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21.
The high power GaN-based blue light emitting diode (LED) on an 80-μ-thick GaN template is proposed and even realized by several technical methods like metal organic chemical vapor deposition (MOCVD), hydride vapor-phase epitaxial (HVPE), and laser lift-off (LLO). Its advantages are demonstrated from material quality and chip processing. It is investigated by high resolution X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), Rutherford back-scattering (RBS), photoluminescence, current-voltage and light output-current measurements. The width of (0002) reflection in XRD rocking curve, which reaches 173" for the thick GaN template LED, is less than that for the conventional one, which reaches 258". The HRTEM images show that the multiple quantum wells (MQWs) in 80-μm-thick GaN template LED have a generally higher crystal quality. The light output at 350 mA from the thick GaN template LED is doubled compared to traditional LEDs and the forward bias is also substantially reduced. The high performance of 80-μm-thick GaN template LED depends on the high crystal quality. However, although the intensity of MQWs emission in PL spectra is doubled, both the wavelength and the width of the emission from thick GaN template LED are increased. This is due to the strain relaxation on the surface of 80-μm-thick GaN template, which changes the strain in InGaN QWs and leads to InGaN phase separation. 相似文献
22.
Strain effects on the polarized optical properties of InGaN with different In compositions 下载免费PDF全文
Strain effects on the polarized optical properties of c-plane and
m-plane Inx1-xN were discussed for different In
compositions (x=0, 0.05, 0.10, 0.15) by analyzing the relative
oscillator strength (ROS) and energy level splitting of the three
transitions related to the top three valence bands (VBs). The ROS
was calculated by applying the effective-mass Hamiltonian based on
k. p perturbation theory. For c-plane
InxGa1-xN, it was found that the ROS of | X >
and | Y >-like states were superposed with each
other. Especially, under compressive strain, they dominated in the
top VB whose energy level also went up with strain, while the ROS of the
| Z >-like state decreased in the second band.
For m-plane InxGa1-xN under compressive strain, the top
three VBs were dominated by | X >, | Z
>, and | Y >-like states,
respectively, which led to nearly linearly-polarized light
emissions. For the top VB, ROS difference between | X
> and | Z >-like states became
larger with compressive strain.
It was also found that such tendencies were more evident in layers
with higher In compositions. As a result, there would be more TE modes
in total emissions from both c-plane and m-plane InGaN with compressive
strain and In content, leading to a larger polarization degree.
Experimental results of luminescence from InGaN/GaN quantum
wells (QWs) showed good coincidence with our calculations. 相似文献