Construction : A light-emitting diode is a forward- biased pn-junction diode formed from compound semiconductor materials. As shown in Fig. (a), the top metal contact to the n-layer (say) is provided with a window for the emitted light to escape. The diode chip is encapsulated in a transparent plastic lens. The cathode and anode leads from the metal contacts to the n-and p-layers, respectively, are provided for external connections, shown in figure.
The negative electrode (cathode) is identified by a notch or flat spot on the plastic body, or the cathode lead is shorter than the anode.
Led : (a) sectional view (b) side view of encapsulation (c) circuit symbol
