The history of the development of the High Electron Mobility Transistor (HEMT) is an outstanding illustration of how a new device can be successfully marketed. In this paper we discuss a key to successful commercialization of new devices.

As new applications of THz waves emerge, new active and passive components need to be developed. The efficiency of wave guiding systems can be significantly increased with the use of MEMS approaches as well as with the development of new planar antenna concepts with high bunching properties. Generation of sufficient THz power relies on new active devices like Heterostructure Barrier Varactors and cascaded quantum structures, but also in the optimisation of new generation concepts. One of these is photomixing in non-linear materials with very short carrier lifetimes, like low-temperature-grown GaAs.

In this paper, we describe the operation of circuits capable of more than 40-Gbit/s that we have developed using InP HEMT technology. For example, we succeeded in obtaining 43-Gbit/s operation for a full-rate 4:1Multiplier (MUX), 50-Gbit/s operation for a Demultiplexer (DEMUX), 50-Gbit/s operation for a D-type flip-flop (D-FF), and a preamplifier with a bandwidth of 40 GHz. In addition, the achievement of 90-Gbit/s operation for a 2:1MUX and a distributed amplifier with over 110-GHz bandwidth indicates that InP HEMT technology is promising for system operations of over 100 Gbit/s. To achieve these results, we also developed several design techniques to improve frequency response above 80 GHz including a symmetric and separated layout of differential elements in the basic SCFL gate and inverted microstrip.

We describe 150-nm-thick collector InP-based double heterojunction bipolar transistors with two types of thin pseudomorphic bases. The emitter and collector layers are designed for high collector current operation. The collector current blocking is suppressed by the compositionally step-graded collector structure even at J_C of over 500 kA/cm² with practical breakdown characteristics. An HBT with a 20-nm-thick base achieves a high f_T of 351 GHz at high J_C of 667 kA/cm², and a 30-nm-base HBT achieves a high value of 329 GHz for both f_T and f_max at J_C of 583 kA/cm². An equivalent circuit analysis suggests that the extremely small carrier-transit-delay contributes to the ultrahigh f_T.

We study the advantages and limitations of InP/GaAsSb/InP DHBTs for high-speed digital circuit applications. We show that the high-current performance limitation in these devices is electrostatic in nature. Comparison of the location of collector current blocking in various collector designs suggests a smoother, more gradual onset of blocking effects in type-II collectors. A comparison of collector current blocking effects between InP/GaAsSb--based and various designs of InP/GaInAs--based DHBTs provides support for our analysis.

A low energy plasma based on an electron discharge was investigated for the pre-epi clean of silicon wafers and for plasma enhanced homo and hetero epitaxial growth of Si and SiGe layers. VS were produced in a short, completely dry process sequence consisting of LEPC and LEPECVD only. The wafer/epilayer interface obtained in this process sequence was suitable to grow high quality VS with low surface roughness and dislocation densities. Based on this process and its implementation in a 200/300 mm single wafer cluster tool, a high volume and economical production of VS seems possible.

Hetero-interface properties of SiO₂/4H-SiC on (0001), (11-20), and (03-38) crystal orientations are presented. Epitaxial growth on new crystal orientations, (11-20) and (03-38), is described by comparing with the growth on (0001). Using thermal oxidation with wet oxygen, metal-oxide-SiC (MOS) structure was fabricated. From high-frequency capacitance-voltage characteristics measured at 300 K and 100 K, the interface properties were characterized semi-quantitatively. The interface state density was precisely determined using the conductance method for the MOS structure at 300 K. The new crystal orientations have the lower interface state density near the conduction band edge than (0001). From the characteristics of inversion-type planar MOSFETs, higher channel mobilities were obtained on (03-38) and (11-20) than on (0001). The cause of the difference in the channel mobility is speculated by the difference bond configuration of the three crystal orientations.

