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Enhancement-mode Al0.7Ga0.3N-channel high electron mobility transistors (HEMTs) were achieved through a combination of recessed etching and fluorine ion deposition to shift the threshold voltage (VTH) relative to depletion-mode devices by +5.6 V to VTH = +0.5 V. Accounting for the threshold voltage shift (ΔVTH), current densities of approximately 30 to 35 mA/mm and transconductance values of 13 mS/mm were achieved for both the control and enhancement mode devices at gate biases of 1 V and 6.6 V, respectively. Little hysteresis was observed for all devices, with voltage offsets of 20 mV at drain currents of 1.0 × 10−3 mA/mm. Enhancement-mode devices exhibited slightly higher turn-on voltages (+0.38 V) for forward bias gate currents. Piecewise evaluation of a threshold voltage model indicated a ΔVTH of +3.3 V due to a gate recess etching of 12 nm and an additional +2.3 V shift due to fluorine ions near the AlGaN surface. [ABSTRACT FROM AUTHOR]

We demonstrated electrical spin injection into an AlGaAs/GaAs-based high-mobility two-dimensional electron gas (2DEG) system using Co2MnSi as a spin source. A non-local spin-valve signal was observed from 4.2 K to room temperature. Interestingly, the spin-valve signal does not show a monotonic decrease with increasing temperature and reaches a peak at about 80 K. This contrasts with the result observed in bulk GaAs, in which a monotonic decrease in spin-valve signals with increasing temperature was observed. Moreover, the spin-valve signal decreases by a factor of about 5.6 with increasing temperature from 4.2 K to 294 K, and this factor is smaller than those values reported in bulk GaAs devices. This result suggests that the spin-valve signal in a 2DEG device is less sensitive to temperature than that in a bulk device, which is promising for realizing future spin transistors that can operate at room temperature. [ABSTRACT FROM AUTHOR]

Because of aggressive downscaling of the dimensions of future semiconductor devices, they will suffer from increased line resistivity and resistance-capacitance delay. In this work, NiAl thin films are investigated as a potential liner- and barrier-free interconnect material. The results show that NiAl has strong adhesion, does not undergo interdiffusion with SiO2, and has a favorable resistivity size effect. These features suggest that NiAl is a good candidate for replacing Cu as a liner- and barrier-free interconnect for linewidths below 7 nm. [ABSTRACT FROM AUTHOR]

This work reports growth of α-(AlxGa1-x)2O3 single crystals with high incorporation of Al by a Mist Chemical Vapor Deposition two-chamber system, which was rationally designed to avoid side-reactions between different precursors during solution preparation for multi-component thin film growth. Multiple acceleration voltages were used in Energy Dispersive X-ray measurements to reliably obtain the Al composition x of the films. As a result, Vegard's law for lattice constants was verified and found to be valid in the α-(AlxGa1-x)2O3 system. However, Vegard's law for optical bandgaps, derived from different models, required an additional term to account for the bowing effect. At x = 0.71, the gaps were 7.74, 7.03, 7.26, and 7.34 eV as derived from the Tauc plots for the direct bandgap, indirect bandgap, Tauc-Lorentz model, and O'Leary-Johnson-Lim model, respectively. The two-chamber system provides reliable and effective control of the Al content in α-(AlxGa1-x)2O3 alloys and heterostructures. [ABSTRACT FROM AUTHOR]

Aluminum nitride (AlN) is one of piezoelectric materials, which are eagerly anticipated for use in microelectromechanical systems (MEMS) applications such as communication resonators, sensors, and energy harvesters. AlN is particularly excellent in generated voltage characteristics for the MEMS rather than oxide piezoelectric materials such as lead zirconium titanate Pb(Zr, Ti)O3. However, it is necessary to improve the piezoelectric properties of AlN in order to advance the performance of the MEMS. We dramatically increased the piezoelectric coefficient d33 of AlN films by simultaneously adding magnesium (Mg) and niobium (Nb). The d33 of Mg39.3Nb25.0Al35.7N is 22 pC/N, which is about four times that of AlN. The d33 is increased by Mg and Nb simultaneous addition, and is not increased by Mg or Nb single addition. Interestingly, the Nb has multiple chemical states, and which are influenced by the Mg concentration. [ABSTRACT FROM AUTHOR]

