Utpal Das | IIT Kanpur (original) (raw)
Papers by Utpal Das
Aerosol and Air Quality Research, 2011
Micro & Nano Letters, 2019
An inductively coupled C H 4 / H 2 plasma etching process for delineation of InAs/GaSb type-II su... more An inductively coupled C H 4 / H 2 plasma etching process for delineation of InAs/GaSb type-II superlattice pixels is presented. An optimised C H 4 / H 2 etch recipe without alternate O 2 plasma cleaning step showed an etch rate as high as 0.11 μm/min that results in smooth vertical sidewalls for the type-II superlattice pixel arrays with 10 μm pitch size and 2.4 μm deep trenches. At 70 K, the dark current density for the mesa etched + SU-8 polymer passivated type-II superlattice photodiodes was found to be 0.11 A/cm2 at an applied reverse bias voltage of 0.2 V. The activation energy of 13 meV obtained from the Arrhenius plot and a variable area diode array technique showed that the measured dark current is mainly attributed to bulk tunnelling current. This technique of mesa delineation for the type-II superlattice pixel arrays with small pitch size is a viable option in realising next-generation infrared focal plane arrays.
13th International Conference on Fiber Optics and Photonics, 2016
Embedded ring (ER) is fabricated on InGaAsP/InP multi-quantum wells using electron beam lithograp... more Embedded ring (ER) is fabricated on InGaAsP/InP multi-quantum wells using electron beam lithography and methane hydrogen reactive ion etching. Experimental findings of this ER are also compared with the theoretical study.
Conference Proceedings. LEOS'98. 11th Annual Meeting. IEEE Lasers and Electro-Optics Society 1998 Annual Meeting (Cat. No.98CH36243)
A model for refractive index change of F induced disordering of GaAsP-AlGaAs QWs shows that index... more A model for refractive index change of F induced disordering of GaAsP-AlGaAs QWs shows that index changes ~0.1-0.4 at 45 mins anneal provides 99% reflection efficiency of 500 μm long waveguide DBR
Journal of Applied Physics
SPIE Proceedings, 2015
A 775 nm femto-second laser annealed approach for the inter-pixel isolation, without mesa etching... more A 775 nm femto-second laser annealed approach for the inter-pixel isolation, without mesa etching, to reduce dark currents of type-II InAs/GaSb superlattice photodiodes is presented. A greater than two fold improvement of the pixel isolation and a corresponding reduction in the dark current are observed for laser annealed superlattice photodiodes with a 5.5 μm cutoff wavelength, operating at 10K. A higher band gap barrier material from the superlattice structure in the inter-pixel region is expected to form after femto-second laser annealing, which has been explained on the basis of a superlattice inter-diffusion model. The increase in inter-pixel barrier height at 10K is estimated to be ~ 4 meV in the laser annealed superlattice photodiodes.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1993
Abstract The first chemical beam epitaxial growth of InP, InGaP/InP strained layer superlattices ... more Abstract The first chemical beam epitaxial growth of InP, InGaP/InP strained layer superlattices (SLS) and InGaP/InAs/InGaP quantum wells using bisphosphinoethane and tertiarybutylarsine as group V sources is reported. Mirrorlike surface morphology and ...
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1992
... and heterostructures on (111)B GaAs Albert Chin and Paul Martin General Electric Electronics ... more ... and heterostructures on (111)B GaAs Albert Chin and Paul Martin General Electric Electronics Laboratory, Syracuse, New York 13221 U. Das University of Florida ... Modulation-doped heterostructures show a 77-K mobility of 145 500 cmVV s with a sheet density of 5.0x10й cm~ ...
IEEE Photonics Technology Letters, 2015
Impurity Free Quantum Well Intermixing (IFQWI) by cap layer thickness variation for InGaAsP/InP m... more Impurity Free Quantum Well Intermixing (IFQWI) by cap layer thickness variation for InGaAsP/InP multiquantum wells (MQWs) is reported for the first time. The blue-shift is observed to be enhanced or inhibited depending on the thickness of the ZrO2 cap layer used (100-600nm) for anneal conditions of 600-750°C for 40s. The group-V intermixing in InGaAsP/InP dominates the IFQWI resulting in a blue-shift of the MQW band gap and the blue-shift increases with increasing ZrO2 thickness to 400nm. A 600nm ZrO2 cap is found to inhibit the blue-shift. For higher anneal temperatures similar inhibition nature is observed, with larger blue-shifts. An inter-diffusion model shows that the diffusion length ratio for Group-V to Group-III initially increases from 1.25-1.6 for 100-400nm ZrO2 thickness, but decreases to 1.1 for 600nm ZrO2. This technique is promising for the fabrication of tapered waveguides for photonic integration of InGaAsP/InP by IFQWI.
