Ritsumeikan University, Japan
Title: A new laser induced local material engineering to convert from n-type to p-type nitride semiconductor to fabricate high power vertical AlGaN/GaN devices on Si substrate
Biography: Yoshinobu Aoyagi
Statement of the Problem: The n-type aluminum gallium nitride (n-AlGaN) vertical field effect transistors (FETs) are promising devices for future super high power FET electronics beyond Si, SiC and GaN devices. To realize n-AlGaN vertical FETs with carrier blocking layer to concentrate the current flow into the vertical channel region, the local p-type AlGaN formation is indispensable. So far, to realize this local p-type layer, crystal regrowth technique with lithography is carried out but this process is complicated and reduces the crystal quality. To precede local carrier type conversion from n-type to p-type without any crystal regrowth method, the carrier blocking layer can be easily produced without any crystal damages.
Methodology: We used an excimer laser (193 nm) as an irradiation source for material engineering. The irradiation system has a scanning system of the sample to control the irradiation area and an in-situ monitoring system to observe the material surface during the laser irradiation. The material characteristics are observed using Hall effects, Kelvin probe and optical microscope measurement.
Findings: We found the insulating or n-type as grown Mg-doped GaN (Mg: GaN) was converted to p-type GaN (p-GaN) under a proper laser irradiation condition only at the specific local area of the laser irradiation. The lateral resolution for transition from the Mg: GaN to p-type was about 1 µm. The surface has no damage under the irradiation.
Conclusion & Significance: A new technique has been established. This has achieved local activation of Mg: GaN to p-type GaN using the laser irradiation co-operated with in-situ observations of the surface during the laser processing. Using this method, local activation of carriers with the lateral resolution of about 1 µm is possible, thus establishing the potential for fabricating local p-GaN carrier blocking layer and vertical high power devices without using any other fabrication techniques such as crystal regrowth.