DX-centers and long-term effects in the high-frequency hopping conductance in Si-doped <f>GaAs/Al0.3Ga0.7As</f> heterostructures in the quantum Hall regime: acoustical studies

It is discovered that both high-frequency (hf) hopping conductance and electron density in the 2D channel, <f>ns</f>, in Si <f>δ</f>-doped and modulation-doped <f>GaAs/Al0.3Ga0.7As</f> heterostructures at the plateaus of the integer quantum Hall effect depend on cooling rate of the samples. Furthermore, consecutive IR illumination leads to a persistent hf hopping photoconductance, which decreases when the illumination intensity increases, while <f>ns</f> increases. The persistent hf hopping photoconductance occurs when the illumination frequency exceeds a threshold, which is between 0.48 and <f>0.86 eV</f>. The results are attributed to two-electron defects (so-called <f>DX</f>-centers) located in the Si-doped layer of the <f>Al0.3Ga0.7As</f> heterostructure. [Copyright &y& Elsevier]