Nguyên tắc cơ bản của lượng tử ánh sáng P17

Simkon Poisson (1781-1840) developed the probability distribution that describes photodetector noise.A photodetector is a device that measures photon flux or optical power by converting the energy of the absorbed photons into a measurable form.
Nội dung trích xuất từ tài liệu:
Nguyên tắc cơ bản của lượng tử ánh sáng P17Fundamentals of PhotonicsBahaa E. A. Saleh, Malvin Carl TeichCopyright © 1991 John Wiley & Sons, Inc.ISBNs: 0-471-83965-5 (Hardback); 0-471-2-1374-8 (Electronic) CHAPTER 17SEMICONDUCTORPHOTON DETECTORS17.1 PROPERTIES OF SEMICONDUCTOR PHOTODETECTORS A. Quantum Efficiency B. Responsivity C. Response Time17.2 PHOTOCONDUCTORS17.3 PHOTODIODES A. The p-n Photodiode B. The p-i-n Photodiode C. Heterostructure Photodiodes D. Array Detectors17.4 AVALANCHE PHOTODIODES A. Principles of Operation B. Gain and Responsivity C. Response Time17.5 NOISE IN PHOTODETECTORS A. Photoelectron Noise B. Gain Noise C. Circuit Noise D. Signal-to-Noise Ratio and Receiver SensitivityHeinrich Hertz (1857-1894) discovered photo- Simkon Poisson (1781-1840) developed theemission in 1887. probability distribution that describes photo- detector noise.644A photodetector is a device that measures photon flux or optical power by convertingthe energy of the absorbed photons into a measurable form. Photographic film isprobably the most ubiquitous of photodetectors. Two principal classes of photodetec-tors are in common use: thermal detectors and photoelectric detectors: . Thermal detectors operate by converting photon energy into heat. However, most thermal detectors are rather inefficient and relatively slow as a result of the time required to change their temperature. Consequently, they are not suitable for most applications in photonics. . The operation of photoelectric detectors is based on the photoeffect, in which the absorption of photons by some materials results directly in an electronic transi- tion to a higher energy level and the generation of mobile charge carriers. Under the effect of an electric field these carriers move and produce a measurable electric current.We consider only photoelectric detectors in this chapter. The photoeffect takes two forms: external and internal. The former process involvesphotoelectric emission, in which the photogenerated electrons escape from the materialas free electrons. In the latter process, photoconductivity, the excited carriers remainwithin the material, usually a semiconductor, and serve to increase its conductivity.The External Photoeffect: Photoelectron EmissionIf the energy of a photon illuminating the surface of a material in vacuum is sufficientlylarge, the excited electron can escape over the potential barrier of the material surfaceand be liberated into the vacuum as a free electron. The process, called photoelectronemission, is illustrated in Fig. 17.0-l(a). A photon of energy hv incident on a metalreleases a free electron from within the partially filled conduction band. Energyconservation requires that electrons emitted from below the Fermi level, where they Free electron Free electron l = * T t Vacuum level Emax Emax Photon Conduction band -f f X W W hv + 1 Fermi level hv I -5 0 Conduction band (al (bl Figure 17.0-l Photoelectric emission from (a) a metal and (b) a semiconductor. 645646 SEMICONDUCTOR PHOTON DETECTORSare plentiful, have a maximum kinetic energy ...