A Zener diode is specially designed to operate in the reverse breakdown region. To achieve a sharp breakdown voltage, both the p and n regions of the Zener diode are heavily doped. Due to this heavy doping, the depletion region formed is very thin (narrow), not wide, which leads to an extremely high electric field across the junction even for a small reverse bias voltage. Therefore, the statement claiming the depletion region is very wide is incorrect.