Normally‐off vertical‐type mesa‐gate GaN MOSFET

Abstract

A vertical-type mesa-gate GaN metal-oxide semiconductor field-effect transistor (MOSFET) has been fabricated. The mesa-gate structure can be easily achieved by a single deep etch to the n + -GaN which is the drain of the device, whereas the trench-gate structure, the commonly used structure for the vertical-type MOSFETs, requires an additional etching process to define the gate region. The mesa-gate GaN MOSFET exhibited a normally-off operation with the threshold voltage of 3 V, a normalised drain current of ∼ 55 mA/mm and a high on/off current ratio of 10 8 .Introduction: GaN is a promising material for next-generation powerdevice applications, owing to its superior material properties, such as high breakdown electric field (up to 3 MV/cm), high saturation velocity (∼3 × 10 7 cm/s at 150 kV/cm) and good thermal conductivity [1, 2]. Furthermore, a polarisation-induced high two-dimensional electron gas (2DEG) density of ∼1 × 10 13 cm −2 is formed at the AlGaN/GaN heterointerface, which enables high-current operation in lateral-type AlGaN/GaN heterostructure field-effect transistors (HFETs) [3][4][5].For power-switching applications, a normally-off operation is required to minimise the static power consumption and to simplify the driving circuit [6]. However, most of the lateral-type AlGaN/GaN HFETs exhibit normally-on operation, owing to the existence of the 2DEG under the gate, which makes it very difficult to achieve a normally-off operation; hence, additional techniques, such as the recessed-gate [7], the p-GaN gate [8] and the F − treated gate [9] are required. In general, vertical-type devices offer many advantages such as low-specific on-resistance (R on A), high breakdown voltage (V B ) and smaller size. In addition, the vertical-type devices are attractive in easily obtaining normally-off operation with high-current capability. Recently, trench-gate GaN vertical metal-oxide semiconductor field-effect transistors (MOSFETs) [10][11][12], which are similar to the device geometry of the Si vertical power MOSFET [13], were fabricated with surface treatment on the etched GaN surface. They successfully demonstrated normally-off operation with relatively high device performances in terms of current capability and I ON /I OFF ratio.In this Letter, we propose and fabricate a mesa-gate-type GaN vertical MOSFET that requires only a simple single-etching process to define all device geometries and hence simplifies the fabrication process, whereas the commonly used trench-gate-type MOSFET requires an additional etching process to define the gate geometry.

Epitaxial regrowth and characterizations of vertical GaN transistors on silicon

“…Under the OFFstate condition, the gate bias of −25 V produced a large electric field (∼4 MV cm −1 ) on the Al 2 O 3 gate dielectric. This large electric field plays a vital role on high leakage current densities and breakdown of the oxide layer [26][27][28]. In addition, the n − -GaN drift layer in the device structure also acts as a high voltage sustaining layer and by increasing its thickness, the breakdown voltage could be improved [29].…”

Ridge-channel AlGaN/GaN normally-off high-electron mobility transistor based on epitaxial lateral overgrowth

“…Several approaches have been reported to modulate the 2DEG channel and realize normally-off operation, such as recessed-gate structure [1], hybrid MIS gate [2], fluoride-based plasma-treatment [3], thin-barrier structure [4], p-n junction gate [5], ferroelectric gate [6], and some combined approaches [7][8][9][10][11]. Besides, vertical-type mesa-gate GaN transistors and groovetype channel combining polar and nonpolar AlGaN/GaN heterostructures, utilizing etching and regrowth technologies, were also reported [12][13][14]. Among these approaches, etching process was commonly employed to fabricate recessed gate, vertical-mesa or groove-structure, which could inevitably induce some etching damage and hence degrade the device performance [11].…”

Effects of dissipative substrate on the performances of enhancement mode AlInN/GaN HEMTs

“…Moreover, the enhancement mode (E-mode) device has advantages in high-speed and low power dissipation compared to the depletion mode (D-mode) devices normally based on the polar nature of III-N materials. [2][3][4][5] Therefore, AlInN/GaN HEMT with the E-mode is worthy of extensive study. It has been shown that the self-heating effect of GaN-based HEMTs has a significant negative impact on device performance [6][7][8] because of the increase in the channel temperature with the increase in the lattice temperature.…”

“…The HEMT performance is therefore significantly improved. Moreover, the enhancement mode (E‐mode) device has advantages in high‐speed and low power dissipation compared to the depletion mode (D‐mode) devices normally based on the polar nature of III‐N materials . Therefore, AlInN/GaN HEMT with the E‐mode is worthy of extensive study.…”