Question

{"given":"A silicon p-n junction is analysed under two bias conditions: forward bias (external voltage reduces the built-in potential barrier) and reverse bias (external voltage increases the built-in potential barrier).","key_observation":"In forward bias, the reduced barrier allows majority carriers to diffuse across the junction driven by concentration gradients. In reverse bias, the enhanced barrier blocks majority carrier diffusion; instead, minority carriers are swept across by the electric field, which constitutes drift.","option_analysis":[{"label":"(A)","text":"Drift in forward bias; diffusion in reverse bias","verdict":"incorrect","explanation":"This reverses the correct mechanisms. In forward bias, diffusion (not drift) dominates as majority carriers cross the reduced barrier due to concentration gradients."},{"label":"(B)","text":"Diffusion in forward bias; drift in reverse bias","verdict":"correct","explanation":"In forward bias, majority carriers diffuse across the junction; in reverse bias, minority carriers are swept by the electric field (drift). This is the correct description."},{"label":"(C)","text":"Diffusion in both forward and reverse bias","verdict":"incorrect","explanation":"In reverse bias, the large electric field suppresses diffusion of majority carriers; minority carrier drift is the dominant mechanism, not diffusion."},{"label":"(D)","text":"Drift in both forward and reverse bias","verdict":"incorrect","explanation":"In forward bias, the barrier is reduced and diffusion of majority carriers dominates, not drift."}],"answer":"(B)","formula_steps":[]}