chibuzo onwuka - Academia.edu (original) (raw)

Papers by chibuzo onwuka

Research paper thumbnail of Nanophotonic route to control electron behaviors in 2D materials

Nanophotonics, May 10, 2024

Research paper thumbnail of Accurate determination of junction temperature in a GaN-based blue light-emitting diode using nonlinear voltage-temperature relation

Optical and Quantum Electronics, Aug 14, 2021

We investigate the junction temperature measurements for GaN-based blue light emitting diodes (LE... more We investigate the junction temperature measurements for GaN-based blue light emitting diodes (LEDs) using nonlinear dependence of the forward voltage (V f) on temperature. Unlike the conventional linear model of the dependence of V f on temperature, the modeling of the temperature dependent V f with a quadratic function showed good agreements with measured data in the temperature range between 20 and 100 o C. Using the proposed quadratic model, the junction temperature and thermal resistance of the measured LED could be accurately determined as the ambient temperature varied. It was observed that the junction temperature increment remained almost unchanged as the ambient temperature increased from 20 to 80 o C, which could be attributed to the interplay between the decrease in series resistance and the increase in non-radiative recombination with increasing temperature. The presented method for accurate determination of the junction temperature is expected to be advantageously employed for the thermal management of high-power LEDs.

Research paper thumbnail of Determination of the Internal Quantum Efficiency of InGaAsP Multiple Quantum wells using Rate Equation Analysis of Photoluminescence Measurements

Optica Advanced Photonics Congress 2022, 2022

The internal quantum efficiency (η IQE ) of InGaAsP multiple quantum well is determined as a fit ... more The internal quantum efficiency (η IQE ) of InGaAsP multiple quantum well is determined as a fit parameter from a rate equation of the external quantum efficiency (η IQE ) as an explicit function of the laser pump power.

Research paper thumbnail of Efficiency Droop and Effective Active Volume in GaN-Based Light-Emitting Diodes Grown on Sapphire and Silicon Substrates

Applied sciences, Oct 3, 2019

We compared the efficiency droop of InGaN multiple-quantum-well (MQW) blue light-emitting diode (... more We compared the efficiency droop of InGaN multiple-quantum-well (MQW) blue light-emitting diode (LED) structures grown on silicon(111) and c-plane sapphire substrates and analyzed the efficiency droop characteristics using the rate equation model with reduced effective active volume. The efficiency droop of the LED sample on silicon was observed to be reduced considerably compared with that of the identical LED sample on sapphire substrates. When the measured external quantum efficiency was fitted with the rate equation model, the effective active volume of the MQW on silicon was found to be~1.45 times larger than that of the MQW on sapphire. The lower efficiency droop in the LED on silicon could be attributed to its larger effective active volume compared with the LED on sapphire. The simulation results showed that the effective active volume decreased as the internal electric fields increased, as a result of the reduced overlap of the electron and hole distribution inside the quantum well and the inhomogeneous carrier distribution in the MQWs. The difference in the internal electric field of the MQW between the LED on silicon and sapphire could be a major reason for the difference in the effective active volume, and consequently, the efficiency droop.

Research paper thumbnail of Investigation into Color-temperature Stable Illumination Sources Based on Tri-chromatic LEDs

OSA Advanced Photonics Congress 2021, 2021

Temperature and time variations influence the color points of a white light emitting diodes (LEDs... more Temperature and time variations influence the color points of a white light emitting diodes (LEDs). Adjusting the power ratios of the individual LEDs of a trichromatic light, we obtain a stable color temperature operation.

Research paper thumbnail of Temperature dependence of the Auger recombination coefficient in InGaN/GaN multiple-quantum-well light-emitting diodes

Optics Express, Sep 1, 2020

This study investigated the temperature dependence of the Auger recombination coefficient (C) in ... more This study investigated the temperature dependence of the Auger recombination coefficient (C) in an InGaN/GaN blue multiple-quantum-well (MQW) light-emitting diode structure at temperatures between 20 and 100°C. The temperature dependence of C was determined by fitting the measured external quantum efficiency (EQE) data using an analytical model or numerical simulation. In the analytical model, the carrier density in InGaN MQWs was assumed to be constant and independent of temperature. In contrast, the inhomogeneous carrier distribution in MQWs and its temperature-dependent redistribution were included in the numerical simulation. When the analytical model was employed to fit the EQE curve, C decreased with increasing temperature. On the other hand, when the numerical simulation was employed, C increased steadily by ∼31% as the temperature was increased from 20 to 100°C. We found that the temperature-dependent carrier distribution is important to consider when determining the temperature dependence of the Auger recombination coefficient in InGaN MQW structures.

