T HE INFLUENCES OF SURFACE TREATMENT AND GAS ANNEALING CONDITIONS ON THE INVERSION BEHAVIORS OF THE ATOMIC
6.3.2. High-resolution transmission electron microscopy micrographs
Cross-sectional HRTEM micrographs of the samples are shown in Fig. 6.3. Normally, an air-exposed InGaAs, InAs have native oxide layers with thickness of above 2nm [9]. Here, the samples show an abrupt transition from InGaAs, InAs to Al2O3 without interface layers. These imply that most of native oxides were removed and the rest layers are not identified by HRTEM, in consistent with XPS results. The InGaAs, InAs substrates structures are highly order up to the interface as seen from their periodic lattice images and the interface morphologies exhibit good thermal stability after PDA at 400oC. Al2O3
films are amorphous as shown in the figure and the thickness of oxide films estimated
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from TEM graphs are about 13.2 nm, in consistent with the estimation from number of ALD cycles (13 nm).
Figure 6.2. As 3d and In 3d5/2 XPS spectra of (a) native-oxide-corvered InAs surface and (b) 1.5 nm Al2O3/InGaAs, InAs structures, as deposition. After using surface treatment and oxide depositon, As-related oxides were reduced to under XPS detection level, the Ga-O and In-O bonds were also significant removed.
Figure 6.3. High-resolution transmission electron microscopy micrographs of 13nm ALD Al2O3/InGaAs structures after PDA at 400oC in forming gas: a-Al2O3/In0.53Ga0.47As, b-Al2O3/In0.7Ga0.3As, and c-Al2O3/InAs, showing abrupt Al2O3/InGaAs, InAs interfaces.
89 6.3.3. Electrical characteristics
The C-V responses of MOSCAP structures at the frequency of 1MHz is shown in Fig.
6.4. When In content increases, the C-V responses change from high-frequency to low-frequency C-V behaviors. For the case of InAs, strong inversion layer is observed at high frequency of 1 MHz. This implies that the minority carrier (holes) response time, R
decreases with increasing of In content. The minority carrier response time can be described by the relationship R~T/ni [10], where T is the carrier life time and ni is the intrinsic carrier concentration. The intrinsic carrier concentration ni increases rapidly with the increasing of In content, from ~6.31012 cm-3 for In0.53Ga0.47As to ~1015 cm-3 for InAs as shown in Fig. 6.1 [4]. This explains the minority carrier responses faster when In content is higher.
Figure 6.4. Capacitance voltage responses at measured frequency of 1 MHz of Al2O3/InxGa1-xAs MOSCAPs with different In content
The multi-frequency C-V responses of MOSCAP structures shown in Fig. 6.5 indicate small frequency dispersion in accumulation region (< 1.1% per decade). With doping concentration ND of 2x1017 cm-3, the Fermi level lies very close to In0.53Ga0.47As conduction band edge (about 0.0013 eV below EC) and ~0.022 eV above InAs conduction band edge [4, 11]. Thus, in the accumulation region, due to the band bending, the Fermi level at Al2O3/InGaAs, InAs interface would lie inside conduction bands. In this case, traps response time can be determined by.
(6.1)
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where, is the capture cross-section of the trapping state, vth is the thermal velocity of the majority charge carriers, and N is the density of states in the majority carrier band. The traps response time determined by (6.1) is very small, order of 10-10 s, corresponding to response frequencies of order of several hundred MHz. With that very high response frequency, the contribution of traps to the frequency dispersion cannot be realized with traditional C-V measurement (frequencies in range of 100 Hz – 1 MHz). In this case, the frequency dispersion is mostly due to the contribution of border traps which locate near interface, inside oxide. Effects of border traps on Al2O3/InGaAs, InAs structure are very similar as indicated by very similar frequency dispersion values (Fig 6.5).
Bidirectional C-V responses show the reduction of hysteresis with the increase of In content (Fig. 6.5), implying the reduction of traps effect. This results can be explained by the Empirical model which proposed by P. D. Ye [2, 12]. According to this model, when increasing In content, the bandgap is decreased and it will lead to decrease total density of traps and hence their effect is reduced.
