An investigation of highly scaled III-nitride Gallium-face and Nitrogen-face HEMTs

• We conceptually compare the performance of highly scaled III-nitride structures.
• The results show that N-polar HEMTs are promising candidates for further scaling.
• N-face HEMTs provide good thermal properties.
• N-polar HEMT has superior high frequency characteristics relative to Ga-polar HEMTs.
• N-face HEMT shows much less undesirable behaviors seen for scaled devices compared with Ga-polar HEMTs.

Electrical performance of highly scaled III-nitride Ga-face and N-face HEMTs have been investigated using a two-dimensional numerical simulator. Four HEMT structures were studied, in three of which GaN substrate were grown in Ga-polar direction and in the last structure GaN substrate was grown in N-polar direction. Simulation results indicate that N-face structure has superior performance as compared with Ga-face structures. The undesirable effects originated from a potential distribution in the channel and current injection through the buffer effectively decrease and therefore their resultant effects such as low output conductance, threshold voltage shift and soft pinch-off become much less noticeable in N-face HEMT structure as compared with Ga-face HEMTs with similar geometry. Furthermore, superior small signal, high frequency characteristics as compared to Ga-face HEMTs structures can be achieved.