Solid-State Electronics, 1986
A detailed study of strained single and multilayered In-containing III-V compounds grown by molec... more A detailed study of strained single and multilayered In-containing III-V compounds grown by molecular beam epitaxy, their characterization and determination of some important properties of guided wave devices and photodiodes in the 1 to 1.55 micron wavelength range using these materials is presented. The refractive index step of In(x)Ga(1-x)As/GaAs heterojunctions, necessary for optical confinement and guided wave applications, is calculated
16th International Workshop on Physics of Semiconductor Devices, 2012
ABSTRACT SiC nanocrystals of size 4×30×40nm have been fabricated on Si (100)3° by a low cost spin... more ABSTRACT SiC nanocrystals of size 4×30×40nm have been fabricated on Si (100)3° by a low cost spin-on technique in which Htermination produces smaller crystallites but larger crystallite density at the substrate surface steps. Low temperature photoluminescence and atomic force microscopy (AFM) confirms the formation of quantum dashes. It has been observed that the spin speed and H-termination plays a crucial role in the formation of quantized structures on Si.
Asia Optical Fiber Communication and Optoelectronic Exposition and Conference, 2008
Abstract This paper presents the work on InGaAsP/InP multi quantum well impurity intermixed waveg... more Abstract This paper presents the work on InGaAsP/InP multi quantum well impurity intermixed waveguide grating suitable for CWDM wavelength range. A channel bandwidth of 13nm and cross-talk in between-5dB to-10dB is obtained.
2012 7th International Conference on Electrical and Computer Engineering, 2012
ABSTRACT Integrated waveguide Bragg gratings have been designed and fabricated for CWDM wavelengt... more ABSTRACT Integrated waveguide Bragg gratings have been designed and fabricated for CWDM wavelengths using F implantation and annealed quantum well intermixing technique, compatible with microelectronics processing. The measured peaks are blue shifted by ~35nm from that of the design and FWHM width widened by ~1nm due to inaccuracies in the processing. The measured insertion loss is ~4dB.
2012 Photonics Global Conference (PGC), 2012
ABSTRACT This paper reports the ion implantation induced quantum well intermixing used to fabrica... more ABSTRACT This paper reports the ion implantation induced quantum well intermixing used to fabricate waveguide gratings for applications at CWDM wavelengths on InGaAsP/InP multi quantum well structure. The waveguide is fabricated using reactive ion etching (methane chemistry) with a surface roughness 2~3nm. Focused ion beam is used to open windows for fluorine implantation on titanium mask followed by anneal under forming gas environment. The transmission spectrum of the waveguide has been measured and found cross talks of -10dB among the adjacent channels. The insertion loss of the fabricated waveguide gratings is less than 5dB.
2005 Quantum Electronics and Laser Science Conference
Abstract The Bragg reflection coefficients suitable for a CWDM system have been calculated by usi... more Abstract The Bragg reflection coefficients suitable for a CWDM system have been calculated by using coupled mode theory based on perturbation obtained by impurity induced intermixing of quantum wells and analyzed for different order gratings.
16th International Workshop on Physics of Semiconductor Devices, 2012
InGaAsP/InP Multi Quantum Well (MQW) based rib waveguide (WG) multi-wavelength PIN type photodiod... more InGaAsP/InP Multi Quantum Well (MQW) based rib waveguide (WG) multi-wavelength PIN type photodiodes (PD) have been designed for Coarse Wavelength Division Multiplexing (CWDM) systems in which spatial bandgap tailoring have been accomplished by using post growth Fluorine (F) implanted QW Intermixing (QWI) as the integration mechanism. Two separate structures with different composition but same well widths are necessary to detect all CWDM wavelengths in which a In0.5540Ga0.4460As0.9489P0.0511/InP (15nm/15nm) MQW structure has a 14 channel coverage which spans from 1350-1610nm. The thicknesses of the i-MQW layer and different layers constituting the WG have been optimized to give a maximum efficiency of 22%. A carrier tunneling time of 20ps along with the transit time limited bandwidth of 86GHz gives a 3dB bandwidth of 43GHz by optimizing the i-MQW thickness and dopant concentration of the different layers of the waveguide. For all 18 channels insertion loss of 0.4-23dB has been obtained for a detection sensitivity of 21dB. Design issues related to the contact formation for extracting the photo-generated microwave power in such photodiodes have been presented along with few fabrication details of the integration process.