Research paper thumbnail of Low-Threshold Lasing in Strained Germanium under Optical Pumping

We report the first experimental observation of low-threshold lasing in strained germanium nanowi... more We report the first experimental observation of low-threshold lasing in strained germanium nanowires. The lasing threshold is ∼3.0 kW cm−2 which is more than one order of magnitude lower than the state-of-the-art germanium-tin Fabry-Perot laser.

Research paper thumbnail of Temperature Dependence of Electron Leakage Current in InGaN Blue Light-Emitting Diode Structures

Nanomaterials, Jul 14, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of Investigation into the stability condition of correlated color temperature of white illumination sources based on trichromatic light-emitting diodes

Research paper thumbnail of Investigation of the Optimum Mg Doping Concentration in p-Type-Doped Layers of InGaN Blue Laser Diode Structures

Crystals, Nov 1, 2021

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of Theoretical Investigation of the Temperature-Dependent Stable CCT Operation of Trichromatic LED-based Illumination Sources

Advanced Photonics Congress 2023

The temperature-dependent correlated color temperature (CCT) drifts of a trichromatic white LED a... more The temperature-dependent correlated color temperature (CCT) drifts of a trichromatic white LED are investigated, and a theoretical approach to minimizing the drifts is proposed. Adjusting the red-to-blue power ratio enables a temperature-dependent stable CCT operation.

Research paper thumbnail of Investigation into the stability condition of correlated color temperature of white illumination sources based on trichromatic light-emitting diodes

Research paper thumbnail of Temperature Dependence of Electron Leakage Current in InGaN Blue Light-Emitting Diode Structures

Nanomaterials

We investigated the temperature dependence of the electron leakage current in the AlGaN electron-... more We investigated the temperature dependence of the electron leakage current in the AlGaN electron-blocking layer (EBL) of an InGaN/GaN blue light-emitting diode (LED) structure at temperatures between 20 and 100 °C. The percentage of electron leakage current was experimentally determined by fitting the measured external quantum efficiency of an LED using the ABC recombination model. The electron leakage current decreased significantly as the temperature increased from 20 to 100 °C. The experiment obtained temperature-dependent electron leakage current was also found to agree well with the simulation results. This counter-intuitive temperature dependence of the electron leakage current resulted from an increase in potential barrier for electrons with increasing temperature due to the increased ionized acceptor concentration in the EBL with temperature. Moreover, the results obtained for the temperature-dependent electron leakage were consistent with the thermionic emission model. The ...

Research paper thumbnail of Low-Threshold Lasing in Strained Germanium under Optical Pumping

Conference on Lasers and Electro-Optics, 2018

We report the first experimental observation of low-threshold lasing in strained germanium nanowi... more We report the first experimental observation of low-threshold lasing in strained germanium nanowires. The lasing threshold is ∼3.0 kW cm−2 which is more than one order of magnitude lower than the state-of-the-art germanium-tin Fabry-Perot laser.

Research paper thumbnail of Accurate Determination of Junction Temperature in a GaN-Based Blue Light-Emitting Diode using Nonlinear Voltage-Temperature Relation

We investigate the junction temperature measurements for GaN-based blue light emitting diodes (LE... more We investigate the junction temperature measurements for GaN-based blue light emitting diodes (LEDs) using nonlinear dependence of the forward voltage ( V f ) on temperature. Unlike the conventional linear model of the dependence of V f on temperature, the modeling of the temperature dependent V f with a quadratic function showed good agreements with measured data in the temperature range between 20 and 100 o C. Using the proposed quadratic model, the junction temperature and thermal resistance of the measured LED could be accurately determined as the ambient temperature varied. It was observed that the junction temperature increment remained almost unchanged as the ambient temperature increased from 20 to 80 o C, which could be attributed to the interplay between the decrease in series resistance and the increase in non-radiative recombination with increasing temperature. The presented method for accurate determination of the junction temperature is expected to be advantageously em...

Research paper thumbnail of Investigation into Color-temperature Stable Illumination Sources Based on Tri-chromatic LEDs

OSA Advanced Photonics Congress 2021, 2021

Temperature and time variations influence the color points of a white light emitting diodes (LEDs... more Temperature and time variations influence the color points of a white light emitting diodes (LEDs). Adjusting the power ratios of the individual LEDs of a trichromatic light, we obtain a stable color temperature operation.

