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We investigate the impact of interface traps and bulk traps on the performance of n++GaN/InAlN/AlN/GaN high electron mobility transistors (HEMTs) using two-dimensional Sentaurus TCAD simulation. The device uses lattice-matched wide bandgap In0.17Al0.83N as a thin barrier layer. The simulations are performed using the thermodynamic transport model. Interface and bulk traps are accounted for in our simulations. The results indicate a significant influence of both acceptor and donor traps on device operation, as long as the traps are considered in the barrier layer. On the other hand, simulations with donor traps specified at the In0.17Al0.83N/n++GaN cap interface show no influence on the transfer characteristic.

Solar cells made of single-crystalline silicon, as alternative energy sources, became the most widely used solar cells in recent years. The mainstream manufacturing approach is to process the cells and assemble these into photovoltaic (PV) modules. However, the direct conversion of solar energy into electricity using the PV effect suffers from low efficiency. Thus, increasing the conversion efficiency at low production costs becomes the main goal of solar cell manufacturers. One way to increase the efficiency of a solar cell is to use an ultra-wide layer of intrinsic semiconductor as the depletion region of a PN junction. In our work, we present a novel geometrical concept of PIN structure for PV applications. The width of the intrinsic layer in our construction is 5-20 mm. Moreover, in our novel structure, the light irradiation acts directly on the active region of the PV cell, which enables bi-facial irradiation and results in ∼28 % conversion efficiency. A low cost fabrication is ensured in our design due to a new manufacturing technology by eliminating some expensive processes, such as photolithography. The feasibility proof of the novel concept in mono-crystalline silicon solar cells is presented. We demonstrate simulation results and preliminary experimental results confirming our approach.

Hot-electron temperature (T-e) in InAlN/GaN high-electron-mobility transistors (HEMTs) was determined using electroluminescence spectroscopy as a function of gate voltage and correlated with the Te distribution determined by hydrodynamic simulations. Good agreement between measurement and simulations suggests that hot electrons can locally reach temperatures of up to 30 000 K at V-ds = 30 V, i.e., two to three times higher than that typically obtained for similar AlGaN/GaN HEMTs. The consequence of such high Te in InAlN/GaN HEMTs is illustrated by electrical stressing in OFF and semi-ON state at V-gd = 100 V. Prominent channel degradation was observed for devices stressed in semi-ON state, suggesting hot-electron driven degradation. Threshold voltage and drain current transient analyses indicate that hot electrons increase the density of traps in the GaN channel underneath the gate as well as surface/interface traps located in the gate-to-drain access region.

We study the concept of double-heterostructure quantum well (DHQW) InAlN/GaN/AlGaN high electron mobility transistor (HEMT) for higher device robustness and less degradation. Physics-based device simulation proves that the back barrier blocks the carrier injection into the device buffer. However, the energy of the injected electrons in the buffer is higher for any quantum well design in InAlN /GaN than in AlGaN/GaN HEMTs. This energy may be sufficient for releasing hydrogen from GaN point defects.

A thorough approach to the investigation of GaN-based high-electron mobility transistors by device simulation is demonstrated. Due to structure and material peculiarities, new comprehensive hydrodynamic models for the electron mobility are developed and calibrated. Relying on this setup, three different independent device technologies are simulated and compared. We further study the pronounced decrease in the transconductance g m at higher gate bias. We show that the electric field distribution and the resulting carrier velocity quasi-saturation are the main source for the transconductance collapse.

a b s t r a c t The non-linear interaction of space charge waves including the amplification in microwave and millimeter wave range in n-InP films, possessing the negative differential conductance phenomenon, is investigated theoretically. Both the amplified signal and the generation of harmonics of the input signal are demon- strated, which are due to non-linear effect of the negative differential resistance. It is possible to observe an amplification of the space charge waves in n-InP films of submicron thicknesses at essentially higher frequencies f

SUMMARY This work addresses the enormous efficiency and linearity potential of optimized AlGaN/GaN high-electron mobility transistors (HEMT) in conventional Doherty linear base-station amplifiers at 2.7 GHz. Supported by physical device simulation, the work further elaborates on the use of AlGaN/GaN HEMTs in high-speed current-switch-mode classD (CMCD)/class-S MMICs for data rates of up to 8 Gbit/s equivalent to 2 GHz RF-operation. The device needs for switch-mode operation are derived and verified by MMIC results in class-S and class-D operation. To the authors’ knowledge, this is the first time 2 GHz-equivalent digital-switchmode RF-operation is demonstrated with GaN HEMTs with high efficiency.

