Description:Field of Invention
The present invention relates to tunable electronic properties of n-type Zinc-Oxide (ZnO) thin film. More particularly, the present invention relates to RF sputtering deposition method to be employed for the formation n-type Zinc-Oxide (ZnO) thin film which shows tunable opto-electronic properties.

The objectives of this invention
The objective of this invention is to basically engineer its electron mobility and carrier concentration of n-type Zinc-Oxide (ZnO) thin film by means of its compositional variation such as variation of Oxygen (O) composition for its wide range of applications in optoelectronics devices.

Background of the invention
The compositional variation of n-type Zinc-Oxide (ZnO) thin film by using RF (radio frequency) sputtering deposition method results into some change in its optoelectronic properties. Metal oxides have been extensively investigated during last decades due to their special catalytic, anti-bacterial, as well as optical and electrical properties. Because of its outstanding properties, such as high chemical stability, high electrochemical coupling constant, broad range of radiation absorption and high photo stability, Zinc oxide (ZnO), is a metal oxide semiconductor, is a multifunctional material [1], [2]. Its applications range from tyres to ceramics, from pharmaceuticals to agriculture, and from paints to chemicals.
Previous research has primarily focused on the growth of n-type Zinc-Oxide (ZnO) by some other complex methods such as chemical vapor deposition (CVD) and atomic layer deposition (ALD) methods, however, some of these process such as chemical vapor deposition (CVD) require huge infrastructure to deal with toxic gases whereas atomic layer deposition (ALD) methods has low rate of deposition whereas spray pyrolysis processes lacks precise control of variation of its constituents. So, there is need of some ease of deposition method to alter the composition of n-type Zinc-Oxide (ZnO) to tune its optoelectronic properties. Therefore, RF sputtering deposition method have been proposed in order to alter the composition of n-type Zinc-Oxide (ZnO) with a high degree of precision and control along with ease of fabrication as compared to other methods such as chemical vapor deposition (CVD) and atomic layer deposition (ALD) methods.

Earlier research work has predominantly focused on only oxygen mole fraction variation of Zinc-Oxide (ZnO) by some other complex methods such as chemical vapor deposition (CVD) (US4751149A), electron-beam evaporation (US3294660A) and spray pyrolysis (US8182573B2). However, these processes lack precision in regulating the oxygen mole fraction variation of Zinc-Oxide (ZnO). Therefore, some difficulties are encountered in obtaining the desired optoelectronic properties of Tin-Oxide. External doping of Zinc-Oxide (ZnO) thin films by atomic layer deposition (ALD) (US7160819B2) and molecular beam epitaxy (MBE) (US10297721B2) processes have been attempted in order tune its optoelectronic properties. But, these processes are highly expensive. Analyzing the background of the above inventions, a simple and economical method to alter the composition of Zinc-Oxide (ZnO) film with a high degree of precision and ease of deposition is not much explored. Hence, deposition of Zinc-Oxide (ZnO) film have been attempted with RF sputtering method.

