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

Abstract

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.