AlGaN/GaN high electron mobility transistors (HEMTs) are favored for the use in high-power and high-frequency applications. Normally-off operation has been desired for various applications, but proved to be difficult to achieve. Recently, a new approach was proposed by Mizutani et al. [Mizutani T, Ito M, Kishimoto S, Nakamura F. AlGaN/GaN HEMTs with thin InGaN cap layer for normally-off operation. IEEE Elec Dev Lett 2007;28(7):549–51]: a thin InGaN cap layer introduces a polarization field, which raises the conduction band of the AlGaN/GaN interface. As a result, the threshold voltage is shifted in positive direction. Relying on the experimental work of Mizutani et al. we conduct a simulation study of the proposed devices. Our device simulation tool is expanded by material models for InN and InGaN and also an improved high-field mobility model accounting for the specifics of the III-N materials. Using this setup, we further explore the device specific effects and conduct an analysis of the AC characteristics.

Two quantum-kinetic models, governing the transport of an initial highly non-equilibrium carrier distribution generated locally in a nanowire, are explored. Dissipation processes due to phonons govern the carrier relaxation, which at early stages of the evolution is characterized by the lack of energy conservation in the collisions. The models are analyzed and approached numerically by a backward Monte Carlo method. The basic difference between them is in the way of treatment of the finite collision duration time. The latter introduces quantum effects of broadening and retardation, ultrafast spatial transfer and modification of the classical trajectories, which are demonstrated in the presented simulation results.

We present a technology for thermoelectric generators using large area pn-junctions. Thermally generated carriers are separated by the gradient of the built-in potential caused by the pn-junction. The use of these structures for waste heat recovery implies an externally applied temperature gradient in-plane with the pn-junction which causes a current of both electrons and holes from the heated to the cooled side, where electrical contacts are mounted. The device behavior is strongly influenced by the magnitude and the spatial distribution of the generation rate as well as the local transport properties. We present the influence of the alloy composition on the material properties and possibilities to increase the power output by modification of the local material composition. Furthermore, the influence of intentionally implanted gold atoms as additional generation centers is assessed. Effective optimization of thermoelectric generators requires a powerful simulation environment due to the strong correlation of different mechanisms within the device. We present simulation results obtained by the device and circuit simulator Minimos-NT working in conjunction with the optimization framework Siesta.

Strained-Si material has emerged as a strong contender for developing transistors for next-generation electronics, because this material system offers superior transport properties. We suggest a model describing the low-field bulk mobility tensor for electrons in strained-Si layers as a function of strain. Our analytical model includes the effect of strain-induced splitting of the conduction band valleys in Si, intervalley scattering, and doping dependence. Intervalley scattering has been modeled on the equilibrium electron distribution and the valley splitting for a given strain tensor. The effect of different substrate orientations is considered by performing coordinate transformations for the strain tensor and effective masses. Monte Carlo simulations accounting for various scattering mechanisms and the splitting of the anisotropic conduction band valleys due to strain in combination with an accurate ionized impurity scattering model were carried out to verify the results for the complete range of Ge contents and for a general orientation of the SiGe buffer layer. Our mobility model is suitable for implementation into a conventional technology CAD simulation tool.

