C. S. Kim

Electron capture behaviors of deep level traps in unintentionally doped and intentionally doped n-type GaN

In n-type GaN films grown on sapphire substrates by metal-organic chemical vapor deposition such as unintentionally GaN and intentionally Si-doped GaN and In-doped GaN, the electron capture behaviors were investigated by deep level transient spectroscopy with various filling pulse durations. Two distinct deep levels E1 and E2 were typically observed in unintentionally doped n-type GaN. After optimized growth of undoped GaN, deep level E1 disappears. With increasing Si doping, the trap concentration of deep level E2 is increased. However, In doping in n-type GaN growth was found to suppress the formation of deep level E2. The electrons captured at the traps E1 and E2 were found to depend logarithmically on the duration time of the filling pulse. From an analysis of a model involving barrier-limited capture rate, it can be concluded that deep level E1 is associated with linear line defects along dislocation cores while deep level E2 is related to point defects.

Influence of strain relaxation on structural and optical characteristics of InGaN/GaN multiple quantum wells with high indium composition

Influence of strain relaxation on structural and optical properties of the InGaN/GaN multiple quantum wells (MQWs) with high indium composition grown by metalorganic chemical vapor deposition was investigated. From photoluminescence and transmission electron microscopy (TEM), we found that within the MQWs, the formation of misfit dislocation affects the degradation of optical properties more than the formation of stacking faults. For the MQWs with indium composition above the critical indium composition on the formation of misfit dislocation, the position of the main emission peak is significantly affected by the increase of quantum well numbers compared to samples with indium composition below the critical indium composition. The origins of redshift by the increase of quantum well numbers is believed to be caused by the increase of indium segregation in the MQWs using high-resolution TEM and energy dispersive x-ray spectroscopy.

Influence of strain-induced indium clustering on characteristics of InGaN/GaN multiple quantum wells with high indium composition

We report the effect of strain-induced indium clustering on the emission properties of InGaN/GaN multiple quantum wells grown with high indium composition by metalorganic chemical vapor deposition. Indium clustering confirmed by high-resolution transmission electron microscopy results in the redshift of the emission peak and the increase of the integrated photoluminescence (PL) intensity. We found that strong carrier localization in indium clustering induces the increases of the activation energy of PL integrated intensity, the temperature independence of PL decay profiles, and the intensity fluctuation of the cathodoluminescence images. All these observations suggest structurally and optically that the improved emission properties in the InGaN/GaN multiple quantum well with high indium composition are associated with the localized states in the strain-induced indium cluster.

Characteristics of Al/sub 2/O/sub 3/ gate dielectric prepared by atomic layer deposition for giga scale CMOS DRAM devices

This paper demonstrates characteristics of Al/sub 2/O/sub 3/ gate dielectric prepared by atomic layer deposition (ALD) for giga scale CMOS DRAM devices. Interface state density /spl sim/7/spl times/10/sup 10/ eV/sup -1/ cm/sup -2/ near the midgap and excellent reliability with a low gate leakage current were attained from Al/sub 2/O/sub 3//Si MOS system. p/nMOSFETs characteristics in terms of current drivability, transconductance (Gm), and subthreshold swing are described.

Small intestinal angiolipoma: MR imaging appearance

We report the magnetic resonance imaging finding in a case of small intestinal angiolipoma. Small bowel enteroclysis showed a well-defined, lobulated polypoid lesion in the proximal ileum. The mass showed central high signal intensity with peripheral iso-signal intensity on T1-weighted in-phase images. The central high signal intensity changed to low signal intensity on T1-weighted out-of-phase images. After contrast injection, the mass had a strong enhancement along the periphery of the lesion on fat-saturated T1-weighted images. Characteristic decreased signal intensity on out-of-phase T1-weighted images and strong enhancement on postcontrast images of the small bowel mass suggest the diagnosis of angiolipoma.

