chap2 - Chng 2 iot ban dan 1.1 ai cng chat ban dan 1.2 iot...

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1 Chöông 2: Ñioát baùn daãn 1.1 Ñaïi cöông chaát baùn daãn 1.2 Ñioát baùn daãn
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2 1.1 Ñaïi cöông chaát baùn daãn Khaùi nieäm vaät lieäu ñieän Thuyeát mieàn naêng löôïng Chaát baùn daãn Chuyeån ñoäng troâi vaø chuyeån ñoäng khuyeách taùn Lôùp tieáp xuùc P-N
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3 Khaùi nieäm vaät lieäu ñieän Ngöôøi ta chia caùc vaät lieäu ñieän ra laøm 3 nhoùm chính laø : chaát daãn ñieän, chaát caùch ñieän vaø chaát baùn daãn . Chaát baùn daãn (Semi – conductor) laø chaát coù ñieän trôû suaát trung bình giöõa chaát daãn ñieän (kim loaïi) vaø chaát caùch ñieän (ñieän moâi) Chaát daãn ñieän coù ñieän trôû suaát = 10 -6 10 -4 (Ohm- met) Chaát baùn daãn coù ñieän trôû suaát = 10 -4 10 +4 (O-m) Chaát caùch ñieän coù ñieän trôû suaát =10 +4 10 +10 (O-m)
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4 Mieàn naêng löôïng cuûa chaát raén Mieàn (1) ñöôïc goïi laø mieàn hoaù trò hay mieàn ñaày: laø mieàn naêng löôïng bò laáp hoaøn toaøn bôûi caùc e. Mieàn (2) mieàn daãn : laø mieàn naêng löôïng chöa bò caùc e chieám heát. Mieàn caám : laø mieàn cheânh leäch naêng löôïng giöõa mieàn hoùa trò vaø mieàn daãn, khoâng coù caùc e chieám giöõ.
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5 Mieàn naêng löôïng cuûa chaát raén(tt) Chaát daãn ñieän Coù mieàn hoaù trò vaø mieàn daãn keá tieáp nhau hay goái leân nhau, cho neân caùc e ôû caùc möùc naêng löôïng treân mieàn ñaày deã daøng nhaûy sang möùc naêng löôïng cuûa mieàøn daãn (ngay caû khi nhieät ñoä raát thaáp), vaø chuùng tham gia vaøo quaù trình daãn ñieän döôùi taùc duïng cuûa ñieän tröôøng ngoaøi (caû khi E nhoû). Chaát caùch ñieän Mieàn caám coù ñoä roäng lôùn (khoaûng 5 – 10 eV) do ñoù caùc e ôû mieàn hoaù trò khoâng coù khaû naêng nhaûy leân mieàn daãn. Vì vaäy trong nhöõng ñieàu kieän bình thöôøng, chaát naøy khoâng coù khaû naêng daãn ñieän döôùi taùc duïng cuûa ñieän tröôøng ngoaøi (caû khi E coù cöôøng ñoä lôùn). Chaát baùn daãn Coù mieàn hoaù trò vaø mieàn daãn caùch nhau bôûi 1 mieàn caám delta W nhoû (~ 0,2 1,5 eV) cho neân caùc e coù khaû naêng nhaûy möùc töø mieàn hoaù trò leân mieàn daãn
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6 Mieàn naêng löôïng cuûa chaát raén(tt)
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7 Chaát baùn daãn Chaát baùn daãn thuaàn Chaát baùn daãn tieâu bieåu trong ngaønh ñieän töû laø Ge(32) vaø Si(14), caùc chaát naøy thuoäc nhoùm IVa trong baûng tuaàn hoaøn Mendeleev. Ta ñaõ bieát raèng vaät chaát ñöïôc caáu taïo töø nguyeân töû cuûa chaát ñoù. Si vaø Ge coù 4 ñieän töû ngoaøi cuøng, neân caùc ñieän töû naøy seõ lieân keát vôùi 4 ñieän töû ngoaøi cuøng cuûa 4 nguyeân töû keá caän theo kieåu lieân keát ñoàng hoùa trò beàn vöõng. Do ñoù caùc ñieän töû khoù taùch khoûi nguyeân töû trôû thaønh ñieän töû töï do
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