RF diamond FETs have been realized on a hydrogen-terminated diamond surface conductive layer. By utilizing the self-aligned gate fabrication process which is effective for the reduction of the parasitic resistance, the transconductance of diamond FETs has been greatly improved. Consequently, the high frequency operation of 22 GHz has been realized in 0.2 µ m gate diamond MISFETs with a CaF₂ gate insulator. This value is the highest in diamond FETs and is comparable to the maximum value of SiC MESFETs at present.

Recessed 0.15 µm gate-length AlGaN/GaN high electron mobility transistors (HEMTs) were fabricated using inductively-coupled-plasma reactive ion etching (ICP-RIE) on sapphire substrate. These 0.15 µm gate-length devices exhibited maximum drain current density as high as 1.4 A/mm and peak extrinsic transconductance of 346 mS/mm. The threshold voltage was -4.1 V. A unity gain cut-off frequency (f_T) of 80 GHz and maximum frequency of oscillation (f_max) of 73 GHz were measured on these devices. Pulsed I-(V) measurements did not show any significant dispersion. At 20 GHz, a continuous-wave (CW) output power density of 3.1 W/mm with power-added-efficiency (PAE) of 29.9% was obtained.

TCAD is gaining acceptance in the heterostructure industry. This article discusses the specific challenges a device simulator must manage to be a useful tool in designing and optimizing modern heterostructure devices. Example simulation results are given for HEMTs and HBTs, illustrating the complex physical processes in heterostructure devices, such as nonlocal effects in carrier transport, lattice self-heating, hot-electron effects, traps, electron tunneling, and quantum transport.

Results of the modeling work on FET, HBT microwave devices is presented. The models are implemented in CAD tools. Experimental characteristics are compared with simulated ones and there is good match between measurements and simulations.

Field Configurable Self-assembly is a novel programmable force field based heterogeneous integration technology. Herein, we demonstrate application of the method to rapid, parallel assembly of similar and dissimilar sub-200 µm GaAs-based light emitting diodes at silicon chip substrates. We also show that the method is compatible with post-process collective wiring techniques for fully planar hybrid integration of active devices.

This paper describes an experimental study on resonant properties of the plasma-wave field-effect transistors (PW-FET's). The PW-FET is a new type of the electron devices, which utilizes the plasma resonance effect of highly dense two-dimensional conduction electrons in the FET channel. Frequency tunability of plasma-wave resonance in the terahertz range was experimentally investigated for sub 100-nm gate-length GaAs MESFET's by means of laser-photo-mixing terahertz excitation. The measured results, including the first observation of the third-harmonic resonance in the terahertz range, however, fairly deviate from the ideal characteristics expected for an ideal 2-D confined electron systems. The steady-state electronic charge distribution in the MESFET channel under laser illumination was analyzed to study the effect of insufficient carrier confinement on the frequency tunability. The simulated results support the measured results. It was clarified that an ideal heterostructure 2-D electron confinement is essential to assuring smooth, monotonic frequency tunability of plasma-wave resonance.

The DC resistivities of silicon germanium thin films on Si substrates by a non-contact and non-destructive technique using terahertz time domain spectroscopy (THz-TDS) agree with the values obtained by the four-point probe measurement. In the present experiment, the mobility has not been precisely determined owing to the limitation of the frequency range in our equipment (from 0.1 to 1.5 THz). However, when the mobility becomes large enough, this method will be highly useful in evaluating semiconductor thin films, since the method gives the same data as those from Hall measurement without sample processing or electrode contact to sample.

We demonstrated the uniformity and stability as well as the high breakdown voltage of 0.1-µm-gate InP HEMTs with a double recess structure. To overcome the drawbacks regarding the uniformity and stability in the double recess structure, an InP passivation layer that functions as an etch-stopper and a surface passivator was successfully applied to the structure. It was confirmed that there was no degradation in the uniformity and stability of device performance for the double recess HEMTs that had the breakdown voltages in the on-state and off-state improved by a factor of 1.6.

