High-Voltage β-Ga2O3 Schottky Diode with Argon-Implanted Edge Termination
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The edge-terminated Au/Ni/β-Ga2O3 Schottky barrier diodes were fabricated by using argon implantation to form the high-resistivity layers at the periphery of the anode contacts. With the implantation energy of 50 keV and dose of 5 × 1014 cm−2 and 1 × 1016 cm−2, the reverse breakdown voltage increases from 209 to 252 and 451 V (the maximum up to 550 V) and the Baliga figure-of-merit (VBR2/Ron) also increases from 25.7 to 30.2 and 61.6 MW cm−2, about 17.5% and 140% enhancement, respectively. According to the 2D simulation, the electric fields at the junction corner are smoothed out after argon implantation and the position of the maximum breakdown electric filed, 5.05 MV/cm, changes from the anode corner at the interface to the overlap corner just under the implantation region. The temperature dependence of the forward characteristics was also investigated.
Keywordsβ-Ga2O3 Schottky diode Argon implantation Edge termination
Atomic force microscope
Edge-defined film-fed growth
The full width at half-maximum
High resolution x-ray diffraction
Junction termination extension
Metal-oxide-semiconductor field-effect transistor
Root mean square
Schottky barrier diode
Development of high-power devices using ultra-wide-bandgap semiconductor materials such as Ga2O3, AlN, diamond, etc. is accelerating in recent years. The bandgap of β-Ga2O3 is as large as 4.8–4.9 eV and the breakdown field of β-Ga2O3 is estimated to be 8 MV/cm, about three times larger than that of 4H-SiC and GaN. The Baliga’s figure of merit, 3400, is at least ten times larger than that of 4H-SiC and four times larger than that of GaN . Furthermore, the large single crystal and low-cost β-Ga2O3 substrate can be fabricated with melt-growth methods such as floating-zone (FZ)  and edge-defined film-fed growth (EFG) [3, 4]. The electron density can be controlled over a wide range from 1016 to 1019 cm−3 by doping with Sn, Si, or Ge [5, 6, 7]. These excellent properties make β-Ga2O3 ideal for low loss, high-voltage switching and high-power applications, including high-breakdown voltage Schottky barrier diode (SBD) and metal-oxide-semiconductor field-effect transistor (MOSFET) [8, 9, 10, 11, 12]. Schottky barrier diodes possess the advantages of fast switching speed and low forward voltage drop in comparison with p-n junction diode, which can decrease the power loss and improve the efficiency of power supplies.
Although large breakdown voltages of 1016 V, 2300 V, and 1600 V have been obtained in β-Ga2O3 Schottky barrier diodes without edge termination, they are all about 34%, 8%, and 10% of the ideal value [10, 13, 14]. To relieve the electric field crowding effect and fully realize the voltage potential of β-Ga2O3, suitable edge terminations must be designed. There are a number of edge termination techniques to increase the device breakdown voltage such as field plates, floating metal rings, trench MOS structure, implanted guard rings, and junction termination extension (JTE) [12, 15, 16, 17]. However, implanted guard rings and JTE structure are not applicable to Ga2O3 Schottky diode due to the lack of p-type doping. H. Matsunami and B. J. Baliga put forward an edge termination structure, using argon implantation to form a high-resistivity amorphous layer at the edges of anode, to reduce the electric field crowding [18, 19, 20, 21, 22], which is a simple technique with no multi-photolithography or deep trench etching steps required, and it is widely used in SiC and GaN rectifiers to smooth out the electric field distribution around the rectifying contact periphery [15, 23, 24].
In this paper, the vertical edge-terminated β-Ga2O3 Schottky diodes were fabricated with argon implantation at the edges of Schottky contacts. The capacitance–voltage (C–V) and temperature-dependent current density-voltage (J-V) characteristics were recorded using Keithley 4200 semiconductor characterization system and the electric field distribution was also analyzed.
Results and discussion
where A, q, and ε are Schottky contact area, electron charge, and permittivity of β-Ga2O3. Ec, Ef, eΔφ, k, T, and Nc are the conduction band minimum, Fermi level, potential barrier lowering caused by the image force, Boltzmann constant, absolute temperature in K, and effective density of states of the conduction band, respectively.
In order to investigate the effects of argon implantation on the temperature dependence of the forward characteristics, the forward J-V measurements of sample C are conducted from 300 to 423 K, as shown in Fig. 4b. The ideal factor n and Schottky barrier height φb_JV are determined to be 1.06 and 1.22 eV at room temperature, lower than the φb_CV of (1.32 ± 0.08) eV, according to the thermionic emission (TE) model [31, 32]. With the temperature increasing, the n decreases from 1.06 to 1.02 and the barrier height reduces slightly but is almost constant at 1.21 ± 0.01 eV over the temperature range, which is contrary to the barrier height decrease of an ideal Schottky diode with temperature increase but has been observed in fabricated β-Ga2O3 SBD . Using the equation ln(Js/T2) = ln(A*)-qϕb/kT, the barrier height ϕb and the effective Richardson constant A* are determined to be 1.22 eV and 48.5 A/cm2 K2 for sample C from the slope and the y-axis intercept of the linear region of the plot, as shown in Fig. 4c. Furthermore, the extracted A* values for tens of devices on the three samples are between 24 and 58 A/cm2 K2, consistent with the previous experiment results and theoretical value, 24–58 A/cm2 K2, with the effective electron mass m* = 0.23–0.34 m0 of β-Ga2O3 [33, 34, 35, 36, 37].
Vertical Au/Ni/β-Ga2O3 Schottky barrier diodes with edge termination formed by argon implantation were fabricated on β-Ga2O3 drift layer mechanically exfoliated from high-quality (100)-oriented β-Ga2O3 bulk substrate. Compared with the control device, the specific on-resistances (Ron) increases from 1.7 to 2.1 and 3.3 mΩ cm2 and the breakdown voltage increases from 209 to 252 and 451 V for implantation dose of 5 × 1014 cm−2 and 1 × 1016 cm−2, respectively, with a larger reverse leakage current. The maximum electric field at breakdown voltage is about 5.05 MV/cm, much larger than that of SiC and GaN.
This work was supported by the National ey R&D Program of China (No.2018YFB0406504) and the National Natural Science Foundation of China (NSFC) under Grant Nos.61774116, 61334002. This work was also supported by the 111 Project (B12026)..
Availability of Data and Materials
The datasets supporting the conclusions of this article are included with in the article.
QF and JZ proposed the research work. YG carried out the simulation, analyze the experiment results, and wrote the paper. AL fabricated and investigated the characteristics of the device. ZH and ZF prepared the XRD and SEM. WM and ZJ provided the (100)-oriented β-Ga2O3 bulk substrate. All authors helped to correct and polish the manuscript and read and approved the final manuscript.
The authors declare that they have no competing interests.
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