Abstract
The first spatially controlled thermodynamic measurements of a system of free excitons (FE) and excitonic molecules (EM) are reported. Both excitonic phases are confined to Gaussian spatial distributions in a strain-induced potential well. This parabolic well affords a simple analytic description of the thermal expansion of the gases. Recombination emission from the ultrapure Si is detected with spatial, spectral, and time resolution over the temperature range 3.5-10 K. The system is well described by a chemical equilibrium between two ideal gases at the lattice temperature: we observe the quadratic dependence of the EM density on the FE density and the expected form of thermal activation. In addition, the EM-FE thermalization time is found to be much less than the recombination times. The thermodynamically determined binding energy, meV, is in excellent agreement with our measured spectroscopic value meV. These values are several times larger than the most recent theoretical estimates.
- Received 30 November 1978
DOI:https://doi.org/10.1103/PhysRevB.20.3319
©1979 American Physical Society