BALLISTIC INJECTION OF ELECTRONS WITH NEGATIVE EFFECTIVE MASSES

A space-charge-limited ballistic current of electrons, whose dispersio n law contains an interval with negative effective masses, reaches sat uration in a broad intermediate voltage range. The increase in voltage in this range (without a change in current) stems from the onset and expansion of a second space-charge region near the anode. Between the two space-charge regions-that near the cathode and that near the anode -is a quasineutral region in which the ion charge is canceled by the c harge of drifting electrons with a negative effective mass. With a fur ther increase in voltage, a quasineutral layer forms near the anode. I n this layer, the electrons have a positive mass. This layer quickly d isplaces the preceding layer. There is a convective instability of a u niform distribution of drifting electrons in the region in which they have a negative effective mass.