Dr.Lakshminarayan Nariangadu | University of Madras (original) (raw)
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Papers by Dr.Lakshminarayan Nariangadu
Vacuum, 2009
Silicon oxide (SiO x) thin films have been deposited at a substrate temperature of 300 C by induc... more Silicon oxide (SiO x) thin films have been deposited at a substrate temperature of 300 C by inductivelycoupled plasma chemical vapor deposition (ICP-CVD) using N 2 O/SiH 4 plasma. The effect of N 2 O/SiH 4 flow ratios on SiO x film properties and silicon surface passivation were investigated. Initially, the deposition rate increased up to the N 2 O/SiH 4 flow ratio of 2/1, and then decreased with the further increase in N 2 O/ SiH 4 flow ratio. Silicon oxide films with refractive indices of 1.47-2.64 and high optical band-gap values (>3.3 eV) were obtained by varying the nitrous oxide to silane gas ratios. The measured density of the interface states for films was found to have minimum value of 4.3 Â 10 11 eV À1 cm À2. The simultaneous highest s eff and lowest density of interface states indicated that the formation of hydrogen bonds at the SiO x /c-Si interface played an important role in surface passivation of p-type silicon.
Solid-State Electronics, 2011
Effective memory performance of the nonvolatile memory/thin film transistor (NVM/TFT) devices nee... more Effective memory performance of the nonvolatile memory/thin film transistor (NVM/TFT) devices needs good TFT characteristics. The reduction in leakage current of the TFT devices was accomplished with the gate offset (GOF) structure. A simplified fabrication process for the GOF NVM is ...
Journal of The Electrochemical Society, 2011
The fabrication of amorphous silicon/crystalline silicon (a-Si:H/c-Si) heterojunction solar cell ... more The fabrication of amorphous silicon/crystalline silicon (a-Si:H/c-Si) heterojunction solar cell and an understanding of the fundamental conduction mechanism in the device are presented. In the first part, the effect of intrinsic amorphous silicon [a-Si:H(i)] layer ...
Journal of The Electrochemical Society, 2011
We fabricated hydrogenated amorphous silicon/crystalline silicon (a-Si: H/c-Si) heterojunction so... more We fabricated hydrogenated amorphous silicon/crystalline silicon (a-Si: H/c-Si) heterojunction solar cells with different intrinsic buffer layers, to elucidate the effect of the energy band gap, as well as passivation quality on the performance of the a-Si: H/c-Si ...
Current Applied Physics, 2010
Solar Energy, 2010
The influence of various parameters such as buffer intrinsic layers, back-surface fields, densiti... more The influence of various parameters such as buffer intrinsic layers, back-surface fields, densities of interface defects (Dit), the resistivity of p-type silicon substrates (ρ) and then work function of transparent conductive oxide (ϕTCO) on heterojunction with intrinsic thin-...
A red emitting ZnO·Y 2 O 3 :Eu phosphor has been prepared using pyrolysis technique at temperatur... more A red emitting ZnO·Y 2 O 3 :Eu phosphor has been prepared using pyrolysis technique at temperatures ≤1000 °C. When NH 4 Cl was used as an ingredient, its luminescence efficiency was quite high indicating that Cl − ions act as charge compensators since the introduction of Y 3+ and Eu 3+ cations in ZnO lattice demands the introduction of equal amount of excess anions. However, Na + or Li + quenches the luminescence efficiency of ZnO·Y 2 O 3 :Eu. Due to ZnO host absorption, the excitation peaks of ZnO·Y 2 O 3 :Eu phosphor near 260 nm and 394 nm are suppressed while the one at 468 nm is intense. This red emitting phosphor may find applications when monochromatic excitation such as lasers are involved. XRD data of (Zn 0.93 Y 0.07 )O z :Eu 3+ ,Cl − shows the presence of the ZnO phase as well as the Y 2 O 3 phase. It shows that Y 2 O 3 forms a sublattice within ZnO host. This is supported by the PL data of (Zn 0.93 Y 0.07 )O z :Eu 3+ ,Cl − which showed no significant change in the PL effic...
Solid-State Electronics, 2011
Effective memory performance of the nonvolatile memory/thin film transistor (NVM/TFT) devices nee... more Effective memory performance of the nonvolatile memory/thin film transistor (NVM/TFT) devices needs good TFT characteristics. The reduction in leakage current of the TFT devices was accomplished with the gate offset (GOF) structure. A simplified fabrication process for the GOF NVM is ...