Modulation-doped heterostructures are a key enabler for realizing high mobility and better scaling properties for high performance transistors. We report the realization of a modulation-doped twodimensional electron gas (2DEG) at the β-(Al0.2Ga0.8)2O3/Ga2O3 heterojunction by silicon delta doping. The formation of a 2DEG was confirmed using capacitance voltage measurements. A modulation-doped 2DEG channel was used to realize a modulation-doped field-effect transistor. The demonstration of modulation doping in the β-(Al0.2Ga0.8)2O3/Ga2O3 material system could enable heterojunction devices for high performance electronics. [ABSTRACT FROM AUTHOR]

The two-dimensional electron gas (2DEG) at the non-isostructural interface between spinel γ-Al2O3 and perovskite SrTiO3 is featured by a record electron mobility among complex oxide interfaces in addition to a high carrier density up to the order of 1015 cm-2. Herein, we report on the patterning of 2DEG at the γ-Al2O3/SrTiO3 interface grown at 650 °C by pulsed laser deposition using a hard mask of LaMnO3. The patterned 2DEG exhibits a critical thickness of 2 unit cells of γ-Al2O3 for the occurrence of interface conductivity, similar to the unpatterned sample. However, its maximum carrier density is found to be approximately 3×1013 cm-2, much lower than that of the unpatterned sample (∼1015 cm-2). Remarkably, a high electron mobility of approximately 3600 cm2 V-1 s-1 was obtained at low temperatures for the patterned 2DEG at a carrier density of ∼7×1012 cm-2, which exhibits clear Shubnikov-de Haas quantum oscillations. The patterned high-mobility 2DEG at the γ-Al2O3/SrTiO3 interface paves the way for the design and application of spinel/perovskite interfaces for high-mobility all-oxide electronic devices. [ABSTRACT FROM AUTHOR]

The importance of having an optimal material for fabricating Optically Transparent Antennas (OTAs) is crucial for designing highly efficient antennas that can be integrated with photovoltaics. Transparent Conductor Oxides are promising for OTA fabrication due to their capability of being simultaneously transparent at optical frequencies and conductive within the radio frequency (RF) range. Here in this study, thin aluminum and zinc oxide layers were co-sputtered onto Si and a polycrystalline photovoltaic cell and then annealed between 350 °C and 450 °C for 24 and 48 h in a N2 ambient. The annealing process ensured the formation of Aluminum Zinc Oxide (AZO) with low resistivity ≈10-5 Ωcm and a transparency of 86% between 350 and 750 nm. The material was tested by performing RF characterization and by fabricating and testing two different OTAs. Theresults of the optimization process and characterization show that the AZO material is feasible for OTA fabrication. [ABSTRACT FROM AUTHOR]

The electronic structure of Al1-xInxN(1010) surfaces is investigated by cross-sectional scanning tunneling spectroscopy and density functional theory calculations. The surface exhibits empty Al and/or In-derived dangling bond states, which are calculated to be within the fundamental bulk band gap for In compositions smaller than 60%. The energy of the lowest empty In-derived surface state is extracted from the tunnel spectra for lattice-matched Al1-xInxN with In compositions of x=0.19 and x=0.20 to be EC-1.82±0.41 and EC-1.80±0.56 eV, respectively, in good agreement with the calculated energies. Under growth conditions, the Fermi level is hence pinned (unpinned) for In compositions smaller (larger) than 60%. The analysis of the tunnel spectra suggests an electron affinity of ~3.5 eV for nonpolar lattice-matched Al1-xInxN cleavage surfaces, which is large compared to linearly interpolated values of polar AlN and InN (0001) surfaces. [ABSTRACT FROM AUTHOR]

Sn-doped gallium oxide (Ga2O3) wrap-gate fin-array field-effect transistors (finFETs) were formed by top-down BCl3 plasma etching on a native semi-insulating Mg-doped (100) β-Ga2O3 substrate. The fin channels have a triangular cross-section and are approximately 300 nm wide and 200 nm tall. FinFETs, with 20 nm Al2O3 gate dielectric and ~2 µm wrap-gate, demonstrate normally-off operation with a threshold voltage between 0 and +1 V during high-voltage operation. The ION IOFF ratio is greater than 105 and is mainly limited by high on-resistance that can be significantly improved. At VG = 0, a finFET with 21 lm gate-drain spacing achieved a three-terminal breakdown voltage exceeding 600V without a field-plate. [ABSTRACT FROM AUTHOR]

