LED芯片作为LED光源的核心, 其质量直接决定了器件的性能、 寿命等, 因此在内量子效率已达到高水平的情况下, 致力于提高光提取效率是推动LED芯片技术发展的关键一步。 由于蓝宝石衬底具有绝缘特性, 传统LED将N和P电极做在芯片出光面的同一侧, 而芯片出光面上的P电极焊盘金属会遮挡吸收其正下方发光区发出的大部分光而造成光损失, 为改善这一现象并缓解P电极周围的电流拥挤效应, 本文设计制备了在P电极正下方的氧化铟锡(ITO)透明导电层和p-GaN之间插入SiO₂薄膜作为电流阻挡层(CBL)的大功率LED, 并与无CBL结构的大功率LED相比较。 对未封装的有无CBL结构的LED在350 mA电流下进行正向偏压, 辐射通量, 主波长等裸芯性能测试, 结果显示两种芯片的正向偏压均集中在3~3.1 V, 而有CBL结构的LED光输出功率有明显提升, 这是因为CBL阻挡了电流在P电极正下方的扩散, 减少流向有源区的电流密度, 故减小了P电极对光的吸收和遮挡, 且电流通过CBL引导至远离P电极的区域, 缓解了电极周围的电流拥挤。 对两种芯片进行相同结构和工艺条件的封装, 并对封装样品进行热特性及10~600 mA的变电流光电特性测试, 得到两种器件的发光光谱及光功率等光学特性。 结果表明随着电流增加, 两种器件的光谱曲线均发生蓝移, 且有CBL结构的LED主波长偏移量较无CBL结构LED少10 nm, 可见有CBL结构的LED光谱受驱动电流变化的影响更小, 因此其显色性能更为稳定。 而在小电流条件下, CBL对器件光功率的影响不大, 随着工作电流的增大, CBL对器件光功率的改善效果逐渐提升。 在大电流条件下, 无CBL结构的LED结温更高, 正向电压更低, 随电流的增大二者之间的电压差增大。 在25 ℃的环境温度, 350 mA工作电流下, 加入CBL结构使器件电压升高约0.04 V, 但器件光功率最高提升了9.96%, 且热阻明显小于无CBL结构器件, 说明有CBL结构LED产热更少。 因此CBL结构大大提高了器件的光提取效率, 并使其光谱漂移更小, 显色性能更为稳定。

As the core of LED light source, the quality of LED chip directly determines the performance, life and so on of the device. Therefore, the improvement of optical extraction efficiency is the key step to promote the development of LED chip technology when the internal quantum efficiency has reached a fairly high level. Due to the insulating property of sapphire, the N and P electrodes of normal LED are made on the same side of the light output surface of the chip. The P metal electrode on the light output surface absorbs most of the light emitted from the luminous region directly below it, and causes light loss. To improve this phenomenon and alleviate the current crowding around the P electrode, in this paper, we fabricated LED devices with SiO₂ current blocking layer(CBL)that was deposited between ITO transparent conductive layer and P-GaN,and another kind of LED without CBL. We tested voltage,light output power,main wavelength of the two kinds of chips without package under 350mA working current. The results showed that the forward voltage of the two kinds of chips are concentrated in 3~3.1V, while the light output power of the LED with CBL is obviously improved. CBL blocks the current from diffusing below the P electrode and reduces the current density flowing to the active region, thus reducing the absorption and shielding of light by the P electrode, and directing the current to the region far away from the P electrode through CBL, reducing current congestion around the electrode. Then the two kinds of chips were packaged in the same package structure and process conditions. The thermal characteristics and photoelectric properties of two samples were investigated under different current range from 10 to 600 mA, and the spectra and optical power of two kinds of devices were obtained. Results showed that main wavelength of the two samples blue shift with the increasing current, and the main wavelength blue-shifting of LED with CBL is 10nm less than the LED without CBL. It can be seen that the spectra of LED inserted CBL is less affected by the increasing current. Therefore, its color rendering properties is more stable. Under the low current, CBL structure has little effect on the optical power of the device. With the increase of current, the improvement effect of CBL on the optical power is improved gradually. Under the heavy current, the junction temperature of the LED without CBL is higher and the forward voltage is lower, and the voltage difference between the two kinds of devices increases with the increasing current. Under 25℃ ambient temperature, 350 mA working current, the voltage of LED with CBL increases 0.04 V, but it improves optical power, the highest increase is 9.96%, and the thermal resistance is obviously smaller than the device without CBL structure, which indicates that the heat production of LED with CBL is less than the device without CBL structure. Therefore, the optical extraction efficiency of the device is improved by CBL structure. And the spectrum drifting is smaller and the color rendering properties is more stable.