Indian Journal of Pure and Applied Physics
ZnO grown under reducing condition is always Zn excess. These Zn atoms are positioned at intersti... more ZnO grown under reducing condition is always Zn excess. These Zn atoms are positioned at interstitial sites due to the escape of oxygen from ZnO. The oxygen vacancies created by alkali metal dopants in ZnO play a major role in its green luminescence. This is understood on the basis of charge transfer between Zn interstitials and neighbouring oxygen vacancies caused by the doping of monovalent ions such as Li, Na or K at divalent Zn lattice sites followed by Stokes shifted emission. 1 Introduction Wurtzitic zinc oxide (ZnO) has received considerable attention because of its unique optical, semiconducting, piezoelectric and magnetic properties. It is a direct wide band gap (3.4 eV) semiconductor with large exciton binding energy of 60 meV at room temperature. Light emitting diodes made of ZnO are cheaper to manufacture than GaN and its white light is brighter and more like sunlight. Adding phosphorous to ZnO leads to p-type semiconducting material while oxygen vacancies give n-type Zn...
The process conditions for a high-efficiency and low cost crystalline silicon solar cell were opt... more The process conditions for a high-efficiency and low cost crystalline silicon solar cell were optimized. Novel approaches such as wafer cleaning and saw-damage removal using 0.5 wt% of 2,4,6-trichloro-1,3,5-triazine, silicon surface texturing with optimized pyramid heights ($5 mm), and a third step of drive-in after phosphosilicate glass (PSG) removal followed by oxide removal were investigated. A simple method of chemical etching adopted for edge isolation was optimized with edge etching of 5-10 mm, without any penetration of chemicals between the stacked wafers. The conversion efficiency, open-circuit voltage, short-circuit current, and fill factor of the cell fabricated with the optimized process were a maximum of 17.12%, 618.4 mV, 5.32 A, and 77% under AM1.5 conditions, respectively.
Journal of Non-crystalline Solids - J NON-CRYST SOLIDS, 2010
We have investigated surface passivation of n and p type silicon wafers, obtained by controlling ... more We have investigated surface passivation of n and p type silicon wafers, obtained by controlling silicon–hydrogen bonding and fixed charge densities with the use of hydrogenated SiNx films. The hydrogenated SiNx films were deposited by single PECVD at 13.56MHz with SiH4/NH3 gas mixture. The hydrogenated SiNx films of refractive indices 2.55–1.92 and high optical band-gap (>3.1eV) were obtained by varying the hydrogenated SiNx film composition. The fixed charge densities, hydrogen-bonding and carrier lifetime performance in n and p type silicon wafer were analyzed. The highest fixed positive charge of 2.66×1012 (cm−2) was for the hydrogenated SiNx film composition of 1.21. Fourier transform infrared spectroscopy measurement was carried out to evaluate the bonding concentration of Si–H and N–H. The minority carrier lifetimes of the hydrogenated SiNx passivated silicon wafers were up to 153μs and 84μs for p and n type, respectively. Mechanism of surface passivation depends on the ty...
Current Applied …, 2010
Indium tin oxide (ITO) films of low resistivity, high transmittance and good figure of merit were... more Indium tin oxide (ITO) films of low resistivity, high transmittance and good figure of merit were prepared by radio frequency magnetron sputtering, at different substrate temperatures (T s) under such a high k/d value and used as anti-reflection layer in heterojunction solar cells. For film deposition in the T s range 150°C < T s 6 250°C, XRD shows that coexistence of the h1 0 0i and h1 1 1i textures. The resistivity and Hall mobility of ITO films were improved due to thermally induced crystallization. However, carrier concentration of these ITO films is sensitive to the T s. We attributed these effects to the Ar + ions bombardment and differing adatom mobility of the heated atoms on the substrate under such a high k/d value. Those ITO films were used to fabricate single-side heterojunction solar cells. As the T s is increased, the device performance improves and the best photo voltage parameters of the device were found to be V oc = 640 mV, J sc = 36.90 mA/cm 2 , FF = 0.71, g = 16.3% for T s = 200°C. The decrease in performance beyond the T s of 200°C is attributed to hydrogen effusion to the defect in emitter layer. We noted that the figure of merit value of ITO films was reflected in the performance of devices.
Journal of the …, 2011
We fabricated hydrogenated amorphous silicon/crystalline silicon (a-Si: H/c-Si) heterojunction so... more We fabricated hydrogenated amorphous silicon/crystalline silicon (a-Si: H/c-Si) heterojunction solar cells with different intrinsic buffer layers, to elucidate the effect of the energy band gap, as well as passivation quality on the performance of the a-Si: H/c-Si ...
