Abstract
Non-intentionally doped c-plane GaN layers are generally employed as p-side waveguide layers in violet/blue-emitting laser diodes. The recombination and diffusion of charge carriers in the p-side GaN waveguide influence the injection efficiency of holes into the InGaN quantum wells of these devices. In this study, the non-radiative recombination and the diffusivity in the [000-1] direction for charge carriers in such GaN layers are investigated by the photoluminescence of buried InGaN quantum wells, in addition to the GaN photoluminescence. The vertical charge carrier diffusion length and the diffusion constant in GaN were determined by evaluating the intensity from InGaN quantum wells in different depths below a top GaN layer. Additionally, the intensity from the buried InGaN quantum wells was found to be more sensitive to variations in the non-radiative recombination rate in the GaN layer than the intensity from the GaN itself. The study enables conclusions to be drawn on how the growth of a p-side GaN waveguide layer has to be optimized: (1) The charge carrier diffusivity in the [000-1] direction at device operation temperature is limited by phonon scattering and can be only slightly improved by material quality. (2) The use of TMGa (trimethylgallium) instead of TEGa (triethylgallium) as a precursor for the growth of GaN lowers the background silicon doping level and is advantageous for a large hole diffusion length. (3) Small growth rates below 0.5 μm/h when using TMGa or below 0.12 μm/h when using TEGa enhance non-radiative recombination. (4) A V/III gas ratio of 2200 or more is needed for low non-radiative recombination rates in GaN.
Highlights
GaN/InGaN-based violet/blue-emitting LEDs and laser diodes have achieved high emission power and high quantum efficiency.[1,2] the IIInitride semiconductor layers used for these devices are far from being crystallographically perfect
Ldiff, were determined by evaluating the PL intensity from InGaN quantum wells buried under GaN layers of different thicknesses
The diffusion length is related to the GaN purity, since it depends on the effective recombination time and on the non-radiative recombination rate in the material
Summary
GaN/InGaN-based violet/blue-emitting LEDs and laser diodes have achieved high emission power and high quantum efficiency.[1,2] the IIInitride semiconductor layers used for these devices are far from being crystallographically perfect. The experiment provides information (i) on the non-radiative recombination in the top GaN layer via the PL intensity from the GaN, and (ii) on the charge carrier diffusivity in the top GaN layer via the PL intensity from the InGaN quantum wells.
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