Physical models and numerical modeling for 280 nm AlGaN-based emission-and-detection dual functional integrated...

In this work, physical models for 280 nm AlGaN-based light emitting diode (LED) with monolithically integrated photodetector (PD) having the same multiple quantum wells (MQWs) structure have been established for the first time, with the aid of which, numerical calculations have been studied. Asymmetric MQWs have been proposed to improve the optoelectronic coupling efficiency, i.e., the active region is divided into a detection region with thick quantum wells and an emission region with thin quantum wells. The calculated results indicate that thin quantum wells help to suppress the quantum-confined Stark effect (QCSE) and enhance the transverse-electric (TE) polarized light intensity simultaneously. Besides, owing to the modulated effect by quantum well thickness on the energy level for the quantized states, the Stokes shift between the emission spectra and optical absorption spectra can be effectively suppressed. However, it also finds that when the quantum well in the emission region is thinned to 1 nm, the capture capability for holes is weakened and more holes will escape from the emission region and are injected into the detection region. Therefore, we propose linearly increasing the Al composition of quantum barriers in the emission region along [0001] direction, and the positive polarization bulk charges can be generated therein, which increases the valence barrier height for holes and prevents holes from escaping. Thanks to the enhanced IQE and suppressed Stokes shift, the photocurrent level for the on-chip PD gets increased. Our studies also report that although thin quantum wells suppress the Stokes shift and increase the photon-generated carriers, the built-in electric field in the PN junction can be simultaneously screened by the more photon-generated carriers. This sacrifices the on/off speed for the on-chip PD. The proposed structure with Al-composition-graded quantum barriers will retrieve the built-in electric field, which helps to increase the on/off speed for the on-chip PD.