Capacitance-voltage measurements of double barrier In0.53Ga0.47As/AlAs resonant tunneling diodes show a large capacitance peak at a bias near resonance. The measured peak capacitance is about five times larger than the calculated depletion capacitance. This large capacitance is interpreted as the capacitance between the emitter and the quantum well, which is activated near resonance only when the quantum well has a sufficient number of electrons to screen the ac electric field. An equivalent circuit with the new added series RC component is proposed and the effect on the high frequency operation of a resonant tunneling diode is discussed.
Dominant photogenerated valley current has been observed in an optically-excited InGaAs/AlAs double-barrier resonant-tunneling diode. The photogenerated valley current in the resonant-tunneling diode varies with the optical power level. Under intense illumination, the photogenerated valley current increases to such a high level that it becomes dominant over the peak current. As a consequence, the negative differential resistance of the device is removed. The observed photogenerated valley current is described by photogenerating electron-hole pairs in the depletion region adjacent to the double-barrier structure. Transient behavior of the photogenerated carriers is also studied. The observed dominant photogenerated valley current may have useful applications.
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