n-p-n transistor are preferred to p-n-p transistor because they have
Low cost
Low dissipation energy
Capability of handling large power
Electrons having high mobility than holes
n-p-n transistor is formed by combining two n-types crystals between which a thin p type crystal is there. Electrons are charge carriers within the n-p - n transistor whereas holes are charge carriers within the p - n - p transistor. Since, electrons move more easily than holes, hence n-p-n transistors are preferred compared to p-n-p.
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