Device performances related to gate leakage current in al2o3/algan/gan mishfets

In this paper, we have characterized the electrical properties related to gate leakage current in AlGaN/GaN MISHFETs with varying the thickness (0 to 10 nm) of Al₂O₃gate insulator which also serves as a surface protection layer during high-temperature RTP. The sheet resistance of the unprotected TLM pattern after RTP was rapidly increased to 1323 Ω/□ from the value of 400 Ω/□ of the as-grown sample due to thermal damage during high temperature RTP. On the other hand, the sheet resistances of the TLM pattern protected with thin Al2O3 layer (when its thickness is larger than 5 nm) were slightly decreased after high-temperature RTP since the deposited Al₂O₃layer effectively neutralizes the acceptor-like states on the surface of AlGaN layer which in turn increases the 2DEG density. AlGaN/GaN MISHFET with 8 nmthick Al₂O₃gate insulator exhibited extremely low gate leakage current of 10^-9A/mm, which led to superior device performances such as a very low subthreshold swing (SS) of 80 mV/dec and high I_on/I_offratio of ∼ 10¹⁰. The PF emission and FN tunneling models were used to characterize the gate leakage currents of the devices. The device with 5 nm-thick Al₂O₃layer exhibited both PF emission and FN tunneling at relatively lower gate voltages compared to that with 8 nm-thick Al₂O₃layer due to thinner Al₂O₃layer, as expected. The device with 10 nm-thick Al₂O₃layer, however, showed very high gate leakage current of 5.5 ´ 10^-4A/mm due to poly-crystallization of the Al₂O₃layer during the high-temperature RTP, which led to very poor performances.