Resonant Tunnelling Optoelectronic Circuits

Nowadays, most communication networks such as local area networks (LANs), metropolitan area networks (MANs), and wide area networks (WANs) have replaced or are about to replace coaxial cable or twisted copper wire with fiber optical cables. Light-wave communication systems comprise a transmitter based on a visible or near-infrared light source, whose carrier is modulated by the information signal to be transmitted, a transmission media such as an optical fiber, eventually utilizing in-line optical amplification, and a receiver based on a photo-detector that recovers the information signal (Liu, 1996)(Einarsson, 1996). The transmitter consists of a driver circuit along a semiconductor laser or a light emitting diode (LED). The receiver is a signal processing circuit coupled to a photo-detector such as a photodiode, an avalanche photodiode (APD), a phototransistor or a high speed photoconductor that processes the photo-detected signal and recovers the primitive information signal. Transmitters and receivers are classical examples of optoelectronic integrated circuits (OEICs) (Wada, 1994). OEIC technologies aim to emulate CMOS microelectronics by (i) integrating optoelectronic devices and electronic circuitry on the same package or substrate (hybrid integration), (ii) monolithically integrate III-V optoelectronic devices on silicon (difficulty since silicon is not useful for many optoelectronic functions) or (iii) monolithically integrate III-V electronics with optoelectronic devices. The simply way to do hybrid integration is combining packaged devices on a ceramic substrate. More advanced techniques include flip-chip/solder-ball or -bump integration of discrete optoelectronic devices on multi-chip modules or directly on silicon integrated circuit (IC) chips, and flipbonding on IC chips. Although, hybrid integration offers immediate solutions when many different kinds of devices need to be combined it produces OEICs with very low device density. Moreover, in certain cases the advantages of using optical devices is greatly reduced. On the contrary, monolithic integration leads to superior speed, component density, reliability, complexity, and manufacturability (Katz, 1992). There was been substantial efforts towards monolithical integration of III-V electronics with optoelectronic devices to improve the performance of transmitters and receivers. Approaches to light modulation, light detection and light generation at microwave and millimetre-wave frequencies have been investigated by combining double barrier quantum well (DBQW) resonant tunnelling diodes (RTDs) with optical components such as