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A development of the LED TMGa precursor reuse technology
Materials Letters 93 (2013) 153–156
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
A development of the LED TMGa precursor reuse technology Jae-sik Yoon a,n, Jae-yeol Yang a, Ji-myon Lee b,n, Soon-jik Hong c, Hyun-Seon Hong d a
Korea Basic Science Institute, 169-148 Gwahangno Yusung-gu, Daejeon 305-806, Republic of Korea Division of Materials Science and Metallurgical Engineering, Sunchon National University, 315 Maegok-dong, Sunchon 540–742, Republic of Korea Division of Advanced Materials Engineering, Kongju National University, 56 Gongju Daehangno, Gongju 314–701, Republic of Korea d Advanced Materials & Processing Center, Institute for Advanced Engineering, 633-2 Cheoin-gu, Yongin-si, Gyeonggi-do 449–863, Republic of Korea b c
a r t i c l e i n f o
abstract
Article history: Received 24 August 2012 Accepted 16 November 2012 Available online 27 November 2012
Trimethylgallium is adopted as a metal organic precursor to develop GaN, which is a basis for power source, and LED with regard to metal organic chemical vapor deposition. After use, however, about 10% of the total usage of TMGa remains within the canister, and thus this study aims to develop the collection and refinement process through which the remaining amount can be reused. The TMGa storage canister used in the TMGa LED process is collected and transferred to the storage canister for refinement, and it turns out that the amount of recovery is more than 98%. In addition, the result of analyzing the impurity content of TMGa after the refinement process shows that the content of the entire impurities is 0.1 ppm, which is lower than 10–100 ppm, the figure of existing impurities that commercial TMGa may contain. In the NMR analysis of defective chemical bonding of TMGa or (CH3)3Ga, clear (CH3)3Ga peak is observed with no defective structure of bonding. & 2012 Elsevier B.V. All rights reserved.
Keywords: Trimethylgallium Metal organic precursor Metal organic chemical vapor deposition Refinement Collection Reuse
1. Introduction Trimethlygallium (TMGa, (CH3)3Ga) was reported in a thesis (1933) [1–3], and thereafter a number of methods to manufacture (CH3)3Ga have been reported in papers [3–5]. TMGa has been widely used as a source to develop high quality GaAs which is an organic metal vapor phase epitaxy (MOVPE) device [6–9] also used for common organic metal compounds [10–12]. The method to produce TMGa has been widely known, and foreign companies such as Chemtura and Rohm and Haas are exclusively manufacturing and supplying it. Due to the risk of explosion in manufacturing, there is no domestic entity that attempts to manufacture it currently. TMGa chemical properties are shown that formula is (CH3)3Ga with colorless and liquid type, and melting point and boiling point is 16 1C and 56 1C, respectively, also flammable with air. In general, about 17 ppm (0.0017%) of gallium (Ga) is buried under the earth’s crust, and its use is quite limited. In industries, this element has been adopted mainly to LED manufacturing in the forms of ternary and quaternary compounds based on GaN, and recently its demand has been drastically increasing. Further, the usage is being widened to devices of high current and high voltage because of its characteristics. As a result, there is a
n
Corresponding authors. Tel.: þ 82 42 865 3635; fax: þ 82 42 865 3499. E-mail addresses: [email protected] (J.-s. Yoon), [email protected] (J.-m. Lee). 0167-577X/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2012.11.061
deficiency in supply of TMGa in 2010. As GaN is developed on a sapphire electronic board according to MOCVD in utilization of TMGa, a precursor of LED manufacturing processes, TMGa within the canister remains as much as about 10% after use. Thus, this study aims to develop the technology to collect the remaining TMGa in the canister after use, refine it, and reuse it. If the attempt to reuse TMGa through this technology is successful, about 2 t of 20 t of TMGa (or 10% of its yearly domestic consumption) can be reused, which will result in the importrestrictive effect of as much as 10 billion won in economic value.
