Heteroepitaxially grown homojunction gallium oxide PN diodes using ion implantation technologies

Although advancements in n- and p-doping of gallium oxide (Ga₂O₃) are underway, the realization of functional pn diodes remains elusive. Here, we present the successful fabrication of a Ga₂O₃ pn diode utilizing ion implantation technology. The Ga₂O₃ epilayers were grown on c-plane sapphire substrates by metalorganic chemical vapor deposition (MOCVD). P-type conductivity Ga₂O₃ epilayer, confirmed by Hall effect analysis, was achieved by phosphorus (P) ion implantation followed with a rapid thermal annealing (RTA) process. This p-Ga₂O₃ epilayer reveals a significant reduction in resistivity (<10⁶) compared to undoped Ga₂O₃, demonstrating the successful inclusion and activation of P within the crystal lattice. X-ray diffraction analysis shows that the Ga₂O₃ epilayers were grown in high crystal quality. Although the crystallinity of Ga₂O₃ was slightly degraded after P ion implantation, the structure was recovered to high-quality crystal after RTA treatment. For the device structure, p-type Ga₂O₃ was formed first, followed n-type Ga₂O₃ regrowth to create a pn junction diode. The obtained results demonstrate a built-in voltage of 4.8 V, 4.2 V, and 4.308 V from simulation, fabricated pn diodes measured by I–V and C–V, respectively. A high breakdown voltage of 900 V was also obtained for the lateral pn diode grown on sapphire substrate. As concerning temperature stability, I–V curves of Ga₂O₃ pn diode were measured from 25^oC to 150^oC in steps of 25 °C. At elevated temperatures, for both forward and reverse biases, consecutive increasing currents were measured. These could be resulted from dominant diffusion and drift currents over recombination current at a given bias. In addition, the reverse current saturated (@V > 3kT/q) and remained very low at 2✕10⁻⁸ A, as the diode operated at 150^oC. The behavior could be due to Ga₂O₃ being a wide bandgap material.