光致电化学法提高垂直结构发光二极管出光效率的研究

研究了在垂直结构发光二极管(VLED)器件中, 光致电化学法(PEC)刻蚀N极性n-GaN的速率受不同刻蚀条件(刻蚀浓度、刻蚀时间和光照强度)的影响. 并选择N极性n-GaN表面含有较理想六角金字塔结构(侧壁角为31°)的样品制成器件, 研究PEC刻蚀对VLED的欧姆接触和光电性能的影响. 结果表明, 与未粗化样品相比, PEC刻蚀后的样品接触电阻率明显降低, 形成更好的欧姆接触; 其电学特性有较好的改善, 光输出功率有明显提高, 在20 mA电流下光输出功率增强了86.1%. 对不同金字塔侧壁角度的光提取效率用时域有限差分法(FDTD)模拟, 结果显示光提取效率在侧壁角度为20°– 40°有显著提高, 在23.6° (GaN-空气界面的全反射角)时达到最大.

Increase in light extraction efficiency of vertical light emitting diodes by a photo-electro-chemical etching method

The rate of photo-electro-chemical (PEC) etching on N-polar n-GaN using vertical light emitting diodes (V-LEDs) has been investigated in detail, by varying the etching parameters (etchant concentration, etching duration and light intensity). V-LED with optimal hexagonal pyramid structure (the side-wall angle is 31°) has been fabricated, and then the influence of the PEC etching on the electrical and optical properties of V-LED has been analyzed. After PEC etching, the sample has good ohmic contact with the electrode and has lower contact resistance than a reference sample. The electrical characteristics have a better improvement. And the light output power has improved obviously after PEC etching, which shows 86.1% enhancement at 20 mA. Effect of side-wall angle of the pyramids on light extraction efficiency (LEE) in V-LEDs is theoretically calculated by finite difference time domain (FDTD) method. Simulation results show that the LEE is significantly increased for the sidewall angle between 20° and 40°, and the maximum enhancement is realized at a side-wall angle of 23.6° (the total reflection angle at the GaN/air interface).