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Semiconductors & Electronic Devices formula sheet

Every formula in the Semiconductors & Electronic Devices chapter for JEE Main, with one line on when it applies. Topic 1 is open to everyone; sign in free to read all 19 and download the PDF.

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How we count: 7× asked means 7 past JEE Main questions in the PrepWiser bank needed that formula, and "last" is the latest year one appeared. ★ marks formulas asked 8 or more times.

Semiconductors

Energy bands
2× asked, last 2023
Eg(Si)≈1.1 eV,Eg(Ge)≈0.7 eVE_g(\text{Si})\approx1.1\ \text{eV},\qquad E_g(\text{Ge})\approx0.7\ \text{eV}
Conductor: overlap; semiconductor Eg<3E_g<3 eV; insulator >3>3 eV. Heating lowers a semiconductor's ρ\rho.
Photon making a pair
7× asked, last 2024
hν≥Eg,λmax⁡=hcEg=1240Eg(eV) nmh\nu\ge E_g,\qquad \lambda_{\max}=\frac{hc}{E_g}=\frac{1240}{E_g(\text{eV})}\ \text{nm}
Longest (cut-off) wavelength; also an LED's colour.
n-type and p-type
4× asked, last 2025
n-type: ne≫nh,p-type: nh≫ne\text{n-type: }n_e\gg n_h,\qquad \text{p-type: }n_h\gg n_e
n: pentavalent donor (P, As, Sb); p: trivalent acceptor (B, Al, Ga, In). Crystal stays neutral.
Mass action law
2× asked, last 2025
nenh=ni2,σ=e(neμe+nhμh)n_en_h=n_i^2,\qquad \sigma=e(n_e\mu_e+n_h\mu_h)
Equilibrium at fixed TT. Minority density =ni2/=n_i^2/majority.

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15 more formulas in 5 topics

The p–n junction, Diode circuits and rectifiers, Zener diode, Optoelectronic devices and Logic gates. Read the first part free. Sign in free with Google to read the rest and download the PDF.

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The p–n junction

  • Depletion layer5×
  • Forward and reverse bias4×
  • Dynamic resistance4×

Diode circuits and rectifiers

  • Diode in a circuit13×
  • Rectifiers3×
  • Clippers5×

Zener diode

  • Zener regulator11×
  • Regulator limits
  • Power rating12×

Optoelectronic devices

  • LED6×
  • Photodiode and solar cell6×

Logic gates

  • Basic gates11×
  • NAND and NOR10×
  • Universal gates18×
  • De Morgan and simplification11×

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Version 1, October 2026. Free to share for study, as it is. Please don't sell it or remove the PrepWiser name.

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