Operating characteristics of semiconductor lasers Operating characteristics of semiconductor lasers 1. Threshold current. When the current injected into the pn junction is low, only spontaneous radiation is generated, and the gain increases as the current value increases. When the threshold current is reached, the pn junction generates laser light. Several factors that affect the threshold:
(1) The larger the doping concentration of the crystal, the smaller the threshold. Welcome to the company **http://
(2) The loss of the resonant cavity is small, such as increasing the reflectance, the threshold is low.
(3) In relation to the junction of semiconductor materials, the heterojunction threshold current is much lower than the homojunction. At present, the threshold current of the homojunction at room temperature is greater than 30,000 A/cm 2 ; the single heterojunction is about 8000 A/cm 2 ; the double heterojunction is about 1600 A/cm 2 . A heterojunction has now been used to produce a semiconductor laser capable of continuously outputting tens of milliwatts at room temperature.
(4) The higher the temperature, the higher the threshold. Above 100K, the threshold increases with the cubic of T. Therefore, the semiconductor laser preferably operates at low temperature and room temperature.
2. Directionality. Due to the short cavity of the semiconductor laser, the laser directivity is poor. In the vertical plane of the junction, the divergence angle is the largest, up to 20°-30°; in the horizontal plane of the junction, it is about 10°. The quantum efficiency η = the number of photons emitted per second / the number of electron-hole pairs reaching the junction region at 77K per second, the quantum efficiency of the GaAs laser is 70%-80%; at 300K, it is reduced to about 30%. Power efficiency η1 = radiated optical power / electrical power applied to the laser Due to various losses, the current double heterojunction device has a maximum η1 of 10% at room temperature and can reach 30%-40% only at low temperatures.
4. Spectral characteristics. Due to the special electronic structure of the semiconductor material, the excited composite radiation occurs between the energy band (the conduction band and the valence band), so the laser line width is wide, and the GaAs laser has a line width of about several nanometers at room temperature, and the monochrome is visible. Poor sex. The peak wavelength of the output laser is 840 nm at 77 K and 902 nm at 300 K.
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