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(, 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.