Si ya Ge mein se kiska bandgap bada hai, aur kitna fark hai?
Silicon (~1.12 eV) vs Germanium (~0.66 eV); Si ka 0.46 eV zyada hai.
Bada bandgap OFF-state leakage kyun reduce karta hai? ::: Kam electrons ke paas gap jump karne ke liye itni thermal energy hoti hai, isliye kam thermally-generated intrinsic carriers → kam leakage current.
Intrinsic carrier concentration ki temperature-dependence kya hai? ::: ni∝T3/2e−Eg/2kBT.
e−Eg/2kBT mein 2 ka factor kyun hai? ::: Kyunki ni=np aur pair product np∝e−Eg/kBT hai; square root exponent ko aadha kar deta hai.
Silicon ka sabse decisive process advantage kya hai? ::: Uska stable, insulating native oxide SiO₂ (jabki GeO₂ water-soluble aur unstable hai).
Ek aisa area batao jahan germanium abhi bhi silicon se behtar hai. ::: Higher carrier mobility (faster switching, SiGe RF mein use) ya better infrared/fiber-optic photodetection.
300 K par Ge mein Si se roughly kitne zyada intrinsic carriers hote hain? ::: Lagbhag 3–4 orders of magnitude zyada (1013 vs 1010 cm⁻³).
Bada Eg maximum operating temperature kyun badhata hai?
Intrinsic carriers T ke saath zyada dheere badhte hain, isliye wo dopants ko sirf zyada temperature par overwhelm karte hain.
Pehla transistor kis material ka tha, aur ise kya replace kiya?
Germanium (1947); silicon ne ise oxide aur thermal stability ki wajah se replace kiya.
Recall Feynman: 12-saal ke bacche ko samjhao
Socho do gates hain jo free-roaming electrons ke ek maidan ki raksha kar rahe hain. Silicon ka gate UNCCHA hai, germanium ka gate CHHOTA. Heat waise hai jaise bacche jump karne ki koshish kar rahe hain. Chhote gate ke upar bahut saare bacche tab bhi sneek through kar jaate hain jab tum nahi chahte — ye leakage hai, aur ye germanium chips ko overheat aur misbehave karta hai. Unccha silicon gate cheezein quiet rakhta hai jab tak tum khud electrons ko andar aane nahi dete. Bonus: jab tum silicon ko hawaas mein chhod dete ho, toh ye apna perfect glassy raincoat (SiO₂) khud grow kar leta hai jo hum tiny switches banane ke liye use karte hain. Germanium ka raincoat paani mein dissolve ho jaata hai. Plus silicon basically sand hai — dirt cheap. Unccha gate + free raincoat + sasta = silicon jeet jaata hai.
