Studies on Modification of Channel Material and Gate Recess Structures in Metamorphic HEMT

In this study, we have performed both the channel modification of the conventional MHEMT (Metamorphic High Electron Mobility Transistor) and the variation of gate recess. The modified channel consists of the In0.53Ga0.47 As and the InP layers. Since InP has lower impact ionization coefficient than In0.53Ga0.47 As, we have adopted the InP-composite channel in the MHEMT. Also, the gate recess width is both functions of breakdown and RF characteristic of a HEMT structure. Therefore, we have studied the breakdown and RF characteristic for various gate recess widths of MHEMT's. We have compared breakdown characteristic of the InP-composite channel with that of conventional MHEMT's. It is shown that on and off state breakdown voltages of the InP-composite channel MHEMT were increased by about 20 and 27 %, respectively, compared with the conventional structure. Also, breakdown voltage of the InP-composite channel MHEMT was increased with increasing gate recess width. The fmax was increased with decreasing the gate recess width, whereas fmax was increased with increasing the gate recess width. Also, we extracted small-signal parameters. It was shown that Gd of the InP-composite channel MHEMT is decreased about by 30 % compared with the conventional MHEMT. Therefore, the suppression of the impact ionization in the InP-composite channel increases the breakdown voltage and decreases the output conductance.