Growth of InGaN Nanorods as the Blue Light Source for White Light Emitting Devices
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Growth of InGaN Nanorods as the Blue Light Source for White Light Emitting Devices Hwa-Mok Kim1,*, Tae Won Kang1 and Kwan Soo Chung2 1 Quantum-functional Semiconductor Research Center, Dongguk University, Seoul 100-715, Korea 2
School of Electronics and Information, College of Electronics and Information Kyunghee University Yongin 449-701, Korea ABSTRACT
This work demonstrates the properties of InGaN nanorod arrays with various In mole fractions by modified HVPE using In metal at the low growth temperature. The nanorods grown on (0001) sapphire substrates are preferentially oriented in the c-axis direction. We found that the In mole fractions in the nanorods were linearly increased at x ≤ 0.1. However, In mole fractions were slightly increased at x > 0.1 and then were gradually saturated at x = 0.2. CL spectra show strong blue emissions from 428 nm (x = 0.1, 2.89 eV) to 470 nm (x = 0.2, 2.64 eV) at room temperature. From this result, we found the fact that increasing In mole fraction in the InGaN nanorod shift the peak position of CL spectrum emitted from InGaN nanorod to the low energy region.
INTRODUCTION Recent results have challenged the long-standing band gap value for indium nitride (InN) (∼2 eV) and asserted 0.9 eV as the true band gap for high quality InN films.[1] This alone makes indium gallium nitride (InGaN) a promising material for blue/violet emission (and even a
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candidate for deep ultraviolet (UV) and infrared (IR) emission). If InGaN’s indium (In) mole fraction can be successfully turned from 0 to 1, InGaN represents a ternary alloy capable of emitting photons from 0.9 eV to 3.4 eV – that is, from GaN’s UV emission (∼365 nm) to InN’s emission (∼1380 nm). The most common method to achieve white light emission is to combine a phosphor wavelength down-converter with a blue InGaN/GaN light emitting diode (LED). A blue LED is typically placed in a parabolic mirror and subsequently coated with a phosphorcontaining epoxy.[2] The LED emits blue light which is absorbed by the phosphor and re-emitted as longer-wavelength phosphorescence. This occurs via a process known as down-conversion. These two wavelength (generally blue and yellow) combine form white right.[3] Unfortunately, many threading dislocations (TDs) are produced in InGaN/GaN layer, used for blue light source, due to lattice mismatch with the substrate and difference of thermal expansion coefficient with substrate, and thus they affect significantly the device performance as non-radiative recombination centers.[4] On the other hand, the growth mechanism for nanorods is completely different, and threading dislocations can be all but non-existent in nanorods. Therefore, the nanorods have the potential for negligible non-radiative recombination loss, and thus the efficiency of down-conversion is much higher than bulk InGaN/GaN. However, no one has successfully grown InGaN and InGaN/GaN nanorods to data. Here, we demonstrate the optical properties of InGaN nanorod arrays on (0001) sapphire substrate by modified hydride vapor p
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