Browsing by Author "Tu, P. M."

Now showing 1 - 5 of 5

High efficiency light emitting diode with anisotropically etched GaN-sapphire interface
(2009-07-27)
Lo, M. H.
;
Tu, P. M.
;
Wang, C. H.
;
Hung, C. W.
;
Hsu, S. C.
We report the fabrication and study of high efficiency ultraviolet light emitting diodes with inverted micropyramid structures at GaN-sapphire interface. The micropyramid structures were created by anisotropic chemical wet etching. The pyramid structures have significantly enhanced the light output efficiency and at the same time also improved the crystal quality by partially relieving the strain and reducing the dislocation defects in GaN. The electroluminescent output power at normal direction was enhanced by 120% at 20 mA injection current and the output power integrated over all directions was enhanced by 85% compared to a reference sample.
Improved output power of GaN-based ultraviolet light-emitting diodes with sputtered AlN nucleation layer
(2015-03-15)
Chiu, C. H.
;
Lin, Y. W.
;
Tsai, M. T.
;
Lin, B. C.
;
Li, Z. Y.
In this work, the ultraviolet light emitting diodes (UV -LEDs) at 380 no were grown on patterned sapphire substrate (PSS) by atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD). A sputtered AlN nucleation layer was utilized on the PSS to enhance the quality of the epitaxial layer. By using high resolution X-ray diffraction, the full width at half maximum of the rocking curve shows that the UV-LEDs with sputtered AlN nucleation layer had better crystalline quality when compared to conventional GaN nucleation samples. From the scanning electron microscope (SEM) and transmission electron microscopy (TEM) images, it can be observed that the Lip and sidewall portion of the pattern was smooth using the sputtered AlN nucleation layer. The threading dislocation densities (TDDs) are reduced from 6 x 107 cm(-2) to 2.5 x 107 cm(-2) at the interface between the u-GaN layers for conventional and AlN PSS devices, respectively. As a result, a much higher light output povver was achieved. The light output power at an injection current of 20 mA was enhanced by 30%. Further photoluminescence (PL) measurement and numerical simulation confirm that this increase or output power can be attributed to the improvement of material quality and light extraction. (C) 2014 Elsevier B.V. All rights reserved.
Influence of free-standing GaN substrate on ultraviolet light-emitting-diodes by atmospheric-pressure metal-organic chemical vapor deposition
(2013-01-01)
Shieh, C. Y.
;
Li, Z. Y.
;
Chiu, C. H.
;
Tu, P. M.
;
Kuo, H. C.
We reported the influence of free-standing (FS) GaN substrate on ultraviolet light-emitting-diodes (UV LEDs) by atmospheric-pressure metal-organic chemical vapor deposition (APMOCVD). The Raman spectrum shows the in-plane compressive stress of the GaN epitaxial structures grown on FS GaN substrate. Besides, the Raman spectrum reveals the relation between the crystal quality and the carrier localization degree in multi-quantum wells (MQWs). High resolution X-ray diffraction (HRXRD) analysis results show that the In0 025Ga0 975N/Al0 08Ga0 92N MQWs grown on FS GaN substrate has higher indium mole fraction than sapphire at the same growth conditions. The higher indium incorporation is corresponding with the red-shift 6 nm (387 nm) of the room temperature photoluminescence (PL) peak. The full widths at half maximum (FWHM) of omega-scan rocking curve in (002) and (102) reflectance on FS GaN substrate (83 arcsec and 77 arcsec) are narrower than UV LEDs grown on sapphire (288 arcsec and 446 arcsec). This superior quality may attribute to homoepitaxial growth structure and better strain relaxation in the FS GaN substrate. An anomalous temperature behavior of PL in UV LEDs designated as an S-shaped peak position dependence and W-shaped linewidth dependence indicate that exciton/carrier motion occurs via photon-assisted tunneling through localized states, what results in incomplete thermalization of localized excitons at low temperature. The Gaussian broadening parameters of carrier localization is about 16.98 meV from the temperature dependent photoluminescence (TDPL) measurement. The saturation temperature from the TDPL linewidth of UV LEDs on FS GaN substrate at about 175 K represents a crossover from a nonthermalized to thermalized energy distribution of excitons.
Performance enhancement of GaN-based flip-chip ultraviolet light-emitting diodes with a RPD AlN nucleation layer on patterned sapphire substrate
(2014-08-01)
Lin, B. C.
;
Chiu, C. H.
;
Lee, C. Y.
;
Han, H. V.
;
Tu, P. M.
In this work, flip-chip ultraviolet light-emitting diodes (FCUV-LEDs) on patterned sapphire substrate (PSS) at 375 nm were grown by an atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD). A specialized reactive plasma deposited (RPD) AlN nucleation layer was utilized on the PSS to enhance the quality of the epitaxial layer. By using high-resolution X-ray diffraction, the full-width at half-maximum of the rocking curve shows that the FCUV-LEDs with RPD AlN nucleation layer had better crystalline quality when compared to conventional GaN nucleation samples. From the transmission electron microscopy (TEM) image, it can be observed that the tip and incline portion of the pattern was smooth using the RPD AlN nucleation layer. The threading dislocation densities (TDDs) are reduced from 7 x 10(7) cm(-2) to 2.5 x 10(7) cm(-2) at the interface between the u-GaN layers for conventional and AlN PSS devices, respectively. As a result, a much higher light output power was achieved. The improvement of light output power at an injection current of 20 mA was enhanced by 30%. Further photoluminescence measurement and numerical simulation confirm such increase of output power can be attributed to the improvement of material quality and light extraction. (C) 2014 Optical Society of America
Study on GaN micro-rod growth by nature patterned sapphire substrate
(2009)
Hsu, S. C.
;
Tu, P. M.
;
Chen, I. R.
;
Cheng, Y. J.
;
光電工程學系
In this study, we Investigated the kinetics and etched morphology on sapphire substrate by mixing acid solutions We developed different etching conditions to produce various etching morphology patterns on sapphire surface Then, GaN micro-rod embedded with quantum wells (QWs) were grown on the patterned sapphire surface The cathode luminescence (CL) images of these QW embedded micro-rods have shown great crystal quality.