Figure 6.5. Multi-frequency and bidirectional C-V responses of of Al2O3/InxGa1-xAs MOSCAPs with different In content
Temperature dependent C-V, G-V measurements were performed at 77K, 180K, and 300K for all samples. Figure 6.6a shows the multi-frequency C-V and conductance maps Gp/ at different temperatures of Al2O3/n-In0.53Ga0.47As structure. These measurements enable to extract the interface traps at different energy positions inside the bandgap as
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shown in Fig. 6.6b. Except weak inversion C-V responses at frequency of smaller than 4 kHz at room temperature, high-frequency curves are observed in all range of measured frequencies (1kHz-1MHz) and temperatures. This allows us to ensure the accuracy of the extracted conductance contours. From the conductance map, the traces of movement of Fermi level (solid lines, Fig. 6.6a, conductance contours) are observed clearly as the gate voltage is varied, indicating unpinning Fermi level in Al2O3/In0.53Ga0.47As MOSCAPs.
Figure 6 shows the Dit profile of Al2O3/In0.53Ga0.47As structure obtained by simulation [13] and conductance method [14]. Both two method show low Dit of 10-21011 eV-1cm-2 at the energy position from 0.4 to 0.74 eV above valence band minimum and Dit increase at the lower half of the In0.53Ga0.47As bandgap. Notice that in this work the PDA temperature was performed at 400oC to optimize the quality of Al2O3/InAs interface [15].
For Al2O3/In0.53Ga0.47As, lower Dit profile of was achieved for the sample annealed at 500oC (see chapter 5).
Figure 6.6. a-Multi-frequency C-V responses and conductance contours Gp/ (f, V) at different temperatures (77 K, 180 K and 300 K) of Al2O3/In0.53Ga0.47As. Peaks of conductance shows the traces of Fermi level movement (solid lines); b-Characteristic trapping frequencies for electrons in n-In0.53Ga0.47As; c-The interface trap density profile of Al2O3/In0.53Ga0.47As extracted by conductance method is good agreement with that extracted by simulation.
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Figure 6.7 shows the multi-frequency C-V responses and corresponding conductance contours of Al2O3/In0.7Ga0.3As and Al2O3/InAs structures. As shown in the figure and Fig.
6.4, high-frequency C-V responses seem not to be observed even temperature was cooled down to 77K. Since inversion layers always respond all range of measured frequencies and temperatures, their contribution to the conductance will hide the accuracy of conductance method. As can see in the figure, the conductance contours are always closed due to the contribution of inversion carriers. Thus, the extraction of Dit as well as the traces of Fermi level is not obtained. To eliminate the contribution of inversion layer, the application of full conductance method is needed [16].
Figure 6.7. Multi-frequency C-V responses and conductance contours Gp/ (f, V) at different temperatures (77 K, 180 K and 300 K) of a-Al2O3/In0.7Ga0.3As, and b-Al2O3/InAs MOSCAPs.
Conductance contours are closed due to the contribution of inversion layer and thus, the Fermi level traces could not show up.
The leakage current increases with the increase of In content as shown in Fig. 6.8a.
With the increase of In content, the intrinsic carrier density increases rapidly (parameters shown in Fig. 6.1). Thus at native gate bias, the increase of holes tunneling from semiconductor though oxide to gate metal will result in the increase of leakage current. At positive gate voltage, electrons transfer from semiconductor through the oxide to gate metal. The larger In content in InGaAs, the smaller electron effective mass is, thus, it more susceptible to electrons tunneling through oxide.
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The leakage current of samples are plotted in the Flower-Nordheim (FN) form as show in Fig. 6.8b-d [17, 18]. The linear relation of vs indicates the FN tunneling at high electric field. The slope is expressed by:
√
(6.2)
where m* is electron effective mass within Al2O3 and is the tunneling barrier height.
From the measured slope, assume the effective mass m* = 0.23me [19], the barrier heights are evaluated to be 1.89 eV, 1.97 eV and 2.07 eV for Al2O3/In0.53Ga0.47As, Al2O3/In0.7Ga0.3As and Al2O3/InAs, respectively.
Figure 6.8. a- leakage current increases with increasing of In content in InGaAs. The Flower-Nordheim plot for b- Al2O3/In0.53Ga0.47As, c-Al2O3/In0.7Ga0.3As and d-Al2O3/InAs structures.
