Semiconductor Light Sources and Detectors

응용광학 - Optoelectronics

Semiconductor Light Sources and Detectors

Light Emitting Diodes

Photodetector : device that measuresphoton flux or optical power

1. Thermal detector: converting photo energy into heat(inefficient and relatively slow)

2. Photoelectric detector: photoeffect

Ec

Ev

Ec

EFp

M

EFn

eVo

p nEo

Evnp

(a)

VI

np

Eo–E

e(Vo–V)

eV

EcEFn

Ev

Ev

Ec

EFp

(b)

(c)

Vr

np

e(Vo+Vr)

EcEFn

Ev

Ev

Ec

EFp

Eo+E (d)

I = Very SmallVr

np

Thermalgeneration Ec

EFnEv

Ec

EFp

Ev

e(Vo+Vr)

Eo+E

Energy band diagrams for a pn junction under (a) open circuit, (b) forwardbias and (c) reverse bias conditions. (d) Thermal generation of electron holepairs in the depletion region results in a small reverse current.

SCL

?1999 S.O. Kasap, Optoelectronics (Prentice Hall)

Photoconductivity

x

R

E

e–h+

iph

h> Eg

W

Vr

An infinitesimally short light pulse is absorbed throughout thedepletion layer and creates an EHP concentration that decaysexponentially

Photogenerated electron concentrationexp(x) at time t = 0

BA

vde


xeeIxI )(

0.2 0.4 0.6 0.8 1.2 1.4 1.6 1.8

Wavelength (m)

In0.53Ga0.47As

Ge

Si

In0.7Ga0.3As0.64P0.36

InPGaAs

a-Si:H

12345 0.9 0.8 0.7

1103

1104

1105

1106

1107

1108

Photon energy (eV)

Absorption coefficient () vs. wavelength () for various semiconductors(Data selectively collected and combined from various sources.)

(m-1)

1.0

E

CB

VB

k–k

Direct Bandgap Eg Photon

Ec

Ev

(a) GaAs (Direct bandgap)

E

k–k

(b) Si (Indirect bandgap)

VB

CB

Ec

Ev

Indirect Bandgap, Eg

Photon

Phonon

(a) Photon absorption in a direct bandgap semiconductor. (b) Photon absorptionin an indirect bandgap semiconductor (VB, valence band; CB, conduction band)


00.10.20.30.40.50.60.70.8

0.5 1 1.5 2탆Wavelength( )

The responsivity of a commercial Ge pnjunction photodiode

Responsivity(A/W)


0

0.1

0.2

0.3

0.4

0.5

0.6

200 400 600 800 1000 1200Wavelength(nm)

A B

The responsivity of two commercial Si pinphotodiodes

Responsivity(A/W)


0

0.2

0.4

0.6

0.8

1

800 1000 1200 1400 1600 1800Wavelength(nm)

The responsivity of an InGaAs pinphotodiode

Responsivity(A/W)


h> Eg

p+ i-Si

e– E

h+

Wl

Drift

Diffusion

A reverse biased pin photodiode is illuminated with a shortwavelength photon that is absorbed very near the surface.The photogenerated electron has to diffuse to the depletionregion where it is swept into the i-layer and drifted across.

Vr


pin Photodiode

AvalanchePhotodiode

š p+

SiO2Electrode

net

x

x

E(x)

R

Eh > Eg

p

Ip h

e– h+

Absorptionregion

Avalancheregion

(a)

(b)

(c)

(a) A schematic illustration of the structure of an avalanche photodiode (APD) biasedfor avalanche gain. (b) The net space charge density across the photodiode. (c) Thefield across the diode and the identification of absorption and multiplication regions.

Electrode


n+

Vou

Current

Time

Id

Vr

In pn junction and pin devices the main source of noise is shotnoise due to the dark current and photocurrent.

pn

Po

Dark

IlluminatedId + IphId + Ip h + in

R A


Noise of Photodiode

Solar cell panel

Solar roof

Materials:Si, poly-Si, a-SiGaAs 계열유기물 반도체

http://www.nobelprize.org/nobel_prizes/physics/laureates/2009/

Linear CCD array and 2D-CCD

Read Pedrotti Ch.17-3, Wikipedia, and Nobel Prize website information at http://www.nobelprize.org/nobel_prizes/physics/laureates/2009/

An active-pixel sensor (APS) is an image sensor consisting of an integrated circuit containing an array of pixel sensors, each pixel containing a photodetector and an active amplifier. There are many types of active pixel sensors including the complementary metal–oxide–semiconductor (CMOS) APS

CMOS image sensor

Semiconductor Light Sources and Detectors

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