GaAs bipolar transistors with a Ga/sub 0.5/In/sub 0.5/P hole barrier layer and carbon-doped base grown by MOVPE

GaAs bipolar transistors with a 50-AA-thick lattice matched Ga/sub 0.5/In/sub 0.5/P layer between the emitter and base acting as a hole repelling potential barrier in the valence band were fabricated from films grown by metalorganic vapor phase epitaxy (MOVPE). The 1000-AA-thick base was doped with carbon to 2*10/sup 19/ cm/sup -3/, resulting in a base sheet resistance of 250 Omega / Square Operator . Carbon has been chosen because of its low diffusivity. Using the barrier layer as an etch stop the authors fabricated mesa-type broad-area devices. The output characteristics of the devices are ideal with very small offset voltages and infinite Early voltages. Common emitter current gains of up to 70 at 10/sup 4/ A/cm/sup 2/ collector current density were obtained. The current gain is clearly higher than the one calculated for a bipolar junction transistor with the same doping profile because the base-emitter hole current is suppressed by the Ga/sub 0.5/In/sub 0.5/P potential barrier in the valence band.>