Based on multidimensional particle-in-cell simulations of a short laser pulse interaction with a homogeneous planar target, we perform an optimization study to find the best design parameters for maximizing the number of high-energy electrons generated by a sub-petawatt class laser system for deep gamma radiography purposes. We find that a low-density target with an electron density of 10% of the critical density and a thickness of 240 μm irradiated by a 30 fs 4 J laser pulse can generate 7-nC electron bunches with a mean characteristic energy of 100 MeV.