Effects of quantum well growth temperature on the recombination efficiency of InGaN/GaN multiple quantum wells that emit in the green and blue spectral regions

InGaN-based light emitting diodes and multiple quantum wells designed to emit in the green spectral region exhibit, in general, lower internal quantum efficiencies than their blue-emitting counter parts, a phenomenon referred to as the “green gap.” One of the main differences between green-emitting and blue-emitting samples is that the quantum well growth temperature is lower for structures designed to emit at longer wavelengths, in order to reduce the effects of In desorption. In this paper, we report on the impact of the quantum well growth temperature on the optical properties of InGaN/GaN multiple quantum wells designed to emit at 460 nm and 530 nm. It was found that for both sets of samples increasing the temperature at which the InGaN quantum well was grown, while maintaining the same indium composition, led to an increase in the internal quantum efficiency measured at 300 K. These increases in internal quantum efficiency are shown to be due reductions in the non-radiative recombination rate which we attribute to reductions in point defect incorporation.This work was carried out with the financial support of the United Kingdom Engineering and Physical Sciences Research Council under Grant Numbers EP/I012591/1 and EP/H011676/1.This is the final version of the article. It first appeared from AIP via http://dx.doi.org/10.1063/1.4932200 All data created during this research are openly available from the University of Manchester eScholar archive at http://dx.doi.org/10.15127/1.26974

Local carrier recombination and associated dynamics in m-plane InGaN/GaN quantum wells probed by picosecond cathodoluminescence

We report on spatially resolved and time-resolved cathodoluminescence (CL) studies of the recombination mechanisms of InGaN/GaN quantum wells (QWs) grown by metal-organic vapour phase epitaxy on bulk m-plane Ammono GaN substrates. As a result of the 2° miscut of the GaN substrate, the sample surface exhibits step bunches, where semi-polar QWs with a higher indium concentration than the planar m-plane QWs form during the QW growth. Spatially resolved time-integrated CL maps under both continuous and pulsed excitation show a broad emission band originating from the m-plane QWs and a distinct low energy emission originating from the semi-polar QWs at the step bunches. High resolution time-resolved CL maps reveal that when the m-QWs are excited well away from the step bunches the emission from the m-plane QWs decays with a time constant of 350 ps, whereas the emission originating semi-polar QWs decays with a longer time constant of 489 ps. The time constant of the decay from the semi-polar QWs is longer due to the separation of the carrier wavefunctions caused by the electric field across the semi-polar QWs.This work has been funded by the EPSRC (Grant Nos. EP/J003603/1, EP/J001627/1, and EP/M011682/1) and in part by the European Research Council under the European Community's Seventh Framework Programme (FP7/2007-2013)/ERC Grants Agreement No. 279361 (MACONS)

Resonant photoluminescence studies of carrier localisation in c-plane InGaN/GaN quantum well structures

Experimental data used for figures in paper submitted to Applied Physics Letter

Stacking fault-associated polarised surface-emitted photoluminescence from zincblende InGaN/GaN quantum wells

A photoluminescence (PL) study was performed on zincblende-InGaN/GaN quantum wells. These structures contained a high density of stacking faults, which cause the segregation of indium at the intersection with the quantum wells, creating quantum wires. Emission from these quantum wires dominates the room temperature PL spectra and is highly polarised (Fig 1): emission from the quantum wells is additionally observed at 10K (Fig 2). The 10K PL decays show that the emission from the quantum wells is fast and mono-exponential, and the quantum wire emission is a stretched exponential (Fig 3). 10K PL-excitation measurements show absorption into the GaN barriers, which does not shift with emission energy. Absorption into the quantum well is observed and does not shift with emission energy over the quantum wire emission (Fig 5). Low temperature PL spectra show emission from the quantum wells and wires (Fig S1). As the temperature is increased, the quantum well emission quenches at a faster rate than the wire emission and the peaks redshift (Fig. S2). As the excitation power is increased, there is no change in the PL spectra (Fig S3). Changing the polarisation of the excitation has no effect on the PL or PL-excitation spectra (Fig S4). Simple calculations were performed to calculate the band profile and carrier ground states in quantum wire structures (Fig S5). An estimation of the ground and excitated hole state energies was also calculated (Fig S6). This allowed a calculation of the change in the degree of linear polarisation of the quantum wire emission at 300K, compared with 10K (Fig S7)

Optical properties of c-Plane InGaN/GaN single quantum wells as a function of total electric field strength

Conduction and valence band profiles calculated using Nextnano3 for InGaN/GaN single quantum well structures with Si-doped InGaN underlayers and different GaN cap layer thicknesses. Photoluminescence spectra obtained at 10 K for those quantum well structures

Data supporting review paper on cubic GaN

Previously unreported data included in the review paper entitled " Cubic GaN and InGaN / GaN Quantum wells" corresponding to Figure 1 and 5 of that paper. Figure 1 shows the emission wavelengths for quantum well widths between 2 and 10 nm. Figure 5 compares the photoluminescence spectra from epilayers of hexagonal and cubic GaN

Millennia Pro Interlock BoM

A bill of materials for the construction of the Millennia Pro interlock bo

Millennia Pro Interlock custom PCB files

The schematic, PCB layout and associated libraries for the custom board fabricated for the Millennia Pro interlock box. The files were created in Altium Designer 21 but a Gerber version is included and a ready-to-fabricate version is available at https://oshpark.com/shared_projects/TsGSmbmI

Photoluminescence efficiency of zincblende InGaN/GaN quantum wells

Temperature dependent photoluminescence (PL) spectroscopy was performed on zincblende InGaN/GaN quantum wells (QW), along with PL time decay measurements, in order to estimate the recombination efficiency. The 10K PL spectra was seen to redshift as the QW width was increased (Fig. 2). The 10K decay time increased with increasing QW width, but the intensity was approximately constant (Fig. 3). The integrated intensity of the QWs dropped slowly with temperature up to 100K, and fast up to 300K, with more variation for the single QW (Fig. 4). The PL spectra were all polarised in the [1-10} direction (Fig. S2). The degree of polarisation reduced with increasing QW width (Fig. S3). The PL peak energy shift agrees with a simple finite QW model (Fig. S4)

Millennia Pro Interlock ESP32 code

The code that runs on the ESP32 chip to control the logic of the Millennia Pro pump laser interloc