The structural and optical properties of InGaN/GaN multiple quantum wells （MQWs） with different barrier thick-nesses are studied by means of high resolution X-ray diffraction （HRXRD）, a cross-sectional transmissio...The structural and optical properties of InGaN/GaN multiple quantum wells （MQWs） with different barrier thick-nesses are studied by means of high resolution X-ray diffraction （HRXRD）, a cross-sectional transmission electron mi-croscope （TEM）, and temperature-dependent photoluminescence （PL） measurements. HRXRD and cross-sectional TEM measurements show that the interfaces between wells and barriers are abrupt and the entire MQW region has good periodic- ity for all three samples. As the barrier thickness is increased, the temperature of the turning point from blueshift to redshift of the S-shaped temperature-dependent PL peak energy increases monotonously, which indicates that the localization po- tentials due to In-rich clusters is deeper. From the Arrhenius plot of the normalized integrated PL intensity, it is found that there are two kinds of nonradiative recombination processes accounting for the thermal quenching of photoluminescence, and the corresponding activation energy （or the localization potential） increases with the increase of the barrier thickness. The dependence on barrier thickness is attributed to the redistribution of In-rich clusters during the growth of barrier layers, i.e., clusters with lower In contents aggregate into clusters with higher In contents.展开更多
A tunable grating-coupled external cavity(EC)laser is realized by employing a GaN-based laser diode as the gain device.A tuning range of 4.47 nm from 403.82 to 408.29 nm is achieved.Detailed investigations reveal that...A tunable grating-coupled external cavity(EC)laser is realized by employing a GaN-based laser diode as the gain device.A tuning range of 4.47 nm from 403.82 to 408.29 nm is achieved.Detailed investigations reveal that the injection current strongly influences the performance of the EC laser.Below the free-running lasing threshold,EC laser works stably.While above the free-running lasing threshold,a Fabry–Pérot(F-P)resonance peak in the emission spectrum and a smooth kink in the output power-injection current characteristic curve are observed,suggesting the competition between the inner F-P cavity resonance and EC resonance.Furthermore,the tuning range is found to be asymmetric and occurs predominantly on the longer wavelength side.This is interpreted in terms of the asymmetric gain distribution of GaN-based quantum well material.展开更多
Laser lift-off(LLO),by which GaN is separated from sapphire,is demonstrated to be a promising technique for advanced GaN-based optoelectronic devices.Its physical insight,however,is still not fully understood.We study...Laser lift-off(LLO),by which GaN is separated from sapphire,is demonstrated to be a promising technique for advanced GaN-based optoelectronic devices.Its physical insight,however,is still not fully understood.We study systematically the effect of laser pulse width on the LLO process and the property of GaN.To estimate accurately the temperature distribution and the decomposed thickness of GaN,fluctuation in the pulse laser energy is taken into account.It is found that the temperature at the interface is increased in a higher speed for a narrower pulse width.In addition,less damage to the GaN film is expected for a narrower pulse width owing to the smaller heated area,lower transient temperature and lower N2 vapor pressure encountered during LLO.Some experimental results reported in literature are explained well.Our results are useful in understanding the effect of laser pulse width and can be taken as references in LLO of GaN/sapphire structures.展开更多
Silica whispering gallery mode（WGM） microcavities were fabricated by the buffered oxide etcher and potassium hydroxide wet etching technique without any subsequent chemical or laser treatments. The silicon pedestal ...Silica whispering gallery mode（WGM） microcavities were fabricated by the buffered oxide etcher and potassium hydroxide wet etching technique without any subsequent chemical or laser treatments. The silicon pedestal underneath was an octagonal pyramid, thus providing a pointed connection area with the top silica microdisk while weakly influencing the resonance modes. The sidewalls of our microdisks were wedge shaped, which was believed to be an advantage for the mode confinement. Efficient coupling from and to the 60 μm diameter microdisk structure was achieved using tapered optical fibres, exhibiting a quality factor of 1.5×10^4 near a wavelength of 1550 nm. Many resonance modes were observed, and double transverse electric modes were identified by theoretical calculations. The quality factor of the microdisks was also analysed to deduce the cavity roughness. The wet etching technique provides a more convenient avenue to fabricate WGM microdisks than conventional fabrication methods.展开更多
