Applications and markets for semiconductor optoelectronic devices

Materials Science and Engineering, B9 ( 1991) 1-7

1

Applications and markets for semiconductor optoelectronic devices R. C. Goodfellow GEC-Marconi-Plessey Research Caswell Ltd., Caswell, Towcester, Northants, NN12 8EQ (U.K.)

Abstract

Semiconductor optoelectronic devices have now impacted all major areas of information technology. The functional roles of the devices can be categorized under the headings input, output, memory, processing, transmission and others. The applications exploit many physical properties and technologies, many of which have become well understood and controlled only during the last decade. The world market for optoelectronic components is currently around $3 billion per year. This serves an optoelectronic systems market currently of order $20 billion per year. Several recent optoelectronic device advances, such as optical amplifiers, surface emitting microlasers and low power optical modulators and switches will significantly impact the information technology area further. These advances were made possible by new materials capabilities in the design and preparation of multi-heterostructure group III-V materials.

1. Introduction

The applications of optoelectronics fall into the categories shown in Fig. 1. Signal and data transmission underwent a major revolution with the advent of optical fibre communications. However, it is becoming clear that many new capabilities have also been added in other areas due to the dramatic improvements in semiconductor lasers, receivers, detector arrays, amplifiers and other optoelectronic devices. In Fig. 2 the reductions in threshold current reported during the last 25 years are related to particular materials processing and design advances. The first lasers required hundreds of amperes and had to be operated at cryogenic temperatures; but the introduction of heterostructures, stripe geometries and second epitaxy for buried heterostructure stripe confinement, brought the current down to around 15 mA. The lowest values now obtainable are less than a milliampere at 1.5 V. It is now straightforward to interface lasers directly with integrated circuits and to assemble optical systems with several interacting lasers. The recent innovation of strained quantum wells of GaInAs in GaAs has led to the achievement of lasers for high operating temperature (200 °C) [1] reported in September 1990, of 0.98 /zm pump sources for erbium fibre lasers [2] and 0921-5107/91/$3.50

to high power surface grating coupled lasers. Epitaxial dielectric mirror stacks can now be tuned accurately to a precise wavelength owing to better control of the growth processes and, combined with the strained quantum wells, they have made possible surface emitting microlaser arrays [3]. 2. The optoelectronics market

Semiconductor lasers are being used extensively in compact disc players, electronic point of sale terminals, laser printing machines, local area networks and fibre optic telecommunications. Figure 3 presents data on the number of lasers sold in 1989 and the value in U.S. dollars. According to these data [4], semiconductor laser sales now exceed those of helium-neon gas lasers both in numbers and value. The AIGaAs Fabry-Perot lasers used in compact disc players were originaly prepared by liquid phase epitaxy but are under market pressures for replacement by new generation metal-organic chemical vapour deposition (MOCVD) devices and are fast becoming commodity components. Taking several market estimates together, including Frost and Sullivan [5] and the data of the Japanese Optoelectronic Industry Trade Development Association (OITDA) [6] we esti© Elsevier Sequoia/Printedin The Netherlands

mate the world market for optoelectronic devices for use in fibre based systems as circa $2.7 billion currently, with a rise to around $6.7 billion by the year 2000. The Japanese OITDA assessment [6] for the total optoelectronics component market served by Japanese production, which includes gas and solid state lasers, solar cells, display light emitting diodes (LEDs) and fibres is $4.1 billion for this year. A six-fold increase in the Japanese optoelectronic component production occurred in the decade 1 9 8 0 - 1 9 9 0 and OITDA expect a further eight-fold increase to the year 2000. OITDA expect the greatest growth in the component area to be in displays and their optoelectronic equipment projections are dominated by optical memory first and optical sensor products next. The largest market for optoelectronic devices in Europe is currently telecommunications with the data communications and sensor markets running second and third. Significant growth is expected in all of the market sectors, especially in telecommunications, data processing, aerospace and signal processing.

The driving force for the innovation and realization of new optoelectronic devices is the systems market. The optoelectronics systems market is estimated to be currently of the order of $20 billion and the total electronics systems market is circa $800 billion [7].

