THE TOTAL PRESSURE OF ARSENIC OVER MOLTEN GALLIUM-ARSENIDE AT 1260-DEGREES-C

In the design of Bridgman type growth systems for the growth of GaAs, the use of a hermetically sealed fused quartz ampoule is often require d. In addition, if the sample is to be directionally solidified in som e manner, the melt is usually held at a temperature above the melting point of 1238-degrees-C, such as 1260-degrees-C. The literature genera lly supports the value of 0.97 atm for the total pressure of As over m olten GaAs at the melting point, although there is not agreement on th e ratio of the As2 and As4 species. However, only Richman [J. Phys. Ch em. Solids 24 (1963) 11311 lists any data for the total pressure of ar senic over GaAs at temperatures above the melting point. His data indi cate a value of 1.2 atm at 1260-degrees-C. In this paper several exper iments are reported, which were conducted using a pressurized furnace and any subsequent deformation of the fused quartz ampoule, which at 1 260-degrees-C is in viscous flow, was observed. Thus, for no deformati on of the ampoule to occur, the internal ampoule pressure due to the t otal pressure of arsenic over the molten GaAs must be balanced by the externally applied pressure. Based on the results of these experiments , a value of 2.2 atm (18 psig) was measured for the total pressure of arsenic over molten GaAs at 1260-degrees-C. This value was used to con struct ampoules for several different growth systems, all of which yie lded successful ampoules with no deformation.