Photoemission spectroscopy of Al_0.27Ga_0.73As:As photodiodes

We report on photoemission measurements of MBE-grown Al 0.27Ga0.73As p-i-n structures in which the optically active insulating layers contain arsenic precipitates (Al0.27Ga 0.73As). Al0.27Ga0.73As layers were formed by low temperature growth of Al0.27Ga0.73As followed by a high temperature anneal. GaAs layers grown in this way have been reported to be sensitive to subband-gap light. A Fowler plot constructed from an internal photoemission measurement gave a barrier height of 0.93 eV. We compare this result with the barrier height of arsenic in GaAs that was found to be 0.7 eV using the same structure and measurement scheme. This result demonstrates that the barrier height of embedded metallic arsenic clusters in Al xGa1-xAs is consistent with the heterostructure conduction band offset and can be selected by changing the composition of the host material.