Stability of the threshold voltage in fluorine-implanted normally-off AlN/GaN HEMTs co-integrated with commercial normally-on GaN HEMT technology

Description

Fluorine ion migration in normally-off AlN/GaN HEMTs fabricated by fluorine ion plasma implantation technology is evidenced. Devices under test are co-integrated into the OMMIC commercial D006GH/D01GH MMIC process, providing fluorine-free normally-on HEMTs. Gate reverse bias step-stress experiment at a drain fixed voltage of 0 V, carried out as well on normally-on ones as on normally-off ones, shows a permanent negative shift in the threshold voltage V-th of normally-off devices only. V-th degradation is starting at a V-GS,V- stress of -8 V, with a negative shift from 0 V to -0.4 V at V-GS,V-stress = -30 V, while the transconductance g(m) and g(m,max) remains unchanged prior to breakdown that occurred at V-GS,V-stress ranging between -26 and -32 V. Since the positive threshold voltage of these devices is induced by F-ions dose and position, the above result suggests a possible drift of F-ions away from the 2DEG channel. A field-assisted migration mechanism of fluorine ions is proposed and supported by the absence of V-th degradation in fluorine-free normally-on devices.

Abstract

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