The Experts below are selected from a list of 63 Experts worldwide ranked by ideXlab platform
Steven P. Denbaars - One of the best experts on this subject based on the ideXlab platform.
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high speed performance of iii nitride laser diode grown on 2021 Semipolar Plane for visible light communication
IEEE Photonics Conference, 2016Co-Authors: Chong Zhang, DANIEL BECERRA, Robert M. Farrell, Shuji Nakamura, Sang Ho Oh, John E. Bowers, James S. Speck, Steven P. DenbaarsAbstract:III-nitride light emitting diodes (LEDs) have been used for many applications covering the spectrum of ultraviolet (UV) to visible light (VL). Despite of significant improvements on solid-state lighting, LEDs still suffer significant efficiency loss at high carrier density, commonly referred as "efficiency droop" [1]. However, compared to LEDs, laser diodes (LDs) have higher power per chip and the absence of efficiency droop above lasing threshold. In addition to the advantage of solid-state lighting, LDs can be modulated at much higher frequency than LEDs.
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High speed performance of III-nitride laser diode grown on (2021) Semipolar Plane for visible light communication
2016 IEEE Photonics Conference (IPC), 2016Co-Authors: Changmin Lee, DANIEL BECERRA, Seunggeun Lee, Robert M. Farrell, Shuji Nakamura, Sang Ho Oh, Chong Zhang, John E. Bowers, James S. Speck, Steven P. DenbaarsAbstract:Summary form only given. III-nitride light emitting diodes (LEDs) have been used for many applications covering the spectrum of ultraviolet (UV) to visible light (VL). Despite of significant improvements on solid-state lighting, LEDs still suffer significant efficiency loss at high carrier density, commonly referred as "efficiency droop". However, compared to LEDs, laser diodes (LDs) have higher power per chip and the absence of efficiency droop above lasing threshold. In addition to the advantage of solid-state lighting, LDs can be modulated at much higher frequency than LEDs. For visible light communication (VLC) or light fidelity (LiFi), typical LEDs have only 10 ~ 100 MHz of the modulation bandwidth due to the relatively long carrier lifetime and large parasitic effect even though recently reported micro LEDs can have smaller parasitic effect. The low modulation bandwidth on LEDs causes not only low data rates but also the significantly limited to slow phosphor response for white lighting. However, recent our studies on laser-based LiFi shown that GHz operating laser has high data rate as well as almost no phosphor limit in white lighting data transmission for GHz range. In our study, we investigated high-speed characteristics of 410 nm violet continuous-wave (CW) ridge laser diode grown on (202̅1̅) Plane. The ridge laser epitaxial structure was grown on free standing bulk GaN Semipolar (202̅1̅) by MOCVD. The active region consists of a 4-period undoped In0.1Ga0.9N/GaN (3.5 nm/7 nm) multi quantum well (MQW). Symmetrical In0.025Ga0.97In0.1Ga0.9N/GaN5N waveguiding layers on each p- and n-side give optical confinement factor of 0.023. The top-side n-contact design of 1200 m long and 2 m wide cavity was fabricated for low voltage as well as direct ground-signal (GS) RF probing. The light-current-voltage (LIV) curve- on CW operation and the spectra of different injection current were measured at 15 °C. The threshold current and threshold current density in CW were 150 mA and 6.25 kA/cm2, respectively. The frequency response of photodetector (PD) was measured by frequency doubled 410 nm pulses from a mode-locked TiSapphire laser since initial measurement of - 3 dB bandwidth of the LD was only 4.13 GHz with significant roll-off due to the system limit. By correcting the frequency response of LD, 5 GHz of bandwidth, which is highest bandwidth reported for blue-violet LDs, was obtained even though this bandwidth is due to the noise floor from PD limit. The slope efficiency of resonance frequency versus square root of pumping current was well-fitted with 0.51 GHz/mA1/2, resulting in the differential gain of 3.16 × 10-16 cm2. The measured damping factor of 0.35 ns was calculated for the maximum intrinsic bandwidth of 25.6 GHz. High 5 Gbit/s on-off keying (OOK) data transmission was performed with clear open eyes even if the system is still limited by the PD response. With higher-speed PD, higher data rate can be achieved with higher modulation bandwidth than 5 GHz.
