Research On Threshold Voltage Mudulation Technolog Of AlGaN/GaN On-si Enhancement Mode MIS-HFET

Power semiconductor devices play an important role in energy distribution systems. The performance of Si-based devices have encoutered the theoretical boundary over the past decades’ development. In this case, it is very imperative to explore new-generation semiconductor materials that can help us pull through the energy crisis. GaN, a third generation semiconductor material which has a wide band gap, a high breakdown critical electic field and a high electron mobility, has a promising application prospect on RF and power devices fields and attracts widely at home and abroad.In the field of power devices, enhancement-mode(E-mode) devices become the inevitable choice for their fail-safe ability and low complexity in designing drive circuits. However, a natural 2DEG exists in AlGaN/GaN heterojunction because of its inherent polarization effect resulting in a hot and difficult spot in manufacturing E-mode GaN devices. A great mass fervor on the reserch of GaN-on-Si devices has been risen for their low costs and compatibility with silicon process. In this study, a simulated and experimental researchs are executed on the threshold voltage(VTH) modulation technologies of AlGaN/GaN-on-Si enhancement MIS-HFET and the main contents include:(1) Doing research on the VTH modulation effects of etching depth, gate dielectric, gate metal work function and dielectric/semiconductor interface fixed positive charges by software simulation. The results show that when the etching depth increases, the Vth and the transconductance(gm) both increases; when the thickness of the gate dielectric increases, the VTH increases and the gm decreases; when the dielectric constant increases, the VTH decreases and the gm increases; when the gate work function increases, the VTH increases and the gm is not influenced.(2) Doing reasearch on the VTH modulation effects of etching depth by experiment of a new low-damage hybrid recessing technology. The results show that when the etching depth increases, the VTH increases and the gm and saturation current decrease. The remaining 1.5nm barrier effectively decreases the damage caused by the etching process and mitigates electron scattering effect of interface states. By this way, an Emode MIS-HFET that deliver a VTH of 1.5V, a ID, max larger than 690 mA/mm and a power FOM larger than 625 MW/cm-2 is fabricated.(3) Doing reaserch on the VTH modulation effects of Al2O3/GaN interface fixed positive charges by interface charge engineering. As the GaN surface is metal(Ga)-face, the oxygen atoms of Al2O3 attach to Ga substitute for N and form Ga-O bond at Al2O3/GaN interface during the process of ALD, which acts as positive charges. The Ga dangling bonds could be generated during gate recessing and act as the positive charge centers, too. By post-gate annealing(PGA) and post-dielectric annealing(PDA), the Ga-N bonds can recover effectively decreasing the interface fixed positive charges and increasing the VTH By this way, an E-mode devices that deliver a VTH of 7.6V and a ID, max larger than 350 mA/mm is fabricated.