Effect of a highly doped emitting window for increasing output power of 860-nm GaAs VCSELs.

• Highly doped emitting window was fabricated by ZnO film and its thermal treatment. • Higher doping level of emission window limited increased effectively real emission region limited by current window. • Output power of 860 nm VCSEL was greatly enhanced by using highly Zn doped emitting window with optimized thermal condition. A highly doped emitting window for a vertical-cavity surface-emitting laser (VCSEL) was fabricated and its effect on the output power at a wavelength of 860-nm was investigated. The highly doped emitting window, which limited in required specific area, could be obtained by using various thermal conditions for patterned zinc oxide (ZnO). Experimental measurements showed that the highest doping concentration of 1.02 × 1019/cm3 was observed from patterned ZnO treated at 600 °C. The highly doped emitting window obtained by Zn diffusion effectively improved the real emission region confined by the current window owing to increase in the central concentration of the current injected from the top electrode. Among the developed VCSEL chips, the highest output power of 110 mW was observed with the use of a Zn-doped emitting widow at 600 °C, indicating an increase 47% compared with the output power of conventional chips (75 mW). For temperatures other than 600 °C, a relatively lower output power was obtained. The results show that the use of an emitting window highly doped with Zn can improve the output power of the VCSEL at a wavelength of 860-nm. It was verified that there exists an optimal thermal condition for the zinc diffusion process for patterned ZnO film required. [ABSTRACT FROM AUTHOR]