The systematic design, fabrication, and characterization of an isolated, single-mode, 90° bend phononic crystal (PnC) waveguide are presented. A PnC consisting of a 2D square array of circular air holes in an aluminum substrate is used, and waveguides are created by introducing a line defect in the PnC lattice. A high transmission coefficient is observed (-1 dB) for the straight sections of the waveguide, and an overall 2.3 dB transmission loss is observed (a transmission coefficient of 76%) for the 90° bend. Further optimization of the structure may yield higher transmission efficiencies. This manuscript shows the complete design process for an engineered 90° bend PnC waveguide from inception to experimental demonstration. [ABSTRACT FROM AUTHOR]

The continuum state associated with type-II In0.46Al0.54As/Al0.54Ga0.46As quantum dots (QDs) is investigated. Emission from the continuum states of the QDs is directly observed in photoluminescence (PL) spectra. The PL excitation and time-resolved PL spectra reveal an efficient carrier relaxation from the AlGaAs barrier into the InAlAs QD ground state via the continuum states. The temperature dependence of the PL spectra shows a decreasing PL linewidth and a strong redshift of the peak energy at low temperature, indicating that carriers are redistributed through the continuum states by thermal activation and lateral transfer. Published by AIP Publishing. [ABSTRACT FROM AUTHOR]

We report non-linear electronic transport measurement of Al/Si-doped n-type InN nanowire/Al junctions performed at T=0.3 K, below the superconducting transition temperature of the Al electrodes. The proximity effect is observed in these devices through a strong dip in resistance at zero bias. In addition to the resistance dip at zero bias, several resistance peaks can be identified at bias voltages above the superconducting gap of the electrodes, while no resistance dip is observed at the superconducting gap. The resistance peaks disappear as the Al electrodes turn normal beyond the critical magnetic field except one which remains visible at fields several times higher than critical magnetic field. An unexpected non-monotonic magnetic field dependence of the peak position is observed. We discuss the physical origin of these observations and propose that the resistance peaks could be the McMillan-Rowell oscillations arising from different closed paths localized near different regions of the junctions. [ABSTRACT FROM AUTHOR]

The magnetic field effects on the electroluminescence of aluminium tris-(8-hydroxyqinoline) (Alq3) based organic light emitting diodes have been investigated by varying the electron/hole ratio in the emissive layer. Experimental results reveal that a negative high field effect in the magnetoelectroluminescence (MEL) can be found in devices with very low triplet exciton concentration at room temperature. This suggests triplet-triplet annihilation cannot be used to explain the negative high field MEL in the Alq3 system. Our results suggest that hole-exciton interaction may be the origin of the negative high field MEL and also, in parallel with this interaction, there is also the more common positive high field process occurring which has been tentatively attributed to electronexciton interactions. The competition between these different processes decides the final shape of the MEL at high fields. [ABSTRACT FROM AUTHOR]

Polarization induced degenerate n-type doping with electron concentrations up to ~1020cm-3 is achieved in graded AlxGa1-xN layers (x: 0% → 37%) grown on unintentionally doped and on n-doped GaN:Si buffer/reservoir layers by metal organic vapor phase epitaxy. High resolution x-ray diffraction, transmission electron microscopy, and electron dispersive x-ray spectroscopy confirm the gradient in the composition of the AlxGa1-xN layers, while Hall effect studies reveal the formation of a three dimensional electron slab, whose conductivity can be adjusted through the GaN(:Si) buffer/reservoir. [ABSTRACT FROM AUTHOR]

Quantum dots (QDs) embedded in nanowires represent one of the most promising technologies for applications in quantum photonics. Self-assembled bottom-up fabrication is attractive to overcome the technological challenges involved in a top-down approach, but it needs post-growth investigations in order to understand the self-organization process. We investigate the QD formation by self-segregation in AlxGa1-xAs shells as a function of thickness and cross-section morphology. By analysing light emission from several hundreds of emitters, we find that there is a certain thickness threshold for the observation of the QDs. The threshold becomes smaller if a thin AlAs layer is pre-deposited between the GaAs nanowire core and the AlxGa1-xAs shell. Our results evidence the development of the quantum emitters during the shell growth and provide more guidance for their use in quantum photonics. [ABSTRACT FROM AUTHOR]

