avalanchephotodiodetherebandwidth A6.pptx

DSF7GY Y80L

1. PRESENTED BY:- TEJA VARDAHAN ROLL N O : 227Z66A6 AVALANCHE PHOTODIODE & THERE BANDWIDTH

2. INTRO D UCTION The performance of Avalanche photo diode depends upon the efficiency. It convert light energy in to electrical signal.

3. PRIN C IPLE Designed to operate in reverse bias condition. Photo electric effect:

4. Avalanche Photodiodes High gain due to avalanche multiplication effect Increased noise Silicon has high gain but low noise Si-InGaAs APD often used(diagram on right) n + p + p i Electric field Depletion region

5. Avalanche Photodiodes (APDs) High resistivity p-doped layer increases electric field across absorbing region High-energy electron-hole pairs ionize other sites to multiply the current Leads to greater sensitivity

6. APD Detectors   s Si g n a l C u rre n t i  M   q  P  h   APD Structure and field distribution (Albrecht 1986)

7. I ph Detector Equivalent Circuits R d I d C d PIN I ph R d I d C d I n APD I ph =Photocurrent generated by detector C d =Detector Capacitance I d =Dark Current I n =Multiplied noise current in APD R d =Bulk and contact resistance

8. Carrier transit time Transit time is a function of depletion width and carrier drift velocity t d = w/v d

9. Detec t o r x Capacita n ce p x n For a uniformly doped junction W h e r e :  = p e r m i t i v i t y q = e l ec t r on c h a r g e N d =Active dopant density V o = A pp l i e d v o l t a g e V b i = B u i l t i n po t e n ti a l A = J un c ti on a r e a C   A W p-n junction w  x p  x n A  2q  C  N d 2  V o  V b i   1 / 2 q N d W       2  ( V o  V b i )  1 / 2 P N Capacitance must be minimized for high sensitivity (low noise) and for high speed operation Minimize by using the smallest light collecting area consistent with efficient collection of the incident light Minimize by putting low doped “I” region between the P and N doped regions to increase W, the depletion width W can be increased until field required to fully deplete causes excessive dark current, or carrier transit time begins to limit speed.

10. Bandwidth limit C=  K A/w where K is dielectric constant, A is area, w is depletion width, and  is the permittivity of free space (8.85 pF/m) B = 1/2  RC

11. MERITS APD Large gain Greater level of sensitivity High speed

12. DEM E RITS Much higher operating voltage required Much higher level of noise Output is not linear Requires high reverse bias for operation Not as widely used due to low reliability

13. APPLICATIO N Level of gain is of importance for high voltage requirement. Laser range finders Fast receiver modules for data communications High speed laser scanner (2D bar code reader) Speed gun