Sulfuric acid and hydrogen peroxide surface passivation effects on AlGaN/GaN high electron mobility transistors.

In this work, we have compared SiN_x passivation, hydrogen peroxide, and sulfuric acid treatment on μlGaN/GaN HEMTs surface after full device fabrication on Si substrate. Both the chemical treatments resulted in the suppression of device pinch-off gate leakage current below 1 lμ/mm, which is much lower than that for SiN_x passivation. The greatest suppression over the range of devices is observed with the sulfuric acid treatment. The device on/off current ratio is improved (from 10⁴-10⁵ to 10⁷) and a reduction in the device sub-threshold (S.S.) slope (from ∼215 to 90 mV/decade) is achieved. The sulfuric acid is believed to work by oxidizing the surface which has a strong passivating effect on the gate leakage current. The interface trap charge density (D_it) is reduced (from 4.86 to 0.90×10¹²cm^-2 eV^-1), calculated from the change in the device S.S. The gate surface leakage current mechanism is explained by combined Mott hopping conduction and Poole Frenkel models for both untreated and sulfuric acid treated devices. Combining the sulfuric acid treatment underneath the gate with the SiN_x passivation after full device fabrication results in the reduction of D_it and improves the surface related current collapse. [ABSTRACT FROM AUTHOR]