Chih-Hsin Ko

NiSi Schottky Barrier Process-Strained Si (SB-PSS) CMOS Technology for High Performance Applications

State-of-the-art process-strained Si (PSS) technology featuring single-NiSi Schottky source/drain (S/D) and ultra-thin gate oxide of 1.2 nm is demonstrated for Lgate down to 39 nm. +10% performance boost of Schottky-barrier (SB)-PSS NMOS, as compared to its non-Schottky counterpart, is demonstrated due to series resistance reduction of the silicide S/D and enhanced strain effects. Highest SB-PSS PMOS drive current of 821 muA/mum (at VD = -1.2V and Ioff = 100 nA/mum) is recorded when integrated with recessed Si1-x Gex S/D stressor

ZnSe Nanowire Photodetector Prepared on Oxidized Silicon Substrate by Molecular-Beam Epitaxy

We reported the growth of ZnSe nanowires on oxidized Si substrate by molecular-beam epitaxy. It was found that average length, average diameter, and density of the ZnSe nanowires were 1.2 μm, 48 nm, and 1.04 X 10 7 cm -2 , respectively. It was also found that the ZnSe nanowires were structurally uniform and defect-free with a pure zinc blend structure. UV photodetectors were then fabricated by sputtering a thick Au film through an interdigitated shadow mask onto the ZnSe nanowires. It was found that photocurrent to dark current contrast ratio of our ZnSe nanowire photodetector was >90 with 0.1 V applied bias.

Photo-enhanced chemical wet etching of GaN

Abstract In this paper, we report a photo-enhanced chemical etch rate study on two GaN samples of differing structural and electrical quality as a function of the KOH or H3PO4 etch solution molarity. The etch rate of KOH was observed to be higher than that of H3PO4. This was found to be result from the effects of surface band bending, and surface pinning on the chemical etching and photo-assisted etching of the layers. It was also found that the optimal etch rate occurred at different values of molarity for the two samples and that very different morphologies were observed after etching.

InGaN/GaN light emitting diodes with a p-down structure

Nitride-based p-down blue light emitting diodes (LEDs) were successfully fabricated. It was found that we could improve the crystal quality of these nitride-based p-down LEDs by inserting a codoped interlayer between the p-type cladding layer and MQW active layers. It was also found that the turn-on voltage could be reduced from 15 V to less than 5 V for the p-down LED with codoped layer and tunnel layer. The 20 mA output power was 1 mW for the p-down LED with an Mg+Si codoped interlayer and a rough p-tunnel layer.

The Effects of Mechanical Uniaxial Stress on Junction Leakage in Nanoscale CMOSFETs

This paper reports the influences of uniaxial mechanical stress on the reverse-biased source/drain to substrate junction leakage of state-of-the-art 65 nm CMOS transistors. For n-channel metal-oxide-semiconductor (NMOS) transistors, the band-to-band tunneling (BTBT) dominates the junction leakage current due to heavily doped junction and pocket implants. However, for p-channel metal-oxide-semiconductor (PMOS) transistors with embedded SiGe source/drain, the leakage current is found to result from both BTBT and generation current due to defects generated in the SiGe layer and at the SiGe/Si interface. A four-point bending technique is used to apply mechanical uniaxial stress on NMOS and PMOS devices along the longitudinal direction. It was found that the leakage current of both devices increases (decreases) with applied uniaxial compressive (tensile) stress, and that the strain sensitivity of the junction leakage of NMOS transistors is much weaker than that of PMOS transistors. By combining the bending technique with process strained Si (PSS) technology, additional stress was applied to NMOS and PMOS with high built-in stress to investigate the characteristics of junction leakage under extremely high uniaxial stress. It is shown that uniaxial tensile stress can both enhance the NMOS device performance and decrease the junction leakage. However, for the PMOS, there exists a tradeoff between boosting the transistor performance and decreasing the junction leakage current, so there is a limit in the amount of compressive stress that can be beneficially applied.