2. Experiment The reuse process of TMGa is as follows: First of all, the TMGa storage canister is collected after use and the remaining amount is collected to the sealed collecting canister. Since TMGa is combustible and explosive in the air because of its chemical nature, TMGa canister is upset in the atmosphere of N2 within the glove box, N2 gas is infused, and then it is collected in the collecting canister. As stated above, once a certain amount of TMGa is collected, the refining process for high purification is necessary. A small quantity of impurities of heavy metals such as Fe, Cr, Ni, and Si are contained in TMGa, and thus the refinement process is conducted for high purification. The refinement system is represented in Fig. 1(a) below. As the evaporation temperature is 56 1C and the ambient temperature about 60 1C, TMGa flows upward in a gaseous state. The vaporized
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J. Yoon et al. / Materials Letters 93 (2013) 153–156
Fig. 1. The purification system for trimethylgallium (TMGa)(a) and flowchart for purification(b).
Table 1 Analysis of impurities in the TMGa using ICP-MS and ICP-AES(a) and the yield of residual quantity TMGa(b). (a)
(b)
Impurity
Content (ppm)
Impurity
Content (ppm)
Number
Amount of residual(g)
Amount of recovery(g)
Yield(%)
Al Ca Fe Mg Si Zn Li Mg V Cr Mn Co Ni Cu Se Y Nb
o 0.01 o 0.005 o 0.005 o 0.005 o 0.01 o 0.005 o 0.002 o 0.002 o 0.002 o 0.002 o 0.002 o 0.002 o 0.002 o 0.002 o 0.002 o 0.002 o 0.002
Pd Ag Cd Sn Sb Te Ba La Tb W Pt Pb Bi U Ge Hg –
o0.002 0.0048 o0.002 o0.002 o0.002 o0.002 o0.002 o0.002 o0.002 o0.002 o0.002 o0.002 o0.002 o0.002 o0.002 o0.002 –
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
323 350 362 302 327 531 486 394 362 301 383 490 531 384 401 343 490
310 340 360 300 320 530 480 380 360 300 380 490 520 380 400 340 480
95.975 97.143 99.448 99.338 97.859 99.812 98.765 96.447 99.448 99.668 99.217 100.000 97.928 98.958 99.751 99.125 97.959
Fig. 2. NMR spectrum of TMGa.
TMGa through the 2-step column and cooling line becomes liquid and is collected into the receiver. Thereafter, the elements collected in the receiver go through a quantitative analysis and
chemical structure analysis for the impurities. Specimens whose purity and structure are in good condition are transferred to the storage canister, while the defective specimens go through the
J. Yoon et al. / Materials Letters 93 (2013) 153–156
refinement process again. The general order of the TMGa reuse process is presented in Fig. 1(b) below. As for the collection of remaining TMGa within the canister, the weight is measured every time when it is collected to get the average, and the amount of recovery is compared before and after the refinement. To analyze the purity of refined TMGa and the content of impurities, the inductively coupled plasma-mass spectrometer (ICP-MS) and atomic emission spectroscopy or AES (Elan 6100/Perkin Elmer, USA) are used. The pretreatment process for ICP-MS analysis, and the process is conducted in an N2 atmosphere since TMGa is very sensitive when it reacts to air. TMGa and isopropyl alcohol (IPA) are mixed in the ratio of 1:6 for pretreatment. The prepared solution is mixed with 20% nitric acid and heated for 6–8 h up to 130 1C to produce the white powder. This powder is diluted in a 2% nitric acid solution to analyze ICPMS and AES. Changes in the chemical structure after the refinement are examined by means of a nuclear magnetic resonance or NMR (Bruker AVANCE 500 MHz spectrometers). As for the specimen, D6C6 (NMR solvent) and TMGa are combined in the ratio of 5:5 and then measured in the NMR measuring tube. In addition, TMGa is inserted to the MOCVD device as a precursor for the LED GaN development test after refinement and the undoped GaN is developed. The resulting GaN is analyzed with regard to its structural, optical, and electric characteristics. As for the structural characteristics, FWHM of the XRD (BrukerAXS D8) rocking curve is calculated to measure the extent of crystallization, and the XRD phi scan is measured to check if it develops into the hexagonal GaN; that is, an LED GaN. As for the optical characteristics, the photoluminescence is measured to calculate the FWHM of the band edge emission. Lastly, for the electric characteristics, the HALL effect is measured to calculate the carrier concentration. The carrier concentration is calculated by means of Expression 1 below. n¼
Ix Bx edV H
Expression 1
here, I indicates the current, B the magnetic field, e the quantity of electric charge, and d the thickness of the GaN film.
