Transport Mechanism of SiGe Dot MOS Tunneling Diodes

The blockage of hole transport due to excess holes In SiGe dots was observed in the MOS tunneling diodes for the first time. The five layers of self-assembled SiGe dots are separated by 74-nm Si spacers and capped with a 130-nm Si. The hole tunneling current from Pt gate electrode to p-type Si dominates the inversion current at positive gate bias and is seven orders of magnitude higher than the Al gate/oxide/p-Si device. The large work function of Pt is responsible for the hole transport current from Pt to p-Si. The incorporation of SiGe dots confines the excess holes in the valence band and forms a repulsive barrier to reduce the hole transport current from Pt to SiGe dots by 2-3 orders of magnitude in comparison with the Pt/oxide/p-Si device. This repulsive barrier also reduces the hole tunneling current from SiGe dots to Pt at negative gate bias.