Long wavelength InGaN emitters are challenging to fabricate and typically less efficient due to the >10% lattice mismatch between indium nitride (InN) and gallium nitride (GaN). The large lattice mismatch causes high strain in the active region which results in defects, degradation of surface morphology and a reduction of indium incorporation (compositional pulling). Growing the InGaN active region on a strain-relaxed InGaN buffer layer will, however, reduce the lattice mismatch between the two layers. This reduces the compositional pulling effect and allows for higher indium incorporation by hotter growth using MOCVD, the dominant method of commercial epitaxial InGaN growth. Hotter growth temperatures tend to lead to higher crystal quality as well, and together these advancements have realized efficient red InGaN LEDs. Until now, this method was not available to InGaN emitters in the green wavelengths.
Researchers at the University of California, Santa Barbara have achieved high efficiency and high power emission in green emitters while growing the devices on or above a strain-relaxed template (SRT). The SRT uses a thin thermally decomposed InGaN underlayer (DL) below an n-type GaN or low indium composition InGaN decomposition stop layer (DSL), on top of which is grown a buffer layer comprising an n-type InGaN/GaN superlattice (SL). For an LD structure, an n-type InGaN waveguiding layer is then grown, followed by an active region, p-type electron blocking layer (EBL), p-type InGaN waveguide and p-type GaN or p-type InGaN layers. For an LED structure, the n-type, p-type or both InGaN waveguiding layers may be omitted. This technology improves the layer structure and growth conditions for green InGaN emitters, resulting in higher power output and higher efficiency.
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LED, MOCVD, laser diode, green, strain, InGaN