3. Result and discussion Table 1(a) shows the ICP analysis result after the refinement of TMGa. The specimens are designed under the same condition of the TMG specimen pretreatment to enhance the accuracy of the analysis result. As for elements hard to detect with ICP-MS, most of the impurities within TMGa are detected and analyzed by means of ICP-AES. As a result of the analysis, high purity TMGa of
155
class 7 N (99.99999%) is gained, and various impurities such as Ag, Al, Cd, Cr, Cu, Fe, Ni, Sb, Si, Te, and Zn are detected although the content of the impurities is 0.01 ppm or less in general. In particular, impurities of heavy metals such as Si, Fe, and Al show the value of 0.01 ppm before refinement, but it became lower than that after refinement. This indicates that after the canister with TMGa is heated in the refinement, only TMGa is collected after evaporation, and the impurities of some heavy metals within the canister are readily separated, which results in great refinement efficiency. Table 1(b) shows the total amount of the collected TMGa in the canister from the TMGa-using one company. The entire amount of recovery is presented here. As in the table, the remaining amount at the canister after use is measured by means of an electronic scale before collection, and it is measured again after the transferring to the collective storage canister to gain the degree of collection. The degree of collection is gained based on the average after the amount of recovery is measured every time. As illustrated in the table, most of the TMGa that remains in the canister after use is collected, and the degree of collection is more than 98% on average. For the structural analysis after TMGa (chemical formula, (CH3)3Ga), NMR analysis is implemented, and the result is shown in Fig. 2. As in the NMR spectrum, the single peak of (CH3)3Ga is observed in the value of 1.752 ppm with no change in the chemical formation. In the values of 128.582 ppm, 128.390 ppm, and 128.192 ppm, C6D6 peak; that is, NMR solvent, is observed. This result shows that there is no chemical change of TMGa after refinement. It was thought that there would have been peak separation around the (CH3)3Ga peak if there was any chemical change [13]. This study shows that after refinement, TMGa has better characteristics than those of existing commercial TMGa in the analysis of impurities and structure. Based on this result, the refinement process is suitable for the development of GaN for commercial LED production. Thus, the undoped GaN is developed by means of the MOCVD method, and the structural characteristics are shown through X-ray diffraction (XRD) as in Fig. 3 below. Fig. 3(a) shows the XRD rocking curve spectrum. As the extent of crystallization is degraded, FWHM is enlarged. In the case of GaN developed by means of TMGa after refinement in this study, however, the value is 300.6 arcs. This value of FWHM is similar to that of GaN FWHM of elements that are commonly used now [14]. In addition, as in Fig. 3(b), it is clear that the GaN film shows the six-fold azimuthal symmetry consistent with the wurtzite crystal structure as GaN for LED.[15] Fig. 4 shows the PL spectrum of undoped GaN developed by means of TMGa after refinement. As shown in the figure, the band edge emission is observed around 3.45 eV, and two peaks due to emission are observed at the exciton level within the band edge
Fig. 3. The XRD spectra on the undoped GaN developed by mean TMGa after refinement, (a) XRD rocking curve (b) XRD phi scan.
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J. Yoon et al. / Materials Letters 93 (2013) 153–156
refinement are conducted, and the results show that the quality of TMGa is better than those of commonly used TMGa. GaN is developed by means of the MOCVD method with the precursor after refinement, and then the physical property is analyzed. The FWHM of the XRD rocking curve is calculated to determine the extent of crystallization, and the resulting value is 300.6. As 6 peaks are observed with an interval of 601 in the XRD phi scan, the development of GaN in the hexagonal structure is verified. Further, the band edge peak is observed in the optical analysis by means of PL, and the calculation of FWHM of the peak produced the value of 29.05 meV. The undoped GaN is of n-type, and the carrier concentration is 4.05 1016/cm3 according to the Hall effect measuring. As shown in the test result above, the collecting and refining system developed in this study demonstrates that TMGa could be reused in actual commercial lines.
