Crystalline silicon is produced with the Czochralski process (https://en.wikipedia.org/wiki/Czochralski_method https://en.wikipedia.org/wiki/Czochralski_method

Crystalline silicon is produced with the Czochralski process (https://en.wikipedia.org/wiki/Czochralski_method https://en.wikipedia.org/wiki/Czochralski_method), which produces a round ingot. So you'd have to cut away perfectly fine silicon to make something squarish.