InGaN nanorods grown on (1 1 1) silicon substrate by hydride vapor phase epitaxy
Introduction
The group-III nitride systems composed of InN and GaN span the range of band gaps from 0.9 to 3.4 eV [1], [2], [3]. Therefore, the ternary InGaN alloys are capable of emitting photons from 0.9 eV (∼1380 nm infrared) to 3.4 eV (∼365 nm ultra violet) by varying indium mole fraction in InGaN from 0 to 1. The most common method to achieve white light emission is to combine a phosphor wavelength down-converter with a blue InGaN/GaN LED. A blue LED is typically placed in a parabolic mirror and subsequently coated with a phosphor-containing epoxy [4]. 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 wavelengths (generally blue and yellow) combine to form white light [5], [6]. Unfortunately, many threading dislocations (TDs) are produced in bulk GaN and InGaN due to lattice mismatch with the substrate and difference of thermal expansion coefficient between film and substrate, and thus they affect significantly the device performance as non-radiative recombination centers [7]. 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 in bulk InGaN/GaN layer. In spite of this great advantage, no one has successfully grown InGaN nanorods to date. However, we have already grown the single-crystalline and defect-free GaN nanorod arrays by hydride vapor phase epitaxy (HVPE) previously [8], [9].
Here, we report on the growth of the defect-free (dislocation-free) InGaN nanorods as a blue source for white light devices by our hydride vapor phase epitaxy (HVPE) system. Morphological and structural characterization of the InGaN nanorods by high-resolution scanning electron microscopy (HRSEM) and transmission electron microscopy (TEM) indicates that the nanorods are straight and preferentially oriented in the c-axis direction. Cathodoluminescence (CL) characteristic of the single InGaN nanorod shows a strong blue emission peaking at around 428 nm at room temperature.
Section snippets
Experimental
The InGaN nanorods were grown by a horizontal HVPE system similar to our previous works [8], [9]. (1 1 1) silicon wafer was used as a substrate. Substrate was cleaned by an HCl solution and rinsed with deionized water before use. The Ga and In precursor were synthesized via a reaction of HCl gas (5N) (in an N2 diluent gas) with Ga (7N) and In (6N) metal (at 750 °C). These precursors are then transported to the substrate area where it is mixed with NH3 (6N4) to form InGaN nanorods (at 510 °C). In
Result and discussion
Fig. 1 shows the InGaN nanorods grown on (1 1 1) silicon substrate by using our HVPE system. The growth temperature of these nanorods was 510 °C. The average diameter and length of nanorods were 50 nm and 10 μm, respectively. Control of the InGaN nanorod’s diameter and length were achieved by adjusting the growth temperature and growth time, respectively.
Fig. 2 shows TEM images of an InGaN nanorod grown by HVPE method. In this image, the [0 0 1] direction was parallel to the long axis of rods,
Conclusion
This work demonstrates the controllable growth of the straight and well-aligned InGaN nanorods at the low temperature. The method is catalyst- and template-independent similar to our previous works. The nanorods grown on (1 1 1) silicon substrates are preferentially oriented in the c-axis direction. We found that the In content in the nanorod was 10 at.% by EDS analysis. CL spectrum shows a strong blue emission peaking at around 428 nm at room temperature. We believe the presented approach is a
Acknowledgments
This work was supported by KOSEF through the QSRC at Dongguk University in 2003.
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Oxygen photo-adsorption related quenching of photoluminescence in group-III nitride nanocolumns
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