In this letter, we demonstrate the control of dipole alignment of monolayer chloroaluminum phthalocyanine (ClAlPc) molecules via the strain in Au(111) substrates. Local ordering of ClAlPc dipole comprising alternate Cl-up and Cl-down configurations is found on the tensile-strained Au(111)/mica as a result of strain-enhanced absorption of Cl-down ClAlPc's and the dipole-dipole interaction. In contrast, the strain-released single crystal Au(111) substrate shows negligible coupling to Cl-down ClAlPc, therefore, facilitating the formation of unidirectionally aligned Cl-up ClAlPc dipole array. The dipole-dipole interaction becomes less prominent at low ClAlPc coverage where ClAlPc molecules can find their favorable absorption sites more easily according to their inherent dipole orientation. Our results emphasize the superior role of molecule-substrate interaction in functional molecular engineering on metal surface hence provide fundamental insight into the potential applications in molecular nanodevices with tunable and controllable properties. [ABSTRACT FROM AUTHOR]

The internal quantum efficiency (IQE) of Al0.55Ga0.45N/AlN and Al0.55Ga0.45N/Al0.85Ga0.15N UVC MQW structures was analyzed. The use of bulk AlN substrates enabled us to undoubtedly distinguish the effect of growth conditions, such as V/III ratio, on the optical quality of AlGaN based MQWs from the influence of dislocations. At a high V/III ratio, a record high IQE of ~80% at a carrier density of 1018 cm-3 was achieved at ~258nm. The high IQE was correlated with the decrease of the non-radiative coefficient A and a reduction of midgap defect luminescence, all suggesting that, in addition to dislocations, point defects are another major factor that strongly influences optical quality of AlGaN MQW structures. [ABSTRACT FROM AUTHOR]

For the quaternary material (AlyGa1-y)1-xInxAs, the energy level of the silicon-related deep electron trap known as the DX-center is calculated. In addition, the composition range y(x) is derived, for which the silicon-related DX-center level is below the conduction band minimum and thus electronically active. Eventually, the result of the calculation is compared with available measurement data, revealing good agreement regarding the composition when the DX-center energy level crosses the conduction band minimum. [ABSTRACT FROM AUTHOR]

We present an efficient genetic algorithm, integrated with experimental diffraction data, to solve a nanoscale metastable Al20Sm4 phase that evolves during crystallization of an amorphous magnetron sputtered Al90Sm10 alloy. The excellent match between calculated and experimental X-ray diffraction patterns confirms an accurate description of this metastable phase. Molecular dynamic simulations of crystal growth from the liquid phase predict the formation of disordered defects in the devitrified crystal. [ABSTRACT FROM AUTHOR]

A controllable and smooth potassium hydroxide-based wet etching technique was developed for the AlGaN system. High selectivity between AlN and AlxGa1-xN (up to 12×) was found to be critical in achieving effective substrate thinning or removal for AlGaN-based deep ultraviolet light emitting diodes, thus increasing light extraction efficiency. The mechanism of high selectivity of AlGaN as a function of Al composition can be explained as related to the formation and dissolution of oxide/hydroxide on top of N-polar surface. Cross-sectional transmission electron microscopic analysis served as ultimate proof that these hillocks were not related to underlying threading dislocations. [ABSTRACT FROM AUTHOR]

We designed and constructed three dimensional (3D) zinc oxide Nanotetrapods (T-ZnOs) modified AlGaAs/GaAs high electron mobility transistors (HEMTs) for enzymatic uric acid (UA) detection. The chemical vapor deposition synthesized T-ZnOs was distributed on the gate areas of HEMTs in order to immobilize uricase and improve the sensitivity of the HEMTs. Combining with the high efficiency of enzyme immobilization by T-ZnOs and high sensitivity from HEMT, the asconstructed uricase/T-ZnOs/HEMTs biosensor showed fast response towards UA at ~1 s, wide linear range from 0.2nM to 0.2mM and the low detect limit at 0.2 nM. The results point out an avenue to design electronic device as miniaturized lab-on-chip device for high sensitive and specific in biomedical and clinical diagnosis applications. [ABSTRACT FROM AUTHOR]

In this work, the post-breakdown characteristics of metal gate/Al2O3/InGaAs structures were stud-ied using surface analysis by x ray photoelectron spectroscopy. The results show that for dielectric breakdown under positive bias, localized filaments consisting of oxidized substrate atoms (In, Ga and As) were formed, while following breakdown under negative bias, a decrease of oxidized sub-strate atoms was observed. Such differences in the microstructure at the oxide-semiconductor inter-face after breakdown for positive and negative voltages are explained by atomic diffusion of the contact atoms into the gate dielectric in the region of the breakdown spot by the current induced electro-migration effect. These findings show a major difference between Al2O3/InGaAs and SiO2/Si interfaces, opening the way to a better understanding of the breakdown characteristics of III-V complementary-metal-oxide-semiconductor technology [ABSTRACT FROM AUTHOR]

