Nagarajan Balaji

Negative gate-bias temperature stability of N-doped InGaZnO active-layer thin-film transistors

Stability of negative bias temperature stress (NBTS) of nitrogen doped amorphous InGaZnO (a-IGZO) thin-film transistor (TFT) is investigated. Undoped a-IGZO TFT stressed at 333 K exhibit a larger negative ΔVTH (−3.21 V) with an unpredictable sub-threshold swing (SS) of hump shaped transfer curve due to the creation of meta-stable traps. Defects related hump formation has disappeared with small ΔVTH (−1.13 V) and ΔSS (0.018 V/dec) in nitrogen doped a-IGZO TFT. It is observed that nitrogen doping enhances device stability by well controlled oxygen vacancy and trap sites in channel and channel/dielectric interface.

Stability of SiNX/SiNX double stack antireflection coating for single crystalline silicon solar cells.

Double stack antireflection coatings have significant advantages over single-layer antireflection coatings due to their broad-range coverage of the solar spectrum. A solar cell with 60-nm/20-nm SiNX:H double stack coatings has 17.8% efficiency, while that with a 80-nm SiNX:H single coating has 17.2% efficiency. The improvement of the efficiency is due to the effect of better passivation and better antireflection of the double stack antireflection coating. It is important that SiNX:H films have strong resistance against stress factors since they are used as antireflective coating for solar cells. However, the tolerance of SiNX:H films to external stresses has never been studied. In this paper, the stability of SiNX:H films prepared by a plasma-enhanced chemical vapor deposition system is studied. The stability tests are conducted using various forms of stress, such as prolonged thermal cycle, humidity, and UV exposure. The heat and damp test was conducted for 100 h, maintaining humidity at 85% and applying thermal cycles of rapidly changing temperatures from -20°C to 85°C over 5 h. UV exposure was conducted for 50 h using a 180-W UV lamp. This confirmed that the double stack antireflection coating is stable against external stress.

Suppression of temperature instability in InGaZnO thin-film transistors by in situ nitrogen doping

We have investigated the effect of nitrogen doping on the behavior of hysteresis curve and its suppression of temperature instability in amorphous InGaZnO thin-film transistors (a-IGZO TFTs). The in situ nitrogen doping reduced the temperature induced abnormal sub threshold leakage current and traps generation. Large falling-rate (FR) ~ 0.26 eV V−1, low activation energy (Ea) ~ 0.617 eV and a small hysteresis compared to the pure a-IGZO TFTs, shows the best immunity to thermal instability. This is mainly attributed to the reduction of interface trap density and oxygen vacancies due to the passivation of defects and/dangling bonds.

Drain-Induced Barrier Lowering and Parasitic Resistance Induced Instabilities in Short-Channel InSnZnO TFTs

Effect of short-channel induced instabilities in InSnZnO-based thin-film transistors (TFTs) caused by combination of the drain induced barrier lowering (DIBL) and parasitic resistance is reported. As the active channel length decreased below a critical value of around 8 μm, the draincurrent (2.81 μA) are abruptly increased and N-shaped behavior of the transconductance are observed due to the formation of additional current path in the channel. The magnitude of subgap density of states is also depended on the channel size. The higher value of parasitic resistance RSD (~42 kg) and DIBL coefficient (76.8 mV/V) in short-channel ITZO TFT devices are also discussed.

The effect of small pyramid texturing on the enhanced passivation and efficiency of single c-Si solar cells

In this work, a simple method to form small random pyramid texturing (0.5–2 μm size) is proposed to enhance the surface passivation of commercial p-type Cz-Si wafers. Small pyramid texturing was generated with chemical nano-masking for anisotropic etching. The surface recombination velocity obtained after the passivation of the thermal oxide layer reduced from 65 and 10 cm s−1 for the large pyramids (10–15 μm size) and small pyramid (0.5–2 μm) texturing respectively. The solar cell fabricated with large pyramid texturing resulted in an efficiency of 17.82% with a current density (JSC) of 36.91 mA cm−2, an open circuit voltage (VOC) of 620 mV whereas small pyramid texturing resulted in an efficiency of 18.5% with JSC of 37.6 mA cm−2 and VOC of 628 mV. The low surface recombination velocity increases the VOC by 8 mV. The small pyramid textured wafers are found to enhance the quantum efficiency performance in both short and long wavelength regions.

Improvement of Mobility in Oxide-Based Thin Film Transistors: A Brief Review

Copyright ©2015 KIEEME. All rights reserved. This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited. pISSN: 1229-7607 eISSN: 2092-7592 DOI: http://dx.doi.org/10.4313/TEEM.2015.16.5.234 OAK Central: http://central.oak.go.kr

Surface Passivation Schemes for High-Efficiency c-Si Solar Cells - A Review

Copyright ©2015 KIEEME. All rights reserved. This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited. pISSN: 1229-7607 eISSN: 2092-7592 DOI: http://dx.doi.org/10.4313/TEEM.2015.16.5.227 OAK Central: http://central.oak.go.kr TRANSACTIONS ON ELECTRICAL AND ELECTRONIC MATERIALS Vol. 16, No. 5, pp. 227-233, October 25, 2015

Selective emitter using a screen printed etch barrier in crystalline silicon solar cell

The low level doping of a selective emitter by etch back is an easy and low cost process to obtain a better blue response from a solar cell. This work suggests that the contact resistance of the selective emitter can be controlled by wet etching with the commercial acid barrier paste that is commonly applied in screen printing. Wet etching conditions such as acid barrier curing time, etchant concentration, and etching time have been optimized for the process, which is controllable as well as fast. The acid barrier formed by screen printing was etched with HF and HNO3 (1:200) solution for 15 s, resulting in high sheet contact resistance of 90 Ω/sq. Doping concentrations of the electrode contact portion were 2 × 1021 cm−3 in the low sheet resistance (Rs) region and 7 × 1019 cm−3 in the high Rs region. Solar cells of 12.5 × 12.5 cm2 in dimensions with a wet etch back selective emitter Jsc of 37 mAcm−2, open circuit voltage (Voc) of 638.3 mV and efficiency of 18.13% were fabricated. The result showed an improvement of about 13 mV on Voc compared to those of the reference solar cell fabricated with the reactive-ion etching back selective emitter and with Jsc of 36.90 mAcm−2, Voc of 625.7 mV, and efficiency of 17.60%.

Boosting the mobility and bias stability of oxide-based thin-film transistors with ultra- thin nanocrystalline InSnO:Zr layer

Extensive attention on high-definition flat panel displays is the driving force to fabricate high-performance thin-film transistors (TFTs). A hybrid oxide TFTs fabricated using an interfacial layer of nanocrystalline Zr-doped InSnO (nc-ITO:Zr) and an amorphous InSnZnO films as an active channel is reported here. Due to the presence of nc-ITO:Zr layer, an improvement of the field-effect mobility (86.4 cm2/V·s) and threshold voltage (0.43 V) values for TFTs are observed. Positive gate bias stress study indicates the role of nc-ITO:Zr layer in fabricated TFTs through the suppression of charge trapping capability between the channel and insulating layer.

Plasma Textured Glass Surface Morphologies for Amorphous Silicon Thin Film Solar Cells-A review

Copyright ©2016 KIEEME. All rights reserved. This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited. pISSN: 1229-7607 eISSN: 2092-7592 DOI: http://dx.doi.org/10.4313/TEEM.2016.17.2.98 OAK Central: http://central.oak.go.kr