According to Semiconductor physics and devices Book by Donald A. Neamen book. The electric field far from the space charge region is very small and most of the applied voltage happens across the space charge area. Why is that ? I attached pictuures from the book. 
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If you have an electric field outside the depletion region you will have drift current. All the individual current components must sum to a constant as you move through the diode. To balance all the currents you end up with little electric field outside the depletion region.
