Resonant tunneling through two impurities in disordered barriers

In short lateral barriers of GaAs metal-semiconductor field-effect transistor, we have observed resonant tunneling through two impurities. Contrary to a steplike feature in I(V) due to an elementary one-impurity resonance, the two-impurity resonance manifests itself as a peak in the current. A magnetic field strongly suppresses the peak amplitude but has little effect on its width. We analyze the magnetic-field and temperature dependences of the two-impurity resonances.