RESONANT-TUNNELING OF QUASI-BALLISTIC ELECTRONS IN A HOT-ELECTRON TRANSISTOR - EVIDENCE FOR A BREAKDOWN OF MOMENTUM CONSERVATION

Striking evidence for the breakdown of parallel momentum conservation during the resonant tunnelling of 'hot' electrons has been observed. In the system under study, an injected quasi-ballistic electron distribution is allowed to tunnel via the first subband of an AlAs/GaAs/AlAs double-barrier diode incorporated in the collector barrier of a unipolar hot electron transistor. It is proposed that the observed absence of negative differential transconductance (NDT) is due to rapid electron-electron pair scattering events in the n-doped base region. NDT is, however, observed upon Landau quantization of the subband in the quantum well when a severe restriction is placed on the k-spaces states available for electron scattering. In addition we observe a shoulder in the collected current which corresponds to the resonant tunnelling of injected electrons that have lost an LO phonon (the so-called LO phonon replica).