The CV characteristics measured at different temperatures on all heterostructures show very fine fluctuations of capacitance in the voltage range around 0 V, which is suggested to be a result of free carriers¡¯ emission from quantum wells. The absence of GaAs ¡°cap¡± layer in one of the samples shifted its CV characteristic to lower values of capacity.
According to the DLTS measurement it is highly probable that the similar system of defects is present in all samples. The presence of the deep level ET1 is clear in all samples and its parameters were calculated by multi level evaluation (the activation energy of the defect which is approx. ¦¤ET = 0.62 eV, value of effective capture cross-section of the defect ¦ÒT is about 10?16 cm2, and defects concentration NT is about 1014 cm?3).