Radiative recombination of two-dimensional electrons in acceptor δ-doped GaAs-${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As single heterojunctions

We have investigated a new type of heterojunction, which we propose as being especially advantageous for studying the radiative recombination of two-dimensional (2D) electrons. The structure is an n-type GaAs-${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As single heterojunction with a δ layer of acceptors positioned at a well-defined distance from the interface in a wide GaAs buffer layer. The radiative recombination of the 2D electrons with holes bound to these acceptors was investigated and the dependencies of the intensity, broadening, and spectral position of the luminescence line on the distance between the interface and the δ layer were measured. We found that the broadening of the luminescence line due to the holes is very small and this allows direct investigations of the density of states of the 2D electrons.