Measurements have been made of the thermal and optical activation energies of chromium, iron and nickel in gallium arsenide.
The temperature dependence of the broad chromium level may be written in the form E=0·81±0·02−8×10−4
T ev for T>100°K E=0·75±0·01 ev for T->0°K where E is measured from the conduction band.
It is argued that some of the confusion concerning activation energies in the literature results from equating values which are measures of different features of the impurity band and which give significantly different results if the impurity band is broad.