Strain distribution and interface modulation of highly lattice-mismatched InN/GaN heterostructure nanowires

The structural properties of InN/GaN heterostructure nanowires (NWs) were studied using transmission electron microscope techniques to determine strain behavior. A great quantity of the misfit strain between InN and GaN was relaxed through the introduction of misfit dislocations along the interface. Geometric phase analysis revealed a strain-concentration phenomenon in the strain map of the out-of-plane components and a gradual lattice recovery in that of the in-plane components over the InN/GaN interface. Interface structures that were modulated at the atomic-scale were observed in several InN/GaN heterostructure NWs. Complex strain distributions were identified in both InN and GaN.

Retarded C54 transformation and suppressed agglomeration by precipitates in TiSi2 films

We report the effects of excess Si phase on the C54 transformation and the thermal stability of TiSi2 thin films as a function of Si/Ti (x) ratio. The resistivity and x-ray diffraction data of TiSix(x=2.1–2.4) films showed a retardation of C54–TiSi2 transformation with incremental molar ratio x; the TiSixu200a(x=2.1–2.3) films were completely transformed to C54-TiSi2 with rapid thermal annealing (RTA) of 750u200a°C, while the TiSixu200a(x=2.4) films were transmuted to C54–TiSi2 over the RTA of 800u200a°C. Transmission electron microscopy study revealed that the growth of Si precipitates in the Si-rich TiSix films competes with the grain growth during the transformation of C49 to C54u200aTiSi2 phase, resulting in the increase of C54 transformation temperature. An excellent sheet resistance (Rs) and its standard deviation in concert with a reliable gate oxide integrity were attained from the Si-rich TiSi2/polycrystalline-Siu2002(poly-Si) structure up to the solid state annealing of 850u200a°C for 60 min. These attributes are due to th...

Phase transitions in Er1−xLuxFe2O4

Phase transitions have been investigated for polycrystalline samples of Er1−xLuxFe2O4 (0⩽x⩽0.6). The magnetization measurements for ErFe2O4 showed two-step phase transitions at about 220 and 250K. The transition at 250K is an antiferromagnetic transition and that at 220K is a structural transition. However, two phase transitions do not occur for 0.2⩽x⩽0.6, but a thermoremanent magnetization is observed below 220K. This indicates that there is no second phase transition for 0.2⩽x⩽0.6.

Influence of a GaN interfacial layer between n+-GaN and active layer on the characteristics of blue light-emitting diodes

Influence of a GaN interfacial layer with graded growth rate and modulated Si-doping between n+-GaN and InGaN/GaN multiquantum well on device performance of blue light-emitting diodes (LEDs) was investigated. It was found that the introduction of a GaN interfacial layer leads to an improvement of current–voltage characteristics and also an enhancement of output power compared to a conventional LED. These could result from the removal of spiral growth hillocks and smoothened morphology at the interface, as confirmed by atomic force microscopy measurements, which might cause the leakage current to decrease and the current injection into the active layer to enhance.

Impacts of Self-Aligned Epitaxial Silicon Sliver (SESS) in Buried Channel-pFETs Elevated Source/Drain Using Dual-Spacer Structure

Excellent short channel and junction characteristics in buried channel p-type field effect transistors (BC-pFETs) are obtained using the elevated source/drain (ESD) structure with a self-aligned shallow sliver of boron implanted epitaxial silicon. By employing a dual-spacer structure using high temperature oxide (HTO) and nitride, a self-aligned epitaxial silicon sliver (SESS) protruding laterally into the bottom edge of gate sidewall spacers is intentionally formed to reduce the series resistance of source/drain extension of BC-pFET while minimizing the faceting. The trade-off relation between SESS and facet developments is revealed by the control of HTO thickness. As a result, the short channel characteristics of ESD employing SESS are improved without decreasing current drivability for sub-0.25 µm pFETs. Cumulative characteristics of p+-n junction leakage and the contact resistance are also remarkably improved using the elevated junction structure.