LOW-TEMPERATURE C-V CHARACTERISTICS OF SI-DOPED AL0.3GA0.7AS AND NORMAL NORMAL-GAAS/N-AL0.3GA0.7AS ISOTYPE HETEROJUNCTIONS GROWN VIA MOLECULAR-BEAM EPITAXY

C-V measurements on normal isotype GaAs/Al0.3Ga0.7As heterojunctions grown via molecular beam epitaxy were undertaken in the temperature ranges between 300 and 4.2 K. For temperatures less-than-or-equal-to 100 K, we found a persistent conductivity effect due to the field emitted and then capture delayed electrons in the Si-doped Al0.3Ga0.7As Lyer. These capture-delayed free carriers lead to apparent increase of the base doping in the AlGaAs and consequent reappearance of the valley in the concentration-versus-distance profiles of the heterojunctions at temperatures less-than-or-equal-to 100 K. The resultant temperature dependence of the calculated conduction-band offsets and the interface-state densities were found to be an artefact. Apparent shifting of the heterointerface positions observed in inverted heterojunctions was not observed in the normal GaAs/AlGaAs heterojunctions. The normal heterostructure enabled us to distinguish and determine the concentration of each deep donor level.