Thermally stable AuBe-based ohmic contacts to p-type GaP for AlGaInP-based light-emitting diode by using a tungsten barrier layer

We investigated how a tungsten diffusion barrier layer affected the electrical properties of AuBe/Au contacts to a p-GaP window layer (n_a = 5 × 10¹⁹ cm⁻³) for an AlGaInP-based light emitting diode. All of the as-deposited samples were ohmic. After annealing at 500 °C, the AuBe/Au contacts were electrically degraded with a specific contact resistivity of 1.0 × 10⁻⁴ Ωcm². However, the electrical properties of the W-based contacts were improved, having a contact resistivity of 5.0 × 10⁻⁶ Ωcm². The X-ray photoemission spectroscopy (XPS) results showed that the Ga 2p core level for the annealed AuBe/Au contacts shifted to the high binding-energy side. On the other hand, that for the AuBe/W/Au contacts shifted toward the lower binding-energy side. For the AuBe/Au contacts, both Be and P atoms were shown to be outdiffused into the metal contact after annealing. However, for the AuBe/W/Au contacts, the outdiffusion of Be atoms was prevented by the W barrier layer, and the Be atoms were indiffused into GaP. Based on the X-ray photoemission spectroscopy (XPS), Auger electron spectroscopy (AES), and electrical results, the annealing-induced electrical degradation and improvement are described and discussed.