Theoretical study on the quantum confined Stark effect in InGaN/GaN multiple quantum wells for highly efficient light-emitting diodes

Abstract

Long-wavelength light emitting diodes (LEDs) based on wurtzite multiple quantum well (MQW) structures encounter a significant efficiency drop, a phenomenon commonly referred to as the ‘green gap’. To overcome this challenge, eliminating the quantum confined Stark effect by controlling the internal electric field is recognized as a key solution to prevent the reduction in radiative recombination rate. While there have been lots of theoretical and experimental efforts associated with this approach, a lack of comprehensive analysis or quantitative criteria regarding the feasibility of achieving a solution still exists. In this study, we studied the controllability of the electric field in wurtzite MQW based on the interface theorem model. Utilizing this framework, we categorized various factors influencing this control and conducted numerical simulations to explore the implications, using InGaN as the material of interest. We investigate that the electric field in the emitting region mainly arises from the increasing difference of polarization between the constituent materials of the MQW, due to the enhanced piezoelectric polarization from induced strain. We therefore explored the required rates of lattice relaxation in strained materials for the purpose of eliminating the field. Moreover, with practical applications in mind, we extended the previous formalism to provide a more realistic and extensive depiction of the combined effects of these factors. Ultimately, we proposed an optimal model with a gradual In-composed layer in the active layer, which is expected to minimally form an electric field. We anticipate that these guiding rules for controlling the internal electric field will be instrumental in investigating various models to realize highly efficient LEDs.