6.4. Conclusions
We have studied the material and electrical characteristics of ALD Al2O3/InGaAs structures, with In content of 0.53, 0.7, and 1. XPS analysis shows the significant reduction of native oxides after HCl plus TMA treatment. HRTEM micrographs showed abrupt Al2O3/InGaAs, InAs interface layers. Multi-frequency C-V responses show low frequency dispersion in accumulation region. These frequency dispersions seem mostly
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due to border traps in oxide rather than due to interface traps. Conductance method and simulation results showed the low interface trap density distribution at energy position of 0.4 to 0.74 eV above valence band of InGaAs. The conductance contours trace the movement of Fermi level at varied gate bias for the case of In0.53Ga0.47As but not for In0.7Ga0.3As and InAs due to the contribution of inversion layer. The increase of leakage current in In-rich Al2O3/InxGa1-xAs structures indicated larger probability of holes and electrons tunneling though oxide due to the increase of intrinsic carrier density and the reduction of electron effective mass in In-rich samples.
95 References
[1] R. Chau, S. Datta, and A. majumdar, "Opportunities and Challenges of III-V Nanoelectronic for High-speed, Low-power Logic Applications," IEEE CSIC Syposium Technical Digest 17 (2005).
[2] P. D. Ye, "Main determinants for III-V metal-oxide-semiconductor field-effect transistors (invited)," J. Vac. Sci. Technol. A 26, 697-704, (2008).
[3] É. O’Connor, S. Monaghan, R. D. Long, A. O’Mahony, I. M. Povey, K. Cherkaoui, M. E.
Pemble, G. Brammertz, M. Heyns, S. B. Newcomb, V. V. Afanas’ev, and P. K. Hurley,
"Temperature and frequency dependent electrical characterization of HfO2/InxGa1-xAs interfaces using capacitance-voltage and conductance methods," Appl. Phys. Lett. 94, 102902 (2009).
[4] Source: http://www.ioffe.ru/SVA/NSM/.
[5] H. D. Trinh, E. Y. Chang, P. W. Wu, Y. Y. Wong, C. T. Chang, Y. F. Hsieh, C. C. Yu, H. Q.
Nguyen, Y. C. Lin, K. L. Lin, and M. K. Hudait, "The influences of surface treatment and gas annealing conditions on the inversion behaviors of the atomic-layer-deposition Al2O3 /n-In0.53Ga0.47As metal-oxide-semiconductor capacitor," Appl. Phys. Lett. 97, 042903 (2010).
[6] Hai-Dang Trinh, Edward Yi Chang, Yuen-Yee Wong, Chih-Chieh Yu, Chia-Yuan Chang, Yueh-Chin Lin, Hong-Quan Nguyen, and Binh-Tinh Tran "Effects of Wet Chemical and Trimethyl Aluminum Treatments on the Interface Properties in Atomic Layer Deposition of Al2O3 on InAs," Jpn. J. Appl. Phys. 49, 111201 (2010).
[7] C. L. Hinkle, A. M. Sonnet, E. M. Vogel, S. McDonnell, G. J. Hughes, M. Milojevic, B.
Lee, F. S. Aguirre-Tostado, K. J. Choi, H. C. Kim, J. Kim, and R. M. Wallace, "GaAs interfacial self-cleaning by atomic layer deposition," Appl. Phys. Lett. 92, 071901 (2008).
[8] M. Milojevic, C. L. Hinkle, F. S. Aguirre-Tostado, H. C. Kim, E. M. Vogel, J. Kim, and R.
M. Wallace, "Half-cycle atomic layer deposition reaction studies of Al2O3 on (NH4)2S passivated GaAs(100) surfaces," Appl. Phys. Lett. 93, 252905 (2008).
[9] Y. C. Chang, M. L. Huang, K. Y. Lee, Y. J. Lee, T. D. Lin, M. Hong, J. Kwo, T. S. Lay, C.
C. Liao, and K. Y. Cheng, "Atomic-layer-deposited HfO2 on In0.53Ga0.47As: Passivation and energy-band parameters," Appl. Phys. Lett. 92, 072901 (2008).