Correlating drain-current with strain-induced mobility in nanoscale strained CMOSFETs

The correlation between channel mobility gain (Deltamu), linear drain-current gain (DeltaI_dlin), and saturation drain-current gain (DeltaIdsat) of nanoscale strained CMOSFETs are reported. From the plots of DeltaI_dlin versus DeltaI_dsat and ballistic efficiency (Bsat,PSS), the ratio of source/drain parasitic resistance (R_SD,PSS) to channel resistance (R_CH,PSS) of strained CMOSFETs can be extracted. By plotting Deltamu versus DeltaI_dlin, the efficiency of Deltamu translated to DeltaI_dlin is higher for strained pMOSFETs than strained nMOSFETs due to smaller RSD,PSS-to-RCH,PSS ratio of strained pMOSFETs. It suggests that to exploit strain benefits fully, the RSD,PSS reduction for strained nMOSFETs is vital, while for strained pMOSFETs the DeltaI_dlin-to-Deltamu sensitivity is maintained until R_SD,PSS becomes comparable to/or higher than R_CH,PSS

Influences of surface reconstruction on the atomic-layer-deposited HfO2/Al2O3/n-InAs metal-oxide-semiconductor capacitors

We report the characteristics of HfO2/Al2O3/n-InAs metal-oxide-semiconductor capacitors on different reconstructed surface InAs substrates. The HfO2/Al2O3 gate dielectric films deposited on InAs were used to study the interfacial reaction. Compared with (2×4)-surface sample, improvements of capacitance-voltage characteristics for (1×1)-surface sample with lower frequency-dependent capacitance dispersion and higher inversion capacitance are attributed to lower indium composition and less arsenic oxide at Al2O3/InAs interface, as confirmed by x-ray photoelectron spectroscopy. It indicates that the equivalent dangling bond of cations and anions on (1×1)-surface sample tends to avoid the oxidization process and become less pinning.

P-Down InGaN/GaN Multiple Quantum Wells Light-Emitting Diode Structure Grown by Metal-Organic Vapor-Phase Epitaxy.

An inverted or p-down InGaN/GaN multiple quantum wells (MQW) light-emitting diode (LED) structure is studied. The crystalline quality of the quantum wells is comparable to that of the n-down structure by using a Si or In co-doped GaN:Mg layer underneath the active layer. It was found that I–V characteristics can be improved by insertion of a tunnel layer, either a 3D growth GaN:Mg layer or an AlGaN/GaN superlattice layer. The feasibility of such a structure for practical application is also evaluated by luminescence measurement.

Flicker noise of GaN-based heterostructure field-effect transistors with Si-doped AlGaN carrier injection layer

Aluminum gallium nitride/gallium nitride (AlGaN/GaN) heterostructure field effect transistors (HFETs) with and without Si-doped AlGaN layer were fabricated and investigated. HFETs with the Si-doped AlGaN carrier-injection layer show better DC performance, and the transconductance is 150 mS/mm. However, the HFETs with Si-doped AlGaN layer present the deviation from the 1/f noise at low frequency. The Lorentz shape was observed in the noise spectrum. It suggests that traps might be more pronounced in this kind of structure. Therefore, the DC characteristics of HFETs can be improved by the insertion of Si-doped AlGaN layer, but it can result in more low-frequency noise with the carrier-injection layer.

On the Carrier Concentration and Hall Mobility in GaN Epilayers

The dependence of Hall mobility and carrier concentration in GaN epilayers on light illumination was examined. It was found that Hall mobility and electron concentration both increased after illumination with red laser (632.8 nm) and green laser (530 nm). However, no changes in Hall mobility and carrier concentration were found, if IR-laser (850 nm) was used. The results reveal that deep-level defects were excited and hence extra carriers were generated by light illumination. The influence is more pronounced for thinner films. These observations indicate that donor-like defect-related states were located 1.48 to 2.33 eV below the conduction band edge.