Comparative Study of Atomic-Layer-Deposited Stacked (HfO₂/Al₂O₃) and Nanolaminated (HfAlO_<i>x</i>) Dielectrics on In_0.53Ga_0.47As

Mahata, Chandreswar,Byun, Young-Chul,An, Chee-Hong,Choi, Sungho,An, Youngseo,Kim, Hyoungsub American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.10

<P>The high-k gate dielectric structures in stacked (HfO<SUB>2</SUB>/Al<SUB>2</SUB>O<SUB>3</SUB>) and nanolaminated (HfAlO<SUB><I>x</I></SUB>) forms with a similar apparent accumulation capacitance were atomic-layer-deposited on n-type In<SUB>0.53</SUB>Ga<SUB>0.47</SUB>As substrates, and their electrical properties were investigated in comparison with a single-layered HfO<SUB>2</SUB> film. Al-oxide interface passivation in both forms proved to be effective in preventing a significant In incorporation in the high-<I>k</I> film and reducing the interface state density. The measured valence band spectra in combination with the reflection electron energy loss spectra were used to extract the energy band parameters of various dielectric structures on In<SUB>0.53</SUB>Ga<SUB>0.47</SUB>As. A further decrease in the interface state density was achieved in the stacked structure than in the nanolaminated structure. However, in terms of the other electrical properties, the nanolaminated sample exhibited better characteristics than the stacked sample, with a smaller border trap density and lower leakage current under substrate injection conditions with and without voltage stressing.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-10/am400368x/production/images/medium/am-2013-00368x_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am400368x'>ACS Electronic Supporting Info</A></P>

Electrical properties of the HfO2eAl2O3 nanolaminates with homogeneous and graded compositions on InP

Chandreswar Mahata,Youngseo An,Sungho Choi,Young-Chul Byun,Dae-Kyoung Kim,Taeyoon Lee,Jiyoung Kim,Mann-Ho Cho,Hyoungsub Kim 한국물리학회 2016 Current Applied Physics Vol.16 No.3

For possible application to a gate dielectric in high-performance III-V transistors, nanolaminated HfO2e Al2O3 films with artificial compositional profiles were deposited on n-type InP substrates using atomic layer deposition. The films were vertically graded (HfO2 and Al2O3 at the surface and interface regions, respectively) and had a homogeneous composition. To compare their electrical properties, a similar physical thickness and capacitance-equivalent thickness (CET) were maintained, and the graded structure showed an increase in the Al2O3 content near the high-k and InP interface region without an increase in CET, which suppresses the In incorporation at the near-interface region and reduces the density of the interface trap. However, doing so results in a degradation of the leakage current characteristics under voltage stressing when compared to homogeneously-nanolaminated films.

Interfacial stability and electrical properties of atomic layer deposited Ta₁-xZrx O/SiO₂

Chandreswar Mahata,Taeyoon Lee 대한전자공학회 2015 대한전자공학회 학술대회 Vol.2015 No.6

Amorphous Ta₁-xZrxO/SiO₂ composite gate dielectric film and SiO₂ passivation layer are deposited on InP substrate by atomic layer deposition. The interfacial chemical, physical, and electrical properties of the Ta₁-xZrxO/InP and Ta₁-xZrxO/SiO₂/InP MOS structures are compared in details. Electrical conduction properties combined with chemical bonding analysis with x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were examined. Effect on Indium diffusion through Ta₁-xZrxO high-k gate dielectrics were minimized by SiO₂ passivation layer. Significant reduction of the interfacial In and P oxide layer thickness and effectively reduces the interface trap states and thus unpin the Femi level, resulting from indium diffusion upon SiO₂ passivation, is confirmed by the parallel conductance contour plot.

