Abstract
Recently, the use of bottom-TJ geometry in LEDs, which achieves N-polar-like alignment of polarization fields in conventional metal-polar orientations, has enabled enhancements in LED performance due to improved injection efficiency. Here, we elucidate the root causes behind the enhanced injection efficiency by employing mature laser diode structures with optimized heterojunction GaN/In0.17Ga0.83N/GaN TJs and UID GaN spacers to separate the optical mode from the heavily doped absorbing p-cladding regions. In such laser structures, polarization offsets at the electron blocking layer, spacer, and quantum barrier interfaces play discernable roles in carrier transport. By comparing a top-TJ structure to a bottom-TJ structure, and correlating features in the electroluminescence, capacitance-voltage, and current-voltage characteristics to unique signatures of the N- and Ga-polar polarization heterointerfaces in energy band diagram simulations, we identify that improved hole injection at low currents, and improved electron blocking at high currents, leads to higher injection efficiency and higher output power for the bottom-TJ device throughout 5 orders of current density (0.015-1000 A/cm2). Moreover, even with the addition of a UID GaN spacer, differential resistances are state-of-the-art, below 7 × 10-4 Ωcm2. These results highlight the virtues of the bottom-TJ geometry for use in high-efficiency laser diodes.
Highlights
Indium Gallium Nitride (InGaN) based light-emitting diodes (LEDs) and laser diodes (LDs) have garnered much attention for applications in visible lighting, displays, and light fidelity (Li-Fi) communications[1,2,3,4,5,6]
In LDs, this allows for placement of the contact away from the laser ridge; in such geometry, refractive index contrast between the top cladding and the waveguide is increased, allowing for enhanced optical confinement, and for thinning down the resistive p-GaN or pAlGaN cladding[9,10]
A study by Turski et al on the alignment of polarization and p-n junction fields in tunnel junctions (TJs) LEDs has shown that utilizing bottom-TJ geometry, with the TJ grown beneath a p-down LED results in higher injection efficiencies and greater light output than using the standard top-TJ geometry[19]
Summary
Indium Gallium Nitride (InGaN) based light-emitting diodes (LEDs) and laser diodes (LDs) have garnered much attention for applications in visible lighting, displays, and light fidelity (Li-Fi) communications[1,2,3,4,5,6].
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