Energy Band Gaps (Must Memorize)

Doping — Quick Key

• Pentavalent (5$e^{-}$) = N-type → P, As, Sb → Majority: electrons
• Trivalent (3$e^{-}$) = P-type → B, Al, Ga, In → Majority: holes
• BOTH are electrically NEUTRAL
• Mass action: n_e × n_h = n_$i^{2}$ (always)

Special Diodes — One-Line Each

Rectifier Frequencies

• Half-wave: f_out = f_in (1 diode, positive half only)
• Full-wave: f_out = 2 × f_in (2 or 4 diodes, both halves)

Logic Gate Truth — Critical Values

De Morgan's Theorems (Break + Flip)

$\overline{A+B} = \overline{A} \cdot \overline{B}$

$\overline{A \cdot B} = \overline{A} + \overline{B}$

Top 3 NEET Traps — This Chapter

1. n-type is NOT negatively charged → electrically neutral
2. Zener diode works in REVERSE bias (not forward) for regulation
3. Full-wave rectifier → output frequency = 2 × input (not same as input)

Key Numerical Formula

$n_h = \frac{n_i^2}{n_e} \quad \text{(minority carrier concentration)}$

$\lambda(\mu m) = \frac{1.24}{E_g(eV)} \quad \text{(LED wavelength shortcut)}$