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Onset of plastic relaxation in Semipolar (112¯2) InxGa1−xN/GaN heterostructures
Journal of Crystal Growth, 2014Co-Authors: Ingrid Koslow, Steven P. Denbaars, Shuji Nakamura, Matthew T. Hardy, Feng Wu, Alexey E. Romanov, Erin C. Young, James S. SpeckAbstract:Abstract The onset of plastic relaxation via misfit dislocation (MD) formation in In x Ga 1− x N layers grown by metal-organic chemical vapor deposition on the ( 11 2 ¯ 2 ) Semipolar Plane of GaN substrates is investigated using high-resolution X-ray diffraction, transmission electron microscopy and cathodoluminescence. The results of critical thickness calculations for MD formation as a function of In x Ga 1− x N alloy composition x are compared with experimental observations. MD generation is observed initially as a result of slip on the (0001) slip Plane, and subsequently as a result of additional slip on inclined { 1 1 ¯ 00 } - type m -Planes, which eventually leads to an increase in threading dislocation density.
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A Semipolar (10- 1 - 3 ) InGaN/GaN green light emitting diode
MRS Proceedings, 2005Co-Authors: Rajat Sharma, Robert M. Farrell, Steven P. Denbaars, James S. Speck, Feng Wu, P. Morgan Pattison, Troy J. Baker, Benjamin A. Haskell, Hisashi Masui, Shuji NakamuraAbstract:The performance of conventional c-Plane GaN-based optoelectronic devices suffers from the effects of strong polarization-induced electric fields along the conduction direction, which result in a reduced overlap between electron and hole wavefunctions. These devices consequently demonstrate low radiative recombination rates, and a blue-shift in peak emission wavelength with increasing bias. There have been several recent demonstrations of light emitting diodes (LEDs) fabricated on non-polar a- and m- Plane GaN that show greatly reduced to zero blue-shift of peak emission wavelength, and other recent work on non-polar GaN has yielded hole concentrations that are almost an order of magnitude higher than for c-Plane GaN. The effects of the strong polarization-induced electric fields may, conceivably, also be mitigated or potentially eliminated by growing films on so-called ‘Semipolar’ Planes. A Semipolar Plane is any Plane that may not be classified as a c-, a- or m- Plane, and has at least two non-zero h, i, or k Miller indices and a nonzero l Miller index (, and Planes, for example). It is expected that devices grown on these Semipolar Planes should also demonstrate a reduced blue-shift in peak emission wavelength and higher hole concentrations. Further, recent work also suggests that the indium incorporation efficiency for growth on Semipolar Planes is comparable to that for growth on the c-Plane. We demonstrate the first green InGaN/GaN LED grown on a planar Semipolar GaN template. The LED structure is grown by metalorganic chemical vapor deposition (MOCVD), and the 20 μm-thick, specular and optically transparent template is grown by hydride vapor phase epitaxy (HVPE). The fabricated devices have a peak emission wavelength of ∼525 nm and demonstrate rectifying behavior, with a low turn-on voltage of 3.2 V. We observe a small ∼7 nm blue-shift in the peak emission wavelength during electroluminescence measurements, over the range 20 to 250 mA. We also see an almost linear increase in the output power from 5 mA to 200 mA, with no appreciable decrease in the external quantum efficiency over the same range. We also observe evidence of polarization anisotropy in the emission from the Semipolar green LEDs.
Shuji Nakamura - One of the best experts on this subject based on the ideXlab platform.