Research paper thumbnail of Investigation of the Optimum Mg Doping Concentration in p-Type-Doped Layers of InGaN Blue Laser Diode Structures

Crystals, 2021

In GaN-based laser diode (LD) structures, Mg doping in p-type-doped layers has a significant infl... more In GaN-based laser diode (LD) structures, Mg doping in p-type-doped layers has a significant influence on the device performance. As the doping concentration increases, the operation voltage decreases, whereas the output power decreases as a result of increased optical absorption, implying that optimization of the Mg doping concentration is required. In this study, we systematically investigated the effect of the Mg doping concentration in the AlGaN electron-blocking layer (EBL) and the AlGaN p-cladding layer on the output power, forward voltage, and wall-plug efficiency (WPE) of InGaN blue LD structures using numerical simulations. In the optimization of the EBL, an Al composition of 20% and an Mg doping concentration of 3 × 1019 cm−3 exhibited the best performance, with negligible electron leakage and a high WPE. The optimum Mg concentration of the p-AlGaN cladding layer was found to be ~1.5 × 1019 cm−3, where the maximum WPE of 38.6% was obtained for a blue LD with a threshold cu...

Research paper thumbnail of Temperature dependence of the Auger recombination coefficient in InGaN/GaN multiple-quantum-well light-emitting diodes

Optics Express, 2020

This study investigated the temperature dependence of the Auger recombination coefficient (C) in ... more This study investigated the temperature dependence of the Auger recombination coefficient (C) in an InGaN/GaN blue multiple-quantum-well (MQW) light-emitting diode structure at temperatures between 20 and 100°C. The temperature dependence of C was determined by fitting the measured external quantum efficiency (EQE) data using an analytical model or numerical simulation. In the analytical model, the carrier density in InGaN MQWs was assumed to be constant and independent of temperature. In contrast, the inhomogeneous carrier distribution in MQWs and its temperature-dependent redistribution were included in the numerical simulation. When the analytical model was employed to fit the EQE curve, C decreased with increasing temperature. On the other hand, when the numerical simulation was employed, C increased steadily by ∼31% as the temperature was increased from 20 to 100°C. We found that the temperature-dependent carrier distribution is important to consider when determining the temper...

Research paper thumbnail of Efficiency Droop and Effective Active Volume in GaN-Based Light-Emitting Diodes Grown on Sapphire and Silicon Substrates

Applied Sciences, 2019

We compared the efficiency droop of InGaN multiple-quantum-well (MQW) blue light-emitting diode (... more We compared the efficiency droop of InGaN multiple-quantum-well (MQW) blue light-emitting diode (LED) structures grown on silicon(111) and c-plane sapphire substrates and analyzed the efficiency droop characteristics using the rate equation model with reduced effective active volume. The efficiency droop of the LED sample on silicon was observed to be reduced considerably compared with that of the identical LED sample on sapphire substrates. When the measured external quantum efficiency was fitted with the rate equation model, the effective active volume of the MQW on silicon was found to be ~1.45 times larger than that of the MQW on sapphire. The lower efficiency droop in the LED on silicon could be attributed to its larger effective active volume compared with the LED on sapphire. The simulation results showed that the effective active volume decreased as the internal electric fields increased, as a result of the reduced overlap of the electron and hole distribution inside the qua...

Research paper thumbnail of Low-threshold optically pumped lasing in highly strained germanium nanowires

Nature communications, Jan 29, 2017

The integration of efficient, miniaturized group IV lasers into CMOS architecture holds the key t... more The integration of efficient, miniaturized group IV lasers into CMOS architecture holds the key to the realization of fully functional photonic-integrated circuits. Despite several years of progress, however, all group IV lasers reported to date exhibit impractically high thresholds owing to their unfavourable bandstructures. Highly strained germanium with its fundamentally altered bandstructure has emerged as a potential low-threshold gain medium, but there has yet to be a successful demonstration of lasing from this seemingly promising material system. Here we demonstrate a low-threshold, compact group IV laser that employs a germanium nanowire under a 1.6% uniaxial tensile strain as the gain medium. The amplified material gain in strained germanium can sufficiently overcome optical losses at 83 K, thus allowing the observation of multimode lasing with an optical pumping threshold density of ~3.0 kW cm-2. Our demonstration opens new possibilities for group IV lasers for photonic-i...

