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Electron-phonon interactions in subband excited photoluminescence of hexagonal boron nitride
摘要： The h-BN microcrystalline powder with carbon and oxygen impurities have been studied at 83 and 296 K using Raman and photoluminescence (PL) spectroscopies. The observed blue shift of Raman peaks with temperature decreasing have been discussed allowing for the enhanced role of the optical vibrational modes. Two series of phonon replicas in PL emission spectra with a zero-phonon line at 4.08 eV have been registered under 4.28 eV excitation. The energy levels model of the impurity (CN-ON)-complex responsible for observe luminescence was proposed. It was shown that the optically active center retains its electroneutrality in the processes of radiative recombination under subband (in 4.28 eV) or band-to-band excitation. Possible mechanisms of electron-phonon scattering and phonon replicas forming under subband excitation of (CN-ON)-complex were analyzed. It was substantiated that the longitudinal optical (?ωLO = 174 meV) and transverse acoustic (?ωTA = 60 meV) phonons at the middle points of high symmetry in the first Brillouin zone participate in the processes of intravalley (M- and Κ-scattering) and intervalley (Κ → Μ)-scattering, respectively.
关键词： ultraviolet luminescence,intravalley scattering,point defect,intervalley scattering,phonon replicas,h-BN,carbon-oxygen complex
更新于2025-09-23 15:23:52
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Cryostat setup for measuring spectral and electrical properties of light-emitting diodes at junction temperatures from 81 K to 297 K
摘要： We introduce a cryostat setup for measuring fundamental optical and electrical properties of light-emitting diodes (LEDs). With the setup, the cryostat pressure and the LED properties of the forward voltage, junction temperature, and electroluminescence spectrum are monitored with temperature steps less than 1.5 K, over the junction temperature range of 81–297 K. We applied the setup to commercial yellow AlGaInP and blue InGaN LEDs. At cryogenic temperatures, the fine structure of the electroluminescence spectra became resolved. For the yellow LED, we observed the phonon replica at 2.094 eV that was located 87 meV below the peak energy at the junction temperature of 81 K. For the blue LED, we observed the cascade phonon replicas at 2.599 eV, 2.510 eV, and 2.422 eV with the energy interval of 89 meV. For both LED types, the forward voltage increased sharply toward the lower temperatures due to the increased resistivity of materials in the LED components. We found significant differences between the temperature dependent behaviors of the forward voltages, spectral peak energies, and bandgap energies of LEDs obtained from the Varshni formula. We also noted a sharp pressure peak at 180–185 K arising from the solid-vapor phase transition of water when the base level of the cryostat pressure was approximately 0.4 mPa.
关键词： spectral properties,light-emitting diodes,electrical properties,junction temperature,phonon replicas,cryostat setup
更新于2025-09-16 10:30:52