InGaP/GaAs HBT with novel ledge coupled capacitor (LCC) structure has been proposed and demonstrated for the first time. The LCC employs an extrinsic InGaP ledge layer as a capacitor parallel to the base resistor. This configuration enables feeding RF signals directly into the base without passing them through the base resistor. With the fabricated HBT, no increase of leakage current between emitter and base electrode was observed. The maximum oscillation frequency (f_max) of the HBT was improved by 10 GHz as compared with an HBT without the LCC.

We report for the first time the design, process and characterization of InP-based micrometer emitter InGaAlAs/GaAsSb/InP Double HBTs (DHBTs) and their microwave performance. The layer structure not only allows the implementation of InP collector free of current blocking, but also enables small turn-on voltage and ballistic launching of electrons due to the positive conduction band discontinuity of emitter to base. The DHBT structure was grown on nominal (001) InP substrates using MBE. Solid Si and CBr₄ gas were used for n-type and p-type doing respectively. Fabricated large DHBTs showed high DC gain (> 80), small turn-on voltage 0.62 V, almost zero offset voltage, and nearly ideal base and collector current characteristics (ideality factors 1.0 for both B-E and B-C junctions). Small DHBTs demonstrated V_CEO > 8 V and stable operation at high current density exceeding 100 kA/cm². Maximum f_T of 57 GHz and maximum f_max of 66 GHz were achieved from 1 20 µm² devices at similar bias condition: J_C = 8.0 10⁴ A/cm² and V_CE =3.5 V. The InGaAlAs/GaAsSb/InP DHBTs appear to be a very promising HBT solution having simultaneous excellent RF and DC performances.

We propose an analysis method for Franz-Keldysh (FK) oscillations appearing in photoreflectance (PR) spectra of heterojunction device structures, which enables precise and simultaneous evaluation of the built-in electric field strength and band-gap energy. Samples for PR measurements were n⁺-GaAs/n-Al_0.3 Ga_0.7 As/i-GaAs heterostructures with different Al_0.3Ga_0.7As-layer thickness. We have found that the phase of the FK oscillations originating from the i-GaAs buffer layer depends on the Al_0.3 Ga_0.7 As-layer thickness. We have derived a calculation model for FK oscillations that includes the interference of probe light. From the comparison of the calculated spectra with the measured spectra, we conclude that mixing of the real and imaginary parts of a modulated dielectric function, which is caused by the probe-light interference, gives rise to the phase shift of the FK oscillations. Our FK-oscillation analysis method reduces ambiguity in the estimation of band-gap energy that is considerable in a conventional analysis.

We present excellent performance of a novel two-stage SiGe hetero-bipolar transistor (HBT) power amplifier (PA) in which different collector doping structures were employed for the first and second stages. A selectively ion implanted collector (SIC) structure was employed for the first stage HBT in order to obtain a high gain, while without-SIC structure was used for the second stage HBT in order to achieve a high breakdown voltage. At 1.95 GHz, the total PAE of 31% and a gain of 28 dB with an output power (P_out) of 26 dBm were obtained while the adjacent channel power ratio (ACPR) was less than -38 dBc for W-CDMA modulation signals.

Schottky gas sensors of CO were fabricated using high quality AlGaN/GaN/Si heterostructures. The CO sensors show good sensitivity in the temperature range of 250 to 300 (530%, at 160 ppm CO in N₂) and fast response comparable with SnO₂ sensors. A two-region linear regime was observed for the dependence of sensitivity on CO concentration. GaN sensors on Si substrate offer the possibility of integration with Si based electronics. The gas sensors show slow response with time, the change of material properties possibly in the presence of large thermal stress.

This work presents the results of an extensive DC current aging and failure analysis carried out on blue InGaN/GaN LEDs which identify failure mechanisms related to package degradation, changes in effective doping profile, and generation of deep levels. DLTS and ElectroLuminescence (EL) spectra indicate the creation of extended defects in devices aged at very high current density.

DC and RF performances of AlGaN/GaN HEMTs are simulated using a two-dimensional device simulator with the material parameters of GaN and AlGaN. The cut-off frequency is estimated as 205 GHz at the gate length of 0.05 µm and the drain breakdown voltage at this gate length is over 10 V. The values are satisfactory for millimeter wavelength power applications. The use of thin AlGaN layers has key importance to alleviate gate parasitic capacitance effects at this gate length.

