1993 Volume 113 Issue 7 Pages 556-565
The Lateral diffusion length of Zn in Si-doped GaAs under a SiO2 or SiNx diffusion mask was evaluated using (1) the TLM resistor pattern method, (2) the p-n capacitance method, (3) the EBIC method, and (4) the cleaved stain-etching method. The SiO2 was deposited at 250°C using SiH4 and N2O gases, and SiNx was deposited by plasma-chemical-vapor-deposition at 300°C using SiH4 and N2 gases. Employing the open-tube method, Zn was diffused into GaAs through windows opened in the dielectric films at 600_??_650°C for 2.5_??_22.5 minutes in a nitrogen gas ambient. ZnAs2 was used as a diffusion source. The anomalous fast lateral diffusion of Zn was observed only for the SiO2-deposited GaAs. The ratio of the lateral to vertical diffusion length was about 4 for 0.3μm-thick SiO2 and was strongly dependent on SiO2 film thickness. For SiNx on the other hand, the ratio was about 0.9 regardless of film thickness. Similar results were obtained by each evaluation method. The anomalous diffusion mechanism for SiO2 is not clear, however, the results of our systematic experiment suggests that the defects at GaAs surface, which were produced during SiO2 deposition, correlate with the anomalous diffusion.