Step Doping Research Articles

Modeling and Design Considerations of HgCdTe Infrared Photodiodes under Nonequilibrium Operation

The general approach and effects of nonequilibrium operation of Auger suppressed HgCdTe infrared detectors are well understood. However, the complex relationships of carrier generation and dependencies on nonuniform carrier profiles in the device prevent the development of simplistic analytical device models with acceptable accuracy. In this work, finite element methods are used to accurately model the devices, including self-consistent, steady-state solutions of Poisson’s equation and the carrier continuity equations for carrier densities, Boltzmann transport theory, and published models for recombination/generation processes in HgCdTe. Numerical simulations are used to optimize the material structure and doping levels for an Auger suppressed detector with λ c = 5.5 μm at 200 K. The optimized detector structure with step doping and compositional profiles is then compared to a device with realistic gradient doping and compositional profiles.

Modeling and design of the high performance step SOI-LIGBT power devices by partition mid-point method

In this paper, a partition method is proposed to study the high voltage devices with the step doping profile for the first time. It has been proposed that its breakdown voltage can be approached to that of the linearly graded devices with similar forward voltage drop ( V ce). In addition, by this method, the breakdown voltage can be deduced and its corresponding issue location is also fingered out in the step drift region. Furthermore, in order to reduce the undesirable additional masks, the degraded factor ( D) is developed to obtain better performance with the least number of frames. Eventually, a 660 V step analytical results are compared with a 606.6 V MEDICI simulation and this shows that the partition method is very effective.

Initial Coarsening and Microstructural Evolution of Fast‐Fired and MgO‐Doped Al2O3

The effect of an initial coarsening step (50‐200 h at 800°C) on the subsequent densification and microstructural evolution of high–quality compacts of undoped and MgO–doped Al2O3 has been investigated during fast–firing (5 min at 1750°C) and during constant–heating–rate sintering (4°C/min to 1450°C). In constant–heating–rate sintering of both the undoped and MgO–doped Al2O3, a refinement of the microstructure has been achieved for the compact subjected to the coarsening step. A combination of the coarsening step and MgO doping produces the most significant refinement of the microstructure. In fast–firing of the MgO–doped Al2O3, the coarsening step produces a measurable increase in the density and a small refinement of the grain size, when compared with similar compacts fast–fired conventionally (i.e., without the coarsening step). This result indicates that the accepted view of the deleterious role of coarsening in the sintering of real powder compacts must be reexamined. Although extensive coarsening after the onset of densification must be reduced for the achievement of high density, limited coarsening prior to densification is beneficial for subsequent sintering.

PHYSICAL MODELING OF POWER SEMICONDUCTORS FOR THE CAE-DESIGN OF POWER ELECTRONIC CIRCUITS

CAE-tools can help to develop any traditional or novel power conversion topology more efficiently, by providing both the possibilities of investigation without the risk of destruction and of access to each signal in the circuit. However, a prerequisite are trustworthy simulation results both qualitatively for operation observation and quantitatively for power dissipation examination as well as for SOA control. This implies that precise power semiconductor models have to be used. In the variety of different possible modeling strategies there is only the strictly physical way which offers topology independent accurate results. In this paper a new class of physical high performance and high accuracy circuit models for today's relevant power semiconductors (Power-Diode, GTO, IGBT, Power-MOSFET) is presented. A modular concept, handling typical features of power devices like ν-zones, MOSFET controlling units or diffusion zones as basic structures, is used which allows a considerable flexibility to model future devices time efficiently. The core of this modular concept, constituted by a module of the ν-zone, employs a universal and powerful solution technique of the ambipolar diffusion equation. This technique is the only possibility for circuit models to consider physically semiconductor technology measures for improving device characteristics, such as particle irradiation for lifetime reduction, step doping of substrate or epitaxial layers as well as double diffused layers.

Computation of current and transconductance of a nonuniformly doped channel MOSFET with an arbitrary doping profile

For MOSFETs with a non-uniformly doped channel (NUDC), an efficient modeling method ensuring current continuity in the channel region, has been developed. Using the same set of equations, we can generate continuous and differentiable drain current vs gate voltage ( I D vs V G) curves from subthreshold region to linear region. The amount of reverse threshold voltage ( V T) vs gate length ( L) roll-off effect in NUDC devices can be calculated. Special transconductance properties of NUDC MOSFETs are investigated with this method. Bulk bias effects, doping and field dependent mobility are also included in modeling. Use of this method is illustrated for a Gaussian profile and a step doping profile. As a result, I D vs V G nonlinearity, and transconductance g m peaking in the linear region are severe in NUDC MOSFETs, and such effects weaken as the degree of channel doping non-uniformity is reduced. Moreover, positioning of the nonuniform doping along the channel, as represented by the peak position of the Gaussian is found to relate to the degree of I D vs V G nonlinearity. This method is suitable for use in process parameter design, as well as an NUDC device model for SPICE capable of handling an arbitrary channel doping profile.

