Capacitance-voltage and photoluminescence study of high-k/GaAs interfaces controlled by Si interface control layer

The authors performed a detailed capacitance-voltage (C-V) and photoluminescence (PL) study of the high-k dielectric/GaAs interface controlled by the Si interface control layer (Si ICL) grown by molecular beam epitaxy to investigate the feasibility of a PL method for interface characterization and to find out the optimum thickness of the Si ICL. The sample had a HfO₂/SiN_x/Si ICL/n-GaAs structure where the ultrathin SiN_x buffer layer was formed by in situ partial nitridation of the Si ICL itself. For this structure, they measured the quantum efficiency of photoluminescence as a function of the excitation photon flux density and carried out a computer analysis to determine the most likely distribution of the interface state density D_it. Remarkably good agreements were obtained between the high-frequency C-V method and the PL method, indicating that the present PL method may serve as a powerful contactless and nondestructive tool for developing an optimal surface passivation structure and its processing technology. Using C-V and PL methods, they found the optimum initial thickness of Si ICL before partial nitridation to be 5–6 ML. With this thickness, a D_it minimum value of (1–2)×10¹¹ cm^-2 eV^-1 was achieved in the HfO₂/SiN_x/Si ICL/n-GaAs structure. When the thickness was too large, it led to the generation- of misfit dislocations, whereas a too thin Si ICL led to subcutaneous nitridation of GaAs during partial nitridation of the Si ICL, leading to interface disorder.