Ultraviolet photoluminescence from undoped and zn doped AlxGa1−xN with x between 0 and 0.75

The origin of the abrupt decrease withxboth in electron concentration and in mobility of AlxGa1−xN in the range ofxbetween 0.4 and 0.6 was investigated by photoluminescence from epitaxial layers covering the entire range of alloy composition. Band edge luminescence from undoped layers was observed out to anxvalue of 0.75. Whenxwas larger than 0.2, a peak 0.2–0.5 eV below the band edge peak was also observed both from undoped and from Zn doped samples. This is tentatively ascribed to an unidentified acceptor (or acceptors) related to the presence of Al. No luminescence which could be attributed to a deep native donor defect was observed in semi-insulating AlxGa1−xN layers. When Zn was added in the lowxrange of the alloys, a broad band 0.5–0.8 eV below the band edge peak was observed as well as a relatively narrow peak.