GaN/InGaN light emitting diodes(LEDs)grown on sapphire substrates have current transport along the lateral direction.This often results in non-uniform current spreading

which leads to the non-uni-formity of luminescence and the reduction of lifetime.Therefore

proper mesa structure should be designed to improve current spreading.The characteristics of the GaN/InGaN LED have been examined from the view point of uniform current spreading and low series resistance.A steady-state current field model is employed to describe the current spreading of GaN based LED.Finite element method is used to simulate the current distribution of different types of LEDs in three dimensions.The series resistance of the LED is derived from the calculated current spreading.Standards to quantitatively evaluate the uniformity of current spreading are presented.By quantitatively comparing the series resistance and current spreading of LEDs with different mesa structures

we find that that the LED with the interdigitated mesa structure has the lowest series resistance under the process conditions of our lab.Parameters of the interdigitated mesa structure are further optimized based on our model to achieve the smallest series resistance.Two types of LEDs

denoted as Sample A and Sample B

are prepared with a chip size of 1mm×1mm.Sample A is fabricated using the optimized interdigitated electrode pattern as described above

while Sample B is fabricated using a ring electrode pattern without optimization for comparison.By measuring the I-V curve

the values of series resistance of the three samples are derived

which are 1.6Ω and 3.6Ω for Sample A and Sample B

respectively.The resistance of the former one is only 44.4% of the latter one

which is consistent with the calculated results based on our model.The reduction in resistance will lead to the improvement of the efficiency of LEDs.