Anti aliased borders after deleting area in photoshop

Basically what I did is use the pen tool to select the little triangle in the empty space you see to the left, change it to selection, and then hit the delete key. (initially, the entire thing was white.) As a result there is an anti aliased margin after deleting the white area. How do I stop the anti aliasing from occuring when I press delete?

I had this problem earlier. My friend helped me to resolve it by telling me to check out feathering settings. It worked then, but since then it's come back. I checked feathering this time (that was the problem last time) and it's at 0 px, anti-aliasing is also set to off. As such I currently have no idea what could be causing it. How do I get it to delete cleanly?