Browsing by Author "Wu, Y. H."

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Advanced Metal-Gate/High-kappa CMOS with Small EOT and Better High Field Mobility
(2012)
Chin, Albert
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Chen, W. B.
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Chen, P. C.
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Wu, Y. H.
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Chi, C. C.
Continuously down-scaling the operation voltage, saving energy, and maintaining high performance are the major challenge for CMOS device. Small 0.95 similar to 1.4 nm equivalent-oxide thickness (EOT) and 1.4 similar to 2.5X better mobility than universal SiO2/Si data are achieved in metal-gate/high-kappa/Ge CMOS at 1 MV/cm effective field (E-eff). These excellent performances were achieved by using interface engineering and novel process, to overcome the poor high-kappa/Ge interface reaction, low source-drain dopant activation, and n(+)/p ohmic contact. The all-Ge CMOS with measured higher electron and hole mobility has irreplaceable merits of much simpler process, lower cost, and potentially higher yield than the InGaAs-nMOS/Ge-pMOS platform for IC manufacture.
Bimodel onset strain relaxation in InAs quantum dots with an InGaAs capping layer
(2010-08-30)
Chen, J. F.
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Chen, Ross C. C.
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Chiang, C. H.
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Chen, Y. F.
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Wu, Y. H.
Capping InAs quantum dots (QDs) with an InGaAs layer allows strain relaxation to induce a low-energy electron state below a set of fine dot family states, which is consistent with photoluminescence (PL) spectra. The evolution of InAs thickness suggests a bimodal onset relaxation, i.e., a fine dot family that is strain-relieved by indium outdiffusion from the QDs, as suggested by transmission electron microscopy, and a low-energy dot family that is strain relaxed by the generation of lattice misfits. The indium outdiffusion can explain an abnormal PL blueshift in 70 meV in the fine dot family at onset of strain relaxation. (C) 2010 American Institute of Physics. [doi:10.1063/1.3483757]
Channel Modification Engineering by Plasma Processing in Tin-Oxide Thin Film Transistor: Experimental Results and First-Principles Calculation
(2017-01-01)
Chiu, Y. C.
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Chen, P. C.
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Chang, S. L.
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Zheng, Z. W.
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Cheng, C. H.
In this paper, we investigated the effects of oxygen plasma treatment on tin oxide (SnOx) thin film transistors (TFTs). By using oxygen plasma treatment on SnOx active channel layer, excess oxygen was incorporated to the channel layer and converted oxygen-deficient SnOx to oxygen-rich SnO2-x, which in turn causes the device operation from p-type to n-type. Tuning the different exposure time of oxygen plasma, the optimal TFT device exhibits n-type properties with an on/off current ratio of 2.6 x 10(4), a very high field-effect mobility of 89 cm(2) V-1 s(-1), and a threshold voltage of -0.95 V. Furthermore, the effects of oxygen plasma treatment on band structure, density of states and electron density difference of the SnOx channel layer were performed by the first-principles calculation using density functional theory. The results show that the oxygen plasma treatment approach has high potential for high-performance TFT applications. (C) 2017 The Electrochemical Society. All rights reserved.
Effect of antimony incorporation on the density, shape, and luminescence of InAs quantum dots
(2008-07-15)
Chen, J. F.
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Chiang, C. H.
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Wu, Y. H.
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Chang, L.
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Chi, J. Y.
This work investigates the surfactant effect on exposed and buried InAs quantum dots (QDs) by incorporating Sb into the QD layers with various Sb beam equivalent pressures (BEPs). Secondary ion mass spectroscopy shows the presence of Sb in the exposed and buried QD layers with the Sb intensity in the exposed layer substantially exceeding that in the buried layer. Incorporating Sb can reduce the density of the exposed QDs by more than two orders of magnitude. However, a high Sb BEP yields a surface morphology with a regular periodic structure of ellipsoid terraces. A good room-temperature photoluminescence (PL) at similar to 1600 nm from the exposed QDs is observed, suggesting that the Sb incorporation probably improves the emission efficiency by reducing the surface recombination velocity at the surface of the exposed QDs. Increasing Sb BEP causes a blueshift of the emission from the exposed QDs due to a reduction in the dot height as suggested by atomic force microscopy. Increasing Sb BEP can also blueshift the similar to 1300 nm emission from the buried QDs by decreasing the dot height. However, a high Sb BEP yields a quantum well-like PL feature formed by the clustering of the buried QDs into an undulated planar layer. These results indicate a marked Sb surfactant effect that can be used to control the density, shape, and luminescence of the exposed and buried QDs. (C) 2008 American Institute of Physics.
