Pd/Ge(or Si)/Pd/Ti/Au ohmic contacts to n-type InGaAs for AlGaAs/GaAs HBTs

Abstract

Pd/Ge/Pd/Ti/Au and Pd/Si/Pd/Ti/Au ohmic contacts to n-type InGaAs were investigated for applications to AlGaAs/GaAs HBT emitter ohmic contacts. In the Pd/Ge/Pd/Ti/Au ohmic contact, a minimum specific contact resistivity of 1.1×10⁻⁶ Ωcm² was achieved by annealing at 425°C/10s, but the ohmic performance was slightly degraded with increasing annealing temperature due to the reaction between the ohmic contact materials and the InGaAs substrate. However, a non-spiking planar interface and relatively good ohmic contact (high-10⁻⁶ Ωcm²) were maintained after annealing at 450°C/10s. In the Pd/Si/Pd/Ti/Au ohmic contact, in spite of the lower barrier height of the metal-InGaAs junction, as-deposited contacts showed non-ohmic behaviors due to the presence of the insulating Si layer. However, the specific contact resistivity decreased remarkably to 4.3×10⁻⁷ Ωcm² by annealing at 425°C/10s. Minimum specific contact resistivity of 3.9×10⁻⁷ Ωcm² was achieved by annealing at 400°C/20s. RF performance of the AlGaAs/GaAs HBT was also examined by employing the Pd/Ge/Pd/Ti/Au and Pd/Si/Pd/Ti/Au systems as emitter ohmic contacts. Cutoff frequencies were 65.0 GHz and 74.4 GHz, respectively, and maximum oscillation frequencies were 51.3 GHz and 52.5 GHz, respectively, indicating very successful high frequency operations.