates), but this technology is still young and rapidly evolving. SiPM
technology has a strong potential to become superior to the PMT one in terms of
photon detection efficiency and price per square mm of detector area. While the
advantage of SiPMs has been proven for high-density, small size cameras, it is
yet to be demonstrated for large area cameras such as the one of the LST. We
are working to develop a SiPM-based module for the LST camera, in view of a
possible camera upgrade. We will describe the solutions we are exploring in
order to balance a competitive performance with a minimal impact on the overall
LST camera design.
