Recent developments in GaAs-based high-speed devices

The recent advances in the crystal growth, device concepts, and fabrication of electronic and opti­ cal devices in GaAs and other III-V semiconduc­ tors have inspired the scientists in several labora­ tories to work on combining both types of devices into one circuit to create a new, powerful class of highspeed optoelectronic integrated circuits for opti­ cal communications and many other high-speed ap­ plications l ike digital optical computers. Such an ap­ proach would enable electronic processing of optical signals on a single chip for such operations as filter­ ing, switching, amplifying, and mult iplexing. Conversely, electronic signals can be processed op­ tically to avoid interconnects wh ich add parasitic reactances to the circuit. The interconnects are no less important than the devices in determining the speed of a circuit, and their effects are more important as the devices become smaller and faster because in­ terconnection-related parasitics do not scale down proportionally as the device dimensions are reduced to increase the speed. Integration of optical and electronic devices is a challenging task, and researchers in one field must know the latest about the other. For this very reason, this article w i l l briefly review some of the recent de­ velopments in GaAs technology. O f the various III-V semiconductors suitable for both electronic and optical devices, GaAs has attract­ ed the most attention because of its more mature technology. 1 , 2 It has a direct band gap necessary for optical sources. In addition GaAs has better transport