Research paper thumbnail of Nanophotonic route to control electron behaviors in 2D materials

Nanophotonics, May 10, 2024

Research paper thumbnail of Accurate determination of junction temperature in a GaN-based blue light-emitting diode using nonlinear voltage-temperature relation

Optical and Quantum Electronics, Aug 14, 2021

We investigate the junction temperature measurements for GaN-based blue light emitting diodes (LE... more We investigate the junction temperature measurements for GaN-based blue light emitting diodes (LEDs) using nonlinear dependence of the forward voltage (V f) on temperature. Unlike the conventional linear model of the dependence of V f on temperature, the modeling of the temperature dependent V f with a quadratic function showed good agreements with measured data in the temperature range between 20 and 100 o C. Using the proposed quadratic model, the junction temperature and thermal resistance of the measured LED could be accurately determined as the ambient temperature varied. It was observed that the junction temperature increment remained almost unchanged as the ambient temperature increased from 20 to 80 o C, which could be attributed to the interplay between the decrease in series resistance and the increase in non-radiative recombination with increasing temperature. The presented method for accurate determination of the junction temperature is expected to be advantageously employed for the thermal management of high-power LEDs.

Research paper thumbnail of Determination of the Internal Quantum Efficiency of InGaAsP Multiple Quantum wells using Rate Equation Analysis of Photoluminescence Measurements

Optica Advanced Photonics Congress 2022, 2022

The internal quantum efficiency (η IQE ) of InGaAsP multiple quantum well is determined as a fit ... more The internal quantum efficiency (η IQE ) of InGaAsP multiple quantum well is determined as a fit parameter from a rate equation of the external quantum efficiency (η IQE ) as an explicit function of the laser pump power.

Research paper thumbnail of Efficiency Droop and Effective Active Volume in GaN-Based Light-Emitting Diodes Grown on Sapphire and Silicon Substrates

Applied sciences, Oct 3, 2019

We compared the efficiency droop of InGaN multiple-quantum-well (MQW) blue light-emitting diode (... more We compared the efficiency droop of InGaN multiple-quantum-well (MQW) blue light-emitting diode (LED) structures grown on silicon(111) and c-plane sapphire substrates and analyzed the efficiency droop characteristics using the rate equation model with reduced effective active volume. The efficiency droop of the LED sample on silicon was observed to be reduced considerably compared with that of the identical LED sample on sapphire substrates. When the measured external quantum efficiency was fitted with the rate equation model, the effective active volume of the MQW on silicon was found to be~1.45 times larger than that of the MQW on sapphire. The lower efficiency droop in the LED on silicon could be attributed to its larger effective active volume compared with the LED on sapphire. The simulation results showed that the effective active volume decreased as the internal electric fields increased, as a result of the reduced overlap of the electron and hole distribution inside the quantum well and the inhomogeneous carrier distribution in the MQWs. The difference in the internal electric field of the MQW between the LED on silicon and sapphire could be a major reason for the difference in the effective active volume, and consequently, the efficiency droop.

Research paper thumbnail of Investigation into Color-temperature Stable Illumination Sources Based on Tri-chromatic LEDs

OSA Advanced Photonics Congress 2021, 2021

Temperature and time variations influence the color points of a white light emitting diodes (LEDs... more Temperature and time variations influence the color points of a white light emitting diodes (LEDs). Adjusting the power ratios of the individual LEDs of a trichromatic light, we obtain a stable color temperature operation.

Research paper thumbnail of Temperature dependence of the Auger recombination coefficient in InGaN/GaN multiple-quantum-well light-emitting diodes

Optics Express, Sep 1, 2020

This study investigated the temperature dependence of the Auger recombination coefficient (C) in ... more This study investigated the temperature dependence of the Auger recombination coefficient (C) in an InGaN/GaN blue multiple-quantum-well (MQW) light-emitting diode structure at temperatures between 20 and 100°C. The temperature dependence of C was determined by fitting the measured external quantum efficiency (EQE) data using an analytical model or numerical simulation. In the analytical model, the carrier density in InGaN MQWs was assumed to be constant and independent of temperature. In contrast, the inhomogeneous carrier distribution in MQWs and its temperature-dependent redistribution were included in the numerical simulation. When the analytical model was employed to fit the EQE curve, C decreased with increasing temperature. On the other hand, when the numerical simulation was employed, C increased steadily by ∼31% as the temperature was increased from 20 to 100°C. We found that the temperature-dependent carrier distribution is important to consider when determining the temperature dependence of the Auger recombination coefficient in InGaN MQW structures.

