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 the12C(γ, n)11C reaction. Chemical isolation of the radiocarbon 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 1.4·1016 atoms · cm−1.