InGaN-delta-InN Quantum Wells on InGaN Substrates for High-Efficiency Red Emission

摘要

Multi-color red, green, and blue (RGB) micro-light emitting diode (LED) displays often require the use different material systems to obtain high-efficiency RGB pixels. While blue and green micro-LEDs can be fabricated with sufficiently high external quantum efficiencies (η_(EQE)) using the InGaN materials system, red InGaN emitters currently exhibit much lower η_(EQE). The reduction of InGaN LED efficiency at longer wavelengths can be attributed to the Quantum Confined Stark Effect (QCSE), which reduces the electron-hole wavefunction overlap (Γ_(e_hh)) and radiative recombination rate (R_(sp)), and worsens at longer wavelengths with increasing QW In-content. Consequently, higher efficiency AlInGaP LEDs are usually used for the red pixels in micro-LEDs, complicating the fabrication process. In this work, InGaN-delta-InN quantum well (QW) LEDs with InGaN quantum barriers on InGaN substrates are shown to produce significant enhancement in electron-hole wavefunction overlap and R_(sp) over the entire red emission regime and into the near-infrared. Analysis and comparison of various InGaN-delta-InN QWs with InGaN barriers and InGaN/InGaN QWs emitting at 630 nm was performed using self-consistent six-band k · p formalism. Wavefunction overlap from InGaN-delta-InN QWs was shown to increase by 3.5x when compared to an InGaN/InGaN QW at 630 nm. These improvements in wavefunction overlap were shown to lead to ～5 - 7x and ～3 - 10x enhancements in R_(sp) and IQE, respectively. With growth of InN monolayers on InGaN now readily achievable, this novel delta-InN active region on InGaN substrate design could pave the way for high efficiency, native red-emitting InGaN LEDs and allow for monolithic fabrication of InGaN micro-LED displays.