InGaN/GaN multi-quantum well (MQW) light emitting diodes with heavily Mg doped and unintentionally doped (UID) low-temperature Al0.2Ga0.8N electron blocking layer (EBL) were investigated. Broad short-wavelength electroluminescence peak, which has strong relative intensity to the main emission, was found in the UID-EBL sample at cryogenic temperatures. Study suggests that the broad peak is emitted by the sidewall MQWs. This result indicates that the electroluminescence of sidewall MQWs, in which the carrier density is high enough, can be detected at cryogenic temperatures. The lineshape variation with current density reveals detailed information on the process of carrier injection into the sidewall MQWs. [ABSTRACT FROM AUTHOR]

Interfacial misfit arrays were embedded within two avalanche photodiode (APD) structures. This allowed GaSb absorption layers to be combined with wide-bandgap multiplication regions, consisting of GaAs and Al0.8Ga0.2As, respectively. The GaAs APD represents the simplest case. The Al0.8Ga0.2As APD shows reduced dark currents of 5.07 μAcm-2 at 90% of the breakdown voltage, and values for effective k = β/α below 0.2. Random-path-length modeled excess noise is compared with experimental data, for both samples. The designs could be developed further, allowing operation to be extended to longer wavelengths, using other established absorber materials which are lattice matched to GaSb. [ABSTRACT FROM AUTHOR]

The band alignment of Al2O3/n-Ga2O3 was investigated by x-ray photoelectron spectroscopy (XPS). With a band gap of 6.8±0.2 eV measured for Al2O3, the conduction and valence band offsets at the interface were estimated to be 1.5±0.2 eV and 0.7±0.2 eV, respectively. The conduction band offset was also obtained from tunneling current in Al2O3/n-Ga2O3 (201) metal-oxide-semiconductor (MOS) diodes using the Fowler-Nordheim model. The electrically extracted value was in good agreement with the XPS data. Furthermore, the MOS diodes exhibited small capacitance-voltage hysteresis loops, indicating the successful engineering of a high-quality Al2O3/Ga2O3 interface. [ABSTRACT FROM AUTHOR]

We investigated the dependence of the indium content of tenfold Al1-xInxN/GaN superlattice structures grown by metal organic vapor phase epitaxy on layer thickness and strain state. Growth conditions taken from a thick lattice-matched reference sample with an indium content of about 18% lead to reduced indium contents from 3% for 0.5 nm of Al1-xInxN to 16.5% for 5.0 nm, respectively. There is no evidence for dependences of the indium incorporation on the lattice mismatch between the Al1-xInxN and the subjacent layer. Additional supply of trimethylindium only shows a very slight, almost negligible influence on the indium content of these superlattice structures. Finally, we present a model explaining the behavior of the indium content of the Al1-xInxN layer assuming the growth of an indium depleted phase in the initial stage of growth. [ABSTRACT FROM AUTHOR]

The band-alignment of atomic layer deposited (ALD)-HfO2/Al0.25Ga0.75N was studied by high resolution x-ray photoelectron spectroscopy measurements for both the non-passivated and SiH4 passivated AlGaN surfaces. The valence band offset and the conduction band offset for the ALD-HfO2/Al0.25Ga0.75N interface were found to be 0.43 eV and 1.47 eV, respectively, for the non-passivated sample, and 0.59 eV and 1.31 eV, respectively, for the SiH4-passivated sample. The difference in the band alignment is dominated by the band bending or band shift in the AlGaN substrate as a result of the different interlayers formed by the two surface preparations. [ABSTRACT FROM AUTHOR]

The intrinsic stress evolution during formation of ultrathin amorphous oxide films on Al(111) and Al(100) surfaces by thermal oxidation at room temperature was investigated in real-time by in-situ substrate curvature measurements and detailed atomic-scale microstructural analyses. During thickening of the oxide a considerable amount of growth stresses is generated in, remarkably even amorphous, ultrathin Al2O3 films. The surface orientation-dependent stress evolutions during O adsorption on the bare Al surfaces and during subsequent oxide-film growth can be interpreted as a result of (i) adsorption-induced surface stress changes and (ii) competing processes of free volume generation and structural relaxation, respectively. [ABSTRACT FROM AUTHOR]

