L. Kolaklieva - Academia.edu (original) (raw)
Papers by L. Kolaklieva
In the present work, TiN was deposited on stainless steel (SS420) using the cathode-spot arc meth... more In the present work, TiN was deposited on stainless steel (SS420) using the cathode-spot arc method and the effect of the N2 flow and the chamber pressure on the coating microstructure was studied. TEM examination showed a columnar growth of TiN crystals with different size, while the average thickness was about 0.7 to 1.05 mum and increased as the chamber pressure increased.
Materials Science Forum, 2004
Page 1. High temperature and high power stability investigation of Al-based ohmic contacts to p-t... more Page 1. High temperature and high power stability investigation of Al-based ohmic contacts to p-type 4H-SiC R. Kakanakov 1) , L. Kasamakova Kolaklieva 1) , N. Hristeva 1) , G. Lepoeva 1) , JB Gomes 2) , I. Avramova 2) , Ts. ... Acad. G. Bonchev str., bl.11, 1113 Sofia, Bulgaria ...
2010 27th International Conference on Microelectronics Proceedings, 2010
The electrical properties of Ti/Al-based ohmic contacts with two types of barrier films, Ti and M... more The electrical properties of Ti/Al-based ohmic contacts with two types of barrier films, Ti and Mo, are investigated in dependence on the Ti/Al ratio and the type of the barrier layer. They are explored by I-V, resistivity and surface potential measurements. It is found out that the Ti/Al/Ti/Au contact composition with Ti/Al ratio of 0.43 exhibits the lowest contact resistivity and smallest variations of the surface potential amplitude. The contacts with the same Ti/Al ratio and a Mo barrier layer show better surface morphology but poorer electrical properties.
2004 24th International Conference on Microelectronics (IEEE Cat. No.04TH8716), 2004
A new Au/Ti(70%)/Al(30%) composition has been proposed and investigated as an ohmic contact to p-... more A new Au/Ti(70%)/Al(30%) composition has been proposed and investigated as an ohmic contact to p-type SiC. The dependence of the resistivity on the annealing conditions has been studied at temperatures ranging from 700 °C to 950 °C. The lowest contact resistivity of 1.40 × 10-5 Ω.cm2 is achieved after annealing at 900 °C. The study of the thermal properties determines the contact stability during the ageing at temperatures of 500-700 °C, operating temperatures up to 450 °C and current densities of 103 A/cm2. XPS depth analysis of annealed and aged contacts has been performed to understand the origin of the ohmic properties and the thermal and power stability observed.
2002 23rd International Conference on Microelectronics. Proceedings (Cat. No.02TH8595), 2002
Ti/Al/p-SiC and Ni/n-SiC ohmic contacts with improved electrical and thermal properties in respec... more Ti/Al/p-SiC and Ni/n-SiC ohmic contacts with improved electrical and thermal properties in respect to their application in high power and high temperature SiC devices are reported in this work. Contact resistivity as a function of annealing was investigated over the temperature range of 700 o C -950 o C. The lowest resistivity of 1.42x10 -5 Ω.cm 2 for the Ti/Al contact was obtained after annealing at 900 o C while for the Ni contact the lowest resistivity of 4.9x10 -6 Ω.cm 2 was achieved at 950 o C.
2006 25th International Conference on Microelectronics, 2006
4H-SiC p-i-n diodes with very good switching characteristics have been developed and used in high... more 4H-SiC p-i-n diodes with very good switching characteristics have been developed and used in high speed modulator in the Q-band range. The diode has a voltage drop at forward direction as low as 3.4 V at current density of 100 A/cm2. Leakage currents less than 1 muA are measured at reverse voltages of 1200 V and 1700 V in air and a SF6 atmosphere, respectively. The operating speed of the modulator is 5-7 ns which make it very perspective for applications in Q-band range. In the frequency range of 26-38 GHz, the modulator has insertion losses not more than 2 dB and isolation losses not less than 20 dB
Materials Science Forum, 2003
ABSTRACT
Materials Science Forum, 2003
ABSTRACT
2008 26th International Conference on Microelectronics, 2008
Properties of spry pyrolysed CdS layers were changed purposefully using annealing by a pulsed-las... more Properties of spry pyrolysed CdS layers were changed purposefully using annealing by a pulsed-laser in oxygen ambient. The structural, phase and electrical characteristics before and after annealing have been compared. The layer surface has been studied by SEM, XRD and XPS analyses. The electrical and optic parameters have been measured as well. Layers with different structure and electro-optical characteristics have
Semiconductors, 2005
The possibility of fabricating heavily doped ( N a -N d ≥ 1 × 10 19 cm -3 ) p + -4 H -SiC layers ... more The possibility of fabricating heavily doped ( N a -N d ≥ 1 × 10 19 cm -3 ) p + -4 H -SiC layers on CVD-grown lightly doped n -4 H -SiC layers by sublimation epitaxy has been demonstrated. It is shown that a Au/Pd/Ti/Pd contact, which combines a low specific contact resistance (~2 × 10 -5 Ω cm 2 ) with high thermal stability (up to 700 ° C), is the optimal contact to p-4 H -SiC. The p -n structures obtained are used to fabricate packaged diodes with a breakdown voltage of up to 1400 V.
