Ilesanmi Adesida

Bio: Ilesanmi Adesida is an academic researcher from University of Illinois at Urbana–Champaign. The author has contributed to research in topics: Reactive-ion etching & High-electron-mobility transistor. The author has an hindex of 50, co-authored 383 publications receiving 9732 citations. Previous affiliations of Ilesanmi Adesida include Nazarbayev University & Cornell University.

Recessed-gate enhancement-mode GaN HEMT with high threshold voltage

Abstract: Fabrication of enhancement-mode high electron mobility transistors (E-HEMTs) on GaN/AlGaN heterostructures grown on SiC substrates is reported. Enhancement-mode operation was achieved with high threshold voltage (V/sub T/) through the combination of low-damage and controllable dry gate-recessing and the annealing of the Ni/Au gates. As-recessed E-HEMTs with 1.0 /spl mu/m gates exhibited a threshold voltage (V/sub T/) of 0.35 V, maximum drain current (I/sub D,max/) of 505 mA/mm, and maximum transconductance (g/sub m,max/) of 345 mS/mm; the corresponding post-gate anneal characteristics were 0.47 V, 455 mA/mm and 310 mS/mm, respectively. The RF performance is unaffected by the post-gate anneal process with a unity current gain cutoff frequency (f/sub T/) of 10 GHz.

AlGaN/GaN HEMTs on SiC with over 100 GHz f/sub T/ and low microwave noise

Abstract: High performance AlGaN/GaN high electron mobility transistors (HEMTs) with 0.12 /spl mu/m gate-length have been fabricated on an insulating SiC substrate. The devices exhibited an extrinsic transconductance of 217 mS/mm and current drive capability as high as 1.19 A/mm. The threshold voltage of the devices was -5.5 V. For AlGaN/GaN HEMTs with the same gate-length, a record high unity current gain cut-off frequency (f/sub T/) of 101 GHz and a maximum oscillation frequency (f/sub max/) of 155 GHz were measured at V/sub ds/=16.5 V and V/sub gs/=5.0 V. The microwave noise performances of the devices were characterized from 2 to 18 GHz at different drain biases and drain currents. At a drain bias of 10 V and a gate bias of -4.8 V, the devices exhibited a minimum noise figure (NF/sub min/) of 0.53 dB and an associated gain (G/sub a/) of 12.1 dB at 8 GHz. Also, at a fixed drain bias of 10 V with the drain current swept, the lowest NF/sub min/ of 0.72 dB at 12 GHz was obtained at I/sub ds/=100 mA/mm and a peak G, of 10.59 dB at 12 GHz was obtained at I/sub ds/=150 mA/mm. With the drain current held at 114 mA/mm and drain bias swept, the lowest NF/sub min/ of 0.42 dB and 0.77 dB were obtained at V/sub ds/=8 V at 8 GHz and 12 GHz, respectively. To our knowledge, these are the best microwave noise performances of any GaN-based FETs ever reported.

Gallium nitride whiskers formed by selective photoenhanced wet etching of dislocations

Abstract: Gallium nitride is used to fabricate high brightness blue and green light-emitting diodes in spite of high densities of extended structural defects. We describe a photoelectrochemical etching process that reveals the dislocation microstructure of n-type GaN films by selectively removing material between dislocations. The GaN whiskers formed by the etching have diameters between 10 and 50 nm and lengths of up to 1 μm. A correlation between the etched features and threading dislocations in the unetched film is confirmed through transmission electron microscopy studies. The whisker formation is believed to be indicative of electrical activity at dislocations in GaN.

AlGaN/GaN HEMTs on SiC with f/sub T/ of over 120 GHz

Abstract: AlGaN/GaN high electron mobility transistors (HEMTs) grown on semi-insulating SiC substrates with a 0.12 /spl mu/m gate length have been fabricated. These 0.12-/spl mu/m gate-length devices exhibited maximum drain current density as high as 1.23 A/mm and peak extrinsic transconductance of 314 mS/mm. The threshold voltage was -5.2 V. A unity current gain cutoff frequency (f/sub T/) of 121 GHz and maximum frequency of oscillation (f/sub max/) of 162 GHz were measured on these devices. These f/sub T/ and f/sub max/ values are the highest ever reported values for GaN-based HEMTs.

Highly anisotropic photoenhanced wet etching of n-type GaN

Abstract: A room-temperature photoelectrochemical etching process for n-type GaN films using a 0.04 M KOH solution and Hg arc lamp illumination is described. The process provides highly anisotropic etch profiles and high etch rates (>300 nm/min) at moderate light intensities (50 mW/cm2 @365 nm). The etch rate and photocurrent are characterized as a function of light intensity for stirred and unstirred solutions, and the etch process is found to be diffusion limited for light intensities greater than 20 mW/cm2 @365 nm. A reaction mechanism for the etch process is proposed.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

A comprehensive review of zno materials and devices

Abstract: The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

Large‐band‐gap SiC, III‐V nitride, and II‐VI ZnSe‐based semiconductor device technologies

Abstract: In the past several years, research in each of the wide‐band‐gap semiconductors, SiC, GaN, and ZnSe, has led to major advances which now make them viable for device applications. The merits of each contender for high‐temperature electronics and short‐wavelength optical applications are compared. The outstanding thermal and chemical stability of SiC and GaN should enable them to operate at high temperatures and in hostile environments, and also make them attractive for high‐power operation. The present advanced stage of development of SiC substrates and metal‐oxide‐semiconductor technology makes SiC the leading contender for high‐temperature and high‐power applications if ohmic contacts and interface‐state densities can be further improved. GaN, despite fundamentally superior electronic properties and better ohmic contact resistances, must overcome the lack of an ideal substrate material and a relatively advanced SiC infrastructure in order to compete in electronics applications. Prototype transistors have been fabricated from both SiC and GaN, and the microwave characteristics and high‐temperature performance of SiC transistors have been studied. For optical emitters and detectors, ZnSe, SiC, and GaN all have demonstrated operation in the green, blue, or ultraviolet (UV) spectra. Blue SiC light‐emitting diodes (LEDs) have been on the market for several years, joined recently by UV and blue GaN‐based LEDs. These products should find wide use in full color display and other technologies. Promising prototype UV photodetectors have been fabricated from both SiC and GaN. In laser development, ZnSe leads the way with more sophisticated designs having further improved performance being rapidly demonstrated. If the low damage threshold of ZnSe continues to limit practical laser applications, GaN appears poised to become the semiconductor of choice for short‐wavelength lasers in optical memory and other applications. For further development of these materials to be realized, doping densities (especially p type) and ohmic contact technologies have to be improved. Economies of scale need to be realized through the development of larger SiC substrates. Improved substrate materials, ideally GaN itself, need to be aggressively pursued to further develop the GaN‐based material system and enable the fabrication of lasers. ZnSe material quality is already outstanding and now researchers must focus their attention on addressing the short lifetimes of ZnSe‐based lasers to determine whether the material is sufficiently durable for practical laser applications. The problems related to these three wide‐band‐gap semiconductor systems have moved away from materials science toward the device arena, where their technological development can rapidly be brought to maturity.

Nanostructured plasmonic sensors.

Abstract: Surface plasmons (SPs) are coherent oscillations of conduction electrons on a metal surface excited by electromagnetic radiation at a metal -dielectric interface. The growing field of research on such light -metal interactions is known as ‘plasmonics’. 1-3 This branch of research has attracted much attention due to its potential applications in miniaturized optical devices, sensors, and photonic circuits as well as in medical diagnostics and therapeutics. 4-8