• summary_type: application
• word_count: 170

Forward bias (positive to p, negative to n) reduces the barrier: V_eff = V_0 - V_ext. Depletion narrows, majority carriers cross the junction, current rises exponentially: I = I_0*(e^(eV/nkT) - 1). The threshold voltage (~0.7 V Si, ~0.3 V Ge) is where significant current begins. Dynamic resistance r_d = nkT/(eI) — very low at operating point. Reverse bias (positive to n, negative to p) increases the barrier: V_eff = V_0 + V_ext. Depletion widens, only minority carriers (thermally generated) contribute a tiny saturation current I_0 (~nA for Si). Current is nearly voltage-independent until breakdown. Zener breakdown occurs in thin junctions (heavy doping): strong field ionizes covalent bonds. Avalanche breakdown occurs in thick junctions: accelerated carriers cause impact ionization cascade. The diode equation I = I_0*(e^(eV/nkT) - 1) describes both regions: positive V gives exponential forward current, negative V gives -I_0 (saturation). At room temperature, eV/kT ≈ V/0.026.