Fig. 4. The PL spectrum on the undoped GaN developed by means of TMGa after refinement.
emission. Thus, to calculate FWHM of one peak, two peaks are distinguished by means of the multi-peak Gaussian function, and the result of FWHM calculation on the distinguished peak is 29.05 meV, which also is similar to the PL value of GaN currently utilized as an element [16]. The result of the Hall effect measurement, the value of carrier concentration is 4.05 1016/cm 3, which is similar to the value of common undoped GaN carrier concentration value; that is, 7 1016/cm 3 [14], thus the refined TMGa in this study is suitable for MOCVD as a precursor.
Acknowledgement This work was supported by the Korea Basic Science Institute (KBSI) Grant (T32604) to J.S. Yoon. Reference [1] [2] [3] [4] [5] [6] [7] [8]
4. Conclusion This study aims to develop a technology to collect the remaining amount of TMGa used in GaN manufacturing for LED, and to reuse it after refinement. Accordingly, the system to collect and refine TMGa after use is established, and the collecting and refining process is developed as well. In addition, to verify whether the process could be applied to actual LED industry, analyses on the impurities within TMGa and the structure after
[9] [10] [11] [12] [13] [14] [15] [16]
Kraus CA, Toonder FE. Proc Acad Sci 1933;19:292. Kraus CA, Toonder FE. Proc Acad Sci 1933;19:298. Kraus CA, Toonder FE. J Am Chem Soc 1933;55:3547. Starowieyski KB, Chwojnowski A, Jankowski K, Lewinski J, Zachara. J Appl Organomet Chem 2000;14:616. Wilberg E, Johannsen T, Strecher O. Z Anorg Allg Chem 1943;251:114. Zhang Z, Huang B, Cui D. Master Sci Eng B 2001;86:147. Barfels T, Fitting HJ, Jansons J, Tale IA, Veispals A, Von Czarnowski A, et al. Appl Surf Sci 2001;179:191. Watkins SP, Pinnington T, Hu J, Yeo P, Kluth M, Mason N, et al. J Cryst Growth 2000;221:166. Liu Z J, Atakan B, Kohse-Hoinghaus K, Katharina. J Cryst Growth 2000;219:176. Schwering H U, Olapinski H, Jungk E, Weidlein J. J Organomet Chem 1974;76:315. Wilson IL, Dehnicke K. J Organomet Chem 1974;67(2):229. Grimes RN, Rademaker WJ, Denniston ML, Bryan RF, Greene PT. J Am Chem Soc 1972;94:1865. Cerny Z, Machacek J, Fusek J, Kriz O, Casensky B. J Organomet Chem 1993;456:25. Kim KS, Oh CS, Lee WH, Lee KJ, Yang GM, Hong CH, et al. J Cryst Growth 2000;210:505. Nahhas A, Kim HK, Blachere. J Appl Phys Lett 2001;78:1511. Chichibu S, Azuhata T, Sota T, Nakamura S. J Appl Phys 1996;79:5.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
A development of the LED TMGa precursor reuse technology Jae-sik Yoon a,n, Jae-yeol Yang a, Ji-myon Lee b,n, Soon-jik Hong c, Hyun-Seon Hong d a
Korea Basic Science Institute, 169-148 Gwahangno Yusung-gu, Daejeon 305-806, Republic of Korea Division of Materials Science and Metallurgical Engineering, Sunchon National University, 315 Maegok-dong, Sunchon 540–742, Republic of Korea Division of Advanced Materials Engineering, Kongju National University, 56 Gongju Daehangno, Gongju 314–701, Republic of Korea d Advanced Materials & Processing Center, Institute for Advanced Engineering, 633-2 Cheoin-gu, Yongin-si, Gyeonggi-do 449–863, Republic of Korea b c
a r t i c l e i n f o
abstract
Article history: Received 24 August 2012 Accepted 16 November 2012 Available online 27 November 2012
Trimethylgallium is adopted as a metal organic precursor to develop GaN, which is a basis for power source, and LED with regard to metal organic chemical vapor deposition. After use, however, about 10% of the total usage of TMGa remains within the canister, and thus this study aims to develop the collection and refinement process through which the remaining amount can be reused. The TMGa storage canister used in the TMGa LED process is collected and transferred to the storage canister for refinement, and it turns out that the amount of recovery is more than 98%. In addition, the result of analyzing the impurity content of TMGa after the refinement process shows that the content of the entire impurities is 0.1 ppm, which is lower than 10–100 ppm, the figure of existing impurities that commercial TMGa may contain. In the NMR analysis of defective chemical bonding of TMGa or (CH3)3Ga, clear (CH3)3Ga peak is observed with no defective structure of bonding. & 2012 Elsevier B.V. All rights reserved.
