Depletion- and Enhancement-Mode p-Channel MISHFET Based on GaN/AlGaN Single Heterostructures on Sapphire Substrates

We report on p-channel metal-insulator-semiconductor heterostructure field-effect transistors (MISHFET) based on p-GaN/uid-GaN/Al textsubscript 0.29Ga textsubscript 0.71N single heterostructures on sapphire substrates, grown by metalorganic vapor phase epitaxy (MOVPE). The impact of p-GaN layer removal and channel layer thickness adjustment by dry-etching on the characteristics of the MISHFET are investigated. Depending on the remaining GaN thickness $(t_{\mathrm{ GaN}})$ , the fabricated MISHFET show either depletion-mode (d-mode) operation with a threshold voltage $V_{\mathrm{ th}}$ of 3.8 V and an on-current $\unicode{0x007C}I_{\mathrm{ D,on}} \unicode{0x007C}$ of 9.5 mA/mm ( $t_{\mathrm{ GaN}} = 21$ nm) or enhancement-mode (e-mode) operation with $V_{\mathrm{ th}}$ of −2.3 V and $\unicode{0x007C}I_{\mathrm{ D,on}} \unicode{0x007C}$ of 1.5 mA/mm ( $t_{\mathrm{ GaN}}= 12$ nm). Independent of the etching depth, all devices exhibit a very low off-state drain current $\left|I_{\mathrm{D}, \mathrm{off}}\right| \sim 10^{-8}$ mA/mm and a steep subthreshold swing (SS) between 80 and 89 mV/dec. Similar to n-channel devices, a $V_{th}$ instability caused by charge trapping at the dielectric/semiconductor interface is found, emphasizing that careful interface engineering is required for good device performance.