Structural and Morphological Characteristics of Inxga1-xN Films Grown on SI (111) by Reactive Magnetron Sputtering

Under various power ratios and temperatures, InxGa1-xN films with different indium composition x were grown on Si(111) substrates by reactive magnetron sputtering, and then annealed at ammonia atmosphere around 700 for 2 hours. The indium composition x can be adjusted by the growth temperature over the range of 600~800 . There is no InN phase and In droplet formation in the InXGa1-XN films due to the low-temperature advantages of reactive magnetron sputtering. The rich In composition in InXGa1-XN films is caused by the higher sputtering yield of In2O3 target than Ga2O3 target. Raman scattering analysis revealed that the InXGa1-XN films obtained at different temperatures were wurtzite structure, and the compositional inhomogeneity is caused by the relaxation of momentum conservation and increase of lattice disorder.


Introduction
Recently, the III-nitride semiconductor materials has attracted significant attention on account of its outstanding performance applied in ultraviolet light-emitting diodes and laser diodes, etc. In X Ga 1-X N has been widely studied owning to its efficient photovoltaic applications. While adjusting the In composition ratio, the band gap energy of In X Ga 1-X N is tunable from 0.7eV to 3.4eV, which covers full solar spectrum [1]. However, it is a technical bottleneck to grow In X Ga 1-X N thin film with well crystallization quality due to the obvious lattice mismatch between InN and GaN [2]. Traditional techniques to prepare In X Ga 1-X N film including MOCVD, MBE and MOVPE, which need very high cost. In our work, In X Ga 1-X N films are grown by reactive sputtering technique.

Experimental
In the present work, the films were prepared by a reactive radio-frequency magnetron sputtering system (MSP-3200C2). Ga 2 O 3 was chosen as gallium source, and In 2 O 3 as indium source. After the pretreatment of substrates, the first set of In X Ga 1-X N was performed at growth temperature of 600 , and the sputtering power ratios of In 2 O 3 and  There is no InN phase and In droplet formation at the In X Ga 1-X N films, which manifested that the films has single crystal phase.  Fig.2 shows the SEM and EDS analysis of In X Ga 1-X N films at different power ratios.

Results and discussion
In Fig.2(a), there are a few crystal grains at the surface, less than in Fig.2(b). Since the energy supplied by RF-power(1:2) was less than the sputter power ratio of 1:1, fewer atoms were sputtered from targets and the reaction of atoms at substrate surface decreased greatly.
The In/(Ga+In) ratios were 0.07 and 0.75 under the sputtering power ratios of 1:2 and 1:1 respectively, which demonstrates that the sputtering yield of In is much higher than Ga and is the same as Cheng-Che Li et al [3]. In words, it denotes that the RF-power ratio of 1:1 is suitable for obtaining In-rich alloy films. The corresponding XRD spectra of the second set of films is given in Fig.3. It is clearly observed that the 2Ʌ angular position shifts towards higher values while the temperature increases, meanwhile In composition x decreases, which is the same as [4] and [5]. It was caused by the process of In adsorption and desorption in deposition, the suppression of In desorption reserves more In atoms in films at lower temperature. When the temperature increases, In-N bond begins to split and In atoms will divorce from the film surface because the evaporated temperature of In is around 700 or more.  The SEM morphology of In X Ga 1-X N samples with different temperature were shown in  Fig. 5 shows Raman spectra with different In composition at different temperatures. The spectra was recorded in the backscattering geometry configuration with a He-Ne laser at 633nm. InN and GaN are both ‫ܥ‬ ௩ ସ point group symmetry structure (belong to wurtzite structure) [6], which is represented by A 1 (LO) and E 2 (high) modes. The silicon substrate peak at 520cm -1 is so strong that makes the E 2 (high) weakened. The A 1 (LO) mode of three samples in different temperatures are observed in the region 584~612cm -1 which refers that the A 1 (LO) mode of InN located in 570cm -1 and 733.07cm -1 for GaN [7]. The peak positions move towards lower wavenumbers while the In compositions x increases, the main reason for this shift is structural defects in films. The A 1 (LO) mode of In X Ga 1-X N films with different In compositions manifested that the alloy films are wurtzite structure [8]. The rough curve of the main board band in the region 584~612cm -1 can attribute to the relaxation in momentum conservation and increasing lattice disorder due to the compositional inhomogeneity [9].

Conclusion
In this work, we have grown In X Ga 1-X N of different indium composition x at variation of power ratios and temperatures by reactive magnetron sputtering. It was demonstrated that the indium composition x was not linear with power ratios, which was caused by the high sputtering yield of the In 2 O 3 target. The monotonic decrease in x is caused by the more In evaporation with increasing temperatures. Raman scattering analysis revealed that the reasons for the shift of A 1 (LO) phonon in the region 584~612cm -1 are In composition variation. The results of the experiment also implied that pure In X Ga 1-X N alloy film in reactive magnetron sputtering may apply in development optoelectronic devices.