Glancing Angle X-ray Diffraction Results Research Articles

RF plasma MOCVD of Y2O3 thin films: Effect of RF self-bias on the substrates during deposition

Yttrium oxide (Y2O3) thin films have been deposited by radio frequency plasma assisted metal organic chemical vapor deposition (MOCVD) process using (2,2,6,6-tetramethyl-3,5-heptanedionate) yttrium (commonly known as Y(thd)3) precursor in a plasma of argon and oxygen gases at a substrate temperature of 350°C. The films have been deposited under influence of varying RF self-bias (−50V to −175V) on silicon, quartz, stainless steel and tantalum substrates. The deposited coatings are characterized by glancing angle X-ray diffraction (GIXRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry and scanning electron microscopy (SEM). GIXRD and FTIR results indicate deposition of Y2O3 (BCC structure) in all cases. However, XPS results indicate nonstoichiometric cubic phase deposition on the surface of deposited films. The degree of nonstoichiometry varies with bias during deposition. Ellipsometry results indicate that the refractive index for the deposited films is varying from 1.70 to 1.83 that is typical for Y2O3. All films are transparent in the investigated wavelength range 300–1200nm. SEM results indicate that the microstructure of the films is changing with applied bias. Results indicate that it is possible to deposit single phase cubic Y2O3 thin films at low substrate temperature by RF plasma MOCVD process. RF self-bias that decides about the energy of impinging ions on the substrates plays an important role in controlling the texture of deposited Y2O3 films on the substrates. Results indicate that to control the structure of films and its texture, it is important to control the bias on the substrate during deposition. The films deposited at high bias level show degradation in the crystallinity and reduction of thickness.

Structural and optical studies of 100 MeV Au irradiated thin films of tin oxide

Thin films of tin(IV) oxide (SnO2) of 100nm thickness were grown on silicon (100) matrices by electron beam evaporation deposition technique under high vacuum. The thicknesses of these films were monitored by piezo-sensor attached to the deposition chamber. Nanocrystallinity is achieved in these thin films by 100MeV Au8+ using 1pnA current at normal incidence with ion fluences varying from 1×1011ions/cm2 to 5×1013ions/cm2. Swift Heavy Ion beam irradiation was carried out by using 15 UD Pelletron Accelerator at IUAC, New Delhi, India. Optical studies of pristine and ion irradiated thin films were characterized by UV–Visible spectroscopy and Fourier Transform Infrared (FTIR) spectroscopy. Prominent peak at 610cm−1 in FTIR spectrum confirmed the O–Sn–O bonding of tin(IV) oxide. For Surface topographical studies and grain size calculations, these films were characterized by Atomic Force Microscope (AFM) using Nanoscope III-A. Crystallinity and phase transformation due to irradiation of pristine and irradiated films were characterized by Glancing Angle X-ray Diffraction (GAXRD) using Brucker-D8 advance model. GAXRD results show improvement in crystallinity and phase transformation due to swift heavy ion irradiation. Grain size distribution was verified by AFM and GAXRD results. Swift heavy ion induced modifications in thin films of SnO2 were confirmed by the presence of prominent peaks at 2θ values of 30.65°, 32.045°, 43.94°, 44.96° and 52.36° in GAXRD spectrum.

Electrical, structural and surface morphological properties of thermally stable low-resistance W/Ti/Au multilayer ohmic contacts to n-type GaN

A W/Ti/Au multilayer scheme has been fabricated for achieving thermally stable low-resistance ohmic contact to n-type GaN (4.0 × 10 18 cm −3). It is shown that the as-deposited W/Ti/Au contact exhibits near linear I– V behaviour. However, annealing at temperature below 800 °C the contacts exhibit non-linear behaviour. After annealing at a temperature in excess of 850 °C, the W/Ti/Au contact showed ohmic behaviour. The W/Ti/Au contact produced specific contact resistance as low as 6.7 × 10 −6 Ω cm 2 after annealing at 900 °C for 1 min in a N 2 ambient. It is noted that the specific contact resistance decreases with increase in annealing temperature. It is also noted that annealing the contacts at 900 °C for 30 min causes insignificant degradation of the electrical and thermal properties. It is further shown that the overall surface morphology of the W/Ti/Au stayed fairly smooth even after annealing at 900 °C. The W/Ti/Au ohmic contact showed good edge sharpness after annealing at 900 °C for 30 min. Based on the Auger electron spectroscopy and glancing angle X-ray diffraction results, possible explanation for the annealing dependence of the specific contact resistance of the W/Ti/Au contacts are described and discussed.

