傳統的氮化鋁鎵/氮化鎵高電子遷移率電晶體屬於空乏型電晶體，這是因氮化鋁鎵/氮化鎵的結構存在極化效應，導致在異質接面處產生二維電子氣。空乏型高電子遷移率電晶體須在閘極施加負偏壓才能關閉，而這會造成功率的損耗。因此，我們發展增強型電晶體來減低額外的功率消耗。此外，除了減低功耗，增強型電晶體也可以減化電路的偏壓設計以及提供防錯的保護。
在本論文中，我們利用閘極掘入的方式來減少氮化鋁鎵/氮化鎵高電子遷移率電晶體閘極下方的二維電子氣濃度，使高電子遷移率電晶體從空乏型轉變為增強型；並以液相沉積的方式，在閘極下方成長二氧化鋯做為絕緣層，以此來減低閘極漏電流。另一方面，為了分析高電子遷移率電晶體之電性，我們根據漸變通道近似法分析高電子遷移率電晶體的電流與轉導特性，並將計算結果與實驗值相互驗證。
我們以閘極掘入及液相沉積法順利完成氮化鋁鎵/氮化鎵增強型金氧半高電子遷移率電晶體。元件的臨界電壓成功提升至0.3V，最大電流密度可達347 mA/mm，轉導值則為146 mS/mm，電流開關比和次臨界擺幅分別改善至1.4×108和89 mV/dec，閘極漏電流及崩潰電壓則為2.06×10-7 A/mm和92 V。

Conventional AlGaN/GaN high electron mobility transistors (HEMTs) are depletion-mode (D-mode) HEMTs due to the inherent two-dimensional electron gas (2DEG) induced by polarization effects. It is necessary to apply a negative gate bias to turn off a D-mode HEMT, and that will cause additional power loss. Therefore, the enhancement-mode (E-mode) HEMT is developed to reduce extra power consumption. Moreover, the E-mode HEMT is also required for circuit simplicity and fail-safe operation.
In the thesis, gate recess process was used to convert a depletion-mode HEMT to an enhancement-mode HEMT through the reduction of the 2DEG density under the gate region. To suppress gate leakage current, a ZrO2 film was deposited as a gate dielectric by using liquid-phase deposition (LPD) method. Besides, in order to investigate the electrical characteristics of HEMTs, we presented an analytical model based on the gradual channel approximation to simulate the drain current and transconductance. In addition, the simulation results were compared with experimental data.
The E-mode AlGaN/GaN MOSHEMT was achieved by using gate recess technique and the LPD process. The threshold voltage is successfully shifted to 0.3 V. The maximum drain current density reaches about 347 mA/mm. The maximum transconductance is 146 mS/mm. The Ion/Ioff ratio and the subthreshold swing are improved to 1.4×108 and 89 mV/dec. The gate leakage current and the breakdown voltage are 2.06×10-7 A/mm and 92 V,respectively.

[1] S.J. Peartona, F. Renb, A.P. Zhang, and K.P. Lee, “Fabrication and performance of GaN electronic devices,” Materials Science and Engineering: R: Reports, vol. 30, pp. 55-212, 2000.
[2] B. G. Streetman and S. Banerjee, Solid State Electronic Devices, 5th ed. Mishawaka: Prentice Hall, p. 524, 2000.
[3] S. C. Jain, M. Willander, J. Narayan, and R. V. Overstraeten, “III–nitrides: growth, characterization, and properties,” Journal of Applied Physics, vol. 87, no. 3, pp. 965-1006, Feb. 2000.
[4] W. Saito, Y. Takada, M. Kuraguchi, K. Tsuda, and I. Omura, “Recessed-gate structure approach toward normally off high-voltage AlGaN/GaN HEMT for power electronics applications,” IEEE Transactions on Electron Devices, vol. 53, no. 2, pp. 356-362, Feb. 2006.
