GaN基LED电流扩展的有限元模型及电极结构优化

针对目前蓝宝石衬底上外延生长制备的GaN基半导体发光二极管(LED)器件存在电流分布不均匀的问题,建立了LED的电流扩展模型,提出了定量评价其特性的参数和标准。通过用有限元方法计算LED中电流的三维空间分布,对不同的电极结构进行了定量的比较,给出了优化的电极结构。计算结果显示,在相同工艺参数下,采用插指型电极结构的LED与采用传统型电极结构和扩展正极型电极结构的LED相比,电流扩展更均匀,串联电阻更小。在此基础上,对插指型电极结构作了进一步的参数优化,得出了使LED的串联电阻取最小值时的插指型电极的结构参数。根据优化得到的参数制作了相应的LED样品,并与采用扩展正极型电极结构的LED做了对比实验。实验结果表明,计算得出的结果与实验结果符合得很好。采用了优化后的插指型电极结构的LED与采用扩展正极型电极结构的LED相比,前者的串联电阻仅为后者的44.4%。

Finite Element Model of GaN Based LED and the Optimization of the Mesa Structure

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.