Parasitic effects and traps in AlGaN/GaN HEMT on sapphire substrate O. Fathallah, M. Gassoumi, B. Grimbert, C. Gaquière and H. Maaref Eur. Phys. J. Appl. Phys., 51 1 (2010) 10304 Published online: 24 June 2010 DOI: 10.1051/epjap/2010085