Research paper thumbnail of Low-Threshold Lasing in Strained Germanium under Optical Pumping

We report the first experimental observation of low-threshold lasing in strained germanium nanowi... more We report the first experimental observation of low-threshold lasing in strained germanium nanowires. The lasing threshold is ∼3.0 kW cm−2 which is more than one order of magnitude lower than the state-of-the-art germanium-tin Fabry-Perot laser.

Research paper thumbnail of Temperature Dependence of Electron Leakage Current in InGaN Blue Light-Emitting Diode Structures

Nanomaterials, Jul 14, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of Investigation into the stability condition of correlated color temperature of white illumination sources based on trichromatic light-emitting diodes

Research paper thumbnail of Investigation of the Optimum Mg Doping Concentration in p-Type-Doped Layers of InGaN Blue Laser Diode Structures

Crystals, Nov 1, 2021

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of Theoretical Investigation of the Temperature-Dependent Stable CCT Operation of Trichromatic LED-based Illumination Sources

Advanced Photonics Congress 2023

The temperature-dependent correlated color temperature (CCT) drifts of a trichromatic white LED a... more The temperature-dependent correlated color temperature (CCT) drifts of a trichromatic white LED are investigated, and a theoretical approach to minimizing the drifts is proposed. Adjusting the red-to-blue power ratio enables a temperature-dependent stable CCT operation.

Research paper thumbnail of Investigation into the stability condition of correlated color temperature of white illumination sources based on trichromatic light-emitting diodes

Research paper thumbnail of Temperature Dependence of Electron Leakage Current in InGaN Blue Light-Emitting Diode Structures

Nanomaterials

We investigated the temperature dependence of the electron leakage current in the AlGaN electron-... more We investigated the temperature dependence of the electron leakage current in the AlGaN electron-blocking layer (EBL) of an InGaN/GaN blue light-emitting diode (LED) structure at temperatures between 20 and 100 °C. The percentage of electron leakage current was experimentally determined by fitting the measured external quantum efficiency of an LED using the ABC recombination model. The electron leakage current decreased significantly as the temperature increased from 20 to 100 °C. The experiment obtained temperature-dependent electron leakage current was also found to agree well with the simulation results. This counter-intuitive temperature dependence of the electron leakage current resulted from an increase in potential barrier for electrons with increasing temperature due to the increased ionized acceptor concentration in the EBL with temperature. Moreover, the results obtained for the temperature-dependent electron leakage were consistent with the thermionic emission model. The ...

Research paper thumbnail of Low-Threshold Lasing in Strained Germanium under Optical Pumping

Conference on Lasers and Electro-Optics, 2018

We report the first experimental observation of low-threshold lasing in strained germanium nanowi... more We report the first experimental observation of low-threshold lasing in strained germanium nanowires. The lasing threshold is ∼3.0 kW cm−2 which is more than one order of magnitude lower than the state-of-the-art germanium-tin Fabry-Perot laser.

Research paper thumbnail of Accurate Determination of Junction Temperature in a GaN-Based Blue Light-Emitting Diode using Nonlinear Voltage-Temperature Relation

We investigate the junction temperature measurements for GaN-based blue light emitting diodes (LE... more We investigate the junction temperature measurements for GaN-based blue light emitting diodes (LEDs) using nonlinear dependence of the forward voltage ( V f ) on temperature. Unlike the conventional linear model of the dependence of V f on temperature, the modeling of the temperature dependent V f with a quadratic function showed good agreements with measured data in the temperature range between 20 and 100 o C. Using the proposed quadratic model, the junction temperature and thermal resistance of the measured LED could be accurately determined as the ambient temperature varied. It was observed that the junction temperature increment remained almost unchanged as the ambient temperature increased from 20 to 80 o C, which could be attributed to the interplay between the decrease in series resistance and the increase in non-radiative recombination with increasing temperature. The presented method for accurate determination of the junction temperature is expected to be advantageously em...

Research paper thumbnail of Investigation into Color-temperature Stable Illumination Sources Based on Tri-chromatic LEDs

OSA Advanced Photonics Congress 2021, 2021

Temperature and time variations influence the color points of a white light emitting diodes (LEDs... more Temperature and time variations influence the color points of a white light emitting diodes (LEDs). Adjusting the power ratios of the individual LEDs of a trichromatic light, we obtain a stable color temperature operation.

