Overview of Laser Diode

A Laser Diode or semiconductor laser is the simplest form of Solid-State Laser.  Laser diodes are commonly referred to as edge emitting laser diodes because the laser light is emitted from the edge of the substrate. The light emitting region of the laser diode is commonly called the emitter.  The emitter size and the number of emitters determine output power and beam quality of a laser diode.

Electrically speaking, a laser diode is a PIN diode. The intrinsic (I) region is the active region of the laser diode. The N and P regions provide the active region with the carriers (electrons and holes). Initially, research on laser diodes was carried out using P-N diodes. However, all modern laser diodes utilize the double-hetero-structure implementation. This design confines the carriers and photons, allowing a maximization of recombination and light generation.

Laser Diode Epitaxy: the epitaxial structure of a laser diode is typically grown utilizing one of the crystal growth techniques, starting with an N-doped substrate, then growing the I-doped layer (active region), proceeded by the P-doped layer, and finally, a contact layer. The active region of a laser diode typically consists of quantum wells. These wells allow for a lower threshold current and a higher operating efficiency in laser diodes.

· Single-mode laser diodes typically have an emitter that is approximately 3µm – 7µm x 1µm, dependent on the wavelength. The emitter allows only a single mode to propagate along the active region. 

· Multimode laser diodes have the emitter width enlarged to allow multiple modes in the active region. The emitters can be 30µm – 300 µm x ≈ 1 µm.