1.The reverse breakdown voltage of LEDs are very low, which is around 5V. So enough care is to be taken while fabricating a pn-junction diode such that the high reverse voltages do not occur across them.
2. There exist very small resistance to limit the current in LED. So a resistor must be placed in series with the LED such that no damage is occurred to the LED.
The semiconductor used for fabrication of visible LEDs must at least have a band gap of 1.8 eV