Piezojunction effect in heterojunctions under external bias for ultrasensitive strain sensing

This paper investigates for the first time the piezojunction effect in heterojunctions under external bias for ultrasensitive strain sensing. As a proof of concept, we used sensing devices made of 3C-SiC/Si heterostructure with vertically aligned electrodes. Applying the beam bending method to characterize the sensing effect, the bending strain was introduced along the typical orientation [100] or [110] on (100) Si plane. Experimental results show a linear relationship between the relative change in the forward current and the applied strain from 0 to 500 ppm, decreasing under the tensile strain while increasing under the compressive strain. At the forward bias of 8 V, the obtained gauge factors (GFs) are 199.7 for [100] orientation and 173.1 for [110] orientation, which significantly enhance about 630 % and 540 % compared to the highest GF of n-type 3C-SiC in the literature. Interestingly, the GFs of the n+-3C-SiC/p-Si heterostructure are positive in contrast to the negative GFs of n-3C-SiC thin films. The results were explained by the strain modulation on the band split and electron mass shift along the out-of-plane direction as well as by the change in the barrier height, depletion region width, and carrier concentrations under the forward bias. The ultrasensitive piezojunction effect in the 3C-SiC/Si heterojunction demonstrated in this study can pave the way toward developing ultrasensitive mechanical sensors.