Composition of arsenic and phosphorus vapour in different annealing geometries determined by Raman spectroscopy

Furnace annealing of GaAs, InP and related compounds in arsenic and phosphorus atmosphere, respectively, is carried out usually either in single-zone or in double-zone arrangements. By use of the double-zone furnace, the independent control both of the annealing temperature and of the total pressure is possible. The composition of vapour, i.e. the As2/As4 and P2/P4 ratio, respectively, depending both on the temperature up to 1318 K and on the total pressure (10−2–1 bar) was determined by Raman spectroscopy analysing the intensity ratio of the vibrational modes of As2, As4 and P2, P4, respectively. These experimental data were compared with the partial pressure ratio calculated by means of the ChemSage database. Raman and ChemSage data show a satisfactory agreement in case of single-zone experiments. But a systematic decrease of the As2/As4-ratio was found in case of the double-zone furnace. This decrease is attributed to the As4 flow from the source (Ts) to the optical zone (Ta) depending on the temperature difference (Ta – Ts). The Raman mode of P2 at 775 cm−1 was shown for the first time