Hypofractionated Radiotherapy for Breast Cancers - Preliminary Results from a Tertiary Care Center in Eastern India

Nandi, Moujhuri,Mahata, Anurupa,Mallick, Indranil,Achari, Rimpa,Chatterjee, Sanjoy Asian Pacific Journal of Cancer Prevention 2014 Asian Pacific journal of cancer prevention Vol.15 No.6

Background: The standard radiotherapy (RT) fractionation practiced in India and worldwide is 50Gy in 25 fractions over 5 weeks to the chest wall or whole breast followed by tumour bed boost in case of breast conservation (BCS). A body of validated data exists regarding hypofractionation in breast cancer. We here report initial results for 135 patients treated at our center with the START-B type of fractionation. Materials and Methods: From May 2011 till July 2012, women with all stages of breast cancer (excluding metastatic), who had undergone BCS or mastectomy were planned for 40Gy in 15 fractions over 3weeks to chest wall/whole breast and supraclavicular fossa (where indicated) followed by tumour bed boost in BCS patients. Planning was done using Casebow's technique. The primary end point was to assess the acute toxicity and the cosmetic outcomes. Using cosmetic scales; patients were assessed during radiotherapy and at subsequent follow up visits with the radiation oncologist. Results: Of the 135 patients, 62 had undergone BCS and 73 mastectomy. Median age of the population was 52 years. Some 80% were T1&T2 tumours in BCS whereas most patients in mastectomy group were T3&T4 tumours (60%). 45% were node negative in BCS group whilst it was 23% in the mastectomy group. Average NPI scores were 3.9 and 4.9, respectively. Most frequently reported histopathology report was infiltrating ductal carcinoma (87%), grade III being most common (58%), and 69% were ER positive tumours, and 30% were Her 2 Neu positive. Triple negative tumours accounted for 13% and their mean age was young (43 yrs.) The maximum acute skin toxicity at the end of treatment was Grade 1 in 94% of the mastectomy grouppatients and 71% in BCS patients. Grade 2 toxicity was 6% in mast group and 23% in BCS group. Grade 3 was 6% in BCS group, no grade 3 toxicity in mastectomy patients and there was no grade 4 skin toxicity in any case. Post RT at 1 month; 39% of BCS patients had persisting Grade I skin reaction which was only 2% in mastectomy patients. At 3 months post RT, 18% patients had persisting hyperpigmentation. At 6 months 8% patients had persisting erythema in the BCS group only. Some 3% BCS and 8% mastectomy patients had lymph edema till the date of evaluation. Cosmetic outcome in BCS patients remained good to excellent 6 months post surgery and radiotherapy. 1 patient of BCS and 3 patients of mast had developed metastatic disease at the time of evaluation. Conclusions: Hypofractionated RT is well tolerated in Indian population with reduced acute skin toxicity and good cosmetic outcome. Regimens such as these should be encouraged in other centers to increase machine output time. The study is on-going to assess long term results.

Atomic layer deposition of Y-stabilized ZrO₂ for advanced DRAM capacitors

Park, Bo-Eun,Oh, Il-Kwon,Mahata, Chandreswar,Lee, Chang Wan,Thompson, David,Lee, Han-Bo-Ram,Maeng, Wan Joo,Kim, Hyungjun ELSEVIER SCIENCE 2017 Journal of Alloys and Compounds Vol.722 No.-

<P><B>Abstract</B></P> <P>With accelerated shrinking of integrated circuit, the fabrication of metal-insulator-metal (MIM) capacitors having a high capacitance density and low leakage current for dynamic random access memory (DRAM) has become a challenge. In this study, we investigated Y-stabilized ZrO<SUB>2</SUB> as a novel high-<I>k</I> material for DRAM capacitors. We used atomic layer deposition (ALD) to produce Y-stabilized ZrO<SUB>2</SUB>; this technique enables easy control of the Y concentration by changing the ratio of ZrO<SUB>2</SUB> to Y<SUB>2</SUB>O<SUB>3</SUB> ALD cycles. This technique is suitable for future DRAM capacitors, as it provides superior thickness controllability and conformality. Y doping into ZrO<SUB>2</SUB> increases the oxygen vacancy content in the films and transforms the ZrO<SUB>2</SUB> crystal structure from monoclinic to cubic. As a result, the dielectric constant is significantly increased from 19.1 to 30.2. Moreover, Y doping shifts the defect level into the conduction band rather than the energy bandgap, resulting in about 60 times lower leakage current density for Y-doped ZrO<SUB>2</SUB> compared to undoped ZrO<SUB>2</SUB>. It is notable that the dielectric properties and the leakage current density are simultaneously enhanced, indicating that Y-doped ZrO<SUB>2</SUB> is a promising candidate to satisfy the requirements of future DRAM capacitors.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Significant enhanced performance of DRAM capacitor with ALD Y-stabilized ZrO<SUB>2</SUB> (YSZ) films as a capacitor dielectric. </LI> <LI> Production of YSZ films using the supercycle process of ALD. </LI> <LI> The increase in dielectric constant up to ∼1.58 times due to the change of crystallinity. </LI> <LI> The decrease in leakage currents ∼60 times due to the change of bandgap structure. </LI> <LI> In-depth study chemical composition, crystal structure, energy gap, and energy level of defect state. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Defect Analysis And Performance Evaluation Of P-type Epitaxial GaAs Layer On Ge Substrate For GaAs/Ge Based Advanced Device