In order to clarify the mechanism of gate leakage in AlGaN/GaN heterostructure field effect transistors (HFETs), temperature (T)-dependent current-voltage (I-V) characteristics of Ni/n-AlGaN Schottky contact were measured in detail. Large deviations from the thermionic emission transport were observed in I-V-T behavior with anomalously large reverse leakage currents. An analysis based on the thin surface barrier (TSB) model showed that the nitrogen-vacancy-related near-surface donors play a dominant role in the leakage through the AlGaN Schottky interface. As a practical scheme for suppressing the leakage currents, use of an insulated gate (IG) structure was investigated. As the insulator, Al₂O₃ was selected, and an Al₂O₃ IG structure was formed on the AlGaN/GaN heterostructure surface after an ECR-N₂ plasma treatment. An in-situ XPS analysis exhibited successful formation of an ultrathin stoichiometric Al₂O₃ layer which has a large conduction band offset of 2.1 eV at the Al₂O₃/Al_0.3Ga_0.7N interface. The fabricated Al₂O₃ IG HFET achieved pronounced reduction of gate leakage, resulting in the good gate control of drain currents up to V_GS = +3 V. The maximum drain saturation current and transconductance were 0.8 A/mm and 120 mS/mm, respectively. No current collapse was observed in the Al₂O₃ IG-HFETs, indicating a remarkable advantage of the present Al₂O₃-based insulated gate and passivation structure.

High-temperature stability of copper (Cu) gate AlGaN/GaN high electron mobility transistors (HEMTs) was investigated. Samples were annealed at various temperatures to monitor the changes on device performances. Current-voltage performance such as drain-source current, transconductance, threshold voltage and gate leakage current has no obvious degradation up to annealing temperature of 500 and time of 5 minutes. Also up to this temperature, no copper diffusion was found at the Cu and AlGaN interface by secondary ion mass spectrometry determination. At annealing temperature of 700 and time of 5 minutes, device performance was found to have degraded. Gate voltage swing increased and threshold voltage shifted due to Cu diffusion into AlGaN. These results indicate that the Schottky contact and device performance of Cu-gate AlGaN/GaN HEMT is stable up to annealing temperature of 500. Cu is a promising candidate as gate metallization for high-performance power AlGaN/GaN HEMTs.

We present ultra low noise- and wide dynamic range performances of an AlGaN/GaN heterostructure FET (HFET). An HFET fabricated on a high quality epitaxial layers grown on a semi-insulating SiC substrate exhibited impressively low minimum noise figure (NF _min ) of 0.4 dB with 16 dB associated gain at 2 GHz. The low NF (near NF _min ) operation was possible in a wide drain bias voltage range, i.e. from 3 V to 15 V. At the same time, the device showed low distortion character as indicated by the high third order input intercept point (IIP3), +13 dBm. The excellent characteristics are attributed to three major factors: (1) high quality epitaxial layers that realized a high transconductance and very low buffer leakage current; (2) excellent device isolation made by selective thermal oxidation; (3) ultra low gate leakage current realized by Pd based gate. The results demonstrate that the AlGaN/GaN HFET is a strong candidate for front-end LNAs in various mobile communication systems where both the low noise and the wide dynamic range are required.

High-frequency characterization and delay-time analysis have been performed for a short channel AlGaN/GaN heterojunction FET. The fabricated device with a short gate length (L_g) of 0.07 µm exhibited an extrinsic current gain cutoff frequency of 81 GHz and a maximum frequency of oscillation of 190 GHz with a maximum stable gain (MSG) of 8.2 dB at 60 GHz. A new scheme for the delay-time analysis was proposed, in which the effects of rather large series resistance R_S + R_D are properly taken into account. By applying the new scheme to a device with L_g=0.25 µm, we obtained an effective high-field electron velocity of 1.7510⁷ cm/s, which is consistent with our previous results calculated using Monte Carlo simulation.

