Charge density maps and band diagrams below and above turn-on. The charge density and electron potential of the proposed device model both (a) below and (b) above the turn-on voltage. Removal of electrons from traps in Region 1 leaves fixed positive charge that supports a large electric field (106 V/cm). The steady state width of Region 1 is determined by balancing the injection of electrons by thermionic emission below the turn-on voltage or tunneling current above the turn-on voltage with the removal of electrons by Poole-Frenkel current through Region 2. (a) Below the turn-on voltage a small electric field (103 V/cm) is required in Region 2 to remove the electrons injected by thermionic emission. (b) Above the turn-on voltage a larger electric field (105 V/cm) is required in Region 2 to remove electrons injected by tunneling.