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We report the direct observation of hot carriers generated by Auger recombination via photoluminescence spectroscopy on tailored (AlGaIn)N multiple quantum well (QW) structures containing alternating green and ultra-violet (UV) emitting (GaIn)N QWs. Optically pumping solely the green QWs using a blue emitting high power laser diode, carrier densities similar to electrical light-emitting diode (LED) operation were achieved, circumventing possible leakage and injection effects. This way, luminescence from the UV QWs could be observed for excitation where the emission from the green QWs showed significant droop, giving direct evidence for Auger generated hot electrons and holes being injected into the UV QWs. An examination of the quantitative relation between the intensity of the UV luminescence and the amount of charge carriers lost due to drooping of the QWs supports the conclusion that Auger processes contribute significantly to the droop phenomenon in (AlGaIn)N based light-emitting diodes. Due to their high lifetimes and efficiencies along with rapidly declining prices, light-emitting diodes (LEDs) based on (AlGaIn)N multiple quantum well (MQW) structures are on their way to replace incandescent as well as fluorescent lighting. Despite great progress in recent years, resulting in peak power conversion efficiencies of up to 81%, 1 one obstacle still to overcome is the decrease in efficiency towards high operating current densities, a phenomenon commonly known as droop. 2,3 The current dependency of the internal quantum efficiency (IQE) can be modeled in good quantitative agreement with experimental data using an ABC rate equation model [4][5][6]

This paper reports an investigation of the physical origin of the thermal droop (the drop of the optical power at high temperatures) in InGaN-based light-emitting diodes. We critically investigate the role of various mechanisms including Shockley-Read-Hall recombination, thermionic escape from the quantum well, phonon-assisted tunneling, and thermionic trap-assisted tunneling; in addition, to explain the thermal droop, we propose a closed-form model which is able to accurately fit the experimental data by using values extracted from measurements and simulations and a limited set of fitting parameters. The model is based on a two-step phonon-assisted tunneling over an intermediate defective state, corrected in order to take into account the pure thermionic component at zero bias and the field-assisted term. V

This paper presents an extensive investigation of the deep levels related to non-radiative recombination in InGaN/GaN light-emitting diodes (LEDs). The study is based on combined optical and deep-level transient spectroscopy measurements, carried out on LEDs with identical structure and with different values of the non-radiative recombination coefficient. Experimental data lead to the following, relevant, results: (i) LEDs with a high non-radiative recombination coefficient have a higher concentration of a trap (labeled as “e2”) with an activation energy of 0.7 eV, which is supposed to be located close to/within the active region; (ii) measurements carried out with varying filling pulse duration suggest that this deep level behaves as a point-defect/dislocation complex. The Arrhenius plot of this deep level is critically compared with the previous literature reports, to identify its physical origin

Capacitance–voltage measurements have been performed on deuterated boron-doped synthetic-type IIb diamond. They demonstrate the electrical passivation of the boron acceptors, which was manifested by a persistent decrease in capacitance after deuteration. The capacitance–voltage dependence is explained by means of a two-layer depletion width model.

We report on a systematic study of the determination of the internal quantum efficiency (IQE) in AlGaN-based multiple-quantum-well (MQW) structures using different optical evaluation methodologies and experimental conditions, in order to derive a standard set of measurement conditions for reliable IQE determination. Several potential sources of error that may distort the IQE obtained by optical measurements are discussed, such as carrier transport effects, excitation conditions failing to fulfill ideal resonance conditions, and morphology issues. A series of nominally identical AlGaN-based MQW structures is grown on an AlGaN layer separated by an AlN interlayer of varying thickness. The MQW structures are studied both by resonant and quasiresonant photoluminescence spectroscopy, and IQEs are determined via different commonly employed methods. The obtained values are shown to be significantly affected by the employed excitation conditions, as well as the evaluation techniques. In addition, growth morphology issues and carrier transport effects need to be considered in the interpretation of the measured data, with the latter being investigated in greater detail. The results emphasize the need for an appropriate choice of both experimental conditions and evaluation methodology in order to extract reliable and comparable IQE values.

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We have studied the electrical and optical characteristics of (AlGaIn)N multiple quantum well light-emitting diodes. Minimizing contact effects by utilizing platinum as p-contact metal, ideality factors as low as 1.1 have been achieved. In agreement with basic semiconductor theory, a correlation between ideality factor and small-current efficiency was found. We were able to emulate the experimental current-voltage characteristic over seven orders of magnitude utilizing a two diode model. This model enables a very good prediction of internal quantum efficiency at moderate current densities out of purely electrically derived parameters.