Effect of gate sinking on the device performance, of the InGaP/AlGaAs/InGaAs enhancement-mode PHEMT
(2007-02-01)
Chu, L. H.
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Chang, E. Y.
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Chang, L.
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Wu, Y. H.
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Chen, S. H.
An enhancement-mode InGaP/AlGaAs/InGaAs pseudomorphic high-electron mobility transistor using platinum (Pt) as the Schottky contact metal was investigated for the first time. Following the Pt/Ti/Pt/Au gate metal deposition, the devices were thermally annealed at 325 degrees C for gate sinking. After the annealing, the device showed a positive threshold voltage (V-th) shift from 0.17 to 0.41 V and a very low drain leakage current from 1.56 to 0.16 mu A/mm. These improvements are attributed to the Schottky barrier height increase and the decrease of the gate-to-channel distance as Pt sinks into the InGaP Schottky layer during gate-sinking process. The shift in the V-th was very uniform across a 4-in wafer and was reproducible from wafer to wafer. The device also showed excellent RF power performance after the gate-sinking process.
Electron delocalization of tensily strained GaAs quantum dots in GaSb matrix
(2010-12-15)
Lin, T. C.
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Wu, Y. H.
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Li, L. C.
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Sung, Y. T.
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Lin, S. D.
The magneto-optical response of type-II tensily strained GaAs self-assembled quantum dots in GaSb was investigated in magnetic fields up to 14 T. By depositing different GaAs amount, the dot sizes and the corresponding emission energies were varied. We analyzed the carrier wave function extent of different dots using the diamagnetic shift results. It was found that, with the increase in the energy (the reduction in the dot size), the diamagnetic coefficient first rises quickly and then saturates at around 21 mu eV/T(2). Based on a simple calculation model, this unusual tendency is attributed to the electrons gradually spilling out of the quantum dot to the wetting layer as the dots get smaller. This delocalization effect is enhanced in this material system due to the tensile strain relaxation within the dots, which raises the conduction band edge over that in the wetting layer. (c) 2010 American Institute of Physics. [doi: 10.1063/1.3520669]
Geometrical correlations of quantum dots in InAs/GaAs superlattice structure from electron tomography
(2008-10-13)
Wu, Y. H.
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Chang, L.
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Chen, L. C.
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Chen, H. S.
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Chen, F. R.
In this study, the three-dimensional (3D) information about the structural properties of quantum dots (QDs) in InAs/GaAs superlattice structure has been illustrated using electron tomography in the mode of high-angle angular dark-field scanning transmission electron microscopy. Comparison of this 3D reconstruction with the two-dimensional projection at the same positions is made. The structural properties of embedded quantum dots have been evaluated from electron tomography. The correlation relationship of QDs in superlattice structure has been understood by accurate measurements of 3D geometric positions, which can be free of the overlapping effect from 2D cross section along different crystallographic orientations. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2998693]
Highly uniform low-power resistive memory using nitrogen-doped tantalum pentoxide
(2012-07-01)
Cheng, C. H.
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Chen, P. C.
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Wu, Y. H.
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Wu, M. J.
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Yeh, F. S.
Highly uniform current distributions of high resistance state (HRS) and low resistance state (LRS), low 0.6 pJ switching energy, fast 30 ns switching speed, and good 10(6) cycling endurance are achieved in Ni/GeOx/Ta2O5-yNy/TaN resistive random access memory (RRAM) devices. Such good performance is attributed to nitrogen-related acceptor level in Ta2O5-yNy for better hopping conduction, which leads to forming-free resistive switching and low self-compliance switching currents. (C) 2012 Elsevier Ltd. All rights reserved.
How do InAs quantum dots relax when the InAs growth thickness exceeds the dislocation-induced critical thickness?
(2012-01-01)
Chen, J. F.
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Lin, Y. C.
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Chiang, C. H.
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Chen, Ross C. C.
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Chen, Y. F.
