Unambiguous identification of X-point-related resonances in GaAs/AlAs/GaAs tunnel diodes under hydrostatic pressure

We have performed detailed investigations of an asymmetrically doped GaAs/AlAs/GaAs tunnel diode in which a 2D accumulation layer forms at the emitter/barrier interface under forward bias. The systematic application of hydrostatic pressure at 77 K leads to the development of a well resolved peak in d//dV in forward bias above 2 kbar. The peak shifts approximately linearly downwards in voltage as the pressure is increased in constant steps. Comparison with self-consistent theoretical calculations enables us to unambiguously identify the peak as arising from resonant tunnelling between the electron states in the accumulation layer and the longitudinal X-point subbands of the AlAs barrier. To our knowledge this is the first time that quantitative agreement between theory and experiment has been achieved and places our interpretation beyond question. Our conclusions have important implications for the optimization of microwave diodes based on such structures.