Channel profile engineering for MOSFET's with 100 nm channel lengths

The effective inversion electron mobility and several short-channel effects are examined for different channel doping profiles in NMOSFETs with L/sub eff/ near 100 nm using device simulators. For given threshold voltage, the effective mobility depends on the doping profile shape when the ionized dopant impurity scattering near the surface is nonnegligible as may be the case with the high doping required for proper scaling to L/sub eff//spl les/100 nm. In this regime, super-steep retrograde profiles result in higher effective mobility values than conventional step doping profiles while allowing deeper drain/source junctions. >

Two step doping channel FET with symmetric normally on and normally off characteristics

An n −- GaAs n +- InGaAs two step doping channel FET prepared by MOCVD has been built for large input signals circuit applications. The thin InGaAs channel was heavily doped to increase current carrier density, resulting in a maximum current density of 930 mA/mm, and to improve the transconductance linearity, giving a very broad gate voltage range from 2.2 to −2.0 V. On the other hand, thick and lightly doped GaAs channel layer works as carrier confinement to reduce the gate leakage current and to enhance the breakdown voltage. A device with 2 × 100 μm 2 has yielded a maximum extrinsic transconductance of 230 mS/mm, a general gate-drain breakdown voltage of > 17 V and a f t = 15 GHz × μm. The performance of this device shows that two step doping channel FETs are very promising for high speed, high power and large input signal analog circuit applications.

Diffusion behaviour of the BF4 ? anion in polyaniline fibrils. Influence of the physical state of polyaniline

The diffusion coefficients (D) of BF4– in polyaniline at various electrode potentials have been estimated by electrochemical potential-step experiments assuming a cylindrical diffusion system. The D values were constant in the electrode potential region from 3.9 to 3.6 V and also from 3.2 to 2.7 V. However, they were much smaller than those obtained in the potential region from 3.9 to 3.6 V. The diffusion coefficients were independent of the direction of the potential step (doping or undoping). The observed current–time transient in the potential region from 3.9 to 3.6 V was in good agreement with the theoretical one, but a deviation was observed for the potential region from 3.6 to 3.2 V. The concentration profiles of three physical states of polyaniline with the electrode potential were obtained from absorbance changes of polyaniline during the doping or undoping processes of BF4–. By comparing these profiles with results obtained from the potential-step experiments, it can be seen that the deviation of the observed current–time transient from the theoretical one in the potential region between 3.2 and 3.6 V is due to a change in the physical state of polyaniline.

High intensity pulsed ion beams in material processing: Equipment and applications

The accelerators capable of producing short-duration high intensity pulsed ion beams (HIPIB) used so far in surface treatment experiments are outlined. The duration of the beams fall in the range from ns to μs and their current densities are in the range between 50–280 A/cm 2. In the remainder of the paper the experiments illustrating the modification of the surface properties of semiconductors, metals and ceramics are reviewed. They show that in semiconductors, HIPIB may be effective in annealing of ion implantation damage, in formation of p-n junctions in a single step doping process, in alloying the predeposited dopant, and in silicides formation. In metals, properly chosen HIPIB may induce the effects leading to an increase of their microhardness, abrasive wear resistance and corrosion resistance. Also mixing of various kind of coatings with metallic substrates is feasible. In ceramics, HIPIB can be used in polishing their surface by surface melt. It is also demonstrated that with HIPIB technique, the single step process of deposition of well adhesing metallic coatings on metallic and ceramic substrates can be accomplished.

Step doping in hydrogenated amorphous silicon thin-film transistors for threshold voltage shifts

We have developed a way to control the threshold voltage (VT ) in hydrogenated amorphous silicon thin-film transistors (a-Si:H TFTs) by boron doping. The field-effect mobility of uniformly boron-doped TFTs decreases rapidly with increased doping ratios. To keep the field-effect mobility from decreasing, we developed step-doped TFTs (SiN/undoped a-Si:H/boron-doped a-Si:H). With this structure, the decrease in the field-effect mobility by boron doping was lessened. The transfer characteristics calculated using a one-dimensional model were in good agreement with measurements below a doping ratio of 80 ppm. The difference between measurements and calculations for higher doping ratio was decreased using a new step-doped structure with the boron-doped layer under n+a-Si:H removed.

Analytical modelling of depletion-mode MOSFET with short- and narrow-channel effects

As we move into the VLSI era, many investigations have been performed on enhancement-mode MOS transistors, and the results have often been used for the depletion-mode device. In order to evaluate the differences from the usual enhancement-mode device, and to understand its own behaviour, we have first made an accurate modelling of a large and wide buried-channel device, assuming a step doping profile. Then, an attempt was made to model the narrow- and short-channel effects, based on regional approaches. The model relies on the assumption that the narrow-channel effect is due to the increase in bulk charge due to the parasitic p+-n+ (field implant-buried layer) diode. For the short-channel effect, our investigations led us to assume that the effective implanted dose is increased by the diffusion of majority carriers from source and drain, which charge is shared between source, drain, bulk and gate. The excess of positive charge controlled by the gate (instead of the lack of negative charge that characterises the short-channel effect of an enhancement-mode MOSFET) can be evaluated with a geometrical approach, by making a double trapezoidal partioning. The surface and buried-channel conductions, as well as the non-pinch-off current are then taken into account to establish the current equations: IDtot = IDsurf + IDB.C + IDn.pinch-off. where IDsurf or IDB.C = f{VDS, VGS, VBS VT (L, W, VBS, VDS)}. The three kinds of current can exist separately or together, thus defining different equations for the total current flowing from source to drain. Comparison with experiments shows a good agreement, and, furthermore, the extracted parameters are very well related to technological parameters. Short and narrow channel transistors, down to micron dimensions, are fairly well described by the model, and one single set of parameters. In conclusion, the depletion-mode transistor appears to be more sensitive to geometry than the enhancement-mode device because of its special structure, and so we need a peculiar model and parameters for this device to get an efficient simulation of circuits fabricated in HMOS technology, where depletion-mode transistors are extensively used as active loads.