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high speed performance of iii nitride laser diode grown on 2021 Semipolar Plane for visible light communication
IEEE Photonics Conference, 2016Co-Authors: Chong Zhang, DANIEL BECERRA, Robert M. Farrell, Shuji Nakamura, Sang Ho Oh, John E. Bowers, James S. Speck, Steven P. DenbaarsAbstract:III-nitride light emitting diodes (LEDs) have been used for many applications covering the spectrum of ultraviolet (UV) to visible light (VL). Despite of significant improvements on solid-state lighting, LEDs still suffer significant efficiency loss at high carrier density, commonly referred as "efficiency droop" [1]. However, compared to LEDs, laser diodes (LDs) have higher power per chip and the absence of efficiency droop above lasing threshold. In addition to the advantage of solid-state lighting, LDs can be modulated at much higher frequency than LEDs.
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High speed performance of III-nitride laser diode grown on (2021) Semipolar Plane for visible light communication
2016 IEEE Photonics Conference (IPC), 2016Co-Authors: Changmin Lee, DANIEL BECERRA, Seunggeun Lee, Robert M. Farrell, Shuji Nakamura, Sang Ho Oh, Chong Zhang, John E. Bowers, James S. Speck, Steven P. DenbaarsAbstract:Summary form only given. III-nitride light emitting diodes (LEDs) have been used for many applications covering the spectrum of ultraviolet (UV) to visible light (VL). Despite of significant improvements on solid-state lighting, LEDs still suffer significant efficiency loss at high carrier density, commonly referred as "efficiency droop". However, compared to LEDs, laser diodes (LDs) have higher power per chip and the absence of efficiency droop above lasing threshold. In addition to the advantage of solid-state lighting, LDs can be modulated at much higher frequency than LEDs. For visible light communication (VLC) or light fidelity (LiFi), typical LEDs have only 10 ~ 100 MHz of the modulation bandwidth due to the relatively long carrier lifetime and large parasitic effect even though recently reported micro LEDs can have smaller parasitic effect. The low modulation bandwidth on LEDs causes not only low data rates but also the significantly limited to slow phosphor response for white lighting. However, recent our studies on laser-based LiFi shown that GHz operating laser has high data rate as well as almost no phosphor limit in white lighting data transmission for GHz range. In our study, we investigated high-speed characteristics of 410 nm violet continuous-wave (CW) ridge laser diode grown on (202̅1̅) Plane. The ridge laser epitaxial structure was grown on free standing bulk GaN Semipolar (202̅1̅) by MOCVD. The active region consists of a 4-period undoped In0.1Ga0.9N/GaN (3.5 nm/7 nm) multi quantum well (MQW). Symmetrical In0.025Ga0.97In0.1Ga0.9N/GaN5N waveguiding layers on each p- and n-side give optical confinement factor of 0.023. The top-side n-contact design of 1200 m long and 2 m wide cavity was fabricated for low voltage as well as direct ground-signal (GS) RF probing. The light-current-voltage (LIV) curve- on CW operation and the spectra of different injection current were measured at 15 °C. The threshold current and threshold current density in CW were 150 mA and 6.25 kA/cm2, respectively. The frequency response of photodetector (PD) was measured by frequency doubled 410 nm pulses from a mode-locked TiSapphire laser since initial measurement of - 3 dB bandwidth of the LD was only 4.13 GHz with significant roll-off due to the system limit. By correcting the frequency response of LD, 5 GHz of bandwidth, which is highest bandwidth reported for blue-violet LDs, was obtained even though this bandwidth is due to the noise floor from PD limit. The slope efficiency of resonance frequency versus square root of pumping current was well-fitted with 0.51 GHz/mA1/2, resulting in the differential gain of 3.16 × 10-16 cm2. The measured damping factor of 0.35 ns was calculated for the maximum intrinsic bandwidth of 25.6 GHz. High 5 Gbit/s on-off keying (OOK) data transmission was performed with clear open eyes even if the system is still limited by the PD response. With higher-speed PD, higher data rate can be achieved with higher modulation bandwidth than 5 GHz.
