Bridgman–Stockbarger method

The Bridgman–Stockbarger method, or Bridgman–Stockbarger technique, is named after physicists Percy Williams Bridgman (1882–1961) and Donald C. Stockbarger (1895–1952). The method includes two similar but distinct techniques primarily used for growing boules (single-crystal ingots), but which can be used for solidifying polycrystalline ingots as well.

Overview

The methods involve heating polycrystalline material above its melting point and slowly cooling it from one end of its container, where a seed crystal is located. A single crystal of the same crystallographic orientation as the seed material is grown on the seed and is progressively formed along the length of the container. The process can be carried out in a horizontal or vertical orientation, and usually involves a rotating crucible/ampoule to stir the melt. The horizontal configuration can avoid placing stresses on the crystal due to thermal expansion and can purify the crystal at the cost of evaporation but the shape of the liquid-solid interface between the molten material and the crystal is more concave. Compared to the temperature gradient method where a temperature gradient is required along the entire length of the crucible, in vertical Bridgman method allows for a small temperature gradient only near the liquid-solid interface.

The Bridgman method is a popular way of producing certain semiconductor crystals such as gallium arsenide, for which the Czochralski method is more difficult. The process can reliably produce single-crystal ingots, but does not necessarily result in uniform properties through the crystal.

The difference between the Bridgman technique and Stockbarger technique is subtle: While both methods utilize a temperature gradient and a moving crucible, the Bridgman technique utilizes the relatively uncontrolled gradient produced at the exit of the furnace; the Stockbarger technique introduces a baffle, or shelf, separating two coupled furnaces with temperatures above and below the freezing point.