First Operation of AlGaN Channel High Electron Mobility Transistors

Takuma Nanjo, Misaichi Takeuchi, Muneyoshi Suita, Yuji Abe, Toshiyuki Oishi, Yasunori Tokuda, Yoshinobu Aoyagi
2007 Applied Physics Express  
A channel layer substitution of a wider bandgap AlGaN for conventional GaN in high electron mobility transistors (HEMTs) is one possible method of enhancing the breakdown voltage for higher power operation. Wider bandgap AlGaN, however, should also increase the ohmic contact resistance. We utilized a Si ion implantation doping technique to achieve sufficiently low resistive source/drain contacts, and realized the first HEMT operation with an AlGaN channel layer. This result is very promising
more » ... the further higher power operation of high-frequency HEMTs. The continuous-wave (cw) operation of m-plane InGaN-based blue (460nm) laser diodes (LDs) has been achieved. The threshold current and the corresponding threshold current density were 40mA and 5.0kA/cm 2 , respectively, with a 459nm lasing wavelength under cw operation. The electroluminescence peak wavelength shift in pulsed mode was only 10nm (58meV), from spontaneous emission (at 0.3mA) to stimulated emission (at 32mA), which is extremely small when compared with that of c-plane blue LDs. This is first clear experimental demonstration of the advantage in fabricating nonpolar InGaN-based LDs beyond the blue region. The off-state breakdown characteristics of GaN layers with different thicknesses from 0.2 to 2µm grown by metal organic chemical vapor deposition on SiC substrates were discussed using the space-chargelimited current conduction mechanism. With decreasing thickness of the GaN layer, the off-state breakdown voltage increased. The trap density in the GaN layer was estimated from the traps-filled-limit voltage, which determined the off-state breakdown voltage. We found that the thusestimated trap density increased with decreasing thickness of the GaN layer. A higher density of threading dislocations in the thinner samples was confirmed by transmission electron microscopy observations. These results suggest that the traps formed by the threading dislocations influence the off-state breakdown voltage of the GaN layer. Blue laser diodes (LDs) were fabricated on m-plane oriented GaN substrates by atmospheric-pressure metalorganic chemical vapor deposition. Typical threshold current for stimulated emission at a wavelength λ of 463nm was 69mA. Blueshift of the spontaneous emission peak with increasing injection current was examined in LDs fabricated on mand c-plane GaN substrates. Blueshifts for the m-plane LD (λ=463nm) and the c-plane LD (λ=454nm) with an injection current density just below threshold were about 10 and 26nm, respectively. These results confirm that the blueshift in quantum-wells fabricated on m-plane oriented substrates is smaller than on c-plane oriented substrates due to the absence of polarization-induced electric fields. Completely vertical trench gate metal oxide semiconductor fieldeffect transistors (MOSFETs) have been produced using gallium nitride (GaN) for the first time. These MOSFETs exhibited enhancement-mode operation with a threshold voltage of 3.7 V and an on-resistance of 9.3 mΩ·cm 2 . The channel mobility was estimated to be 131cm 2 /(V·s) when all the resistances except for that of the channel are considered. Such structures, which satisfy the key words "vertical", "trench gate", and "MOSFET", will enable us to fabricate practical GaN-based power switching devices. Monolithic polychromatic light-emitting diodes (LEDs) based on micro-structured InGaN/GaN quantum wells are demonstrated. The microstructure is created through regrowth on SiO2 mask stripes along the [11 -00] direction and consists of (0001) and {112 -2} facets. The LEDs exhibit polychromatic emission, including white, due to the additive color mixture of facet-dependent emission colors. Altering the growth conditions and mask geometry easily controls the apparent emission color. Furthermore, simulations predict high light extraction efficiencies due to their three-dimensional structures. Those observations suggest that the proposed phosphor-free LEDs may lead to highly efficient solid-state lighting in which the color spectra of light sources are synthesized to satisfy specific requirements for illuminations. This work reports on the performance improvement of a chalcogenide random access memory device by applying germanium nitride as an interfacial layer. The device with an 8-nm-thick GeN film was fabricated using standard 0.18µm complementary metal oxide semiconductor technology. The as-deposited GeN is in the amorphous state and has a smooth surface. An electrical test showed that this N-deficient layer induces a lower threshold voltage during the operation. It is believed that the reduction mainly originated from the excellent interfacial properties, high electrical resistivity, and low thermal conductivity of GeN, which is would be a prospective interfacial material in CRAM devices. A vertical-type Schottky photodetector based on a (100)-oriented β-Ga2O3 substrate has been fabricated with simple processes of thermal annealing and vacuum evaporation. The photodetector exhibited a rectification ratio higher than 10 6 at ± 3 V, and showed deep-ultravioletlight detection at reverse bias. The spectral response showed solar-blind sensitivity with high photoresponsivities of 2.6-8.7A/W at wavelengths of 200 -260 nm. These values were 35 -150 times higher than those derived assuming the internal quantum efficiency to be unity. This fact is attributed to the carrier multiplication occurring in the highly resistive surface region that is subject to a high internal electric field of about 1.0MV/cm at the reverse bias of 10V. We report the direct observation of current-driven domain wall (DW) motion in a CoCrPt wire with perpendicular magnetic anisotropy. Magnetic force microscopy showed that a single DW introduced in the wire is displaced back and forth by positive and negative pulsed current. This is the first demonstration of the current-driven DW motion in a metallic magnetic wire with perpendicular magnetic anisotropy in the absence of a magnetic field. The effects