Suppression of electron injection into a finite superlattice in an appliedmagnetic field - art. no. 195323

We present experimental and theoretical studies of the current-voltage char acteristics, I(V), of undoped GaAs/(AlxGa1-x)As superlattices (SL's) in a s trong magnetic field fl applied parallel to the growth axis. A series of I( V) characteristics measured at B = 1,2,...,10 T shows that increasing the m agnetic field gradually suppresses the current across the whole range of V. We show that at low V this suppression originates from a decrease in the r ate of injection of carriers into the SL from the heavily doped emitter con tact. Because the chemical potential in the emitter contact lies below the lowest miniband of the SL, electrons enter the SL by tunneling through a tr iangular potential barrier formed by the miniband edge. The tunneling rate depends on V and on the electron energy for longitudinal motion along the S L axis. The latter is reduced (by at least (h) over bar omega (c)/2, where omega (c) is the cyclotron frequency) in the magnetic field. Consequently, the tunneling rate decreases with increasing B. This mechanism of suppressi on dominates at low voltages (V<40 mV) when the barrier transmission coeffi cient is low.