Wafer scale Zinc Selenide (ZnSe) single crystals

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Directed Energy (DE);Advanced Materials

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OBJECTIVE: Develop a commercial single crystal growth process for 50mm diameter zinc selenide (ZnSe) wafers

DESCRIPTION: The need for high-brightness, compact infrared lasers operating in the mid-wave infrared (MWIR) through far infrared has long been established in the Global Strike Operational Imperative to address infrared missile threats. Beyond infrared countermeasures (IRCM), such frequencies have applications in spectroscopy, and imaging, for both military and commercial users. Frequency conversion devices based on quasi-phase matching (QPM) have been very successful with PPLN and the more recent development of orientation patterned (OP) GaAs. However, due to the intrinsic absorption losses in PPLN its usefulness is limited to wavelengths shorter than 4 µm. These limitations combined with the need for MWIR to far IR fueled the development of OP-GaAs. As with PPLN there are intrinsic material properties that limit OP-GaAs as a high brightness source for MWIR to far IR radiation. The two primary limitations are the 1.42 eV direct band gap at room temperature and strong absorption at wavelengths longer than 15 µm. GaAs’s band gap leads to strong two photon absorption at wavelengths shorter than 1.75 µm limiting the available pump sources. Zinc Selenide has a wider band gap, a modest nonlinear coefficient, and a wide transparency which are attractive for infrared countermeasure applications. The major obstacle to producing OP-ZnSe has been the lack of high quality wafer scale single crystal substrates, which are required for fabrication of OP-ZnSe templates. To date, single crystals of ZnSe have been grown by vapor phase, melt, and solution growth techniques, but the desired sizes and quality have not been achieved. In order to realize OP-ZnSe IR frequency conversion devices, large single crystals of ZnSe must be produced for fabrication of ZnSe OP-templates. This SBIR call is seeking the development of a crystal growth technique to provide high quality, optically clear ZnSe crystals 50mm in diameter.

PHASE I: Develop a scalable ZnSe growth process and then demonstrate a single crystal of ZnSe with a (100) orientation with at least 10x10x1mm dimensions.

PHASE II: Using the growth process established in Phase I, demonstrate and deliver a single crystal of ZnSe with a (100) orientation with at least 25mm in diameter and a 1mm thickness. Dicing and polishing the 25mm wafers with a scratch dig of 40-20.

PHASE III DUAL USE APPLICATIONS: Demonstrate and deliver a single crystal of ZnSe with a (100) orientation with at least 50mm in diameter and a 1mm thickness. Dicing and polishing the 50mm wafers with a scratch dig of 20-10.

REFERENCES:
1. Singh et al., Journal of Crystal Growth 312 (2010) 1142–1145.
2. Kolb, et al., Journal of Crystal Growth 7 (1970) 199-202.
3. Hum et al., C. R. Physique 8 (2007) 180-198.

KEYWORDS: Zinc Selenide; Crystal Growth; Infrared; Wafer; Single Crystal