Strain-narrowing of excitons in germanium

We have observed a narrowing of the luminescence line from excitons in germanium with the application of a uniaxial stress along the [111] crystallographic axis. In zero stress the line is broadened by the two split excitons and the mass-reversal effect, while at our stress of 15 $\text{kg}\text{mm}{}^2$ only one band is occupied. We find that the high stress density of states varies nearly as the square root of energy.