Magnetic-field-induced resonance in a triple-barrier resonant tunnelling diode

Resonant tunnelling through a GaAs-AlAs triple-barrier structure with coupled quantum wells of unequal widths has been studied experimentally. Peaks in the current-voltage characteristic due to tunnelling via the lowest subband of each well were observed. Application of a magnetic field parallel to the interfaces broadens the peaks and at a certain critical field an additional resonance peak appears at a bias voltage between the original resonances. The field-induced peak is interpreted as a double-resonance effect, even though the subbands are not energetically aligned. This interpretation is supported by detailed calculations of current-voltage characteristics using a transfer-matrix approach.