| Cue (Question) | Notes (Answer) |
|---|---|
| What are the three types of solids by energy band? | Conductor (E_g = 0, bands overlap), Semiconductor (E_g ~ 0.1–3 eV), Insulator (E_g > 3 eV) |
| Energy gaps of Si and Ge? | Si: E_g = 1.1 eV; Ge: E_g = 0.67 eV; Diamond (insulator): E_g = 5.4 eV |
| What is intrinsic semiconductor? | Pure Si or Ge; n_e = n_h = n_i; conductivity increases with temperature |
| Dopant for n-type? Examples? | Pentavalent (group 15): P, As, Sb; majority carriers = electrons |
| Dopant for p-type? Examples? | Trivalent (group 13): B, Al, Ga, In; majority carriers = holes |
| State mass action law. | n_e × n_h = n_ — holds for both intrinsic and extrinsic semiconductors |
| Are doped semiconductors charged? | NO — both n-type and p-type are electrically NEUTRAL |
| Barrier potential of p-n junction? | Si ≈ 0.7 V; Ge ≈ 0.3 V (knee voltage) |
| Effect of forward bias on depletion region? | Narrows depletion region; barrier potential decreases; current flows |
| Special diode bias conditions? | Zener: reverse (regulator); Photodiode: reverse (light detection); LED: forward (light emission); Solar cell: no bias |
| Logic gate Boolean expressions? | OR: Y = A+B; AND: Y = A·B; NOT: Y = A'; NAND: Y = (A·B)'; NOR: Y = (A+B)' |
| Which gates are universal? | NAND and NOR — ANY Boolean function can be built from either alone |
| De Morgan's theorems? | (A+B)' = A'·B' and (A·B)' = A'+B' |
| Full-wave rectifier output frequency? | f_out = 2 × f_in (each half-cycle produces a pulse) |
Summary: Semiconductors are classified by their energy band gap. Doping with pentavalent atoms gives n-type (electron majority); trivalent gives p-type (hole majority). Both remain electrically neutral. The mass action law n_e × n_h = n_ governs carrier concentrations. p-n junctions form depletion regions with barrier potential (~0.7 V Si). Special diodes (Zener, photodiode, LED, solar cell) differ by bias and application. Logic gates (OR, AND, NOT, NAND, NOR) are the digital building blocks; NAND and NOR are universal. De Morgan's theorems connect them.