Study on Laser Doping Parameters of Semi-Insulating 4H-SiC Substrate –
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1. Abstract
Combining simulation with experiment, this study defines the key parameters for laser-assisted boron doping of high-purity semi-insulating 4H-SiC. The optimized process utilizes a 355 nm pulsed ultraviolet laser and a liquid boron precursor. The introduction of boron atoms into SiC at a doping level of approximately 0.3eV alters the hole concentration, resulting in changes in dynamic refractive index and absorption rate, affecting the optical properties of the sample, including transmission, reflection, and absorption behavior. This study demonstrated the feasibility of UV laser doping SiC through optical simulation, using a beam homogenizer to generate a spatially uniform flat spot with uniform intensity, effectively controlling the doping area. The selection of suitable laser processing parameters based on theoretical models provides a reliable basis for experiments.
2. Experiment
A combined approach of numerical simulation and experimental verification was employed to optimize the laser parameters for boron dopant incorporation into semi-insulating high-purity 4H-SiC substrates, aimed at mid-wave infrared waveguide device fabrication. The experiment uses a 355nm nanosecond pulse laser, combined with an optical system containing a quartz hexagonal mixing rod and a focusing lens, to achieve homogenization and precise focusing of Gaussian beam to flat top beam. The spot position and focal plane are controlled by an x-y scanning head and a z-axis moving stage.
Before the experiment, the optical field distribution was simulated and analyzed using Zemax software to verify the homogenization effect and the influence of defocusing on irradiation uniformity. Actual measurements show that 4H-SiC has a high absorption rate (about 75%) at 355nm, making it suitable for laser thermal diffusion doping. The laser power and scanning rate range that can avoid substrate damage were determined based on the thermal model.
In the experiment, liquid boron precursor was first coated on the surface of SiC, and then the boron doping process was achieved through laser scanning. By adjusting power and scanning parameters in real-time, material damage can be avoided while promoting boron diffusion. The optical properties of the doped sample were analyzed by FTIR spectroscopy to evaluate its potential in waveguide applications.
Fig. 1 Measurement of transmittance, reflectance, and absorption of high purity semi-insulating 4H SiC substrate (when receiving) used
3. Conclusion
This study is based on the simulation of the optoelectronic properties of semi-insulating high-purity 4H SiC, and develops a set of ultraviolet laser doping devices. The high absorption rate of high-purity semi insulating SiC at 355nm makes it an ideal candidate material for mid infrared resonant optical waveguides, and its Rayleigh scattering characteristics also support its application in this field. By simulating the optical system response, key parameters such as scanning rate, spot size, and laser power were determined, providing a process basis for efficient doping of SiC. This simulation method can adjust experimental parameters in real time, significantly reduce the number of experiments, lower costs, and improve research and development efficiency. It is suitable for optimizing the doping process of SiC substrates in optoelectronic integrated devices.
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Reference：
Sugrim, C. J., Kulkarni, G., Bougdid, Y., Heylman, K., Kumar, R., Kar, A., & Sundaram, K. (2024). Numerical investigation of laser doping parameters for semi-insulating 4H-SiC substrate. Journal of Laser Applications, 36(2).