ece228 lecture 14

ece228 lecture 14 - Bowers ECE 228A Photodetectors Lecture...

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Bowers ECE 228A Photodetectors Lecture #14 John Bowers CE 228A ECE 228A Read Chapter 4 Class on Friday at noon
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Bowers ECE 228A Types of Photodetectors Photoelectric detectors – Photovoltaic (PIN) – Photoconductive – Avalanche photodetector (APD) – Phototransistor Photoemission detectors – Vacuum photodiode – Photomultiplier Thermal detectors olometer – Bolometer – Thermocouple – Pyroelectric eak interaction Detectors Weak interaction Detectors – Photon drag
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Bowers ECE 228A Definitions • Quantum efficiency : Ratio of the number of electrons collected to the number of photons incident. • Responsivity: current out divided by optical power incident h e R d hc e R d  A W R d / 24 . 1
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Bowers ECE 228A • Photoelectric detectors Gain? hotovoltaic (PIN) o Photovoltaic (PIN) No – Photoconductive Yes – Avalanche photodetector (APD) Yes – Phototransistor Yes p i n
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Bowers ECE 228A Photodetector Classifications Illumination – Surface normal op illuminated • Top illuminated • Substrate illuminated urface perpendicular Su ace pe pe d cu a • Edge absorbing detectors • Waveguide detectors • Traveling wave photodetectors • Contacts – Metal (MSM photodetectors) – Semiconductor
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Bowers ECE 228A Detector Structures: Optical Configuration ptical configuration - ertical illumination Optical configuration Vertical illumination Single pass Double pass Resonant cavity Optical configuration - Horizontal illumination Edge absorbing Waveguide Travelling Wave
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Bowers ECE 228A Detector Structures Electrical Configuration Vertical Collection Interdigitated (MSM) Lateral Collection Absorbing Material Bulk Quantum Well Quantum Wire Quantum Dot
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Bowers ECE 228A PIN Photodetectors imits to bandwidth: Limits to bandwidth: • Carrier transit time urrent is response to carrier movement not current is response to carrier movement, not carrier collection • Carrier diffusion out of low field regions – Significant if absorption occurs outside high field region auses slow tail to impulse response – Causes slow tail to impulse response • Carrier trapping at heterojunctions educed by lowering barrier or use graded Reduced by lowering barrier or use graded interface • Parasitics
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Bowers ECE 228A PIN Detectors Transit Time Current is response to carrier movement: The duration of the pulse is qual to the transit time of the p n v equal to the transit time of the carriers: E x I n env n L Equivalent to bandwidth: x L I n n v n t n f 3 dB 0.45 v n L
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Bowers ECE 228A PIN Photodetectors Bandwidth Efficiency Product For thin intrinsic layers, the 3 dB bandwidth is approximately limited to 5 he quantum efficiency is given by f 3 dB 0.45 v s L The quantum efficiency is given by o the product of bandwidth and efficiency is  1 e L   L So the product of bandwidth and efficiency is independent of intrinsic layer thickness 5 f 3 dB 0.45 v s
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Bowers ECE 228A PIN Photodetector Bandwidth limits iffusion current eterojunction carrier PI N N Diffusion current Heterojunction carrier trapping
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ece228 lecture 14 - Bowers ECE 228A Photodetectors Lecture...

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