Structural and optical properties of InN films prepared by radio frequency magnetron sputtering
Introduction
Among III-nitride semiconductor materials, indium nitride (InN) is an attractive material for long-wavelength optoelectronic and high-speed electronic devices, because of a narrowest direct band-gap energy [1] and superior carrier-transport characteristics in a wide range of temperature [2]. However, the growth of InN has been less studied as compared with those of other III-nitride semiconductor materials such as gallium nitride (GaN) and aluminum nitride (AlN), because of the low thermal stability of InN [3].
Recently, high quality single-crystalline InN films with band-gap energies less than 1.0 eV have been grown by a metalorganic vapor phase epitaxy [4] and a molecular beam epitaxy (MBE) [5], [6], [7]. The band-gap energy is very smaller than the earlier reported value of 1.89 eV for the InN film deposited by a radio frequency (RF) sputtering [8]. The reason for this large band-gap energy has been considered to be due to oxygen incorporation in the InN film [5] or the poly-crystalline InN film [4]. On the other hand, it has been reported by Butcher et al. [9] that the excess nitrogen in the InN film correlated with the increase in band-gap energy. However, these results have not been completely understood. Thus, several parameters of InN including the band-gap energy have not still been well established. Therefore, additional researches on the relationship between the crystalline structure and the band-gap energy of InN will be especially needed.
In this paper, we describe the structural and the optical properties of InN films prepared by a RF magnetron sputtering in N2/Ar mixed gases and at elevated substrate temperatures.
Section snippets
Experimental details
The InN films were deposited in a plasma chamber made of stainless steel cylinder using an indium (5-N grade) target electrode. Prior to the film deposition, the plasma chamber was evacuated to less than 1.33 × 10− 6 Pa by a turbomolecular pump, and the surface contamination layer of the indium target was sufficiently removed by pre-sputtering. Pure N2 (6-N grade) gas mixed with Ar (6-N grade) gas was used as a source gas, which was purified by a liquid N2 trap. Gas flow rates of both N2 and Ar
Results and discussion
The XRD patterns of the InN films deposited on glass substrate at room temperature for various Ar composition ratios in N2/Ar mixed gas, are shown in Fig. 1. At Ar composition ratios of 0% and 3%, only two diffraction peaks at near 31.1° and 64.8° were observed. The intense peak at near 31.1° is associated with wurtzite-type (0002)InN [(0002)α-InN] or zincblend-type (111)InN [(111)β-InN] planes, and the peak at near 64.8° is associated with (0004)α-InN or (222)β-InN planes. These diffraction
Conclusions
The InN films were deposited by a RF magnetron sputtering in N2/Ar mixed gases. All of InN films deposited were hexagonal crystalline InN, and the c-axis lattice constant was decreased with the increase in Ar composition ratio in N2/Ar mixed gas at room temperature, or with the increase in substrate temperature for pure N2 gas. Such decrease in the c-axis lattice constant was related to the decrease in the relative nitrogen concentration in the InN film. The InN films having nitrogen-rich
Acknowledgements
This work was partially supported by the Research Institute for Science and Technology, Tokyo Denki University. The authors would like to thank former students of Mr. H. Fujita, Mr. M. Yoshino, Mr. S. Ohsawa and Mr. M. Shibata for their cooperation during the work.
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