MOVPE, processing and characterization of AlGaN/GaN HEMTs with different Al concentrations on silicon substrates

Abstract

Al x Ga 1− x N/GaN high electron mobility transistor (HEMT) structures with different Al concentrations were grown by metal organic vapor phase epitaxy (MOVPE) on silicon substrates. The influence of both Al concentration and a SiN surface passivation has been investigated. HEMT devices have been processed by standard fabrication steps using optical lithography. An increase of two-dimensional electron gas (2DEG)-sheet carrier concentration and mobility with increasing Al concentration has been observed. Thus, DC as well as small-signal RF performance could be improved with increasing Al concentration. Passivated Al 0.31Ga 0.69N transistors with a gate length of 1 μm exhibit a saturation current density and peak transconductance of 660 mA/mm and 180 mS/mm, respectively. Investigation of Schottky contact characteristics revealed an increase of gate leakage current for increasing Al content. The cut-off frequency and maximum frequency of oscillation were 7 and 9 GHz, respectively. Pulsed measurements of unpassivated and passivated HEMTs carried out at different quiescent bias points demonstrate the influence of the dielectric layer reducing trapping effects associated with the AlGaN surface.