GaN-on-Si Quasi-Vertical Power MOSFETs

Abstract

Abstract-We demonstrate the first GaN vertical transistor on silicon, based on a 6.7-μm-thick n-p-n heterostructure grown on 6-inch silicon substrate by metal organic chemical vapor deposition (MOCVD). The devices consist of trench-gate quasi-vertical metal-oxide-semiconductor field-effect transistors (MOSFETs) with a 4 μm-thick drift layer, exhibiting enhancement-mode (E-mode) operation with a threshold voltage of 6.3 V and an on/off ratio of over 10 8 . A high off-state breakdown voltage of 645 V along with a specific on-resistance of 6.8 mΩ•cm 2 were achieved thanks to the high-quality 4 μm-thick GaN drift layer presenting a relatively low defect density and very high electron mobility (720 cm 2 /V•s). This excellent performance represents a major step towards the realization of high-performance GaN vertical power transistors on low-cost silicon substrates.

Fully Vertical GaN-on-Si power MOSFETs

“…4 (a) shows the output characteristics of the fabricated vertical MOSFETs with metal mask, revealing a very high current density of 1.6 kA/cm 2 and a Ron,sp of 5 mΩcm 2 . These values were normalized by the device active area, defined by the gate trench area of 10 µm × 36 µm [23], [33], after accounting for a lateral current spreading of 2 µm from all the sides of the gate trench (which was confirmed by TCAD simulations). These devices exhibited 2.8x-better current density and 3x-lower Ron,sp as compared to quasi-vertical MOSFETs on a similar GaN epitaxial structure on Si substrate described in [23].…”

“…These values were normalized by the device active area, defined by the gate trench area of 10 µm × 36 µm [23], [33], after accounting for a lateral current spreading of 2 µm from all the sides of the gate trench (which was confirmed by TCAD simulations). These devices exhibited 2.8x-better current density and 3x-lower Ron,sp as compared to quasi-vertical MOSFETs on a similar GaN epitaxial structure on Si substrate described in [23]. This improvement in electrical performance is mainly due to the fully-vertical design of the device [34] and the improved mobility in the p-GaN inversion channel.…”

“…Recently, high-voltage GaN-on-Si quasi-vertical transistors [23], [24] and high-performance quasi-and fully-vertical p-i-n diodes [20], [21] have been demonstrated, but their performance (quasi-vertical) is severely limited by current crowding in the bottom n-GaN layer [25], which significantly increases the Ron,sp, especially in large area devices. While the Ron,sp can be improved by increasing the doping and thickness of the bottom n-GaN layer, this restricts the remainder thickness of the drift layer which can be grown without wafer cracking, thus limiting the effective BV.…”

Vertical GaN-on-Si MOSFETs With Monolithically Integrated Freewheeling Schottky Barrier Diodes

“…GaN-on-Si offers a cost-effective alternative for vertical GaN power devices, due to its large-scale availability, low cost, and a mature fabrication technology. Vertical GaN-on-Si P-i-N and Schottky diodes [10][11][12][13][14][15][16][17][18], and more recently, the first vertical transistor have been demonstrated on 6-inch Si substrates [19]. For practical use of the emerging vertical transistors in several topologies of power converters, such as buck/boost converters, voltage-source inverters, and resonant converters, an extra freewheeling diode is required to allow a reverse flow of current during off-state [20][21][22].…”

“…More details of the epitaxial structure and fabrication process used in this work can be found in Ref. [19].…”