Effects of post-deposition annealing ambient on band alignment of RF magnetron-sputtered Y2O3 film on gallium nitride
© Quah and Cheong; licensee Springer. 2013
Received: 16 December 2012
Accepted: 20 January 2013
Published: 29 January 2013
The effects of different post-deposition annealing ambients (oxygen, argon, forming gas (95% N2 + 5% H2), and nitrogen) on radio frequency magnetron-sputtered yttrium oxide (Y2O3) films on n-type gallium nitride (GaN) substrate were studied in this work. X-ray photoelectron spectroscopy was utilized to extract the bandgap of Y2O3 and interfacial layer as well as establishing the energy band alignment of Y2O3/interfacial layer/GaN structure. Three different structures of energy band alignment were obtained, and the change of band alignment influenced leakage current density-electrical breakdown field characteristics of the samples subjected to different post-deposition annealing ambients. Of these investigated samples, ability of the sample annealed in O2 ambient to withstand the highest electric breakdown field (approximately 6.6 MV/cm) at 10−6 A/cm2 was related to the largest conduction band offset of interfacial layer/GaN (3.77 eV) and barrier height (3.72 eV).
KeywordsYttrium oxide Gallium nitride Post-deposition annealing Band alignment Conduction band offset
Increasing concerns regarding the escalating demand of energy consumption throughout the world has triggered the needs of developing energy-efficient high-power and high-temperature metal-oxide-semiconductor (MOS)-based devices. It has been projected that gallium nitride (GaN) has the potential of conforming to the needs of these MOS-based devices due to its promising properties, which include wide bandgap (3.4 eV), large critical electric field (3 MV/cm), high electron mobility, as well as good thermal conductivity and stability [1–6]. The fabrication of a functional GaN-based MOS device requires a high-quality gate oxide that is capable of resisting a high transverse electric field [7, 8]. Native oxide (Ga2O3) of GaN [9–13] and a relatively low-dielectric-constant (k) SiN x O y  or SiO2[14–19] have been successfully grown and deposited, respectively, as gate oxides in GaN-based MOS devices. However, these gate oxides are not the preferred choices. The shortcoming encountered by the former gate is the slow growth gate, high oxidation temperature (>700°C), and high leakage current [12, 13] while the latter gate with a relatively low k is unable to withstand the high electric field imposed on GaN [7, 20, 21]. Thereafter, numerous high-k gate oxides [3, 20–28] have been selected for investigation on GaN-based MOS devices. Recent exploration on the employment of radio frequency (RF) magnetron-sputtered Y2O3 gate subjected to post-deposition annealing (PDA) from 200°C to 1,000°C for 30 min in argon ambient has revealed that the Y2O3 gate annealed at 400°C has yielded the best current density-breakdown field (J-E) characteristic as well as the lowest effective oxide charge, interface trap density, and total interface trap density . It is noticed that the acquired J-E characteristic for this sample is better than majority of the investigated gate oxide materials . The ability of Y2O3/GaN MOS structure to be driven at a high E and low J is attributed to the fascinating properties possessed by Y2O3, such as high k value (k = 12 to 18), large bandgap (approximately 5.5 eV), and large conduction band offset (approximately 1.97 eV) [25, 29–31]. Despite that, the presence of oxygen-related defects, changes in compositional homogeneity of Y2O3, and formation of interfacial layer (IL) are of particular concern as either of these factors might alter the bandgap of Y2O3 and band alignment of Y2O3 with respect to the GaN, which would influence the J-E characteristic of the MOS structure. Li et al. has reported previously that J-E characteristic of the MOS structure is dependent on the thickness of IL, wherein interface quality of the atomic layer deposited HfO2 on Si can be altered via the IL thickness . In order to reduce oxygen-related defects and restore compositional homogeneity of Y2O3, it is essential to perform post-deposition annealing on the oxide . Besides, the oxygen content near the Y2O3/GaN interface can be regulated by varying the post-deposition annealing ambient and eventually controlling the formation of IL. Therefore, engineering of the bandgap of Y2O3 gate and band alignment of Y2O3 with GaN through different PDA ambients is of technological importance. In this work, effects of different PDA ambients (oxygen (O2), argon (Ar) , nitrogen (N2), and forming gas (FG; 95% N2 + 5% H2)) at 400°C for 30 min on the Y2O3/GaN structure in modifying the bandgap of Y2O3 gate and band alignment of Y2O3/GaN are presented. A correlation on the bandgap of Y2O3 gate and band alignment of Y2O3/GaN with regard to the J-E characteristics is also discussed in this paper.
