Semiconductor microcrystals with ultra-high sensitivity to mechanical strain at cryogenic temperatures

Results of the studies of the low-temperature piezoresistance for p-type silicon microcrystals doped with boron up to $N=7\times 10^{17}-1\times 10^{19}$ cm$^{-3}$ are presented. The dependence of piezoresistance on impurity concentration and temperature was studied. The extremely high piezoresistance was found at the lowest temperatures 4.2-20 K in samples with boron concentration corresponding to the insulating side of the metal-insulator transition in the vicinity of it. A practical application of such a giant piezoresistance in mechanical sensors for cryogenic temperatures is discussed.