能带调控提高GaN/InGaN多量子阱蓝光LED效率研究

Investigation of the GaN-based light-emitting diodes with engineered energy band in InGaN multiple quantum wells

In Ga N/Ga N多量子阱中由于存在极化效应导致能带弯曲,并由此导致电子和空穴在空间上被分离,因此严重降低了Ga N基LED的发光效率.针对此问题,我们设计了一种组分渐变的量子阱结构,利用组分与能带的关系对量子阱进行能带调控,使得量子阱中的能带弯曲减弱.该方法有效增加了LED的光功率和外量子效率.电致发光谱测试显示,在注入电流为35 A/cm2时,具有能带调控量子阱的LED其外量子效率比传统结构的LED提高了10.6%,发光功率提高了9.8%.能带模拟显示,能带调控后的量子阱中能带倾斜现象减弱,且空穴浓度明显增加,因此电子空穴波函数在空间中的重叠面积得到有效提高,最终提高了辐射复合效率.

There is intense spontaneous polarization field in wurtzite nitride materials due to the lack of inversion symmetry. In addition, when the materials are strained, piezoelectric polarization filed will be produced. Hence, large piezoelectric and spontaneous polarizations is appeared in strained InGaN/GaN multiple quantum wells （MQWs）, which is necessary materials for GaN-based blue light-emitting diodes （LEDs）. The large polarization field will cause band bending in InGaN/GaN multiple quantum wells （MQWs）, which caused by polarization effect results in electron-hole separation and reduces the efficiency of GaN-based light-emitting diodes （LEDs）. In this paper, according to the polarization-doped theory, we engineer the energy band of InGaN MQWs by grading In composition to weaken band bending. Meanwhile, according to the polarization-doped theory,the polarization field in the graded InGaN also can induce high density hole in the quantum well. The electrical and optical performances of the conventional LED and the LED with engineered energy band are compared experimentally. Compared with the conventional LED, the optical output power and the EQE of the LED with engineered energy band are enhanced. These are ascribed to less energy band bending by engineering the energy band of InGaN MQWs, which is proved by less EL peak position energy blue shift with injection current increasing and less PL peak position energy blueshift with reverse voltage increasing for the LED with engineered energy band. The calculated results indicate that, the band bending of the LED with engineered energy band is weakened, and the hole concentration in the graded InGaN quantum wells is enhanced. Then the overlap of the electron-hole wave function is enhanced, which results in improved radiative recombination rate.