In this study, we investigated the behaviors of optical and electrical characteristics according to the epitaxial structure conditions for improving the light efficiency of AlGaInP based LEDs. The quaternary AlGaInP material system, grown by metal organic chemical vapor deposition, has proven to be ...
In this study, we investigated the behaviors of optical and electrical characteristics according to the epitaxial structure conditions for improving the light efficiency of AlGaInP based LEDs. The quaternary AlGaInP material system, grown by metal organic chemical vapor deposition, has proven to be the best choice in many application such as interior and exterior automotive lighting, traffic lights, full color displays, and all kinds of indoor and outdoor signs. One of the major issue in quaternary AlGaInP LEDs design is the smaller conduction band offset that limits the electron confining potential leading to electron hetero-barrier leakage. Furthermore, the AlGaInP-based LEDs are grown on GaAs substrates that are opaque for the emitting wavelengths of this quaternary material. In order to prevent the light absorption and improve the light output power, it is important to consider a distributed Bragg reflector (DBR) structure and optimize the structure design for the better external quantum efficiency. This dissertation concentrates on the development and optimization of epitaxial structures for improving AlGaInP-based LEDs. The first part of this work presented the behaviors of optical and electrical characteristics according to the variation of well strain, and the corresponding change of well-thickness. As compressive well strain increased from 0.04 to 0.41 %, integrated PL intensity, radiative carrier lifetime, and device performance were significantly improved. This improvement was explained by that the strain-induced heavy hole-assisted recombination process reduced the radiative recombination lifetime owing to a reduced effective heavy hole mass, and a reduced well thickness resulted in stronger spatial localization of carriers in the well region, hence, an improved spontaneous light-emitting efficiency. Secondly, we have studied the behavior of optical and electrical characteristics according to the number of well pairs. As the number of quantum well was increased from 2 to 35 pairs, the radiative recombination efficiency and device performance significantly improved because of suppressing the carrier overflow by decreasing the carrier density in the active region and shortening the carrier transfer time from the barrier to well. At further increase of the number of QWs to 50 pairs, the optical and device performances started to degrade due to the increase of internal loss in the active region, such as the well volume itself acting as a light absorbing layer and because of the aluminum oxide complexes in the barrier region. The third part focuses on the morphological and optical characteristics of quantum dot-based LED structures and the demonstration of device performances and td 0.33LE0.67P materials quamed 3-D dots at a density of 3 x 109 cm-2, an average d ight of 5.5 nm, and a diameter of 160 nm and tTD-PL data showed a signal of the 2-D wetting layer at 58atnm, as ita snsistent with the S-K growth mode aIn addition, the PL spectrum of the d 0.33LE0.67P Qes was well maintained to a temperature of 300 K and tdevice performance showed a normal p-n diode behavior with a quaward voltage of 1.79 V at 20 mA, and a maximum light output power of 33.8 mW at 480 mA and tlow wavelength shift of 4r 8 x 10-3 nm/mA provides further evidence of the QD nature of the emitting layer. Finally, the growth conditions of the DBR structure are optimized and developed high-brightness resonant cavity (RC) LEDs for the improvement of light extraction efficiency. The characteristics of the DBR structure Relatively are enhanced at the high growth temperature, high AsH3 flow, and low growth pressure owing to the increase of the step mobility. In order to develop high-power RCLEDs, we investigated the effects of reflectivity of p-DBR and the number of QWs. As the reflectivity of p-DBR increased, the FWHM of EL spectrum was reduced from 12.3 to 3.6 nm, whereas the relative integrated intensity decreased from 1.0 to 0.37, which was attributed to the improvement of spectral purity of the peaks with the in-phase condition. As the number of QWs decreased, the optical power increased owing to the reduction of the optical loss of the recycling light in the active region. Using the optimized structural conditions, we demonstrated RCLEDs having a modulation speed up to 130 MHz in free space, which clearly showed that the optimized RCLED structure is a promising candidate for visible light communications.