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3. Optoelectronics applications The optoelectronics applications are shown in Fig. 1. The input category is outlined schematically in Fig. 4. It covers all sensing functions for systems. Devices made using III-V materials have important capabilities for sensors for position, rotation, temperature, specific chemicals, acoustics, ultrasonics, magnetic field and electromagnetic radiation energy and patterns etc. I believe that the band gaps and band structures now accessible by means of quantum wells, superlattice and compositional grading approaches will yield new sensor possibilities, particularly for powerful new IR dynamic imaging sensors. The AIGaAs superlattice photoconductive detector [8] is a recent arrival which uses progressive materials technology. Figure 5 is a schematic diagram of the band structure and the responsivity vs. wavenumber. Incident electromagnetic radiation with an electric field component per-

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upconversion processes which provide access to the blue-green spectral region will also be important. The possibilities in the processing area represented in Fig. 6 are immense. Optoelectronics will be applied to existing systems in an evolutionary way to give steady performance and cost advantages. The leading mainframe computer processors now include optical data links between sub-systems to solve cabling problems. In the near future it is likely that sub-milliampere threshold laser arrays will be incorporated in ribbon fibre links to relieve further power dissipation and space constraints. Optoelectronics also affords more revolutionary possibilities, however. Quantum well asymmetric Fabry-Perot modulator arrays make possible significant reduction in the circuit area needed and in the energy drawn from a CMOS chip for the input and output of data; so higher speed and density of interconnects will be possible. A III-V on silicon heteroepitaxy process which was made compatible with CMOS processes would enable this method of optoelectronic interfacing to be implemented monolithically and could therefore be very powerful for optical interconnects of very-largescale integrated circuits. The latest surface emitting microlaser arrays

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(with 32 x 32 arrays now demonstrated) open up further new options for array signal processing with conventional electronic and also all-optical arithmetic. Figure 7 is a schematic diagram of the AIAs/GaAs/GalnAs vertical cavity surface emitting microlaser developed by Coldren et al. [10]. These devices operated at room temperature with thresholds of 0.7 to 0.9 mA and could lead to many new applications in the processing area. Clausen et al. [11] are also studying such structures and are looking at addressable arrays; Fig. 8 is a schematic diagram of the materials structure, the mesa isolation technique and the power-current characteristic observed. Transmission applications cover optical microwave links, intersatellite links, local area networks as well as optical fibre telecommunications which has probably made the most impact tO date. In the latest trunk systems the capacity has been extended to 1012 bit s- 1 km owing to the achievement and use of increased laser power, higher speed and tighter spectral control together with wavelength multiplexing and improved avalanche photodiode sensitivity. Semiconductor amplifiers and fiber amplifiers have recently been used in laboratory demonstrations with all-optical repeaters to extend the capability further to beyond 1015 bits lkm. More recently the focus has shifted towards communications in the local subscriber telecommunications network and to multiple channel capabilities for this. There are several implementation scenarios for the Access network in the local loop. In the first implementation a single fibre is laid to carry signals to and from the subscriber's home. Light of wavelength 1.3 p m is used to carry broadband data to the subscriber and 1.5 p m light is used for the subscriber's interactive channel. In later scenarios more channels are provided in both directions by going to simple wavelength multiplexing and finally to a fully coherent system. The customer terminal needs to have significant functionality. The optoelectronic integrated circuit (OEIC) promises to provide the necessary complex functionality in a straightforward way. It eliminates the need for multiple fibre alignment and jointing of several components in the optical terminals, it improves testability and reliability, and it reduces component count whilst meeting the needs of multifunction terminals at low enough cost to catalyse the introduction of fibre to the home. Figure 9 shows a functional prototype customer

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Fig. 9. A functional customer access OEIC prepared at our laboratory [12]. This chip incorporates a buried stripe distributed feedback laser (on the left side of the chip), with a 3 dB coupler, wavelength duplexer for separating 1.3 from 1.55/~m wavelength channels and a monitor detector (on the right side of the chip). The coupler and duplexer are waveguide components embodied in waveguides running the length of the OEIC. The chip is 3.65 mm long and 0.6 mm wide.

