Effect of drift layer doping and NiO parameters in achieving 8.9 kV breakdown in 100 μm diameter and 4 kV/4 A in 1 mm diameter NiO/β-Ga2O3 rectifiers

Abstract

The effect of doping in the drift layer and the thickness and extent of extension beyond the cathode contact of a NiO bilayer in vertical NiO/β-Ga2O3 rectifiers is reported. Decreasing the drift layer doping from 8 × 1015 to 6.7 × 1015 cm−3 produced an increase in reverse breakdown voltage (VB) from 7.7 to 8.9 kV, the highest reported to date for small diameter devices (100 μm). Increasing the bottom NiO layer from 10 to 20 nm did not affect the forward current–voltage characteristics but did reduce reverse leakage current for wider guard rings and reduced the reverse recovery switching time. The NiO extension beyond the cathode metal to form guard rings had only a slight effect (∼5%) in reverse breakdown voltage. The use of NiO to form a pn heterojunction made a huge improvement in VB compared to conventional Schottky rectifiers, where the breakdown voltage was ∼1 kV. The on-state resistance (RON) was increased from 7.1 m Ω cm2 in Schottky rectifiers fabricated on the same wafer to 7.9 m Ω cm2 in heterojunctions. The maximum power figure of merit (VB)2/RON was 10.2 GW cm−2 for the 100 μm NiO/Ga2O3 devices. We also fabricated large area (1 mm2) devices on the same wafer, achieving VB of 4 kV and 4.1 A forward current. The figure-of-merit was 9 GW cm−2 for these devices. These parameters are the highest reported for large area Ga2O3 rectifiers. Both the small area and large area devices have performance exceeding the unipolar power device performance of both SiC and GaN.

The Optimization of NiO Doping, Thickness, and Extension in kV-Class NiO/Ga2O3 Vertical Rectifiers

“…The ultra-wide-bandgap semiconductor, Ga 2 O 3 , has advantages over Si electronics in terms of the ability to achieve higher breakdown voltage and lower on-state resistance [1][2][3][4][5][6][7][8][9]. Recent demonstrations of the ability of NiO/β-Ga 2 O 3 vertical geometry rectifiers to achieve excellent performance [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] and breakdown voltages in excess of 8 kV [7,[25][26][27] has revitalized interest in the heterojunction approach to overcome the lack of a practical p-type doping capability for β-Ga 2 O 3 . Several groups have now demonstrated devices with breakdown voltage and on-state resistance beyond the 1D limit of both GaN and SiC, showing the increasing maturity of Ga 2 O 3 power device technology [7,25].…”

“…Recent demonstrations of the ability of NiO/β-Ga 2 O 3 vertical geometry rectifiers to achieve excellent performance [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] and breakdown voltages in excess of 8 kV [7,[25][26][27] has revitalized interest in the heterojunction approach to overcome the lack of a practical p-type doping capability for β-Ga 2 O 3 . Several groups have now demonstrated devices with breakdown voltage and on-state resistance beyond the 1D limit of both GaN and SiC, showing the increasing maturity of Ga 2 O 3 power device technology [7,25]. These devices are intended for power conversion applications in the 1.2-20 kV range such as electric vehicles, solid-state transformers, data centers, motor control, photovoltaic inverters, other renewable energy conversion, and electric grid protection [1,3,4,6].…”

“…The thickness, doping concentration, and extension beyond the anode are varied within the simulation and compared to experimental data. We calibrated the basis of the simulations with real experimental data [15,[25][26][27], as shown below, but the main part of the manuscript is on the simulations themselves, which are designed to allow for the design and optimization of the next generation of rectifiers with an even higher performance.…”

15 MeV proton damage in NiO/β-Ga2O3vertical rectifiers

“…The vertical rectifiers have been described in detail previously [23][24][25], but in brief consist of 10 µm drift region of lightly n-type Ga 2 O 3 grown on a conducting n + Ga 2 O 3 . NiO with a total thickness of 20 nm is deposited on the top surface by sputtering and contacts made to both sides by e-beam evaporation of Ti/Au to the rear surface and Ni/Au to the NiO.…”

“…This has led to recent demonstrations of vertical rectifiers with breakdown voltages more than 8 kV with excellent high temperature operation [9]. While the device performance is promising in terms of dc and switching applications [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26], little is known about the effects of radiation on these heterojunctions. While the Ga 2 O 3 is known to be relatively resistant to total dose damage [27,28], large reversible changes in current-voltage characteristics of the heterojunctions have been observed after Co-60 gamma ray exposure which appears to be due to conductivity changes in the NiO [29].…”