CURRENT TRANSPORT BEHAVIOUR OF Au/n-GaAs SCHOTTKY DIODES GROWN ON Ge SUBSTRATE WITH DIFFERENT EPITAXIAL LAYER THICKNESS OVER A WIDE TEMPERATURE RANGE

The work presents temperature dependent forward and reverse current-voltage (I-V) analyses of n-GaAs/Au Schottky Diodes grown on n(+) Ge substrate with different epitaxial layer thicknesses. While some of the Schottky diodes follow TED mechanism, others exceed significantly from this theory due to existence of patches of reduced barrier height embedded in the Schottky interface. The zero bias barrier heights (phi(bo)) increase (0.649 to 0.809 eV) while the ideality factors (eta) decrease (1.514 to 1.052) with increase in epitaxial layer thickness (1-4 mu m), thus, indicating similar behaviour to that observed for the I-V characteristics of the undertaken Schottky diodes with decreasing temperature. It all indicated the existence of barrier inhomogenities over the M-S interface. The breakdown behaviour analysis of these diodes showed some interesting results; the breakdown voltage (V-BR) decreases with temperature and shows 'Defect Assisted Tunneling' phenomenon through surface or defect states in the 1 mu m thick epitaxial layer Schottky diode while V-BR increases with temperature in 3 mu m and 4 mu m thick epitaxial layer Schottky diodes which demonstrate 'Avalanche Multiplication' mechanism responsible for junction breakdown. The reverse breakdown voltage is also seen to increase (2.7-5.9 Volts) with the increase in epitaxial layer thickness of the diodes. The undertaken diodes have been observed to follow TFE mechanism at low temperatures (below 200 K) in which the tunneling current component increases with epitaxial layer thickness which has been ascribed as an impact of GaAs/Ge hetero-interface over the Au/n-GaAs Schottky barrier.