Electron spin resonance on a two-dimensional electron gas

Electron-spin-resonance (ESR) data obtained from modulation-doped Si/Si_1-yCy heterostructures are reported. The observed signals show that the small number of electron spins in these two-dimensional structures is still sufficient to detect ESR directly, and we have strong indications that the prominent line in the spectra is due to conduction electrons confined in the Si_1-yCy layers, forming a two-dimensional electron gas. We compare our results to the case of confined electrons in III-V heterostructures and quantum wells, where only indirectly detected ESR experiments have been reported so far.