  We report an experimental demonstration of a local amplification of the spin
Hall voltage using an expanding depletion zone at a pn-junction in GaAs/AlGaAs
Hall-bar microdevices. It is demonstrated that the depletion zone can be
spatially expanded by applying reverse bias by at least 10~$\mu$m at low
temperature. In the depleted regime, the spin Hall signals reached more than
one order of magnitude higher values than in the normal regime at the same
electrical current flowing through the micro-device. It is shown that the
pn-bias has two distinct effects on the detected spin Hall signal. It controls
the local drift field at the Hall cross which is highly non-linear in the
pn-bias due to the shift of the depletion front. Simultaneously, it produces a
change in the spin-transport parameters due to the non-linear change in the
carrier density at the Hall cross with the pn-bias.
