Improvement of SiGe oxide grown by electron cyclotron resonance using H2O vapor annealing

The influence of low-temperature annealing in H2O vapor on electron-cyclotron-resonance (ECR) grown SiGe oxides is reported. Annealing the oxides in H2O vapor at 280°C for 3 h 20 min, applied after annealing in forming gas at 450°C for 30 min, has several important effects: It reduces oxide leakage current by up to four orders of magnitude, decreases the density of interface states, and results in a low fixed oxide charge density of - 5.0× 1010 cm-2 in comparison to those of the films subjected to annealing in forming gas only. In addition, higher cumulative dielectric breakdown fields up to 8 MV/cm have been achieved. From the results obtained it is evident that vapor annealing is beneficial for ECR-grown SiGe oxides. © 1996 American Institute of Physics.published_or_final_versio

Integration of GaInP/GaAs heterojunction bipolar transistors and high electron mobility transistors

Integration of carbon-doped GaInP/GaAs heterojunction bipolar transistors (HBT's) and high electron mobility transistors (HEMT's) is demonstrated by growing an HBT on the top of a HEMT. A current gain of 60. a cutoff frequency of 59 GHz and a maximum oscillation frequency of 68 GHz were obtained for a 5 × 15 μm 2 self-aligned HBT. The HEMT with a gate length of 1.5 μm has a transconductance of 210 mS/mm, a cutoff frequency of 9 GHz and a maximum oscillation frequency of 22 GHz. It is shown that the GaInP/GaAs HBT on the HEMT is the simple Bi-FET tecnology suitable for microwave and mixed single applications.published_or_final_versio

Thermal effect on current gains of an AlGaAs/GaAs heterostructure-emitter bipolar transistor

The temperature dependence of current gain was investigated for AlGaAs/GaAs heterostructure-emitter bipolar transistors (HEBT). The current gain of the HEBT was found much less sensitive to temperature variation than that of a heterojunction bipolar transistor. In particular, the HEBT current gain was more or less constant with increasing temperature at the high current regime, indicating great potentials for power applications.published_or_final_versio

Finite element analysis of second order wave resonance by multiple cylinders in a uniform current

The purpose of this paper is to study the diffraction of second order Stokes waves by four cylinders in a uniform current and mainly focus on the near-trapping phenomenon. A time domain second-order theory is employed to establish the mathematical Smodel by splitting the total potential into the disturbed velocity potential caused by current, the first- or linear and second-order potentials, which satisfy their own boundary conditions. Each potential is calculated through the finite element method (FEM). Numerical results for four bottom-mounted cylinders in a uniform current are provided to show the resonant behaviour of waves and hydrodynamic forces including linear and second order at near-trapped frequencies, and the current effect on the wave and force are also analysed and discussed. Some results for a single- and four-cylinder cases are compared with previous studies

CCl4-doped semi-insulating InP as a buffer layer in GaInAs/InP high electron mobility transistors

The application of CCl4-doped semi-insulating InP as a buffer layer in a pseudomorphic Ga0.2In0.8P/Ga0.47In0.53As/InP high electron mobility transistor (HEMT) grown by metalorganic chemical vapor deposition is reported. This Al-free InP-base HEMT with a gate length of 1.3 μm has extrinsic transconductances of 420 and 610 mS/mm at 300 and 77 K, respectively. A cutoff frequency of 15 GHz and a maximum oscillation frequency of 40 GHz are obtained. The results demonstrate the CCl4-doped semi-insulating InP is a promising buffer layer for InP-based HEMT. © 1996 American Institute of Physics.published_or_final_versio

A high-frequency GaInP/GaAs heterojunction bipolar transistor with reduced base-collector capacitance using a selective buried sub-collector

A C-doped GaInP/GaAs HBT using a selective buried sub-cellular has been fabricated by two growth steps. The device was fabricated with minimum overlap of the extrinsic base reduced to about half of that of an HBT without selective buried sub-collector while the base resistance remains unchanged. A current gain of 35, f T of 50 GHz and f max of 140 GHz are obtained with this technology.published_or_final_versio

Three-dimensional interaction between uniform current and a submerged horizontal cylinder in an ice-covered channel