Vacuum, 2009
Silicon oxide (SiO x) thin films have been deposited at a substrate temperature of 300 C by induc... more Silicon oxide (SiO x) thin films have been deposited at a substrate temperature of 300 C by inductivelycoupled plasma chemical vapor deposition (ICP-CVD) using N 2 O/SiH 4 plasma. The effect of N 2 O/SiH 4 flow ratios on SiO x film properties and silicon surface passivation were investigated. Initially, the deposition rate increased up to the N 2 O/SiH 4 flow ratio of 2/1, and then decreased with the further increase in N 2 O/ SiH 4 flow ratio. Silicon oxide films with refractive indices of 1.47-2.64 and high optical band-gap values (>3.3 eV) were obtained by varying the nitrous oxide to silane gas ratios. The measured density of the interface states for films was found to have minimum value of 4.3 Â 10 11 eV À1 cm À2. The simultaneous highest s eff and lowest density of interface states indicated that the formation of hydrogen bonds at the SiO x /c-Si interface played an important role in surface passivation of p-type silicon.
Solid-State Electronics, 2011
Effective memory performance of the nonvolatile memory/thin film transistor (NVM/TFT) devices nee... more Effective memory performance of the nonvolatile memory/thin film transistor (NVM/TFT) devices needs good TFT characteristics. The reduction in leakage current of the TFT devices was accomplished with the gate offset (GOF) structure. A simplified fabrication process for the GOF NVM is ...
Journal of The Electrochemical Society, 2011
The fabrication of amorphous silicon/crystalline silicon (a-Si:H/c-Si) heterojunction solar cell ... more The fabrication of amorphous silicon/crystalline silicon (a-Si:H/c-Si) heterojunction solar cell and an understanding of the fundamental conduction mechanism in the device are presented. In the first part, the effect of intrinsic amorphous silicon [a-Si:H(i)] layer ...
Journal of The Electrochemical Society, 2011
We fabricated hydrogenated amorphous silicon/crystalline silicon (a-Si: H/c-Si) heterojunction so... more We fabricated hydrogenated amorphous silicon/crystalline silicon (a-Si: H/c-Si) heterojunction solar cells with different intrinsic buffer layers, to elucidate the effect of the energy band gap, as well as passivation quality on the performance of the a-Si: H/c-Si ...
Current Applied Physics, 2010
Solar Energy, 2010
The influence of various parameters such as buffer intrinsic layers, back-surface fields, densiti... more The influence of various parameters such as buffer intrinsic layers, back-surface fields, densities of interface defects (Dit), the resistivity of p-type silicon substrates (ρ) and then work function of transparent conductive oxide (ϕTCO) on heterojunction with intrinsic thin-...
A red emitting ZnO·Y 2 O 3 :Eu phosphor has been prepared using pyrolysis technique at temperatur... more A red emitting ZnO·Y 2 O 3 :Eu phosphor has been prepared using pyrolysis technique at temperatures ≤1000 °C. When NH 4 Cl was used as an ingredient, its luminescence efficiency was quite high indicating that Cl − ions act as charge compensators since the introduction of Y 3+ and Eu 3+ cations in ZnO lattice demands the introduction of equal amount of excess anions. However, Na + or Li + quenches the luminescence efficiency of ZnO·Y 2 O 3 :Eu. Due to ZnO host absorption, the excitation peaks of ZnO·Y 2 O 3 :Eu phosphor near 260 nm and 394 nm are suppressed while the one at 468 nm is intense. This red emitting phosphor may find applications when monochromatic excitation such as lasers are involved. XRD data of (Zn 0.93 Y 0.07 )O z :Eu 3+ ,Cl − shows the presence of the ZnO phase as well as the Y 2 O 3 phase. It shows that Y 2 O 3 forms a sublattice within ZnO host. This is supported by the PL data of (Zn 0.93 Y 0.07 )O z :Eu 3+ ,Cl − which showed no significant change in the PL effic...
Solid-State Electronics, 2011
Effective memory performance of the nonvolatile memory/thin film transistor (NVM/TFT) devices nee... more Effective memory performance of the nonvolatile memory/thin film transistor (NVM/TFT) devices needs good TFT characteristics. The reduction in leakage current of the TFT devices was accomplished with the gate offset (GOF) structure. A simplified fabrication process for the GOF NVM is ...
