P. T. Lai

Effects of nitridation and annealing on interface properties of thermally oxidized SiO2/SiC metal–oxide–semiconductor system

The effects of N2O nitridation and subsequent annealing in different conditions on thermally oxidized n-type 6H–silicon carbide (SiC) metal–oxide–semiconductor (MOS) interface properties were investigated. Influence of high-field stress on the MOS system was also studied. The nitrided device annealed in dry or wet O2 is found to have lower interface-state density compared to the device annealed in N2 because the reoxidation can reduce nitridation-induced interface damage. Furthermore, significantly less shift of flatband voltage during high-field stress for all nitrided devices indicates much better oxide reliability by replacing strained Si–O bonds with stronger Si–N bonds during nitridation. This is further supported by the fact that annealing of the nitrided device in dry or wet oxygen slightly reduces the robustness of the oxide. In summary, the O2-annealing conditions have to be optimized to deliver a proper tradoff between interface quality and reliability.

Improved performance and reliability of N 2 O-grown oxynitride on 6H-SiC

This letter reports, for the first time, N/sub 2/O-grown oxides on both n-type and p-type 6H-SiC wafers. It is demonstrated that the N/sub 2/O-grown technique leads to not only greatly improved SiC/SiO/sub 2/ interface and oxide qualities, but also considerably enhanced device reliabilities as compared to N/sub 2/O-nitrided and conventional thermally oxidized devices. These improvements are especially obvious for p-type SiC MOS devices, indicating that N/sub 2/O oxidation could be a promising technique for fabricating enhancement-type n-channel SiC MOSFETs.

Conduction mechanisms in MOS gate dielectric films

Abstract This paper reviews the conduction mechanisms in the gate dielectric films of MOSFETs for VLSI and ULSI technologies. They include Fowler–Nordheim tunneling, internal Schottky (or Pool–Frenkel) effect, two-step (or trap-assisted) tunneling, shallow-trap-assisted tunneling, and band-to-band tunneling. The current transport in the gate dielectric films is manly controlled by film material composition, film processing conditions, film thickness, trap energy level and trap density in the films. In general, for a given gate dielectric film, the current transport behaviors are normally governed by one or two conduction mechanisms.

A high-performance organic field-effect transistor based on platinum(II) porphyrin: peripheral substituents on porphyrin ligand significantly affect film structure and charge mobility.

Organic field-effect transistors incorporating planar pi-conjugated metal-free macrocycles and their metal derivatives are fabricated by vacuum deposition. The crystal structures of [H2(OX)] (H(2)OX=etioporphyrin-I), [Cu(OX)], [Pt(OX)], and [Pt(TBP)] (H2TBP=tetra-(n-butyl)porphyrin) as determined by single crystal X-ray diffraction (XRD), reveal the absence of occluded solvent molecules. The field-effect transistors (FETs) made from thin films of all these metal-free macrocycles and their metal derivatives show a p-type semiconductor behavior with a charge mobility (mu) ranging from 10(-6) to 10(-1) cm(2) V(-1) s(-1). Annealing the as-deposited Pt(OX) film leads to the formation of a polycrystalline film that exhibits excellent overall charge transport properties with a charge mobility of up to 3.2 x 10(-1) cm(2) V(-1) s(-1), which is the best value reported for a metalloporphyrin. Compared with their metal derivatives, the field-effect transistors made from thin films of metal-free macrocycles (except tetra-(n-propyl)porphycene) have significantly lower mu values (3.0 x 10(-6)-3.7 x 10(-5) cm(2) V(-1) s(-1)).

Liver cancer immunoassay with magnetic nanoparticles and MgO-based magnetic tunnel junction sensors

We have demonstrated the detection of alpha-fetoprotein (AFP) labeled with magnetic nanoparticles (MNPs) using MgO-based magnetic tunnel junction (MTJ) sensors. AFP is an important hepatic tumor biomarker and the detection of AFP has significant applications for clinical diagnostics and immunoassay for early-stage liver cancer indications. In this work, MgO-based MTJ sensors and 20-nm iron-oxide magnetic nanoparticles (MNPs) were used for detecting AFP antigens by a sandwich-assay configuration. The MTJ sensors with a sensing area of 4 × 2 μm2 possess tunneling magnetoresistance (TMR) of 122% and sensitivity of 0.95%/Oe at room temperature. The target AFP antigens of three concentrations were successfully detected, and the experimental data indicate that the resistance variations of the MTJ sensor increased with the AFP concentration ratios proportionally. These results demonstrate that MgO-based MTJ sensors together with MNPs are a promising biosensing platform for liver cancer immunoassay.