In this study, we investigated the behaviors of optical and electrical characteristics according to the epitaxial structure conditions for improving the light efficiency of AlGaInP based LEDs. The quaternary AlGaInP material system, grown by metal organic chemical vapor deposition, has proven to be the best choice in many application such as interior and exterior automotive lighting, traffic lights, full color displays, and all kinds of indoor and outdoor signs. One of the major issue in quaternary AlGaInP LEDs design is the smaller conduction band offset that limits the electron confining potential leading to electron hetero-barrier leakage. Furthermore, the AlGaInP-based LEDs are grown on GaAs substrates that are opaque for the emitting wavelengths of this quaternary material. In order to prevent the light absorption and improve the light output power, it is important to consider a distributed Bragg reflector (DBR) structure and optimize the structure design for the better external quantum efficiency. This dissertation concentrates on the development and optimization of epitaxial structures for improving AlGaInP-based LEDs. The first part of this work presented the behaviors of optical and electrical characteristics according to the variation of well strain, and the corresponding change of well-thickness. As compressive well strain increased from 0.04 to 0.41 %, integrated PL intensity, radiative carrier lifetime, and device performance were significantly improved. This improvement was explained by that the strain-induced heavy hole-assisted recombination process reduced the radiative recombination lifetime owing to a reduced effective heavy hole mass, and a reduced well thickness resulted in stronger spatial localization of carriers in the well region, hence, an improved spontaneous light-emitting efficiency. Secondly, we have studied the behavior of optical and electrical characteristics according to the number of well pairs. As the number of quantum well was increased from 2 to 35 pairs, the radiative recombination efficiency and device performance significantly improved because of suppressing the carrier overflow by decreasing the carrier density in the active region and shortening the carrier transfer time from the barrier to well. At further increase of the number of QWs to 50 pairs, the optical and device performances started to degrade due to the increase of internal loss in the active region, such as the well volume itself acting as a light absorbing layer and because of the aluminum oxide complexes in the barrier region. The third part focuses on the morphological and optical characteristics of quantum dot-based LED structures and the demonstration of device performances and td 0.33LE0.67P materials quamed 3-D dots at a density of 3 x 109 cm-2, an average d ight of 5.5 nm, and a diameter of 160 nm and tTD-PL data showed a signal of the 2-D wetting layer at 58atnm, as ita snsistent with the S-K growth mode aIn addition, the PL spectrum of the d 0.33LE0.67P Qes was well maintained to a temperature of 300 K and tdevice performance showed a normal p-n diode behavior with a quaward voltage of 1.79 V at 20 mA, and a maximum light output power of 33.8 mW at 480 mA and tlow wavelength shift of 4r 8 x 10-3 nm/mA provides further evidence of the QD nature of the emitting layer. Finally, the growth conditions of the DBR structure are optimized and developed high-brightness resonant cavity (RC) LEDs for the improvement of light extraction efficiency. The characteristics of the DBR structure Relatively are enhanced at the high growth temperature, high AsH3 flow, and low growth pressure owing to the increase of the step mobility. In order to develop high-power RCLEDs, we investigated the effects of reflectivity of p-DBR and the number of QWs. As the reflectivity of p-DBR increased, the FWHM of EL spectrum was reduced from 12.3 to 3.6 nm, whereas the relative integrated intensity decreased from 1.0 to 0.37, which was attributed to the improvement of spectral purity of the peaks with the in-phase condition. As the number of QWs decreased, the optical power increased owing to the reduction of the optical loss of the recycling light in the active region. Using the optimized structural conditions, we demonstrated RCLEDs having a modulation speed up to 130 MHz in free space, which clearly showed that the optimized RCLED structure is a promising candidate for visible light communications.
주제어
#발광다이오드
※ AI-Helper는 부적절한 답변을 할 수 있습니다.