A simple critical thickness for generating lattice misfits is insufficient to describe the onset strain relaxation in InAs quantum dots (QDs). A predominant dot family is shown to relieve its strain by In/Ga interdiffusion, rather than by lattice misfits, at the onset of strain relaxation. This argument is based on photoluminescence spectra, which show the emergence of a fine blueshifted transition at the onset of strain relaxation, along with a low-energy transition from a dot family degraded by lattice misfits. From the analysis of the temperature-dependent blueshift and energy separation between the ground and excited-state transitions, the blueshift is attributed to In/Ga interdiffusion. Transmission electron microscopy suggests a relaxation-induced indium migration from the interdiffused dot family to the dislocated dot family. Post-growth thermal annealing can further relieve strain by inducing more In/Ga interdiffusion in the interdiffused dot family and more dislocations in the dislocated dot family. This study explains the co-existence of strong carrier confinement in the QDs and enormous misfit-related traps in the capacitance-voltage spectra, and an elongated QD electron-emission time. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3675519]
Improving the photoluminescence properties of self-assembled InAs surface quantum dots by incorporation of antimony
(2011-08-15)
Chiang, C. H.
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Wu, Y. H.
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Hsieh, M. C.
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Yang, C. H.
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Wang, J. F.
This study investigates the effects of surfactant and segregation from InAs surface quantum dots (SQDs) by incorporating antimony (Sb) into the QD layers. The Sb surfactant effect extends planar growth and suppresses dot formation. Incorporating Sb can reduce the density of SQDs by more than two orders of magnitude. Photoluminescence (PL) reveals enhancement in the optical properties of InAs SQDs as the Sb beam equivalent pressure (BEP) increases. This improvement is caused by the segregation of Sb on the surface of SQDs, which reduces non-radiative recombination and suppresses carrier loss. The dark line at the SQDs surface in the transmission electron microscopic image suggests that the incorporated Sb probably segregates close to the surface of the SQDs. These results indicate a marked Sb segregation effect that can be exploited to improve the surface-sensitive properties of SQDs for biological sensing. Crown Copyright (C) 2011 Published by Elsevier B. V. All rights reserved.
Interfacial reactions of Pt-based Schottky contacts on nGaP
(2008-02-25)
Chu, L. H.
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Chang, E. Y.
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Wu, Y. H.
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Huang, J. C.
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Chen, Q. Y.
We have investigated the interfacial reaction between platinum and InGaP in a Schottky diode structure. There was a 7.5-nm-thick amorphous layer formed at the interface between Pt and InGaP after metal deposition. After annealing at 325 degrees C for 1 min, this amorphous layer increased to 12.8 nm and the reverse leakage current also decreased. The diffusion of Pt atoms and the crystallization of amorphous layer took place after annealing at 325 degrees C for 10 min. Prolonging the annealing to 3 h led to formation of Ga(2)Pt and GaPt(3) phases in InGaP and Schottky diodes degraded after these new phases were observed. (C) 2008 American Institute of Physics.
Long-Endurance Nanocrystal TiO(2) Resistive Memory Using a TaON Buffer Layer
(2011-12-01)
Cheng, C. H.
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Chen, P. C.
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Wu, Y. H.
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Yeh, F. S.
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Chin, Albert
Using nanocrystal (nc) TiO(2) and TaON buffer layer, the Ni/GeO(x)/nc-TiO(2)/TaON/TaN resistive random access memory (RRAM) showed forming-free resistive switching, self-compliance set/reset currents, excellent current distribution, low 0.7-pJ switching energy, and long 10(10) cycling endurance. The very long endurance in this novel RRAM may create new applications beyond Flash memory.
Long-Endurance Nanocrystal TiO2 Resistive Memory Using a TaON Buffer Layer
(2011-12-01)
Cheng, C. H.
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Chen, P. C.
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Wu, Y. H.
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Yeh, F. S.
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Chin, Albert
Using nanocrystal (nc) TiO2 and TaON buffer layer, the Ni/GeOx/nc-TiO2/TaON/TaN resistive random access memory (RRAM) showed forming-free resistive switching, self-compliance set/reset currents, excellent current distribution, low 0.7-pJ switching energy, and long 10(10) cycling endurance. The very long endurance in this novel RRAM may create new applications beyond Flash memory.
Nonpolar a-plane GaN grown on r-plane sapphire using multilayer AlN buffer by metalorganic chemical vapor deposition
(2011-01-15)
Chiang, C. H.
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Chen, K. M.
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Wu, Y. H.
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Yeh, Y. S.
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Lee, W. I.