[5] H. K. Lin, F. H. Huang, and H. L. Yu, “DC and RF characterization of AlGaN/GaN HEMTs with different gate recess depths,” Solid-State Electronics, vol. 54, pp. 582-589, Feb. 2010.
[6] R. Wang, Y. Cai, C.-W. Tang, K. M. Lau, and K. J. Chen, “Enhancement-mode Si3N4/AlGaN/GaN MISHFETs,” IEEE Electron Device Letters, vol. 27, no. 10, pp. 793-795, Jul. 2006.
[7] Y. Cai, Y. Zhou, K. M. Lau, and K. J. Chen, “Control of threshold voltage of AlGaN/GaN HEMTs by fluoride-based plasma treatment: from depletion mode to enhancement mode,” IEEE Transactions on Electron Devices, vol. 53, no. 9, pp. 2207-2215, Sep. 2006.
[8] I. Hwang, J. Kim, H. S. Choi, H. Choi, J. Lee, K. Y. Kim, J. B. Park, J. C. Lee, J. Ha, J. Oh, J. Shin, and U. I. Chung, “p-GaN gate HEMTs with tungsten gate metal for high threshold voltage and low gate current,” IEEE Electron Device Letters, vol. 34, no. 2, pp. 202-204, Feb. 2013.
[9] L. Y. Su, F. Lee, and J. J. Huang, “Enhancement-mode GaN-based high-electron mobility transistors on the Si substrate with a p-type GaN cap layer,” IEEE Transactions on Electron Devices, vol. 61, no. 2, pp. 460-465, Feb. 2014.
[10] A. Endoh, Y. Yamashita, K. Ikeda, M. Higashiwaki, K. Hikosaka, T. Matsui1, S. Hiyamizu, and T. Mimura, “Non-recessed-gate enhancement-mode AlGaN/GaN high electron mobility transistors with high RF performance,” Japanese Journal of Applied Physics, vol. 43, no. 4B, pp. 2255-2258, Apr. 2004.
[11] R. Brown, D. Macfarlane, A. AlKhalidi, X. Li, G. Ternent, H. Zhou, I. Thayne, and E. Wasige, “A sub-critical barrier thickness normally-off AlGaN/GaN MOS-HEMT,” IEEE Electron Device Letters, vol. 35, no. 9, pp. 906-908, Sep. 2014.
[12] R. K. Tyagi, A. Ahlawat, M. Pandey, and S. Pandey, “An analytical two-dimensional model for AlGaN/GaN HEMT with polarization effects for high power applications,” Microelectronics Journal, vol. 38, pp. 877-883, Sep. 2007.
[13] F. Sacconi, A. D. Carlo, P. Lugli, and H. Morkoç, “Spontaneous and piezoelectric polarization effects on the output characteristics of AlGaN/GaN heterojunction modulation doped FETs,” IEEE Transactions on Electron Devices, vol. 48, no. 3, pp. 450-457, Mar. 2001.
[14] L. Jia, E. T. Yu, D. Keogh, and P. M. Asbeck, “Polarization charges and polarization-induced barriers in AlxGa1-x/GaN and InyGa1-y/GaN heterostructures,” Applied Physics Letters, vol. 79, no.18, pp. 2916-2918, Oct. 2001.
[15] O. Ambacher, “Growth and applications of Group III-nitrides,” Journal of Physics D: Applied Physics, vol. 31, pp. 2653-2710, Jun. 1998.
[16] F. Bernardini, V. Fiorentini, and D. Vanderbilt, “Spontaneous polarization and piezoelectric constants of III-V nitrides,” Physical Review B, vol. 56, no.16, pp. R10024-R10027, Oct. 1997.
[17] O. Ambacher, J. Smart, J. R. Shealy, N. G. Weimann, K. Chu, M. Murphy, W. J. Schaff, L. F. Eastman, R. Dimitrov, L. Wittmer, M. Stutzmann, W. Rieger, and J. Hilsenbeck, “Two-dimensional electron gases induced by spontaneous and piezoelectric polarization charges in N- and Ga-face AlGaN/GaN heterostructures,” Journal of Applied Physics, vol. 85, no. 6, pp. 3222-3233, Mar. 1999.
