Tunneling-controlled photoluminescence in nonresonantly coupled single quantum wells

Photoluminescence controlled by tunneling of electrons and holes through barriers up to 100 A\r{} wide is investigated in nonresonantly coupled single quantum wells of ${\mathrm{In}}_{0.53}$${\mathrm{Ga}}_{0.47}$As/InP. We study a set of samples each with 100- and 60-A\r{}-wide wells separated by barriers of varying thicknesses ${L}_{b}$. For ${L}_{b}$40 A\r{}, the two excitonic emission lines thermalize with activation energies, demonstrating directly combined tunneling of electrons and holes. For wider barriers, saturation effects in the thermalization are associated with substantially reduced tunneling rates.