Bibhuti Bhusan Sahu

Simultaneous enhancement of carrier mobility and concentration via tailoring of Al-chemical states in Al-ZnO thin films

Simultaneously achieving higher carriers concentration and mobility is a technical challenge against up-scaling the transparent-conductive performances of transparent-conductive oxides. Utilizing one order higher dense (∼1 × 1011 cm−3) plasmas (in comparison to the conventional direct current plasmas), highly c-axis oriented Al-doped ZnO films have been prepared with precise control over relative composition and chemical states of constituting elements. Tailoring of intrinsic (O vacancies) and extrinsic (ionic Al and zero-valent Al) dopants provide simultaneous enhancement in mobility and concentration of charge carriers. Room-temperature resistivity as low as 4.89 × 10−4 Ω cm along the carrier concentration 5.6 × 1020 cm−3 is obtained in 200 nm thick transparent films. Here, the control of atomic Al reduces the charge trapping at grain boundaries and subdues the effects of grain boundary scattering. A mechanism based on the correlation between electron-hole interaction and carrier mobility is proposed for degenerately doped wide band-gap semiconductors.

Langmuir probe and optical emission spectroscopy studies in magnetron sputtering plasmas for Al-doped ZnO film deposition

This work reports investigation of the Al-doped ZnO (AZO) film deposition process, at different working pressures, in a conventional magnetron sputtering system. The primary goal of this study is to investigate the plasma formation and deposition process using various diagnostic tools, by utilizing low-temperature deposition process. In addition, this paper also presents a systematic Langmuir probe (LP) analysis procedure to determine the maximum information about plasma parameters. For the present study, we have extensively used LP method to characterize the deposition process for the control of plasma parameters. Along with the LP method, we have also used optical emission spectroscopy diagnostic to examine the favorable deposition condition for the fabrication of conductive AZO film. Utilizing diagnostics, this also reports measurements of ion current density, substrate temperature, and deposition rates to fabricate low resistivity films of ∼3 mΩ cm.

Effectiveness of plasma diagnostic in ultra high frequency and radio frequency hybrid plasmas for synthesis of silicon nitride film at low temperature

This work presents a systematic plasma diagnostic approach for plasma processing using radio frequency (RF) and RF/UHF (ultra high frequency) hybrid plasmas. The present work also studies the influence of frequency on the deposition of Hydrogenated silicon nitride (SiNx: H) film using N2/SiH4/NH3 discharges. Analysis of data reveals that the UHF power addition to RF is quite effective in the plasma and radicals formation in different operating conditions. For the diagnostics, we have used optical emission spectroscopy, vacuum ultraviolet absorption spectroscopy, and RF compensated Langmuir probe. The presented diagnostic method directly exploits the optimized condition for fabricating high-quality silicon rich nitride (SiNx: H) thin film, at low temperature. With the help of hybrid plasmas, it is possible to fabricate SiNx: H film with high transparency ∼90%.

Experimental evidence of warm electron populations in magnetron sputtering plasmas

This work report on the results obtained using the Langmuir probe (LP) measurements in high-power dc magnetron sputtering discharges. Data show clear evidence of two electron components, such as warm and bulk electrons, in the sputtering plasma in a magnetic trap. We have also used optical emission spectroscopy diagnostic method along with LP to investigate the plasma production. Data show that there is a presence of low-frequency oscillations in the 2–3 MHz range, which are expected to be generated by high-frequency waves. Analysis also suggests that the warm electrons, in the plasmas, can be formed due to the collisionless Landau damping of the bulk electrons.

Tailoring of microstructure in hydrogenated nanocrystalline Si thin films by ICP-assisted RF magnetron sputtering

Utilizing plasma-assisted deposition by combining an RF magnetron and an inductively coupled plasma (ICP) source it is possible to fabricate highly crystallized nc-Si:H films at a relatively low substrate temperature (300 °C). Microstructural analysis reveals enhancement in crystallinity along with (2 2 0) preferential orientation throughout the depth of the film. The possible mechanism of crystallinity enhancement and preferential orientation is presented on the basis of plasma diagnostics using optical emission spectroscopy and various film analysis tools. This work also reports the effectiveness of the ICP source and elevated temperature for the control of film microstructure and crystallinity.

