• Effect of Micron-scale Photoluminescence Variation on Droop Measurements in InGaN/GaN Quantum Wells

      Barrett, R M; Ahumada-Lazo, R; Alanis, J A; Parkinson, P; Church, S A; Kappers, M J; Oliver, R A; Binks, D J; email: david.binks@manchester.ac.uk (IOP Publishing, 2021-05)
      Abstract: Micro-photoluminescence maps reveal micron-scale spatial variation in intensity, peak emission energy and bandwidth across InGaN/GaN quantum wells. To investigate the effect of this spatial variation on measurements of the dependence of emission efficiency on carrier density, excitation power-dependent emission was collected from a bright and dark region on each of blue-and green emitting samples. The onset of efficiency droop was found to occur at a greater carrier density in the dark regions than in the bright, by factors of 1.2 and 1.8 in the blue and green-emitting samples, respectively. By spatially integrating the emission from progressively larger areas, it is also shown that collection areas greater than ∼50 μm in diameter are required to reduce the intensity variation to less than 10%.
    • Effect of Micron-scale Photoluminescence Variation on Droop Measurements in InGaN/GaN Quantum Wells

      Barrett, R M; Ahumada-Lazo, R; Alanis, J A; Parkinson, P; Church, S A; Kappers, M J; Oliver, R A; Binks, D J; email: david.binks@manchester.ac.uk (IOP Publishing, 2021-05)
      Abstract: Micro-photoluminescence maps reveal micron-scale spatial variation in intensity, peak emission energy and bandwidth across InGaN/GaN quantum wells. To investigate the effect of this spatial variation on measurements of the dependence of emission efficiency on carrier density, excitation power-dependent emission was collected from a bright and dark region on each of blue-and green emitting samples. The onset of efficiency droop was found to occur at a greater carrier density in the dark regions than in the bright, by factors of 1.2 and 1.8 in the blue and green-emitting samples, respectively. By spatially integrating the emission from progressively larger areas, it is also shown that collection areas greater than ∼50 μm in diameter are required to reduce the intensity variation to less than 10%.
    • Effect of Micron-scale Photoluminescence Variation on Droop Measurements in InGaN/GaN Quantum Wells

      Barrett, R M; Ahumada-Lazo, R; Alanis, J A; Parkinson, P; Church, S A; Kappers, M J; Oliver, R A; Binks, D J; email: david.binks@manchester.ac.uk (IOP Publishing, 2021-05)
      Abstract: Micro-photoluminescence maps reveal micron-scale spatial variation in intensity, peak emission energy and bandwidth across InGaN/GaN quantum wells. To investigate the effect of this spatial variation on measurements of the dependence of emission efficiency on carrier density, excitation power-dependent emission was collected from a bright and dark region on each of blue-and green emitting samples. The onset of efficiency droop was found to occur at a greater carrier density in the dark regions than in the bright, by factors of 1.2 and 1.8 in the blue and green-emitting samples, respectively. By spatially integrating the emission from progressively larger areas, it is also shown that collection areas greater than ∼50 μm in diameter are required to reduce the intensity variation to less than 10%.
    • Effect of Micron-scale Photoluminescence Variation on Droop Measurements in InGaN/GaN Quantum Wells

      Barrett, R M; Ahumada-Lazo, R; Alanis, J A; Parkinson, P; Church, S A; Kappers, M J; Oliver, R A; Binks, D J; email: david.binks@manchester.ac.uk (IOP Publishing, 2021-05)
      Abstract: Micro-photoluminescence maps reveal micron-scale spatial variation in intensity, peak emission energy and bandwidth across InGaN/GaN quantum wells. To investigate the effect of this spatial variation on measurements of the dependence of emission efficiency on carrier density, excitation power-dependent emission was collected from a bright and dark region on each of blue-and green emitting samples. The onset of efficiency droop was found to occur at a greater carrier density in the dark regions than in the bright, by factors of 1.2 and 1.8 in the blue and green-emitting samples, respectively. By spatially integrating the emission from progressively larger areas, it is also shown that collection areas greater than ∼50 μm in diameter are required to reduce the intensity variation to less than 10%.
    • Effect of Si-doped InGaN underlayers on photoluminescence efficiency and recombination dynamics in InGaN/GaN quantum wells

      Church, S A; Christian, G M; Barrett, R M; orcid: 0000-0001-8512-0930; Hammersley, S; Kappers, M J; Frentrup, M; Oliver, R A; Binks, D J; email: david.binks@manchester.ac.uk (IOP Publishing, 2021-09-10)
      Abstract: A series of single InGaN/GaN quantum wells (QWs) with a Si-doped InGaN underlayer were studied to investigate the impact of the underlayer on photoluminescence efficiency and recombination dynamics. The thickness of the GaN capping layer was varied between samples, which changed the electric field across the QW due to band bending near the surface. When directly exciting the wells, thermionic emission of carriers results in a rapid drop in the photoluminesence efficiency with increasing temperature such that no emission is observed above 100 K. However, exciting above the energy of the barriers caused the intensity of the QW emission to drop more slowly, with up to 12% of the 10 K emission intensity remaining at 300 K. This difference is attributed to hole transfer from the underlayer into the QW, which increases in efficiency at higher temperatures, and is enhanced by stronger electric fields present in the GaN barriers of samples with thinner GaN capping layers. Further, the sample with the narrowest cap layer of 2 nm has a different shape and characteristic time for its photoluminescence decay transient and a different emission energy temperature dependence than the other samples. This behaviour was ascribed to a change in carrier localisation for this sample due to a reversal of the net field across the well compared to the other samples.
    • Effect of Si-doped InGaN underlayers on photoluminescence efficiency and recombination dynamics in InGaN/GaN quantum wells

      Church, S A; Christian, G M; Barrett, R M; orcid: 0000-0001-8512-0930; Hammersley, S; Kappers, M J; Frentrup, M; Oliver, R A; Binks, D J; email: david.binks@manchester.ac.uk (IOP Publishing, 2021-09-10)
      Abstract: A series of single InGaN/GaN quantum wells (QWs) with a Si-doped InGaN underlayer were studied to investigate the impact of the underlayer on photoluminescence efficiency and recombination dynamics. The thickness of the GaN capping layer was varied between samples, which changed the electric field across the QW due to band bending near the surface. When directly exciting the wells, thermionic emission of carriers results in a rapid drop in the photoluminesence efficiency with increasing temperature such that no emission is observed above 100 K. However, exciting above the energy of the barriers caused the intensity of the QW emission to drop more slowly, with up to 12% of the 10 K emission intensity remaining at 300 K. This difference is attributed to hole transfer from the underlayer into the QW, which increases in efficiency at higher temperatures, and is enhanced by stronger electric fields present in the GaN barriers of samples with thinner GaN capping layers. Further, the sample with the narrowest cap layer of 2 nm has a different shape and characteristic time for its photoluminescence decay transient and a different emission energy temperature dependence than the other samples. This behaviour was ascribed to a change in carrier localisation for this sample due to a reversal of the net field across the well compared to the other samples.