[10] E. H. Nicollian and J. R. Brews, "MOS Physics and Technology," John Wiley and Sons, ISBN 0-471-08500-6, 139 (1982).
[11] S. M. Sze and K. K. Ng, "Physics of Semiconductor Devices," John Wiley & Sons, ISBN-I 3: 978-0-47 1-1 4323-9, 19-20 (2007).
[12] Serge Oktyabrsky, and Peide D. Ye, Editors "Fundamentals of III-V Semiconductor MOSFETs," Spring, ISBN 978-1-4419-1546-7, 178-181 (2010).
96
[13] G. Brammertz, H.-C. Lin, M. Caymax, M. Meuris, M. Heyns, and M. Passlack, "On the interface state density at In0.53Ga0.47As/oxide interfaces," Appl. Phys. Lett. 95, 202109 (2009).
[14] G. Brammertz, H.-C. Lin, K. Martens, D. Mercier, S. Sioncke, A. Delabie, W. E. Wang,M.
Caymax, M. Meuris, and M. Heyns, "Capacitance-voltage characterization of GaAs–Al2O3
interfaces," Appl. Phys. Lett. 93, 183504 (2008).
[15] Ning Li, Eric S. Harmon, James Hyland, David B. Salzman, T. P. Ma, Yi Xuan, and P. D.
Ye, "Properties of InAs metal-oxide-semiconductor structures with atomic-layer-deposited Al2O3 Dielectric," Appl. Phys. Lett. 92, 143507 (2008).
[16] K. Martens, C. Chi On, G. Brammertz, B. De Jaeger, D. Kuzum, M. Meuris, M. Heyns, T.
Krishnamohan, K. Saraswat, H. E. Maes, and G. Groeseneken, "On the Correct Extraction of Interface Trap Density of MOS Devices With High-Mobility Semiconductor Substrates,"
IEEE Trans. Electron Devices 55, 547-556 (2008).
[17] T. S. Lay, M. Hong, J. Kwo, J. P. Mannaerts, W. H. Hung, and D. J. Huang, "Energy-band parameters at the GaAs- and GaN-Ga2O3(Gd2O3) interfaces," Solid-State Electron. 45, 1679-1682 (2001).
[18] M. L. Huang, Y. C. Chang, Y. H. Chang, T. D. Lin, J. Kwo, and M. Hong, "Energy-band parameters of atomic layer deposited Al2O3 and HfO2 on InxGa1-xAs," Appl. Phys. Lett. 94, 052106 (2009).
[19] Davood Shahrjerdi,a Emanuel Tutuc, and Sanjay K. Banerjee, "Impact of surface chemical treatment on capacitance-voltage characteristics of GaAs metal-oxide-semiconductor capacitors with Al2O3 gate dielectric," Appl. Phys. Lett. 91, 063501 (2007).
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Chapter 7 C
ONCLUSIONSThis dissertation has focused on characterization and improvement of the atomic layer deposition Al2O3/InGaAs, InAs interfaces. In order to improve the interfaces quality, various combinations of ex-situ chemical treatments and in-situ TMA pretreatment were used and compared. Besides, the effect of annealing conditions on the interfaces quality was also studied. The followings are the conclusions of this work.
We have studied the effect of TMA treatment on the native-oxide-covered, HCl-treated, and sulfide-treated n-InAs surfaces. The effect of TMA on the reduction of InAs native oxides was apparent almost after the first TMA pulse but significant amount of native oxides still remain if only TMA treatment was used. The combination of HCl or sulfide wet chemical treatments with dry TMA pretreatment made a strong effect in the reduction of InAs native oxides. Native oxides were significant removed by wet chemical surface treatments and further reduction was achieved by TMA treatment. Electrical characterization of Al2O3/n-InAs MOSCAPs with different kind of surface treatments showed that Al2O3/InAs interface quality with HCl plus TMA treatment was better than that using sulfide plus TMA treatment.