[18] A. Hangleiter, J. S. Im, H. Kollmer, S. Heppel, J. Off, and F. Scholz, “The role of piezoelectric fields in GaN-based quantum wells,” MRS
Internet J. Nitride Semicond. Res, vol. 3, no. 15, pp. 1-8, Aug. 1998.
[19] E. T. Yu, G. J. Sullivan, P. M. Asbeck, C. D. Wang, D. Qiao, and S. S. Lau, “Measurement of the piezoelectrically induced charge in GaN/AlGaN heterostructure field-effect transitors,” Applied Physics Letters, vol. 71, pp. 2794-2796, Sep. 1997.
[20] A. D. Bykhovski, B. L. Gelmont, and M. S. Shur, “Elastic strain relaxation and piezoeffect in GaN-AlN, GaN-AlGaN and GaN-InGaN superlattices,” Journal of Applied Physics, pp. 6332-6338, Jan. 1997.
[21] P. M. Asbeck, E. T. Yu, S. S. Lau, G. J. Sullivan, J. VanHove, and J. Redwing, “Piezoelectric charge densities in AIGaN/ GaN HFETs,” Electronics Letters, vol. 33, no. 14, pp. 1230-1231, Aug. 2002.
[22] M. B. Nardelli, K. Rapcewicz, and J. Bernholc, “Polarization field effects on the electron-hole recombination dynamics in In0.2Ga0.8N/In1−xGaxN multiple quantum wells,” Applied Physics Letters, vol. 71, no. 21, pp. 3135-3137, Sep. 1997.
[23] A. D. Bykhovski, V. V. Kaminski, M. S. Shur, Q. C. Chen, and M. A. Khan, “Piezoresistive effect in wurtzite n-type GaN,” Applied Physics Letters, vol. 68, pp. 818-819, Feb. 1996.
[24]

T. R. Lenka and A.K. Panda, “Characteristics study of 2DEG transport properties of AlGaN/GaN and AlGaAs/GaAs-based HEMT,” Semiconductors, vol. 45, no. 5, pp. 650-656, May. 2011.
[25] C. T. Sah, “Characteristics of the metal-oxide-semiconductor transistors,” IEEE Transactions on Electron Devices, vol. 11, no.7, pp. 324-345, Jul. 1964.
[26] W. Fikry, G. Ghibaudo, H. Haddara, S. Cristoloveanu, and M. Dutoit, “Method for extracting deep submicrometer MOSFET parameters,” Electronics Letters, vol. 31, no. 9, pp. 762-764, Apr. 1995.
[27] T. J. Anderson, M. J. Tadjer, M. A. Mastro, J. K. Hite, K. D. Hobart, C. R. Eddy, and F.J. Kub, “Characterization of recessed-gate AlGaN/GaN HEMTs as a function of etch depth,” Journal of electronic materials, vol. 39, no. 5, pp. 478-481, Aug. 2010.
[28] M. Quirk and J. Serda, Semiconductor manufacturing technology. Mishawaka: Prentice Hall, pp.439-440, 2001.
[29] L. Ledernez, F. Olcaytug, H. Yasuda, and G. Urban, “A modification of Paschen law for Argon,” International Conference on Phenomena in Ionized Gases (29th ICPIG), Cancun, Mexico, Jul. 12-17, 2009.
[30] S. Basu, P. K. Singh, J. J. Wang, and Y. H. Wang, “Liquid-phase deposition of Al2O3 thin films on GaN, ” Journal of The Electrochemical Society, vol. 154, no. 12. pp. H1041-H1046, Aug. 2007.
[31] C. C. Hu, M. S. Lin, T. Y. Wu, F. Adriyanto, P. W. Sze, C. L. Wu, and Y. H. Wang, “AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistor with liquid-phase-deposited Barium-doped TiO2 as a gate dielectric,” IEEE Transactions on electron devices, vol. 59, no.1, pp. 121-127, Jan. 2012.