Progress in Photovoltaics: Research and Applications, 2013
In this study, we have investigated the Hall majority carrier mobility of p-type, compensated mul... more In this study, we have investigated the Hall majority carrier mobility of p-type, compensated multicrystalline solar grade silicon (SoG-Si) wafers for solar cells in the temperature range 70-373 K. At low temperature (~70 K) the difference in the mobilities measured for the compensated and the uncompensated reference samples is the highest, and the measured mobility shows dependence on the compensation ratio. Mobilities decrease with increasing temperature, and towards room temperature, the mobilities of the different samples are in the same range. The measurements show that, for these samples, the contribution from lattice scattering is dominating over ionized impurity scattering at room temperature. In the range of interest for silicon solar cells (above room temperature), the trend in carrier mobility is similar for all the samples, and the measured value for the sample with low compensation ratio and low doping density is comparable to the uncompensated references. A comparison of resistivity and majority carrier density measured by the Hall setup at room temperature and by four-point probe and glow discharge mass spectroscopy, respectively, is reported as well.
Journal of Thermal Analysis and Calorimetry, 2015
2012 28th International Conference on Microelectronics Proceedings, 2012
Four types of Mo-based ohmic contacts with a varied Al and Ti content are developed and investiga... more Four types of Mo-based ohmic contacts with a varied Al and Ti content are developed and investigated regarding the ohmic properties, surface morphology and edge acuity. It is found out that the Ti/Mo/Ti/Au metallization combines the lowest contact resistivity of 8.8x10 -6 Ω.cm 2 and low surface roughness of 3.8 nm. The presence of Al in the contact composition does not improve the electrical properties and the surface morphology. Its effect on these properties depends strongly on the Ti/Al ratio in the contact composition.
2014 29th International Conference on Microelectronics Proceedings - MIEL 2014, 2014
ABSTRACT The composition and structure of TiAl-based metallizations have been investigated depend... more ABSTRACT The composition and structure of TiAl-based metallizations have been investigated depending on the Ti and Mo barriers. It is found out that the contact resistivity depends mainly on the Ti/Al ratio. The lowest contact resistivity of 4×10-6 Q.cm2 for a Ti barrier and 7×10-6 Q.cm2 for a Mo barrier is obtained at a Ti/Al ratio of 0.43 after annealing at 800°C. The XPS and TEM analyses reveal that Mo does not affect as an effective barrier for the Au in diffusion and Al out diffusion during annealing. The intensive diffusion processes lead to the formation of the semimetal TiN compound at the interface and intermetallic phases of Au, Al and Ti, which structure and composition depend on the barrier metal.
2008 26th International Conference on Microelectronics, 2008
ABSTRACT The role of the former-Ti/Al ratio in the nanolayered ohmic contacts to GaN/AlGaN HEMT s... more ABSTRACT The role of the former-Ti/Al ratio in the nanolayered ohmic contacts to GaN/AlGaN HEMT structures has been studied for three ratios: (30/70) wt.%, (50/50) wt.% and (70/30) wt.%. The dependence of the electrical properties and surface morphology on the initial contact composition and annealing conditions has been investigated. Lowest contact resistivity of 4.22times105 Omegacm2 has been achieved for Ti/Al (30/70 wt.%) and Ti/Al (50/50 wt.%) contacts to semi-insulating GaN/AlGaN heterostructures. Smoothest contact surface and most narrow contact periphery have been obtained with a Ti/Al (70/30 wt.%) contact indicating that increase of the Ti/Al ratio improves the contact morphology. The contact composition with former-Ti/Al ratio of (50/50) wt.% has been found to fulfill the best both requirements for low resistivity and a smooth surface of the contact.