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Onset of plastic relaxation in Semipolar (112¯2) InxGa1−xN/GaN heterostructures
Journal of Crystal Growth, 2014Co-Authors: Ingrid Koslow, Steven P. Denbaars, Shuji Nakamura, Matthew T. Hardy, Feng Wu, Alexey E. Romanov, Erin C. Young, James S. SpeckAbstract:Abstract The onset of plastic relaxation via misfit dislocation (MD) formation in In x Ga 1− x N layers grown by metal-organic chemical vapor deposition on the ( 11 2 ¯ 2 ) Semipolar Plane of GaN substrates is investigated using high-resolution X-ray diffraction, transmission electron microscopy and cathodoluminescence. The results of critical thickness calculations for MD formation as a function of In x Ga 1− x N alloy composition x are compared with experimental observations. MD generation is observed initially as a result of slip on the (0001) slip Plane, and subsequently as a result of additional slip on inclined { 1 1 ¯ 00 } - type m -Planes, which eventually leads to an increase in threading dislocation density.
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A Semipolar (10- 1 - 3 ) InGaN/GaN green light emitting diode
MRS Proceedings, 2005Co-Authors: Rajat Sharma, Robert M. Farrell, Steven P. Denbaars, James S. Speck, Feng Wu, P. Morgan Pattison, Troy J. Baker, Benjamin A. Haskell, Hisashi Masui, Shuji NakamuraAbstract:The performance of conventional c-Plane GaN-based optoelectronic devices suffers from the effects of strong polarization-induced electric fields along the conduction direction, which result in a reduced overlap between electron and hole wavefunctions. These devices consequently demonstrate low radiative recombination rates, and a blue-shift in peak emission wavelength with increasing bias. There have been several recent demonstrations of light emitting diodes (LEDs) fabricated on non-polar a- and m- Plane GaN that show greatly reduced to zero blue-shift of peak emission wavelength, and other recent work on non-polar GaN has yielded hole concentrations that are almost an order of magnitude higher than for c-Plane GaN. The effects of the strong polarization-induced electric fields may, conceivably, also be mitigated or potentially eliminated by growing films on so-called ‘Semipolar’ Planes. A Semipolar Plane is any Plane that may not be classified as a c-, a- or m- Plane, and has at least two non-zero h, i, or k Miller indices and a nonzero l Miller index (, and Planes, for example). It is expected that devices grown on these Semipolar Planes should also demonstrate a reduced blue-shift in peak emission wavelength and higher hole concentrations. Further, recent work also suggests that the indium incorporation efficiency for growth on Semipolar Planes is comparable to that for growth on the c-Plane. We demonstrate the first green InGaN/GaN LED grown on a planar Semipolar GaN template. The LED structure is grown by metalorganic chemical vapor deposition (MOCVD), and the 20 μm-thick, specular and optically transparent template is grown by hydride vapor phase epitaxy (HVPE). The fabricated devices have a peak emission wavelength of ∼525 nm and demonstrate rectifying behavior, with a low turn-on voltage of 3.2 V. We observe a small ∼7 nm blue-shift in the peak emission wavelength during electroluminescence measurements, over the range 20 to 250 mA. We also see an almost linear increase in the output power from 5 mA to 200 mA, with no appreciable decrease in the external quantum efficiency over the same range. We also observe evidence of polarization anisotropy in the emission from the Semipolar green LEDs.
James S. Speck - One of the best experts on this subject based on the ideXlab platform.
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high speed performance of iii nitride laser diode grown on 2021 Semipolar Plane for visible light communication
IEEE Photonics Conference, 2016Co-Authors: Chong Zhang, DANIEL BECERRA, Robert M. Farrell, Shuji Nakamura, Sang Ho Oh, John E. Bowers, James S. Speck, Steven P. DenbaarsAbstract:III-nitride light emitting diodes (LEDs) have been used for many applications covering the spectrum of ultraviolet (UV) to visible light (VL). Despite of significant improvements on solid-state lighting, LEDs still suffer significant efficiency loss at high carrier density, commonly referred as "efficiency droop" [1]. However, compared to LEDs, laser diodes (LDs) have higher power per chip and the absence of efficiency droop above lasing threshold. In addition to the advantage of solid-state lighting, LDs can be modulated at much higher frequency than LEDs.