The problem of interaction of a uniform current with a submerged horizontal circular cylinder in an ice-covered channel is considered. The fluid flow is described by linearized velocity potential theory and the ice sheet is treated as a thin elastic plate. The potential due to a source or the Green function satisfying all boundary conditions apart from that on the body surface is first derived. This can be used to derive the boundary integral equation for a body of arbitrary shape. It can also be used to obtain the solution due to multipoles by differentiating the Green function with its position directly. For a transverse circular cylinder, through distributing multipoles along its centre line, the velocity potential can be written in an infinite series with unknown coefficients, which can be determined from the impermeable condition on a body surface. A major feature here is that different from the free surface problem, or a channel without the ice sheet cover, this problem is fully three-dimensional because of the constraints along the intersection of the ice sheet with the channel wall. It has been also confirmed that there is an infinite number of critical speeds. Whenever the current speed passes a critical value, the force on the body and wave pattern change rapidly, and two more wave components are generated at the far-field. Extensive results are provided for hydroelastic waves and hydrodynamic forces when the ice sheet is under different edge conditions, and the insight of their physical features is discussed

Hydroelastic wave diffraction by a vertical circular cylinder standing in a channel with an ice cover

The problem of hydroelastic wave diffraction by a surface-piercing vertical circular cylinder mounted on the bottom of an ice-covered channel is considered. The ice sheet is modelled as an elastic thin plate with homogeneous properties, while the linearized velocity potential theory is adopted to describe the motion of the fluid. The solution starts from the Green function satisfying all other boundary conditions apart from that on the body surface. This is obtained through applying a Fourier transform in the longitudinal direction of the channel and adopting an eigenfunction expansion in the vertical direction. The boundary conditions on the side walls and ice edges are imposed through an orthogonal product. Through the Green function, the velocity potential due to a surface-piercing structure with arbitrary shape can be expressed through a source distribution formula derived in this work, in which only integrals over the body surface and its interaction line with the ice sheet need to be retained. For a vertical circular cylinder, the unknown source distribution can be expanded further into a Fourier series in the circumferential direction, and then the analytical solution of the velocity potential can be obtained further. Extensive results and discussions are provided for the hydrodynamic forces and vertical shear forces on the cylinder, as well as the deflection and strain of the ice sheet. In particular, the behaviour of the solution near one of the natural frequencies of the channel is investigated in detail

Fabrication and characteristics of a GaInP/GaAs heterojunction bipolar transistor using a selective buried sub-collector

A C-doped GaInP/GaAs heterojunction bipolar transistor (HBT) with a selective buried sub-collector has been fabricated by two growth steps. The active HBT region was made on the selective buried sub-collector layer with minimum overlap of the extrinsic base and the sub-collector region resulting in substantial reduction of the base-collector capacitance. The experiment shows that the base-collector capacitance is reduced to about half of that of a conventional HBT while the base resistance remains unchanged resulting in a 40-50% increase in the maximum oscillation frequency. Both DC and RF characteristics are investigated and compared with a conventional HBT. A current gain of 40 cutoff frequency of 50 GHz and maximum oscillation frequency of 140 GHz were obtained for the GaInP/GaAs HBT. It is demonstrated that the selective buried sub-collector provides an effective means for enhancing RF performance of an HBT. © 1997 IEEE.published_or_final_versio

Temperature dependence of current gain of GalnP/GaAs heteroj unction and heterostructure-emitter bipolar transistors

The temperature effect on current gain is presented for GalnP/GaAs heterojunction and heterostructure-emitter bipolar transistors (HBT's and HEBT's). Experimental results showed that the current gain of the HEBT increases with the increase of temperature in the temperature range of 25-125 °C and decreases slightly at temperatures above 150 °C. The smaller the collector current, the larger is the positive differential temperature coefficient. At high current levels, the current gain dependence on temperature is significantly reduced. On the other hand, a large negative coefficient is observed in the HBT in all current range. This finding indicates that the HEBT is a better candidate than the HBT for power devices. © 1999 IEEE Publisher Item Identifier S 0018-9383(99)00257-9.published_or_final_versio