InGaN thin film deposition on Si(100) and glass substrates by termionic vacuum arc

Group-III nitride semiconductors covering infrared, visible and ultraviolet spectral range has direct band gaps changing from 0,7 eV (InN) to 3,4 eV (GaN). LEDs emit red, blue, green light, ultraviolet (UV) laser diodes (LD), UV light detectors and high power electronic devices are obtained and commercialized based on group-III nitride materials. InGaN semiconductor can be deposited by different techniques such as molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD). In this study, InGaN thin films were prepared on Si and glass substrates as well as on GaN layer by termionic vacuum arc (TVA) which is a plasma asisted thin film deposition technique. The film was deposited at 10-6 torr working pressure, 18A filament current. Plasma was produced at 200 V with 0,6A plasma current. The purpose of this research is to investigate the properties of InGaN thin films. X-ray diffraction (XRD) spectrophotometer was used to analyze microstructure of the deposited films. Scanning electon microscopy (SEM) were used for surface morphology characterizations. Compositional analysis was done by energy dispersive X-ray spectroscopy (EDAX).


Introduction
Semiconductors underlies the today's technology due to their tunable energy band gaps [1]. Elemental semiconductors are formed by same type af atoms, such as; silicon and germanium. Silicon technology has used in the construction of electronic circuits as the substrate for 20 years [2]. These conventional semiconductors are not suitable for fabrication of devices working on short wavelength optoelectronics. Devices based on these classical semiconductors are not tolerant on high temperatures.
III-V group semiconductors, including GaN(Gallium nitride), InN(Indium nitrite), and AlN (Aluminum nitride) are quite attracted attention and were examined separately. Group-III nitride semiconductors cover spectral range of infrared, visible and ultraviolet and they have direct band gap, ranging from 0.7eV (InN) to 6.2eV (AlN) [3]. Figure 1. shows the band gap versus lattice parameter of the group-III nitrides [4]. III-Nitrides have been used for a wide range of applications. Ligth emitting devices (LED), laser diodes, photovoltaics and high power electronic devices have been achieved based on III-Nitrides material systems [5,6]. There are two types of crystal structures of group III-Nitrides: cubic zincblende and hexagonal wurtzite. Both can coexist under various parameters for crsytal growth. Wurtzite structure is thermodinamically stable. InGaN material formed by GaN and InN has also wurtzite structure [7]. Lattice parameters of InGaN compund are given by the linear relationship between the lattice constant of the two compounds (GaN and InN). In this study, InGaN thin films were prepared and deposited on Si and glass substrates as well as on GaN layer. The purpose of this research is to investigate the properties of InGaN thin films. X-ray diffraction (XRD) spectrophotometer was used to analyze microstructure of the deposited films. Scanning electon microscopy (SEM) were used for surface morphology characterizations. Compositional analysis was done by energy dispersive X-ray spectroscopy (EDAX).

Figure 2.
Schematic view of the TVA system [16] International  Figure 2. represents a schematic view of the deposition technique. The film was deposited at 10 -6 torr working pressure; hence there is no need to buffer gas for deposition at this high vacuum level. Plasma is established between the anode and cathode. The filament current is applied as 18 A to heat the cathode and the voltage is applied to move the electrons from the cathode the anode in order to melt the anode material. In this voltage value, the plasma current is established and is about 0.6 A. Then, melting material will be evaporated in the vacuum chamber. The ions in the chamber are combined with each other. Therefore, detected layers on substrate will be occurred [17].   Figure. 3 (c), GaN peak was observed at 32.75 degree, while InGaN peak was observed at 36.12 degree. In addition, the glass has a peak, eich are between the 20-25 degress. The GaN and InGaN peaks deposited on glass substrate are shifted to right on the XRD spectra, compared to that of the GaN and InGaN peaks deposited on silicon substrate. The observed diffraction peaks are sharp, indicating good crystalline quality.

Surface Morphological Analysis
It is very impartant to investigate surface morphology of the films. For studying surface morphology, scanning electron microscopy (SEM, JEOL-JSM5600) was used. SEM images are shown in Figure 4. It is observed that the films are crystalline with uniform dimension of crystals. Figure 4.  Energy dispersive X-ray spectroscopy (EDX) is a chemical microanalysis technique. Table-1 shows the weight and atomic ratio of elements which found in the films and substrates for deposited GaN and InGaN films on glass.  . indicates the EDX spectrum ogf the InGaN thin film on silicon substrate. As can be seen from Figure 6, presence of the Si, Ga. N and In atoms were detected by the EDX analysis.

Conclusion
InGaN thin films were succesfully deposited on silicon substrate and also deposited on glass substrate with GaN film using TVA technique. The main advantage of this deposition technique is its high deposition rate without any loss in the quality of the thin film. The material properties of the produced thin film were investigated. XRD peaks have been observed that the films have sharp diffraction peaks and good crystalline quality. SEM analysis of the produced films show that the thin films have grunalar structure and they are dense, homogenous and continue without any cracks and holes. EDX analysis are also investigated. From the EDX spectrum, presence of the atoms in the film is confirmed.
The results show that TVA is suitable for deposition of thin films on silicon and glass substrates.