[32] M. Kanamura, T. Ohki, K. Imanishi, K. Makiyama, N. Okamoto, T. Kikkawa, N. Hara, and K. Joshin, “High power and high gain AlGaN/GaN MIS-HEMTs with high-k dielectric layer,” Physica Status Solidi (c), vol. 5, no. 6, pp. 2037-2040, May. 2008.
[33] Y. Dora, S. Han, D. Klenov, P. J. Hansen, K. S. No, U. K. Mishra, S. Stemmer, and J. S. Speck, “ZrO2 gate dielectrics produced by ultraviolet ozone oxidation for GaN and AlGaN∕GaN transistors,” Journal of Vacuum Science & Technology B, vol. 24, pp. 575-581, Feb. 2006.
[34] R. D. Clark, “Emerging Applications for High K Materials in VLSI Technology,” Materials, vol. 7, no 4, pp. 2913-2944, Apr. 2014.
[35] Y. Z. Yue, Y. Hao, and J. C. Zhang, “AlGaN/GaN MOS-HEMT with Stack Gate HfO2/Al2O3 Structure Grown by Atomic Layer Deposition,” Compound Semiconductor Integrated Circuits Symposium, pp. 1-4, Oct. 2008.
[36] R. Shao, C. Wang, D. E. McCready, T. C. Droubay, and S. A. Chambers, “Growth and structure of MBE grown TiO2 anatase films with rutile nano-crystallites,” Surface Science, vol. 601, no. 6, pp. 1582-1589, Mar. 2007.
[37] V. Tilak, B. Green, H. Kim, R. Dimitrov, J. Smart, W. J. Schaff, J. R. Shealy, and L. F. Eastman, “Effect of passivation on AlGaN/GaN HEMT device performance,” International Symposium on Compound Semiconductors, pp. 357-363, Oct. 2000.
[38] L. Li , Y. Xu , Q. Wang , R. Nakamura , Y. Jiang, and J. P. Ao, “Metal-oxide-semiconductor AlGaN/GaN heterostructure field-effect transistors using TiN/AlO stack gate layer deposited by reactive sputtering,” Semiconductor Science and Technology, vol. 30, no. 1, pp. 1-6, Jan. 2015.
[39] H. Nagayama, H. Honda, and H. Kawahara, “A new process for silica coating,” Journal of The Electrochemical Society, vol. 135, no. 8, pp. 2013-2016, 1988.
[40] H. R. Wu, K. W. Lee, T. B. Nian, D. W. Chou, J. J. H. Wu, Y. H. Wang, M. P. Houng, P. W. Sze, Y. K. Su, S.J. Chang, C. H. Ho, C.I. Chiang, Y. T. Chern, F. S. Juang, T. C. Wen, W. I. Lee, and J. I. Chyi, “Liquid phase deposited SiO2 on GaN,” Materials Chemistry and Physics, vol. 80, no. 1, pp. 329-333, Apr. 2003.
[41] D. W. Chou, K. W. Lee, J. J. Huang, P. W. Sze, H. R. Wu, Y. H. Wang, M. P. Houng, S. J. Chang, and Y. K. Su, “AlGaN/GaN metal oxide semiconductor heterostructure field-effect transistor based on a liquid phase deposited oxide,” Japanese Journal of Applied Physics, vol. 41, no. 7A, pp. L748-L750, Jul. 2002.
[42] S. Basu, P. K. Singh, P. W. Sze, and Y. H. Wang, “AlGaN/GaN metal-oxide-semiconductor high electron mobility transistor with liquid phase deposited Al2O3 as gate dielectric,” Journal of The Electrochemical Society, vol. 157, no. 10, pp. H947-H951, Aug. 2010.