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High speed performance of III-nitride laser diode grown on (2021) Semipolar Plane for visible light communication
2016 IEEE Photonics Conference (IPC), 2016Co-Authors: Changmin Lee, DANIEL BECERRA, Seunggeun Lee, Robert M. Farrell, Shuji Nakamura, Sang Ho Oh, Chong Zhang, John E. Bowers, James S. Speck, Steven P. DenbaarsAbstract:Summary form only given. III-nitride light emitting diodes (LEDs) have been used for many applications covering the spectrum of ultraviolet (UV) to visible light (VL). Despite of significant improvements on solid-state lighting, LEDs still suffer significant efficiency loss at high carrier density, commonly referred as "efficiency droop". However, compared to LEDs, laser diodes (LDs) have higher power per chip and the absence of efficiency droop above lasing threshold. In addition to the advantage of solid-state lighting, LDs can be modulated at much higher frequency than LEDs. For visible light communication (VLC) or light fidelity (LiFi), typical LEDs have only 10 ~ 100 MHz of the modulation bandwidth due to the relatively long carrier lifetime and large parasitic effect even though recently reported micro LEDs can have smaller parasitic effect. The low modulation bandwidth on LEDs causes not only low data rates but also the significantly limited to slow phosphor response for white lighting. However, recent our studies on laser-based LiFi shown that GHz operating laser has high data rate as well as almost no phosphor limit in white lighting data transmission for GHz range. In our study, we investigated high-speed characteristics of 410 nm violet continuous-wave (CW) ridge laser diode grown on (202̅1̅) Plane. The ridge laser epitaxial structure was grown on free standing bulk GaN Semipolar (202̅1̅) by MOCVD. The active region consists of a 4-period undoped In0.1Ga0.9N/GaN (3.5 nm/7 nm) multi quantum well (MQW). Symmetrical In0.025Ga0.97In0.1Ga0.9N/GaN5N waveguiding layers on each p- and n-side give optical confinement factor of 0.023. The top-side n-contact design of 1200 m long and 2 m wide cavity was fabricated for low voltage as well as direct ground-signal (GS) RF probing. The light-current-voltage (LIV) curve- on CW operation and the spectra of different injection current were measured at 15 °C. The threshold current and threshold current density in CW were 150 mA and 6.25 kA/cm2, respectively. The frequency response of photodetector (PD) was measured by frequency doubled 410 nm pulses from a mode-locked TiSapphire laser since initial measurement of - 3 dB bandwidth of the LD was only 4.13 GHz with significant roll-off due to the system limit. By correcting the frequency response of LD, 5 GHz of bandwidth, which is highest bandwidth reported for blue-violet LDs, was obtained even though this bandwidth is due to the noise floor from PD limit. The slope efficiency of resonance frequency versus square root of pumping current was well-fitted with 0.51 GHz/mA1/2, resulting in the differential gain of 3.16 × 10-16 cm2. The measured damping factor of 0.35 ns was calculated for the maximum intrinsic bandwidth of 25.6 GHz. High 5 Gbit/s on-off keying (OOK) data transmission was performed with clear open eyes even if the system is still limited by the PD response. With higher-speed PD, higher data rate can be achieved with higher modulation bandwidth than 5 GHz.