We investigated alkali metal doping mechanism by comparative analysis between an Mg-Alq3 co-deposition (Mg:Alq3) and an Mg deposition on Alq3 films (Mg/Alq3). The operating voltage decreased by 0.4 V and the luminance increased by 60 cd/m2 at 11 mA/cm2 for devices constructed from the Mg:Alq3. However, the device characteristics of Mg/Alq3 samples were degraded. Our experimental results using an in-situ photoemission study showed that alkali metal doping in Alq3 did not induce band bending, but reduce electron injection barrier by charge transfer from alkali metals to Alq3 molecules. [ABSTRACT FROM AUTHOR]

Photoexcited carrier dynamics and localization potentials in Al0.86In0.14N/GaN heterostructures have been examined by time-resolved and scanning near-field photoluminescence (PL) spectroscopy. The large GaN and AlInN PL intensity difference, and the short AlInN PL decay and GaN PL rise times indicate efficient photoexcited hole transfer from AlInN to GaN via sub-band-gap states. These states are attributed to extended defects and In clusters. Near-field PL scans show that diameter of the localization sites and the distance between them are below 100 nm. Spatial variations of the GaN PL wavelength have been assigned to the electric field inhomogeneities at the heterostructure interface. [ABSTRACT FROM AUTHOR]

We investigated molecular beam epitaxial growth characteristics on (001) GaAs substrates with a pair of etched grooves along the <110> direction. It is found that, as the growth proceeds, the mesa width between the pair of grooves gradually decreases and that the grown mesa surface becomes slightly concave. These results offer great advantages for precisely defining the lateral width of index guided lasers during growth. A pair-groove-substrate GaAs/AlGaAs multiquantum well laser has been newly developed, which shows stable fundamental transverse mode oscillation and a high external differential quantum efficiency of 68% as well as a low threshold current of 23 mA. [ABSTRACT FROM AUTHOR]

The GaAs/AlGaAs material system is believed to have a band offset without remarkable influence from the interface. We report here probing a slightly higher (5-10 meV) valence-band offset at the GaAs-on-Al0.57Ga0.43As interface compared to that of the Al0.57Ga0.43As-on-GaAs interface, by using internal photoemission spectroscopy. This indicates the non-commutativity of band offset for GaAs/AlGaAs, i.e., the dependence on the order of the growth of the layers. This result is consistently confirmed by observations at various experimental conditions including different applied biases and temperatures. [ABSTRACT FROM AUTHOR]

A concept for the precise tailoring of a wide variety of nanogranular composites with a gas aggregation cluster source and a magnetron is presented. Electrical charging of the preformed clusters and the substrate in a plasma is discussed as a fundamental physical hindrance for conventional co-sputtering with a cluster source. The proposed concept overcomes this hindrance and is experimentally demonstrated for the deposition of a dielectric aluminum nitride matrix with embedded magnetic cobalt clusters. Chemical, magnetic, and structural analyses of the composite confirm the feasibility of the proposed concept as a versatile route for the preparation of nanocomposites. [ABSTRACT FROM AUTHOR]

Using integrated interdigital transducers (IDTs), we demonstrate the emission of surface acoustic waves (SAWs) by AlGaN/GaN high electron mobility transistors (HEMTs) under certain bias conditions through dynamic screening of the HEMTs vertical field by modulation of its two-dimensional electron gas. We show that a strong SAW signal can be detected if the IDT geometry replicates the HEMT electrode geometry at which RF bias is applied. In addition to characterizing SAW emission during both gate-source and drain-source modulation, we demonstrate SAW detection by HEMTs. Integrated HEMT-IDT structures could enable real-time evaluation of epitaxial degradation as well as high-speed, amplified detection of SAWs. [ABSTRACT FROM AUTHOR]

The dependence of device characteristics on cavity length is used to determine the injection efficiency, internal loss, and material gain of electrically injected AlGaN-cladding-free m-plane InGaN/GaN laser diodes. Estimates for the transparency carrier density are discussed in the context of recombination coefficients that have been reported for c-plane InGaN-based light-emitting devices. [ABSTRACT FROM AUTHOR]

We demonstrate AlGaN-cladding-free (ACF) m-plane InGaN/GaN laser diodes (LDs) with peak output powers and estimated front facet optical power densities that are comparable to the state-of-the-art single-stripe emitter c-plane LDs. The threshold current density, slope efficiency, and peak output power were 4.66 kA/cm2, 1.29 W/A, and 1.6 W, respectively, after facet coating and under pulsed conditions. Catastrophic optical mirror damage was not observed up to an estimated optical power density of 51.2 MW/cm2 at the front mirror facet, indicating the potential for using ACF m-plane InGaN/GaN LDs in high-power LD applications. [ABSTRACT FROM AUTHOR]

