Impact of Crucible Bottom Shape on the Growth of Congruent Lithium Niobate Crystals by Czochralski Method

doi:10.15541/jim20240207

Abstract

Abstract:

Lithium niobate crystal, combining its piezoelectric, nonlinear, electro-optical, and photorefractive properties, along with its stable physicochemical characteristics, has great potential for applications in integrated optics. However, designing thermal field for large-size lithium niobate crystal growth presents considerable challenges, considering the crucible shape being an important factor that significantly influences the crystal growth in which the diameter and height are compulsively restricted to the factors such as load capacity and crystal diameters. In this study, 4-inch congruent lithium niobate crystals were grown by using crucibles with two types of bottom shapes. The impacts of crucible bottom shape on the axial temperature gradient within the crystal and the melt near the crystal-melt interface, and the temperature distribution within the melt below the crystal-melt interface, were analyzed by numerical simulation. The impact of the crucible bottom shape on crystal growth was analyzed in contrast to crystal growth results. It is found that changes in the crucible bottom shape lead to variations in the temperature difference along the crucible sidewall and the temperature gradient within the melt, thereby altering the strength of natural convection in the melt. Compared to crucible with slipped bottom corner, the axial temperature gradient near the crystal-melt interface within the crystal and melt is large when using the crucible with curved bottom corner, and the axial temperature gradient within the melt below the crystal-melt interface is also large, and the natural convection is strong. Therefore, this study helps to solve the problems such as the unwanted crystal growth ridge spreading and the overgrowth of cellular interface.

Key words: crystal growth, lithium niobate crystal, crucible, temperature gradient, natural convection, crystal- melt interface

CLC Number:

O782

HAO Yongxin, QIN Juan, SUN Jun, YANG Jinfeng, LI Qinglian, HUANG Guijun, XU Jingjun. Impact of Crucible Bottom Shape on the Growth of Congruent Lithium Niobate Crystals by Czochralski Method[J]. Journal of Inorganic Materials, 2024, 39(10): 1167-1174.

Figures/Tables 11

Fig. 1 Schematic diagram of the 4-inch CLN crystal growth thermal field by Czochralski method Unit: mm

Fig. 2 Schematic diagram of the crucible bottom shape and position of the crucible relative to the induction coil for 7 times crystal growth (a) Experiment 1; (b) Experiment 2; (c) Experiment 3; (d) Experiment 4-7

Table 1 Operating parameters used for numerical simulation

Description	Value
Crucible inner radius /mm	160
Crucible wall thickness /mm	1.5
Height and width of the slipped bottom corner /mm	30
Radius of the curved bottom corner /mm	15
Crystal density /(kg·m^-3)	4640
Melt density /(kg·m^-3)	3530-3670
Crystal thermal conductivity /(W·m^-1·K^-1)	3.539
Melt thermal conductivity /(W·m^-1·K^-1)	4.5
Melt point /℃	1252
Thermal expansion coefficient /K^-1	1.7×10^-4
Crystal diameter /mm	105
Emissivity	0.3
Pulling rate /(mm·h^-1)	1.5
Rotate rate /(r·min^-1)	7

Fig. 3 Axial temperature gradients within the melt near the crystal-melt interface at different stages of body growth

Fig. 4 Axial temperature gradients within the crystal near the crystal-melt interface at different stages of body growth

Table 2 Axial temperature gradient at the melt centre near the crystal-melt interface (Gmelt)

L/mm	G_melt by using C-S /(℃·cm^-1)	G_meltby using C-C/(℃·cm^-1)	Percentage of promotion/%
5	8.05	9.48	17.8
20	5.75	7.28	26.6
35	3.78	5.63	48.9
50	1.39	3.80	173.3

Table 3 Axial temperature gradient at the crystal centre near the crystal-melt interface (Gcrystal)

L/mm	G_crystal by using C-S/(℃·cm^-1)	G_crystal by using C-C/(℃·cm^-1)	Percentage of promotion/%
5	14.35	16.92	17.9
20	10.36	12.87	24.2
35	7.06	10.07	42.6
50	3.06	7.15	133.7

Fig. 5 Schematic temperature distributions of crystal, melt and crucible at different stages of body growth (a) L=5 mm @C-S; (b) L=20 mm @C-S; (c) L=35 mm @C-S; (d) L=50 mm @C-S; (e) L=5 mm @C-C; (f) L=20 mm @C-C; (g) L=35 mm @C-C; (h) L=50 mm @C-C

Fig. 6 Temperature distributions along the axis of central melt at different stage of body growth

Fig. 7 Pictures of crystals grown before and after promoting the position of the crucible relative to the induction coil using crucible with slipped bottom corner (experiments 1, 2) (a) Side of crystal CLN-CS-1; (b) Bottom interface of crystal CLN-CS-1; (c) Side of crystal CLN-CS-2; (d) Bottom interface of crystal CLN-CS-2

Fig. 8 Pictures of crystals grown by using crucible with curved bottom corner (experiments 4-7) (a) Side of crystal CLN-CC-1; (b) Bottom interface of crystal CLN-CC-1; (c) Side of crystal CLN-CC-2; (d) Bottom interface of crystal CLN-CC-2; (e) Side of crystal CLN-CC-3; (f) Bottom interface of crystal CLN-CC-3; (g) Side of crystal CLN-CC-4; (h) Bottom interface of crystal CLN-CC-4