Dalapati, Goutam Kumar,Suresh, Vignesh,Chakraborty, Sandipan,Mahata, Chandreswar,Ren, Yi,Bhat, Thirumaleshawara,Tripathy, Sudhiranjan,Lee, Taeyoon,Bera, Lakshmi Kanta,Chi, Dongzhi VBRI Press AB 2016 Advanced materials letters Vol.7 No.7

Enhancement of X-ray detection by single-walled carbon nanotube enriched flexible polymer composite

Han, Heetak,Lee, Sanggeun,Seo, Jungmok,Mahata, Chandreswar,Cho, Sung Hwan,Han, A-Reum,Hong, Keun-Sung,Park, Joon-Ho,Soh, Myung-Jin,Park, Cheolmin,Lee, Taeyoon Springer-Verlag 2014 NANOSCALE RESEARCH LETTERS Vol.9 No.1

<P><B>Abstract</B></P><P>Although organic-based direct conversion X-ray detectors have been developed, their photocurrent generation efficiency has been limited by recombination of excitons due to the intrinsically poor electrical properties of organic materials. In this report, we fabricated a polymer-based flexible X-ray detector and enhanced the X-ray detection sensitivity using a single-walled carbon nanotube (SWNT) enriched polymer composite. When this SWNT enriched polymer composite was used as the active layer of an X-ray detector, it efficiently separated charges at the interface between the SWNTs and polymer, preventing recombination of X-ray-induced excitons. This increased the photocurrent generation efficiency, as measured from current-voltage characteristics. Therefore, X-ray-induced photocurrent and X-ray detection sensitivity were enhanced as the concentration of SWNTs in the composite was increased. However, this benefit was counterbalanced by the slow and unstable time-dependent response at high SWNT concentrations, arising from reduced Schottky barrier heights between the active layer and electrodes. At high SWNT concentration, the dark current also increased due to the reduced Schottky barrier height, leading to decrease the signal-to-noise ratio (SNR) of the device. Experimental results indicated that 0.005 wt.% SWNT in the composite was the optimum composition for practical X-ray detector operation because it showed enhanced performance in both sensitivity and SNR. In mechanical flexibility tests, the device exhibited a stable response up to a bending radius of 0.5 cm, and the device had no noticeable change in diode current after 1,000 bending cycles.</P><P><B>PACS code</B></P><P>8.67.Sc</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/1556-276X-9-610) contains supplementary material, which is available to authorized users.</P>

Evolution and Analysis of Nitride Surface and Interfaces by Statistical Techniques: A Correlation with RHEED through Kinetic Roughening

Ankush Bag,Rahul Kumar,Partha Mukhopadhyay,Mihir K. Mahata,Apurba Chakraborty,Saptarsi Ghosh,Sanjay K. Jana,Dhrubes Biswas 대한금속·재료학회 2015 ELECTRONIC MATERIALS LETTERS Vol.11 No.4