Photoluminescence(PL)characteristics of the structure consisting of green InGaN/GaN multiple quantum wells(MQWs)and low indium content InGaN/GaN pre-wells are investigated.Several PL peaks from pre-wells and green InG...Photoluminescence(PL)characteristics of the structure consisting of green InGaN/GaN multiple quantum wells(MQWs)and low indium content InGaN/GaN pre-wells are investigated.Several PL peaks from pre-wells and green InGaN/GaN MQWs are observed.The peak energy values for both pre-wells and green InGaN/GaN MQWs display an S-shaped variation with temperature.In addition,the differences in the carrier localization effect,defect density,and phonon-exciton interaction between the pre-wells and green InGaN/GaN MQWs,and the internal quantum efficiency of the sample are studied.The obtained results elucidate the mechanism of the luminescence characteristics of the sample and demonstrate the significant stress blocking effect of pre-wells.展开更多
In diffusion to blue light-emitting diode （LED） wafers is performed by the inductive coupled plasma （ICP） treatment of a covering layer of indium tin oxide （ITO） on the wafer surface. The electrical property of ...In diffusion to blue light-emitting diode （LED） wafers is performed by the inductive coupled plasma （ICP） treatment of a covering layer of indium tin oxide （ITO） on the wafer surface. The electrical property of the p- type contact is improved and the redshift of photoluminescence （PL） from the InGaN quantum well of the wafer is found. Measurements by x-ray photoelectron spectroscopy （XPS） demonstrate that In atoms have diffused into p-GaN. Reflectance spectra of the sample surface reveal the variation caused by the ICP treatment. A model of compensation of the in-plane strain of the InGaN layer is used to explain the redshift of the PL data. Finally, LEDs are fabricated by using as-grown and ICP-treated wafers and their properties are compared. Under an injection current of 20mA, LEDs with ICP-induced In doping show a decrease of 0.3 V in the forward voltage and an increase of 23% in the light output, respectively.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61106044 and 61274052)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20110121110029)+1 种基金the Fundamental Research Funds for the Central Universities of Ministry of Education of China(Grant No.2013121024)the Natural Science Foundation of Fujian Province of China(Grant No.2013J05096)
文摘The structural and optical properties of InGaN/GaN multiple quantum wells （MQWs） with different barrier thick-nesses are studied by means of high resolution X-ray diffraction （HRXRD）, a cross-sectional transmission electron mi-croscope （TEM）, and temperature-dependent photoluminescence （PL） measurements. HRXRD and cross-sectional TEM measurements show that the interfaces between wells and barriers are abrupt and the entire MQW region has good periodic- ity for all three samples. As the barrier thickness is increased, the temperature of the turning point from blueshift to redshift of the S-shaped temperature-dependent PL peak energy increases monotonously, which indicates that the localization po- tentials due to In-rich clusters is deeper. From the Arrhenius plot of the normalized integrated PL intensity, it is found that there are two kinds of nonradiative recombination processes accounting for the thermal quenching of photoluminescence, and the corresponding activation energy （or the localization potential） increases with the increase of the barrier thickness. The dependence on barrier thickness is attributed to the redistribution of In-rich clusters during the growth of barrier layers, i.e., clusters with lower In contents aggregate into clusters with higher In contents.
基金Supported by the National Natural Science Foundation of China under grant Nos 91023048,61106044,and 61274052.
文摘A tunable grating-coupled external cavity(EC)laser is realized by employing a GaN-based laser diode as the gain device.A tuning range of 4.47 nm from 403.82 to 408.29 nm is achieved.Detailed investigations reveal that the injection current strongly influences the performance of the EC laser.Below the free-running lasing threshold,EC laser works stably.While above the free-running lasing threshold,a Fabry–Pérot(F-P)resonance peak in the emission spectrum and a smooth kink in the output power-injection current characteristic curve are observed,suggesting the competition between the inner F-P cavity resonance and EC resonance.Furthermore,the tuning range is found to be asymmetric and occurs predominantly on the longer wavelength side.This is interpreted in terms of the asymmetric gain distribution of GaN-based quantum well material.
