Tuning electronic properties in tin-assisted n-type ε-Ga2O3:Zr thin films via PLD for p-n heterojunction

Abstract

The orthorhombic ε-Ga2O3 has received attention due to its ultra-wide bandgap (4.9 eV), high lattice symmetry and unique theoretically spontaneous polarization, etc. Controlled carrier concentration of ε-Ga2O3 is essential for device fabrication. In this work, we successfully deposited tin-assisted n-type Zr-doped ε-Ga2O3 on epi-GaN/sapphire substrate using PLD with tunable carrier concentration merely by adjusting growth parameters of oxygen partial pressure and laser pulses, without further post-sputter annealing process. Furthermore, Sn element was a surfactant to stabilize epsilon phase rather than provide electrons as donors, while Zr acted as a shallow donor to generate carriers. The results show that the growth window of orthorhombic ε-Ga2O3:Zr is oxygen pressure between 0.005-0.03 mbar and laser pulses between 3000-8000. Both the oxygen pressure and laser pulses affect the Zr component in n-type ε-Ga2O3 thin films. The optimal deposition conditions of ε-Ga2O3:Zr thin films are as follows: 0.012 mbar oxygen pressure and 7000 laser pulses, where the ε-Ga2O3:Zr films have a minimum resistivity 2.4 Ω·cm, a carrier concentration of 1.6×1017 cm−3, and the mobility of 17.4 cm2V−1s−1. In this paper, the n-type ε-Ga2O3 thin film was deposited on p-GaN substrate and p-GaN/n-Ga2O3 heterojunction diodes were fabricated. This device exhibited a rectification ratio of 104-105, turn-on voltage of 2.05–2.3 V, and high breakdown voltage of −954 V.