Standard stripe-length dependent optical-pumping measurements have been performed on AlGaN/AlGaN multiple quantum wells (MQWs) on an AlN buffer grown using two different kinds of technologies, i.e., 'GaN interlayer' and 'porous AlN buffer.' The net modal gains of the two samples along both m- and a-axis have been obtained, showing that the net modal gain of the MQWs on the AlN grown using 'GaN interlayer' is higher than that on the AlN grown using 'porous AlN buffer.' Reciprocal space mapping measurements have indicated that the MQW structure on the AlN structure grown using 'GaN interlayer' is fully strained while that on the AlN grown using 'porous AlN buffer' is partially strain-relaxed. The net modal gain along the m-axis is higher than that along the a-axis in both samples, highly reasonably indicating that the most favourable orientation for forming the cavity facets is not <11-20> direction of c-plane sapphire, along which III-nitride on c-plane sapphire is normally cleaved. [ABSTRACT FROM AUTHOR]

We characterize and compress sub-nJ visible white-light continuum (WLC) pulses generated by self-phase modulation in yttrium aluminium garnet. The spectral phase is retrieved by spectrally resolving the transient reflectivity from an optically excited transition metal oxide. This measured phase is compensated by applying the appropriate distortion to a deformable mirror. By comparing the response of two different materials, we show that the white-light pulses can be compressed to approximately 10 fs duration. [ABSTRACT FROM AUTHOR]

The mechanism limiting the channel mobility in metal-oxide-semiconductor field-effect transistors (MOSFETs) fabricated in Al-implanted 4H-SiC is discussed comparing different post-implantation annealings. In spite of the improved interfacial morphology in carbon capped samples during annealing, the observed reduction of the mobility (from 40 to 24 cm2 V-1 s-1) suggests that interfacial roughness does not significantly impact the transport in the channel. Furthermore, the temperature dependence of the mobility demonstrates that Coulomb scattering is the main degradation mechanism due to the presence of trapped charges at the SiO2/SiC interface. [ABSTRACT FROM AUTHOR]

We report on Raman scattering experiments on InAs/AlxGa1-xAs quantum dot heterostructures with 0≤x≤0.6. The samples were prepared by using molecular beam epitaxy (MBE) and atomic layer MBE for the growth of different layers. For x>0, we detected several lines originating from the AlxGa1-xAs alloy. These can be related to scattering from GaAs-like and AlAs-like phonons with q≅0, and weaker scattering from disorder-activated phonons with q≠0. In particular, we identified a line at ∼250 cm-1 as due to disorder-activated longitudinal optical phonons in the alloy. This conclusion is different than the attribution of this line to scattering from dots and, consequently, we do not recognize the possibility of deriving any information about the actual composition of the dots from an analysis of this line as proposed by other authors. [ABSTRACT FROM AUTHOR]

The surface leakage currents and the surface trapping effects of the AlGaN/GaN high electron mobility transistors (HEMTs) on silicon with different passivation schemes, namely, a 120 nm plasma enhanced chemical vapor deposited SiN, a 10 nm atomic layer deposited (ALD) Al2O3 and a bilayer of SiN/Al2O3 (120/10 nm) have been investigated. After SiN passivation, the surface leakage current of the GaN HEMT was found to increase by about six orders; while it only increased by three orders after the insertion of Al2O3 between SiN and AlGaN/GaN. The surface conduction mechanism is believed to be the two-dimensional variable range hopping for all the samples. The leakage current in the etched GaN buffer layer with SiN/Al2O3 bilayer passivation was also much smaller than that with only SiN passivation. The pulse measurement shows that the bilayer of SiN/Al2O3 passivation scheme can effectively reduce the surface states and suppress the trapping effects. [ABSTRACT FROM AUTHOR]

In this work, the structure with gradually increased barrier thicknesses from the n-layers to p-layers is proposed to replace the traditional structure with equal barrier thickness in deep-ultraviolet AlGaN light-emitting diodes. Simulation approach yields to a result that, when increased barrier thicknesses are used, the distribution of electron and hole carriers inside the active region becomes quite uniform, which leads to efficient recombination of electrons and holes and thereby a significant enhancement in output power. [ABSTRACT FROM AUTHOR]

