[工学]集成光学课程第九章.ppt

Integrated Optical Detectors Detectors for use in integrated-optic applications must have high sensitivity, short response time, large quantum efficiency and low consumption. In this chapter, a number of different detector structures having these performance characteristics are discussed. 9.1 Depletion Layer Photodiodes 9.2 Specialized Photodiode Structure 9.3 Techniques for Modifying Spectral Response 9.4 Factors Limiting Performance of Integrated Detectors 9.1 Depletion Layer Photodiodes The most common type of semiconductor optical detector, used in both integrated optic and discrete device applications, is the depletion-layer photodiode. The depletion-layer photodiode is essentially a reverse-biased semiconductor diode in which reverse current is modulated by the electron-hole pairs produced in or near the depletion layer by the absorption of photons light. The diode is generally operated in the photodiode mode, with relatively large bias voltage. 9.1.1 Conventional Discrete Photodiode The simplest type of depletion layer photodiode is the p-n junction diode. The energy band diagram for such a device, with reverse bias voltage Va applied is shown in Fig.9.1. The total current of the depletion layer photodiode consists of two components: a drift component originating from carriers generated in region (b) and a diffusion component originating in regions (a) and (c). Holes and electrons generated in region (b) are separated by the reverse bias field, with holes being swept into the p-region (c) and electrons being swept into n-region (a). Holes generated in the n-region or electrons generated in the p-region have a certain probability of diffusing to the edge of the depletion region (b), at which point they are swept across by the field. Majority carriers, electrons in (a) or holes in (c) are held in their respective regions by the reverse bias voltage, and are not swept across the depletion layer. The quantum efficiency of the detector, or the number of c