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Concepts Of Physics MCQ Edition [Volume 2]PhysicsSemiconductors and Semiconductor Devices

A semiconducting material possesses a band gap of 1 eV . It is doped with acceptor impurities that establish acceptor levels 1 meV above the valence band. Suppose that a transition from one energy level to another is practically forbidden if kT is less than 1/50 of the energy gap. Furthermore, if kT exceeds twice the gap, the upper levels achieve maximum population. The temperature of the semiconductor is raised from

Options

  1. A12 K to 11600 K
  2. B10 K to 115 K
  3. C40 K to 460 K
  4. D20 K to 230 K

Correct answer

D. 20 K to 230 K

Step-by-step solution

The energy required to excite an electron from the valence band to the acceptor level is E_a = 1 meV = 10⁻³ eV . The acceptor levels achieve maximum population when kT₁ = 2 E_a = 2 10⁻³ eV . Using the Boltzmann constant k 1 11600 eV/K , we get: T₁ = 2 10⁻³ 11600 = 23.2 K At this temperature, all acceptor levels are occupied by electrons, meaning the hole concentration in the valence band reaches a constant value. The hole concentration remains constant until electrons from the valence band start getting excited to

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