Step buffer layer of Al_0.25Ga_0.75N/Al_0.08Ga_0.92N on P-InAlN gate normally-off high electron mobility transistors

Abstract

Normally-off AlGaN/GaN high electron mobility transistors (HEMTs) are indispensable devices for power electronics as they can greatly simplify circuit designs in a cost-effective way. In this work, the electrical characteristics of p-type InAlN gate normally-off AlGaN/GaN HEMTs with a step buffer layer of Al 0.25 Ga 0.75 N/Al 0.1 Ga 0.9 N is studied numerically. Our device simulation shows that a p-InAlN gate with a step buffer layer allows the transistor to possess normally-off behavior with high drain current and high breakdown voltage simultaneously. The gate modulation by the p-InAlN gate and the induced holes appearing beneath the gate at the GaN/ Al 0.25 Ga 0.75 N interface is because a hole appearing in the p-InAlN layer can effectively vary the threshold voltage positively. The estimated threshold voltage of the normally-off HEMTs explored is 2.5 V at a drain bias of 25 V, which is 220% higher than the conventional p-AlGaN normally-off AlGaN/GaN gate injection transistor (GIT). Concurrently, the maximum current density of the explored HEMT at a drain bias of 10 V slightly decreases by about 7% (from 240 to 223 mA mm −1 ). At a drain bias of 15 V, the current density reached 263 mA mm −1 . The explored structure is promising owing to tunable positive threshold voltage and the maintenance of similar current density; notably, its breakdown voltage significantly increases by 36% (from 800 V, GIT, to 1086 V). The engineering findings of this study indicate that novel p-InAlN for both the gate and the step buffer layer can feature a high threshold voltage, large current density and high operating voltage for advanced AlGaN/GaN HEMT devices.

Device characteristics of enhancement mode double heterostructure DH‐HEMT with boron‐doped GaN gate cap layer for full‐bridge inverter circuit

“…Comparison of V T and I ds,sat with different value of V ds at V gs = 6 V with published state of art normally OFF AlGaN HEMTs . highest V T and I ds,sat are observed on the proposed devices in this work…”

“…The presence of B‐doping in GaN on AlGaN layer causes a large conduction band offset shows improved Schottky barrier height with low surface‐related defects would cause V T change toward positive (E‐mode type) V T = 1.92 V for Al 0.23 Ga 0.77 N/GaN/Al 0.07 Ga 0.93 N DH‐HEMT devices through the application of high quality B‐doped GaN cap layer on top of Al 0.23 Ga 0.77 N barrier with a GaN channel. It is to be noted that the obtained V T values are better than the reported GaN cap gate HEMT structures . Figure shows the variation of V T and ON‐state resistance ( R ON ) for various values of “x” in the Al x Ga 1‐x N buffer for B and Mg‐doped GaN cap DH‐HEMTs.…”

“…The benchmark on V T and I ds,sat with different value of V ds at V gs = 6 V with reported normally OFF AlGaN HEMTs is shown in Figure . In this work, B‐doped GaN cap is used as a gate in Al 0.23 Ga 0.77 N/GaN/Al x Ga 1‐x N DH‐HEMT results in relatively higher V T with competitive I ds,sat than other commonly used GaN cap material gate devices …”

“…Therefore, enhancing V BR,OFF and V T is one of the most significant challenges in the evolution of GaN‐based efficient power switches . While, both aspects still need the consideration by researchers, certainly, obtaining enhancement mode (E‐mode) behavior in GaN‐based devices with sufficiently high V T has always been a struggle . Several approaches, such as high Al content channels or the use of quaternary barriers to allow a zero polarization difference at the barrier/channel interface, cap layer doping under the gate (p‐InGaN, p‐AlGaN), and recessed gate etching techniques have been implemented to achieve the E‐mode AlGaN/GaN HEMTs.…”

“…However, the reported devices and GaN‐based cap gate HEMTs show drawbacks such as low I ON , V T , high gate and drain leakage currents, and low V BR,OFF. Thus, in order to overcome the current drawbacks of GaN‐cap HEMTs, it is crucial to achieve a much higher value of V T than the reported data for safe E‐mode operation of low‐power consumption, circuit simplicity, and fail‐safe requirements. In this respect, boron (B) or magnesium (Mg) doped GaN cap‐layer is used under the gate to achieve high V T , low‐leakage, and high V BR,OFF DH‐HEMT devices.…”