Abstract
Modern multi-color RGB micro-light emitting diode (μLED) displays and digital micro-mirror laser projectors often require the use of both III-V and III-Nitride material systems for different pixel/laser colors. This is due primarily to the conventionally low efficiencies of red emitters based on the InGaN materials system, which is used to create green and blue emitters for RGB displays. The main challenges for InGaN red emitters are the quantum confined stark effect (QCSE) and the difficulty of incorporating high In-content into the active region. In this work, InGaN/InGaN/delta-InN quantum wells (QWs) on InGaN substrates are proposed and demonstrated to show significant enhancement in electron-hole wavefunction overlap ( Γe_hh ) and spontaneous emission radiative recombination rate (Rsp) in the red emission regime. Analysis of InGaN/InGaN/delta-InN QWs with InGaN barriers emitting at 630 nm was performed using a self-consistent six-band $k \cdot p$ formalism. The Γe_hh was shown to increase by more than 230% compared to an InGaN/InGaN QW emitting at 630 nm, leading to significant increases in Rsp and internal quantum efficiency ( ηIQE ). With growth of InN monolayers on InGaN now readily achievable, this novel active region design could pave the way for high-efficiency, native red-emitting InGaN LEDs and lasers.
Highlights
InGaN quantum well (QW) light emitting diodes (LEDs) and lasers have seen a significant increase in utilization over the past decade thanks to substantial increases in efficiency
The low ηEQE of red-emitting InGaN QWs can be attributed to the difficulty of incorporating high In-content layers into the active region, as well as the large internal electrostatic fields which exist within GaN/InGaN QWs, which can be on the order of 1–5 MV/cm [13], [15]
Calculations for conventional and delta-InN structures with GaN quantum barriers (QBs) and substrates, emitting at 630 nm, show an e_hh of 10% for a conventional GaN/InxGa1-xN QW and an e_hh of 18% for a GaN/InxGa1-xN/delta-InN QW. These enhancements demonstrate the effectiveness of using an InGaN substrate and InGaN QB layers, which lead to reduced interfacial lattice mismatch-based piezoelectric strain between epitaxial layers, which in turn reduces the electric field strength within the active region and improves e_hh
Summary
InGaN quantum well (QW) light emitting diodes (LEDs) and lasers have seen a significant increase in utilization over the past decade thanks to substantial increases in efficiency. The low ηEQE of red-emitting InGaN QWs can be attributed to the difficulty of incorporating high In-content layers into the active region, as well as the large internal electrostatic fields which exist within GaN/InGaN QWs, which can be on the order of 1–5 MV/cm [13], [15] These internal electric fields serve to confine the electron and hole wavefunctions to the edges of the QW, reducing the electron-hole wavefunction overlap ( e_hh) which in turn reduces the spontaneous emission radiative recombination rate (Rsp). Results show an Rsp enhancement of ∼5–7x for In0.15Ga0.85N/In0.3Ga0.7N/delta-InN QWs with a 3 Adelta-InN layer when compared to a In0.15Ga0.85N/In0.38Ga0.62N QW, with both emitting with λpeak = 630 nm These results are extremely promising and show that InxGa1-xN/InyGa1-yN/delta-InN QWs may be a superior alternative to GaN/InGaN QWs for high efficiency red emission
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