Effect of deep‐level states on current–voltage characteristics and electroluminescence of blue and UV light‐emitting diodes

Abstract

Phone: 334 727 8994, Fax: 334 724 4806.Current-voltage (I-V) characteristics and electroluminescence spectra of several ultraviolet and blue light-emitting diodes (LEDs) emitting nominally at 380, 400, 430, and 468 nm were studied. These diodes exhibited an Ohmic regime at low forward biases; then the current increased sharply as bias increased. Several changes in the slope of logarithmic I-V plots indicated that, I / V x . These changes in the slope were interpreted as single-carrier space-charge-limited (SCL) transport across the diode active region. As bias increased the deep states were filled and for the 400-and 468-nm diodes ideality factors of $2 were obtained. This indicated that, as bias increased the transport mechanism changed from SCL conduction to recombination of injected carriers in the spacecharge region. For the 380-and 430-nm diodes, ideality factors >>2 were obtained, although the observed electroluminescence spectrum indicated substantial radiative recombination. For the diode emitting at 430 nm, several peaks including the major peak at $424 nm appeared to have resulted from transitions between the conduction-band edge and deep states, identified from the I-V characteristics, likely to be associated with Zn doping of the InGaN active region. Deep states in the other diodes appeared to be ineffective in the radiative recombination process.

Physics‐based modeling and experimental implications of trap‐assisted tunneling in InGaN/GaN light‐emitting diodes

“…a. While ideality factors from 1 to 2 are usually ascribed to diffusion/recombination processes in the space‐charge region (SCR) or in the neutral regions , tunneling processes are a widely accepted explanation of decreasing with T (see e.g. ).…”

“…Many rigorous studies are dealing with the origin and the experimental evidence of different slopes for each bias range of the characteristics and their corresponding high values of η , concluding that the main responsible features may be represented by the mass of the tunneling carriers involved in the TAT process or by the energy of the trap states . However, so far a complete investigation taking into account simultaneously both the experimental analysis and a tunneling modeling approach seems not well developed yet.…”

Enhancement and tuning of the defect-induced electroluminescence of ZnO mesoporous layers in the visible range

“…This observation is indicative of a space-chargelimited current (SCLC), a regime already observed in several transport studies on ZnO [27][28][29][30][31]. In some instances, the value of the exponents used to fit the different parts of the curve, as well as the voltage ranges at which each power law occurs can be used to extract quantitative information on the nature and the density of the defect states [32]. However, such an analysis can only be performed for continuous layers where quantities such as the permittivity, length, and intrinsic semiconducting parameters can be defined, which is impossible with our samples due to the discontinuous nature of the ZnO film above the Au patterns.…”

Modeling challenges for high-efficiency visible light-emitting diodes

“…Through its signature on the sub-threshold forward-bias characteristics, TAT may represent a useful indicator of the presence of defects and then, in turn, of device growth quality [20] or degradation due to accelerated stress testing [21]. But the importance of TAT does not seem to be limited to the sub-threshold regime; for example, reports attempting to peg the efficiency degradation to TAT have been presented by [22][23][24].…”

“…An electron (hole) in the conduction (valence) band tunneling from the n-(p-)side of the diode to the opposite side is captured by a defect. According to multiphonon emission (MPE) theory, the energy of the incoming carrier and the trap energy need not to match for the trapping process to take place (semiclassical theories neglect energy renormalizations of filled traps and assume monomodal phonon emission [22], i.e., a constant phonon dispersion relation). Finally, the capture process is followed by non-radiative recombination.…”