Materials Science Forum, 2009
In the present work, TiN was deposited on stainless steel (SS420) using the cathode-spot arc meth... more In the present work, TiN was deposited on stainless steel (SS420) using the cathode-spot arc method and the effect of the N2 flow and the chamber pressure on the coating microstructure was studied. TEM examination showed a columnar growth of TiN crystals with different size, while the average thickness was about 0.7 to 1.05 mum and increased as the chamber pressure increased.
Materials Science Forum, 2004
Page 1. High temperature and high power stability investigation of Al-based ohmic contacts to p-t... more Page 1. High temperature and high power stability investigation of Al-based ohmic contacts to p-type 4H-SiC R. Kakanakov 1) , L. Kasamakova Kolaklieva 1) , N. Hristeva 1) , G. Lepoeva 1) , JB Gomes 2) , I. Avramova 2) , Ts. ... Acad. G. Bonchev str., bl.11, 1113 Sofia, Bulgaria ...
2010 27th International Conference on Microelectronics Proceedings, 2010
The electrical properties of Ti/Al-based ohmic contacts with two types of barrier films, Ti and M... more The electrical properties of Ti/Al-based ohmic contacts with two types of barrier films, Ti and Mo, are investigated in dependence on the Ti/Al ratio and the type of the barrier layer. They are explored by I-V, resistivity and surface potential measurements. It is found out that the Ti/Al/Ti/Au contact composition with Ti/Al ratio of 0.43 exhibits the lowest contact resistivity and smallest variations of the surface potential amplitude. The contacts with the same Ti/Al ratio and a Mo barrier layer show better surface morphology but poorer electrical properties.
2004 24th International Conference on Microelectronics (IEEE Cat. No.04TH8716), 2004
A new Au/Ti(70%)/Al(30%) composition has been proposed and investigated as an ohmic contact to p-... more A new Au/Ti(70%)/Al(30%) composition has been proposed and investigated as an ohmic contact to p-type SiC. The dependence of the resistivity on the annealing conditions has been studied at temperatures ranging from 700 °C to 950 °C. The lowest contact resistivity of 1.40 × 10-5 Ω.cm2 is achieved after annealing at 900 °C. The study of the thermal properties determines the contact stability during the ageing at temperatures of 500-700 °C, operating temperatures up to 450 °C and current densities of 103 A/cm2. XPS depth analysis of annealed and aged contacts has been performed to understand the origin of the ohmic properties and the thermal and power stability observed.
2002 23rd International Conference on Microelectronics. Proceedings (Cat. No.02TH8595), 2002
Ti/Al/p-SiC and Ni/n-SiC ohmic contacts with improved electrical and thermal properties in respec... more Ti/Al/p-SiC and Ni/n-SiC ohmic contacts with improved electrical and thermal properties in respect to their application in high power and high temperature SiC devices are reported in this work. Contact resistivity as a function of annealing was investigated over the temperature range of 700 o C -950 o C. The lowest resistivity of 1.42x10 -5 Ω.cm 2 for the Ti/Al contact was obtained after annealing at 900 o C while for the Ni contact the lowest resistivity of 4.9x10 -6 Ω.cm 2 was achieved at 950 o C.
2006 25th International Conference on Microelectronics, 2006
4H-SiC p-i-n diodes with very good switching characteristics have been developed and used in high... more 4H-SiC p-i-n diodes with very good switching characteristics have been developed and used in high speed modulator in the Q-band range. The diode has a voltage drop at forward direction as low as 3.4 V at current density of 100 A/cm2. Leakage currents less than 1 muA are measured at reverse voltages of 1200 V and 1700 V in air and a SF6 atmosphere, respectively. The operating speed of the modulator is 5-7 ns which make it very perspective for applications in Q-band range. In the frequency range of 26-38 GHz, the modulator has insertion losses not more than 2 dB and isolation losses not less than 20 dB
Materials Science Forum, 2003
ABSTRACT
Materials Science Forum, 2003
ABSTRACT
2008 26th International Conference on Microelectronics, 2008
Properties of spry pyrolysed CdS layers were changed purposefully using annealing by a pulsed-las... more Properties of spry pyrolysed CdS layers were changed purposefully using annealing by a pulsed-laser in oxygen ambient. The structural, phase and electrical characteristics before and after annealing have been compared. The layer surface has been studied by SEM, XRD and XPS analyses. The electrical and optic parameters have been measured as well. Layers with different structure and electro-optical characteristics have
Semiconductors, 2005
The possibility of fabricating heavily doped ( N a -N d ≥ 1 × 10 19 cm -3 ) p + -4 H -SiC layers ... more The possibility of fabricating heavily doped ( N a -N d ≥ 1 × 10 19 cm -3 ) p + -4 H -SiC layers on CVD-grown lightly doped n -4 H -SiC layers by sublimation epitaxy has been demonstrated. It is shown that a Au/Pd/Ti/Pd contact, which combines a low specific contact resistance (~2 × 10 -5 Ω cm 2 ) with high thermal stability (up to 700 ° C), is the optimal contact to p-4 H -SiC. The p -n structures obtained are used to fabricate packaged diodes with a breakdown voltage of up to 1400 V.
