eye, semiconductors and the photoelectric effect -...

1- Introdução a detectoreseye, semiconductors and the photoelectric effect

AGA 5802: Astrofísica ObservacionalAluno: André Luís SampaioData: 09/04/2013

BIBLIOGRAFIA

• Kitchin – Astrophysical Techniques (5th Ed, 2009), Chapter 1 – Detectors

Pag 1 a 14

COMPLEMENTO AO LIVRO

• Fernald, R. D. (2006), Casting a Genetic Light on the Evolution of Eyes (Science, Volume 313, Issue 5795)

1 http://www.sciencemag.org/content/313/5795/1914.abstract

2 http://ekendil.angelfire.com/Doc/IC/Casting_a_Genetic_Light_on_the.pdf

• Stolfi, Guido (2000), PEE-647 Princípios Televisão Digital EPUSP

• Yoshinori Shichida & T. Matsuyama, Evolution of opsins and phototransduction (Philos Trans Royal Society 2009 October ) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2781858/

AGENDA DESTE SEMINÁRIO

• CHAPTER 1 – DETECTORS– OPTICAL AND INFRARED DETECTION

• INTRODUCTION• DETECTOR TYPES• EYE• SEMICONDUCTORS

– Photoelectric Effect

• CCDs

• Photomultipliers

– RADIO AND MICROWAVE DETECTION– X-RAY AND γ-RAY DETECTION– COSMIC RAY DETECTORS...

DEMAIS SEMINÁRIOS

Kitchin – Astrophysical Techniques 5th, Chapter 1 – Detectors1.1 OPTICAL AND INFRARED DETECTION

1.1.1 Introduction

From Astronomy Methods, H. Bradt

In Astrophysical Techniques, Kitchin

OPTICAL REGION

Besides visual, includes InfraRed + UltraViolet ~ from 100µm to 10nm

Techniques and physical process over this extended region are similar

� Conveniently dicussed together


1.1.2 Detector Types

OPTICAL REGION

Detectors fall into two main groups:

� Thermal

� Quantum (or photon)

•Detect radiation through the increase in temperaturethat its absorption causes

•Integrate absortion with analog output.

• - Generaly less sensitive and slower in time response.

• + Broader spectral response

•Examples: thermocouples, pyroeletric and bolometers

Thermal

Applications in astronomyFar InfraRed ~ 200 µm to 1 mm

bolometers

•Individual photons of optical signal interact directly with the electrons of the detector

•Photon counting or Integrated with analog output.

• + Generaly more sensitive and faster in time response.

• - Narrower spectral response.

•Examples: EYE, photographic emulsion, photomultiplier, photodiode and CCD

Quantum

Both incoherentPhase information is lost


1.1.3 Eye

Eye in astronomy

Now rarely used, but still a few applications (eg. double star / planetary observation)

- find and/or guide objects visually

- amateur astronomers who gaze into the sky

� Some importance in understanding , especially its DEFECTS

• Basic optics is not enough• The eye and the brain act together• Image detected on the retina (is/has):

1. inverted;2. chromatic aberration;3. narrowed spectrum detection λ (390-700 nm);4. logarithmic luminosity response (log(L));5. subjective luminosity dynamical range;6. variable angular resolution α <- (θ, λ);7. variable scintillation perception (α, θ, λ).8. slow dark adaptation

EVALUATING HUMAN VISION

WHY ? HOW MUCH?


1.1.3 Eye – Light Detection

Light detection in

the eye

Two types of receptors : Cones (color) and Rods(black and white)

� Rods have Rhodopsin pigments (opsin + retinal chromophore)

� Cones have Iodopsin pigments (different opsin + retinal chromophore)

100 x 106 rod cells006 x 106 cone cells

001 x 106 nerve cells opsin protein (40k amu)

11-cis-retinal chromophore(286 amu)


1.1.3 Eye – Absorption Curves

PURKINJE EFFECTS � shift in sensitivityRODS peaking at 510nm and CONES at 550nm

• CONES• Bright light vision• Center Vision

• RODS• Faint light vision• Peripherical vision

AVERTED VISION � only peripherical can see faint objects

ILUMINATION RANGE � by a factor up to 1010


1.1.3 Eye – Big Picture

Big Picture

Under influence of light, cis-retinal changes to trans configuration < 1ps

Rhodopsin splits into Opsin + Retinal

Excitation occurs during the splitting (precise mechanism not yet understood)