[43] T. Y. Wu, P. W. Sze, C. C. Hu, T. J. Huang, and Y. H. Wang, “AlGaN/GaN metal oxide semiconductor high electron mobility transistor using liquid-phase deposited strontium titanate,” Solid State Electronics, vol. 82, pp. 1-5, Feb. 2013.
[44] S. Basu, P. K. Singh, S. K. Lin, P. W. Sze, and Y. H. Wang, “Effects of short-term DC-bias-induced stress on n-GaN/AlGaN/GaN MOSHEMTs with liquid-phase-deposited Al2O3 as a gate dielectric,” Solid State Electronics, vol. 57, no. 11, pp. 2978-2987, Nov. 2010.
[45] T. Y. Wu, S. K. Lin, P. W. Sze, J. J. Huang, W. C. Chien, C. C. Hu, M. J. Tsai, and Y. H. Wang, “AlGaN/GaN MOSHEMTs with liquid-phase-deposited TiO2 as gate dielectric,” IEEE Transactions on Electron Devices, vol. 56, no. 12, pp. 2911-2916, Dec. 2009.
[46] J. M. Lin, M. C. Hsu, and K. Z. Fung, “Deposition of ZrO2 film by liquid phase deposition,” Journal of Power Sources, vol. 159, pp. 49-54,
Jul. 2006.
[47] R. Jerome, P. h. Teyssie, J. J. Pireaux, and J. J. Verbist, “Surface analysis of polymers end-capped with metal carboxylates using X-ray photoelectron spectroscopy,” Applied Surface Science, vol. 27, no. 1, pp. 93-105, Oct. 1986.
[48] S. Sinha, S. Badrinarayanan, and A. P. B. Sinha, “Interaction of oxygen with Zr76Fe24 metglass: an X-ray photoelectron spectroscopy study,” Journal of the Less-Common Metals, vol. 125, pp. 85-95, Nov. 1986.
[49] J. J. Wierer, M. R. Krames, J. E. Epler, N. F. Gardner, M. G. Craford, J. R. Wendt, J. A. Simmons, and M. M.Sigalas, “XPS studies of the thermal behaviour of passivated Zircaloy-4 surfaces,” Surface and Interface Analysis, vol. 11, pp. 502-509, Jul. 1988.
[50] Q. Zhou, S. Huang, H. Chen, C. Zhou, Z. Feng, S. Cai, and K. Chen, “Schottky source/drain Al2O3/InAlN/GaN MIS-HEMT with steep sub-threshold swing and high ON/OFF current ratio,” in IEEE International Electron Devices Meeting (IEDM), pp. 33.4.1-33.4.4, Dec. 2011.
[51] J. J. Freedsman, T. Kubo, S. L. Selvaraj, and T. Egawa, “ Suppression of gate leakage and enhancement of breakdown voltage using thermally oxidized Al layer as gate dielectric for AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors,” Japanese Journal of Applied Physics, vol. 50, pp. 04DF03-1-04DF03-4, Apr. 2011.
[52] T. E. Hsieh, E. Y. Chang, Y. Z. Song, Y. C. Lin, H. C. Wang, S. C. Liu, S. Salahuddin, and C. C. Hu, “Gate recessed quasi-normally off Al2O3/AlGaN/GaN MIS-HEMT with low threshold voltage hysteresis using PEALD AlN interfacial passivation layer,” IEEE Electron Device Letters, vol. 35, no. 7, pp. 732-734, Jul. 2014.
[53] H. C. Chiu, C. W. Yang, C. H. Chen, J. S. Fu, and F. T. Chien, “Characterization of enhancement-mode AlGaN/GaN high electron mobility transistor using N2O plasma oxidation technology,” Applied Physics Letters, vol. 99, pp. 15308-1-15308-3, Oct. 2011.
[54] F. Medjdoub, M. V. Hove, K. Cheng, D. Marcon, M. Leys, and S. Decoutere, “Novel E-mode GaN-on-Si MOSHEMT using a selective thermal oxidation,” IEEE Electron Device Letters, vol. 31, no. 9, pp. 948-950, Sep. 2010.