A Schottky-barrier normally off InAlN-based high-electron-mobility transistor (HEMT) with selectively etched access regions, high off-state breakdown, and low gate leakage is presented. Metal-organic chemical vapor deposition-grown 1-nm InAlN/1-nm AlN barrier stack is capped with a 2-nm-thick undoped GaN creating a negative polarization charge at a GaN/InAlN heterojunction. Consequently, the gate effective barrier height is increased, and the gate leakage as well as the equilibrium carrier concentration in the channel is decreased. After removal of the GaN cap at access regions by using a highly selective dry process, the extrinsic channel becomes populated by carriers. Normally off HEMTs with 8-μm source-to-drain distance and 1.8-μm -long symmetrically placed gate showed a source drain current of about 140 mA/mm. The HEMT gate leakage at a drain voltage of 200 V and grounded gate is below 10-7 A/mm with a three-terminal device breakdown of 255 V. The passivated InAlN surface potential has been calculated to be 1.45 V; significant drain current increase is predicted for even lower potential.

We present a direct approach to obtain scattering parameters (S-parameters) and other derived figures of merit of SiGe-HBTs by means of small-signal (ac) analysis. Therefore, an additional simulation mode has been implemented in the three-dimensional device simulator MINIMOS-NT. Several additional features are provided for efficiently obtaining various small-signal parameters. The accuracy of the results is proven by analytical methods and by comparison with measurements.

We present results of fully two-dimensional numerical simulations of silicon–germanium (SiGe) heterojunction bipolar transistors (HBTs) in comparison with experimental data. Among the critical modeling issues discussed in the paper, special attention is focused on the description of the anisotropic majority/minority electron mobility in strained SiGe grown in Si.

We present the state-of-the-art in simulation for industrial application of heterostructure devices based on the SiGe/Si material system. The work includes a detailed comparison of device simulators and current transport models to be used, and addresses critical modeling issues. Results from two-dimensional hydrodynamic analyses of SiGe-heterojunction bipolar transistors (HBTs) with MINIMOS-NT are presented in good agreement with measured data. The examples are chosen to demonstrate technologically important issues which can be addressed and solved by device simulation.

The quality of Si3N4 thin film passivation is of importance for the reliability of III-V based Heterojunction Bipolar Transistors (HBTs). Both theoretical and experimental studies have been conducted in order to minimize base leakage currents as a major source of degradation. In the present work we investigate the effectiveness of the passivation of devices before and after electrothermal stress aging by the means of two-dimensional numerical simulations. For that purpose proper electrical and thermal models were implemented in our simulator MINIMOS-NT allowing simulation of silicon nitride as a wide bandgap semiconductor material.

Considerable effort was spent on our two-dimensional device simulator MINIMOS-NT to get it ready for simulation of devices with high complexity in respect to materials, geometries, etc. Many of the existing physical models (band gap, mobility, thermal conductivity, energy relaxation times, specific heat, etc.) were refined, some of them were replaced by promising new ones, and many new models were added as well. Being an ancestor of the well-known MOS device simulator MINIMOS [1], its experience with Si devices was inherited. Thereby, MINIMOS-NT became a generic device simulator accounting for a variety of micro-materials, including group IV semiconductors, III-V compound semiconductors and their alloys, and non-ideal dielectrics.

We give an overview of the state-of-the-art of heterostructure RF-device simulation for industrial application based on III-V compound semiconductors. The work includes a detailed comparison of device simulators and current transport models to be used, and addresses critical modeling issues. Results from two-dimensional hydrodynamic simulations of heterojunction bipolar transistors (HBTs) and high electron mobility transistors (HEMTs) with MINIMOS-NT are presented in good agreement with measured data. The simulation examples are chosen to demonstrate technologically important issues which can be addressed and solved by device simulation.

We demonstrate the results of two-dimensional (2-D) hydrodynamic simulations of one-finger power heterojunction bipolar transistors (HBTs) on GaAs. An overview of the physical models used and comparisons with experimental data are given. We present models for the thermal conductivity and the specific heat applicable to all relevant diamond and zinc-blende structure semiconductors. They are expressed as functions of the lattice temperature and in the case of semiconductor alloys, of the material composition.

We present a novel methodology for characterization of sub-quartermicron CMOS technologies. It involves process calibration, device calibration employing two-dimensional device simulation and automated Technology Computer Aided Design (TCAD) optimization and, finally, transient mixed-mode device/circuit simulation. The proposed methodology was tested on 0.25 /spl mu/m technology and applied to 0.13 /spl mu/m technology in order to estimate ring oscillator speed. The simulation results show an excellent agreement with available experimental data.