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Onset of plastic relaxation in Semipolar (112¯2) InxGa1−xN/GaN heterostructures
Journal of Crystal Growth, 2014Co-Authors: Ingrid Koslow, Steven P. Denbaars, Shuji Nakamura, Matthew T. Hardy, Feng Wu, Alexey E. Romanov, Erin C. Young, James S. SpeckAbstract:Abstract The onset of plastic relaxation via misfit dislocation (MD) formation in In x Ga 1− x N layers grown by metal-organic chemical vapor deposition on the ( 11 2 ¯ 2 ) Semipolar Plane of GaN substrates is investigated using high-resolution X-ray diffraction, transmission electron microscopy and cathodoluminescence. The results of critical thickness calculations for MD formation as a function of In x Ga 1− x N alloy composition x are compared with experimental observations. MD generation is observed initially as a result of slip on the (0001) slip Plane, and subsequently as a result of additional slip on inclined { 1 1 ¯ 00 } - type m -Planes, which eventually leads to an increase in threading dislocation density.
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A Semipolar (10- 1 - 3 ) InGaN/GaN green light emitting diode
MRS Proceedings, 2005Co-Authors: Rajat Sharma, Robert M. Farrell, Steven P. Denbaars, James S. Speck, Feng Wu, P. Morgan Pattison, Troy J. Baker, Benjamin A. Haskell, Hisashi Masui, Shuji NakamuraAbstract:The performance of conventional c-Plane GaN-based optoelectronic devices suffers from the effects of strong polarization-induced electric fields along the conduction direction, which result in a reduced overlap between electron and hole wavefunctions. These devices consequently demonstrate low radiative recombination rates, and a blue-shift in peak emission wavelength with increasing bias. There have been several recent demonstrations of light emitting diodes (LEDs) fabricated on non-polar a- and m- Plane GaN that show greatly reduced to zero blue-shift of peak emission wavelength, and other recent work on non-polar GaN has yielded hole concentrations that are almost an order of magnitude higher than for c-Plane GaN. The effects of the strong polarization-induced electric fields may, conceivably, also be mitigated or potentially eliminated by growing films on so-called ‘Semipolar’ Planes. A Semipolar Plane is any Plane that may not be classified as a c-, a- or m- Plane, and has at least two non-zero h, i, or k Miller indices and a nonzero l Miller index (, and Planes, for example). It is expected that devices grown on these Semipolar Planes should also demonstrate a reduced blue-shift in peak emission wavelength and higher hole concentrations. Further, recent work also suggests that the indium incorporation efficiency for growth on Semipolar Planes is comparable to that for growth on the c-Plane. We demonstrate the first green InGaN/GaN LED grown on a planar Semipolar GaN template. The LED structure is grown by metalorganic chemical vapor deposition (MOCVD), and the 20 μm-thick, specular and optically transparent template is grown by hydride vapor phase epitaxy (HVPE). The fabricated devices have a peak emission wavelength of ∼525 nm and demonstrate rectifying behavior, with a low turn-on voltage of 3.2 V. We observe a small ∼7 nm blue-shift in the peak emission wavelength during electroluminescence measurements, over the range 20 to 250 mA. We also see an almost linear increase in the output power from 5 mA to 200 mA, with no appreciable decrease in the external quantum efficiency over the same range. We also observe evidence of polarization anisotropy in the emission from the Semipolar green LEDs.
Robert M. Farrell - One of the best experts on this subject based on the ideXlab platform.
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high speed performance of iii nitride laser diode grown on 2021 Semipolar Plane for visible light communication
IEEE Photonics Conference, 2016Co-Authors: Chong Zhang, DANIEL BECERRA, Robert M. Farrell, Shuji Nakamura, Sang Ho Oh, John E. Bowers, James S. Speck, Steven P. DenbaarsAbstract:III-nitride light emitting diodes (LEDs) have been used for many applications covering the spectrum of ultraviolet (UV) to visible light (VL). Despite of significant improvements on solid-state lighting, LEDs still suffer significant efficiency loss at high carrier density, commonly referred as "efficiency droop" [1]. However, compared to LEDs, laser diodes (LDs) have higher power per chip and the absence of efficiency droop above lasing threshold. In addition to the advantage of solid-state lighting, LDs can be modulated at much higher frequency than LEDs.
