Precision defect engineering of metal/insulator/metal diodes using atomic layer deposition to localize Ni impurities in Al2O3 tunnel barriers

Abstract

Extrinsic impurity defect engineering is demonstrated to increase the maximum asymmetry of metal/insulator/metal (MIM) tunnel diodes. Using atomic layer deposition, transition metal Ni impurities are inserted at precise physical locations within the thickness of the insulating tunnel barrier in asymmetric electrode TiN/Al2O3/Al MIM diodes. The presence of Ni in Al2O3 is found to suppress the onset of Fowler–Nordheim tunneling from the Al electrode without changing the relative dielectric constant or refractive index of the insulator. Current–voltage asymmetry, a performance metric for MIM diodes, is reversed in Al2O3(Ni) devices and is increased over the control Al2O3 device (without Ni impurities) when the Ni impurities are placed close to the Al electrode. Capacitance–voltage measurements on MIM and metal/oxide/semiconductor devices along with Fowler–Nordheim derivative analysis all indicate the introduction of negative charge highly correlated with the position of the Ni defect layer within the Al2O3. Internal photoemission measurements show little change in zero-field energy barrier heights at the electrode interfaces, but varying field dependencies with respect to the position of the Ni defect layer. Combined results suggest that the level of the deep states introduced by the Ni atoms in Al2O3 is consistent with DFT predictions for the corundum Al2O3 system. Overall, this work demonstrates the possibility of improving MIM diode performance using precisely placed extrinsic defects.