By deposition of Al2O3 at 300oC, the quality of Al2O3/InAs interfaces was improved significantly. C-V characteristics of Al2O3/n-InAs exhibited strong inversion behaviors and low frequency dispersion in both inversion and accumulation regimes. Low-frequency simulations were performed and Al2O3/InAs interface trap states profiles were extracted. The derived Dit profiles present a U-shape with a minimum in the Dit profiles located around the InAs conduction band minimum, i.e. donor-like traps are dominant inside bandgap. These donor-like traps were significant reduced by using wet chemical
98
plus TMA treatments. In addition, this study confirmed again the HCl plus TMA treatment is more effective than sulfide treatment in the improvement Al2O3/InAs interface quality.
The influence of surface treatment and gas annealing conditions on the inversions behaviors of Al2O3/n-In0.53Ga0.47As MOSCAPs structures has been studied. By using sulfide plus TMA treatment along with post deposition annealing in pure H2 gas at 500oC, Al2O3/n-In0.53Ga0.47As MOSCAPs exhibit strong inversion C-V responses. This behavior in Al2O3/n-In0.53Ga0.47As MOSCAPs was first time observed by using an ex-situ method.
In this study, beside the surface treatment, the H2 gas treatment also showed strong effect in the improvement of Al2O3/In0.53Ga0.47As interface quality, especially in the reduction of interface traps at lower-half In0.53Ga0.47As bandgap. Low Dit profiles were observed by simulation and the minimum Dit value of ~11011 eV-1cm-2 was confirmed by both simulation and conductance method.
The electrical properties of Al2O3/InxGa1-xAs MOSCAPs structures with different In content of 0.53, 0.7 and 1 (InAs) have been investigated. Higher In content materials usually have lower band gap, higher electron mobility and higher intrinsic carrier density.
These properties lead to the different electrical properties for the Al2O3/InxGa1-xAs structures. Results showed clearly the decrease of minority carrier response time R with the increase of In content. C-V frequency dispersions in accumulation regions seem mostly due to border traps in oxide rather than due to interface traps. The conductance contours at different temperatures trace the movement of Fermi level at varied gate bias for the case of In0.53Ga0.47As but not for In0.7Ga0.3As and InAs due to the contribution of inversion layer. Al2O3/In0.53Ga0.47As Dit profile extracted by conductance method is in good agreement with that extracted by simulation. The increase of leakage current in In-rich Al2O3/InxGa1-xAs structures indicated larger probability of holes and electrons tunneling though oxide due to the increase of intrinsic carrier density and the reduction of electron effective mass in In-rich samples.
99
B
IOGRAPHYTrinh Hai Dang was born in Thanh Hoa, Vietnam in October 1979. He received his bachelor of physics degree in Faculty of Physics, Hanoi National University of Education (HNUE), Hanoi, Vietnam in July 2001 and Master of Science degree in International Training Institute for Materials Science (ITIMS), Hanoi University of Technology (HUT), Hanoi, Vietnam in July 2003. He worked at Faculty of Physics, HNUE, Hanoi, Vietnam as a lecture from August 2001 to January 2007. From February 2007 to present, he enrolled into the Doctoral program at Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan under the guidance of Prof. Dr.
Edward Yi Chang. His research interests include high k/III-V interface engineering and III-V MOSFET application for high speed, low power logic devices.
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L
IST OFP
UBLICATIONS Journal Articles1. H. D. Trinh, G. Brammertz, E. Y. Chang, C. I. Kuo, C. Y. Lu, Y. C. Lin, H. Q.
Nguyen, Y. Y. Wong, B. T. Tran, K. Kakushima, and H. Iwai, “Electrical Characterization of Al2O3/n-InAs Metal-Oxide-Semiconductor Capacitors with Various Surface Treatments,” IEEE Electron Device Lett. 32, 752-754 (2011).
2. Hai-Dang Trinh, Edward Yi Chang, Yuen-Yee Wong, Chih-Chieh Yu, Chia-Yuan Chang, Yueh-Chin Lin, Hong-Quan Nguyen, and Binh-Tinh Tran, “Effects of Wet Chemical and Trimethyl Aluminum Treatments on the Interface Properties in Atomic Layer Deposition of Al2O3 on InAs,” Japanese J. Appl. Phys. 49, 111201 (2010).