Keywords: Trimethylgallium Metal organic precursor Metal organic chemical vapor deposition Refinement Collection Reuse
1. Introduction Trimethlygallium (TMGa, (CH3)3Ga) was reported in a thesis (1933) [1–3], and thereafter a number of methods to manufacture (CH3)3Ga have been reported in papers [3–5]. TMGa has been widely used as a source to develop high quality GaAs which is an organic metal vapor phase epitaxy (MOVPE) device [6–9] also used for common organic metal compounds [10–12]. The method to produce TMGa has been widely known, and foreign companies such as Chemtura and Rohm and Haas are exclusively manufacturing and supplying it. Due to the risk of explosion in manufacturing, there is no domestic entity that attempts to manufacture it currently. TMGa chemical properties are shown that formula is (CH3)3Ga with colorless and liquid type, and melting point and boiling point is 16 1C and 56 1C, respectively, also flammable with air. In general, about 17 ppm (0.0017%) of gallium (Ga) is buried under the earth’s crust, and its use is quite limited. In industries, this element has been adopted mainly to LED manufacturing in the forms of ternary and quaternary compounds based on GaN, and recently its demand has been drastically increasing. Further, the usage is being widened to devices of high current and high voltage because of its characteristics. As a result, there is a
n
Corresponding authors. Tel.: þ 82 42 865 3635; fax: þ 82 42 865 3499. E-mail addresses: [email protected] (J.-s. Yoon), [email protected] (J.-m. Lee). 0167-577X/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2012.11.061
deficiency in supply of TMGa in 2010. As GaN is developed on a sapphire electronic board according to MOCVD in utilization of TMGa, a precursor of LED manufacturing processes, TMGa within the canister remains as much as about 10% after use. Thus, this study aims to develop the technology to collect the remaining TMGa in the canister after use, refine it, and reuse it. If the attempt to reuse TMGa through this technology is successful, about 2 t of 20 t of TMGa (or 10% of its yearly domestic consumption) can be reused, which will result in the importrestrictive effect of as much as 10 billion won in economic value.
2. Experiment The reuse process of TMGa is as follows: First of all, the TMGa storage canister is collected after use and the remaining amount is collected to the sealed collecting canister. Since TMGa is combustible and explosive in the air because of its chemical nature, TMGa canister is upset in the atmosphere of N2 within the glove box, N2 gas is infused, and then it is collected in the collecting canister. As stated above, once a certain amount of TMGa is collected, the refining process for high purification is necessary. A small quantity of impurities of heavy metals such as Fe, Cr, Ni, and Si are contained in TMGa, and thus the refinement process is conducted for high purification. The refinement system is represented in Fig. 1(a) below. As the evaporation temperature is 56 1C and the ambient temperature about 60 1C, TMGa flows upward in a gaseous state. The vaporized
154
J. Yoon et al. / Materials Letters 93 (2013) 153–156
Fig. 1. The purification system for trimethylgallium (TMGa)(a) and flowchart for purification(b).
