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

Abstract

1 Abstract-We demonstrate for the first time the monolithic integration of vertical GaN MOSFETs with freewheeling Schottky barrier diodes (SBD), based on a 6.7-μm-thick n-p-n heterostructure grown on 6-inch silicon substrates by metal organic chemical vapor deposition. The anode of the SBD is integrated in the source pad of the MOSFET and the cathode is directly connected to the MOSFET drain through the bottom n + -GaN layer, eliminating the need of any metal wire interconnection. This monolithic integration scheme offers reduced footprint, minimized parasitic components and simplified packaging. The integrated MOSFET-SBD showed enhancement-mode operation with a threshold voltage of 3.9 V, an on/off ratio of over 10 8 and a dramatic improvement in reverse conduction, without degradation in on-state performance from the integration of the SBD. The integrated GaN-on-Si vertical SBD exhibited excellent performance, with a specific on-resistance of 1.6 mΩ·cm 2 , a turn-on voltage of 0.76 V, an ideality factor of 1.5, along with a breakdown voltage of 254 V. These results reveal the promising potential of emerging GaN vertical devices for future power converters.

Fully Vertical GaN-on-Si power MOSFETs

“…5(b) presents the benchmarking of our fully-vertical GaN-on-Si MOSFETs against other GaN vertical transistors demonstrated on bulk GaN and Si substrates [12][13][14][15][16][17][18][19][20][21], [24], [25], [36], [37]. Compared to other GaN-on-Si transistors, our device presented a much lower Ron,sp of 5 mΩcm 2 and BV similar to previous reports on GaN-on-Si MOSFETs [23], [24] with a similar epitaxial structure and without field plates. The gate-edge breakdown can be improved with a smoother and rounded corner at the sidewall base [27], and by improving the quality of the gate oxide [37].…”

“…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.…”

Review of the Recent Progress on GaN-Based Vertical Power Schottky Barrier Diodes (SBDs)

“…After that, the samples were annealed at a certain condition to further improve the ohmic behavior. (Ti/Al/Ni/Au at 600-840 • C in N 2 for 20-30s [2,26,29,33,65,67,71,72]; Ti/Al/Pt/Au at 700 • C-850 • C in N 2 for 30s [5,53,54,86]; Ti/Al [19,31,37,38,68,75,76,82]; Ti/Al/Ti/Au [32,67,83,87]; Ti/Al/Au [18,81].) Then, the nickel layer is formed on ohmic contact metal by an electroplating process, as shown in Figure 11b.…”

“…Most studies of vertical GaN-on-GaN SBD power devices have appeared in the last decade [31,32]. Moreover, with the appearance of the quasi-vertical device and novel device structures [33,34], sapphire and Si substrates have been investigated in recent years [35][36][37][38]. The main objective in the design of power devices is to obtain a high breakdown voltage (BV) while keeping the RON,sp as low as possible [39].…”

Ultrahigh GaN:SiO2etch selectivity byin situsurface modification of SiO2in a Cl2-Ar plasma

“…It is considered a successor to silicon for many power applications due to its superior properties such as a wider bandgap for higher temperature operation [1], higher electron mobility for faster switching [2], greater critical electric field for higher voltages [3], and direct bandgap for optoelectronics [4]. Many realized [5][6][7][8][9] and proposed devices such as superjunctions [10][11][12] promise to revolutionize power conversion and transmission but require highly selective etch processes to realize their device geometries. There are no practical wet etchants for selective anisotropic etching of GaN [13], and like other wide bandgap semiconductors, it is difficult to plasma etch without creating rough and damaged surfaces [14].…”