Mg Doping of 3D Semipolar InGaN/GaN-Based Light Emitting Diodes

The effects of different Mg doping concentrations in the main p-GaN layer and the pGaN capping layer on the electroluminescence (EL) property of three-dimensional (3D) stripe semipolar InGaN/GaN based light emitting diodes (LEDs) were investigated. Secondary ion mass spectrometry (SIMS) analysis revealed the Mg concentration of the 3D semipolar p-GaN, indicating a higher Mg incorporation efficiency on the {101̄1} facet compared to the {112̄2} facet. Low-temperature μ-photoluminescence was measured on a series of 3D LED structures varying the Mg doping concentration. For the LEDs with the {101̄1} facet, pronounced donor-acceptor-pair (DAP) luminescence at 3.24 eV with characteristic LO-replicas was observed with the molar flow ratio between Cp2Mg and TMGa (Cp2Mg/TMGa) of 0.04% and 0.06%. With further increasing Cp2Mg/TMGa of 0.10% and 0.21%, the DAP band shifts to a broad band emission at a lower energy presenting the emergence of self-compensation. In contrary, self-compensation was not observed up to Cp2Mg/TMGa of 0.21% for the LEDs with the {112̄2} facet. Thus, the Mg incorporation efficiency on the {101̄1} facet is concluded to be higher than that on the {112̄2} facet, consistent with the SIMS data. The EL output power is low with a too low Cp2Mg/TMGa of 0.04% due to the inferior hole injection efficiency and stays almost constant with Cp2Mg/TMGa ranging from 0.06% until 0.21% for the 3D LEDs with the {101̄1} facet. Since Hall measurement is not applicable and SIMS is difficult on 3D structures, the good range of the hole conductivity for high EL output power could be recorgnized by the line shape of the Mg DAP band. Heavy Mg doping in the p-GaN capping layer is required to achieve good ohmic contact performance.