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The capacitance-voltage (C-V) characteristics of Al0.25Ga0.75N/GaN heterostructure barrier varactors (HBV) grown by metal-organic chemical vapor deposition on a c-oriented sapphire substrate were studied. The favorable material properties of wide-band-gap III-N's are important in realizing the HBVs for frequency triples and distributed line pulse sharpens for practical use. The HBV structure consists of a 10-nm-thick undoped Al0.25Ga0.75N barrier sandwiched between two undoped GaN layers with a thickness of 5 nm. The barrier structure is further sandwiched between two n-GaN (n = 5 × 1017 cm–3) layers with respective thicknesses of 500 nm and 1 µm to form the top and the bottom ohmic contacts. At room temperature, the C-V characteristics show a maximum capacitance Cmax at approximately –1.8 V because of the induced piezoelectric field within the heterostructure, and the I-V characteristics show an increase in leakage current below –1.5 V and above 0.5 V. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A low frequency noise and charge carrier transport mechanisms were investigated on tantalum capacitors made by various producers. The model of Ta–Ta2O5–MnO2 MIS structure was used to give physical interpretation of I–V characteristics in normal and reverse modes. The noise in time and frequency domain was examined and noise sources were identified. We evaluated correlation between leakage current and noise spectral density and discussed corresponding quality and reliability indicators.

The InAs quantum well heterostructure was successfully grown on a semi-insulating GaAs substrate by MBE. On the GaAs substrate, the semi-insulating AlGaAsSb was grown to a thickness of 600 nm as the buffer layer, followed by a 15 nm InAs channel layer and a 35 nm AlGaAsSb doped layer together with 10 nm GaAsSb cap layer successively. The electron mobility and the sheet carrier concentration of the 15 nm InAs heterostructure was about 1 m2 V−1 s−1 and 4.5×1012 cm−2, respectively, at room temperature. This heterostructure is equivalent to the heavily doped InAs substrate with little change of the electron mobility on temperature. This device has typical 1/f noise characteristics without any large bulge throughout the frequency and the temperature ranges observed. The Hooge parameter was αH=1×10−3 at room temperature, decreasing monotonically with the decreasing temperature down to 5×10−4 at 50 K, indicating characteristics of the virtually constant mobility and constant carrier concentration device.

Low frequency noise characteristics of GaN/AlGaN HFET structures grown either on sapphire or SiC substrates were measured in wide temperature range 13 K to 300 K and activation energy of traps determined by several methods around 0.42 eV (SiC) and 63 meV (sapphire). Conceptual approach to trap parameters estimation was tested on RTS noise time-trace. The Hooge parameter alpha of GaN/AlGaN on SiC HFETs was of the order of 10-4 to 10-5, whereas two orders higher values for sapphire based devices were given by strong g-r noise.

We fabricated the first ultrafast active transmission lines with low dielectric constant (low-k) polyimide integrated with ultrafast photoconductive switches formed by the nano-anodization process. Electrical pulses as short as 290 fs were measured on this transmission line by an electrooptic sampling system based on a femtosecond laser. P-n junctions were inserted in the transmission line to control dispersion in lines, and low-k polyimide was introduced to reduce dielectric and radiation losses.

DC leakage currents of MLCC (Multi Layerd Ceramc Capacitor)s show the typical Poole Frenkel relationship between the normalized current log (I/V) and the normalized voltage V within the specified voltage across the device without any local breakdown characteristics, giving the PF constants and the barrier heights of the insulating BaTiO 3 layers. The typical 1/f noise characteristics are also observed, and the normalized noise amplitudes are obtained as the function of the MLCC series resistance, noise amplitudes of which are found more than 60 dB larger than those of the metal resistors. Both the leakage current and 1/f noise amplitudes give time saving reliability information much faster than those of the conventional MTTF method. The emerging needs of the ecological vehicles or the two cycle motor inverter systems accelerate the development of the high voltage MLCCs sharing a large part of capacitor applications. Up to 80 % of the total capacitors are made now by the MLCC. The MTTF method is usually applied as the standard conventional reliability test for these capacitors. Both the leakage current and 1/f noise amplitudes give time saving reliability information much faster than those of the conventional MTTF method. The leakage current in MLCC can be explained by the Poole-Frenkel tunneling effect. The normalized current (I/V) is linearly dependent on SQRT(V), noise levels are 60 to 80 dB larger than those of the conventional carbon resistors, with typical 1/f characteristics, dependent on the lots and independent of the biasing voltage.