Research paper thumbnail of Investigation of the Optimum Mg Doping Concentration in p-Type-Doped Layers of InGaN Blue Laser Diode Structures

Crystals, 2021

In GaN-based laser diode (LD) structures, Mg doping in p-type-doped layers has a significant infl... more In GaN-based laser diode (LD) structures, Mg doping in p-type-doped layers has a significant influence on the device performance. As the doping concentration increases, the operation voltage decreases, whereas the output power decreases as a result of increased optical absorption, implying that optimization of the Mg doping concentration is required. In this study, we systematically investigated the effect of the Mg doping concentration in the AlGaN electron-blocking layer (EBL) and the AlGaN p-cladding layer on the output power, forward voltage, and wall-plug efficiency (WPE) of InGaN blue LD structures using numerical simulations. In the optimization of the EBL, an Al composition of 20% and an Mg doping concentration of 3 × 1019 cm−3 exhibited the best performance, with negligible electron leakage and a high WPE. The optimum Mg concentration of the p-AlGaN cladding layer was found to be ~1.5 × 1019 cm−3, where the maximum WPE of 38.6% was obtained for a blue LD with a threshold cu...

Research paper thumbnail of Temperature dependence of the Auger recombination coefficient in InGaN/GaN multiple-quantum-well light-emitting diodes

Optics Express, 2020

This study investigated the temperature dependence of the Auger recombination coefficient (C) in ... more This study investigated the temperature dependence of the Auger recombination coefficient (C) in an InGaN/GaN blue multiple-quantum-well (MQW) light-emitting diode structure at temperatures between 20 and 100°C. The temperature dependence of C was determined by fitting the measured external quantum efficiency (EQE) data using an analytical model or numerical simulation. In the analytical model, the carrier density in InGaN MQWs was assumed to be constant and independent of temperature. In contrast, the inhomogeneous carrier distribution in MQWs and its temperature-dependent redistribution were included in the numerical simulation. When the analytical model was employed to fit the EQE curve, C decreased with increasing temperature. On the other hand, when the numerical simulation was employed, C increased steadily by ∼31% as the temperature was increased from 20 to 100°C. We found that the temperature-dependent carrier distribution is important to consider when determining the temper...

Research paper thumbnail of Efficiency Droop and Effective Active Volume in GaN-Based Light-Emitting Diodes Grown on Sapphire and Silicon Substrates

Applied Sciences, 2019

We compared the efficiency droop of InGaN multiple-quantum-well (MQW) blue light-emitting diode (... more We compared the efficiency droop of InGaN multiple-quantum-well (MQW) blue light-emitting diode (LED) structures grown on silicon(111) and c-plane sapphire substrates and analyzed the efficiency droop characteristics using the rate equation model with reduced effective active volume. The efficiency droop of the LED sample on silicon was observed to be reduced considerably compared with that of the identical LED sample on sapphire substrates. When the measured external quantum efficiency was fitted with the rate equation model, the effective active volume of the MQW on silicon was found to be ~1.45 times larger than that of the MQW on sapphire. The lower efficiency droop in the LED on silicon could be attributed to its larger effective active volume compared with the LED on sapphire. The simulation results showed that the effective active volume decreased as the internal electric fields increased, as a result of the reduced overlap of the electron and hole distribution inside the qua...

Research paper thumbnail of Low-threshold optically pumped lasing in highly strained germanium nanowires

Nature communications, Jan 29, 2017

The integration of efficient, miniaturized group IV lasers into CMOS architecture holds the key t... more The integration of efficient, miniaturized group IV lasers into CMOS architecture holds the key to the realization of fully functional photonic-integrated circuits. Despite several years of progress, however, all group IV lasers reported to date exhibit impractically high thresholds owing to their unfavourable bandstructures. Highly strained germanium with its fundamentally altered bandstructure has emerged as a potential low-threshold gain medium, but there has yet to be a successful demonstration of lasing from this seemingly promising material system. Here we demonstrate a low-threshold, compact group IV laser that employs a germanium nanowire under a 1.6% uniaxial tensile strain as the gain medium. The amplified material gain in strained germanium can sufficiently overcome optical losses at 83 K, thus allowing the observation of multimode lasing with an optical pumping threshold density of ~3.0 kW cm-2. Our demonstration opens new possibilities for group IV lasers for photonic-i...