Lasing in GaN microdisks pivoted on Si

Arrays of pivoted GaN microdisks have been fabricated on a GaN∕Si material by a combination of dry and wet etching. The Si material beneath the GaN microdisks is removed by wet etching, leaving behind a fine pillar to support the disks. Raman spectroscopy reveals substantial strain relaxation in these structures. Resonant modes, corresponding to whispering gallery modes, are observed in the photoluminescence spectra. Stimulated emission is achieved at higher optical pumping intensities.

A Reliability Study on Green InGaN–GaN Light-Emitting Diodes

In this letter, the reliability of green InGaN-GaN light-emitting diodes (LEDs) has been analyzed by correlating the defect density of wafers with various device parameters, including leakage current, 1/f noise, and degradation rate. It was found that as the wavelength of green LEDs increases from 520 to 550 nm by increasing the indium content in the quantum wells, the defect density also increases, thus leading to larger leakage current, enhanced noise magnitude, and shortened device lifetime.

Characterization of charge trapping and high-field endurance for 15-nm thermally nitrided oxides

Device-quality gate oxides have been nitrided using both rapid thermal processing and conventional furnace treatment. Charge trapping and high-field endurance including breakdown field and time-dependent dielectric breakdown, are investigated in detail. It is found that proper nitridation can eliminate positive charge accumulation in oxides, increase charge to breakdown, suppress high-field injection-induced interface state generation, and decrease the dependence of the breakdown field on the gate area as a result of the reduced density of microdefects. Experimental results show that although both the density and capture cross-section of the bulk and interface traps increased by nitridation, the combined effects of bulk and interface traps induced by high-field injection can improve the stability of the flatband voltage. For lightly nitrided oxides, the trap generation rate is greatly decreased as compared with the as-grown oxide. Not only are the density and capture cross-section of the traps affected by nitridation, but also the locations of the trapped-charge centroids are changed. The experimental results for postnitridation annealing suggest that these property modifications most likely result from nitridation-induced structural changes rather than hydrogenation alone. >

Simplified closed‐form trap‐assisted tunneling model applied to nitrided oxide dielectric capacitors

Conduction has been studied in ultrathin nitrided oxide, re‐oxidized nitrided oxide, and nitrogen‐annealed nitrided oxide film capacitors in which the nitridation step was performed by a low‐partial‐pressure nitridation technique. Results indicate that, as well as some degree of barrier lowering due to the build‐up of nitrogen at the injecting interface, a trap‐assisted mechanism could be responsible for the enhanced conduction exhibited by the nitrided oxide devices. A simplified closed‐form trap‐assisted tunneling model is employed that produces a fit to the data with a trap depth of 2.1 eV. The difference between this trap model and a model requiring numerical integration was negligibly small (∼2%).

Efficient white and red light emission from GaN/tris-(8-hydroxyquinolato) aluminum/platinum(II) meso-tetrakis(pentafluorophenyl) porphyrin hybrid light-emitting diodes

We report efficient white and red light emission from GaN light-emitting diode (LED)/tris-(8-hydroxyquinolato) aluminum (Alq3)/platinum(II) meso-tetrakis(pentafluorophenyl) porphyrin (PtF20TPP) hybrid LEDs. Alq3 was employed to enhance the efficiency of red and white luminescence conversion (LC) LEDs through energy transfer from Alq3 to PtF20TPP. In the white LC-LED, an intense, highly pure white-light emission with CIE_1931 coordinates at x=0.32 and y=0.31 is obtained. The LC-LEDs in this work have relatively high efficiencies, 3.3% for white LC-LED and 4.0% for red LC-LED. The color temperature (Tc), color rendering index (Ra) and luminous efficiency (ηL) of the white LC-LED at 20 mA are 6800 K, 90.6 and 10 lm/W, respectively.