N-polar GaN HEMT with Al2O3gate insulator

Insulator deposition directly on the GaN channel is necessary for the reduction of gate leakage current in N-polar GaN HEMTs. For higher speed, a thinner insulator is preferable. Therefore, the N-polar GaN HEMT with Al2O3gate insulator was fabricated by atomic layer deposition. An on-current ($\boldsymbol{V}_{\boldsymbol{D}\boldsymbol{S}}=5\mathbf{V},\ \boldsymbol{V}_{\boldsymbol{G}\boldsymbol{S}}=0\mathbf{V}$) of 170 mA/mm, off-current $(\boldsymbol{V}_{\boldsymbol{D}\boldsymbol{S}}=5\mathbf{V},\boldsymbol{V}_{\boldsymbol{G}\boldsymbol{S}}=-12\mathbf{V})$ of $2.39\times 10^{-6}\mathbf{mA}/\mathbf{mn}$, on/off-current ratio of $7.1\times 10^{7}$, and a maximum transconductance of 28.7 mS/mm were observed. The contact resistivity and the sheet resistance were degraded from $7.7\times 10^{-6}\Omega \mathbf{cm}^{2}$ and $800\ \Omega/\square$ to $3.5\times 10^{-5}\ \Omega \mathbf{cm}^{2}$ and $6700\Omega/\square$, respectively, because of the HEMT fabrication process. Thus, the passivation of the channel and optimization of the insulating film are necessary for the improvements.