Double heterojunction GaAs-GaAlAs bipolar transistors grown by MOCVD for emitter coupled logic circuits

Double heterojonction N-p-N GaAlAs-GaAs-GaAlAs bipolar transistors (DHBT\´s) have been developed using MOCVD growth. We have investigated the influence of growth conditions on the d.c. characteristics of DHBT\´s. Devices with 0.2 µm base thichness and p = 2.10¹⁸cm^-3exihibited common emitter current gain, β, of up to 5500. The recombination current has been reduced such as for current densites as low as 2.10^-4A/cm². The offset voltage appearing in characteristics of simple-heterojunction bipolar transistors is eliminated for some of DHBT\´s. Reverse current gains, βIof 15 are demontrated. DHBT\´ have been fabricated with a diffused structure on semi insulating substrate for ECL circuits including the implantation of the resistors. A reduction of the base collector junction area is obtained with emitter-collector interchangeability. Simulation results have shown that the propagation delay time of an ECL inverter using DHBT\´s with 4 microns line lithography is less thant 300 ps with a speed-power product of 70 fJ.