What Substrates Are Used to Fabricate Semiconductor Lasers?

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Video: Principle of Semiconductor Lasers



What Are Semiconductor Lasers?

Semiconductor lasers, also known as laser diodes, are solid-state light sources that produce coherent and monochromatic light. They consist of a p-n junction formed by a p-type semiconductor and an n-type semiconductor, which is placed within a cavity that provides feedback to the light produced. When a current is applied, electrons and holes recombine in the junction and produce light. The light is then amplified and confined within the cavity to produce a laser beam. Semiconductor lasers are compact, efficient, and have a fast response time, making them useful in a wide range of applications, such as optical communication, laser printing, and laser scanning. They also find use in scientific and industrial applications, such as spectroscopy and material processing.

What Substrates are Used to Fabricate Semiconductor Lasers?

The substrate used to fabricate semiconductor lasers is typically a material that provides a smooth, uniform, and electrically insulating surface on which to grow the active layer of the laser diode. Some common substrates used in semiconductor laser fabrication include:

  1. Silicon (Si):

    Silicon is a commonly used substrate due to its availability, low cost, and compatibility with silicon-based microelectronics.

  2. Gallium Arsenide (GaAs):

    GaAs is a commonly used substrate for high-performance laser diodes due to its high electron mobility, which results in fast response times.

  3. Indium Phosphide (InP):

    InP is a high-performance substrate that is commonly used for high-power laser diodes and for lasers operating in the near-infrared spectral range.

  4. Sapphire (Al2O3):

    Sapphire is a hard and durable substrate that is commonly used for laser diodes that need to withstand harsh environments.

  5. Zinc Selenide (ZnSe):

    ZnSe is a substrate that is commonly used for laser diodes operating in the mid-infrared spectral range.

These are just a few examples of substrates commonly used for semiconductor laser fabrication. The choice of substrate depends on the specific requirements of the laser, such as the wavelength of the light produced, the power output, and the operating environment.

What Are The Benefits of Semiconductor Lasers?

Semiconductor lasers are solid-state devices that produce a focused beam of light with high spatial and spectral coherence. They can be used in many applications such as fiber-optic communications, pattern recognition and pollution detection.

The semiconductor material used for lasers has to meet certain requirements, including crystal direction, etch pit density (EPD), impurity concentration and substrate thickness. These parameters affect the lifetime of the laser.

They are made of semiconductors

Semiconductor lasers, also called diode lasers (DLs), are a special class of solid-state lasers that use semiconductor material. They have many different properties and are used in a variety of applications.

The semiconductor material used to make a semiconductor laser has to be specially fabricated in order to produce the desired output. For example, the material must have a high enough bandgap to allow photon emission. This requires searching for a material that is both suitable for the wavelength and has a proper lattice constant on the substrate.

This is not an easy task, especially for a material that has a narrow bandgap. For instance, silicon and germanium have bandgaps that are not aligned in the right way to allow for photon emission.

Nevertheless, some materials, like gallium arsenide and indium phosphide, can be found that meet both requirements. Other materials, including some compound semiconductors, have alternating atomic arrangements that break the bandgap symmetry and allow for photon emission.

In these materials, a large amount of electrons and holes are injected in the n-type region, causing recombination to occur. The resulting emitted light is coherent. This is because the recombination occurs across the semiconductor's p-n junction, which is known as a 'homojunction' or 'diode'.

* The recombination of electrons and holes causes an increase in the optical gain within the semiconductor material. The gain is a measure of the number of photons emitted by the semiconductor and thus represents direct conversion of electricity to light.

When the rate of stimulated emission is significantly higher than the rate of loss, the device enters a state called lasing. This is the most stable laser state.

Another interesting aspect of a semiconductor laser is that it can be operated at room temperature, as long as the power losses are acceptable and the current density is high enough. A common method of cooling these devices is to place them in liquid nitrogen.

These lasers can also be tunable, which allows the user to control the output of the device. This is achieved through a method called feedback. In a laser that uses feedback, a small grating is often replaced by a resonator mirror, which reflects the light back at the same frequency. This technique is known as distributed feedback (DFB).

They are tunable

Tunable lasers are an important component of today’s fiber-optic networks because they offer a means of adding and dropping wavelengths, which can be used to provide new bandwidth and on-demand services. Tunable lasers can be controlled remotely from a central location, allowing carriers to reconfigure wavelengths to suit the needs of customers. Such flexible bandwidth provisioning allows them to better manage inventory, reduce the need for replacement transponders and minimize service interruptions.

Several types of semiconductor lasers are tunable: distributed-feedback (DFB) lasers, distributed Bragg reflector (DBR) lasers, and external cavity diode lasers (ECDL). These all have one or more mirrors that reflect light back into the laser diode chip.

