Polarity Control by Inversion Domain Suppression in N-Polar III-Nitride Heterostructures

Nitrogen-polar III-nitride heterostructures offer advantages over metal-polar structures in high frequency and high power applications. However, polarity control in III-nitrides is difficult to achieve as a result of unintentional polarity inversion domains (IDs). Herein, we present a comprehensive structural investigation with both atomic detail and thermodynamic analysis of the polarity evolution in low-and high-temperature AlN layers on on-axis and 4 degrees off-axis carbon-face 4H-SiC (000 (1) over bar) grown by hot-wall metal organic chemical vapor deposition. A polarity control strategy has been developed by variation of thermodynamic Al supersaturation and substrate misorientation angle in order to achieve the desired growth mode and polarity. We demonstrate that IDs are completely suppressed for high-temperature AlN nucleation layers when a step-flow growth mode is achieved on the off-axis substrates. We employ this approach to demonstrate high quality N-polar epitaxial AlGaN/GaN/AlN heterostructures.

Automated summary

Nitrogen-polar III-nitride heterostructures show advantages in high frequency and high power applications compared to metal-polar structures. However, polarity control in III-nitrides is difficult due to unintentional polarity inversion domains (IDs). In this study, we conducted a comprehensive structural investigation and thermodynamic analysis to understand the polarity evolution in low- and high-temperature AlN layers on on-axis and off-axis carbon-face 4H-SiC (000 (1) over bar) substrates. By controlling the Al supersaturation and substrate misorientation angle, we developed a polarity control strategy to achieve the desired growth mode and polarity. Our findings show that ID suppression is possible by achieving a step-flow growth mode on off-axis substrates for high-temperature AlN nucleation layers, and we successfully demonstrated high-quality N-polar epitaxial AlGaN/GaN/AlN heterostructures.