A new model suggests that lattice defects are responsible for the way some semiconductors become harder under illumination.
Understanding how semiconductors respond to illumination has been crucial to the development of photovoltaics and optical sensors. But some light-induced behaviors have been less thoroughly investigated. For example, when some semiconductors are illuminated, their mechanical properties can change drastically, a phenomenon known as photoelasticity. Photoelastic materials could be useful in the development of flexible electronics, but researchers do not understand in detail the mechanism behind the effect. Now, based on experiments and simulations, Rafael Jaramillo of the Massachusetts Institute of Technology and colleagues present a new theoretical framework that explains photoelasticity in terms of lattice defects [1].
The researchers used a diamond-tipped probe to make nanometer-scale indentations in samples of zinc oxide, zinc sulfide, and cadmium sulfide—first in the dark, and then under a range of visible and ultraviolet wavelengths. All three materials hardened to varying degrees when illuminated, with cadmium sulfide showing the largest and most consistent response. For every sample, the effect increased as the photon energy increased toward the material’s band gap.
