Bae Systems Information and Electronic Systems Integration Inc.

Kevin T Zawilski

Peter G Schunemann

Jeremy B Reeves

GaAs IR window slabs having largest dimensions that are greater than 8 inches, and preferably greater than 12 inches, are grown using the Horizontal Gradient Freeze (HGF) method. Heat extraction is simplified by using a shallow horizontal boat that is only slightly deeper than the desired window thickness, thereby enabling growth of large slabs while also minimizing material waste and fabrication cost as compared to slicing and shaping thick plates from large, melt-grown boules. Single crystal seeds can be used to optimize the final orientation of the slabs and minimize secondary nucleation, thereby maximizing yield. A conductive doped GaAs layer can be applied to the IR window slab to provide EMI shielding. The temperature gradient during HGF can be between 1° C./cm and 3° C./cm, and the directional solidification can be at a rate of between 0.25 mm/h and 2.5 mm/h.

Method of producing large EMI shielded GaAs infrared windows

A method of manufacturing a structurally competent, EMI-shielded IR window includes using a mathematical model that combines the Sotoodeh and Nag models to determine an optimal thickness and dopant concentration of a doped layer of GaAs or GaP. A slab of GaAs or GaP is prepared, and a doped layer of the same material having the optimal thickness and dopant concentration is applied thereto. In embodiments, the doped layer is applied by an HVPE method such as LP-HVPE, which can also provide enhanced GaAs transparency near 1 micron. The Drude model can be applied to assist in selecting an anti-reflective coating. If the model predicts that the requirements of an application cannot be met by a doped layer alone, a doped layer can be applied that exceeds the required IR transparency, and a metallic grid can be applied to improve the EMI shielding, thereby satisfying the requirements.

Method of optimizing the EMI shielding and infrared transparency of GaAs IR windows

A method of growing large GaAs or GaP IR window slabs by HVPE, and in embodiments by LP-HVPE, includes obtaining a plurality of thin, single crystal, epitaxial-quality GaAs or GaP wafers, cleaving the wafers into tiles having ultra-flat, atomically smooth, substantially perpendicular edges, and then butting the tiles together to form an HVPE substrate larger than 4 inches for GaP, and larger than 8 inches or even 12 inches for GaAs. Subsequent HVPE growth causes the individual tiles to fuse by optical bonding into a large 'tiled' single crystal wafer, while any defects nucleated at the tile boundaries are healed, causing the tiles to merge with themselves and with the slab with no physical boundaries, and no degradation in optical quality. A dopant such as Si can be added to the epitaxial gases during the final HVPE growth stage to produce EMI shielded GaAs windows.

Method of producing large GaAs and GaP infrared windows

A method of making GaP window slabs having largest dimensions of greater than 4 inches and GaAs IR window slabs having largest dimensions of greater than 8 inches, includes slicing and dicing at least one smaller GaAs or GaP single crystal boule, which can be a commercial boule, to form a plurality of rectangular slabs. The slabs are ground to have precisely perpendicular edges, which are polished to be ultra-flat and ultra-smooth, for example to a flatness of at least λ/10, and a roughness Ra of less than 10 nanometers. The slab edges are then aligned and fused via optical-contacting/bonding to create a large GaAs or GaP slab having negligible bond interface losses. A conductive, doped GaAs or GaP layer can be applied to the window for EMI shielding in a subsequent vacuum deposition step, followed by applying anti-reflection (AR) coatings to one or both of the slab faces.

Method of producing large EMI shielded GaAs and GaP infrared windows

A system and method for producing bulk GaAs with an increased carrier lifetime of at least 10 microseconds is provided. The system and method of producing the GaAs crystal involves using a technique called low pressure hydride vapor phase epitaxy (LP-HVPE). In this technique, a gas containing Ga (typically GaCl) is reacted with a gas containing As (typically AsH) at the surface of a GaAs substrate. When grown under the proper conditions, the epitaxial, vapor grown GaAs crystal has ultra-long free carrier lifetimes of at least one order of magnitude greater than that of the previous lifetime of 1 microsecond. This very long free carrier lifetime GaAs will be particularly useful as a semiconductor radiation detector material and is also expected to be useful for many other applications than include medical imaging, solar cells, diode lasers, and optical limiters and other applications.

Ultra long lifetime gallium arsenide

A novel bulk GaAs with an increased carrier lifetime of at least 10 microseconds has been produced. This novel GaAs has many uses to improve optical and electrical devices. The method of producing the GaAs crystal involves using a technique called low pressure hydride vapor phase epitaxy (LP-HVPE). In this technique, a gas containing Ga (typically GaCl) is reacted with a gas containing As (typically AsH) at the surface of a GaAs substrate. When grown under the proper conditions, the epitaxial, vapor grown GaAs crystal has ultra-long free carrier lifetimes of at least one order of magnitude greater than that of the previous art of 1 microsecond. This very long free carrier lifetime GaAs will be particularly useful as a semiconductor radiation detector material and is also expected to be useful for many other applications than include medical imaging, solar cells, diode lasers, and optical limiters and other applications.

CdSiPcrystals with sizes and optical quality suitable for use as nonlinear optical devices are disclosed, as well as NLO devices based thereupon. A method of growing the crystals by directional solidification from a stoichiometric melt is also disclosed. The disclosed NLO crystals have a higher nonlinear coefficient than prior art crystals that can be pumped by solid state lasers, and are particularly useful for frequency shifting 1.06 &#x3bc;m, 1.55 &#x3bc;m, and 2 &#x3bc;m lasers to wavelengths between 2 &#x3bc;m and 10 &#x3bc;m. Due to the high thermal conductivity and low losses of the claimed CdSiPcrystals, average output power can exceed 10 W without severe thermal lensing. A 6.45 &#x3bc;m laser source for use as a medical laser scalpel is also disclosed, in which a CdSiPcrystal is configured for non-critical phase matching, pumped by a 1064 nm Nd:YAG laser, and temperature-tuned to produce output at 6.45 &#x3bc;m.

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Arlington, MA, United States of America

Kevin T Zawilski