Results and discussion
Typical valence band photoelectron spectra of Y2O3 and IL for the sample annealed in O2 ambient are presented in Figure 2b. By means of linear extrapolation method, the valence band edges (Ev) of Y2O3 and IL could be determined by extrapolating the maximum negative slope to the minimum horizontal baseline . The acquired valence band offset (ΔEv) values of Y2O3 and IL with respect to GaN substrate are in the range of −0.04 to −1.43 eV and −0.21 to −3.23 eV with a tolerance of 0.05 eV, respectively, for all of the investigated samples. The ΔEv values of Y2O3/GaN and IL/GaN are shown in Figure 3b as a function of PDA ambient.
Comparison of the obtained Δ E c and Φ B values
XPS: conduction band offset
Y 2 O 3 /GaN
Y 2 O 3 /IL
In conclusion, three different energy band alignment models of Y2O3/interfacial layer/GaN structure subjected to post-deposition annealing at 400°C in different ambients (O2, Ar, forming gas (95% N2 + 5% H2), and N2) have been established using X-ray photoelectron spectroscopy. It was proven that the dielectric breakdown field (EB) of the sample annealed in O2 ambient was dominated by the breakdown of IL, while the EB of the samples annealed in Ar, FG, and N2 ambient was dominated by the breakdown of bulk Y2O3. The sample annealed in O2 ambient demonstrated the best leakage current density-breakdown field due to the attainment of the largest bandgap, the largest conduction band offset, and the highest barrier height value.
HJQ received his MSc degree in 2010 from Universiti Sains Malaysia, Penang, Malaysia, where he is currently working on a PhD degree in Materials Engineering in the School of Materials and Mineral Resources Engineering. KYC received his PhD degree from the School of Microelectronic Engineering, Griffith University, Brisbane, Australia, in 2004. He is currently an associate professor with Universiti Sains Malaysia, Penang, Malaysia.
One of the authors (HJQ) would like to acknowledge Universiti Sains Malaysia, The USM RU-PRGS (8044041), and The Universiti Sains Malaysia Vice Chancellor’s Award for their financial support.
- Huang W, Khan T, Chow TP: Enhancement-mode n-channel GaN MOSFETs on p and n-GaN/sapphire substrates. IEEE Electron Device Lett 2006, 27: 796–798.View Article
- Chang SJ, Wang CK, Su YK, Chang CS, Lin TK, Ko TK, Liu HL: GaN MIS capacitors with photo-CVD SiNxOy insulating layers. J Electrochem Soc 2005, 152: G423-G426. 10.1149/1.1896308View Article
- Chang YC, Chang WH, Chiu HC, Tung LT, Lee CH, Shiu KH, Hong M, Kwo J, Hong JM, Tsai CC: Inversion-channel GaN metal-oxide-semiconductor field-effect transistor with atomic-layer-deposited Al2O3 as gate dielectric. Appl Phys Lett 2008, 93: 053504–1-053504–3.
- Li S, Ware ME, Wu J, Kunets VP, Hawkridge M, Minor P, Wang Z, Wu Z, Jiang Y, Salamo GJ: Polarization doping: reservoir effects of the substrate in AlGaN graded layers. J Appl Phys 2012, 112: 053711–1-053711–5.
- Li S, Ware M, Wu J, Minor P, Wang Z, Wu Z, Jiang Y, Salamo GJ: Polarization induced pn-junction without dopant in graded AlGaN coherently strained on GaN. Appl Phys Lett 2012, 101: 122103–1-122103–3.