References 25

[1]	BOES A, CHANG L, LANGROCK C, et al. Lithium niobate photonics: unlocking the electromagnetic spectrum. Science, 2023, 379(6627): eabj4396.
[2]	KONG Y F, BO F, WANG W W, et al. Recent progress in lithium niobate: optical damage, defect simulation, and on-chip devices. Advanced Materials, 2020, 32(3): 1806452.
[3]	SÁNCHEZ-DENA O, FIERRO-RUIZ C D, VILLALOBOS- MENDOZA S D, et al. Lithium niobate single crystals and powders reviewed—Part I. Crystals, 2020, 10(11): 973.
[4]	LIU H D, WANG W W, ZHANG Z Z, et al. Defect structure of lithium niobate crystals. Journal of Synthetic Crystals, 2024, 53(3): 355.
[5]	BURROWS L. Now entering, lithium niobate valley. (2017-12-21) [2024-04-13]. https://seas.harvard.edu/news/2017/12/now-entering-lithium-niobate-valley.
[6]	XIE Z D, BO F, LIN J T, et al. Recent development in integrated lithium niobate photonics. Advances in Physics: X, 2024, 9(1): 2322739.
[7]	TIAN X H, SHANG M H, ZHU S N, et al. Lithium niobate based photonic quantum devices and integration technology: opportunities and challenges. Physics, 2023, 52(8): 534.
[8]	YANG R G, CHEN G. Thermal conductivity modeling of periodic two-dimensional nanocomposites. Physical Review B, 2004, 69(19): 195316.
[9]	SAADATIRAD M, TAVAKOLI M H, KHODAMORADI H, et al. Effect of the pulling, crystal and crucible rotation rate on the thermal stress and the melt-crystal interface in the Czochralski growth of germanium crystals. CrystEngComm, 2021, 23(39): 6967.
[10]	LU C W, CHEN J C. Numerical simulation of thermal and mass transport during Czochralski crystal growth of sapphire. Crystal Research and Technology, 2010, 45(4): 371.
[11]	YAO S, WANG J, LIU H, et al. Growth, optical and thermal properties of near-stoichiometric LiNbO₃ single crystal. Journal of Alloys and Compounds, 2008, 455(1/2): 501.
[12]	TAO D J, ZHU G X, YAN R S, et al. Czochralski growth of gadolinium gallium garnet (GGG) crystals. Chinese Journal of Quantum Electronics, 2003, 20(5): 550.
[13]	TAVAKOLI M H, WILKE H, CRNOGORAC N. Influence of the crucible bottom shape on the heat transport and fluid flow during the seeding process of oxide Czochralski crystal growth. Crystal Research and Technology, 2007, 42(12): 1252.
[14]	MOKHTARI F, BOUABDALLAH A, ZIZI M, et al. Combined effects of crucible geometry and Marangoni convection on silicon Czochralski crystal growth. Crystal Research and Technology, 2009, 44(8): 787.
[15]	TAVAKOLI M H, MOHAMMADI-MANESH E, OJAGHI A. Influence of crucible geometry and position on the induction heating process in crystal growth systems. Journal of Crystal Growth, 2009, 311(17): 4281.
[16]	SAEEDI H, ASADIAN M, ENAYATI S, et al. The effect of crucible bottom deformation on the quality of Nd: GGG crystals grown by Czochralski method. Crystal Research and Technology, 2011, 46(12): 1229.
[17]	KHODAMORADI H, TAVAKOLI M H, MOHAMMADI K. Influence of crucible and coil geometry on the induction heating process in Czochralski crystal growth system. Journal of Crystal Growth, 2015, 421: 66.
[18]	NGUYEN T H U, CHEN J C, CHEN C C. Effects of different crucible shapes on heat and oxygen transport during continuous Czochralski silicon crystal growth. Journal of Crystal Growth, 2024, 626: 127474.
[19]	QIN J, SUN J, HAO Y X, et al. Effect of exposed crucible wall on the Czochralski growth of an LN crystal. CrystEngComm, 2023, 25(3): 450.
[20]	闵乃本. 晶体生长的物理基础. 南京: 南京大学出版社, 2019: 21-23
[21]	TSUKADA T, KAKINOKI K, HOZAWA M, et al. Numerical and experimental studies on crack formation in LiNbO₃ single crystal. Journal of Crystal Growth, 1997, 180(3/4): 543.
[22]	ZHONG W Z, LUO H S, HUA S K. Growth units and crystal morphology of lithium niobate (LN) crystal. Journal of Synthetic Crystals, 1994, 23(4): 255.
[23]	HUA S K, JAN Y, ZHONG W Z. Crystallisation habits of lithium niobate crystals. Journal of Synthetic Crystals, 1983, 12(1): 7.
[24]	MIN N B. Cellular interface and cellular structure due to constitutional supercooling in Czochralski growth LiNbO₃ single crystals. Acta Physics Sinica, 1979, 28(1): 33.
[25]	MIN N B, ZHOU F Q. Experimental investigation of stability of planar crystal-melt interface and evolution of cellular interface during Czochralski growth of LiNbO₃ single crystals doped with yttrium. Acta Physica Sinica, 1986, 35(12): 1603.