Semiconductor Laser: Construction, Working, Diagram & Applications
Quick Exam Notes
- Type: Solid-state laser (Laser Diode)
- Material: Gallium Arsenide (GaAs)
- Wavelength: 7000 Å – 30,000 Å (Infrared)
- Pumping Method: Forward bias of p-n junction
- Applications: Optical communication, CD/DVD reading, surgery
Semiconductor laser is made up of an active layer of gallium arsenide (GaAs) of thickness 0.2 microns. This is sandwiched in between a n-type GaAs and p-type GaAs layer as shown in Fig. 1. The resonant cavity is provided by polishing opposite faces of the GaAs crystal and the pumping occurs by passing electrical current from an ordinary source (Power Supply). From this system GaAs semiconductor, laser beams of wavelength ranging from 7000 Å to 30,000 Å can be produced.
Figure 1: Semiconductor Laser Construction Diagram (GaAs p-n junction)
Working principle
When a p-n junction is forward biased, the electrons will be injected into conduction band along and side, and the number of holes are produced in the valence band along the p-side of the junction. Thus, there will be more electrons in the conduction band than that in the valence band. Hence, population inversion is achieved. When the forward – biased voltage is increased, more and more light photons are emitted and the light production instantly becomes stronger. These photons will trigger a chain of stimulated recombination resulting in the release of photons in phase.
Figure 2: Energy Band Diagram showing the Working Principle of a Semiconductor Laser
Applications of semiconductor laser
- Semiconductor lasers provide signals in optical telecommunications.
- Semiconductor lasers are focused into the disk grooves to detect digitally coded information
- Semiconductor lasers can emit various wavelengths, making them useful for spectroscopy and other high-end scientific applications.
- Semiconductor lasers can be used to remove excess material or coating without damaging the product.
Advantages of Semiconductor Laser
- Compact and lightweight (Laser Diode).
- Highly efficient with low power consumption.
- Operates at room temperature.
- Direct electrical pumping (no flash lamp required).
Limitations of Semiconductor Laser
- Emits incoherent light compared to gas/solid-state lasers.
- Has a relatively short lifespan.
- Output power is limited.
Summary
A semiconductor laser, also called a laser diode, consists of a forward-biased p–n junction in gallium arsenide (GaAs). Electrons and holes recombine, releasing photons. With sufficient current, population inversion occurs, and stimulated emission inside the polished surfaces generates a compact, coherent infrared laser beam.
MCQs on Semiconductor Laser
-
A semiconductor laser is also commonly known as:
- a) LED
- b) Laser diode
- c) Gas laser
- d) Ruby laser
Answer
b) Laser diode
-
The working principle of a semiconductor laser is based on:
- a) Spontaneous emission
- b) Electroluminescence
- c) Stimulated emission in a p-n junction
- d) Optical pumping
Answer
c) Stimulated emission in a p-n junction
-
Which of the following is a major drawback of semiconductor lasers?
- a) Large size
- b) High threshold current
- c) Low efficiency
- d) Cannot be modulated
Answer
b) High threshold current
-
The typical emission wavelength range of semiconductor lasers is:
- a) 100–200 nm
- b) 400–700 nm
- c) 630–1550 nm
- d) 2000–3000 nm
Answer
c) 630–1550 nm
-
One common application of semiconductor lasers is:
- a) Metal cutting
- b) Barcode scanning and CD/DVD players
- c) Tattoo removal
- d) Nuclear fusion research
Answer
b) Barcode scanning and CD/DVD players