Observation of a two-dimensional electron gas in modulation-doped ZnTe/CdSe quantum wells

We demonstrate the formation of a two-dimensional electron gas in lattice-matched, modulation-doped ZnTe/CdSe quantum well structures. Despite the well-known difficulty in n doping the II-VI semiconductor ZnTe, we find that the unusual type-II band alignment between ZnTe and CdSe allows the efficient transfer of free carriers from n-ZnTe into a CdSe quantum well since the deep donor levels in the n-ZnTe barrier lie above the confined ground state in the CdSe well. The sizeable well depth (∼1.35eV) enables the fabrication of two-dimensional electron gases with sheet concentrations up to ∼6×10¹²cm^-2, and with a low-temperature mobility up to 1.4×10⁴cm²/Vs.