Reaction changes the permeability of the cell´s membrane to ions

Ions change electrical potential and propagates to nerves

Rhodopsin slowly regenerated

Response of the cones has similar mechanism

NOT ANYMOREG-Protein coupled Receptors

now well understood

G-Protein coupled receptors

Um exemplo desse tipo de interação, citado na apresentação emEstocolmo, é o do contato da adrenalina com as células. O hormônio não entra nacélula para surtir seu efeito - ele age sobre os receptores que são alvo daspesquisas de Kobilka e Lefkowitz, que então desencadeiam uma reação nometabolismo celular.

Além da adrenalina, a família dos GPCRs inclui receptores para

dopamina, serotonina, luz, paladar e odor. A maioria dos processos fisiológicosdepende dos GPCRs, destaca a entidade que concede o Nobel.

O prêmio é um reconhecimento a seus estudos sobre receptores acoplados à proteína G (GPCRs, na sigla em inglês) - uma família de receptores situados nas membranas celulares que se ligam a moléculas no exterior e enviam "sinais" para dentro, ...



©2009 by The Royal Society

Mechanism of phototransductionin mammalian eyes

Gα

Gβ

Gγ

RhodOpsin


G-Protein coupling RhodOpsinMammalian Gt

GTP GDPGTP

GDP

photoisomerization


1.1.3 Eye – DEFECTS

THE EYE AND THE BRAIN ACT TOGETHER

CO

MP

LEM

ENTO

AO

LIV

RO

A – Squares have same gray color, but right one looks darkerB – Bends have no steps, but it looks likeC – Circles are totaly white, but blink in black

Why so many perceptional defects ?

• Evolutional echoes:

– Vertebrates eye chambers

– Opsin and G-Protein coupled receptors

– Mammal and primates ecological niches


Science 29 September 2006: Vol. 313 no. 5795 pp. 1914-1918DOI: 10.1126/science.1127889

1. Opsins type 1 are much older and are used for collecting energy and information from photons found in archaea and eukaryotic microbes.

2. Opsins type 2 (no phylogenetic relationship), include coupled Gt (vertebrate) , Go and Gq (invertebrate) subfamilies:

• c-Opsin and r-Opsin

shadows refraction reflection

eyes form images using:


molluscs and basal chordates

Arthropods-> Color VisionVertebrates-> Circadianrhythm

Vertebrates-> Vision

1. First eyes were simple eyespots (Cambrian, 570 to 500 Mya)

2. All vertebrates have eyes with phylogenetic relationship

NARROWED SPECTRUM DETECTION λ (390-700 nm)

Human Trichromacy

� Mammal and primates ecological niches


teleost fish, Reptiles and birdstetrachromacy

Liquid Water Absorption

remote vertebrates tetrachromacy

placental mammals (ancestors were nocturnal)

dichromacy

Primates trichromacy

KT event


Stolfi G. (2000), PEE-647

Fovea

• > One-to-one relationship• more cones

retina

• > One-to-many relationship• more rods (bastonetes)

VARIABLE ANGULAR RESOLUTION α <- (θ, λ)



LOGARITHMIC LUMINOSITY RESPONSE (L)

SUBJECTIVE DYNAMICAL RANGE

� Scotopic and Photopic ilumination response

Weber-Fechner lawastounding range of light intensities,from bright sunlight to dim starlight


VARIABLE SCINTILLATION PERCEPTION (α, θ, λ).



SLOW DARK ADAPTATION

Reason � Chrmophore and Opsin biochemistry cycle

Opsin + 11_cis_Retinal = RhodOpsin


1.1.3 Eye – SUMMARY FACTS

• Rayleigh limit of resolution of the eye is 20“ � iris maximum 5 - 7mm• Fovea actual resolution 1’ - 2’• Average human eye resolution 5’ - 10’

• Brighter area � seen larger than real � irradiation

• Response to changes in ilumanation is logarithmic (Weber-Fechner)• Reason for magnitude scale used by astronomers


1.1.4 Semiconductors

Abstract � Why to study semiconductors in Optical and InfraRed Detection ?

