Browsing by Author "Chang, Sheng-Po"

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Efficiency Enhancement in InGaN Photovoltaic Cells With Inverted Textured Surface
(2017-08-15)
Wu, Ming-Hsien
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Horng, Ray-Hua
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Liao, Wen-Yih
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Chang, Sheng-Po
;
Chang, Shoou-Jinn
We report on the improvement of conversion efficiency of InGaN photovoltaic (PV) cells with inverted textured surface (ITS). InGaN PV cells with ITS showed short-circuit current density and conversion efficiency of 0.63 mA/cm(2) and 1.01%, which are 68.17% and 73.33% higher than the characteristics of conventional InGaN PV cells, respectively. The improvement can be attributed to the reduction of both the shading effect of the electrode contact pad and surface reflection of the incident irradiation under one-sun air-mass 1.5-G illumination (100 mW/cm(2)).
Growth and Crystal Structure Investigation of InAs/GaSb Heterostructure Nanowires on Si Substrate
(2018-11-01)
Kakkerla, Ramesh Kumar
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Hsiao, Chih-Jen
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Anandan, Deepak
;
Singh, Sankalp Kumar
;
Chang, Sheng-Po
We report gold-free growth of vertically aligned InAs/GaSb heterostructure nanowires (NWs) on Si(111) substrate by metal organic chemical vapor deposition technique. The effect of growth temperature on morphology and growth rate for InAs and InAs/GaSb heterostructure NWs were investigated. A combination of high material flow rates and optimum temperature (600 degrees C) has given better crystal quality of InAs nanowires. The morphology and shell thickness of NWs as observed by scanning electron microscope and transmission electron microscope (TEM) measurements can be tuned by the growth temperature. Electron microscopy also shows the formation of GaSb both in radial and axial directions outside the InAs NW core at certain growth temperatures. Crystal structure of InAs and InAs/GaSb heterostructure NWs was analyzed by high-resolution TEM and fast Fourier transform analysis. Using good crystalline InAs core grown at optimized growth temperature (600 degrees C), GaSb shell has been grown without any misfit dislocations at the core-shell interface. Basic electrical properties have been measured by forming ohmic contacts. I-V characteristics exhibit linear response indicating good ohmic behavior. These results show good control over InAs NWs growth, the GaSb shell thickness, and its crystal quality, which are essential for future nanoelectronic devices such as tunneling FET.
Growth of ultrathin GaSb layer on GaAs using metal-organic chemical vapor deposition with Sb interfacial treatment
(2016-09)
Hsiao, Chih-Jen
;
Minh-Thien-Huu Ha
;
Hsu, Ching-Yi
;
Lin, Yueh-Chin
;
Chang, Sheng-Po
GaSb epitaxial layers were directly grown on GaAs substrates by metal-organic chemical vapor deposition involving Sb interfacial treatment with optimized growth temperature and V/III ratio. The interfacial treatment effectively reduces the surface energy and strain energy difference, resulting in a quasi-2D growth mode. When the GaSb layer was grown at 520 degrees C, the strain induced by lattice mismatch was accommodated by 90 degrees dislocations with a period of 5.67 nm. By optimizing the V/III ratio, the surface roughness of the ultrathin GaSb/GaAs heterostructure was reduced, resulting in a reduced carrier scattering and improved electronic properties. (C) 2016 The Japan Society of Applied Physics
Performance improvement of highly mismatched GaSb layers on GaAs by interfacial-treatment-assisted chemical vapor deposition
(2017-01)
Hsiao, Chih-Jen
;
Minh-Thien-Huu Ha
;
Liu, Chun-Kuan
;
Hong-Quan Nguyen
;
Yu, Hung-Wei
Strain-relieved GaSb quantum dots on GaAs can be achieved by either periodic interfacial misfit (IMF) or the conventional Stranski-Krastanov (SK) growth modes by changing the growth parameters. In this study, the Sb interfacial treatment was employed to improve the GaSb crystal quality including low defect density, smooth surface morphology, and high hole mobility. This technique yields two-dimensional (2D) islands with a height as low as 1.7 nm and width up to 190 nm in the IMF growth mode. In contrast to the interfacial treatments conventionally employed in the initial strain relaxation of GaSb/GaAs hererostructure, the Sb treatment promotes the formation of strong Ga-Sb bonds on the surface of the grown island, which effectively reduces the interfacial free energy and thus promotes the formation of 2D islands. With the Sb interfacial treatment, a high-relaxation 100-nm GaSb epilayer was grown on the GaAs substrate, the epilayers was strain relaxed and exhibited enhanced electrical properties with a high hole mobility of similar to 667 cm(2) V-1 s(-1) and with superior optical properties as evidenced by the photoluminescence B-line peak. The results of this study demonstrate an effective interfacial-treatment growth technique to relax the initial strain for the highly mismatched GaSb layers grown on a GaAs substrate.