Progress in Photovoltaics: Research and Applications, 2013
In this study, we have investigated the Hall majority carrier mobility of p-type, compensated mul... more In this study, we have investigated the Hall majority carrier mobility of p-type, compensated multicrystalline solar grade silicon (SoG-Si) wafers for solar cells in the temperature range 70-373 K. At low temperature (~70 K) the difference in the mobilities measured for the compensated and the uncompensated reference samples is the highest, and the measured mobility shows dependence on the compensation ratio. Mobilities decrease with increasing temperature, and towards room temperature, the mobilities of the different samples are in the same range. The measurements show that, for these samples, the contribution from lattice scattering is dominating over ionized impurity scattering at room temperature. In the range of interest for silicon solar cells (above room temperature), the trend in carrier mobility is similar for all the samples, and the measured value for the sample with low compensation ratio and low doping density is comparable to the uncompensated references. A comparison of resistivity and majority carrier density measured by the Hall setup at room temperature and by four-point probe and glow discharge mass spectroscopy, respectively, is reported as well.
Journal of Thermal Analysis and Calorimetry, 2015
2012 28th International Conference on Microelectronics Proceedings, 2012
Four types of Mo-based ohmic contacts with a varied Al and Ti content are developed and investiga... more Four types of Mo-based ohmic contacts with a varied Al and Ti content are developed and investigated regarding the ohmic properties, surface morphology and edge acuity. It is found out that the Ti/Mo/Ti/Au metallization combines the lowest contact resistivity of 8.8x10 -6 Ω.cm 2 and low surface roughness of 3.8 nm. The presence of Al in the contact composition does not improve the electrical properties and the surface morphology. Its effect on these properties depends strongly on the Ti/Al ratio in the contact composition.
2014 29th International Conference on Microelectronics Proceedings - MIEL 2014, 2014
ABSTRACT The composition and structure of TiAl-based metallizations have been investigated depend... more ABSTRACT The composition and structure of TiAl-based metallizations have been investigated depending on the Ti and Mo barriers. It is found out that the contact resistivity depends mainly on the Ti/Al ratio. The lowest contact resistivity of 4×10-6 Q.cm2 for a Ti barrier and 7×10-6 Q.cm2 for a Mo barrier is obtained at a Ti/Al ratio of 0.43 after annealing at 800°C. The XPS and TEM analyses reveal that Mo does not affect as an effective barrier for the Au in diffusion and Al out diffusion during annealing. The intensive diffusion processes lead to the formation of the semimetal TiN compound at the interface and intermetallic phases of Au, Al and Ti, which structure and composition depend on the barrier metal.
2008 26th International Conference on Microelectronics, 2008
ABSTRACT The role of the former-Ti/Al ratio in the nanolayered ohmic contacts to GaN/AlGaN HEMT s... more ABSTRACT The role of the former-Ti/Al ratio in the nanolayered ohmic contacts to GaN/AlGaN HEMT structures has been studied for three ratios: (30/70) wt.%, (50/50) wt.% and (70/30) wt.%. The dependence of the electrical properties and surface morphology on the initial contact composition and annealing conditions has been investigated. Lowest contact resistivity of 4.22times105 Omegacm2 has been achieved for Ti/Al (30/70 wt.%) and Ti/Al (50/50 wt.%) contacts to semi-insulating GaN/AlGaN heterostructures. Smoothest contact surface and most narrow contact periphery have been obtained with a Ti/Al (70/30 wt.%) contact indicating that increase of the Ti/Al ratio improves the contact morphology. The contact composition with former-Ti/Al ratio of (50/50) wt.% has been found to fulfill the best both requirements for low resistivity and a smooth surface of the contact.
Materials Science Forum, 2009