physics-class-12-unit-14-chapter-02-doping-in-semiconductors-l-2-8-lb2iinnipr4

<p><Success style="float:center;text-align:center;font-size:28px;" ><B>Doping in Semiconductors</B></Success></p>
<p><Primary style="float:center;text-align:center;font-size:24px;"><B>Semiconductor</B></Primary></p>
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<li>For an isolated atom, the possible energies $\rightarrow 3p$</li>
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<p>Of quantum states are discrete. We talk of $\rightarrow 3s$</p>
<p>Is 2s, 3s, 3p etc orbitals having different $\rightarrow 2p$</p>
<p>Energies. $\rightarrow 2s$</p>
<p>$\rightarrow 1s$</p>
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<p>======</p>
<p><Success style="float:center;text-align:center;font-size:28px;" ><B>Doping in Semiconductors</B></Success>
<Primary style="float:center;text-align:center;font-size:24px;"><B>Semiconductor</B></Primary></p>
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<p>For a gas/vapour of that material, the same energies are available. Number of quantum states increases according to the number of atoms.</p>
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<p>Electrons fill the orbitals from lowest energy states, one per quantum state. The last non empty level may be completely or partially filled.</p>
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<p>======</p>
<p><Success style="float:center;text-align:center;font-size:28px;" ><B>Doping in Semiconductors</B></Success>
<Primary style="float:center;text-align:center;font-size:24px;"><B>Semiconductor</B></Primary></p>
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<p>As the atoms are brought closer to form
the solid crystalline state, outer electrons also start interacting through bonding and
the energies are split to form almost continuous energy bands</p>
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<p>The lower energy levels are populated by inner electrons and are not affected by the inter atomic electron interactions but the higher ones spread more</p>
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<p>The highest completely filled energy band is called valence band and the next higher band is called conduction band.</p>
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<span style="color:blue">Semiconductor</span>$\to$Intrinsic and Extrinsic Semiconductors$\to$Example$\to$Instrinsic Semi Conductors$\to$Impurity Levels / Donor Levels$\to$Numercial Problems$\to$Solution$\to$Summary$\to$Intrinsic Semiconductor$\to$Charge Density
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<p>======</p>
<p><Success style="float:center;text-align:center;font-size:28px;" ><B>Doping in Semiconductors</B></Success></p>
<p><Primary style="float:center;text-align:center;font-size:24px;"><B>Semiconductor</B></Primary></p>
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<p>In good conductors, the conduction band is partially filled, there are enough electrons and enough empty state even at very low temperatures</p>
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<p>In insulators the conduction band is completely empty and the energy gap between the valance band and conduction band is large, say 3-6 eV. At usual temperatures no electrons populate the quantum states in conduction band</p>
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<p>======</p>
<p><Success style="float:center;text-align:center;font-size:28px;" ><B>Doping in Semiconductors</B></Success></p>
<p><Primary style="float:center;text-align:center;font-size:24px;"><B>Semiconductors</B></Primary></p>
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<p>In Semiconductors, the conduction band is completely empty at very low temperatures. The energy gap between the (CB) valance band and conduction band is (VB) relatively small, say around or less than 3 $\mathrm{eV}$. For Silicon it is $1.12 \mathrm{eV}$</p>
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<p>At higher temperatures (say at room temperature), some of the electrons in the valance band get sufficient energy from thermal interactions to cross over the gap and occupy quantum states in the conduction band. This leaves behind vacant quantum states in the valence band</p>
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