We investigated the effect of a middle temperature intermediate layer (MTIL) of AlGaN and AlN/AlGaN super lattice structure (SLS) on the crystal quality of AlGaN epilayers grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). MTIL-Al0.17Ga0.83N layers could enhance the lateral growth area at 950 degrees C, and the dislocations made dislocation loop. The full-width at half-maximum from (1 0 1 2) X-ray rocking curve peak of HT-Al0.17Ga0.83N epilayers grown on MTIL decreased from 1220 to 525 arcsec. The dislocation density evaluated by atomic force microscopy density decreased from 1.0 x 10(10) to 1.3 x 10(9) cm(-2), respectively. These results reveal that MTIL technique is very useful to further improve the quality of AlGaN-based films, and to fabricate the high-efficiency ultraviolet light emitting diode (UV-LED). (c) 2006 Elsevier B.V. All rights reserved.