[BlackTalon]

I do not have a contractor to recommend, just some info to provide. The voids are likely from the soil settling over time, and/ or surface drainage. Not much you can do except try to pack some soil in at the top, regrade at the top and maybe extend any downspouts away (pics would help -- I have no idea which -- if any -- of these apply in your particular case). You can also hire a mudjacking company to come out and core through the stairs in a grid pattern and pump a flowable grout underneath, but good chance the soil will continue to settle and after a short period the grout will no longer be in contact with the stairs. BTW, this is not uncommon; I have the same issue at my house, and it is compounded by the marine clay that was in the soil used to regrade/ backfill. The voids under the carport slab are even worse!

If you want to go the mudjacking route, go to the BlueBook web site and look for a DC-area contractor. That is one of the contracting categories.