We report photoconductivity measurements on LaAl1-x CrxO3/SrTiO3 (x = 0, 0.4) heterostructures. A polar layer modification of metallic LaAlO3/SrTiO3 heterostructure with Cr in the Al sites resulted in an increased photo-response (PR) and relaxation time, in addition to a distinct shift in the spectral weight toward the red end of the spectrum. The visible light photoconductivity is explained by d-d photoconductivity of Cr3+ valence states of the x = 0.4 sample. Besides the established UV sensitivity, we observe a weak peak in PR around 690 nm possibly emanating from the mid-gap states arising from oxygen vacancies.
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