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Advanced

Semiconductor

Devices

Lecture 5

Advanced

Semiconductor

Devices

Lecture 5

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2 V. Ariel 2013 Advanced Semiconductor Devices Lecture 5

Lecture outline

Review

Photodiode

Pixel Structure

MOS Transistor overview and fabrication

Basic two-terminal MOS structure

Regions of operation

Solution for charges and potentials

Approximations for regions of operation

All figures based on Tsividis, McAndrew, Operation ans Modeling of the

MOS Transistor Copyright Oxford University Press

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Photo-current generation

Practical pn-junction photodiode under reverse bias

x

Ap N;

nx0

cxp

x

W

( )LG xn+hn

hn

0,n px x W One-side junction D An N p N +

= =?

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4 V. Ariel 2013 Advanced Semiconductor Devices Lecture 5

Junction current

The total current is the sum of dark and photon generated currents

J

0J

AV

0 0 0

11

1

W nPH p

n n

DJ J J qF e qn

L L

a

a

- = + = - + +

0PHJ qF

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3T APS design

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MOS Transistor overview

Lilienfield patent from 1930

Basic MOS Transistor

structure

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MOS Transistor fabrication techniques

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MOS Transistor Crossection

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MOS Transistor SEM imsage

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Basic semiconductor equations

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Contact potentials

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Basic two-terminal MOS structure - capacitor

Gate

Insulator

Semiconductor Body

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Interface charge

Parasistic interface charges

Contact potential

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Flatband voltage

Assume

Need to apply external voltage in order to

straighten energy bands

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Voltage and charge balance

Total charge in semiconductor body

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Electron charge density

Surface electron charge density

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Charge inversion

Inversion charge basis of current transport

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Flatband

Accumulation

Depletion and inversion

Regions of operation

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Charge density and Poisson equation

Solution for semiconductor

charge

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Charge density and Poisson equation

Charge density as a

function of distance

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Solution of Poisson equation

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Solution of Poisson equation

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Solution for surface electric field

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Solution for semiconductor charge

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Charge and potential balance

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Semiconductor charges andpotentials

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Solution for gate voltage

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Accumulation

Condition for charge accumulation

Approximate solution for charge accumulation

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Deep Depletion

Condition for depletion

Approximation for gate voltage in depletion

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Inversion

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Gate voltage and surface potential ininversion

W k i i

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Weak inversion

Since

Approximation for inversion charge

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Approximation for inversion chargein strong inversion

St i i

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Strong inversion

M d t i i

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Moderate inversion

No simple solution for semiconductor charges and

potentials in moderate inversion !!!