OBSERVATION OF DEEP DONOR CENTER RELATED TUNNELING PEAK IN THE ALXGA1-XAS ALAS/ALXGA1-XAS/ALAS/ALXGA1-XAS ESS-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) c enters 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-e qual-to 0.50). Since the carriers are frozen out in AlxGa1-xAs (x grea ter-than-or-equal-to 0.35) at low temperature, the current-voltage (I- V) characteristics can only be measured under laser illumination condi tion. It was found that this DX center related tunneling peak initiall y appeared at higher voltage when the laser was turned on, and it grad ually shifted to lower voltage over several minutes. This peak eventua lly 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 i solated double charged states DX- (X)!. This tunneling peak is not ob served when the AlAs mole fraction x is reduced to 0.35.