Direct coupled logic using an integrated, emitter-down, Schottky collector, heterojunction bipolar transistor with a MESFET load

Demonstrates that a simple form of direct-coupled logic (DCL) in the GaAs/AlGaAs system could offer a viable alternative to the highly complex emitter-coupled logic (ECL) favoured by the industry. DCL is best effected using bipolar transistors operating in the `inverted´ mode with grounded emitters next to the substrate and logic levels occurring at interconnected base and collector nodes. However, whilst this configuration is easily achievable in principle by the III/V technology and has the added advantage of being optimum for photo-operation allowing mixed optical/digital devices, there are materials problems associated with the epitaxial growth of binary upon ternary semiconductors. These problems and work currently in progress to overcome them, are explained. The structure and its advantages are described and problems associated with circuit operation outlined