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/SiNx/Si ICL/n-GaAs structure where the ultrathin SiNx 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)x10(11) cm(-2) eV(-1) was achieved in the HfO2/SiNx/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.