We report a modified dots-in-a-well (DWELL) infrared photodetector by inserting some very thin GaAs or AlGaAs layers into the InAs dots. The photoluminescence (PL) measurements indicate that the modified DWELL structure with the insertion layers (ILs) of GaAs has a larger peak intensity and a narrower PL linewidth than that without the ILs. For the modified DWELL detector with AlGaAs ILs, the peak detection wavelength reaches very long infrared window of 14.1 μm. The peak detectivity D* is 1.1×108 cm Hz1/2/W at 77 K under normal incidence infrared irradiation. [ABSTRACT FROM AUTHOR]

The free-charge carrier mobility, sheet density, and effective mass of a two-dimensional electron gas are exemplarily determined in the spectral range from 640 GHz to 1 THz in a AlGaN/GaN heterostructure using the optical-Hall effect at room temperature. Complementary midinfrared spectroscopic ellipsometry measurements are performed for analysis of heterostructure constituents layer thickness, phonon mode, and free-charge carrier parameters. The electron effective mass is determined to be (0.22±0.04)m0. The high-frequency sheet density and carrier mobility parameters are in good agreement with results from dc electrical Hall effect measurements, indicative for frequency-independent carrier scattering mechanisms of the two-dimensional carrier distribution. [ABSTRACT FROM AUTHOR]

The pulsed optoelectronic terahertz emitter based on a δ-doped p-i-n-i GaAs/AlxGa1-xAs heterostructure, which was suggested by Reklaitis [Phys. Rev. B 77, 153309 (2008)], is investigated experimentally. It is shown that the heterostructure can serve as efficient antenna- and bias-free surface emitter. Its power exceeds the emission from InGaAs and InAs surfaces for optical excitation fluences below 0.7 μJ/cm2 at 82 MHz pulse repetition rate, respectively, 7 μJ/cm2 at 1 kHz, with potential for further improvement by carrier recombination management. [ABSTRACT FROM AUTHOR]

Structural, magnetic, electrical, and thermal transport properties of antiperovskite compounds AlNxMn3 (x=1,1.1,1.2) have been investigated systematically. With increasing x, the lattice constant increases monotonously while the Curie temperature TC decreases. Both the high TC and small coercive fields consistently indicate AlNxMn3 may be a promising high-temperature soft magnetic material. The resistivity displays T2-dependence below 30 K and the Kadowaki-Woods ratio is about 107.7 μΩ cm/K2, indicating a possible strongly correlated Fermi-liquid behavior in AlNMn3. Further analysis suggests that the electron-type carriers are dominant and the thermal conductivity mainly originates from the lattice contribution. [ABSTRACT FROM AUTHOR]

The sub-Tg enthalpy relaxation in glasses far from equilibrium (i.e., hyperquenched glasses) is usually manifested as a monotonic increase in both the onset temperature and the extent of enthalpy recovery with increasing the annealing temperature. Here we report an abnormal three-steplike relaxation pattern in hyperquenched Cu45Zr45Al10 and Cu48Zr48Al4 glasses below Tg, i.e., the usual monotonic increase is inverted when the annealing temperature increases to a critical value. This abnormal relaxation pattern could be attributed to the high extent of chemical heterogeneity in the CuZrAl supercooled liquids, and present a thermodynamic evidence for the dynamic fragile-to-strong transition in metallic glass-forming liquids. [ABSTRACT FROM AUTHOR]

From internal photoemission and photoconductivity measurements at the (100)GaSb/Al2O3 interface, the semiconductor valence band is found to be 3.05±0.10 eV below the oxide conduction band. This band alignment corresponds to conduction and valence band offsets of 2.3±0.10 and 3.05±0.15 eV, respectively. These results indicate that the valence band in GaSb lies energetically well above the valence band in InxGa1-xAs (0≤x≤0.53) or InP, suggesting the possibility of fabrication of hole quantum-well channel structures. [ABSTRACT FROM AUTHOR]

From internal photoemission and photoconductivity measurements at the (100)GaSb/Al2O3 interface, the semiconductor valence band is found to be 3.05±0.10 eV below the oxide conduction band. This band alignment corresponds to conduction and valence band offsets of 2.3±0.10 and 3.05±0.15 eV, respectively. These results indicate that the valence band in GaSb lies energetically well above the valence band in InxGa1-xAs (0≤x≤0.53) or InP, suggesting the possibility of fabrication of hole quantum-well channel structures. [ABSTRACT FROM AUTHOR]