Summary of Invention
This patent discuss about the utility of RF sputtering deposition method the alter the composition of n-type Zinc-Oxide (ZnO) with ease of fabrication. The electrical properties such as as mobility and carrier concentration of n-type Zinc-Oxide (ZnO) changes with variation in its oxygen mole fractions. A simple as well as economical method having ease of fabrication for n-type Zinc-Oxide (ZnO) thin film have been proposed and variation in its The electrical properties such as mobility and carrier concentration of n-type Zinc-Oxide (ZnO) have been discussed in order to find its usage in wide range of optoelectronic devices.
Detailed description of the invention
The n-type Zinc-Oxide (ZnO)thin films have been deposited on quartz glass substrate using a customized RF Sputtering method as shown by schematic diagram in figure 1. Quartz glass substrates are cleaned ultrasonically with acetone and isopropanol first. Subsequently substrates are dipped into the de-ionized water and finally dried with nitrogen gun.Cleaned substrate is placed into the substrate holder inside the RF sputtering chamber and vacuum level of 1×10-6 mbar is achieved by two steps, using roughing and high vacuum pumps (Turbo Molecular Pump) sequentially. The high vacuum pump is allowed to operate for sometime to ensure the base pressure in the order of 1×10-6 mbar inside the e-beam chamber. After evacuating the chamber to a base pressure of 10-6 mbar, oxygen gas (99.999% purity) is purged into the chamber through MFC (Mass Flow Controller) to maintain the flow rate of 2 sccm (standard cubic centimetres per minute). Now, RF sputtering power is turned on and 60 Watt power is applied, which sputtered Zinc (Zn) metal target (99.99%, purity) placed in target holder of RF sputtering chamber. The sputtered Zinc (Zn) metal reacts with the oxygen gas in the vicinity of quartz glass substrate initially to form Zinc-Oxide (ZnO) film. The growth rate of deposition Zinc (Zn) metal was maintained at 1 Angstrom/second and the flow rate of Oxygen was maintained at 2sccm for 2000 seconds. Similarly, the whole process is repeated for different flow rate of oxygen, that is, 4 sccm, 6 sccm, 8sccm and 10 sccm, keeping the RF power constant at 60 Watt. Different types of Zinc-Oxide (ZnO) films which have been gown by RF sputtering method have been named here as Type-I, Type-II, Type-III, Type-IV and Type-V, respectively. Type-I corresponds to Zinc-Oxide (ZnO) film grown by RF spuuering method under flow rate of 2 sccm of oxygen, Type-I corresponds to Zinc-Oxide (ZnO) film grown by RF spuuering method under flow rate of 2 sccm of oxygen, Type-I corresponds to Zinc-Oxide (ZnO) film grown by RF spuuering method under flow rate of 2 sccm of oxygen, Type-I corresponds to Zinc-Oxide (ZnO) film grown by RF spuuering method under flow rate of 2 sccm of oxygen, and Type-V Type-I corresponds to Zinc-Oxide (ZnO) film grown by RF spuuering method under flow rate of 2 sccm of oxygen. It is important to note here that all growth processes related to the formation Zinc-Oxide (ZnO) film grown by RF spuuering method have been carried out room temperature.
The Hall measurement of all five types of Zinc Oxide(ZnO) have been performed to find out carrier concentration, Hall mobility and sheet resistivity of samples.
The Hall measurement of all five types of Zinc-Oxide (ZnO) film grown by RF sputtering method have been performed in order to find out nature of sample, its carrier concentration, Hall mobility and sheet resistivity using equations given below. The equation 2 represents the formula for calculation Hall coefficient, equation 3 represents the formula for calculation of carrier concentration and equation 4represents the formula for calculation of Hall mobility of Aluminum (Al) doped Tin-Oxide (Al:SnO).
Hall coefficient of Aluminum (Al) doped Tin-Oxide (Al:SnO) sample,
(1)
Electron carrier concentration of Zinc-Oxide (ZnO) film grown by RF spuuering method,
(2)
Hall mobility (µe) of Zinc-Oxide (ZnO) film grown by RF spuuering method,
(3)
Where RH is Hall coefficient of Zinc-Oxide (ZnO) film grown by RF spuuering method, p is electron carrier concentration of Zinc-Oxide (ZnO) film grown by RF spuuering method,? is resistivity of Aluminum (Al) doped Tin-Oxide (Al:SnO) sample and q is electronic charge( Coulombs) and d is the thickness of Zinc-Oxide (ZnO) film coating on quartz glass substrate. I is the current and B is the applied magnetic field.
The resistivity of Zinc-Oxide (ZnO) film grown by RF sputtering method is given by equation 5.
(4)
Where d is the thickness of Zinc-Oxide (ZnO) film coating on quartz glass substrate. RS is sheet resistance of Zinc-Oxide (ZnO) film on quartz glass substrate.
It is important to note that all four types of Zinc-Oxide (ZnO) film grown by RF spuuering method obtained from Hall measurement shows n-type nature.
The electron carrier concentration of all five sample of Zinc-Oxide (ZnO) film grown by RF sputtering method (Type-I, Type-II, Type-III, Type-IV and Type-V) were obtained to be 1.9 x 1019cm-3,2.4 x 1018 cm-3, 6.3 x 1017 cm-3 and 1.2 x 1017 cm-3, 4.4 x 1016 cm-3 respectively. In terms of electron carrier concentration, Type-I Zinc-Oxide (ZnO) film sample has relatively highest electron carrier concentration and Type-V Zinc-Oxide (ZnO) film has relatively lowest electron carrier concentration.
