  Spin-orbit coupled semiconductor nanowires with Zeeman splitting in proximity
contact with bulk $s$-wave superconductivity have recently been proposed as a
promising platform for realizing Majorana fermions. However, in this setup the
chemical potential of the nanowire is generally pinned by the Fermi surface of
the superconductor. This makes the tuning of the chemical potential by external
electrical gates, a crucial requirement for unambiguous detection of Majorana
fermions, very challenging in experiments. Here we show that tunable
topological superconducting regime supporting Majorana fermions can be realized
in semiconductor nanowires using uniaxial stress. For n-type nanowires the
uniaxial stress tunes the effective chemical potential, while for p-type
systems the effective pairing may also be modified by stress, thus
significantly enhancing the topological minigap. We show that the required
stress, of the order of 0.1%, is within current experimental reach using
conventional piezo crystals.