Optical and Quantum Electronics, 2010
Aerosol and Air Quality Research, 2011
Micro & Nano Letters, 2019
An inductively coupled C H 4 / H 2 plasma etching process for delineation of InAs/GaSb type-II su... more An inductively coupled C H 4 / H 2 plasma etching process for delineation of InAs/GaSb type-II superlattice pixels is presented. An optimised C H 4 / H 2 etch recipe without alternate O 2 plasma cleaning step showed an etch rate as high as 0.11 μm/min that results in smooth vertical sidewalls for the type-II superlattice pixel arrays with 10 μm pitch size and 2.4 μm deep trenches. At 70 K, the dark current density for the mesa etched + SU-8 polymer passivated type-II superlattice photodiodes was found to be 0.11 A/cm2 at an applied reverse bias voltage of 0.2 V. The activation energy of 13 meV obtained from the Arrhenius plot and a variable area diode array technique showed that the measured dark current is mainly attributed to bulk tunnelling current. This technique of mesa delineation for the type-II superlattice pixel arrays with small pitch size is a viable option in realising next-generation infrared focal plane arrays.
13th International Conference on Fiber Optics and Photonics, 2016
Embedded ring (ER) is fabricated on InGaAsP/InP multi-quantum wells using electron beam lithograp... more Embedded ring (ER) is fabricated on InGaAsP/InP multi-quantum wells using electron beam lithography and methane hydrogen reactive ion etching. Experimental findings of this ER are also compared with the theoretical study.
Conference Proceedings. LEOS'98. 11th Annual Meeting. IEEE Lasers and Electro-Optics Society 1998 Annual Meeting (Cat. No.98CH36243)
A model for refractive index change of F induced disordering of GaAsP-AlGaAs QWs shows that index... more A model for refractive index change of F induced disordering of GaAsP-AlGaAs QWs shows that index changes ~0.1-0.4 at 45 mins anneal provides 99% reflection efficiency of 500 μm long waveguide DBR
Journal of Applied Physics
SPIE Proceedings, 2015
A 775 nm femto-second laser annealed approach for the inter-pixel isolation, without mesa etching... more A 775 nm femto-second laser annealed approach for the inter-pixel isolation, without mesa etching, to reduce dark currents of type-II InAs/GaSb superlattice photodiodes is presented. A greater than two fold improvement of the pixel isolation and a corresponding reduction in the dark current are observed for laser annealed superlattice photodiodes with a 5.5 μm cutoff wavelength, operating at 10K. A higher band gap barrier material from the superlattice structure in the inter-pixel region is expected to form after femto-second laser annealing, which has been explained on the basis of a superlattice inter-diffusion model. The increase in inter-pixel barrier height at 10K is estimated to be ~ 4 meV in the laser annealed superlattice photodiodes.
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1993
Abstract The first chemical beam epitaxial growth of InP, InGaP/InP strained layer superlattices ... more Abstract The first chemical beam epitaxial growth of InP, InGaP/InP strained layer superlattices (SLS) and InGaP/InAs/InGaP quantum wells using bisphosphinoethane and tertiarybutylarsine as group V sources is reported. Mirrorlike surface morphology and ...
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1992
... and heterostructures on (111)B GaAs Albert Chin and Paul Martin General Electric Electronics ... more ... and heterostructures on (111)B GaAs Albert Chin and Paul Martin General Electric Electronics Laboratory, Syracuse, New York 13221 U. Das University of Florida ... Modulation-doped heterostructures show a 77-K mobility of 145 500 cmVV s with a sheet density of 5.0x10й cm~ ...
IEEE Photonics Technology Letters, 2015
Impurity Free Quantum Well Intermixing (IFQWI) by cap layer thickness variation for InGaAsP/InP m... more Impurity Free Quantum Well Intermixing (IFQWI) by cap layer thickness variation for InGaAsP/InP multiquantum wells (MQWs) is reported for the first time. The blue-shift is observed to be enhanced or inhibited depending on the thickness of the ZrO2 cap layer used (100-600nm) for anneal conditions of 600-750°C for 40s. The group-V intermixing in InGaAsP/InP dominates the IFQWI resulting in a blue-shift of the MQW band gap and the blue-shift increases with increasing ZrO2 thickness to 400nm. A 600nm ZrO2 cap is found to inhibit the blue-shift. For higher anneal temperatures similar inhibition nature is observed, with larger blue-shifts. An inter-diffusion model shows that the diffusion length ratio for Group-V to Group-III initially increases from 1.25-1.6 for 100-400nm ZrO2 thickness, but decreases to 1.1 for 600nm ZrO2. This technique is promising for the fabrication of tapered waveguides for photonic integration of InGaAsP/InP by IFQWI.
