We present the results of direct photoionization studies of Mg and C doped cubic GaN. Photocurrent was measured with use of a Fourier transform spectrometer in the spectral range of 50 to 500 meV. The investigated samples were grown on (100) GaAs substrate by plasma‐assisted molecular beam epitaxy, with room temperature hole concentrations varying from 1.4 ⋅ 1016 to 4.5 ⋅ 1017 cm−3. No structure in the broad‐band photocurrent spectra was observed. The onset of the photoionization band was found to start at about 150 meV in a lightly doped samples and move towards lower energies with increasing hole concentration, indicating the formation of an impurity band.

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