Spectroscopic studies of low dimensional electron and hole systems in high quality GaAs-AlGaAs micro-structures

A highly sensitive photoconductivity (PC) technique has been applied to undoped GaAs-AlGaAs micro-structures with either a single interface or a single quantum well and a gate-controlled variable density of electrons or holes. In zero magnetic field measurements we have found a wide absorption band below the fundamental gap of bulk GaAs, which correlates with the population of 2D states. The PC technique has potential for spectroscopic studies of semiconductor nano-structures, such as quantum wire devices, which present difficulties for other conventional spectroscopy methods.