The Cardiff University (Cardiff University) and other researchers on silicon (Si), the heteroepitaxial growth form of quantum dots composed of III-V compounds (QD) type semiconductor laser, and achieved very low current density and long life. The popularity of "Silicon Photonics" to form an optical circuit on a silicon chip is a step forward.
The emission wavelength of the QD type semiconductor laser formed on silicon is 1310nm. Threshold current density is only 62.5A/cm2. At room temperature, the luminous power is 105mW, the maximum operating temperature is 120. According to the results of 3100 hours of continuous light emission, the luminescence lifetime is 100158 hours. QD diameter is about 20nm, thickness is about InAs of 7Nm and GaAs.
Substantial reduction through defects
Previously, the III-V compound was very difficult to epitaxial growth on silicon. Because of the lattice constant and the structure of the crystal, the silicon and the compound are obviously different. Even if it is forced to grow, it will produce a lot of crystal lattice defects. Especially when a large number of through defects reach the active layer, the carrier will not be conducive to the combination of the luminescence, the luminous efficiency will be significantly reduced.
In the past, there are examples of the III-V family of compounds on silicon chips, but these are implemented by the method of "wafer bonding (WB)".
However, there are some problems such as high vacuum, water and other impurities in the wafer bonding method. Under some conditions, the alignment accuracy of the fitting is a subject. If you can make use of the heterogeneous epitaxial growth method, it is not necessary to use the wafer bonding method.
The Cardiff University and the University of Sheffield (University of Sheffield) team of researchers and the like by drastically reduce lattice defects, especially through defects, success in silicon formed by heteroepitaxial growth of semiconductor lasers with high quality.
One of the measures to reduce through defects is to tilt the silicon (100) to 4 degrees. This is the 1986 discovery of the method, can reduce the AlAs and GaAs and other crystal produced a variety of defects.
As a buffer layer of the deviation of the lattice constant of absorption, the m layer in the silicon layer is stacked about AlAs thick and about 1 mu GaAs thick. The growth temperature of the GaAs layer is divided into 350 degrees, 450 degrees C and 590 degrees C, which can prevent the growth of through defects under the same conditions. But the surface of the buffer layer through the defect density is still a lot, 1 x 109 - /cm.
Another measure is the formation of a GaAs layer on the layer to prevent the defects of the strain layer superlattice (Superlattices SLS, Strained-Layer) layer. The SLS layer is composed of 10nm thick InGaAs layer and GaAs thick 10nm layer. After the SLS layer is formed at 660 C, the temperature of the is about 6 minutes.
The SLS layer consists of 5 layers, which are alternately formed with the GaAs layer of about 60NM thick. Each layer of a layer of SLS, can make the breakthrough to the original defect density to one of the 1/10, on the surface of the fifth layer of SLS, through the defect density is 1 x 105 - /cm, much less than before the formation of SLS layer. Although compared with the formation of GaAs semiconductor laser at GaAs on the substrate through the defect density of 1 * 10 ~ 1 * 104 fand /cm - difference, but in the silicon heteroepitaxial growth form the laser example is the highest quality, so as to realize the long life of laser light.