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High speed performance of III-nitride laser diode grown on (2021) Semipolar Plane for visible light communication
2016 IEEE Photonics Conference (IPC), 2016Co-Authors: Changmin Lee, DANIEL BECERRA, Seunggeun Lee, Robert M. Farrell, Shuji Nakamura, Sang Ho Oh, Chong Zhang, John E. Bowers, James S. Speck, Steven P. DenbaarsAbstract:Summary form only given. III-nitride light emitting diodes (LEDs) have been used for many applications covering the spectrum of ultraviolet (UV) to visible light (VL). Despite of significant improvements on solid-state lighting, LEDs still suffer significant efficiency loss at high carrier density, commonly referred as "efficiency droop". However, compared to LEDs, laser diodes (LDs) have higher power per chip and the absence of efficiency droop above lasing threshold. In addition to the advantage of solid-state lighting, LDs can be modulated at much higher frequency than LEDs. For visible light communication (VLC) or light fidelity (LiFi), typical LEDs have only 10 ~ 100 MHz of the modulation bandwidth due to the relatively long carrier lifetime and large parasitic effect even though recently reported micro LEDs can have smaller parasitic effect. The low modulation bandwidth on LEDs causes not only low data rates but also the significantly limited to slow phosphor response for white lighting. However, recent our studies on laser-based LiFi shown that GHz operating laser has high data rate as well as almost no phosphor limit in white lighting data transmission for GHz range. In our study, we investigated high-speed characteristics of 410 nm violet continuous-wave (CW) ridge laser diode grown on (202̅1̅) Plane. The ridge laser epitaxial structure was grown on free standing bulk GaN Semipolar (202̅1̅) by MOCVD. The active region consists of a 4-period undoped In0.1Ga0.9N/GaN (3.5 nm/7 nm) multi quantum well (MQW). Symmetrical In0.025Ga0.97In0.1Ga0.9N/GaN5N waveguiding layers on each p- and n-side give optical confinement factor of 0.023. The top-side n-contact design of 1200 m long and 2 m wide cavity was fabricated for low voltage as well as direct ground-signal (GS) RF probing. The light-current-voltage (LIV) curve- on CW operation and the spectra of different injection current were measured at 15 °C. The threshold current and threshold current density in CW were 150 mA and 6.25 kA/cm2, respectively. The frequency response of photodetector (PD) was measured by frequency doubled 410 nm pulses from a mode-locked TiSapphire laser since initial measurement of - 3 dB bandwidth of the LD was only 4.13 GHz with significant roll-off due to the system limit. By correcting the frequency response of LD, 5 GHz of bandwidth, which is highest bandwidth reported for blue-violet LDs, was obtained even though this bandwidth is due to the noise floor from PD limit. The slope efficiency of resonance frequency versus square root of pumping current was well-fitted with 0.51 GHz/mA1/2, resulting in the differential gain of 3.16 × 10-16 cm2. The measured damping factor of 0.35 ns was calculated for the maximum intrinsic bandwidth of 25.6 GHz. High 5 Gbit/s on-off keying (OOK) data transmission was performed with clear open eyes even if the system is still limited by the PD response. With higher-speed PD, higher data rate can be achieved with higher modulation bandwidth than 5 GHz.