3. H. D. Trinh, E. Y. Chang, P. W. Wu, Y. Y. Wong, C. T. Chang, Y. F. Hsieh, C. C.
Yu, H. Q. Nguyen, Y. C. Lin, K. L. Lin, and M. K. Hudait, “The influences of surface treatment and gas annealing conditions on the inversion behaviors of the atomic-layer-deposition Al2O3/n-In0.53Ga0.47As metal-oxide-semiconductor capacitor,” Appl. Phys. Lett. 97, 042903 (2010).
4. 張翼 金海光 謝廷恩 張嘉華 林岳欽, “高介電氧化層/三五族金屬氧化物半導體
場效電晶體：發展近況,” (E. Y. Chang, H. D. Trinh, T. G. Xie, C. H. Chang, Y. C.
Lin, “High k/III-V Metal Oxide Semiconductor Field Effect Transistors: Current Status”), Taiwan nano newsletter 23, 37-41 (2010).
5. Shih-Hsuan Tang, Edward Yi Chang, Mantu Hudait, Jer-Shen Maa, Chee-Wee Liu, Guang-Li Luo, Hai-Dang Trinh, and Yung-Hsuan Su, “High quality Ge thin film grown by ultrahigh vacuum chemical vapor deposition on GaAs substrate,” Appl.
Phys. Lett. 98, 161905 (2011).
6. C.-T. Chang, T.-H. Hsu, E.Y. Chang, Y.-C. Chen, H.-D. Trinh and K.J. Chen,
“Normally-off operation AlGaN/GaN MOS-HEMT with high threshold voltage,”
Electron. Lett. 46, 1280-1281 (2010).
7. C.-Y. Chang, H.-T. Hsu, E. Y. Chang, H.-D. Trinh, and Y. Miyamoto, “InAs-Channel Metal-Oxide-Semiconductor HEMTs with Atomic-Layer-Deposited Al2O3 Gate Dielectric,” Electrochem. Solid-State Lett. 12, H456-H459 (2009).
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8. Nguyen Minh Thuy, Do Thi Sam, Trinh Hai Dang and Le Van Hong. “Electrical properties of superconducting Bi-2212 thick films,” J. Magnetism and Magnetic Material 262, 526-531 (2003).
Conferences
1. C. C. Yu, H. D. Trinh, B. H. Liu, C. C. Kei, C. N. Hsiao, D. P. Tsai, “Dielectric Performance of Post Deposition Treated Al2O3 Films Prepared by Using Parallel-Plate Electrode PEALD,” the AVS 58th Annual International Symposium and Exhibition, Nashville, Tennessee, USA, Oct 30 - Nov 4, 2011 (accepted).
2. H. D. Trinh, E.Y. Chang, C. I. Kuo, H. Q. Nguyen, K. L. Lin, Y. Y. Wong, C. C.
Chung, Y. C. Lin, C. H. Chang, Y. S. Chiu, B. T. Tran, and C. L. Nguyen, “Atomic Layer Deposition of Al2O3/n-InxGa1-xAs structures with different In content (x = 0.53-1),” the 38th International Symposium on Compound Semiconductors (ISCS 2011), Berlin, Germany, May 22-26, 2011.
3. H. Q. Nguyen, E. Y. Chang, H. D. Trinh, H.W. Yu, Y.Y. Wong, H. H. Vu, T. B.
Tran, K. L. Lin, C. C. Chung, C. H. Hsu, W .C. Wang and C. L Nguyen, “High quality 1eV InGaAs on GaAs substrate for inverted metamorphic solar cell by MOCVD,” the 38th International Symposium on Compound Semiconductors (ISCS 2011), Berlin, Germany, May 22-26, 2011.
4. Yuen-Yee Wong, Edward Yi Chang, Wei-Ching Huang, Hai-Dang Trinh, Chun-Yen Chang, “Reduction of Parallel Conduction at the Regrowth Interface of GaN Template Using Nitridation,” the 38th International Symposium on Compound Semiconductors (ISCS 2011), Berlin, Germany, May 22-26, 2011.
5. B. Tran, E. Chang, K. Lin, H. Nguyen, and H. Trinh, “The Growth of High Quality
5. B. Tran, E. Chang, K. Lin, H. Nguyen, and H. Trinh, “The Growth of High Quality