Detectors derive their properties from the behavior of semiconductors

Phomomultiplier, CCDs and several others

PHOTOMULTIPLIER CCD

Scientific Preview

Band theory explains electron conduction in solid matterials: conductors, insulators and semiconductors

Differing atomic species changes Fermi energy levels (n-type and p-type)

Several techlogical applications manipulating pure/doped substract layers



Monocrystallinesilicon ingot

Pictures

Si [Ne] 3s2 3p2

Pure SiliconSi Wafers

CHIPs

Substract Layers

Transistors, Diodes, LEDs, CCDs etc



BAND THEORY

Atoms have discrete energy levels

As two atoms aproaches, interaction causes the leves to split

For N atoms, original level is split into N sublevels

Razumovsky Alexey S


- Conductors : conduction band and the valence band are overlapped �electrons with any acceptable low energy can move freely;

- Dielectrics : the bands are not overlapped / distance exceeds 3 eV� electron transfer requires more power, so insulators -> no electrical current

- Semiconductors : the bands are not overlapped / distance in the range from 0.1 to 3 eV� so pure semiconductors conduct poorly

Conduction in Solid Materials

The Fermi-Dirac Distribution

FERMIONS: • particles with half-integer spin • characterized by Fermi–Dirac statistics • following the Pauli exclusion principle

hyperphysics.phy-astr.gsu.edu


FERMIONS

intrinsic

Band model of Doped SemiconductorsCOMPLEMENTO AO LIVRO

n-type p-type

http://www.ece.umd.edu/~dilli/courses/enee313_spr09/files/supplement1_carrierconc.pdf

intrinsic

n-type p-typeintrinsic

22

3

Perdas 32211

SiIntrínseco

Wiefetivo11

Witeórico

P-type tem menos perdas

P-type tem Wteórico maior

SiIntrínseco

Witeórico

Wpefetivo

SiP-type

Wpteórico

• O Si intrínseco tem mais perdas por formação de pares, phonos e por banda de condução

• Com menos perdas, o Si p-type tem Wefetivo menor mesmo com Wteórico maior

REDUÇÃOWefetivo


Not in scale

Discussão sobre W em p-type


1.1.4.1 PhotoElectric Effect

Photoeletric

Effect

The material absorbs a photon with λ < than its limit

A electron is emitted (Kmax = hc/λ - W)

• Absorb radiation efficiently

• Realease the electron promptly

• Mean free path MFP(e-) [electron] >> MFP( Ύ) [photon]

A goodphotoemitter

• Conductors (so many vacant sublevels & many moving e- conduction)

• Light reflection & collisions -> photo e- may even not escape

• MFP(e-) ~ 1nm << MFP (Ύ) = 10nm Metals

• As insolators (no vacant sublevels & few e- in conduction)

• still can lose energy by producing pairs of electrons & holes

• Also by sound waves (phonons), very significatively if e- originate deepSemiconductors


1.1.4.1 PhotoElectric Effect

Pratical good photoemitter

Since Photoelectron energy loss effects (phonos , formation pairs and collisions) increase W

� Strongly p-type to reduce collisions of electrons in the conduction band

� Lower temperature to reduce phonos

� Energy E1 > E2 to avoid production of pairs of electrons & holes

E1 > E2 eliminate production ofpairs electrons & holes

E2

E1

W

W (Work Function) = E(ionizartion limit) – E(top Valence Band)

Material lower temperaturereduce sound waves (phonos)

Strongly p-type reduce W

AGENDA DESTE SEMINÁRIO

• CHAPTER 1 – DETECTORS– OPTICAL AND INFRARED DETECTION

• INTRODUCTION• DETECTOR TYPES• EYE• SEMICONDUCTORS

– Photoelectric Effect

Thats all folks!


EXTE

ND

ED O

PTI

CA

L R

EGIO

N

ANEXO 1 – Extended Optical Region

http://www.ece.umd.edu/~dilli/courses/enee313_spr09/files/supplement1_carrierconc.pdf

ANEXO 2 – Intrinsic Fermi Level

ANEXO 3 – Scotopic & Photopic


http://www.telescope-optics.net/eye_spectral_response.htm

eye, semiconductors and the photoelectric effect -...

Documents