DETERMINATION OF CARBON IMPURITY IN GALLIUM-ARSENIDE CRYSTALS BY PHOTON-ACTIVATION ANALYSIS

Determination of carbon impurity in GaAs crystals has been investigated by photon activation analysis using the C-12(gamma, n) C-11 reaction. Chemical isolation of the radio-carbon as CO2 was carried out by the combustion method using Pb3O4 as a fusing agent and/or oxidizing accelerator in a high flow rate of oxygen stream. The CO2 was then collected by passing through a double trap containing NaOH solution, and precipitated finally as BaCO3. By measuring positron annihilation gamma-rays due to the isolated radiocarbon, it was proved that determination of the above carbon impurity can be achieved easily and favourably. On the basis of the results obtained, a conversion factor for the LVM absorption of carbon at room temperature in Fourier-transform infrared spectroscopy was found to be 1.4 . 10(1 6) atoms . cm-1.