Distributed-feedback lasers are made up of a gain section, a mirror (grating) section and a phase section, which can be adjusted to change the effective refractive index. Tuning is achieved by injecting current into the phase and mirror sections, which changes the carrier density in these regions. This can be accomplished by thermal effect or carrier injection.

The first widely-tunable lasers were dye lasers, which use Rhodamine 6G to alter the laser’s output wavelength. Tunable dye lasers can be tuned over a range of 3-4 nm, making them cheaper than fixed-wavelength lasers.

Another type of widely-tunable laser is a semiconductor micro-ring resonator (MRR) laser, which is realized in monolithic III/V or heterogeneous silicon process. This device is able to tune over wide wavelength ranges and provides single mode lasing, which is ideal for communications and sensing applications.

Tunable VCSELs are also available, and these devices are based on mechanical modification of the laser cavity using microelectromechanical systems (MEMS) technology. This allows them to be tunable over a large wavelength range, such as 28-32 nm.

These tunable VCSELs have a movable mirror that can be moved to adjust the wavelength of the beam. The mirror can be either a Fabry-Perot or an elliptical grating.

In addition to wavelength flexibility, these tunable lasers have other benefits, such as reduced technical noise and improved linewidth performance. These advantages are especially useful for communication systems because they allow them to transmit multiple channels over a single fiber.

They are energy efficient

Semiconductor lasers are a class of semiconductor light sources that can be powered electrically, rather than optically. This has several advantages, including the ability to pump the laser with a very low power input, which reduces power consumption. These devices have also been shown to be capable of producing a large number of pulses, which can be used for high-speed communication, in compact disk players and other applications.

They can be used for telecommunications, range-finding, spectroscopic sensing, and generation of radio and terahertz waves. They can also be used for frequency doubling and conversion, water purification (in the UV), and photodynamic therapy.

Most lasers use a diode structure to drive their emission. A forward electrical bias across the laser diode causes the holes and electrons injected from opposite sides of the p-n junction to recombine, thus producing stimulated emission. This recombination generates a photon that travels in the same direction as the original photon. The amount of gain (or increase in amplitude) that is produced increases as the number of holes and electrons is increased.

These lasers are based on a variety of materials and their bandgap energy determines the spectral range that they can emit in. Some materials can produce very narrow spectral outputs, while others can emit in the red and near infrared. Moreover, some lasers are now available in blue and green wavelengths as well.

Optical feedback in these semiconductor lasers produces a rich variety of chaotic dynamics, which can be investigated mathematically. This is important because the time series of these chaotic attractors can be used to analyze laser oscillations and the effects that they have on the diffraction pattern.

This type of laser can be made from a thin layer of low-bandgap material sandwiched between two high-bandgap layers. Typical materials include gallium arsenide and aluminium gallium arsenide, each with different gaps between the valence and conduction bands.

Because they are based on a very thin active layer, the threshold current of these lasers is very low, which allows for efficient operation without significant loss of laser output power. This makes them ideal for many applications, such as in communications, in compact disk players and for high-speed printing systems and laser pointers.

They are cheap

Semiconductor lasers are cheap and efficient light sources. They are used for a variety of applications such as communication, compact disk players and laser pointers. They are also used in 3D printing.

They have a large output power and can produce pulsed beams of high power and wavelength. They are also very compact.

Unlike other types of lasers, semiconductor lasers do not require mirrors to produce a beam. They are also very energy efficient and can be operated at room temperature without the need for cooling.

These semiconductor lasers are made up of p-n junctions and both the p and n regions are doped in a certain way to generate coherent light when a forward bias is applied. The p region has a lot of holes and the n region has a small amount of electrons. When an incoming photon strikes the junction, some of its excess energy is converted into a photon and more free electrons are injected into the junction. This process is called stimulated emission.

Because semiconductor lasers are tunable, they can be used to generate a wide range of wavelengths, which is useful for many types of application. The wavelength can be changed by adjusting the current injected into the device or directly changing its temperature.

The gain medium in these laser structures is typically a single film containing several atomic monolayers embedded in barrier material with a larger bandgap than the active layers. The barrier material has a lower refractive index than the active layers, which confines the carriers to a narrow region.

Another common form of semiconductor laser structure is a double heterostructure, in which two or more stacked layers of barrier and active materials provide optical and charge-carrier confinement. For example, a thin GaAs or ternary compound AlGaAs active layer is sandwiched between layers of n- and p-doped AlGaAs barrier material with higher Al fractions than the active layer.

This design allows for a much better control of the recombination rate in the active region, thus achieving a longer lasing time and more stable operation. This design has also helped reduce the threshold current required for a semiconductor laser to produce a powerful output.