Band Offsets and Interfacial Properties of HfAlO Gate Dielectric Grown on InP by Atomic Layer Deposition
© The Author(s). 2017
Received: 27 December 2016
Accepted: 22 April 2017
Published: 8 May 2017
X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy have been used to determine interfacial properties of HfO2 and HfAlO gate dielectrics grown on InP by atomic layer deposition. An undesirable interfacial InPxOy layer is easily formed at the HfO2/InP interface, which can severely degrade the electrical performance. However, an abrupt interface can be achieved when the growth of the HfAlO dielectric on InP starts with an ultrathin Al2O3 layer. The valence and conduction band offsets for HfAlO/InP heterojunctions have been determined to be 1.87 ± 0.1 and 2.83 ± 0.1 eV, respectively. These advantages make HfAlO a potential dielectric for InP MOSFETs.
As silicon-based complementary metal-oxide-semiconductor (CMOS) devices approach their fundamental limits when scaled down, the adoption of new technologies is urgently required to meet the demands for higher performance and less power dissipation integrated circuits. The integration of III–V compound semiconductors with high-k gate dielectrics is the leading candidate to address many of these issues [1–6]. III–V compound semiconductors including GaAs, InGaAs, and InP have drawn quite a lot of attention as alternative channel materials due to their high electron mobility and low effective mass over Si. Of these candidates, InP could be promising because it is a material with weak Fermi-level pinning effect and has a high electron saturation velocity (2.5 × 107 cm/s) . However, there are still some bottlenecks impeding the actual implementation of InP channel material. One of the major challenges is finding thermodynamically stable dielectric on InP surface with good interfacial properties like SiO2/Si counterpart . Various chemical treatments have been extensively explored to achieve effective passivation on the InP surface. Such methods include NH4OH, (NH4)2S, H2S, and F treatment [7, 9–11].
Band alignment of high-k/InP interface is of great importance for InP-based MOSFET researches. Recently, Chou et al. measured the band offset between InP (100) and ALD Al2O3 with various passivation methods using internal photoemission (IPE) . The barrier heights from the top of InP valence band (VB) to the bottom of Al2O3 conduction band (CB) and conduction band offset were determined to be 4.05 and 2.7 ± 0.10 eV, respectively. With a high k of ~20–25, HfO2 has been extensively studied as an alternative high-k gate dielectric both in Si-based and III–V technology. The barrier height at HfO2/InP interface is also measured using IPE by Xu et al. to be 3.89 eV for the sample without passivation treatment . To improve the interfacial and thermal properties, gate dielectric engineering has been successfully adopted in high-k/III–V compound semiconductor technology by using a combination of Al2O3 and HfO2 films recently. Kim et al. reported that the In out-diffusion and the subsequent In-related phase generation can be effectively suppressed by introducing Al2O3 to the HfO2 film grown on InP. Moreover, intermixing of Al2O3 with HfO2 to form HfAlO on InP is expected to adjust the band offset. In this study, HfAlO gate dielectrics were grown on InP substrates using alternative cycles atomic layer deposition (ALD) of Al2O3 and HfO2 starting with an ultrathin Al2O layer. ALD has manifested itself as a technique suitable for the semiconductor industry due to its capability of growing uniform and conformal thin films . Accurate controls over chemical stoichiometry and thickness at atomic scale can also be achieved by ALD. The ultrathin Al2O3 layer was introduced to the interface between HfAlO dielectrics and InP substrate to diminish the undesirable interfacial InPxOy layer. The band offset and interfacial properties of the formed HfAlO gate dielectric grown on InP has been investigated using x-ray photoelectron spectroscopy (XPS). The energy band diagrams of the HfAlO/InP heterojunction is then constructed, which can provide vital information on fabricating InP MOSFET.
