OPTICAL AND ELECTRICAL-PROPERTIES OF QUANTUM-WELLS WITH ELECTRICALLY TUNABLE 2-DIMENSIONAL ELECTRON-DENSITY BY SELECTIVE CONTACTS

We report on photoluminescence and absorption measurements in type-I h etero n-i-p-i structures. The electron density in the pseudomorphic In GaAs/GaAs quantum wells is tunable between zero and more then 5 . 10(1 2) cm(-2). This electrical tuning of the subband filling is achieved b y a variable voltage applied between selective nand p-contacts fabrica ted by epitaxial shadow mask MBE. One of the advantages of having sele ctive contacts to the n- and p-layers is to get reliable information a bout the electron density, independent of measured absorption and lumi nescence spectra. This allows a more rigorous analysis of the data on bandgap renormalization, bandfilling and k(parallel to)-conservation. Moreover, the experiments can be performed at low optical power and lo w carrier temperatures. In the present investigation a bandgap renorma lization of -20 meV and a bandfilling induced shift of the absorption edge as large as +50 meV was observed for a sheet electron density of 5 . 10(12) cm(-2).