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A Semipolar (10- 1 - 3 ) InGaN/GaN green light emitting diode
MRS Proceedings, 2005Co-Authors: Rajat Sharma, Robert M. Farrell, Steven P. Denbaars, James S. Speck, Feng Wu, P. Morgan Pattison, Troy J. Baker, Benjamin A. Haskell, Hisashi Masui, Shuji NakamuraAbstract:The performance of conventional c-Plane GaN-based optoelectronic devices suffers from the effects of strong polarization-induced electric fields along the conduction direction, which result in a reduced overlap between electron and hole wavefunctions. These devices consequently demonstrate low radiative recombination rates, and a blue-shift in peak emission wavelength with increasing bias. There have been several recent demonstrations of light emitting diodes (LEDs) fabricated on non-polar a- and m- Plane GaN that show greatly reduced to zero blue-shift of peak emission wavelength, and other recent work on non-polar GaN has yielded hole concentrations that are almost an order of magnitude higher than for c-Plane GaN. The effects of the strong polarization-induced electric fields may, conceivably, also be mitigated or potentially eliminated by growing films on so-called ‘Semipolar’ Planes. A Semipolar Plane is any Plane that may not be classified as a c-, a- or m- Plane, and has at least two non-zero h, i, or k Miller indices and a nonzero l Miller index (, and Planes, for example). It is expected that devices grown on these Semipolar Planes should also demonstrate a reduced blue-shift in peak emission wavelength and higher hole concentrations. Further, recent work also suggests that the indium incorporation efficiency for growth on Semipolar Planes is comparable to that for growth on the c-Plane. We demonstrate the first green InGaN/GaN LED grown on a planar Semipolar GaN template. The LED structure is grown by metalorganic chemical vapor deposition (MOCVD), and the 20 μm-thick, specular and optically transparent template is grown by hydride vapor phase epitaxy (HVPE). The fabricated devices have a peak emission wavelength of ∼525 nm and demonstrate rectifying behavior, with a low turn-on voltage of 3.2 V. We observe a small ∼7 nm blue-shift in the peak emission wavelength during electroluminescence measurements, over the range 20 to 250 mA. We also see an almost linear increase in the output power from 5 mA to 200 mA, with no appreciable decrease in the external quantum efficiency over the same range. We also observe evidence of polarization anisotropy in the emission from the Semipolar green LEDs.
R. Bhat - One of the best experts on this subject based on the ideXlab platform.
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Development of Semipolar laser diode
Physica Status Solidi (a), 2013Co-Authors: Dmitry Sizov, R. Bhat, Jie Wang, Donald Allen, Barry PaddockAbstract:In this paper, we discuss experimental results and the potential for improvement of blue and green laser diode (LD) performance by using Semipolar substrates. We show that the InGaN quantum well (QW) grown on a Semipolar Plane allows higher characteristic temperature, T0, and higher optical gain, which are important for improving laser efficiency, thanks to its unique electronic spectrum properties. Epitaxial structure growth benefits from the wider process window for certain orientations. At the same time it is associated with a risk of strain relaxation, which can be addressed by appropriate strain relaxation management and/or strain balancing of waveguide core.
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Gallium Indium Nitride-Based Green Lasers
Journal of Lightwave Technology, 2012Co-Authors: Dmitry Sizov, R. BhatAbstract:In this review article, we describe group-III nitride laser diodes that emit light in the green spectral range, using epitaxial structures grown on gallium nitride (GaN) substrates with c- and Semipolar-Plane orientations. We address the motivation for these lasers, the challenges faced in creating them, and the progress made in this field to date. Different structural design choices are described, taking into account specific material properties and crystal growth requirements for these orientations. We review various properties of the materials involved, including optical gain, optical confinement, internal optical losses and carrier injection. We also discuss mechanical strain during the growth of active and passive regions, and the way in which it limits the structural design. Various aspects of laser chip fabrication are discussed, including self-aligned ridge waveguides and facet formation. Finally, we outline the status of green laser reliability and challenges in this area.
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Challenges and approaches of fabricating GaN-based green lasers
2011 International Semiconductor Device Research Symposium (ISDRS), 2011Co-Authors: Dmitry Sizov, R. BhatAbstract:During recent years, several research groups have demonstrated a steady progress in increasing InGaN quantum well (QW) laser emission wavelength [1–5], however the threshold current (Fig. 1) and wall plug efficiency (WPE) are still worse than those for blue LDs. Reduction of operation current is needed to improve device reliability while keeping WPE comparable with alternative portable green laser technologies. In this paper we discuss the motivation, challenges, and progress in making group-III nitride lasers emitting in the green spectral range, and compare the devices created using epitaxial structures grown on GaN substrates with c-Plane (i.e. Plane with (0001) crystallographic orientation) and Semipolar-Plane (i.e. with the Plane tilted from c-Plane by >0 and