access OEIC prepared at our laboratory. This incorporates a distributed feedback 1.3/~m laser, a waveguide 1.3 to 1.5/~m duplexor coupler and a detector diode for laser monitoring. Preparation of this device requires four epitaxy stages and overgrowth of a 0.4/~m period grating. However, such chips can be prepared on whole wafers and therefore in large numbers, so the prospects for low cost are very promising. Tunable lasers, narrowed linewidth lasers, tunable filters, amplifiers, switches and duplexors have also now been integrated and several laboratories are examining OEIC technologies. The optoelectronic integration approach will

allow the implementation of high performance but complex techniques such as coherent multichannel and dense wavelength division multiplexing, which open up exciting possibilities for Broadband ISDN, telecommunications switching. Applications which fall into the other category might include "energy" devices (such as solar cells) and illuminators, laser surgery and other non information technology applications. According to the OITDA surveys these represent less than 5% of the total value of the current optoelectronics market. It is quite hard, in the early stages of a new technology, to identify where the impact will be

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felt most. Recently Canham [13] observed bright red light emission from porous silicon under a few milliwatts of green excitation at room temperature. The phenomenon is not well understood yet but might lead to spontaneous and possibly even lasing emission from silicon. Hence it might impact the optical intereonnection of circuits and may lead to silicon displays. Figure 10 shows schematically how the anodic etching followed by free etching leads to columnar, illamentary structures and quantum wires. With several hours free etching the band edge emission seems consistent with 20-50 A diameter wires. It will be interesting to see what emerges from Canham's interesting finding. 4. Conclusions Important achievements in semiconductor optoelectronics have been made over the past 25 years and these have resulted in devices which are impacting all major areas of information technology. The optoelectronic components market is very significant but is small in comparison with the equipment and systems market that it serves. Optoelectronics materials and devices are strategic enabling components for systems. There are many application areas where optoelectronics has only just started to

penetrate such as interconnections in computer processors, system switches, sensors and memory. Even in the telecommunications area one can see new devices such as optical amplifiers, OEICs and tunable surface emitting microlasers which will lead to very different second generation networks and systems. This broad perspective of the application areas of optoelectronics devices shows that a broader range of materials and yet more advanced materials capabilities and understanding will enable even greater market possibilities. References 1 R. J. Fu, C. S. Hong, E. Y. Chan, D. J. Booher and L. Figueroa, High temperature operation of InGaAs strained QW lasers, Proc. 12th IEEE Semiconductor Laser Conf., Davos, September, 1990, pp. 54-55. 2 M. Okayashi et al., High power 0.98 GaInAs strained quantum well lasers for Er 3÷-doped fibre amplifier, Electron. Lett., 9(1989) 1563-1565. 3 C. J. Chang-Husnain, M. W. Maeda, N. G. Stoffel, J. R. Harbison, L. T. F|orez and J. Jewell, Proc. 12th IEEE Semiconductor Laser Conf., Davos, September, 1990, p. 18. 4 Laser and Optronics, (January 1990). 5 Frost and Sullivan market survey reports. 6 OITDA Rep., 1990. S. Ishihara, Proc. SPIE Syrup. on Advances in Interconnects and Packaging, Boston, U.S.A., November 1990, SPIE 1389, to be published.

7 D. Ankri, Thomson CSF, private communication, October 1990. 8 B.F. Levine, K. K. Choi, C. G. Bethea, J. Walker and R. J. Malik, New 10/am infrared detector using intersubband absorption in resonant tunnelling GaA1As superlattices, AppL Phys. Lett., 50(16)(1987) 1092-1094. 9 S. Andrews, GEC-Hirst Research Centre, London, U.K., private communication, 1990. 10 L. A. Coldren et al., High-efficiency vertical cavity lasers and modulators, SPIE Aachen, October, 1990, to be published.

11 E. M. Clausen, Jr., et al., Fabrication of ultra low threshold vertical cavity surface emitting lasers by a unique etching process, to be published. 12 P. J. Williams, R. G. Walker, P. M. Charles, A. K. Wood, N. Carr, R. I. Taylor and A. C. Carter, Optoelectronic integrated circuits for telephony/broadband passive optical networks: design and experimental results, Proc. 12th IEEE Semiconductor Laser Conf., Davos, September, 1990, p. 164. 13 L. T. Canham, Appl. Phys. Lett., 57 (10) (1990) .1046-1048.