Thermal Annealing Effects on I-V-T Characteristics of Pd/Ge/Ti/Pt/Au-Si-Gaas Contact at High Temperatures

Refractory metal (Pd/Ge/Ti/Pt/Au) on semi-insulated GaAs (SI-GaAs) have been prepared and annealed at 380,400 and 425℃. Optical microscope and SEM images show that there is no significant difference in refractory metal surface morphology before and after annealing, compared with the standard AuGeNi electrode of a large number of massive crystals precipitated after annealing, and the specific contact resistivity of Pd/Ge/Ti/Pt/Au-SI-GaAs is the lowest at 400℃ annealing. The current-voltage-temperature (I-V-T) characteristics of the as-deposited and annealed devices have been measured in in the high temperature of 300-400 K with steps of 20 K. The behavior of the forward I-V-T characteristics of inhomogeneous Pd/Ge/Ti/Pt/Au-SI-GaAs contact before and after annealing has been investigated. The experimental results show that the barrier height (Φ b ) and ideality factor (n) derived from the ideal thermionic emission model were strongly temperature dependent. Such behavior of the parameters is attributed to the inhomogeneous barrier height by assuming a Gaussian distribution at the metal/semiconductor (M/S) interface. We draw Φ b versus 1/2kT plots to obtain the mean barrier height (`Φ b ) and standard deviation (σ). The values of`Φ b are 1.373 eV, 1.275 eV, 1.199 eV and 0.130 eV, with of 0.205 V, 0.184 V, 0.173 V, and 0.193 V for the as-deposited and 380,400 and 425℃ annealed devices, respectively. A modified ln(I 0 /T 2 )-q 2 σ 2 /2k 2 T 2 versus 1/kT plots give the mean barrier height(`Φ b ) and Richardson constant(A * ). The values of `Φ b are consistent with the previous calculations. A * of 6.46 A/K 2 ·cm 2 for 400℃ annealed device is in closer agreement with the known value for SI-GaAs. Thus, it has been seen that the morphology of refractory metal electrode is better than that of AuGeNi electrode, and the Pd/Ge/Ti/Pt/Au-SI-GaAs contact by the thermal annealing at 400℃ is expected to be used as electrodes in SI-GaAs photoconductive switch instead of the standard AuGeNi metal