Optical creation of a metastable two-dimensional electron gas in a ZnSe/BeTe quantum structure

A microstructure has been designed in which an electron gas is created opti cally with variable density. ZnSe and BeTe quantum wells are separated by a BeZnMgSe alloy with band gap 3 eV. When electron-hole pairs are created by ultraviolet light in the barriers, electrons accumulate in the ZnSe quantu m well, and holes in the BeTe quantum well. This is because the BeTe valenc e band lies 900 meV higher than that of ZnSe. Reflectivity and luminescence spectra of the ZnSe well show the destabilization of excitons by an electr on gas and formation of trions. The metastable charge-separated state has a very long lifetime (2 s at 2 K). (C) 1998 American Institute of Physics. [ S0003-6951(98)02731-4].