A very high electron mobility pseudomorphic Si-doped In 0.48 Al 0.52 As/ undoped In 0.8 Ga 0.2 As heterostructure is successfully grown on the InP substrate by the newly invented technology of stabilizing the transient vapor flux of group-III cells with SQRT control and inserting an InAs monolayer in the heterointerface between the channel layer and the spacer. The actual critical thickness of the pseudomorphic heterostructure as determined by the Hall measurement is found to follow the energy balance model, and the highest 2DEG mobilities over 1.6 and 16 m 2 /V·s with 1.6×10 12 cm -2 at 293 and 10 K, respectively, are obtained for the InP-based pseudomorphic In 0.52 Al 0.48 As/In 0.2 Ga 0.2 As heterostructure.

A very high electron mobility pseudomorphic In0.8Ga0.2As heterostructure is successfully grown on InP both by the elimination of the overshoot of flux densities and by the precise control of the flux ratio through a new calibration technique of RHEED oscillations in an MBE system. The critical layer thickness for the pseudomorphic growth of InGaAs on InP is found to follow the energy balance model, and a very high 2DEG mobility of over 1.5 and 16 m2/Vs at 293 and 10 K, respectively, is obtained.

The drain voltage noise of commercial AlGaAs/GaAs HEMTs shows typical ƒ −1.0 noise characteristics with a Hooge noise parameter of about 6 × 10−5, while that of conventional GaAs MESFETs has a large GR noise bulge at about 15 Hz. The noise levels of the HEMT are smaller than those of the MESFET by 19 dB Hz−0.5 at the same bias conditions, manifesting the advantage of HEMT as a low-noise device.

Noise characteristics of epitaxial n‐GaN on sapphire layers and GaN/AlGaN on sapphire or SiC HFET structures were investigated in the temperature range of 13K to 300K. Ohmic contacts were made using Ti/Al/Ni/Au and contact noise was found negligible by TLM analysis. The Hooge parameter αH of epitaxial GaN was 2×10−3 at 300K, gradually decreasing to 10−4 around 50K. For GaN/AlGaN on sapphire HFET the g‐r noise was dominant at almost every temperature, allowing only to determine αH=2×10−4 at 22K. The GaN/AlGaN on SiC HFETs were characterized by αH values of 10−4 to 10−5.

The downscaling of electronic devices makes high field transport effects more important. In deep submicron technology high transversal and high lateral electric field exists. Application of drain voltage 1V results in electric field, which exceeds the silicon critical electric field. Electron temperature is then higher than lattice one and field dependent electron mobility must be considered. Due to small gate area we were able to activate one trap only and then in time domain two levels signal was observed. A systematic analysis of two level RTS signal was made to obtain information on capture and emission processes as a function of gate voltage, drain current and temperature for low and high lateral electric field. With increasing drain voltage capture time increases, while dependence on gate voltage is almost the same as for low drain voltage. For constant gate voltage and variable drain voltage emission process is independent on lateral field intensity, while capture time increases with lateral field ...

We have fabricated ultrafast electrical waveguides with low-k polyimide integrated with ultrafast photoconductive switches formed by nano-anodization process for the first time. Electrical signals are affected by nonlinear capacitance of p-n junctions in this waveguides, and pass through the low-k polyimide, so the dielectric loss and the radiation loss are dramatically reduced. The electrical pulses as short as 290 fs were measured on this waveguide by an electro-optic sampling system based on a femtosecond laser.

The growth of a very high electron mobility pseudomorphic In/sub 0.8/Ga/sub 0.2/As heterostructure on InP using an overshoot-free control of flux densities and precise control of the flux ratio through a calibration technique of reflection high energy electron diffraction (RHEED) oscillations in a molecular beam epitaxial (MBE) system is described. The critical layer thickness for the pseudomorphic growth of InGaAs on InP is found to follow the energy balance model, and a very high two-dimensional electron gas mobility of over 1.5 m/sup 2//Vs and over 15 m/sup 2//Vs at 293 K and 10 K, respectively, is obtained. >

