GAAs High-Speed Devices: Physics, Technology, and Circuit Applications

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HIGH-SPEED PHOTONIC DEVICES

15.1 INTRODUCTION TO PHOTONIC DEVICES

Semiconductor light-emitting diodes (LEDs), lasers, and photodetectors are critically important devices in optical fiber communications system [Tsa90] because of their small size and high reliability. Figure 15.1 shows a chart of some possible important applications of these devices. As sources, LEDs and lasers are easy to modulate to encode information. As optical receivers, semiconductor photodetectors have high quantum efficiency in converting the input optical signal back into the original electrical format. The LEDs and laser can be integrated monolithically with other optical and electronic devices to form optoelectronic integrated circuits (OEICs).

This chapter will focus on the high-speed aspects of semiconductor photonic devices. Since the silica fibers have the least loss and chromatic dispersion in the wavelength range of 1.0 to 1.6μm, the devices considered here will be built out of quaternary III–V compounds. InGaAsP alloy systems that span this wavelength range with InP (0.9μm) and In_0.53Ga_0.47As (1.67μm) at their end compositions. InP is a binary compound semiconductor and is used as the substrate. Thin crystalline layers of InGaAsP, having different compositions, are grown epitaxially over the substrate. The lattice constants of these layers are kept the same as the InP substrate underneath. The different compositions result in different energy band gaps, and hence the layers emit photons with ...