- Quah HJ, Cheong KY, Hassan Z: Forthcoming gallium nitride based power devices in prompting the development of high power applications. Mod Phys Lett B 2011, 25: 77–88. 10.1142/S021798491102564XView Article
- Quah HJ, Cheong KY, Hassan Z, Lockman Z: Effect of postdeposition annealing in oxygen ambient on gallium-nitride-based MOS capacitors with cerium oxide gate. IEEE Trans Electron Dev 2011, 58: 122–131.View Article
- Cheong KY, Moon JH, Kim HJ, Bahng W, Kim NK: Current conduction mechanisms in atomic-layer-deposited HfO2/nitrided SiO2 stacked gate on 4H silicon carbide. J Appl Phys 2008, 103: 084113–1-084113–8.View Article
- Nakano Y, Jimbo T: Interface properties of thermally oxidized n-GaN metal-oxide-semiconductor capacitors. Appl Phys Lett 2003, 82: 218–220. 10.1063/1.1536029View Article
- Nakano Y, Kachi T, Jimbo T: Electrical properties of thermally oxidized p-GaN metal-oxide-semiconductor diodes. Appl Phys Lett 2003, 82: 2443–2445. 10.1063/1.1567811View Article
- Readinger ED, Wolter SD, Waltemyer DL, Delucca M, Mohney SE, Prenitzer BI, Giannuzzi LA, Molnar RJ: Wet thermal oxidation of GaN. J Electron Mat 1999, 28: 257–260. 10.1007/s11664-999-0024-zView Article
- Lin LM, Luo Y, Lai PT, Lau KM: Influence of oxidation and annealing temperatures on quality of Ga2O3 film grown on GaN. Thin Solid Films 2006, 515: 2111–2115. 10.1016/j.tsf.2006.07.036View Article
- Zhou Y, Ahyi C, Smith TI, Bozack M, Tin C, Williams J, Park M, Cheng A, Park J, Kim D, Wang D, Preble EA, Hanser A, Evans K: Formation, etching and electrical characterization of a thermally grown gallium oxide on the Ga-face of a bulk GaN substrate. Solid State Electron 2008, 52: 756–764. 10.1016/j.sse.2007.10.045View Article
- Reddy VR, Reddy MSP, Lakshmi BP, Kumar AA: Electrical characterization of Au/SiO2/n-GaN metal-insulator-semiconductor structures. J Alloys Compd 2011, 31: 8001–8007.View Article
- Arulkumaran S, Egawa T, Ishikawa H, Jimbo T, Umeno M: Investigation of SiO2/n-GaN and Si3N4/n-GaN insulator-semiconductor interfaces with low interface state density. Appl Phys Lett 1998, 73: 809–811. 10.1063/1.122009View Article
- Chang SJ, Su YK, Chiou YZ, Chiou JR, Huang BR, Chang CS, Chen JF: Deposition of SiO2 layers on GaN by photochemical vapor deposition. J Electrochem Soc 2003, 150: C77-C80. 10.1149/1.1534598View Article
- Chiou YZ, Su YK, Chang SJ, Gong J, Chang CS, Liu SH: The properties of photo chemical-vapor deposition SiO2 and its application in GaN metal-insulator semiconductor ultraviolet photodetectors. J Electron Mater 2003, 32: 395–399. 10.1007/s11664-003-0164-5View Article
- Lee M, Ho C, Zeng J: Electrical properties of liquid phase deposited SiO2 on photochemical treated GaN. Electrochem Solid-State Lett 2008, 11: D9-D12. 10.1149/1.2803054View Article
- Wu HR, Lee KW, Nian TB, Chou DW, Wu JJH, Wang YH, Houng MP, Sze PW, Su YK, Chang SJ, Ho CH, Chiang CI, Chern YT, Juang FS, Wen TC, Lee WI, Chyi JI: Liquid phase deposited SiO2 on GaN. Mater Chem Phys 2003, 80: 329–333. 10.1016/S0254-0584(02)00504-7View Article
- Quah HJ, Cheong KY, Hassan Z, Lockman Z: MOS characteristics of metallorganic-decomposed CeO2 spin-coated on GaN. Electrochem Solid-State Lett 2010, 13: H116-H118. 10.1149/1.3290679View Article
- Quah HJ, Cheong KY, Hassan Z, Lockman Z: Effects of N2O postdeposition annealing on metal-organic decomposed CeO2 gate oxide spin-coated on GaN substrate. J Electrochem Soc 2011, 158: H423-H432. 10.1149/1.3548542View Article
- Chang YC, Chiu HC, Lee YJ, Huang ML, Lee KY, Hong M, Chiu YN, Kwo J, Wang YH: Structural and electrical characteristics of atomic layer deposited high k HfO2 on GaN. Appl Phys Lett 2007, 90: 232904–1-232904–3.
- Kim J, Gila BP, Mehandru R, Johnson JW, Shin JH, Lee KP, Luo B, Onstine A, Abernathy CR, Pearton SJ, Ren F: Electrical characterization of GaN metal-oxide-semiconductor diodes using MgO as the gate oxide. J Electrochem Soc 2002, 149: G482-G484. 10.1149/1.1489689View Article
- Liu C, Chor EF, Tan LS, Dong Y: Structural and electrical characterizations of the pulsed-laser-deposition-grown Sc2O3/GaN heterostructure. Appl Phys Lett 2006, 88: 222113–1-222113–3.
