  The CMS detector will undergo significant improvements to face the 10-fold
increase in integrated luminosity of LHC, the so-called High-Luminosity LHC,
scheduled to start in 2027. This will include a completely new calorimeter in
the CMS endcap regions, which should be able to withstand fluences of up to 10
16 n$_{eq}$ /cm$^2$ . The new High Granularity Calorimeter (HGCAL) will have
unprecedented transverse and longitudinal readout and trigger segmentation that
will facilitate the particle-flow approach to reconstruct electromagnetic and
hadronic particle showers and their energies. In regions of low radiation,
HGCAL will be equipped with small plastic scintillator tiles as active material
coupled to on-tile silicon photomultipliers. In the higher radiation zone,
silicon has been chosen due to its intrinsic radiation hardness. The silicon
sensors will be of hexagonal shape, with three nominal thicknesses of 120
{\mu}m, 200 {\mu}m and 300 {\mu}m, optimized for regions of different radiation
levels. They will be segmented into several hundred cells with hexagonal shape
of 0.5 to 1.1 cm$^2$ in size, each of which is read out individually. A
comprehensive campaign is in progress to converge on optimal sensor design
choices and parameters, such as bulk doping, layouts and production methods.
Results from full electrical sensor characterization are presented for
different sensors, together with first results from an irradiation campaign of
large-area silicon sensors.
