Effects of Electric Fields on Cathodoluminescence from II-VI Quantum Well Light Emitting Diodes
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Effects of Electric Fields on Cathodoluminescence from II-VI Quantum Well Light Emitting Diodes A. Y. Nikiforov,1 G. S. Cargill III,1 M. C. Tamargo,2 S. P. Guo,2,4 and Y.-C. Chen 3 1
Department of Materials Science and Engineering, Lehigh Univ., Bethlehem, PA 18015, U.S.A. Department of Chemistry, City College-CUNY, New York, NY 10031, U.S.A. 3 Department of Physics, Hunter College, CUNY, New York, NY 10021, U.S.A. 4 Present address: EMCORE Corp., Somerset, NJ 08873, U.S.A. 2
ABSTRACT Effects of electrical bias on the cathodoluminescence (CL) have been investigated for a blue II-VI quantum well (QW) light emitting diode structure of ZnCdMgSe, lattice-matched to InP. In CL wavelength scans, the observed effects include largely reversible changes in QW CL intensity and wavelength and changes in cladding CL intensity. In CL time-based scans, the QW CL intensity showed both immediate and long term changes with bias. Irreversible, degradationrelated decreases in QW CL intensity were also observed. Effects of bias on CL were modeled by calculating the rates of carrier production by electron bombardment and the resulting electron and hole currents with different applied bias fields. These model calculations do not explain many of the experimental observations, because the model does not include effects of bias on carrier escape and redistribution in the QW and effects of bias on generation and transport of atomic scale defects.
INTRODUCTION ZnSe-based light emitting diodes have potential applications in full-color projection displays, traffic signals, and more efficient white light sources [1-5]. Although remarkable progress has been made, practical devices have not been yet achieved because of luminescent intensity degradation during device operation. The quaternary wide-gap ZnCdMgSe system (figure 1) can be grown lattice matched to (001) InP substrates by molecular beam epitaxy with a wide range of band gaps from blue to red depending on composition [3]. QW structures based on these materials exhibit excellent optical characteristics with very strong luminescence intensity and quantum confinement [4-5]. These diodes show no formation of dark line defects and have lifetimes about three orders of magnitude longer [6,7] than diodes with a comparable density of extended defects grown on GaAs substrates. Understanding how electrical bias affects carrier transport and defect behavior may help in further improvement of performance and lifetimes of QW-based light emitting diodes (LEDs) and laser diodes [8]. Gundel et al. [8] studied the influence of reverse bias on degradation of a ZnCdSe QW-based laser diode by photoluminescence. They [8] argued that the observed changes in the degradation rate with bias were caused by the effects of bias fields on diffusion of charged defect complexes from the p-doped waveguide into the QW.
H9.26.1
5-10nm Au electrode
In
14nm p+-ZnSeTe cap layer, Na~2 ⋅1019cm-3 100nm p-Zn0.27Cd0.27Mg0.46Se:N Cladding layer, Na~1016cm-3
A
6nm Zn0.28Cd0.34Mg0.28Se QW 500nm n+- Zn0.27Cd0.27Mg0.46Se:Cl,
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