The Hall mobility of all five sample of Zinc-Oxide (ZnO) film grown by RF sputtering method were obtained to be 45 cm2/Vs, 70 cm2/Vs, 90 cm2/Vs, 110 cm2/Vs and 120 cm2/Vs , respectively. In terms of Hall mobility, Type-V Zinc-Oxide (ZnO) film sample has relatively highest Hall mobility and Type-I Zinc-Oxide (ZnO) film has lowest Hall mobility.
The sheet resistivity of all five sample of Zinc-Oxide (ZnO) film grown by RF sputtering method were obtained to be were obtained to be 9.0 ×10-3 O-cm, 2.0×10-3 O-cm, 3.0 ×10-3 O-cm and 8.0×10-2 O-cm and 1.0×10-1 O-cm , respectively, using four point probe method of Hall measurement. In terms of resistivity, Type-V Zinc-Oxide (ZnO) film sample has relatively highest resistivity and Type-II Zinc-Oxide (ZnO) film has relatively lowest resistivity.
Brief description of Drawing
Figure 1 Schematic diagram of RF sputtering process for formation of different types of Zinc-Oxide (ZnO) films.
Figure 2 Graph showing the variation of electron concentration of all five types different types of Zinc-Oxide (ZnO) films.
Figure 3 Graph showing the variation of Hall mobility of all five types different types of Zinc-Oxide (ZnO) films.
Figure 4 Graph showing the variation of sheet resistivity of all five types different types of Zinc-Oxide (ZnO) films.
Detailed description of the drawing
Figure 1 shows Schematic diagram of RF sputtering process for formation of different types of Zinc-Oxide (ZnO) films.The n-type Zinc-Oxide (ZnO) thin films have been deposited on quartz glass substrate using a customized RF Sputtering method. Cleaned glass substrate is placed into the substrate holder inside the RF sputtering chamber and vacuum level of 1×10-6 mbar is achieved by two steps, using roughing and high vacuum pumps (Turbo Molecular Pump) sequentially. The high vacuum pump is allowed to operate for some time to ensure the base pressure in the order of 1×10-6 mbar inside the RF sputtering chamber. After evacuating the chamber to a base pressure of 10-6 mbar, argon and oxygen gas (99.999% purity) is purged into the chamber through MFC (Mass Flow Controller) to maintain the flow rate of 2 sccm, 4 sccm, 6 sccm,8 sccm and 10 sccm (standard cubic centimeters per minute). Now, RF sputtering power is turned on and 60 Watt power is applied, which sputtered Zinc (Zn) metal target (99.99%, purity) placed in target holder of RF sputtering chamber. The sputtered Zinc (Zn) metal reacts with the oxygen gas in the vicinity of quartz glass substrate initially to form different types Zinc-Oxide (ZnO) film, which are named here as Type-I, Type-II, Type-III, Type-IV and Type-V.
Figure 2 shows the variation of electron concentration of all five types’ different types of Zinc-Oxide (ZnO) films. It has been obtained from Hall measurement. It represent conducting ability of all five types of Zinc-Oxide (ZnO) films. Higher the electron concentration, more is the conductivity of ZnO film. Type-I Zinc-Oxide (ZnO) film sample has relatively highest electron concentration and Type-V Zinc-Oxide (ZnO) film sample has lowest electron concentration.
Figure 3 shows the variation of Hall mobility of all five types’ different types of Zinc-Oxide (ZnO) films. It has been obtained from Hall measurement. It represent conducting ability of all five types of Zinc-Oxide (ZnO) films. Type-I Zinc-Oxide (ZnO) film sample has lowest Hall mobility and Type-V Zinc-Oxide (ZnO) film sample has relatively highest Hall mobility.
Figure 4 shows the variation of sheet resistivity of all five types’ different types of Zinc-Oxide (ZnO) films. It has been obtained from Hall measurement. It represent conducting ability of all five types of Zinc-Oxide (ZnO) films. Type-II Zinc-Oxide (ZnO) film sample has lowest resistivity and Type-V Zinc-Oxide (ZnO) film sample has relatively highest resistivity.
4 Claims and 4 Figures , Claims:The scope of the invention is defined by the following claims:

Claims:
1. A method for the growth of n-type Zinc-oxide (ZnO) film comprises of following steps:
(a) The RF (radio frequency) sputtering deposition carried out at room temperature for the formation of different types of n-type Zinc-oxide (ZnO) film samples.
(b) The fabricated samples of n-type Zinc-oxide (ZnO) film shows n type nature,.
(c) The fabricated samples of n-type Zinc-oxide (ZnO) film shows different electron concentration, Hall electron mobility and sheet resistivity.
2. As mentioned in claim 1, wherein tunable electronic properties includes, electron carrier concentration, Hall mobility of electrons and sheet resistivity.
3. As mentioned in claim 1, wherein room temperature denotes 27 0C inside the RF (radio frequency) sputtering chamber.
4. As mentioned in claim 1, wherein the flow rate of oxygen maintained at different sccm (standard cubic centimeters per minute) which includes 2 sccm, 4 sccm,6 sccm,8 sccm and 10 sccm inside the RF (radio frequency) sputtering chamber to fabricate different types of ZnO film samples.