2. - 九州大学(kyushu university)o.ed.kyushu-u.ac.jp/de/2019/ch2.1.pdf · 2.1.2...
TRANSCRIPT
2.������Switching device
2019��������� �����
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