The heterostructures were prepared on n-type (100) InP wafers with a doping concentration of ~1 × 1017 cm−3. Prior to the ALD process, the InP substrates were degreased using acetone and methanol for 5 min each, followed by a diluted 2% hydrofluoric acid (HF) solution etching for 1 min to remove native oxide. After cleaning, the substrate was immediately transferred to a BENEQ TFS-200 ALD reactor where HfO2 and HfAlO thin films were prepared at 300 °C. Thin HfAlO film was grown using alternative cycles ALD of Al2O3 and HfO2 starting with Al2O3. The precursors used were trimethylaluminum (TMA) and H2O for Al2O3 and tetrakis(ethylmethylamido)hafnium (TEMAH) and H2O for HfO2. Four sets of samples were prepared for XPS measurements: (1) a 4 nm thick HfO2 film grown on InP substrate to detect the interface property of the HfO2/InP heterojunction; (2) a 30 nm thick HfAlO film grown on InP substrate to measure the valence band maximum (VBM) and Al 2p 3/2 of bulk HfAlO; (3) a 4 nm thick HfAlO film grown on InP substrate to determine the energy difference between Al 2p 3/2 and In 3d 5/2 at the HfAlO/InP heterojunction’s interface; and (4) a clean InP substrate (HF-dipped) to measure the VBM and In 3d 5/2 of bulk InP.
High-resolution transmission electron microscopy (HR-TEM) was used to obtain the images of high-k/InP interface at atomic scale. Both TEM with low and high magnification were performed to investigate the interfacial profile and fringe atom arrangement. Accurate film thicknesses can also be measured directly. The XPS spectra were recorded using a Thermo Scientific ESCALAB 250 XPS system equipped with a monochromatic Al Kα source (hv = 1486.6 eV). The source power is 150 W (15 kV × 10 mA) at a takeoff angle of 90°. Scans with a step of 0.05 eV and pass energy of 20 eV were performed for 20 times for binding energy of specific elements. The chemical compositions for the prepared HfAlO thin film were detected to be 14.23% for Hf, 22.36% for Al, and 62.55% for O, respectively. Valence band scans with a step of 0.01 eV and pass energy of 20 eV were performed for 30 times for valence band spectra. Charge correction was performed using the known position of C 1s spectra at 284.8 eV. The XPS spectrometer energy scale was also calibrated using Cu 2p 3/2, Ag 3d 5/2, and Au 4f 7/2 photoelectron lines located at 932.67, 368.26, and 83.98 eV, respectively.
Results and Discussion
Binding energies (in eV) of core level spectra for all the samples and the valence band maximum (VBM) values (in eV) for the bulk InP and HfAlO (30 nm)/InP samples
HfAlO (30 nm)/InP
HfAlO (4 nm)/InP
In 3d 5/2
Hf 4f 7/2
Al 2p 3/2
0.79 ± 0.05
2.89 ± 0.05
The energy band gaps (E g) measured by spectroscopic ellipsometry are 5.70 and 6.04 eV for as-deposited HfO2 and HfAlO films, respectively. Using 1.34 eV energy gap for InP , the ΔE c at the HfAlO /InP interface is thus calculated to be 2.83 ± 0.1 eV. According to the investigation above, both of the ΔE v and ΔE c values are larger than 1 eV, which means the HfAlO film supplies enough barrier heights for both electrons and holes. Compared with the ΔE c extracted to be 2.55 eV at the interface of HfO2/InP by Xu et al. , the ΔE c for HfAlO/InP is a little larger. Furthermore, the ΔE v at the interface of HfO2/InP can also be calculated to be 1.81 eV using equation (2), which is a little smaller than that of HfAlO/InP heterojunction. As a result, the dielectric HfAlO film can suppress both the electrons induced and holes induced leakage current more effectively than the HfO2 film when InP is chosen as channel material. Considering the better interface condition and higher potential barrier heights, HfAlO can be relatively preferable than HfO2 as the dielectric film for InP.
