A study on MOCVD growth window for high quality N-polar GaN for vertical device applications

Lateral N-polar GaN devices have outperformed Ga-polar GaN counterparts in mm-wave applications. A vertical N-polar GaN device structure with higher breakdown voltage is expected to further improve the output power density. This paper is aimed at understanding the growth conditions for such a vertical N-polar GaN device stack. A vertical device stack requires high-quality n-GaN layer with low unintentional dopant concentration and high electron mobility for better ON resistance-breakdown voltage performance. A systematic study by varying reactor temperature, pressure and NH3 flow rate is performed in the metal organic chemical vapor deposition growth of N-polar GaN for vertical device structure. Structural quality of the sample is increased with increase growth temperature and higher NH3 flow rate, yet an increase in surface roughness is observed for highest temperature used. The N-polar GaN grown at the optimized conditions exhibited a x-ray diffraction rocking curve full width half maximum of symmetric (0002) and skew-symmetric (20 (2) over bar (1) over bar) scans of 358 '' and 569 '' respectively with a low oxygen and carbon concentration of 6 x 10(16) cm(-3) and 5 x 10(16) cm(-3), respectively. The optimized sample exhibited a low screw dislocation density of 2.5 x 10(8) cm(-2) on sapphire substrate. A gradual increase in the bulk mobility of electrons with decrease in screw dislocation density in N-polar GaN is also reported.

Automated summary

Lateral N-polar GaN devices have shown better performance than Ga-polar GaN counterparts in mm-wave applications. This study focuses on the growth conditions for a vertical N-polar GaN device stack, aiming to improve the output power density. The results show that higher growth temperature and NH3 flow rate contribute to increased structural quality, while also causing an increase in surface roughness. The optimized sample exhibited excellent structural quality and low oxygen and carbon concentration, and showed a low screw dislocation density on the sapphire substrate.