The University of Tokyo in Japan claims to achieve a 1.3-micron lasing wavelength in an electrically pumped silicon-based indium arsenide / gallium arsenide quantum dot laser for the first time. Molecular beam epitaxy was used to directly grow gallium arsenide on the silicon (001) axis.
Before the quantum dot layer is grown using molecular beam epitaxy, metal organic chemical vapor deposition is usually used to grow along the silicon (001) axis. Alternative techniques to achieve the molecular beam epitaxy seeding technique involve cutting the substrate to avoid crystal defects such as penetrating dislocations, antiphase boundaries, and cracks. Unfortunately, off-axis silicon is not compatible with mainstream CMOS-based electronics. Metal organic chemical vapor deposition cannot effectively filter dislocations or grow laser pointer quantum dots that emit light effectively.
The team believes that the development of 1.3 micron lasers will help promote silicon photonics to solve metal wiring problems such as low bandwidth density and high power consumption for next generation computing.
The researchers used n-type substrates for solid-source molecular beam epitaxy. The temperature of the growth chamber was first heated to 950 ° C, and the substrate was annealed for 5 minutes. By growing three 300-nm-thick gallium arsenide layers and indium gallium arsenide / gallium arsenide strained superlattices grown on the gallium arsenide layer, penetrating dislocations are prevented from reaching the quantum dot layer. The quantum dislocation density of the quantum dot layer is 5 × 107 / cm 2. The research team pointed out that thermal cycling annealing during the film deposition process can further reduce the dislocation density.
By controlling the growth temperature at 500 ° C, and rapidly growing a 40-nm-thick aluminum gallium arsenic seed layer at a speed of 1.1 micrometers per hour, the inverse boundary disappeared within 400 nanometers of the deposited gallium arsenide buffer layer. To avoid the creation of laser pointers with inverse boundaries.
Quantum dots measure about 30 nanometers across and have a density of 5 × 1010 / cm2. The photoluminescence intensity of this structure is 80% of the structure grown on a GaAs substrate. The peak wavelength is 1250 nm and the full width at half maximum is 31 millielectron volts. Excitation levels with a wavelength of 1150 nm and a full width at half maximum of 86 millielectron volts are also visible in the spectrum.
The material is manufactured as a wide-area Fabry-Perot laser with a width of 80 microns. The contact layer is gold-germanium-nickel / gold. The back of the substrate was thinned to 100 microns. The structure was then cut into a 2 mm long laser. Without the use of a high reflectance coating, it is cut to form a mirror surface.
Under pulse injection, the lowest lasing threshold is 320 A / cm2. The maximum output power of a single plane exceeds 30 mW. When measured in the range of 25 to 70 ° C, the characteristic temperature of the laser threshold is 51 Kelvin. At 25 ° C, the slope efficiency is 0.052 W / A. With continuous wave current injection of up to 1000 milliamps, the device cannot radiate laser light.
Researchers acknowledge that silicon-based laser pointers exhibit "degradation of several characteristics such as output and thermal characteristics" compared to gallium arsenide-based lasers. The team hopes to optimize the growth process, especially the seed layer, to improve the performance of the laser. The silicon-based quantum dot laser grown this time has the disadvantages of low quality GaAs buffer layer and large mesa width. The research team hopes to further optimize the growth process, especially the seed layer, to improve laser performance. In addition, the narrow mesa width can also increase the current threshold and improve thermal management.