Structural and optical properties of Cr doped AlN thin lms before and after ions implantation

Thin lms of Chromium (Cr) doped Aluminum Nitride (AlN) have been prepared by radio frequency magnetron sputtering technique at room temperature and pressure conditions in a Nitrogen (N) atmosphere. One of the samples was left as-deposited and the other was irradiated with proton at a uence of 1x10 14 ions/cm 2 at a dose of 335 keV. The impact of ions doping on the structural and optical characteristics were investigated systematically. RBS and XRD were utilized to study the stoichiometry, thickness and structural information of the thin lms respectively. FTIR was utilized to understand the bonding chemistry of the specimens. We concluded that the optical properties of the thin lms have been changed selectively with irradiation leaving by structural unaltered.


Introduction
Aluminum Nitride thin lms semiconductor is providing fascinating properties in the eld of optoelectronics and optics due to its unique bandgap (6.2 eV), high thermal and electrical characteristics. It is also considering a useful semiconductor host in order to enhance the luminescence depending upon the excitation in the EM spectrum lying in the visible, infrared and ultraviolet range. The rare earth elements when doped into these high bandgap semiconductors nds variety in diverse applications such as lasing, displays, biomedical and electronic applications [3][4][5][6]. The 4f orbitals of rare earth elements are shielded by the 4d and 5p orbitals electrons which upon excitation is producing the EM spectrum containing infrared, visible and ultraviolet range [7]. The diameter of the atom of Cr is comparably higher so this mismatch perturb the crystallinity of AlN whereas AlN can be found in the structure of wurtzite, zincblende and rocksalt. This mismatch has role in the easy growth of thin lms due to elimination of grain boundaries at low temperature growth [8,9]. The goal of this doping is the achievement of more e cient phosphor materials and/or in the development of photonic devices.
Irradiation of ions has been found a great tool in tuning the desired materials characteristics such as magnetic, electrical, piezoelectric, electronic, structural and mechanical characteristics [10][11][12][13].
In this manuscript we have investigated in uence of the implanted ions into matrix of Cr doped AlN thin lms on the structure, dimension and optical properties. We concluded that Cr doped AlN specimens remained unaffected from the structural standpoint while the optical properties have undergone changes.

Synthesis And Irradiation On Samples
The single crystalline Silicon (Si) wafer was used as the substrate of the thin lms which was either cut along (100) or (111) plane. Different plane results different impact on the lm's growth. The synthesis was carried out using RF magnetron sputtering method. The sputtering system was maintained by varying power ranged from 100 to 200 W. An ultrahigh vacuum pump was connected to the system to maintain a vacuum less than 3x10 − 5 Torr at room temperature. The Nitrogen (N) was used as the sputtering gas while the target disk is Aluminum (Al). Figure. 1 shows the schematic representation of the deposition of the samples.
The sputtered N ions interact with the Al due to chemical a nity between them and deposit over there.
The sputtering of Cr + 3 is also taking place in parallel to Nitrogen's and the Cr + 3 ions replace the Al by having substitutional sites [1]. After the deposition the samples were annealed thermally at a temperature of 900 0 C in order to remove the porosity and homogeneous. The deposited and annealed sample was then cut into two halves and the one was left as grown and the other half was irradiated with protons in a room temperature and pressure at a dose of 1x10 14   conducted the Fourier Transform Infrared (FTIR) Spectroscopy using the FT/IR-6600 type setup. This spectroscopy informs us that each molecule within the samples has an associated frequency whereby re ecting or transmitting the rest of the existing frequencies which could carry the information about the strength and nature of the bond [14]. These vibration motions consist of vibrational transitions with distinct energies. The goal of this experiment was to nd the amount of light that to be transmitted. Figure. 3 is contrasting the transmittance in percent value against the wavenumber for the thin lm Cr doped AlN thin lms.
The result concluded that the transmittance has been lowered with the irradiation and the number and positions of the peaks have been altered. The transmittance has been lowered down by almost 3 orders of magnitude. The existence of peaks in the range from 2270-2420 cm − 1 represents CO 2 , which is due to the spectrometer path and is not from composition of the lms [15,16]

Conclusions
Thin lms of Cr doped AlN has been prepared with reactive magnetron sputtering technique in a room temperature and pressure. After annealing at 900 0 C the lm was irradiated with protons using 1x10 14 ions/cm 2 dose with an impinging energy of 335 keV. The structural and optical properties were investigated and found that the irradiated has signi cantly altered the optical properties by decreasing the transmittance while the structure of the lms remained unaffected with selective irradiations parameters which prove that the irradiation can selectively modify desired characteristics of the semiconductor.