Prospects for Monolithic GaAs/Si Integration
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PROSPECTS FOR MONOLITHIC GaAs/Si INTEGRATION
H. K. Choi, G. W. Turner, and B-Y. Tsaur Lincoln Laboratory, Massachusetts Institute of Technology Lexington, Massachusetts 02173-0073 ABSTRACT The status of monolithic GaAs/Si (MGS) integration is reviewed and its The MGS material now available is satisfacfuture prospects are discussed. tory for majority-carrier devices, but improvement in quality is needed for minority-carrier devices. By using a suitable sequence of processing steps, fabrication of GaAs MESFETs and Si MOSFETs on the same wafer and monolithic integration of GaAs/AlGaAs double-heterostructure LEDs and Si MOSFETs have been achieved. The GaAs and Si FETs show characteristics comparable to those for devices fabricated on separate GaAs and Si substrates. The LEDs have been modulated up to 27 Mb/s by applying a pattern of voltage pulses to the MOSFET gate. Two promising applications of MGS integration are optical interconnects between Si VLSI chips and monolithic microwave integrated cirMuch better performance should be obtained by operating MGS ICs at cuits. liquid nitrogen temperature. INTRODUCTION In the past few years there has been growing interest in the heteroepitaxy of GaAs on Si. This interest is motivated by the numerous potential applications of monolithic GaAs/Si (MGS) technology and has been stimulated by the encouraging progress made to date in both material and devices. One application would be the use of Si substrates in GaAs LSI circuit fabrication, because the maximum diameter of commercial wafers is currently 8 in. for Si, compared with 3 in. for GaAs, and because the mechanical and thermal properties of Si are superior to those of GaAs. Since this subject is discussed in Ref. 1, it will not be considered here. More substantial benefits of MGS technology would be realized by monolithic integration of GaAs optoelectronic circuits and high-speed electronic circuits with Si VLSI circuits. One potential application of MGS integration is in the fabrication of optical interconnects between Si VLSI chips. As the complexity and speed of these chips increase, conventional wire interconnects impose serious limitations on system performance, such as high power requirements for driving the extremely large numbers of interconnects necessary, electromagnetic interference between closely-spaced lines, and low data transmission rates. Optical interconnects are immune to crosstalk and interference, and because of their large available bandwidth the number of interconnects can be substantially reduced by multiplexing/demultiplexing. An optical interconnect requires a transceiver consisting of an optical source and a receiver. Although it is feasible to employ a hybrid approach using separate GaAs transceiver chips wire-connected to the Si VLSI chips, monolithic integration would more fully utilize the advantages of optical interconnects. Another potential application of MGS technology is the integration of high-speed digital and/or microwave GaAs circuits with Si VLSI circuits to achieve greatly enhanced s
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