<title>InP-based MSM-HEMT receiver OEICs for long-wavelength lightwave systems (Invited Paper)</title>

Abstract

AbstractThis paper reviews the recent progress in researching a planar receiver OEIC technology utilizingInGaAs MSM photodetectors and InAlAs/InGaAs HEMT amplifiers. The epitaxial materials havebeen grown by the low-pressure OMCVD technique on patterned InP substrates. This planar integra-tion process has been used to address a number of different system needs. These include a balanced dual detector receiver for coherent detection, a trans-impedance amplifier receiver with a planar detector and waveguide integrated detector for direct detection, and a electronically-switched four-channel receiver for wavelength-division-multiplexing based lightwave systems. This MSM-HEMTOEIC technology represents a major advance towards achieving high-performance and low-cost components for long-wavelength lightwave systems.1. INTRODUCTION Future lightwave systems will require a variety of optoelectronic integrated circuit (OEIC) compo-nents that interface optical devices with high-performance electronic devices. Development of suchintegrated components has been driven mainly by the requirements of advanced system architectureswhereby components with high performance and increased functionality can be used in lightwaveinformation processing and communication systems. As for the case of integrated electronics, mono-lithic integration offers significant advantages over hybrid circuits in compactness, reliability, possibleperformance improvements resulting frym reduced parasitics, and potentially significant reductionsin cost, particularly in the case of arrays'. However, all these advantages have not been fully realizedyet mainly due to the difficult materials and fabrication challenges presented by integration of verydifferent devices on a single chip. In an effort to planarize the process, optical devices are usuallygrown in the etched well, and electronic devices occupy different locations on the chip. As a conse-quence, interconnction yield deteriorates due to surface steps formed between optical and electricaldevices. Different material compositions are also required for optical and electronic devices. As forthe design of front-end photoreceiver OEIC's consisting of photodetectors and pre-amplifiers, p-i-nphotodetectors and field-effect transistor (FET) amplifiers have been mostly used. However, p-i-nphotodetectors and FET's are not compatible in terms of fabrication.It is therefore important to search for the new compatible component designs. The planar metal-semiconductor-metal (MSM) photodetector has attracted a considerable attention for receiver OEICapplications. It consists of a semiconductor absorbing layer oil which interdigitated metal electrodesare deposited to form back-to-back Schottky contacts. Therefore the MSM photodetector is verysimple to fabricate. Since the MSM photodetector has a planar geometry with Schottky contacts it isfully process compatible with standard metal-semiconductor FET's (MESFET's) or high-electron-mobility-transistors (HEMT's). In addition to its planjtrity and compatibility with FET's, the MSMphotodetector has a very low capacitance per unit area .