Browsing by Author "Cheng, Hui-Yu"

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3D structural construction of GaN-based light emitting diode by confocal micro-Raman spectroscopy
(2016-01-01)
Li, Heng
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Chang, Chiao-Yun
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Cheng, Hui-Yu
;
Chen, Wei-Liang
;
Huang, Yi-Hsin
The key issue for light emission strength of GaN-based LEDs is the high defect density and strain in MQWs causing the electric polarization fields. In this work, we construct 3D confocal microspectroscopy to clarify strain distribution and the relationship between photoluminescence (PL) intensity and pattern sapphire substrate (PSS). From 3D construction of E-2(high) Raman and PL mapping, the dislocation in MQW can be traced to the cone tip of PSS and the difference in E-2(high) Raman mapping between substrate and surface is also measured. The ability to measure strain change in 3D structure nondestructively can be applied to explore many structural problems of GaN-based optoelectronic devices.
Layer-Dependent and In-Plane Anisotropic Properties of Low-Temperature Synthesized Few-Layer PdSe2 Single Crystals
(2020-04-28)
Lu, Li-Syuan
;
Chen, Guan-Hao
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Cheng, Hui-Yu
;
Chuu, Chih-Piao
;
Lu, Kuan-Cheng
Palladium diselenide (PdSe2), a peculiar noble metal dichalcogenide, has emerged as a new two-dimensional material with high predicted carrier mobility and a widely tunable band gap for device applications. The inherent in-plane anisotropy endowed by the pentagonal structure further renders PdSe2 promising for novel electronic, photonic, and thermoelectric applications. However, the direct synthesis of few-layer PdSe2 is still challenging and rarely reported. Here, we demonstrate that few-layer, single-crystal PdSe2 flakes can be synthesized at a relatively low growth temperature (300 degrees C) on sapphire substrates using low-pressure chemical vapor deposition (CVD). The well-defined rectangular domain shape and precisely determined layer number of the CVD-grown PdSe2 enable us to investigate their layer-dependent and in-plane anisotropic properties. The experimentally determined layer-dependent band gap shrinkage combined with first-principle calculations suggest that the interlayer interaction is weaker in few-layer PdSe2 in comparison with that in bulk crystals. Field-effect transistors based on the CVD-grown PdSe2 also show performances comparable to those based on exfoliated samples. The low-temperature synthesis method reported here provides a feasible approach to fabricate high-quality few-layer PdSe2 for device applications.
Three dimensional characterization of GaN-based light emitting diode grown on patterned sapphire substrate by confocal Raman and photoluminescence spectromicroscopy
(2017-03-30)
Li, Heng
;
Cheng, Hui-Yu
;
Chen, Wei-Liang
;
Huang, Yi-Hsin
;
Li, Chi-Kang
We performed depth-resolved PL and Raman spectral mappings of a GaN-based LED structure grown on a patterned sapphire substrate (PSS). Our results showed that the Raman mapping in the PSS-GaN heterointerface and the PL mapping in the InxGa1-xN/GaN MQWs active layer are spatially correlated. Based on the 3D construction of E2(high) Raman peak intensity and frequency shift, V-shaped pits in the MQWs can be traced down to the dislocations originated in the cone tip area of PSS. Detail analysis of the PL peak distribution further revealed that the indium composition in the MQWs is related to the residual strain propagating from the PSS-GaN heterointerface toward the LED surface. Numerical simulation based on the indium composition distribution also led to a radiative recombination rate distribution that shows agreement with the experimental PL intensity distribution in the InxGa1-xN/GaN MQWs active layer.
Three dimensional compressive strain and its effect on optical properties of GaN-based light emitting diode grown on patterned sapphire substrate by confocal spectromicroscopy
(2017-01-01)
Li, Heng
;
Cheng, Hui-Yu
;
Chen, Wei-Liang
;
Huang, Yi-Hsin
;
Li, Chi-Kang
We performed depth-resolved spectral mappings of GaN-based LED and results showed that the strain distribution propagating from PSS-GaN heterointerface toward surface and the PL intensity are spatially correlated. Numerical simulation based on indium composition distribution led to a radiative recombination rate distribution shows agreement with the experimental PL intensity distribution.