![]() (1) Avalanche gain coefficient M (also called multiplication factor), the main characteristics of abrupt junction avalanche diodes Response speed, at which point a layer of graded layer can be inserted in the middle of the abrupt heterojunction to reduce the effect of ΔEv). The disadvantage of this APD is that there is a process of tunnel current multiplication, which will generate large shot noise (reduced p-zone doping, which can reduce the tunnel current, but the avalanche voltage will increase).Īn improved structure is the so-called SAM-APD: the multiplication zone uses a wider band gap material (so that it does not absorb light), and the light absorption zone uses a narrow band gap material here, due to the heterojunction, Decreasing the doping concentration of the multiplication zone without affecting the light absorption region, so that the tunneling current is reduced (if it is a mutant heterojunction, because of the existence of ΔEv, the photogenerated holes will accumulate and affect the device. In the manufacture of APD, it is necessary to add a guard ring on the surface of the device to improve the reverse withstand voltage performance the semiconductor material is superior to Si (used widely for detecting light below 0.9 um), but when detecting long-wavelength light of 1 um or more Commonly used Ge and InGaAs (noise noise and dark current). In the InGaAsP (indium gallium arsenide) transition region of the band gap gradation, SAGM (absorption, classification, and multiplication) structures are formed. In view of the fact that the hole ionization coefficient in the InP material is larger than the electron ionization coefficient, the avalanche region uses n-type InP, and the n-InP and n-InGaAs heterointerfaces have a large valence band barrier, which easily causes the photo-generated holes to collapse. ![]() In order to avoid the InGaAs homojunction tunnel breakdown before the avalanche breakdown, the avalanche region is The absorption is separated, that is, the PN junction is made in the InP window layer. ![]() The light absorbing layer uses InGaAs material, which has a high absorption coefficient for 1.3μm and 1.55μn light. The optimized structure is shown in the figure. InGaAs (Indium Gallium Arsenide) / InP (Indium Phosphorus) APD is an ideal photodetector for long-wavelength (1.3μn, 1.55μm) fiber-optic communication. In the 0.6 to 0.9 μm band, silicon APD has near-ideal performance. These carriers It also constantly causes new impact ionization, causing the avalanche of carriers to multiply and gain current gain. They collide with the lattice to generate a new electron-hole pair. The PN junction is coupled with a suitable high reverse bias voltage to accelerate the strong electric field in the depletion layer to obtain a sufficiently high kinetic energy. The zone is substantially identical to the multiplication zone (the P zone and the I zone where there is a high electric field).Īvalanche Photodiode Definition: What is Avalanche Photodiode? The basic structure often adopts a Read diode structure (ie, N+PIP+ type structure, P+ side receives light) which is easy to generate avalanche multiplication effect, and a large reverse bias is applied during operation, so that it reaches an avalanche multiplication state its light absorption. Ⅴ Difference between Photo Multiplier Tube and Avalanche Photodiodeĥ.2 The Difference Between Photo Multiplier Tube and Avalanche PhotodiodeĪvalanche photodiode is a p-n junction type photodetecting diode in which the avalanche multiplication effect of carriers is utilized to amplify the photoelectric signal to improve the sensitivity of detection. Ⅲ Working Principle of Avalanche Photodiode 1 born 2, 2 born 4, increased carriers like an avalanche. The newly generated carriers in turn generate free electron-hole pairs by collision, which is the multiplication effect. Avalanche breakdown is caused by the electric field, the carrier energy increases, and it collides with the crystal atoms, causing the electrons in the covalent bond to excite to form free electron-hole pairs. Avalanche breakdown is when the PN junction reverse voltage increases to a value, the carrier multiplication is like an avalanche, increasing much faster, and the diode fabricated using this characteristic is an avalanche diode. It is divided into avalanche breakdown and Zener breakdown (tunnel breakdown). When the reverse voltage increases to a certain value, the reverse current suddenly increases. The PN junction has unidirectional conductivity, a small forward resistance, and a large reverse resistance. Warm hints: This article contains about 5000 words and reading time is about 15 mins.
0 Comments
Leave a Reply. |