EN
A small "precursor" of resonance is observed before the main resonance peak in the current-voltage characteristic of double-barrier resonant-tunnelling devices. The competition between the precursor and main-peak current is examined within the temperature range 4.2-400 K. The precursor is interpreted as 3DEG contribution to the resonant tunnelling dominated by a 2DEG injection from a triangular well formed under bias in the emitter spacer layer.