Trap states induced by reactive ion etching in AlGaN/GaN high-electron-mobility transistors

Frequency-dependent conductance measurements were carried out to investigate the trap states induced by reactive ion etching in AlGaN/GaN high-electron-mobility transistors (HEMTs) quantitatively. For the non-recessed HEMT, the trap state density decreases from 2.48 x 10(13) cm(-2).eV(-1) at an energy of 0.29 eV to 2.79 x 10(12) cm(-2).eV(-1) at E-T = 0.33 eV. In contrast, the trap state density of 2.38 x 10(13)-1.10 x 10(14) cm(-2).eV(-1) is located at ET in a range of 0.30-0.33 eV for the recessed HEMT. Thus, lots of trap states with shallow energy levels are induced by the gate recess etching. The induced shallow trap states can be changed into deep trap states by 350 degrees C annealing process. As a result, there are two different types of trap sates, fast and slow, in the annealed HEMT. The parameters of the annealed HEMT are E-T = 0.29-0.31 eV and D-T = 8.16 x 10(12)-5.58 x 10(13) cm(-2).eV(-1) for the fast trap states, and E-T = 0.37-0.45 eV and D-T = 1.84 x 10(13)-8.50 x 10(13) cm(-2).eV(-1) for the slow trap states. The gate leakage currents are changed by the etching and following annealing process, and this change can be explained by the analysis of the trap states.