We have demonstrated AlGaN/GaN high electron mobility transistors (HEMTs) grown on epitaxial AlN/sapphire templates. The crystal qualities and fabricated device performances between AlGaN/GaN HEMTs on epitaxial AlN/sapphire templates and conventional AlGaN/GaN HEMTs on sapphire substrates with low-temperature buffer layer (LT-BLs) are compared with each other. By using epitaxial AlN/sapphire templates instead of LT-BLs, higher mobility was exhibited and superior crystal qualities were observed, as confirmed by X-ray diffraction (XRD), atomic force microscopy (AFM) images and capacitance-voltage measurements. In addition, the dc characteristics of the fabricated devices on epitaxial AlN/sapphire templates were enhanced. AlGaN/GaN HEMTs on epitaxial AlN/sapphire templates are promising candidates for practical applications of nitride-based electronic devices.

For the mass production of GaN-based electronic devices, growth of AlGaN/GaN heterostructures on substrates larger than 100 mm in diameter is indispensable. In this study, we demonstrate the growth of 100-mm-diameter Al_0.26Ga_0.74N/GaN heterostructures on sapphire substrates by metalorganic vapor phase epitaxy (MOVPE). The obtained films have specular surfaces, good crystal quality and good uniformity of alloy composition across the entire 100-mm-diameter epitaxial wafer. The bowing value of the 100-mm-diameter epitaxial wafer on c-face sapphire substrates is about 40 µm. This bowing value seems to be preferable for electronic device fabrication processes. These epitaxial wafers show good electrical properties.

A TlGaAs/GaAs multiple quantum-well (MQW) structure having four identical well layers was grown on a GaAs (001) substrate by low-temperature molecular-beam epitaxy (MBE) at 190. The (004) X-ray diffraction (XRD) curve of this sample showed satellite peaks up to the 3rd order at least. The measured XRD curve agreed well with the theoretically simulated one with a Tl content of x=7% and a width of 57 for the Tl_xGa_1-xAs well layers. This result indicates that the grown MQW structure has good single-crystalline quality as well as flat and sharp interfaces.

This paper describes a method for the fast evaluation of the Sommerfeld integrals for modeling a vertical dipole antenna array in a borehole. When we analyze the antenna inside a medium modeled by multiple cylindrical layers with the Method of Moment (MoM), we need a Green's function including the scattered field from the cylindrical boundaries. We focus on the calculation of Green's functions under the condition that both the detector and the source are situated in the innermost layer, since the Green's functions are used to form the impedance matrix of the antenna. Considering bounds on the location of singularities on a complex wave number plane, a fast convergent integration path where pole tracking is unnecessary is considered for numerical integration. Furthermore, as an approximation of the Sommerfeld integral, we describe an asymptotic expansion of the integrals along the branch cuts. The pole contribution of TM₀₁ and HE₁₁ modes are considered in the asymptotic expansion. To obtain numerical results, we use a fast convergent integration path that always proves to be accurate and efficient. The asymptotic expansion works well under specific conditions. The Sommerfeld integral values calculated with the fast evaluation method is used to model the array antenna in a borehole with the MoM. We compare the MoM data with experimental data, and we show the validity of the fast evaluation method.

We propose a frequency stabilization system for laser diodes (LDs), in which the electrical feedback loop response can be determined using an on-line genetic algorithm (GA) so as to attain lower LD frequency noise power within the specific Fourier frequency range of interest. At the initial stage of the stabilization, the feedback loop response has been controlled through GA, manipulating the proportional gain, integration time, and derivative time of conventional analog PID controller. Individuals having 12-bit chromosomes encoded by combinations of PID parameters have converged evolutionarily toward an optimal solution providing a suitable feedback loop response. A fitness function has been calculated for each individual in real time based on the power spectral density (PSD) of the frequency noise. The performance of this system has been tested by stabilizing a 50 mW visible LD. Long-term (τ > 0.01 s) frequency stability and its repeatability have been improved.

