Surface passivation of composition graded base in GaAlAs/GaInP/GaAs heterojunction bipolar transistor R. Bourguiga, H. Sik and A. Scavennec Eur. Phys. J. AP, 6 3 (1999) 299-301 Published online: 15 June 1999 DOI: 10.1051/epjap:1999187