Browsing by Author "Kao, Pin-Hsu"

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Broadband antireflection and field emission properties of TiN-coated Si-nanopillars
(2014-08-21)
Chang, Yuan-Ming
;
Ravipati, Srikanth
;
Kao, Pin-Hsu
;
Shieh, Jiann
;
Ko, Fu-Hsiang
Broadband antireflection and field emission characteristics of silicon nanopillars (Si-NPs) fabricated by self-masking dry etching in hydrogen-containing plasma were systematically investigated. In particular, the effects of ultrathin (5-20 nm) titanium nitride (TiN) films deposited on Si-NPs by atomic layer deposition (ALD) on the optoelectronic properties were explored. The results showed that by coating the Si-NPs with a thin layer of TiN the antirefiection capability of pristine Si-NPs can be significantly improved, especially in the wavelength range of 1000-1500 nm. The enhanced field emission characteristics of these TiN/Si-NP heterostructures suggest that, in addition to the reflectance suppression in the long wavelength range arising from the strong wavelength-dependent refractive index of TiN, the TiN-coating may have also significantly modified the effective work function at the TiN/Si interface as well.
Enhanced field emission characteristics in metal-coated Si-nanocones
(2013)
Chang, Yuan-Ming
;
Kao, Pin-Hsu
;
Tai, Hung-Ming
;
Wang, Hau-Wei
;
Lin, Chih-Ming
Metallic gold (Au) and platinum (Pt) thin films were deposited on silicon nanocones (Si-NCs) by sputtering to elucidate the effects of work function and conductivities on the field electron emission characteristics of surface-modified Si-NCs. The results showed that for Pt/Si-NCs and Au/Si-NCs, although the turn-on field defined at a corresponding current density of 10 mu A cm(-2) only improved from 4.20 V mu m(-1) for bare Si-NCs to 3.65 and 2.90 V mu m(-1), respectively, the emission current density measured at 5.00 V mu m(-1) was enhanced by orders of magnitude, reaching 1.82 mA cm(-2) for Au/Si-NCs. Compared to those obtained from various surface-modified Si-nanostructures, such as ZnO/Si-nanopillars and ferroelectrics/Si-nanotips, the current results represent an interesting alternative route for producing surface-modified Si-NCs that might be useful for optical and electronic applications.
Fabrication and optoelectronic properties of core-shell biomimetic ZnO/Si nanoball arrays
(2012)
Chang, Yuan-Ming
;
Kao, Pin-Hsu
;
Liu, Mao-Chen
;
Lin, Chih-Ming
;
Lee, Hsin-Yi
We report an effective process scheme comprising a single-step Ag sputtering with subsequent dry etching and atomic layer deposition (ALD) process for fabricating biomimetic ZnO/Si nanoball (ZnO/Si-NB) core-shell nanostructures directly on Si substrates. The obtained ZnO/Si-NB core-shell nanostructures consist of similar to 30 nm thick ZnO films grown on Si frustums produced by means of dry etching masked by the self-assembled silver nanodots created by single-step sputtering. The ZnO films were deposited using atomic layer deposition under an ambient temperature of 200 degrees C. The photoluminescence (PL) measurements on these ZnO/Si-NB core-shell nanostructures showed that the visible range emission was almost completely absent and only the ultraviolet emission (3.28 eV peak) resulting from the free excitons was observed, indicating that the films indeed have high crystalline quality. Moreover, a dramatic improvement of the field emission performance was observed for ZnO/Si-NB core-shell nanostructures as compared to the bare Si frustum arrays. The detailed analyses on the field enhancement factor (beta value) based on the Fowler-Nordheim field emission model indicate that the effective work function of the ZnO/Si-NB core-shell nanostructures might be significantly different from that of either ZnO or Si.
Field Emission in Vertically Aligned ZnO/Si-Nanopillars with Ultra Low Turn-On Field
(2012-03-01)
Chang, Yuan-Ming
;
Liu, Mao-Chen
;
Kao, Pin-Hsu
;
Lin, Chih-Ming
;
Lee, Hsin-Yi
An effective method of fabricating vertically aligned silicon nanopillars (Si-NPs) was realized by using the self-assembled silver (Ag) nanodots as natural metal-nanomask during dry etching process. The obtained Si-NPs were preferentially aligned along the c-axis direction. Ultrathin ZnO films (similar to 9 nm) were subsequently deposited on the Si-NPs by atomic layer deposition (ALD) to enhance the field emission property. The average diameter of the ZnO/Si-NPs is in the order of tens of nanometers, which enables efficient field emission and gives rise to marked improvement in the field enhancement factor, beta. The turn-on field defined by the 10 mu A/cm(2) current density criterion is similar to 0.74 V/mu m with an estimated beta approximate to 1.33x10(4). The low turn-on field and marked enhancement in beta were attributed to the small radius of curvature, high aspect ratio, and perhaps more importantly, proper density distribution of the ZnO/Si-NPs.
Optoelectronic properties in vertically aligned ZnO/Si-nanopillars
(2012)
Lee, Hsin-Yi
;
Chang, Yuan-Ming
;
Tseng, Wen-Shou
;
Kao, Pin-Hsu
;
Wang, Hau-Wei
An effective method of fabricating vertically aligned silicon nanopillars (Si-NPs) was realized by using the self-assembled silver nanodots as natural metal-nanomask for subsequent etching process. Ultrathin (similar to 9 nm) ZnO films were deposited on the Si-NPs by atomic layer deposition to enhance the field emission property. The turn-on field defined by the 10 mu A/cm(2) current density criterion is similar to 0.74 V/mu m with an estimated beta similar to 1.33X10(4). The low turn-on field and marked enhancement in beta were attributed to the small radius of curvature, high aspect ratio, and perhaps more importantly, proper density distribution of the ZnO/Si-NPs. On the other hand, room-temperature ultraviolet (UV) luminescence was investigated for the atomic layer deposited ZnO films grown on Si nanowires fabricated by self-masking dry etching in hydrogen-containing plasma. For films deposited at 200 degrees C, an intensive UV emission corresponding to free-exciton recombination was observed with a nearly complete suppression of the defect-associated broad visible range emission peak.