Energy bands: metal, insulator, semiconductorऊर्जा बैंड: धातु, विद्युतरोधी, अर्धचालकEnergy bands: metal, insulator, semiconductor

NCERT Fig 14.2 · Class 12 Physics · Chapter 14 · interactive diagram

Parts and what they mean

• (a) Metal — conduction band ((a) धातु — चालन बैंड) — In a metal the conduction band is partly filled, or it overlaps the valence band, so plenty of electrons are free to conduct. Resistance is low.
• Metal — valence band (धातु — संयोजकता बैंड) — Its top lies above the bottom of the conduction band.
• Band overlap (बैंड अतिव्यापन) — EC lies below EV: electrons pass into the conduction band with no energy needed (Eg ≈ 0).
• (b) Insulator — empty conduction band ((b) विद्युतरोधी — खाली चालन बैंड) — No electrons in the conduction band, so no conduction.
• Insulator — full valence band (विद्युतरोधी — भरा संयोजकता बैंड) — All valence electrons stay bound.
• Large gap, Eg > 3 eV (बड़ा अंतराल, Eg > 3 eV) — Too large for thermal energy to lift electrons across (e.g. diamond, 5.4 eV).
• (c) Semiconductor — conduction band ((c) अर्धचालक — चालन बैंड) — At room temperature a few electrons reach it from the valence band and can move.
• Semiconductor — valence band (अर्धचालक — संयोजकता बैंड) — Each electron that leaves creates a vacancy (hole) here, which also helps conduction.
• Small gap, Eg < 3 eV (छोटा अंतराल, Eg < 3 eV) — Si 1.1 eV, Ge 0.7 eV: small enough for some electrons to cross at room temperature.
• Thermally excited electrons (ऊष्मीय रूप से उत्तेजित इलेक्ट्रॉन) — Few in number, so resistance is between that of metals and insulators.
• Holes left in the valence band (संयोजकता बैंड में बने होल) — One hole for every electron that went up.

Original diagram drawn by Simple Learning Hub, based on NCERT Fig 14.2. Report a mistake