Elsevier

Journal of Alloys and Compounds

Volume 624, 5 March 2015, Pages 241-246
Journal of Alloys and Compounds

Effect of Mg doping on growth and photoluminescence of AlN hexagonal nanorods

https://doi.org/10.1016/j.jallcom.2014.11.095Get rights and content

Highlights

  • Pure and Mg-doped AlN hexagonal nanorods were synthesized successfully.

  • Mg incorporation promoted not only axial but also radial growth rate of AlN HNRs.

  • Mg doping has modulated the native point defects states which changed the relative intensity of peaks.

Abstract

Pure and Mg-doped AlN hexagonal nanorods (HNRs) were synthesized by a simple thermal chemical vapor deposition process without structure-directing templates or catalysts. Mg incorporation promoted not only axial but also radial growth rate of AlN HNRs compared to undoped sample. The corresponding optical properties of the products were investigated by room-temperature photoluminescence (PL) measurement. Quite broad ultraviolet emission bands centered at 280 nm and 330 nm for AlN HNRs and AlN:Mg HNRs, respectively, were observed. Multi-peak fitting analysis shows that various defects conduced to the broad emission bands of the two samples, and Mg doping has increased the proportion of VN which changed the relative intensity of peaks, instead of forming Mg impurity energy levels that directly affect luminescence.

Introduction

As an important member of the group III–V materials, AlN has been attracted considerable interest because of its excellent properties, including direct wide band-gap (6.2 eV), high thermal conductivity, well mechanical strength, high piezoelectric response, and negative electron affinity, which determine it will have great potential applications [1], [2]. Moreover, in recent years, low dimensional especially one dimensional (1D) AlN nanostructures have become alluring due to their shape-dependent and enhanced properties like well-defined anisotropic physical and chemical properties, high surface–volume ratio, thus they have higher efficiencies on light emission and absorption than conventional bulk materials in optoelectronic devices [2], [3]. Regarding on this application, great progress have been made in modulation of growth or optoelectronic property of 1D AlN nanostructures such as nanowires, nanofibers, nanocones and nanorods [2], [4], [5], [6], [7], which will have the expectant integration of the remarkable low dimensional property and intrinsic merits of AlN. Additionally, doping is considered as an available method to modify the optical property of AlN materials. AlN has one of the largest band gap (6.2 eV) among all known semiconductors, and thus it not only provides a very short wavelength (200 nm) of band-edge emission but also allows for wide band operation from UV to infrared wavelengths by defects or dopants [8]. Therefore, low dimensional AlN nanostructures doped with different elements such as Mg, Si, Cr and rare-earth have been prepared [9], [10], [11], [12], [13], [14]. In terms of previous reported Mg-doped AlN nanostructures, most of them focused on the electronic or magnetic properties [9], [10], [11], however, there are relatively few studies on the optical properties, not mention to any detailed reports involving Mg doping affects the crystal growth and luminescence of AlN nanostructures.

In this paper, we investigated the effect of Mg doping on the growth and ultraviolet photoluminescence properties of well-aligned AlN HNRs prepared by simple thermal chemical vapor deposition. Mg doping could not only improve growth rate of AlN HNRs, but also modulate the defects states in AlN crystals. Moreover, native point defects states of AlN change with the Mg doping and bring about the broad ultraviolet emission band, instead of forming Mg impurity energy level that directly affect luminescence.

Section snippets

Experimental

Undoped and Mg-doped AlN NRs were grown by a simple thermal chemical vapor deposition method. The experiment setup for material synthesis has been described in previous studies [12], [15], [16]. The precursors of Al, N, and Mg were aluminum chloride (AlCl3, 1.0 g, 99.0%), ammonia (NH3; 20 SCCM that denotes standard cubic centimeter per minute; 99.995%), and anhydrous magnesium chloride (MgCl2, 0.03 g, CP, 99.0%), respectively. AlCl3 powder in a ceramic boat was placed upstream of quartz tube. MgCl

Results and discussion

The XRD patterns of the two as-synthesized products are shown in Fig. 1. All the peaks can be indexed to the hexagonal AlN phase with lattice parameters of a = 3.099 Å and c = 4.997 Å (JCPDS 792497). The highest intensity and the smallest full width half maximum (FWHM) of (0 0 2) peak of the two samples illustrate that the products grew preferentially along the c-axis direction. It seems that Mg doping has enhanced the preferred orientation. The diffraction peaks from the doped samples slightly shifted

Conclusions

In summary, we demonstrated the effect of Mg doping on growth and optical properties of AlN HNRs prepared by simple thermal chemical vapor deposition method on Si (1 0 0) substrates without structure-directing templates or catalysts. Mg doping promoted surface diffusion, which increased not only axial but also radial growth rate of AlN HNRs. A broad ultraviolet emission band emerged from whether undoped or Mg-doped sample. The center of emission band of Mg-doped AlN HNRs shifted to 330 nm compared

Acknowledgments

This work is supported by a fund from the National Natural Science Foundation of China (Grant Nos. 11004089 and 11204114), Innovation Funds of China Electronics Technology Group Corporation No. 46 Research Institute (Grant No. CJ20120204), and the Fundamental Research Funds for the Central Universities (No. lzujbky-2013-185)

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