Precise modeling of the saturation velocity is a key element for device simulation, especially for advanced devices such as e.g. High Electron Mobility Transistors (HEMTs) where the saturation velocity v(sat) is directly related to the available gain of the device. We present a model implementing the temperature dependence of the saturation velocity v(sat) into the two-dimensional device simulator MINIMOS-NT. The new model covers all relevant materials such as the elementary semiconductors Si and Ge, and the binary III-V group semiconductors GaAs, AlAs, InAs, GaP and InP. Furthermore, a composition dependent modeling for alloyed semiconductors such as e.g. Si(1-x)Ge(x) Al(x)Ga(1-x)As or In(x)Ga(1-x)As is included. The implementation reflects a comprehensive literature survey on available experimental data and Monte Carlo (MC) simulation data. The work is completed by new MC simulations, especially for material compositions, where no experimental data are available. The extraction of the saturation velocity reveals a significant difference between the saturation velocity in the bulk and the effective (saturation) velocity extracted from rf-measurements e.g. for High Electron Mobility Transistors. Since this effective value is often used for device characterization, the difference gives insight into modeling the determining quantities of HEMTs.

Band gap narrowing (BGN) is one of the crucial heavy-doping effects to be considered for bipolar devices. Using a physically-based approach (E.F. Schubert, Doping in III-V Semiconductors, Cambridge University Press, 1993), we suggest a new BGN model which considers the semiconductor material and the dopant species for arbitrary finite temperatures. This unified treatment is especially useful for accurate device simulation. A comparison with experimental data and other existing models is presented and study of BGN in III-V group semiconductors is performed. Finally, as a particular example we investigated with our two-dimensional device simulator MINIMOS-NT (Simlinger et al., Simulation of submicron double-heterojunction high electron mobility transistors with MINIMOS-NT, IEEE Trans. Electron. Devices, Vol. 44, 1997, pp. 700‐707), the electrical behavior of a graded composition Si:SiGe HBT using a hydrodynamic transport model. © 1999 Elsevier Science S.A. All rights reserved.

We present an empirical model for the electron energy relaxation time. It is based on Monte-Carlo simulation results and is applicable to all relevant diamond and zinc-blende structure semiconductors. The energy relaxation times are expressed as functions of the carrier and lattice temperatures, and in the case of semiconductor alloys, of the material composition.

Band gap narrowing is one of the crucial heavy-doping effects to be considered for bipolar devices. We present a new band gap narrowing model which considers the semiconductor material and the dopant species for arbitrary finite temperatures. As the minority carrier mobility is of considerable importance for modeling advanced n-p-n bipolar transistors, we implemented the new universal low field mobility model [1] in MINIMOS-NT [2]. This model distinguishes between majority and minority electron mobilities on one hand, and between different dopant species on the other hand, both as a function of temperature and dopant concentration. This unified treatment is especially useful for accurate device simulation. As a particular example we present the results for SiGe HBT.

InAlN/GaN High Electron Mobility Transistors (HEMTs) are very popular because of their promising electrical and thermal properties. With the innovation of these structures and the development of fabrication processes, there are still many serious issues like current collapse or self-heating effects, which must be addressed. In this work, the DC device behavior is studied both experimentally and by means of two-dimensional hydrodynamic device simulations. Very good agreement between measurements and simulations with Minimos-NT is achieved using the hydrodynamic transport model including self-heating and impact ionization effects.

The ongoing interest in the development of GaN-based enhancement-mode high electron mobility transistors (EHEMTs) resulted in several different approaches being proposed, one of them employing a reduction of the gate-to-channel distance. In order to facilitate gate recessing, a technique using a n++ cap layer was suggested by Kuzmik et al. [1], who also analyzed the contribution of the cap layer to current conduction and on the mechanism of the off-state breakdown. In this work we complement the experimental results with two-dimensional device simulation using Minimos-NT [2]. We have employed it previously for the optimization studies of a whole generation of AlGaN/GaN HEMTs [3], but also for high-temperature simulations [4].

