Growth of Shaped Crystals

Abstract

Shaped crystal growth refers to the growth of single crystals with a predetermined cross sectional configuration designed for a specific application. The quest to develop such techniques has been driven by the need to minimize costs associated with device fabrication such as cutting or polishing, the loss of expensive materials during these fabrication processes, and the damage created by machining processes.Perhaps the first intentionally shaped crystals were the metal filaments grown by Von Gomperz [1] in Germany in 1922 through a hole in a mica plate positioned on the melt surface. In 1938, Stepanov [2] in the USSR, began studies on the growth of shaped crystals using mechanical means to control the forces of surface tension. In his approach, the melt column was crystallized outside of the container by inserting wettable or nonwettable dies of different shapes into the melt.In the United States, work on growing sapphire filaments and single crystal superalloy jet engine turbine blades began in the late 1960's [3,4]. The former led several years later to the development of the EdgeDefined Film Growth Process (EFG) [5] for the production of sapphire tubes, filaments, ribbons and other shapes for special purposes. The EFG process (which is similar to the Stepanov method) and the unidirectional casting method for single crystal turbine blades were the first shaped crystal growth methods to find practical commercial applications.Aside from these two applications, shaped crystal growth technology would probably have remained a laboratory curiosity were it not for the energy crisis in the mid-seventies and the emergence of an urgent need to produce high quality silicon for solar cell applications. The cost of producing silicon single crystals had to be reduced dramatically to make these devices competitive with other energy sources. Increased growth rates compared with conventional methods and reduction in machining costs and material losses were necessary. Development of production methods for the preparation of high quality single crystal silicon ribbon at very high growth velocities was therefore a highly desirable approach to minimize fabrication costs. As a result, existing methods such as the Stepanov, EFG, and Dendritic Web Processes were studied for this application, and 275 H. Arend et al. (eds.), Crystal Growth in Science and Technology

Crystal Growth through the Ages

“…It is not quite so obvious since almost all Bridgman crystals are grown from cylindrical ampoules. [140] and elsewhere. Using oriented seeds, they grew crystals not only aligned along the c-axis, but also so that the flat crystal side faces would to be normal to the [110] planes in which light propagates during type 1 phase-matched nonlinear interactions.…”

“…Some other methods include the ribbon against drop (RAD) method [152], where silicon is deposited as aligned grains on a carbon substrate, and the silicon on ceramic process [153], which is similar to the RAD process except that the substrate is a ceramic material. [140]. The former is a laser heated float-zone technique using a poly ribbon as the source and the latter involves pulling a ribbon (cooled from the top) horizontally from a free melt surface.…”

Synthesis, characterization, and applications of shaped single crystals

“…Characterization of the fibers with regard to physical and mechanical properties can be done using the myriad of standard techniques such as X-ray diffractometry, crystal birefringence, microprobe analysis and optical microscopy [4].…”

“…Another method that enabled us to grow single crystal fibers of the desired length and diameter, in the proper crystallographic orientation and of proper composition and doping is the Laser Heated Pedestal Growth (LHPG) method of fiber synthesis [4].…”

The effect of the pressure difference across the free surface in case of a NdYAG micro fiber growth by the micro-pulling-down process

“…There are several methods for growing fiber crystals [4]. The micro-pulling down (μ-PD) process, a variant of the inverse edge-defined film-fed growth, developed by Fukuda's laboratory in Japan [5][6][7][8][9], has been promising in producing single crystal fibers with good diameter control and concentration uniformity.…”