  We have studied the variation in fine-structure splitting (FSS) under
application of vertical electric field in a range of quantum dots grown by
different methods. In each sample we confirm that this energy splitting changes
linearly over the field range we can access. We conclude that this linear
tuning is a general feature of self-assembled quantum dots, observed under
different growth conditions, emission wavelengths and in different material
systems. Statistical measurements of characteristic parameters such as emission
energy, Stark shift and FSS tuning are presented which may provide a guide for
future attempts to increase the yield of quantum dots that can be tuned to a
minimal value of FSS with vertical electric field.