of gate bias on hole effective mass (m * ) and Hall mobility were studied in strained-Ge channel modulation-doped structures. Shubnikov -de Haas oscillations were analyzed with and without the bias and a significant m * increase from 0.15 to 0.22 m0 was observed with the increase in the carrier density due to the strong nonparabolicity of the valence band. This is a clear demonstration that modification of carrier density via gating considerably affects m * , which may have critical effects on device properties. The gate bias dependence of Hall mobility was also investigated and the dominant scattering mechanism was clarified in various temperature and carrier density regions. High-piezoelectricity lead-free films of (K,Na)NbO3 (KNN) were successfully deposited on Pt / MgO and Pt / Ti / SiO2 / Si substrates by RF magnetron sputtering. The KNN film was epitaxially grown on Pt / MgO with a high <001> orientation in the pseudo-cubic perovskite structure. The KNN film on Pt / Ti / SiO2 / Si was polycrystalline with a preferential <001> orientation in the pseudo-cubic perovskite structure. The piezoelectric properties of the KNN films were determined from the tip displacement of KNN / Pt / MgO or KNN / Pt / Ti / SiO2 / Si unimorph cantilevers. The transverse piezoelectric coefficients e31 * (d31 / s11 E ) of the KNN films on Pt / MgO and Pt / Ti / SiO2 / Si were calculated to be -3.6 and -5.5C/ m 2 , respectively, which are amongst the highest values for KNN films ever reported. The valence state of Mn-doped BiFeO3 -BaTiO3 ceramics has been probed by soft X-ray absorption spectroscopy (XAS). Mn-doped BiFeO3 -BaTiO3 has valence states of Fe 3+ and Ti 4+ , although BiFeO3 and Mn-doped BiFeO3 have mixed valence states of Fe 2+ and Fe 3+ . The Mn 2p-XAS peak of Mn-doped BiFeO3 -BaTiO3 locates at a lower energy side than that of Mn-doped BiFeO3 that corresponds to the Mn 3+ valence state. These findings may indicate that the Fe 3+ valence state of Mn-doped BiFeO3 -BaTiO3 is stabilized by charge transfer from the Mn 3d state to the Fe 3d state through the Ti 3d state in BaTiO3. A light emitting diode with superconducting Nb electrodes was fabricated to investigate the contribution of cooper pairs to radiative recombination in a semiconductor. Electroluminescence observed from the active layer in which electron cooper pairs and normal holes are injected was drastically enhanced at the temperature lower than the superconducting transition temperature of the Nb electrodes. This is the first experimental evidence that cooper pairs enhance radiative recombinations by the superradiance effect. Electrical tuning of laser wavelength is demonstrated using a liquidcrystal / polymer grating fabricated by nanoimprint lithography. Laser emission occurs at a wavelength near 700nm, which corresponds to the first order of a 200nm period grating. With increasing applied voltage, the lasing spectrum begins to shift to shorter wavelengths at 10V, and then a 10nm shift is achieved with an applied voltage of 30V. This is due to the refractive index change of the liquid crystal in the trench of the polymer grating by field-induced molecular reorientation. We report Coulomb blockade oscillations in an atomically thin graphite ribbon fabricated by the micromechanical cleavage technique. Aperiodic current oscillations as a function of the gate voltage indicate the formation of multiple Coulomb islands inside the thin graphite ribbon. We conclude that the Coulomb islands originate from puddles of electrons and holes caused by the inhomogeneous interface between the ribbon and the substrate. The trade-off between resolution, sensitivity, and line edge roughness (LER) is the most serious problem for the development of sub-30nm resists based on chemical amplification. Because of this trade-off, the increase in acid generation efficiency is essentially required for highresolution patterning with high sensitivity and low LER. In this study, we investigated the dependences of acid generation efficiency on the molecular structure and concentration of acid generators upon exposure to extreme ultraviolet (EUV) radiation. The acid generation efficiency (the number of acid molecules generated by a single EUV photon) was obtained within the acid generator concentration range of 0 -30wt % for five types of ionic and nonionic acid generators. A laser-cooling experiment of a 40keV 24 Mg + beam was carried out in the small laser-equipped storage ring (S-LSR). A laser co-propagating with the beam and an induction accelerator were utilized in the experiment. The lowest longitudinal temperature achieved in the present experiment was 3.6K for 3 × 10 4 ions stored in the ring. It was found that the number of stored ions is related to the temperature at the final equilibrium state of the laser cooling. This relation shows that the longitudinal temperature of the laser-cooled beam linearly couples with the transverse one through intra-beam scattering. We observed the growth process of tungsten oxide nanowires in real-time with a field emission scanning electron microscope (SEM). The observation was performed by a new in-situ observation system designed to perform two functions: heating of tungsten film and local supply of O2 gas. The nanowires grew after the nucleation on the surface. Their length extended with time keeping the direction constant. The growth rate decreased with exponential. The adsorption properties of a recombinant apoferritin protein fused to a gold-binding peptide were characterized. The results of quartz crystal microbalance measurements showed that the fusion protein preferentially adsorbs to gold surfaces. Scanning electron microscopy also revealed that the protein selectively adsorbed onto a nanometer-scale gold pattern on a SiO2 surface fabricated by electron-beam lithography. Our results indicate that nanodots and nanowires synthesized using a biotemplate can be selectively placed onto a gold surface by genetically modifying the outer surface of the biotemplate. This technique represents an important step toward biotemplate-mediated fabrication of a nanometer-scaled device that utilizes gold electrodes.
doi:10.1143/apex.1.011101 fatcat:z26xgvxevrhlbg4mfksbksjgby