In-situ RHEED and ex-situ AFM characterizations have been employed to investigate transformations of surface topography with the thickness of PAMBE grown AlGaN and InGaN on GaN. The ternary alloys have been grown with identical growth-front roughness as confirmed by XRR and RHEED observations. The spottier RHEED has been observed with increased thickness of the InGaN as opposed to streakier behavior of AlGaN. We have noticed incremental nature of RMS roughness, skewness and kurtosis of InGaN surface compared to GaN or AlGaN from AFM as evident by final spotty RHEED for InGaN. However, the analyzed fractal dimension is lower for InGaN as opposed to AlGaN ( ). From the kinetic roughening perspective of adatoms, the experimental evidences lead to the high correlation between binding energy of the cluster atoms ( ) and the modified DDA growth model with dissociation and evaporation to confirm the efficacy of the study. The initial streaky and spotty RHEED of InGaN and AlGaN, respectively, can be attributed to their Eb that causes smoothing and roughening of the GaN surface due to adatoms surface mobility behavior. Therefore, the fractal description reveals the fact during formation of nitride hetero-interface while other AFM results describe the top surface.

Graphene as an atomically thin barrier to Cu diffusion into Si

Hong, Juree,Lee, Sanggeun,Lee, Seulah,Han, Heetak,Mahata, Chandreswar,Yeon, Han-Wool,Koo, Bonwoong,Kim, Seong-Il,Nam, Taewook,Byun, Kisik,Min, Byung-Wook,Kim, Young-Woon,Kim, Hyungjun,Joo, Young-Chang The Royal Society of Chemistry 2014 Nanoscale Vol.6 No.13

<P>The evolution of copper-based interconnects requires the realization of an ultrathin diffusion barrier layer between the Cu interconnect and insulating layers. The present work reports the use of atomically thin layer graphene as a diffusion barrier to Cu metallization. The diffusion barrier performance is investigated by varying the grain size and thickness of the graphene layer; single-layer graphene of average grain size 2 ± 1 μm (denoted small-grain SLG), single-layer graphene of average grain size 10 ± 2 μm (denoted large-grain SLG), and multi-layer graphene (MLG) of thickness 5-10 nm. The thermal stability of these barriers is investigated after annealing Cu/small-grain SLG/Si, Cu/large-grain SLG/Si, and Cu/MLG/Si stacks at different temperatures ranging from 500 to 900 °C. X-ray diffraction, transmission electron microscopy, and time-of-flight secondary ion mass spectroscopy analyses confirm that the small-grain SLG barrier is stable after annealing up to 700 °C and that the large-grain SLG and MLG barriers are stable after annealing at 900 °C for 30 min under a mixed Ar and H2gas atmosphere. The time-dependent dielectric breakdown (TDDB) test is used to evaluate graphene as a Cu diffusion barrier under real device operating conditions, revealing that both large-grain SLG and MLG have excellent barrier performance, while small-grain SLG fails quickly. Notably, the large-grain SLG acts as a better diffusion barrier than the thicker MLG in the TDDB test, indicating that the grain boundary density of a graphene diffusion barrier is more important than its thickness. The near-zero-thickness SLG serves as a promising Cu diffusion barrier for advanced metallization.</P>

The spatial clustering of dengue disease and risk susceptibility mapping: an approach towards sustainable health management in Kharagpur city, India

Subrata Ghosh,Santanu Dinda,Nilanjana Das Chatterjee,Kousik Das,Riya Mahata 대한공간정보학회 2019 Spatial Information Research Vol.27 No.2

Dengue fever becomes one of the serious vectorborne diseases in the world, particularly in tropical countries. Mosquitoes borne disease transmission are mainly transpired by physical, environmental and socio-economic variables. Therefore, disease mapping is essential for monitoring, prediction, and prevention of dengue. Accordingly, the aims of this research are to find out the dengue outbreak, spatial pattern, understand the factors and construct a risk map to accurately predict and control of dengue. For this purpose, the Kharagpur city of West Bengal has been selected which is frequently encountered with the dengue outbreak. Epidemiological data were collected from the district health department. The spatial scan statistics of the Poisson model and Local Moran’s I is used for the mapping of spatial patterns and concentration of dengue and Monte Carlo hypothesis testing was applied to test the significance of the result. Therefore, multiple logistic regression analysis has been applied with selected parameters to produce a risk map for the entire study area. Finally, this study has proposed suitable site-specific management strategies. However, this study provides an example of disease risk estimation which will be remarkable for spatial analysis of epidemiological research as well as health planning and disease surveillance.