Final answer:
An electric field does exist within a diode at zero bias across the depletion region due to the inherent properties of the semiconductor materials, despite no external voltage being applied.
Step-by-step explanation:
When a diode is at zero bias, it means that there is no external voltage applied across the diode's p-n junction. However, even in this state, an electric field does exist within the diode, particularly across the depletion region. This internal electric field is created by the separation of positive and negative charges within the depletion region. It is a natural consequence of the p-type and n-type semiconductor materials having differing concentrations of charge carriers. These intrinsic charge separations give rise to an electric field that opposes the diffusion of carriers, thus establishing what is known as the built-in potential or built-in electric field.
In general, conductive materials tend to distribute their charges uniformly in the absence of an external electric field, leading to a zero internal electric field. This is not the case for a diode at zero bias due to the intrinsic properties of the semiconductor materials involved in the construction of the p-n junction. The relative directions of the electric field and area can cause the flux through the area to be zero. Still, the electric potential difference at the junction gives rise to the field despite external bias being absent.
Therefore, it is not accurate to assume that there is no electric field in a diode at zero bias. The presence of an electric field is fundamental to the operation of the diode and distinguishes it from a simple conductor, where indeed an electric field might not exist without an external bias.