Effects of Post-Deposition Annealing on ZrO2/n-GaN MOS Capacitors with H2O and O3 as the Oxidizers
© The Author(s). 2017
Received: 1 January 2017
Accepted: 29 March 2017
Published: 11 April 2017
GaN-based metal-oxide-semiconductor capacitors with ZrO2 as the dielectric layer have been prepared by atomic layer deposition. The accumulation and depletion regions can be clearly distinguished when the voltage was swept from −4 to 4 V. Post-annealing results suggested that the capacitance in accumulation region went up gradually as the annealing temperature increased from 300 to 500 °C. A minimum leakage current density of 3 × 10−9 A/cm2 at 1 V was obtained when O3 was used for the growth of ZrO2. Leakage analysis revealed that Schottky emission and Fowler-Nordheim tunneling were the main leakage mechanisms.
Gallium nitride (GaN)-based wide bandgap semiconductors have seen enormous success during the past few decades due to their intriguing properties such as high breakdown electric field (4.2 MV/cm), high saturation velocity (~3 × 107 cm/s) , excellent chemical stability, and the ability to resist radiation damage . Owing to these characteristics, GaN and its alloys can be applied in high-power electronics, such as thin film transistors and high electron-mobility transistors (HEMTs) [3, 4]. The conventional HEMTs apply Schottky barrier as the control gate which usually produces a large leakage current and, thus, results in a declined breakdown voltage and an enlarged power consumption as well as an increased noise coefficient [5, 6]. To reduce the leakage current, metal-oxide-semiconductor (MOS) structures are proposed to replace the ordinary Schottky gate . However, the surface passivation of GaN is usually difficult due to the existing surface defects, dangling bonds, and some impurities, which distort the interface energy band. Hence, it is crucial to analyze and optimize the MOS structures before fabricating the MOS HEMTs.
In terms of dielectric films, high-k oxides are always among the candidates, because the high dielectric constant means much smaller featured size and lower power consumption [8, 9]. Many high-k materials such as Al2O3 , ZrO2 , MgO , and TiO2  have been investigated for GaN-based MOS capacitors. Among them, ZrO2 is attractive because it has a high permittivity (~24), large bandgap (5.8 eV), and more importantly, an appropriate value of band offset with GaN (valance band offset ~1.6 eV, conduction band offset ~1.1 eV) . As for the deposition methods, atomic layer deposition (ALD) has become the mainstream technique due to its unique self-limited reactions, which demonstrates many advantages such as precise thickness control, high uniformity over a large area, and excellent conformity in many complex nanostructures. In 2013, P. von Hauff et al. reported a kind of GaN-based MOS capacitors with ZrO2 as the dielectric layer. The capacitance reached 3.8 μF/cm2 in the accumulation region. However, the leakage current reached an enormous 0.88 A/cm2 at 1 V which was too large to be applied in electronic devices . In 2014, Gand Ye et al. investigated the band alignment of ZrO2 and GaN using X-ray photoelectron spectroscopy . However, the related devices were not fabricated.
In this work, we systematically studied the properties of ZrO2 films grown on n-GaN substrates by ALD. H2O or O3 was used as the oxidizer to examine which precursor was more effective to grow high-quality ZrO2 films. In addition, post-annealing treatments were carried out to improve the electrical performances of the MOS capacitors. Meanwhile, the leakage mechanisms of the MOS capacitors were also discussed.
Results and Discussion
In terms of leakage properties, as shown in Fig. 4, the leakage current in the negative voltage range was remarkably lower than that in the positive voltage range for capacitors with H2O or O3 as the oxidizer. This phenomenon can be attributed to the formation of the depletion region when the negative voltage was added. The depletion region decreases the electric field intensity on the dielectric layer, which resulted in a much lower leakage current density. The leakage current density of the capacitors without annealing was improved from 1 × 10−8 to 3 × 10−9 A/cm2 at 1 V when O3 was used as the oxidizer instead of H2O. This could be explained in this way that O3 is highly volatile and has a stronger oxidizing ability than H2O, based on the fact that the prepared ZrO2 films using O3 oxidizer have less impurities  and more accurate stoichiometry composition. The improved ZrO2 qualities enhanced the insulating properties. As the annealing temperature gradually increased from 300 to 600 °C, the leakage current increased correspondingly because of the increased crystalline boundaries which served as the leakage channels.
In summary, we have fabricated GaN-based MOS capacitors with ZrO2 as dielectrics. We observed clearly distinguished accumulation and depletion regions from C-V results. The accumulated capacitance increased gradually as the annealing temperature increased. In addition, a low leakage current density of 3 × 10−9 A/cm2 at 1 V was obtained by using O3 oxidant. Based on the leakage current analyses, it can be concluded that Schottky emission dominated at low fields, while F-N tunneling governed at high fields.
This work is supported by the NSFC under Grant No. 11574235. The authors would like to thank D. X. Zhang and F. P. Zhang for the technical support.
MJZ carried out the experiments and drafted the manuscript. GZZ participated in the design of the study and performed the analysis. XW and JXW participated in the measurements. HW conceived the study and participated in its design. CL supervised the overall study and polished the manuscript. All authors read and approved the final manuscript.
The authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
- Ozbek AM, Baliga BJ (2011) Planar nearly ideal edge-termination technique for GaN devices. IEEE Electron Device Lett 32(3):300–302View ArticleGoogle Scholar
- Kim HY, Anderson T, Mastro MA, Freitas JA, Jang S, Hite J, Eddy CR, Kim J (2011) Optical and electrical characterization of AlGaN/GaN high electron mobility transistors irradiated with 5 MeV protons. J Cryst Growth 326(1):62–64View ArticleGoogle Scholar
- Zimmermann T, Deen D, Cao Y, Simon J, Fay P, Jena D, Xing HG (2008) AlN/GaN insulated-gate HEMTs with 2.3 A/mm output current and 480 mS/mm transconductance. IEEE Electron Device Lett 29(7):661–664View ArticleGoogle Scholar
- Huang W, Chow TP, Niiyama Y, Nomura T, Yoshida S (2009) Experimental demonstration of novel high-voltage epilayer RESURF GaN MOSFET. IEEE Electron Device Lett 30(10):1018–1020View ArticleGoogle Scholar
- Dora Y, Han S, Klenov D, Hansen PJ, No KS, Mishra UK, Stemmer S, Speck JS (2006) ZrO2 gate dielectrics produced by ultraviolet ozone oxidation for GaN and AlGaN/GaN transistors. J Vac Sci Technol B 24(2):575–581View ArticleGoogle Scholar
- Liao CN, Zou XM, Huang CW, Wang JL, Zhang K, Kong YC, Chen TS, Wu WW, Xiao XH, Jiang CZ, Liao L (2015) Low interface trap densities and enhanced performance of AlGaN/GaN MOS high-electron mobility transistors using thermal oxidized Y2O3 interlayer. IEEE Electron Device 36(12):1284–1286View ArticleGoogle Scholar
- Chung JW, Roberts JC, Piner EL, Palacios T (2008) Effect of gate leakage in the subthreshold characteristics of AlGaN/GaN HEMTs. IEEE Electron Device Lett 29(11):1196–1198View ArticleGoogle Scholar
- Xie Q, Deng S, Schaekers M, Lin D, Caymax M, Delabie A, Qu XP, Jiang YL, Deduytsche D, Detavernier C (2012) Germanium surface passivation and atomic layer deposition of high-k dielectrics—a tutorial review on Ge-based MOS capacitors. Semicond Sci Tech 27(7):074012View ArticleGoogle Scholar
- Suzuki M (2012) Comprehensive study of lanthanum aluminate high-dielectric-constant gate oxides for advanced CMOS devices. Materials 5(3):443–477View ArticleGoogle Scholar
- Yang S, Tang ZK, Wong KY, Lin YS, Liu C, Lu YY, Huang S, Chen KJ (2013) High-quality interface in MIS structures with in situ pre-gate plasma nitridation. IEEE Electron Device Lett 34(12):1497–1499View ArticleGoogle Scholar
- Bothe KM, von Hauff PA, Afshar A, Foroughi-Abari A, Cadien KC, Barlage DW (2013) Electrical comparison of and gate dielectrics on GaN. IEEE T Electron Dev 60(12):4119–4124View ArticleGoogle Scholar
- Kim J, Gila B, Mehandru R, Johnson JW, Shin JH, Lee KP, Luo B, Onstine A, Abernathy CR, Pearton SJ, Ren F (2002) Electrical characterization of GaN metal oxide semiconductor diodes using MgO as the gate oxide. J Electrochem Soc 149(8):G482–G484View ArticleGoogle Scholar
- Chou BY, Lee CS, Yang CL, Hsu WC, Liu HY, Sun WC, Wei SY, Yu SM (2014) TiO2-dielectric AlGaN/GaN/Si metal-oxide-semiconductor high electron mobility transistors by using nonvacuum ultrasonic spray pyrolysis deposition. IEEE Electron Device Lett 35(11):1091–1093View ArticleGoogle Scholar
- Robertson J, Falabretti B (2006) Band offsets of high K gate oxides on III-V semiconductors. J Appl Phys 100(1):4111View ArticleGoogle Scholar
- von Hauff P, Afshar A, Foroughi-Abari A, Bothe K, Cadien K, Barlage D (2013) ZrO2 on GaN metal oxide semiconductor capacitors via plasma assisted atomic layer deposition. Appl Phys Lett 102(25):251601View ArticleGoogle Scholar
- Ye G, Wang H, Arulkumaran S, Ng GI, Li Y, Liu ZH, Ang KS (2014) Band alignment between GaN and ZrO2 formed by atomic layer deposition. Appl Phys Lett 105(2):022106View ArticleGoogle Scholar
- Weinreich W, Wilde L, Müller J, Sundqviet J, Erben E, Heimann J, Lemberger M, Bauer AJ (2013) Structural properties of as deposited and annealed ZrO2 influenced by atomic layer deposition, substrate, and doping. J Vac Sci Technol A 31(1):01A119View ArticleGoogle Scholar
- Zhang GZ, Wu H, Chen C, Wang T, Wang PY, Mai LQ, Yue J, Liu C (2014) Transparent capacitors based on nanolaminate Al2O3/TiO2/Al2O3 with H2O and O3 as oxidizers. Appl Phys Lett 104(16):163503View ArticleGoogle Scholar
- Ye G, Wang H, Ng SLG, Ji R, Arulkumaran S, Ng GI, Li Y, Liu ZH, Ang KS (2014) Influence of post-deposition annealing on interfacial properties between GaN and ZrO2 grown by atomic layer deposition. Appl Phys Lett 105(15):152104View ArticleGoogle Scholar
- Zhang GZ, Wu H, Chen C, Wang T, Wu WH, Yue J, Liu C (2015) Transparent nanotubular capacitors based on transplanted anodic aluminum oxide templates. ACS Appl Mater Inter 7(9):5522–5527View ArticleGoogle Scholar