Solid-State Electronics, 1986
A detailed study of strained single and multilayered In-containing III-V compounds grown by molec... more A detailed study of strained single and multilayered In-containing III-V compounds grown by molecular beam epitaxy, their characterization and determination of some important properties of guided wave devices and photodiodes in the 1 to 1.55 micron wavelength range using these materials is presented. The refractive index step of In(x)Ga(1-x)As/GaAs heterojunctions, necessary for optical confinement and guided wave applications, is calculated
16th International Workshop on Physics of Semiconductor Devices, 2012
ABSTRACT SiC nanocrystals of size 4×30×40nm have been fabricated on Si (100)3° by a low cost spin... more ABSTRACT SiC nanocrystals of size 4×30×40nm have been fabricated on Si (100)3° by a low cost spin-on technique in which Htermination produces smaller crystallites but larger crystallite density at the substrate surface steps. Low temperature photoluminescence and atomic force microscopy (AFM) confirms the formation of quantum dashes. It has been observed that the spin speed and H-termination plays a crucial role in the formation of quantized structures on Si.
Asia Optical Fiber Communication and Optoelectronic Exposition and Conference, 2008
Abstract This paper presents the work on InGaAsP/InP multi quantum well impurity intermixed waveg... more Abstract This paper presents the work on InGaAsP/InP multi quantum well impurity intermixed waveguide grating suitable for CWDM wavelength range. A channel bandwidth of 13nm and cross-talk in between-5dB to-10dB is obtained.
2012 7th International Conference on Electrical and Computer Engineering, 2012
ABSTRACT Integrated waveguide Bragg gratings have been designed and fabricated for CWDM wavelengt... more ABSTRACT Integrated waveguide Bragg gratings have been designed and fabricated for CWDM wavelengths using F implantation and annealed quantum well intermixing technique, compatible with microelectronics processing. The measured peaks are blue shifted by ~35nm from that of the design and FWHM width widened by ~1nm due to inaccuracies in the processing. The measured insertion loss is ~4dB.
2012 Photonics Global Conference (PGC), 2012
ABSTRACT This paper reports the ion implantation induced quantum well intermixing used to fabrica... more ABSTRACT This paper reports the ion implantation induced quantum well intermixing used to fabricate waveguide gratings for applications at CWDM wavelengths on InGaAsP/InP multi quantum well structure. The waveguide is fabricated using reactive ion etching (methane chemistry) with a surface roughness 2~3nm. Focused ion beam is used to open windows for fluorine implantation on titanium mask followed by anneal under forming gas environment. The transmission spectrum of the waveguide has been measured and found cross talks of -10dB among the adjacent channels. The insertion loss of the fabricated waveguide gratings is less than 5dB.
2005 Quantum Electronics and Laser Science Conference
Abstract The Bragg reflection coefficients suitable for a CWDM system have been calculated by usi... more Abstract The Bragg reflection coefficients suitable for a CWDM system have been calculated by using coupled mode theory based on perturbation obtained by impurity induced intermixing of quantum wells and analyzed for different order gratings.
16th International Workshop on Physics of Semiconductor Devices, 2012
InGaAsP/InP Multi Quantum Well (MQW) based rib waveguide (WG) multi-wavelength PIN type photodiod... more InGaAsP/InP Multi Quantum Well (MQW) based rib waveguide (WG) multi-wavelength PIN type photodiodes (PD) have been designed for Coarse Wavelength Division Multiplexing (CWDM) systems in which spatial bandgap tailoring have been accomplished by using post growth Fluorine (F) implanted QW Intermixing (QWI) as the integration mechanism. Two separate structures with different composition but same well widths are necessary to detect all CWDM wavelengths in which a In0.5540Ga0.4460As0.9489P0.0511/InP (15nm/15nm) MQW structure has a 14 channel coverage which spans from 1350-1610nm. The thicknesses of the i-MQW layer and different layers constituting the WG have been optimized to give a maximum efficiency of 22%. A carrier tunneling time of 20ps along with the transit time limited bandwidth of 86GHz gives a 3dB bandwidth of 43GHz by optimizing the i-MQW thickness and dopant concentration of the different layers of the waveguide. For all 18 channels insertion loss of 0.4-23dB has been obtained for a detection sensitivity of 21dB. Design issues related to the contact formation for extracting the photo-generated microwave power in such photodiodes have been presented along with few fabrication details of the integration process.
Optical and Quantum Electronics, 2010