Correlation between p-GaN growth environment with electrical and optical properties of blue LEDs

Two blue (450 nm) light–emitting diodes (LED), which only differ in top p-GaN layer growth conditions, were comparatively investigated. I-V, C-V, TLM, Electroluminescence (EL) and Photoluminescence (PL) techniques were applied to clarify a correlation between MOCVD carrier gas and internal properties. The A-structure grown in the pure N2 environment demonstrated better parameters than the B-structure grown in the N2/H2 (1:1) gas mixture. The mixed growth atmosphere leaded to an increase of sheet resistances of p-GaN layer. EL and PL measurements confirmed the advantage of the pure N2 utilization, and C(VR) measurement pointed the increase of static charge concentration near the p-GaN interface in the B structure

MOCVD Grown InGaN/GaN Three-Dimensional Islands: Growth Approaches, Strain-Composition Characterization, Exploitation for LEDs

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Compositional accuracy in atom probe tomography analyses performed on III-N light emitting diodes

Laser-assisted atom probe tomography (APT) and high-resolution dark-field electron holography (HR-DFEH) were performed to investigate the composition of a polar [0001] GaN/AlxGa1 - xN/InyGa1 - yN light emitting diode. In particular, the III-site fraction of both AlxGa1 - xN and InyGa1 - yN alloys was studied adopting a comparative approach. HR-DFEH allows mapping the projected strain with a subnanometer spatial resolution which is used for the calculation of the two-dimensional alloy composition distribution. APT provides three-dimensional alloys composition distribution with a nanometer spatial resolution. However, here we reveal that important inaccuracies affect local composition measurements. A Ga-poor composition is obtained in high DC-electric field regions. Moreover, such inaccuracies may be locally enhanced where the [0001] pole intersects the surface of the analyzed specimen, leading to a lower fraction of Ga measured. III-site fractions closer to the nominal values were measured at low field conditions. Ga loss is thought to be due to preferential DC field induced evaporation of Ga ions between laser pulses. This is explained in terms of formation of a metallic layer on the tip surface during APT analysis, where weak Ga-Ga bonds are formed, promoting the loss of Ga at high field conditions

Formation of three-dimensional islands in the active region of InGaN based light emitting diodes using a growth interruption approach

cited By 4International audienceHere, we develop a technological approach to the formation of three-dimensional island-like structures in the active medium of InGaN/GaN based light emitting diodes with an enhanced efficiency with respect to reference quantum wells emitting at the same wavelengths. The reference structures contain two-dimensional In x Ga1– x N quantum wells with x ≤ 18% immediately overgrown after their formation. The method consists in the application of a growth interruption in N2 or N2–H2 mixed atmospheres at different H2 flows and times after the deposition of In0.18Ga0.82N quantum wells, prior to their overgrowth by a GaN layer. The growth interruptions allow a controlled blue shift of the emission peak position with respect to that of the In0.18Ga0.82N structure. The integrated photoluminescence intensity of the so-formed structures is about 1.5 times higher than that of the reference structures emitting at the same peak wavelengths. Light emitting diode structures subjected to growth interruption exhibit higher external quantum efficiency than the reference structures emitting at the same wavelengths. We demonstrate that the observed phenomenon is related to a better charge carrier confinement within a quantum well due to the transformation of planar InGaN layers into laterally connected flat islands