High-temperature DC characteristics of Al/sub x/Ga/sub 0.52-x/In/sub 0.48/P/GaAs heterojunction bipolar transistors grown by metal organic vapor phase epitaxy

A series of Al/sub x/Ga/sub 0.52-x/In/sub 0.48/P/GaAs heterojunction bipolar transistors (HBT's) with x=0 to x=0.52 showed ideality factors close to unity for both base current and collector current and small variation in gain with temperature up to at least T=623 K across the whole range of x composition. Hole current injection from the base into the emitter in these devices was shown to be negligible. The current gain, /spl beta/, which is temperature insensitive was thought to be limited by bulk base recombination for x/spl les/0.3 and recombination at the graded emitter region for x>0.3. The optimum emitter composition (highest /spl beta/, and good /spl beta/ stability with collector current and temperature) was found to be x=0.18-0.30. Useful transistor action with very high gain and output resistance is possible up to at least T=623 K, limited only by the thermal performance of the unoptimized ohmic contacts employed in the devices.