RADIATIVE RECOMBINATION IN DOPED ALGAAS/GAAS HETEROSTRUCTURES

The radiative recombination processes of two-dimensional (2D) carriers have been studied for n-channel AlGaAs/GaAs heterojunctions with different doping levels. The recombination involving the 2D carriers confined on the GaAs side of the interface notch gives rise to two different photoluminescence (PL) bands, the so-called H-bands. A considerable variation of these bands in PL spectra is observed concerning shape, broadening, energy position and decay times. This variation depends on the experimental conditions, such as the temperature, intensity and photon energy of the excitation, but also on the design of the sample. Also, the dependence on these parameters is different for the two H-bands. The results are consistent with a general model for the origin of the two H-bands in n-channel heterojunctions as due to the recombination between 2D electrons confined in the GaAs notch and holes from either the valence band or the neutral acceptors in the active GaAs layer. The observed variations are explained as due to a corresponding variation in the band bending across the active GaAs layer. The spatial separation between the holes and the electrons involved in the H-band recombination processes depends critically on this band bending.