Alloy dependence of the carrier concentration and negative persistant photoconductivity in Ga1-xAlxSb/InAs/Ga1-xAlxSb single quantum wells

The magnetoconductivity of the two dimensional electron gas (2-DEG) in undoped single quantum wells Ga1-xAlxSb/InAs/Ga1-xAlxSb of various alloy compositions 0.1&lex&le1.0 was studied by the electron paramagnetic resonance technique. The carrier concentrations for semi-metallic (x<0.2) and non semi-metallic (x≥0.6) structures were determined at 4 K. The independence of the carrier concentration on the band structure off-sets (semi-metallic / semi-insulating transition) demonstrates the extrinsic origin of the 2-DEG. The 2-DEG concentration is modified by low temperature optical excitation: both negative and positive persistent variations were observed depending on the excitation wavelength and the alloy composition. No NPPC is observed in single quantum wells with x = 0.1 barrier composition.