OBSERVATION OF DEEP DONOR CENTER RELATED TUNNELING PEAK IN THE ALXGA1-XAS/ALAS/ALXGA1-XAS/ALAS/ALXGA1-XAS (0.40-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.50) RESONANT-TUNNELING DIODES

The tunneling peak due to electron transport through deep donor (DX) centers was observed in the AlxGa1-xAs/AlAs/AlxGa1-xAs/AlAs/AlxGa1-xAs resonant tunneling diodes (0.40 less-than-or-equal-to x less-than-or-equal-to 0.50). Since the carriers are frozen out in AlxGa1-xAs (x greater-than-or-equal-to 0.35) at low temperature, the current-voltage (I-V) characteristics can only be measured under laser illumination condition. It was found that this DX center related tunneling peak initially appeared at higher voltage when the laser was turned on, and it gradually shifted to lower voltage over several minutes. This peak eventually merged into the lower voltage tunneling peak at temperature below 76 K, but stayed apart at higher temperature. This unusual behavior is attributed to the simultaneous existence of the impurity band formed by the metastable DX states associated with X band [DX(X)] and their isolated double charged states [DX- (X)]. This tunneling peak is not observed when the AlAs mole fraction x is reduced to 0.35.