The non-linear interaction of space charge waves including the amplification in microwave and millimeter wave range in n-InP films, possessing the negative differential conductance phenomenon, is investigated theoretically. Both the amplified signal and the generation of harmonics of the input signal are demonstrated, which are due to non-linear effect of the negative differential resistance. It is possible to observe an amplification of the space charge waves in n-InP films of submicron thicknesses at essentially higher frequencies ƒ < 70 GHz, when compared with n-GaAs films ƒ < 44 GHz. The increment observed in the gain is due to the larger dynamic range in n-InP than in n-GaAs films.

The nonlinear interaction of space charge waves including the amplification in microwave range at high electric fields (10–300 kV/cm) in n-GaAs films, possessing the negative differential conductance phenomenon, is presented. Both the amplified signal at the first harmonic of the input signal and the generation of second and third harmonics of the input signal, which are due to the negative differential resistance effect at very high electric fields are shown.

Wide bandgap, high saturation velocity, and high thermal stability are some of the properties of GaN, which make it an excellent material for high-power, high-frequency, and high-temperature applications. As several application areas require the devices to operate at elevated temperatures, a proper modeling of the temperature dependences of the band structure and transport parameters is very important. We present two-dimensional hydrodynamic simulations of AlGaN/GaN high electron mobility transistors (HEMTs) at high temperatures. The simulator is calibrated against measurement data of a real device and delivers good predictive results for the DC and RF characteristics of another. The temperature dependence of the maximum current and cut-off frequency of submicron devices is further studied.

A Monte Carlo (MC) technique is employed to investigate stationary electron transport in lead telluride (PbTe). Results for electron mobility as a function of lattice temperature, free carrier concentration, and electric field are compared with experimental data and the few available other Monte Carlo simulation results.

We use a Monte Carlo (MC) approach to investigate the electron transport in Indium Nitride (InN). Simulations with two different setups (one with a bandgap of 1.89 eV and one with bandgap of 0.69 eV) and accounting for all relevant scattering mechanisms are conducted. Results for electron mobility as a function of free carrier concentration and electric field are compared to previous studies and discussed.

AlGaN/GaN high electron mobility transistors (HEMTs) are favored for the use in high-power and high-frequency applications. However, in order to successfully apply them in circuit design normally-off HEMTs are needed. Conventional normally-off HEMTs are plagued by several production and performance issues. Recently, a new approach was proposed by Mizutani et al.: a thin InGaN cap layer introduces a polarization field, which raises the conduction band of the AlGaN/GaN interface. As a result a threshold voltage shift to the positive direction is observed. Relying on the experimental work of Mizutani et al. we conduct a theoretical study of the proposed devices. We calibrate our simulation tool against the measured DC characteristics. Using this setup, we can further explore the device specific effects and conduct a predictive analysis of the AC characteristics. The presented methodology is a valuable tool for the design and optimization of novel devices.

For the development of next-generation AlGaN/GaN based high electron mobility transistors (HEMTs) in industry, reliable software tools for DC and AC simulation are required. Our device simulator Minimos-NT was calibrated against experimental data for this purpose. Subsequently, AC and DC simulations for both scaled devices from the same generation and new generation HEMTs were performed. A good accuracy for all relevant characteristics in comparison to measurement results is achieved.

A non-parabolic piezoelectric model of electron-phonon interaction in Gallium Nitride is discussed. The Monte Carlo aspects of the model, needed for the simulation tools which provide the characteristics of GaN-based devices are analyzed in details. The piezo-scattering rate is derived by using quantum-mechanical considerations. The angular dependence is avoided by a proper spherical averaging and the non-parabolicity of the bands is accounted for. For the selection of the after-scattering state we deploy the rejection technique. The model is implemented in a simulation software. We employ a calibrated experimentally verified set of input material parameters to obtain valuable data for the transport characteristics of GaN. The simulation results are in good agreement with experimental data available for different physical conditions.