Microstructural investigation of nickel silicide thin films and the silicide–silicon interface using transmission electron microscopy

This article discusses the results of transmission electron microscopy (TEM)-based investigation of nickel silicide (NiSi) thin films grown on silicon. Nickel silicide is currently used as the CMOS technology standard for local interconnects and in electrical contacts. Films were characterized with a range of TEM-based techniques along with glancing angle X-ray diffraction. The nickel silicide thin films were formed by vacuum annealing thin films of nickel (50 nm) deposited on (1 0 0) silicon. The cross-sectional samples indicated a final silicide thickness of about 110 nm. This investigation studied and reports on three aspects of the thermally formed thin films: the uniformity in composition of the film using jump ratio maps; the nature of the interface using high resolution imaging; and the crystalline orientation of the thin films using selected-area electron diffraction (SAED). The analysis highlighted uniform composition in the thin films, which was also substantiated by spectroscopy techniques; an interface exhibiting the desired abrupt transition from silicide to silicon; and desired and preferential crystalline orientation corresponding to stoichiometric NiSi, supported by glancing angle X-ray diffraction results.

Ohmic Contact Behavior of Pt/Ni/Au to p-ZnO

ABSTRACTThe electrical properties of single Pt (30 nm) and Pt (30 nm)/Ni (30nm)/Au(50nm) multilayer contacts on moderately doped p-ZnO (Na = 5.0 × 1017 /−3) were investigated. Although linear current-voltage characteristics were observed for all samples, a sample that was annealed for 1 min at a temperature above 500 °C resulted in an ohmic contact with good characteristics. The best ohmic contact to p-type ZnO was obtained using a Pt/Ni/Au multilayer contact that was annealed at 600 °C for 1 min under a N2 ambient, showing a specific contact resistance Rc of 1.97 × 10−5 Ω cm2. The fundamental mechanisms for the lower contact resistivity of Pt/Ni/Au contacts are discussed based on glancing angle x-ray diffraction results and Auger depth profile analysis of the multilayer alloying process. Furthermore, we fabricated a ZnO p-n homojunction using Pt/Ni/Au and Ti/Au as the p-type and n-type ohmic contact metal, respectively. The threshold voltage was determined to be about 3.7 V, comparable to the bandgap energy of ZnO.

Electrical and structural properties of Ti/W/Au ohmic contacts on n-type GaN

The electrical and structural properties of Ti/W/Au ohmic contacts to moderately doped n-GaN (4.07 × 1018 cm−3) have been investigated. The as-deposited and annealing contacts at temperatures below 750 °C exhibit non-linear behaviour. However, the contact showed ohmic behaviour after annealing at a temperature in excess of 850 °C. Specific contact resistance as low as 8.4 × 10−6 Ω cm2 is obtained from the Ti(12 nm)/W(20 nm)/Au(50 nm) contact annealed at 900 °C for 1 min in N2 ambient. It is observed that annealing results in a large reduction (by ∼160 meV) in the Schottky barrier height of the contacts, compared to the as-deposited one. The atomic force microscopy results showed that the surface morphology of the contact annealed at 900 °C is fairly smooth with a RMS roughness of 3.8 nm. Based on the Auger electron spectroscopy and glancing angle x-ray diffraction results, possible explanations are given to describe the annealing temperature dependence of the specific contact resistance of the contacts.

Formation of vanadium-based ohmic contacts to n-GaN

We investigate vanadium (V)-based ohmic contacts on n-GaN (Nd=2.0×1018 cm−3) as a function of annealing temperature. It is shown that the V (60 nm) contacts become ohmic with specific contact resistances of 10−3–10−4 Ω cm2 upon annealing at 650 and 850 °C. The V (20 nm)/Ti (60 nm)/Au (20 nm) contacts produce very low specific contact resistances of 2.2×10−5 and 4.0×10−6 Ω cm2 when annealed at 650 and 850 °C, respectively. A comparison shows that the use of the overlayers (Ti/Au) is very effective in improving ohmic property. Based on Auger electron spectroscopy and glancing-angle x-ray diffraction results, possible explanations for the annealing temperature dependence of the ohmic behavior of the V-based contacts are described and discussed.

Modelling of the structure of CdS thin films

The structure of CdS thin films produced by chemical bath deposition for window layers for photovoltaic devices has been investigated using the techniques of standard θ–2θ X-ray diffraction (XRD) and glancing angle XRD (GAXRD). The relative peak intensities observed in the diffraction patterns were consistent neither with a cubic nor a hexagonal microstructure. By employing both diffraction geometries on the same sample it was established that the CdS layers were un-textured, thus a structure different from either the cubic or hexagonal modifications was inferred. In order to elucidate the crystalline structure of the material a Rietveld analysis program was employed, together with a special program written to generate appropriate input parameter files. It was found that a good match between experimental and simulated patterns could be obtained by postulating a polytype CdS structure, consisting of nearly random stacking sequences of the hexagonal planes that form the basis for both the cubic (zinc-blende) and hexagonal (wurzite) modifications. The GAXRD results indicate that little structural change occurs in the polytype CdS upon annealing in air, despite a pronounced colour change. The structural difference between films deposited under different conditions is much more pronounced than that between as-deposited and annealed material. The results are discussed with reference to investigations by other authors of CdS thin films and of CdS nanoparticles using the techniques of transmission electron microscopy and/or X-ray or electron diffraction.