The electrical and optical properties of micro-light emitting diodes (μ-LEDs), including current-voltage (I-V), capacitance-voltage (C-V) curves, photoluminescence (PL) as well as electroluminescence (EL) spectra have been measured and analyzed. It is found that the unit area emitting intensity of small size μ-LED is stronger that of big size μ-LED at the same conditions, due to the enhancement of both the internal quantum efficiency ηint and extraction efficiency Cex. The present method of utilizing the μ-LED for improving the unit area brightness of LEDs is applicable to high efficiency surface emitting device on GaN-on-silicon platform.