- Quah HJ, Cheong KY: Study on gallium nitride-based metal-oxide-semiconductor capacitors with RF magnetron sputtered Y2O3 gate. IEEE Trans Electron Dev 2012, 59: 3009–3016.View Article
- Chang WH, Lee CH, Chang P, Chang YC, Lee YJ, Kwo J, Tsai CC, Hong JM, Hsu CH, Hong M: High k dielectric single-crystal monoclinic Gd2O3 on GaN with excellent thermal, structure, and electrical properties. J Cryst Growth 2009, 311: 2183–2186. 10.1016/j.jcrysgro.2008.10.079View Article
- Chang WH, Chang P, Lee WC, Lai TY, Kwo J, Hsu CH, Hong JM, Hong M: Epitaxial stabilization of a monoclinic phase in Y2O3 films on c-plane GaN. J Cryst Growth 2011, 323: 107–110. 10.1016/j.jcrysgro.2010.10.006View Article
- Quah HJ, Lim WF, Cheong KY, Hassan Z, Lockman Z: Comparison of metal-organic decomposed (MOD) cerium oxide (CeO2) gate deposited on GaN and SiC substrates. J Crys Growth 2011, 326: 2–8. 10.1016/j.jcrysgro.2011.01.040View Article
- Quah HJ, Cheong KY: Deposition and post-deposition annealing of thin Y2O3 film on n-type Si in argon ambient. Mat Chem Phys 2011, 130: 1007–1015. 10.1016/j.matchemphys.2011.08.024View Article
- Quah HJ, Cheong KY: Effects of post-deposition annealing ambient on Y2O3 gate deposited on silicon by RF magnetron sputtering. J Alloys Compd 2012, 529: 73–83.View Article
- Robertson J, Falabretti B: Band offsets of high K gate oxides on III-V semiconductors. J Appl Phys 2006, 100: 014111–1-014111–8.View Article
- Li S, Han L, Chen Z: The interfacial quality of HfO2 on silicon with different thicknesses of the chemical oxide interfacial layer. J Electrochem Soc 2010, 157: G221-G224. 10.1149/1.3483789View Article
- Rastogi AC, Sharma RN: Interfacial charge trapping in extrinsic Y2O3/SiO2 bilayer gate dielectric based MIS devices on Si(100). Semicond Sci Technol 2011, 16: 641–650.View Article
- Kraut EA, Grant RW, Waldrop JR, Kowalczyk SP: Semiconductor core-level to valence-band maximum binding-energy differences: precise determination by X-ray photoelectron spectroscopy. Phys Rev B 1983, 28: 1965–1977. 10.1103/PhysRevB.28.1965View Article
- Kraut EA, Grant RW, Waldrop JR, Kowalczyk SP: Precise Determination of the valence-band edge in X-ray photoemission spectra: application to measurement of semiconductor interface potentials. Phys Rev Lett 1980, 44: 1620–1623. 10.1103/PhysRevLett.44.1620View Article
- Miyazaki S: Characterization of high-k gate dielectric/silicon interfaces. Appl Surf Sci 2002, 190: 66–74. 10.1016/S0169-4332(01)00841-8View Article
- Wang XJ, Liu M, Zhang LD: Temperature dependence of chemical states and band alignments in ultrathin HfOxNy/Si gate stacks. J Phys D: Appl Phys 2012, 45: 335103–1-335103–5.
- Umezawa N, Shiraishi K, Ohno T, Watanabe H, Chikyow T, Torii K, Yamabe K, Yamada K, Kitajima H, Arikado T: First-principle studies of the intrinsic effect of nitrogen atoms on reduction in gate leakage current through Hf-based high-k dielectrics. Appl Phys Lett 2005, 86: 143507–1-143507–3.View Article
- Quah HJ, Lim WF, Wimbush SC, Lockman Z, Cheong KY: Electrical properties of pulsed laser deposited Y2O3 gate oxide on 4H-SiC. Electrochem Solid-State Lett 2010, 13: H396-H398. 10.1149/1.3481926View Article
- Schroder DK: Semiconductor Material and Device Characterization. New York: Wiley; 1998.
- Jinesh KB, Lamy Y, Tois E, Besling WFA: Charge conduction mechanisms of atomic-layer-deposited Er2O3 thin films. Appl Phys Lett 2009, 94: 252906–1-252906–3.View Article
- Kohl AS, Conforto AB, Z’Graggen WJ, Lang A: An integration transcranial magnetic stimulation mapping technique using non-linear curve fitting. J Neurosci Meth 2006, 157: 278–284. 10.1016/j.jneumeth.2006.04.018View Article
- Kumar KV: Pseudo-second order models for the adsorption of safranin onto activated carbon: comparison of linear and non-linear regression methods. J Hazard Mater 2007, 142: 564–567. 10.1016/j.jhazmat.2006.08.018View Article
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.