During my attempts to make a cat’s whisker detector from SiC I happened to notice a faint glow. Probing further, I found that one of the largest crystals emitted quite a lot of light over an amazingly large area. Like any normal person would, I broke off that particular crystal, and mounted it on a brass plate with JB Weld, afterwards soldering some safety pins in a way where they always touch the right spots.
Below are two pictures of the device emitting light. One picture forward biased and one reverse. It emits light both ways!
It appears that I have made a pair of schottky diodes in antiseries. Each metal-semiconductor contact formed a PN junction, which could point in either direction depending on whether the work function of my pins is greater or smaller than that of the SiC crystal. When a sufficient bias is applied, one diode will enter reverse breakdown and the other will be forward biased and able to emit light.
It is by no means efficient. The entire assembly draws 3A at 12v to emit a measly estimated 0.5 millicandela of orange light. Everything else turns to heat, VERY fast.