Experimental and theoretical studies of low-voltage electroluminescence of ZnS single crystals

Blue Anti-Stokes Electroluminescence in GaN

“…This is consistent with the observed efficiency of 3xl0" 4 . In contrast, the one-electron process with a ASkT energy deficiency would have the negligible excitation efficiency of ~10" 21 .…”

Thermophotonics for ultra-high efficiency visible LEDs

“…As the authors have pointed out, low-bias operation can be realized at high current density; WPE of 84% at approximately 4 A/cm 2 but low-bias ( < ℎ / ) is realized up to current densities of 75 A/cm 2 . Because the low-bias WPE and EQE in this device is well-above 50%, this device also clearly illustrates that low-bias emission (or anti-Stokes emission) is not the result of multi-electron processes as suggested in [8,9,10].…”

“…Nathan, et al later postulated that the higher energy photons were the result of Auger process near the GaAs active region that were populating high lying energy states [8]. A similar mechanism was proposed by Bitter, et al where they suggested that tunneling assisted impact ionization was responsible for populating these high lying states [9]. Finally, Pankove postulated that the low bias emission observed in GaN (2.9 eV photons from a bias as low as 1.62 V) was the result of simultaneous two-electron impact ionization that resulted again in the population of high energy states [10].…”

“…Their paper, "Light Emission Produced by Current Injected into a Green Silicon-Carbide Crystal," included a report of light emission where applied voltage across the contacts was 1.8 V but the energy of the light quanta was 2 eV [6]. Over the subsequent decades, lowbias operation was observed in various material systems ranging from GaAs [7,8], ZnS [9], and even early GaN [10]. In each of these early experiments, a unique mechanism was postulated to explain the emission of photons when qV < hv.…”

Direct current electroluminescence in ZnS

“…All crystals have tended to lack reproducibility owing to the high density of defects and poor control of stoichiometry. The effects of non-stoichiometry on the electroluminescent characteristics of ZnS crystals have been high-lighted recently by Biter et al (1969).…”