2.������Switching device

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2.1 �������� �Metal�Semiconductor�Insulatpr

• 2.1.1 ���� � / Metal, Insulator• 2.1.2 ��� Semiconductor• 2.1.3 n�����p���� / n-, p-type semiconductor• 2.1.4 ����������� / Major, minor carrier• 2.1.5 ����������� / Carrier conduction/diffusion

using Blackboard

2.1.1 �����Metal, Insulator

• ����� / Free electron model

2.1.2 ���Semiconductor

• ������� �� / Energy level of electron in atom• ���� / Covalent bond• ���� / Band structure, diagram

Ø ��!� �� / Metal: Open shell structureØ �������!� �� / Semiconductor, Insulator: closed

shell

2.1.3 n1p���n-/p-type semiconductor

• n���/ n-type semiconductor

Ø Si��%/02P3+���$�"�*)2dope35P'��+��)��2donor3#4� ���'����&�� 2carrier3$�"�)��5�&�2negative3&-./,+�!������+n���$(5

Ø Si crystal becomes n-type semiconductor if doped with P (phosphorous) as impurity material. P atom works as donor which provides negatively-charged carrier electron , which is generated from surplus covalent electron bond between B and Si.

• p���/ p-type semiconductor

Ø Si� %589;4/�=B<,2:3�*>B'��"�()+!�$���,��=�&��%�����&��'�&167-#�!�*��;hole<>��,��� �B ;acceptor<'�%.09��*>

Ø p-type semiconductor is doped with B (boron) as impurity material into Si crystal. B atom works as acceptor which provides positively-charged carrier hole, which is generated from vacant covalent bond between B and Si.

2.1.4 ���� ���� Major/Minor carrier

• �����/ intrinsic semiconductor

• n���/ n-type semiconductorØ� #��$���������→� ����!"�#����������!"�#�����

Ø Doner level; carrier electron is weakly bound to crystal; energy level is slightly-below the free-electron energy level

• p����/ p-type semiconductor

2.1.5 CLN?7%&Carrier transport

• ��7��RDiffusion of particleSØ)��U��7�'�Rthermal motion; random directionS

��7!��7�!8��JDHO"#7�$ =&

'()

*+'

$ , = $ - $ =&'()

*+' -&

'()

*+' =&

'()

*+' - +' + &

'(),0(),'10

*+' - +0 = ! + ,

Ø !��7�-<8 !��65=T�!U��3BAE��Rposition: Gaussian distributionS�7��VFP Raverage displacement = 0S

r1r2

r3

R

+#4+27�.8MQGK3�$-�1/�>=73 �8FP

07�-<6:<��7 �-��-*+(,;�+(97��7�>-�2=U��

00,;EM@I6:=#"

���!���'homogeneous distribution(�P$���"����� �����)�# %&'total flow = 0(

Ø���!����'inhomogeneous distribution(� �!"�#'total flow = diffusion flow ∝ #$

#%(

P=

P

≠

!&'() = !+,-.)

!&'() > !+,-.)

P$��"����$��'only particles crossing P are illustrated(

Ø���������external force acts on particles������� ���total flow = drift flow ∝ "�

P

≠"→ > %

drift: thermal motion + external force

R:drift

R

"→ = 0"→ > 0

$�3'�� Electric resistance of metal

• '�)��,91)7�+.6�-8Ø'�3��>��3��7*<!�3�9<� �

Ø"��%:relaxation time; τ

����:lattice vibration;

� �(impurity)

!���:grain boundary;

e-t/τ

τ t

1

€

e−t /τ dt0

∞

∫ = τ��,9/(1('�3�4��τ0��&��2�=#�503��3�%4τ

��,9/(1('�3��ratio of non-collision electron

Appendix

;>@:2�Drude’s formula

• "�(=?9<1�%.%6�1"�E 8�&6Ø"�3� f=-eE8)C��� α=f/m /� �!τ,)E2�1��+76AdriftBDE�2"�2� ��Adrift velocityBE

Ø"�(��v/��1�%.%60�&60C +|v|dt2��1%6"�(�#A8��6D*2���2��3A|v|dt/$6'5CC=-neA|v|dt2"�(�476D�-.C���!C���#�8��6"�2�3

vdt

A

€

j =CAdt

= −nev

v = aτ = −eEτ /m

Appendix

��� 5current density6(v%�"��'2.03�$

��)+

Ø j=σE %��!7�����5���; conductivity6σ(

Ø����τ-���'�� *��#,%7Cu$(�$2.7�10-14 s%&,8

€

j =ne2τmE

€

σ =ne2τm 134/'� 5Drude’s formula6

€

j = −nev

Appendix

��!�Diffusion current

• ����+.0��Ø Fick,��=�,�1-���+��'0<

&1+!�-e2�%0)!,��!���)*0<

586,��-

Ø���,�9��� !" ≈ $%:• ��;347 $ ≈ 10() m+/s, !" ≈ 30µm• �� $ ≈ 10(0~10(2m+/s, !" ≈ 0.3~1 cm• !9Si: $5 ≈ 3.5×10(8 m+/s, !" ≈ 6 cm• 5869Si: $: ≈ 1.25×10(8 m+/s, !" ≈ 3.5 cm

< = −$?@

< = A$5?@

< = −A$:?@

$=���9Diffusion constant:

lD

D: 1s#(/, $/,"�

��+.0�1

� �

Appendix

��

• IUG?QDM*2eV2=HS?V1� ,7�2�%.��:�56Z

• ��JHS0/1�987"�&�3ITOW$�;UA<PBCYIUG?QDM=3.75eVX0/2T;G?QDM���:�(7Z+2&�*"�-'7��:!46Z

ØKUF[L>FU2=HS?V3Ep=hν-'7Z�2��167=HS?V3ET=kBT-'7Z0)Y�#3c=3x108

m/s, MRU@�3h=6.6x10-34 Js, &2�&�3e=1.6x10-19 CYNESOU�3kB=1.38x10-23 J/K-'7Z

ØKUF2[ � �3�%*360nm�830nm2��2�-'7Z

��

• E=hν=hc/λ#$ λ=hc/Eg=619 nm• T=2 eV/kB=2.31�104 K

��,� ('*)�TF=8.12x104 K('*)� vF=1.57�108 cm/s

• 3.75 eV!�#�330 nm ���� ��%�"ITO ��� ��!���&������+

vF =!kFm

=2EFm