On the contrary, heavily doped N-type semiconductor in the energy below the Fermi level electronic states are filled, although the temperature is very low, the conduction band also has a free electron. This condition is called N-type degenerate semiconductor. In the non-equilibrium conditions, there will be so-called "double-degenerate semiconductors," then there are two in the semiconductor Fermi level, as shown in Figure (5-25) (f) below (see discussion below). When light shines on a variety of semiconductor as shown in Figure 5-25, in a-e of the five cases, only one of the semiconductor Fermi level, on top of it is not electronic, it has been under full electronic, Therefore, the electron will not be to occupy the empty-state electronic transitions, but only the external photon absorption. The details of technology innovation of green laser pointer will be discussed in the meeting.
Shown in Figure 5-25f case is different, the two Fermi level makes the free electrons in the conduction band, holes in the valence band. If the external photon energy and the electron energy band and lower band in the energy difference between the same hole, it will induce electrons in the conduction band to the valence band hole transitions issued a similar photon. When the external photon energy is greater than two between the Fermi level and the energy difference, or less than the bottom of the conduction band energy level and the top valence band energy difference between the energy levels, it will not induce stimulated emission. Therefore, generated in the semiconductor optical amplification conditions are present in pairs in the semiconductor band degeneracy and the frequency of incident light to meet. Figure (5-25a-e) of the five cases that use the same material, whether it is P-type or N-type semiconductor is only one Fermi level, can not produce optical amplification conditions. The quality group of green laser pointer is in charge of the quality assurance of green laser pointer .
So, the P-and N-type semiconductor production together, that is, P-and N-type link at the formation of a PN junction, the junction is likely to produce two Fermi level it? No electric field, due to the electron and hole diffusion in the PN will have a link at the self field, and cause drift movement. When the diffusion and drift motion balance, according to thermodynamic principles, P zone and the Fermi level N zone must meet the same level, as shown in Figure (5-26). Then in the P and N respectively, P-type region and N-type degenerate degenerate area, P area of the top valence band is full of holes, while the N region conduction band is filled with electronics, resulting in the junction can band bending. Meanwhile, the self field, the formation of the contact potential difference VD, the barrier height eVD. The chip used in this kind of green laser pointer is imported overseas.
In the P-N junction to be forward voltage V, partially offset by the external electric field the role of self-built field, so that PN junction barrier fell, N area of the Fermi level relative to the P region increased eV. Has a positive applied voltage makes the current generation, a phenomenon known as "carrier injection." In this non-equilibrium state, the junction area of the unified Fermi level no longer exists, the formation of junction of the two Fermi level and, subject to the Fermi level, said, as shown in Figure (5-27). In the junction of a thin active region, while a large number of conduction band electrons and valence band holes to form a double-degenerate band structure. Applied voltage generated by carrier injection to the active area of the conduction band electrons and valence band holes resulting composite transition radiation photons. This process produces a non-coherent light, the transition probability of spontaneous emission of electrons in the active area is inversely proportional to the average life expectancy. The information process of green laser pointer is helpful to the site management of green laser pointer workshop.
Produced by stimulated emission of radiation conditions in the junction area of the bottom of the conduction band and valence band at the top of the formation of inversion distribution. To consider laser operating in continuous light of the dynamic balance condition, bottom of conduction band electrons can occupy the probability of N area to calculate the quasi-Fermi equation, respectively, N area and P area of the quasi-Fermi level. Respectively, and the conduction band energy levels of the valence band top, and bottom, respectively, for the conduction band and valence band electrons to occupy the top chance. In the junction conduction band and valence band top to achieve particle (electron) inversion of the conditions is that this means that, in the end zone on the conduction band that occupy energy levels of the electron probability, greater than the valence band top of the next level the electron occupation probability, will be (5-5) and (5-6) into the condition and simplifying to get. The working state of green laser pointer is normal.
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