• $summary_{type}$: revision
• $word_{count}$: 180

Essential formulas: Band gap: Si = 1.1 eV, Ge = 0.67 eV. $n_e$$n_h$ = $n_i^2$. Barrier: 0.7 V (Si), 0.3 V (Ge). I = $I_0$(e^$\frac{eV}{kT}$-1). LED: lambda = 1240/$E_g$(eV) nm. Transistor: $I_E$ = $I_B$ + $I_C$, beta = $\frac{I_C}{I_B}$, alpha = $\frac{I_C}{I_E}$, beta = $\frac{alpha}{1-alpha}$. Zener regulator: $I_Z$ = $I_s$ - $I_L$, $I_s$ = $\frac{V_in-V_Z}{R_s}$, $I_L$ = $\frac{V_Z}{R_L}$.

JEE strategy: (1) n-type and p-type are neutral — don't confuse majority carriers with net charge. (2) Forward bias reduces barrier, narrows depletion; reverse does the opposite. (3) For Zener problems: always check $I_Z$ > 0 for valid regulation. (4) LED wavelength from band gap: use lambda = 1240/$E_g$. (5) Transistor: use $I_E$ = $I_B$ + $I_C$ as a check. (6) Logic gates: write the Boolean expression first, then build truth table row by row. (7) De Morgan's is the key to simplifying or converting between gate types. (8) Photodiode operates in reverse bias; solar cell is unbiased. (9) Mass action law always holds regardless of doping level.