Indian Journal of Pure and Applied Physics
ZnO grown under reducing condition is always Zn excess. These Zn atoms are positioned at intersti... more ZnO grown under reducing condition is always Zn excess. These Zn atoms are positioned at interstitial sites due to the escape of oxygen from ZnO. The oxygen vacancies created by alkali metal dopants in ZnO play a major role in its green luminescence. This is understood on the basis of charge transfer between Zn interstitials and neighbouring oxygen vacancies caused by the doping of monovalent ions such as Li, Na or K at divalent Zn lattice sites followed by Stokes shifted emission. 1 Introduction Wurtzitic zinc oxide (ZnO) has received considerable attention because of its unique optical, semiconducting, piezoelectric and magnetic properties. It is a direct wide band gap (3.4 eV) semiconductor with large exciton binding energy of 60 meV at room temperature. Light emitting diodes made of ZnO are cheaper to manufacture than GaN and its white light is brighter and more like sunlight. Adding phosphorous to ZnO leads to p-type semiconducting material while oxygen vacancies give n-type Zn...
The process conditions for a high-efficiency and low cost crystalline silicon solar cell were opt... more The process conditions for a high-efficiency and low cost crystalline silicon solar cell were optimized. Novel approaches such as wafer cleaning and saw-damage removal using 0.5 wt% of 2,4,6-trichloro-1,3,5-triazine, silicon surface texturing with optimized pyramid heights ($5 mm), and a third step of drive-in after phosphosilicate glass (PSG) removal followed by oxide removal were investigated. A simple method of chemical etching adopted for edge isolation was optimized with edge etching of 5-10 mm, without any penetration of chemicals between the stacked wafers. The conversion efficiency, open-circuit voltage, short-circuit current, and fill factor of the cell fabricated with the optimized process were a maximum of 17.12%, 618.4 mV, 5.32 A, and 77% under AM1.5 conditions, respectively.
Journal of Non-crystalline Solids - J NON-CRYST SOLIDS, 2010
We have investigated surface passivation of n and p type silicon wafers, obtained by controlling ... more We have investigated surface passivation of n and p type silicon wafers, obtained by controlling silicon–hydrogen bonding and fixed charge densities with the use of hydrogenated SiNx films. The hydrogenated SiNx films were deposited by single PECVD at 13.56MHz with SiH4/NH3 gas mixture. The hydrogenated SiNx films of refractive indices 2.55–1.92 and high optical band-gap (>3.1eV) were obtained by varying the hydrogenated SiNx film composition. The fixed charge densities, hydrogen-bonding and carrier lifetime performance in n and p type silicon wafer were analyzed. The highest fixed positive charge of 2.66×1012 (cm−2) was for the hydrogenated SiNx film composition of 1.21. Fourier transform infrared spectroscopy measurement was carried out to evaluate the bonding concentration of Si–H and N–H. The minority carrier lifetimes of the hydrogenated SiNx passivated silicon wafers were up to 153μs and 84μs for p and n type, respectively. Mechanism of surface passivation depends on the ty...
Current Applied …, 2010
Indium tin oxide (ITO) films of low resistivity, high transmittance and good figure of merit were... more Indium tin oxide (ITO) films of low resistivity, high transmittance and good figure of merit were prepared by radio frequency magnetron sputtering, at different substrate temperatures (T s) under such a high k/d value and used as anti-reflection layer in heterojunction solar cells. For film deposition in the T s range 150°C < T s 6 250°C, XRD shows that coexistence of the h1 0 0i and h1 1 1i textures. The resistivity and Hall mobility of ITO films were improved due to thermally induced crystallization. However, carrier concentration of these ITO films is sensitive to the T s. We attributed these effects to the Ar + ions bombardment and differing adatom mobility of the heated atoms on the substrate under such a high k/d value. Those ITO films were used to fabricate single-side heterojunction solar cells. As the T s is increased, the device performance improves and the best photo voltage parameters of the device were found to be V oc = 640 mV, J sc = 36.90 mA/cm 2 , FF = 0.71, g = 16.3% for T s = 200°C. The decrease in performance beyond the T s of 200°C is attributed to hydrogen effusion to the defect in emitter layer. We noted that the figure of merit value of ITO films was reflected in the performance of devices.
Journal of the …, 2011
We fabricated hydrogenated amorphous silicon/crystalline silicon (a-Si: H/c-Si) heterojunction so... more We fabricated hydrogenated amorphous silicon/crystalline silicon (a-Si: H/c-Si) heterojunction solar cells with different intrinsic buffer layers, to elucidate the effect of the energy band gap, as well as passivation quality on the performance of the a-Si: H/c-Si ...