基金Supported by the Major Research Plan of the National Natural Science Foundation of China under Grant No 91023048the National Natural Science Foundation of China under Grant Nos 61106044 and 10974165the Doctoral Program Foundation of Institutions of Higher Education of China under Grant No 20110121110029.
文摘Laser lift-off(LLO),by which GaN is separated from sapphire,is demonstrated to be a promising technique for advanced GaN-based optoelectronic devices.Its physical insight,however,is still not fully understood.We study systematically the effect of laser pulse width on the LLO process and the property of GaN.To estimate accurately the temperature distribution and the decomposed thickness of GaN,fluctuation in the pulse laser energy is taken into account.It is found that the temperature at the interface is increased in a higher speed for a narrower pulse width.In addition,less damage to the GaN film is expected for a narrower pulse width owing to the smaller heated area,lower transient temperature and lower N2 vapor pressure encountered during LLO.Some experimental results reported in literature are explained well.Our results are useful in understanding the effect of laser pulse width and can be taken as references in LLO of GaN/sapphire structures.
基金Project supported by the Postdoctoral Science Foundation of China(Grant No.2015M582041)the Special Project on the Integration of Industry,Education and Research of Aviation Industry Corporation of China
文摘Silica whispering gallery mode（WGM） microcavities were fabricated by the buffered oxide etcher and potassium hydroxide wet etching technique without any subsequent chemical or laser treatments. The silicon pedestal underneath was an octagonal pyramid, thus providing a pointed connection area with the top silica microdisk while weakly influencing the resonance modes. The sidewalls of our microdisks were wedge shaped, which was believed to be an advantage for the mode confinement. Efficient coupling from and to the 60 μm diameter microdisk structure was achieved using tapered optical fibres, exhibiting a quality factor of 1.5×10^4 near a wavelength of 1550 nm. Many resonance modes were observed, and double transverse electric modes were identified by theoretical calculations. The quality factor of the microdisks was also analysed to deduce the cavity roughness. The wet etching technique provides a more convenient avenue to fabricate WGM microdisks than conventional fabrication methods.
基金Project supported by the Science Challenge Project,China(Grant No.TZ2016003)National Key Research and Development Program of China(Grant Nos.2016YFB0400803 and 2017YFE0131500)the Fund from the State Key Laboratory of Optoelectronic Materials and Technologies,Sun Yat-sen University,China。
文摘Photoluminescence(PL)characteristics of the structure consisting of green InGaN/GaN multiple quantum wells(MQWs)and low indium content InGaN/GaN pre-wells are investigated.Several PL peaks from pre-wells and green InGaN/GaN MQWs are observed.The peak energy values for both pre-wells and green InGaN/GaN MQWs display an S-shaped variation with temperature.In addition,the differences in the carrier localization effect,defect density,and phonon-exciton interaction between the pre-wells and green InGaN/GaN MQWs,and the internal quantum efficiency of the sample are studied.The obtained results elucidate the mechanism of the luminescence characteristics of the sample and demonstrate the significant stress blocking effect of pre-wells.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11474235 and 61274052the Fundamental Research Funds for the Central Universities under Grant No 2013121024the Key Lab of Nanodevices and Nanoapplications,Suzhou Institute of Nano-Tech and Nano-Bionics of Chinese Academy of Sciences under Grant No 14ZS02
文摘In diffusion to blue light-emitting diode （LED） wafers is performed by the inductive coupled plasma （ICP） treatment of a covering layer of indium tin oxide （ITO） on the wafer surface. The electrical property of the p- type contact is improved and the redshift of photoluminescence （PL） from the InGaN quantum well of the wafer is found. Measurements by x-ray photoelectron spectroscopy （XPS） demonstrate that In atoms have diffused into p-GaN. Reflectance spectra of the sample surface reveal the variation caused by the ICP treatment. A model of compensation of the in-plane strain of the InGaN layer is used to explain the redshift of the PL data. Finally, LEDs are fabricated by using as-grown and ICP-treated wafers and their properties are compared. Under an injection current of 20mA, LEDs with ICP-induced In doping show a decrease of 0.3 V in the forward voltage and an increase of 23% in the light output, respectively.
基金supported by the National Key Research and Development Program of China(2017YFE0131500)the National Natural Science Foundation of China(62104204 and U21A20493)。