In summary, interfacial properties for HfO2/InP and HfAlO/InP heterojunctions have been studied by XPS and HR-TEM. When HfO2 is deposited on InP substrate by ALD, an undesirable interfacial InPxOy layer is easily formed at the HfO2/InP interface, which will degrade the electrical properties. Fortunately, a thin Al2O3 layer can act as a barrier layer to form an abrupt interface between HfAlO and InP channel layer. The band alignment at the interface of HfAlO/InP heterojunction was studied, and the VBM for HfAlO/InP is 1.87 ± 0.1 eV at interface, leading to a ΔE c of 2.83 ± 0.1 eV for HfAlO/InP based on the analysis. This result indicates that HfAlO dielectric film can supply sufficient barrier heights for holes and electrons when InP is chosen as channel material. More researches are needed to make further efforts to optimize the heterojunction’s interface condition.
This work was supported by the National Natural Science Foundation of China (No. U1632121, 51102048, and 61376008), SRFDP (No. 20110071120017), and the Innovation Program of Shanghai Municipal Education Commission (14ZZ004).
LFY and TW carried out the deposition along with its characterization (XPS, TEM). YZ participated in the characterization. LFY, TW, YZ, and HLL participated in the analysis and discussion of the results obtained from the experiments. HLL supervised this study. 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.
- del Alamo JA (2011) Nanometre-scale electronics with III–V compound semiconductors. Nature 479(7373):317–323View ArticleGoogle Scholar
- Ye PD (2008) Main determinants for III-V metal-oxide-semiconductor field-effect transistors. J Vac Sci Technol A 26(4):697–704View ArticleGoogle Scholar
- Robertson J, Falabretti B (2006) Band offsets of high K gate oxides on III-V semiconductors. Appl Phys Lett 100(1):014111Google Scholar
- He G, Chen XS, Sun ZQ (2014) Interface engineering and chemistry of Hf-based high-k dielectrics on III-V substrates. Surf Sci Rep 68(1):68–107View ArticleGoogle Scholar
- He G, Gao J, Chen HS, Cui JB, Chen XS, Sun ZQ (2014) Modulating the interface quality and electrical properties of HfTiO/InGaAs gate stack by atomic-layer-deposied Al2O3 passivation layer. ACS Appl Mater Interfaces 6(24):22013–22025View ArticleGoogle Scholar
- He G, Liu JW, Chen HS, Liu YM, Sun ZQ, Chen XS, Liu M, Zhang LD (2014) Interface control and modification of band alignment and electrical properties of HfTiO/GaAs gate stacks by nitrogen incorporation. J Mater Chem C 2(27):5299–5308View ArticleGoogle Scholar
- Wang Y, Chen YT, Zhao H, Xue F, Zhou F, Lee JC (2011) Impact of SF6 plasma treatment on performance of TaN-HfO2-InP metal-oxide-semiconductor field-effect transistor. Appl Phys Lett 98(4):043506View ArticleGoogle Scholar
- Kim HS, Ok I, Zhang M, Zhu F, Park S, Yum J, Zhao H, Lee JC, Majhi P, Goel N, Tsai W, Gaspe CK, Santos MB (2008) A study of metal-oxide-semiconductor capacitors on GaAs, In0.53Ga0.47As, InAs, and InSb substrates using a germanium interfacial passivation layer. Appl Phys Lett 93(6):062111View ArticleGoogle Scholar
- Garcia-Gutierrez DI, Shahrjerdi D, Kaushik V, Banerjee SK (2009) Physical and electrical characterizations of metal-oxide-semiconductor capacitors fabricated on GaAs substrates with different surface chemical treatments and Al2O3 gate dielectric. J Vac Sci Technol B 27(6):2390–2395View ArticleGoogle Scholar
