Persistent photoconductivity and photoluminescence measurements were made of radio-frequency plasma-assisted molecular beam epitaxially grown undoped material. Hexagonal-type epilayers which had been grown onto sapphire, and cubic-type epilayers which had been grown onto GaAs or cubic SiC substrates, were used. Clear experimental evidence was found that a commonly observed persistent photoconductivity and yellow luminescence were related to each other via the same defect. That is, persistent photoconductivity was observed only in those samples which exhibited showed yellow luminescence. Secondly, the threshold (minimum photon) energy needed to observe persistent photoconductivity was 1.6eV. This was almost the same energy at which the yellow luminescence band began to appear. Thirdly, the photocurrent increased monotonically from 1.8 to 2.2eV; which was consistent with the broad nature of the yellow luminescence band.

The origin of persistent photoconductivity and its relationship to yellow luminescence in molecular beam epitaxially grown undoped GaN C.V.Reddy, K.Balakrishnan, H.Okumura, S.Yoshida: Applied Physics Letters, 1998, 73[2], 244-6