A pseudomorphic InAlAs/In0.8Ga0.2As/InP heterostructure, with the very high electron mobility of over 1.5 m2/V at room temperature, is successfully grown on InP by our molecular beam epitaxial growth system. This is the ultimate and the most promising substrate for the high electron mobility transistors (HEMT), and the high speed logic circuits as well. An ideal 1/f characteristics was observed in this material throughout the temperature range between 300 and 50 K for the electric field between 1 and 200 V/cm. The Hooge noise parameter αH of a bridge type Hall element was of the order of 10−4 at room temperature, increasing with decreasing the temperature. The parameter αH increased with the electric field at room temperature, and was independent of the electric field at 77 K

Current collapse has been studied in unpassivated and SiN-passivated AlGaN/GaN heterostructure devices grown on a sapphire substrate by means of low-frequency-noise measurement at low temperatures, indicating this to be the most sensitive and powerful tool for assigning the deep levels in these complex and complicated structures. Generation–recombination (G–R) noise was explicitly observed in the unpassivated AlGaN/GaN heterostructure at low temperatures (T = 50–110 K) with the activation energy of 47 meV. This level was found to be dramatically decreased by the SiN passivation, from −205 dBA Hz−1/2 down to −217 dBA Hz−1/2, the current collapse being cured at the same time. With the SiN passivation a further G–R noise corresponding to the deeper traps of 131 and 235 meV became comparable to that corresponding to 47 meV.

Photoluminescence (PL) analysis on n-In0.52Al0.48As/In0.8Ga0.2As/In0.52Al0.48As/InP pseudomorphic heterostructures grown by molecular beam epitaxy has been carried out to investigate the critical layer thickness. Crystal quality degradation is followed by the relaxation of the lattice-mismatched layer. The critical layer thickness for this material system that is measured by PL is found to agree with the value from the energy balance model.

Low-frequency noise in AlGaAs/GaAs single-heterostructure is studied systematically for various contact metals and device dimensions. The low frequency noise spectra varies at a rate of ƒ −1 in the devices with SnAu contacts, and a rate of ƒ −1.5 in those with AuGe contacts. Contact resistances have no effect on the ƒ −1 noise levels, but change the generation-recombination ( G − R ) noise levels induced by the trap level at 0.23 eV. A large G − R noise bulge by the trap level at 0.8 eV is observed in the AuGe contact devices, but not in those with the SnAu contacts. The noise levels of the SnAu contact device are about 22 dB lower than thoe of the AuGe contact device around 1 Hz.

Since the two-dimensinoal electron gas in the modulation-doped A1GaAs/GaAs heterojunction is as thin as 10 nm and the electron mobility is over 7000 cm2/Vs, this structure is suitable for highly sensitive Hall devices. As the room temperature device the following conditions must be satisfied: the carriers should be supplied sufficiently to the two-dimensional gas, but no excess carriers should exist in the highly doped A1GaAs layer. Thus the number of the two-dimensional electron gas should have little dependence on the temperature. The fabrication conditions of the heterojunction and the magnetic property of the devices are discussed. The product sensitivity and the figure of merit of the heterojunction Hall device were 1000 V/AT and 27 (V/A)1/2/T, respectively. These values are comparable to those of InSb Hall devices. The temperature dependence of our device was three times less than that of the InSb Hall device.

Low-frequency noise in n-GaAs layers grown by molecular beam epitaxy has been systematically studied for various carrier concentrations and device dimensions. The noise decreases linearly with an increase in total carriers and layer thickness. The frequency dependence of the noise varies at a rate of ƒ −1.5 in the devices with SnAu contacts, and at the rates of ƒ −1.2 to ƒ −2.0 in those with AuGe contacts. SnAu ohmic contacts have noise levels 20 dB lower than those of AuGe contacts. Surface cap layers either doped to n- or p-type have little effect on the overall frequency dependence of the noise.

Fabrication processes to make an excellent p + n-junction on bulk n-InP by 24Mg-ion implantation are described. The leakage-current density through a junction was less than 10-7 A/cm2 with a rectification ratio larger than 106 at a bias voltage of - 1 V and a junction breakdown voltage below - 60 V without any guardring structure. A 2.0-mm long junction waveguide was used to control the long-wavelength (λ=1.135 µm) light with an extinction of 8.6 dB at 10 V.

A self-aligned-gate inversion-mode InP metal-insulator-semiconductor field-effect transistor (MISFET) was successfully fabricated by using plasma-assisted chemical-vapor-deposited Si3N4 film both as the insulator and as the capping layer for the annealing process. A channel mobility of 2700 cm2/Vs and a transconductance of 55 mS/mm at a gate voltage of 4 V were achieved with a reasonably low source-drain leakage current.