The application of visible laser is very extensive. Some people even say that visible laser is a better light source than LED. However, the main difficulty in its development is how to select appropriate active layer, limiting layer material and corresponding growth process.
We know that the 632.8nm He-Ne laser is widely used. He-Ne laser is a gas laser with neutral atomic gas helium and neon as working materials. Continuous laser is output by continuous excitation. In the visible and near-infrared region, there are mainly three spectral lines of 0.6328 μ m, 3.39 μ m and 1.15 μ m, of which the red light of 0.6328 μ m is most commonly used. The output power of He-Ne laser is generally several milliwatts to several hundred milliwatts. He-Ne laser has been widely used.
However, He-Ne laser has some disadvantages, such as low efficiency and low power. So in laser surgery, drilling, cutting, welding and other industries, people now mostly use CO2 lasers, pulsed lasers or semiconductor lasers and other high-power lasers. Because He-Ne laser has the characteristics of stable working property and long service life, it is now more widely developed and used in the measurement of flow rate and flow, and also widely used in precision measurement.
In the GaAlAs/GaAs material system, by changing the composition of AlAs, the direct band gap can reach 1.42~1.88eV, and the corresponding wavelength is 0.87~0.65um. However, with the increase of AlAs content, the direct band gap conduction band bottom rises faster than the indirect band gap conduction band bottom, and the relative proportion of electrons injected into the indirect band into the energy valley increases. When the content of AlAs is 0.37, the width of the direct and indirect bandgap is the same, and the threshold current density increases significantly with the shorter wavelength. At the same time, the segregation coefficient of Al is large, so it is difficult to use liquid phase epitaxy technology to produce epitaxial layers with high Al content and good crystal quality.
General four-layer epitaxial structure: GaAs substrate, limiting layer, active layer, limiting layer and GaAs top layer. Due to the different lattice constants and thermal expansion coefficients of each layer, mismatch stress and thermal stress will be generated.
The theoretical wavelength of the common AlGaInP quaternary compound can reach 580 nm - 680 nm. At the same time, he can grow lattice matching on binary GaAs compounds. Therefore, it is considered to be a suitable material for the preparation of wavelength<700nm.
Source: OFweek
