Improved AlGaAs/InGaAs high-electron mobility transistor

This study develops improved AlGaAs/InGaAs pseudomorphic high-electron mobility transistor (pHEMT) grown by low-pressure metallorganic chemical vapor deposition (LP-MOCVD). A treatment with ammonium polysulfide (NH₄)₂S_X to passivate the surface of AlGaAs barrier layer is performed. The two-terminal gate-drain breakdown voltage of the passivated pHEMT is as great as 25 V, which represents an improvement of 2 V over the unpassivated pHEMT. At 300 K, the peak extrinsic transconductance g_m,ext of the unpassivated pHEMT at V_DS=3 V is 214 mS/mm. The passivated pHEMT yields a peak g_m,ext of 249 mS/mm. A peak g_m,ext enhancement of 16.35% is obtained. The unpassivated HEMT exhibits a current gain cutoff frequency (f_T) of 15.7 GHz and a maximum frequency of oscillation (f_max) of 54 GHz, while the passivated pHEMT exhibits an f_T of 18.3 GHz and an f_max of 72 GHz. Experimental data reveal that the passivated pHEMT provides enhanced breakdown voltage, improved g_m,ext, enhanced f_T, and enhanced f_max.