def hole_current_density(mu=0,density=0,d_phi_d_z=0,
                         diffusivity=0,dp_dz=0):
    """
    returns the hole current density

    Parameters
    ----------
    mu : TYPE, required
        DESCRIPTION. The default is 0.
    density : TYPE, required
        DESCRIPTION. The default is 0.
    d_phi_d_z : TYPE, required
        DESCRIPTION. The default is 0.
    diffusivity : TYPE, required
        DESCRIPTION. The default is 0.
    dp_dz : TYPE, required
        DESCRIPTION. The default is 0.

    Returns
    -------
    The hole current density

    """
    j = -(mu*density*d_phi_d_z) - (diffusivity*dp_dz)
    return j