We propose and describe a free-space optical interconnection device with a photorefractive semi-linear resonator. The hologram in the photorefractive crystal is, in general, volatile and the erasing of it coincides with the diffraction of the signal beam. Therefore we have to reform the hologram again after several transmissions of the data or use some fixing techniques such as thermal fixing and electrical fixing. In our interconnection device, the hologram is enhanced by the feedback beam that is a part of the input signal divided by the beam splitter within semi-linear resonator, therefore the sustentation time of the connection can be extended. We explain the sustentation mechanism and investigate the optimum reflectivity of the beam splitters, which determine the feedback rate of the input signal, within feedback circuit for the high output conversion efficiency. We also analyze the coupling strength threshold for sustentation of the connection. We give a basic experiment on 33 interconnection by using BaTiO₃ crystal and Ar⁺ laser whose wavelength is 514 [nm]. We show that the connections are held for long time without the continuous illumination of the control beam.

In an optical time domain reflectometer type strain measurement system, we theoretically derive the shape of the Brillouin gain spectrum produced in an optical fiber under a parabolic strain distribution which is formed in a uniformly loaded beam. Based on the derived result, we investigate the effects of the parabolic strain distribution parameters and the measurement conditions such as the launched pulse width and the measurement position on the beam on the deformation of the Brillouin backscattered-light power spectrum shape. In addition, we investigate the strain measurement error resulting from the deformation of the power spectrum shape by analyzing the peak-power frequency at which the power spectrum is maximized.

A high-speed high-resolution sample-and-hold amplifier (SHA) is designed for time-interleaved analog-to-digital converter applications. Using the techniques of precharging and output capacitor coupling can mitigate the stringent performance requirements for the opamp, resulting in low power dissipation. Implemented in a standard 0.25 µm CMOS technology, the SHA achieves 80 dB spurious-free dynamic range (SFDR) for a 1.8 Vpp output at 100 MHz Nyquist sampling rate. The SHA occupies a die area of 0.35 mm² and dissipates 33 mW from a single 2.5 V supply.

We have developed a novel self-alignment process using the surface tension of the liquid resin for assembly of electronic and optoelectronic devices. Due to their characteristics of low surface tension, however, the parametric design guidelines are necessary for resin self-alignment capability. In this paper, a shape prediction mathematical model and a numerical method are developed. The developed system is capable of achieving the liquid joint geometry and the parametric design for self-alignment capability. The influences of geometric parameters such as liquid volume, component weight, pad radius, liquid surface tension on the shape of liquid joint are investigated. Furthermore, the parametric design guidelines considered the process-related practical matters of misalignment level, distribution of the supplied liquid volumes and coplanarity deviation includes difference of the height between the pads are provided.

Embedded processors are used in numerous devices executing dedicated applications. This setting makes it worthwhile to optimize the processor to the application it executes, in order to increase its power-efficiency. This paper proposes to enhance direct mapped data caches with automatically tuned randomized set index functions to achieve that goal. We show how randomization functions can be automatically generated and compare them to traditional set-associative caches in terms of performance and energy consumption. A 16 kB randomized direct mapped cache consumes 22% less energy than a 2-way set-associative cache, while it is less than 3% slower. When the randomization function is made configurable (i.e., it can be adapted to the program), the additional reduction of conflicts outweighs the added complexity of the hardware, provided there is a sufficient amount of conflict misses.

This study investigate the rectangular microstrip patch antenna on anisotropy substrates with superstrate and air gap, based on rigorous full-wave analysis and Galerkin's moment method. Results show that radiation patterns with varying air gap, permittivity of the superstrate and substrate, and thickness of the superstrate can be determined and analyzed.

In this paper, we proposed the doubly tapered electromagnetic periodic structure (DT-EPS) bandstop filters in coplanar waveguide (CPW) and cylindrical coplanar waveguide (CCPW). The DT-EPS bandstop filter not only can effectively improve the stopband rejection but also increase its bandwidth. In addition, this technique can significantly reduce the passband ripples compared with conventional case.