The basic structure of the layers of the simplest laser diode is shown in figure 6.24.

These layers of semiconductor materials are arranged such that at the p-n junction an active region is created, in which photons are created by the recombination process.
On the top and bottom layers, a layer of metal allows connecting external voltage to the laser.
The voltage is applied to metal contacts above and below the semiconductor layers.
The side of the crystalline semiconductor are cut to serve as mirrors at the end of the optical cavity.