Investigation On The Double-Heterostructure AlGaN/GaN HFETs

AlGaN/GaN HFETs are generally promising candidates for switching power transistors due to their high breakdown voltage?BV?,low switching loss and low on-state resistance?Ron,sp?.However,their inherent normally-on behavior resulting in the negative threshold voltage(V_TH)would exclude them from most power-electronic applications.Moreover,electric potential's crowed near the Schottky Gate contact may limit the device to exhibit the advantage of high critical breakdown electric field?Ec?in GaN.In fact,the BV and V_TH are influenced by the distribution of charge.Therefore,to address these issues on BV and V_TH,in this paper,the characteristics of charge based on the polarization effect are discussed.And the major innovations are as follows:?1?Based on the analysis of the conventional AlGaN/GaN HFET,the charge characteristics of double-heterstructure AlGaN/GaN HFET are studied.At blocking state,the exhausted in the double heterstructure can induce the fixed charge with different polarity at each sides of the AlGaN barrier layer,respectively.In special,the negative charges are at the interface of the AlGaN modulating layer?ML-AlGaN?/AlGaN barrier layer?BL-AlGAN?and the positive charges are at the interface of the BL-AlGAN/GaN substrate layer?SL-GaN?.The negative charges can absorb some of the electric lines induced from positive charges at the interface of the BL-AlGAN/SL-GaN,thus the crowed of electric potential near the gate is relaxed to improve the BV of the device.Moreover,the negative charge at the interface of ML-AlGaN/BL-AlGAN may induce the two-dimensional hole gas?2DHG?.These 2DHG may help drive the two-dimensional electron gas?2DEG?to be exhausted to extend the depleted region.Therefore,the voltage sustained region is also extended to improve the BV.?2?Based on the modulating principle of the double heterstructure,a novel high-improved breakdown voltage double-heterstructure AlGaN/GaN HFET with normally-off characteristics is proposed.Simulated results show that the proposed device exhibits a V_THH of about 1.8 V and BV of about 200 V,which is more than 2 times higher than the conventional AlGaN/GaN HFET.?3?Based on the double-heterstructure AlGaN/GaN HFET,the field plate?FP?technoledge is applied and discussed about its modulating effect on the electric field in the drift region.Specially,at blocking state,the gate FP and drain FP may exhibit different electric polarity.These electric polarity characteristic of FP can lead to an influence on the charge distributed both sides of the double heterstructure,thus the electric field at both gate and drain contact can all be modulated.Therefore,the BV of the device is improved deeply.Simulated results show that the double-heterstructure AlGaN/GaN HFET with double FP can achieve a BV of 298 V,which is about improved by 50%compared with the conventional double-heterstructure AlGaN/GaN HFET.