optical absorption in GaAs

Hi,

I am studying the plasmonic effects of gold photoconductive antenna on a substrate of GaAs and I follow the model of Plasmonic Wire Grating. I try to calculate the optical absorption on each point in GaAs using the Total Power Dissipation Density (emw.Qh). I am expecting to have enhanced absorption around the gold antenna.
However, emw.Qh gives both positive and negative value which I cannot understand. I thought that the total power dissipation density should be positive. Can anyone comment on this and tell me where I am going wrong?

Best,
Lu