- Xu M, Gu J, Wang C, Zhernokletov DM, Wallace RM, Ye PD (2013) New insights in the passivation of high-k/InP through interface characterization and metal-oxide-semiconductor field effect transistor demonstration: impact of crystal orientation. J Appl Phys 113(1):013711View ArticleGoogle Scholar
- Lu HL, Terada Y, Shimogaki Y, Nakano Y, Sugiyama M (2009) In situ passivation of InP surface using H2S during metal organic vapor phase epitaxy. Appl Phys Lett 95(15):152103View ArticleGoogle Scholar
- Chou HY, Afanas’ev VV, Stesmans A, Lin HC, Hurley PK, Newcomb SB (2010) Electron band alignment between (100)InP and atomic-layer deposited Al2O3. Appl Phys Lett 97(13):132112View ArticleGoogle Scholar
- Xu K, Sio H, Kirillov OA, Dong L, Xu M, Ye PD, Gundlach D, Nguyen NV (2013) Band offset determination of atomic-layer-deposited Al2O3 and HfO2 on InP by internal photoemission and spectroscopic ellipsometry. J Appl Phys 113(2):024504View ArticleGoogle Scholar
- George SM (2010) Atomic layer deposition: an overview. Chem Rev 110(1):111–131View ArticleGoogle Scholar
- Dong H, Brennan B, Zhernokletov D, Kim J, Hinkle CL, Wallace RM (2013) In situ study of HfO2 atomic layer deposition on InP(100). Appl Phys Lett 102(17):171602View ArticleGoogle Scholar
- Dong H, Santosh KC, Qin X, Brennan B, McDonnell S, Zhernokletov D, Hinkle CL, Kim J, Cho K, Wallace RM (2013) In situ study of the role of substrate temperature during atomic layer deposition of HfO2 on InP. J Appl Phys 114(15):154105View ArticleGoogle Scholar
- Kang YS, Kim CY, Cho MH, Chung KB, An CH, Kim H, Lee HJ, Kim CS, Lee TG (2010) Thickness dependence on crystalline structure and interfacial reactions in HfO2 films on InP (001) grown by atomic layer deposition. Appl Phys Lett 97(17):172108View ArticleGoogle Scholar
- Chen YT, Zhao H, Yum JH, Wang YZ, Lee JC (2009) Metal-oxide-semiconductor field-effect-transistors on indium phosphide using HfO2 and silicon passivation layer with equivalent oxide thickness of 18 Å. Appl Phys Lett 94(21):213505View ArticleGoogle Scholar
- Driad R, Sah RE, Schmidt R, Kirste L (2012) Passivation of InP heterojunction bipolar transistors by strain controlled plasma assisted electron beam evaporated hafnium oxide. Appl Phys Lett 100(1):014102View ArticleGoogle Scholar
- Hinkle CL, Sonnet AM, Vogel EM, McDonnell S, Hughes GJ, Milojevic M, Lee B, Aguirre-Tostado FS, Choi KJ, Kim HC, Kim J, Wallace RM (2008) GaAs interfacial self-cleaning by atomic layer deposition. Appl Phys Lett 92(7):071901View ArticleGoogle Scholar
- Kraut EA, Grant RW, Waldrop JR, Eowalczyk SP (1980) Precise determination of the valence-band edge in x-ray photoemission spectra: application to measurement of semiconductor interface potentials. Phys Rev Lett 44(24):1620–1624View ArticleGoogle Scholar
- Perego M, Seguini G, Scarel G, Fanciulli M, Wallrapp F (2008) Energy band alignment at TiO2/Si interface with various interlayers. J Appl Phys 103(4):043509View ArticleGoogle Scholar
- Xie ZY, Lu HL, Xu SS, Geng Y, Sun QQ, Ding SJ, Zhang DW (2012) Energy band alignment of InGaZnO4/Si heterojunction determined by x-ray photoelectron spectroscopy. Appl Phys Lett 101(25):252111View ArticleGoogle Scholar
- Yu HY, Li MF, Cho BJ, Yeo CC, Joo MS, Kwong DL, Pan JS, Ang CH, Zheng JZ, Ramanathan S (2002) Energy gap and band alignment for (HfO2)(x)(Al2O3)(1-x) on (100) Si. Appl Phys Lett 81(2):376–378View ArticleGoogle Scholar
- Mahapatra R, Chakraborty AK, Horsfall AB, Wright NG, Beamson G, Coleman KS (2008) Energy-band alignment of HfO2/SiO2/SiC gate dielectric stack. Appl Phys Lett 92(4):042904View ArticleGoogle Scholar