The Heat Exchanger Method (HEM) of crystal growing was combined with the Fixed Abrasive Slicing Technology (FAST) to produce low-cost, high-quality sapphire substrates for deposition of the GaN family of compounds. Production quantities of 2-inch diameter blanks have been supplied, and 3-inch diameter material has been qualified. Current technology can be used to prepare sapphire blanks up to 6-inch diameter.

Multicrystalline silicon ingots of 55 cm × 55 cm cross section, 100 kg have been grown by the Heat Exchanger Method (HEM). Controlled growth features have been used to produce large grain size, vertically oriented grain boundaries, large areas of twins with low defect density and rejection of impurities to the top of the ingot. Ambient control has reduced C, N, and O concentration and minimized precipitates with no detectable metallic impurities. High performance solar cells have ben fabricated, and further improvements can be achieved by minimizing dislocation tangles and impurities in localized regions.

In modelocked laser systems, the shortest possible pulse width is determined by the Fourier transform of the spectral bandwidth of the pulse; the wider the spectral bandwidth, the shorter the pulse. Titanium-doped sapphire (Ti:sapphire) offers the widest gain bandwidth of any currently available laser gain material, enabling systems to deliver pulse widths shorter than 10fs (10−14s). Because of the short pulse durations, the peak power can be extremely high, and therefore Ti:sapphire lasers have been at the forefront of research into ultrafast, ultrahigh power lasers. These intense ultrashort laser pulses are the light source for fundamental studies of light–matter interactions. Interesting scientific results have been achieved with these lasers in the fields of high order harmonic and short pulse X-ray generations, high density plasmas, relativistic acceleration, relativistic nonlinear optics, time resolved X-ray diffraction with unprecedented time resolution and others. Researchers have recently achieved near petawatt (1015W) peak power laser operation using large diameter Ti:sapphire amplifiers, and are developing higher power lasers for research into high energy physics. However, the saturation fluence of the Ti:sapphire gain medium is limited to about 1J/cm2. Thus, continued scale up in peak laser energy requires the scale up of high-quality Ti:sapphire crystals for laser amplifiers. Current demand is for 100mm diameter crystals, and this requirement is projected to grow up to 250mm diameter crystals in a few years. To address this technological bottleneck, Crystal Systems has upgraded its heat exchanger method (HEM) furnaces and fabrication and metrology to scale up the production of Ti:sapphire crystals. Currently, 175mm diameter Ti:sapphire amplifier crystals are being fabricated from high-quality 208mm boules.

Magneto-rheological finishing (MRF) imprinting techniques have been applied to Ti:sapphire crystals to compensate for submillimeter distortions, thereby, improving the transmitted wavefront and increasing the availability of large aperture parts.

Signifigant enhancements of the flexural strength of a- and c- plane sapphire by means of "super polishing" was first reported be McHargue and Snyder [Proc. SPIE 2013, 135 (1993)]. The improvement was attributed to the removal of residual mechanical polishing damage. More recently, a comprehensive series of eperiements was carried out by Crystal Systems for the specific purpose of assessing the effects of various polishing procedures on the high-temperature strength of c-plane sapphire. Subsequent testing at room temperature confirmed that chemomechanical polishing improves both the effective strength and the strength distriution. In this contribution we take advantage of the methodology previously used by Klein et al. [Opt. Eng. 41, 3151 (2002)] to perform a correct Weibull statistical analysis of biaxial flexure-strength data genenrated in the course of Crystal Systems' investigations. We demonstrate that chemomechanical polishing procedures can improve the high-temperature characteristic strength of c-plane sapphire by 150% and the room-temperature Weibull modulus by 100%.

