Enhancing P-type Conductivity in Mg-doped GaN Using Oxygen and Nitrogen Plasma Activation

Abstract

Plasma-assisted activation (PAA) has been studied in detail to enhance the electrical and optical performance of Mg-doped GaN surface layers. The plasma-assisted activation technique was carried out in a plasma-enhanced chemical vapor deposition (PECVD) system with various ratios of N2 to O2 environments at 400 and 640°C. Plasma energy in our studies was used to decompose the Mg–H complex, and H atoms were absorbed by O2 gas to form H2O. On the other hand, N2 gas was introduced to compensate for nitrogen vacancies. A hole concentration higher than 2.44×1017 cm-3 was determined near the GaN surface and a specific contact resistance of 8.6×10-5 Ω·cm2 was achieved, this is better than that of conventional 700°C thermal annealing. A 400°C PAA sample exhibits the same specific contact resistance of 2.1×10-4 Ω·cm2 as that of a 700°C thermal annealed sample. Moreover, room temperature-photoluminescence (RT-PL) showed that the 400 and 640°C PAA samples had a stronger intensity compared to that of conventional samples. Peak intensities of RT-PL were centered at 438 nm for all samples. The best electrical and optical properties appeared at a N2 to O2 ratio of 5:3 in our study. A possible explanation is that a self-compensation mechanism is dominant in our plasma-assisted activation.