Multiple “collapsing” field domains are a physical reason for superfast switching and sub-terahertz (sub-THz) emission experimentally observed in powerfully avalanching GaAs structures. This phenomenon, however, has been studied so far without considering carrier energy relaxation and that essentially has restricted the possibility of correct interpretation of experimental results. Here, we apply a hydrodynamic approach accounting for non-local hot-carrier effects. The results confirm the collapsing domain concept, but show that the domains cannot reduce well below 100 nm in width, since a moving collapsing domain leaves behind it a tail of hot carriers, which causes broadening in the rear wall of the domain. This puts principal restrictions on the emission band achievable with our unique avalanche mm-wave source to about 1 THz. Another finding suggested here is a physical mechanism for the single collapsing domain's quasi-steady-state motion determined by powerful impact ionization. The results are of si...

An investigation on the field plate technique in AlGaN/GaN power HEMTs is presented. The critical geometrical variables controlling the field distribution in the channel are determined and optimized for improved device reliability using two-dimensional numerical simulations. The results are implemented in the design of devices fabricated with 600 nm down to 150 nm gate lengths. Good agreement between experimental and simulation data is achieved.

We present a stochastic approach for solving the quantum-kinetic equation introduced in Part I. A Monte Carlo method based on backward time evolution of the numerical trajectories is developed. The computational complexity and the stochastic error are investigated numerically. Variance reduction techniques are applied, which demonstrate a clear advantage with respect to the approaches based on symmetry transformation. Parallel implementation is realized on a GRID infrastructure.

The ultrafast evolution of optically excited carriers which propagate in a quantum wire and interact with three dimensional phonons is investigated. The equation, relevant to this physical problem, is derived by a first principle approach. The electron-phonon interaction is described on a quantum-kinetic level by the Levinson equation, but the evolution problem becomes inhomogeneous due to the spatial dependence of the initial condition. The initial carrier distribution is assumed Gaussian both in energy and space coordinates, an electric field can be applied along the wire. A stochastic method, described in Part II of the work, is used for solving the equation. The obtained simulation results characterize the space and energy dependence of the evolution in the zero field case. Quantum effects introduced by the early time electron-phonon interaction are analyzed.

Two quantum-kinetic models of ultrafast electron transport in quantum wires are derived from the generalized electron-phonon Wigner equation. The various assumptions and approximations allowing one to find closed equations for the reduced electron Wigner function are discussed with an emphasis on their physical relevance. The models correspond to the Levinson and Barker-Ferry equations, now generalized to account for a space-dependent evolution. They are applied to study the quantum effects in the dynamics of an initial packet of highly nonequilibrium carriers, locally generated in the wire. The properties of the two model equations are compared and analyzed.

We present a review of industrial heterostructure devices, based on SiGe/Si and III-V compound semiconductors, analyzed by means of numerical simulation. Critical modeling issues are addressed. Results from 2D hydrodynamic analyses of heterojunction bipolar transistors (HBTs) and field-effect transistors (FETs) are presented, and are in good agreement with measured data.

A slipstream design flow from process via device to circuit simulation is proposed. Simulation results of the device simulator Minimos-NT and the circuit simulator Spectre are evaluated. A ring oscillator circuit is used as an example of the coherence between these simulators is demonstrated.

We present the state-of-the-art in simulation for industrial heterostructure devices based on SiGe/Si and III-V compound semiconductors. The work includes a detailed comparison of device simulators and current transport models to be used, and addresses critical modeling issues. Results from two-dimensional hydrodynamic analyses of Heterojunction Bipolar transistors (HBTs) and High Electron Mobility Transistors (HEMTs) with Minimos-NT are presented in good agreement with measured data. The examples are chosen to demonstrate technologically important issues which can be addressed and solved by device simulation.

This chapter addresses the extraction of RF quantities such as Y- and related parameters, derived quantities such as stability factors and cut-off frequencies, and, last but not least, small-signal equivalent circuit elements for various topologies. It further provides a view of the physical understanding of the bias dependence of small-signal equivalent circuit elements in HEMTs and HBTs in analytcial models and TCAD approaches.