Critical heterostructure design for low on-resistance normally-off double-channel MOS-HEMT

A normally-off gate-recessed double-channel MOS-HEMT (DC-MOS-HEMT) has been recently demonstrated with the advantages of (1) low on-resistance and (2) low sensitivity of threshold voltage on recess depth. A critical design parameter for achieving a low overall ON-resistance is identified to be the separation of the two heterojunction channels that determines the strength of electrical coupling between the two channels. When the coupling is weak as a result of a larger separation, the upper channel in the access region is electrically isolated from the gate-controlled lower channel and cannot contribute to lowering the access resistance. When the coupling is strong as a result of a smaller separation, the upper and lower channels are electrically “merged” so that both the upper and lower heterojunction channels in the access region are effectively connected to the lower heterojunction channel controlled by the gate, enabling a low ON-resistance.