ece228 lecture 15

ece228 lecture 15 - Lecture 15 Optical Photodetectors and R...

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Lecture 15 - Optical Photodetectors and Receivers 15.1

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eading and Homework Reading and Homework Read Chapter 4 of Agrawal p g ECE 228A: Homework 4 Due: May 27, 2010 esign an InGaAs/Si APD i e 1) determine the thickness of the absorber Design an InGaAs/Si APD i.e. 1) determine the thickness of the absorber to achieve a responsivity of 0.5 A/W for a gain of 1 at a wavelength of 1.3 mm if the absorption coefficient is 1 mm -1 , 2) determine the electric field the multiplication layer necessary to give a gain of 10 if the multiplier in the multiplication layer necessary to give a gain of 10 if the multiplier thickness is 1 mm. 3) determine the charge value (between the absorber and gain regions so that the carriers move at saturated velocity in the absorber but do not have significant gain in the absorber, 4) Determine the gg , ) APD voltage for a gain of 10. 5) draw the band diagram at 0V and at a gain of 10, 6) What is the k value at that electric field? 7) What is the noise figure? (Neglect background doping in the absorber and 15.2 multiplication layers for all questions).
Avalanche Photodiodes (APDs) va a c e otod odes ( s) Rate at which electrons multiply Rate at which holes multiply A large ratio of  or  results in a large gain bandwidth product and low noise amplification. True for Si Most III-Vs have a small ratio, and limited gain bandwidth roduct. The noise is larger, but still lower than a PIN product. receiver. 15.3

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Ionization Coefficients for Semiconductors GaAs 10e6 ] In 0 . 53 Ga 0 . 47 As electrons holes 10e4 10e5 ts[cm -1 InP 1000 oefficien t From: Si: P.P. Webb, "Measurements of Ionization Coefficients in 10 100 ation C o Silicon at Low Electric Fields", GE Canada Inc. InP: L.W. Cook, et. al., Appl. Phys. Lett. 40 (7) , 1 April 1982 InGaAs: T.P. Pearsall, Appl. Phys. Lett. 36 (3), 1 February 1980 GaAs: H.D. Law and C.A. Lee, Solid-State Electronics , 21 , 1978 1 Ioniz a Electric Field [kV/cm] 200 300 400 500 0.1
The Avalanche Multiplication Process - - - - - - - - - - + + + - - - - + + - - + + - + - - + + + + - - + + P+ N+ - + - - + + P+ N+ + + Si Multiplication Layer - + - - + InP Multiplication Layer

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SAM APDs, SAGM APDs: Need for Separate Absorption and Multiplication Regions mall bandgap avalanche regions tend to have Small bandgap avalanche regions tend to have large dark current. Absorption Region Multiplication egion Region e- e- e- Electric ield Field position
SiGe SAM APDs 10m 0 10μ 100μ 1m 0 Total current Dark current Gain 20 25 30 n 10n 100n Current [A ] 10 15 Gain Ge -30 -25 -20 -15 -10 -5 0 10p 100p 1n 0 5 Si Voltage [V]

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SiGe SAM APDs 500 600 GHz) Si APD, k=0.09 00 400 Product ( G This work InGaAs/Si 200 300 bandwidth 0.0 0.4 0.8 1.2 1.6 2.0 0 100 InAlAs APD, k=0.2 InP APD, k=0.4 Gain- b 350 GHz Multiplication Layer Thickness ( m) 100 GHz 350 GHz Kang et al. Nature Photonics, Dec. 2008 >500 GHz Zaoui et al., OFC 2009
PDs APDs in h e P M I Photocurrent: I Input optical power: Pin in RP I =quantum efficiency M: gain R: responsivity Noise: Thermal noise (same as PIN) Shot noise is larger: results from generation of secondary electron hole pairs through impact ionization. Excess noise factor is largest when ionization coefficients are equal: Excess noise ctor factor: ) 2 )( 1 ( ) ( 1 M A A r k M k M F 1 0 / / A A k or k

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xcess Noise of APDs Excess Noise of APDs
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This note was uploaded on 05/27/2010 for the course ECE 228a taught by Professor Bowers,j during the Spring '08 term at UCSB.

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ece228 lecture 15 - Lecture 15 Optical Photodetectors and R...

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