Mapping tensorial shear stress with light-emitting GaN nanopillars

Abstract

A novel force sensor capable of determining both the direction and magnitude of the force is proposed and demonstrated. The sensor structure is based on two orthogonally oriented arrays of GaN (Gallium Nitride) elliptical nanopillars and a digital CMOS (Complementary Metal Oxide Semiconductor) image sensor. The pixelated array also enables twodimensional force mapping. The directional sensitivity originates from the breaking of the nanopillar symmetry and the orthogonal orientation of the arrays. Each array is more sensitive to stress along the long axis of the nanopillars as opposed to the short axis of the nanopillars. Shear stress on the nanopillars causes a decrease in the overlap of the electron and hole wavefunctions which is proportional to the intensity of the light emitted from the nanopillars. Only a common bias, either optical or electrical, is needed across the entire device, making two-dimensional mapping simple and easily completed using a common digital CMOS camera. No stringent uniformity requirement across the sensor array is necessary. The data from an unstressed array is compared to the data from the same array under stress so that the relative change of emission intensity can be determined. With a combination two arrays, we showed that the direction and magnitude of the force can be determined by comparing the emission intensity change between two orthogonal arrays.