Table 1 Analysis of impurities in the TMGa using ICP-MS and ICP-AES(a) and the yield of residual quantity TMGa(b). (a)
(b)
Impurity
Content (ppm)
Impurity
Content (ppm)
Number
Amount of residual(g)
Amount of recovery(g)
Yield(%)
Al Ca Fe Mg Si Zn Li Mg V Cr Mn Co Ni Cu Se Y Nb
o 0.01 o 0.005 o 0.005 o 0.005 o 0.01 o 0.005 o 0.002 o 0.002 o 0.002 o 0.002 o 0.002 o 0.002 o 0.002 o 0.002 o 0.002 o 0.002 o 0.002
Pd Ag Cd Sn Sb Te Ba La Tb W Pt Pb Bi U Ge Hg –
o0.002 0.0048 o0.002 o0.002 o0.002 o0.002 o0.002 o0.002 o0.002 o0.002 o0.002 o0.002 o0.002 o0.002 o0.002 o0.002 –
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
323 350 362 302 327 531 486 394 362 301 383 490 531 384 401 343 490
310 340 360 300 320 530 480 380 360 300 380 490 520 380 400 340 480
95.975 97.143 99.448 99.338 97.859 99.812 98.765 96.447 99.448 99.668 99.217 100.000 97.928 98.958 99.751 99.125 97.959
Fig. 2. NMR spectrum of TMGa.
TMGa through the 2-step column and cooling line becomes liquid and is collected into the receiver. Thereafter, the elements collected in the receiver go through a quantitative analysis and
chemical structure analysis for the impurities. Specimens whose purity and structure are in good condition are transferred to the storage canister, while the defective specimens go through the
J. Yoon et al. / Materials Letters 93 (2013) 153–156
refinement process again. The general order of the TMGa reuse process is presented in Fig. 1(b) below. As for the collection of remaining TMGa within the canister, the weight is measured every time when it is collected to get the average, and the amount of recovery is compared before and after the refinement. To analyze the purity of refined TMGa and the content of impurities, the inductively coupled plasma-mass spectrometer (ICP-MS) and atomic emission spectroscopy or AES (Elan 6100/Perkin Elmer, USA) are used. The pretreatment process for ICP-MS analysis, and the process is conducted in an N2 atmosphere since TMGa is very sensitive when it reacts to air. TMGa and isopropyl alcohol (IPA) are mixed in the ratio of 1:6 for pretreatment. The prepared solution is mixed with 20% nitric acid and heated for 6–8 h up to 130 1C to produce the white powder. This powder is diluted in a 2% nitric acid solution to analyze ICPMS and AES. Changes in the chemical structure after the refinement are examined by means of a nuclear magnetic resonance or NMR (Bruker AVANCE 500 MHz spectrometers). As for the specimen, D6C6 (NMR solvent) and TMGa are combined in the ratio of 5:5 and then measured in the NMR measuring tube. In addition, TMGa is inserted to the MOCVD device as a precursor for the LED GaN development test after refinement and the undoped GaN is developed. The resulting GaN is analyzed with regard to its structural, optical, and electric characteristics. As for the structural characteristics, FWHM of the XRD (BrukerAXS D8) rocking curve is calculated to measure the extent of crystallization, and the XRD phi scan is measured to check if it develops into the hexagonal GaN; that is, an LED GaN. As for the optical characteristics, the photoluminescence is measured to calculate the FWHM of the band edge emission. Lastly, for the electric characteristics, the HALL effect is measured to calculate the carrier concentration. The carrier concentration is calculated by means of Expression 1 below. n¼
Ix Bx edV H
Expression 1
here, I indicates the current, B the magnetic field, e the quantity of electric charge, and d the thickness of the GaN film.
