DETERMINATION OF THE VALENCE-BAND DISCONTINUITY IN BE-DOPED GAAS AL0.3GA0.7AS MULTIPLE-QUANTUM WELLS USING ADMITTANCE SPECTROSCOPY/

Admittance spectroscopy has been used to determine the value of the va lence-band discontinuity in a p-type GaAs/Al0.3Ga0.7As multiple-quantu m-well system. The structures were multiple quantum wells grown by mol ecular-beam epitaxy on semi-insulating GaAs substrates. Three Be-doped (p-type) GaAs wells, 30, 35, and 40 Angstrom wide, were used in these measurements. The barriers were undoped. Based on our measurements an d a Fermi-level determination from an 8X8 envelope function approximat ion calculation of the valence electronic structure of the GaAs/AlGaAs system, the valence-band discontinuity, Delta E(nu), was found to be 0.165 eV. Using established relations, the band-gap difference in the GaAs/AlGaAs system Delta E(g) for x(Al)=0.3 was calculated to be 0.429 eV, which, together with the valence-band offset determined in this w ork, gives the ratio of the conduction-to-valence-band offsets as 60:4 0. These values are in excellent agreement with those determined by ca pacitance-voltage profiling, thus confirming the utility of the admitt ance spectroscopic technique for determining the band discontinuities in band-gap-engineered materials.