Mirror-like and pit-free non-polar a-plane (11-20) GaN films are grown on r-plane (1-102) sapphire substrates using metalorganic chemical vapor deposition (MOCVD) with multilayer high-low-high temperature AlN buffer layers. The buffer layer structure and film quality are essential to the growth of a flat, crack-free and pit-free a-plane GaN film. The multilayer AlN buffer structure includes a thin low-temperature- deposited AlN (LT-AlN) layer inserted into the high-temperature-deposited AlN (HT-AlN) layer. The results demonstrate that the multilayer AlN buffer structure can improve the surface morphology of the upper a-plane GaN film. The grown multilayer AlN buffer structure reduced the tensile stress on the AlN buffer layers and increased the compressive stress on the a-plane GaN film. The multilayer AlN buffer structure markedly improves the surface morphology of the a-plane GaN film, as revealed by scanning electron microscopy. The effects of various growth V/III ratios was investigated to obtain a-plane GaN films with better surface morphology. The mean roughness of the surface was 1.02 nm, as revealed by atomic force microscopy. Accordingly, the multilayer AlN buffer structure improves the surface morphology and facilitates the complete coalescence of the a-plane GaN layer. (C) 2010 Elsevier B.V. All rights reserved.
Relaxation-induced lattice misfits and their effects on the emission properties of InAs quantum dots
(2007-09-05)
Chen, J. F.
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Wang, Y. Z.
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Chiang, C. H.
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Hsiao, R. S.
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Wu, Y. H.
Strain relaxation in InAs/InGaAs quantum dots (QDs) is shown to introduce misfits in the QD and neighboring GaAs bottom layer. A capacitance -voltage profiling shows an electron accumulation peak at the QD with a long emission time, followed by additional carrier depletion caused by the misfits in the GaAs bottom layer. The emission-time increase is explained by the suppression of tunneling for the QD excited states due to the additional carrier depletion. As a result, electrons are thermally activated from the QD states to the GaAs conduction band, consistent with observed emission energies of 0.160 and 0.068 eV which are comparable to the confinement energies of the QD electron ground and first-excited states, respectively, relative to the GaAs conduction band. This is in contrast to non-relaxed samples in which emission energy of 60 meV is observed, corresponding to the emission from the QD ground state to the first-excited state.
Strain relaxation and induced defects in InAsSb self-assembled quantum dots
(2006-06-05)
Chen, J. F.
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Hsiao, R. S.
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Huang, W. D.
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Wu, Y. H.
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Chang, L.
The onset of strain relaxation and induced defects in InAs0.94Sb0.06 quantum dots are investigated. We show that the relaxation causes partial carrier depletion in the dots and drastic carrier depletion in the top GaAs layer due to the introduction of two defect traps At 0.35 and 0.64 eV. This result is consistent with transmission electron microscopy data which show misfit dislocations on the edges of the dot upper boundary and threading dislocations in the top GaAs layer. The bottom GaAs layer is dislocation-free, and thus the strain relaxation may initially occur on the edges of the dots. (c) 2006 American Institute of Physics.
Strain relaxation in InAs self-assembled quantum dots induced by a high N incorporation
(2008-11-15)
Chen, J. F.
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Yang, C. H.
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Wu, Y. H.
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Chang, L.
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Chi, J. Y.
The effect of a high N incorporation in self-assembled InAs quantum dots (QDs) is investigated by analyzing the electronic and structural properties around QD region. Capacitance-voltage profiling and admittance spectroscopy shows that N incorporation into the InAs QD layer leads to drastic carrier depletion in the QD layer and neighboring GaAs layers due to the formation of a deep defect state at 0.34-0.41 eV. The signature of this defect state is similar to those defects observed in strain relaxed QDs or InGaAs/GaAs quantum wells when the InAs deposition thickness exceeds a critical thickness. Accordingly, the N incorporation might result in strain relaxation either by increasing localized strain or by inducing composition inhomogeneities, which provide nucleation sources for strain relaxation. The argument of strain relaxation is supported by transmission electron microscopy that reveals lattice misfits at the QD layer and neighboring GaAs layers.
Structural and optical properties of buried InAs/GaAs quantum dots on GaAsSb buffer layer
(2009-09-21)
Wu, Y. H.
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Chang, Li
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Lin, P. Y.
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Chiang, C. H.
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Chen, J. F.
In this work, we investigated the effect of a 1 nm thick GaAs(94.3)Sb(0.57) buffer layer on structural and optical properties of buried InAs quantum dots (QDs) and wetting layers (WLs) in GaAs using photoluminescence (PL) and transmission electron microscopy (TEM). The density and emission wavelength of the QDs on the buffer were increased due to the size and the shape modification in comparison with those without a buffer. PL analysis of the ground-state (GS) peak of the QDs on the buffer showed a red-shift of 18 meV with an enhanced intensity. In addition, PL and TEM show that the buffer has a weak effect on the WLs and no apparent changes occur for the buffer during QD deposition and the capping process.