Structural and Electrical Characteristics of GaN HEMTs With In Situ SiNx Gate Dielectrics Grown by Rationally Modulated N2/H2 Carrier Gas

In situ SiNx is recognized as a promising dielectric and passivation layer for GaN high-electron-mobility transistors (HEMTs). Herein, the growth mechanisms and material properties of the in situ SiNx are studied by comparing the dielectrics grown under three different carrier gases including N2 (N2-SiNx), H2 (H2-SiNx), and mixed N2/H2 atmosphere (N/H-SiNx). It is found that the growth rates (GRs) of three types of in situ SiNx always follow the relationship of N2-
${\text {SiN}}_{x}~\gt $
N/H-
${\text {SiN}}_{x}~\gt $
H2-SiNx, due to the prohibition effect of H2 on the forward SiH4 + NH3 reaction. In addition, thanks to the H2 incorporation, the surface morphologies and interface quality of both H2- and N/H-SiNx are improved compared with those of N2-SiNx, enabled by the uniform in situ H2 etching to the AlGaN barrier. Interestingly, the N/H-SiNx passivated HEMT shows smaller capacitance-voltage dispersion/hysteresis and improved device stability under long-term electrical stress than the H2-SiNx passivated device. This can be attributed to reduced and milder H2 etching to the device, “diluted” by N2 carrier gas, leading to less surface damage. These results provide possible guidance for further modulation of in situ SiNx growth schemes toward the stable operation of GaN HEMTs.