فایل ورد کامل دیودهای ساطع کننده نور با چند چاه-کوانتوم با یک ترکیب InN درجه بندی برای حذف نوترکیبی Auger

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بخشی از مقاله انگلیسیعنوان انگلیسی:InGaN/GaN multiple-quantum-well light-emitting diodes with a grading InN composition suppressing the Auger recombination~~en~~

In conventional InGaN/GaN light-emitting diodes (LEDs), thin InGaN quantum wells are usually adopted to mitigate the quantum confined Stark effect (QCSE), caused due to strong polarization induced electric field, through spatially confining electrons and holes in small recombination volumes. However, this inevitably increases the carrier density in quantum wells, which in turn aggravates the Auger recombination, since the Auger recombination scales with the third power of the carrier density. As a result, the efficiency droop of the Auger recombination severely limits the LED performance. Here, we proposed and showed wide InGaN quantum wells with the InN composition linearly grading along the growth orientation in LED structures suppressing the Auger recombination and the QCSE simultaneously. Theoretically, the physical mechanisms behind the Auger recombination suppression are also revealed. The proposed LED structure has experimentally demonstrated significant improvement in optical output power and efficiency droop, proving to be an effective solution to this important problem of Auger recombination.

Both electrically and optically, InGaN/GaN light-emitting diodes (LEDs) have promised higher efficiency and reliability as the blue light sources for white light generation. Hence, they are regarded as excellent candidates for artificial lighting to replace the incumbent conventional fluorescent and incandescent lighting sources. For that a significant progress has been made for InGaN/GaN LEDs in the past several decades.1 However, the LED efficiency has been so far still limited and especially high levels of efficiency droop have commonly been observed at high current density, caused by several factors including electron overflow,2,3 Shockley-Read-Hall (SRH) recombination,4,5 and Auger recombination.6 Among them, the Auger recombination is more severe under a high injection current level, since the Auger recombination scales with the third power of the carrier density (n3 with n denoted as the density of the captured carriers in quantum wells). Therefore, it is very important to suppress the Auger recombination to improve the LED performance. To address the Auger-related issues and enhance the LED performance, one can consider increasing the quantum well thickness and homogenizing the carrier distribution within the quantum wells to reduce the carrier density. Nevertheless, InGaN/GaN LEDs grown along the [0001] orientation suffer from the strong polarization induced electric field in the quantum wells.7 Consequently, a tilted energy band alignment is produced, which in turn causes electron and hole separation and carrier accumulation at the opposite interfaces of the polarization mismatched quantum well and quantum barrier heterojunction. A more homogeneous carrier distribution can be realized by the LED structures based on nonpolar and semipolar growth planes.8,9 Moreover, even in the case of the [0001] orientation, the polarization matched condition can be realized by embedding InGaN quantum wells between the properly alloyed quaternary AlGaInN quantum barriers.10 However, the cost of the nonpolar/semipolar substrates and the limited freedom of epitaxial growth for the quaternary AlGaInN compounds hinder the wide adoption of these solutions. On the other hand, due to the mobility and doping asymmetry for electrons and holes, the electron density is normally higher than the hole density in the quantum wells, and hence the Auger recombination can be effectively reduced if the electrons are evenly distributed in the quantum wells under high current injection level.

In this work, we proposed and demonstrated a LED architecture grown along the [0001] orientation with wide quantum well thickness of grading InN composition in the InGaN/GaN quantum wells. We achieved an enhanced level of optical power and a reduced efficiency droop both in numerical simulations and experimental measurements, which is well attributed to the Auger recombination rate suppression by the proposed structure. The computations show a more flattened conduction band and a more even electron distribution profile in the quantum wells for the proposed LED. The Auger recombination is found to be less supported in the proposed LED structure according to our calculations.

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