Integrated approach for low-temperature synthesis of high-quality silicon nitride films in PECVD using RF–UHF hybrid plasmas

This study investigates low-temperature plasma nitriding of hydrogenated silicon (SiN x :H) film in radio frequency (RF) and RF–ultra-high frequency (UHF) hybrid plasmas. To study the optimized conditions for the deposition of SiN x :H film, this work adopts a systematic plasma diagnostic approach in the nitrogen–silane and nitrogen–silane–ammonia plasmas. This work also evaluates the capability of plasma and radical formation by utilizing different plasma sources in the PECVD process. For the plasma diagnostics, we have purposefully used the combination of optical emission spectroscopy (OES), intensified CCD (ICCD) camera, vacuum ultraviolet absorption spectroscopy (VUVAS), and RF compensated Langmuir probe (LP). Data reveal that there is significant enhancement in the atomic nitrogen radicals, plasma densities, and film properties using the hybrid plasmas. Measurements show that addition of a small amount of NH3 can significantly reduce the electron temperature, plasma, and radical density. Also, optical and chemical properties of the deposited films are investigated on the basis of plasma diagnostics. Good quality SiN x :H films, with atomic nitrogen to hydrogen ratio of 4:1, are fabricated. The plasma chemistry of the hybrid plasmas is also discussed for its utility for plasma applications.

Flexible OLED fabrication with ITO thin film on polymer substrate

This paper reports the synthesis of flexible indium tin oxide (ITO) films in a dual pulse magnetron sputtering (DPMS) system at low temperature (<100 °C) deposition condition. This study also presents experimental demonstration of the ITO films for their possible use in the fabrication of organic light emitting diode (OLED) device, and the device performance on the super polycarbonate substrates. The presented data reveals the feasibility of ITO films, with a very low sheet resistance of ~30 Ω/ and high transmittance of ~88% at 550 nm, simply by the magnetron pulse mode operations with increasing pulse frequency from 0 to 50 kHz.

Controlling conductivity of carbon film for L-929 cell biocompatibility using magnetron sputtering plasmas

As a material of current interest compatible with many living organisms, carbon has received considerable attention for applications in medicine. To improve and investigate the performance and applications of diamond-like carbon (DLC) films for implantable bio-organs, it is important to optimize the synthesis process from the original deposition conditions to control the characterization of DLC. Simultaneously, it is necessary to develop new techniques and processes that yield DLC films with stronger adhesion to the substrate and better biocompatibility. This work investigates the suitability of sputtering plasmas for application of carbon film biocompatibility in cell growth. This work also reports an approach to the study of the biomedical response of the well-characterized carbon films deposited by a DC unbalanced magnetron sputtering system (UBMS). Conductive carbon films are prepared at a working pressure of 3 mTorr, and their properties are studied under different operating conditions by varying the target power density. In the present work, we have used L-929 cells as the biomaterial. The influence of L-929 cells on the carbon films fabricated using closed field UBMS is studied. The data reveal that the change in L-929 cell growth with 1-5 days proliferation is caused by the decreasing electrical resistivity with increasing sp2 bonding structure.

Utility of dual frequency hybrid source for plasma and radical generation in plasma enhanced chemical vapor deposition process

Looking into the aspect of material processing, this work evaluates alternative plasma concepts in SiH4/H2 plasmas to investigate the radical and plasma generation in the plasma enhanced chemical vapor deposition (PECVD) synthesis of nanocrystalline Si (nc-Si:H). Simultaneous measurements by vacuum ultraviolet absorption spectroscopy (VUVAS), optical emission spectroscopy (OES), and radio frequency (RF) compensated Langmuir probe (LP) reveal that RF/ultrahigh frequency (UHF) hybrid source can efficiently produce H radicals and plasmas that are accountable for nc-Si:H film synthesis. The efficacy of hybrid plasmas is also discussed.

Effect of plasma parameters on characteristics of silicon nitride film deposited by single and dual frequency plasma enhanced chemical vapor deposition

This work investigates the deposition of hydrogenated amorphous silicon nitride films using various low-temperature plasmas. Utilizing radio-frequency (RF, 13.56 MHz) and ultra-high frequency (UHF, 320 MHz) powers, different plasma enhanced chemical vapor deposition processes are conducted in the mixture of reactive N2/NH3/SiH4 gases. The processes are extensively characterized using different plasma diagnostic tools to study their plasma and radical generation capabilities. A typical transition of the electron energy distribution function from single- to bi-Maxwellian type is achieved by combining RF and ultra-high powers. Data analysis revealed that the RF/UHF dual frequency power enhances the plasma surface heating and produces hot electron population with relatively low electron temperature and high plasma density. Using various film analysis methods, we have investigated the role of plasma parameters on the compositional, structural, and optical properties of the deposited films to optimize the proce...