Experimental Results for AlGaN/GaN HEMTs Improving Breakdown Voltage and Output Current by Electric Field Modulation

A depletion-mode AlGaN/GaN high electron mobility transistors (HEMTs) have been proposed in this article with the partial GaN cap, which applies the electric field modulation effect to optimize the surface electric field and two-dimensional electron gas (2DEG) distribution. The 2DEG density under the partial GaN cap is reduced due to the polarization effect formed by the partial GaN cap and AlGaN layers. The surface electric field is reshaped by the electric field modulation effect due to the partial GaN cap, featuring an extra electric field peak far away from the gate edge, which, therefore, improves the breakdown voltage (BV). Moreover, the output current (IDS) is also improved slightly resulting from the increased mobility of 2DEG, which compensates for the decrease in the 2DEG density. The experimental BV is increased greatly from 378 V for the conventional AlGaN/GaN HEMTs to 656 V for the depletion-mode partial cap layer AlGaN/GaN HEMTs because of the optimized surface electric field by the electric field modulation effect. The maximum output current (Imax) is increased from 538 to 558 mA/mm. It is concluded that the BV can be improved significantly and IDS increased slightly for AlGaN/GaN HEMTs by the electric field modulation technique using the partial GaN cap, which optimizes the BV and specific on-resistance (Ron, sp) simultaneously.