The world's largest sapphire boules up to 340-mm. diameter are produced by the Heat Exchanger Method (HEM). In order to meet all applications, the highest purity crackle is used so the product has impurity levels very near the detectability limit of Glow Discharge Mass Spectroscopy (GDMS). The charge size of production 340-mm diameter sapphire boules was increased from 55-kg to 70-kg, and larger 380-mm diameter, 84-kg boules were produced. These boules were used to produce 315-mm diameter, 132-mm high sapphire cylinders to meet customer requirements. Efforts have been taken to produce a nearly flat top surface of HEM-grown boules with minimal undulations along the sidewalls to allow fabrication of larger sapphire pieces for production boules.

A new multiwire Fixed Abrasive Slicing Technology (FAST) was developed that combines the low kerf loss and high material utilization of multiwire slicing (MWS), low consumable costs of internal diameter (ID) slicing and low cost of multiblade slicing (MBS) technologies. Recent improvements in FAST allow it to be utilized for effective slicing of hard materials at low cost. For over two years, 2-inch diameter sapphire has been sliced in prototype mode for supplying wafers to the industry.

It is necessary to develop solar grade (SoG) silicon for the photovoltaic industry. A desirable approach is to upgrade metallurgical grade (MG) silicon. The most problematic impurities to remove from MG silicon are B and P. A simple process to remove B from MG silicon has been developed by refining MG silicon in the molten state followed by directional solidification. With this approach, B has been reduced to 0.3ppma, P to <10ppma and all other impurities to <0.1ppma using commercially available, as-received MG silicon. It remains to develop a similar P reduction process so that SoG silicon production from MG silicon can be commercialized. The B-removal process was applied to B overdoped electronic grade silicon, and the resulting material was used for crystal growth. Test solar cells of 12.5–13.4% (1cm2) efficiency were produced.

Various ways to increase the 600C strength of sapphire were explored, including heat treatments, doping and improvement of fabrication techniques. Different grinding and polishing procedures were performed on sapphire disks and compression specimens. Measured strength showed correlation with fabrication procedures, with less aggressive, multi-step processes resulting in the highest strength. Simple heat treatments in oxidizing atmosphere significantly improve both compressive and biaxial flexure strength of sapphire. MgO doping was found to be very effective in increasing the compressive strength of sapphire when combined with the heat treatment.

Flexure strength testing of single crystal sapphire was conducted in the 500-600 degreesC temperature range using thin sheets of Grafoil(TM) to reduce failures due to the contact stresses at the loading points. Load-point failures occur often in high temperature testing of sapphire when twinning mechanisms activate above 500 degreesC. Bend bars of three different orientations were tested, and the flexure strength was found to be strongly dependent on the orientation type both in Grafoil and non-Grafoil tests. Use of Grafoil increases measured flexure strength up to the factor of three due to the reduction of contact stress. The effect of using Grafoil in mechanical testing of sapphire, including flexure strength, compressive strength and biaxial flexure strength testing is discussed.

The growth of the photovoltaic industry will be limited by the availability of silicon feedstock. Currently, feedstock supplies are scraps and surplus from the microelectronics industry. A program has been initiated to produce solar grade (SoG) silicon by upgrading metallurgical grade (MG) silicon using pyrometallurgical techniques in the liquid state followed by directional solidification. This approach is based on earlier results when all impurities, including B and P, were reduced to <1 ppm level. It is intended to analyze the earlier data, undertake thermodynamic analysis and produce SoG silicon that can be extended to a commercial scale operation. The feasibility of this approach will be demonstrated in charge sizes up to 500 kg.

Sapphire's strength at elevated temperature is highly dependent on the test conditions. Tests that involve compressive forces at localized contact points can cause failure at low strengths due to rhombohedral twinning. High contact stress can result at the load points due to roughness of surfaces. A thin sheet of Grafoil serves as a compliant layer between the load surface and the specimen and reduces the contact stress, and this increased the compression strength by a factor of 4 and the biaxial flexure of c oriented specimens by 2X at 600 degrees C. The strength reported by different testing facilities was comparable when Grafoil was used. The use of Grafoil has made it possible to evaluate the effect of process parameters on the compressive and biaxial flexure strength at 600 degrees C.