3. Result and discussion Table 1(a) shows the ICP analysis result after the refinement of TMGa. The specimens are designed under the same condition of the TMG specimen pretreatment to enhance the accuracy of the analysis result. As for elements hard to detect with ICP-MS, most of the impurities within TMGa are detected and analyzed by means of ICP-AES. As a result of the analysis, high purity TMGa of
155
class 7 N (99.99999%) is gained, and various impurities such as Ag, Al, Cd, Cr, Cu, Fe, Ni, Sb, Si, Te, and Zn are detected although the content of the impurities is 0.01 ppm or less in general. In particular, impurities of heavy metals such as Si, Fe, and Al show the value of 0.01 ppm before refinement, but it became lower than that after refinement. This indicates that after the canister with TMGa is heated in the refinement, only TMGa is collected after evaporation, and the impurities of some heavy metals within the canister are readily separated, which results in great refinement efficiency. Table 1(b) shows the total amount of the collected TMGa in the canister from the TMGa-using one company. The entire amount of recovery is presented here. As in the table, the remaining amount at the canister after use is measured by means of an electronic scale before collection, and it is measured again after the transferring to the collective storage canister to gain the degree of collection. The degree of collection is gained based on the average after the amount of recovery is measured every time. As illustrated in the table, most of the TMGa that remains in the canister after use is collected, and the degree of collection is more than 98% on average. For the structural analysis after TMGa (chemical formula, (CH3)3Ga), NMR analysis is implemented, and the result is shown in Fig. 2. As in the NMR spectrum, the single peak of (CH3)3Ga is observed in the value of 1.752 ppm with no change in the chemical formation. In the values of 128.582 ppm, 128.390 ppm, and 128.192 ppm, C6D6 peak; that is, NMR solvent, is observed. This result shows that there is no chemical change of TMGa after refinement. It was thought that there would have been peak separation around the (CH3)3Ga peak if there was any chemical change [13]. This study shows that after refinement, TMGa has better characteristics than those of existing commercial TMGa in the analysis of impurities and structure. Based on this result, the refinement process is suitable for the development of GaN for commercial LED production. Thus, the undoped GaN is developed by means of the MOCVD method, and the structural characteristics are shown through X-ray diffraction (XRD) as in Fig. 3 below. Fig. 3(a) shows the XRD rocking curve spectrum. As the extent of crystallization is degraded, FWHM is enlarged. In the case of GaN developed by means of TMGa after refinement in this study, however, the value is 300.6 arcs. This value of FWHM is similar to that of GaN FWHM of elements that are commonly used now [14]. In addition, as in Fig. 3(b), it is clear that the GaN film shows the six-fold azimuthal symmetry consistent with the wurtzite crystal structure as GaN for LED.[15] Fig. 4 shows the PL spectrum of undoped GaN developed by means of TMGa after refinement. As shown in the figure, the band edge emission is observed around 3.45 eV, and two peaks due to emission are observed at the exciton level within the band edge
Fig. 3. The XRD spectra on the undoped GaN developed by mean TMGa after refinement, (a) XRD rocking curve (b) XRD phi scan.
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J. Yoon et al. / Materials Letters 93 (2013) 153–156
refinement are conducted, and the results show that the quality of TMGa is better than those of commonly used TMGa. GaN is developed by means of the MOCVD method with the precursor after refinement, and then the physical property is analyzed. The FWHM of the XRD rocking curve is calculated to determine the extent of crystallization, and the resulting value is 300.6. As 6 peaks are observed with an interval of 601 in the XRD phi scan, the development of GaN in the hexagonal structure is verified. Further, the band edge peak is observed in the optical analysis by means of PL, and the calculation of FWHM of the peak produced the value of 29.05 meV. The undoped GaN is of n-type, and the carrier concentration is 4.05 1016/cm3 according to the Hall effect measuring. As shown in the test result above, the collecting and refining system developed in this study demonstrates that TMGa could be reused in actual commercial lines.
Fig. 4. The PL spectrum on the undoped GaN developed by means of TMGa after refinement.
emission. Thus, to calculate FWHM of one peak, two peaks are distinguished by means of the multi-peak Gaussian function, and the result of FWHM calculation on the distinguished peak is 29.05 meV, which also is similar to the PL value of GaN currently utilized as an element [16]. The result of the Hall effect measurement, the value of carrier concentration is 4.05 1016/cm 3, which is similar to the value of common undoped GaN carrier concentration value; that is, 7 1016/cm 3 [14], thus the refined TMGa in this study is suitable for MOCVD as a precursor.
Acknowledgement This work was supported by the Korea Basic Science Institute (KBSI) Grant (T32604) to J.S. Yoon. Reference [1] [2] [3] [4] [5] [6] [7] [8]
4. Conclusion This study aims to develop a technology to collect the remaining amount of TMGa used in GaN manufacturing for LED, and to reuse it after refinement. Accordingly, the system to collect and refine TMGa after use is established, and the collecting and refining process is developed as well. In addition, to verify whether the process could be applied to actual LED industry, analyses on the impurities within TMGa and the structure after
[9] [10] [11] [12] [13] [14] [15] [16]
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