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Vertical Bridgman Growth of Large ZnGeP2 Single Crystals for High Power Applications
|Chunhui Yang 1, Zuotao Lei 1, Chong-Qiang Zhu 1, Chao Xu 1, Galina A. Verozubova 2|
1. Harbin Institute of Technology (HIT), No.92, West Da-Zhi Street,Harbin, Heilongjiang, Harbin 150001, China
Zinc germanium diphosohide (ZnGeP2) belongs to the chalcopyrite family with a direct band gap, and it is a ternary analog of the III-V group binary compound GaP with the zinc-blende structure. However, the chalcopyrite structure is tetragonally distorted from the simpler zinc-blende structure. Due to the distorted structure relative to its binary analogue, ZnGeP2 exhibits a far wider range of physical properties. ZnGeP2 has large nonlinear optical coefficient (d36=75 pm·V-1), a wide transparency range from 0.74 to 12μm, sufficient birefringence (Δn= 0.04) for type I and type II phase matching, and relatively high thermal conductivity (0.35W·cm-1·K-1) for high average power applications. All these physical properties make ZnGeP2 suitable for frequency conversion applications such as tunable mid-infrared optical parametric oscillator (OPO) laser systems. The main goal of the present work is to systematically study and deeply discuss the growth, optical properties and applications of ZnGeP2.
Firstly, ZnGeP2 polycrystalline ingots were synthesized by two-temperature method, and the maximum mass is about 470g for one run. Fig.1 shows the synthesized ZnGeP2 ingots with 470g. The XRD suggests that they show chalcopyrite structure, high pure and good crystallinity. The ingots are suitable for growth as raw materials. Moreover, the study indicates that the more the charge amount, the higher the yield of product.
Fig.1 The synthesized ZnGeP2 polycrystalline ingots with 470g
Secondly, ZnGeP2 crystals were grown by Vertical Bridgman technique, and the largest size is about Φ50mm×140mm. Fig.2 shows the as-grown ZnGeP2 crystals.The XRD and rocking curves suggest that they show good crystallinity and single phase, the XRF indicates that the as-grown ZnGeP2 is stoichiometric, and the absorption coefficients of as-grown ZnGeP2 are 0.05-0.08cm-1 at 2.05µm for o-light. However, the absorption coefficients of annealed and other post-treated ZnGeP2 reduce to 0.01-0.03cm-1 at 2.05µm for o-light. The crystals are suitable for frequency conversion applications.
Fig.2 The as-grown ZnGeP2 crystals
Finally, the ZnGeP2 devices were tested for OPO. The ZnGeP2 crystals were cut to 6mm×6mm×24mm in sizes after thermal annealing. Both surfaces of the crystal were carefully polished and antireflection coated for pump, signal, and idler lights. The ZnGeP2-OPO devices are shown in Fig.3. Fig.4 shows the ZnGeP2-OPO experiment setup. The OPO output wavelengths were in the spectral range of 3-5 mm. The results suggest that the output power of 30W is obtained pumping at 2.09µm and the conversion efficiency is 56%. Thus, ZnGeP2 is an excellent OPO material and is acceptable for the fabrication of the infrared nonlinear optical device
Fig.3 The ZnGeP2-OPO devices
Fig.4 The ZnGeP2-OPO experiment setup
Presentation: Oral at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, General Session 2, by Chunhui Yang
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17
Submitted: 2013-04-14 16:21 Revised: 2013-07-19 10:11