Incomplete Ionization Research Articles

Theoretical investigation of incomplete ionization of dopants effect on p+nn-n+ 4H-SiC IMPATT diode

The effect of incomplete ionization of dopants on p+nn-n+ 4H silicon carbide (4H-SiC) impact-ionization-avalanche-transit-time (IMPATT) diodes has been investigated. Breakdown voltage, avalanche region width, DC to RF conversion efficiency and RF output power of the 4H-SiC IMPATT device with incomplete and complete ionization are given at different temperatures. Theoretical analysis reveals that the influence of the incomplete ionization of dopants on the performance of the p+nn-n+ 4H-SiC IMPATT devices cannot be ignored.

Modeling and Analysis of Normally-OFF p-GaN Gate AlGaN/GaN HEMT as an ON-Chip Capacitor

An accurate physics-based analytical model for the gate capacitance of p-GaN gate AlGaN/GaN high electron mobility transistor (HEMT) is presented. The Poisson’s equation is formulated considering the incomplete ionization of acceptors in the p-GaN cap layer and the out-diffusion of Mg acceptors into the AlGaN barrier layer, which is solved in conjunction with the charge equation in the AlGaN/GaN quantum well. The model is validated across a wide bias range and shows a good agreement with the experimental results. The effect of individual device parameters on the capacitance–voltage ( ${C}$ – ${V}$ ) characteristics is also analyzed using this model. A simplified equivalent circuit model is also presented to intuitively explain the ${C}$ – ${V}$ characteristics of these normally- OFF devices.

Structure and energetics of microscopically inhomogeneous nanoplasmas in exploding clusters

Abstract We present a theoretical-computational study of the formation, structure, composition, energetics, dynamics and expansion of nanoplasmas consisting of high-energy matter on the nanoscale of ions and electrons. Molecular dynamics simulations explored the structure and energetics of hydrogen and neon persistent nanoplasmas formed under the condition of incomplete outer ionization by the laser field. We observed a marked microscopic inhomogeneity of the structure and the charge distribution of exploding nanoplasmas on the nanoscale. This is characterized by a nearly neutral, uniform, interior domain observed for the first time, and a highly positively charged, exterior domain, with these two domains being separated by a transition domain. We established the universality of the general features of the shape of the charge distribution, as well as of the energetics and dynamics of individual ions in expanding persistent nanoplasmas containing different positive ions. The inhomogeneous three-domain shell structure of exploding nanoplasmas exerts major effects on the local ion energies, which are larger by one order of magnitude in the exterior, electron-depleted domain than in the interior, electron-rich domain, with the major contribution to the ion energies originating from electrostatic interactions. The radial structural inhomogeneity of exploding nanoplasmas bears analogy to the inhomogeneous transport regime in expanded and supercritical metals undergoing metal-nonmetal transition.

Modelling the static on-state current voltage characteristics for a 10 kV 4H–SiC PiN diode

A 10 kV 4H–SiC epitaxial PiN diode is fabricated and the measured static on-state current voltage characteristics are used to tune the physical models and parameters included in TCAD device simulations. From the measurements it is found that the on-state voltage drop decreases more than 0.5 V at a current density of 100 A/cm2, as the temperature is raised from room temperature to 300 °C. The steep slope of the IV-curve is, furthermore, maintained at elevated temperatures in contrast to most silicon PiN structures, where the decrease in mobility at higher temperatures typically decreases the IV slope, resulting in an increased voltage drop. Physical device simulations, involving common models for bandgap, incomplete ionization, charge carrier lifetime and mobility, are systematically compared and optimized to obtain the best fit with measured data. The negative temperature dependence can be simulated with good precision although the fitting is very sensitive to the choice of mobility models and, in particular, the acceptor ionization energy.

Advanced TCAD Simulation and Calibration of Gallium Oxide Vertical Transistor

In this paper, advanced β-Ga2O3 TCAD simulation parameters and methodologies are presented by calibrating simulation setup to vertical junctionless multi-gate transistor experimental data. Through careful calibration, several important β-Ga2O3 device physics are identified. The effects of compensation doping and incomplete ionization of dopants are investigated. Electron Philips unified carrier mobility (PhuMob) model, which can capture the temperature effect, is used. We also show that interfacial traps possibly play no role on the non-ideal sub-threshold slope (SS) and short channel effect is the major cause of SS degradation. The breakdown mechanism of the junctionless Ga2O3 transistor is also discussed and is shown to be limited by channel punch-through in off-state. The calibrated models match experimental Capacitance-Voltage (CV) and Current-Voltage (IV) well and can be used to predict the electrical performance of novel β-Ga2O3 devices.

Peculiarities of admittance spectroscopy study of wide bandgap semiconductors on the example of diamond

To improve the performance characteristics of power and high-frequency electronics, wide bandgap semiconductors are now widely used. This paper presents consideration of features arising during exploration of electronic characteristics of wide bandgap materials. We use the admittance spectroscopy method for analyzing free carrier concentration and boron-impurity activation energy in semiconductor diamond. The special aspect that should be taken into account while studying wide bandgap materials is incomplete ionization of impurity. In this work we adjust the experimental conditions, basing on the previous experience, in particular reduce signal/noise ratio and reckon with heat capacity of the samples and substrate. As a result we obtained high quality conductance spectra and activation energy of boron impurity in low-doped diamond.

On the threshold voltage of normally-OFF AlGaN/GaN heterostructure field effect transistors (HFETs) with p-(Al)GaN gate

A physics-based analytical model has been developed to correctly estimate the threshold voltage of normally-OFF AlGaN/GaN heterostructure field effect transistors (HFETs) with p-(Al)GaN gate. This analysis considers the effect of all polarization charges at different interfaces/surface, the layer structure, doping concentration of deep acceptors in p-(Al)GaN cap layer, incomplete ionization of deep Mg acceptors, out-diffusion of Mg to AlGaN barrier layer as well as the effect of compensated buffer/back barrier. Threshold voltage extracted from this analytical model is rigorously validated with experimental results. This analysis also provides a physical insight of charge distribution, gate voltage division in the heterostructure and the effect of device parameters on the threshold voltage. Besides, this model can also be extended to estimate the threshold voltage of normally-OFF MIS-HFETs with p-GaN gate.

Incomplete ionization in aluminum-doped 4H-silicon carbide

In this work, we investigate the degree of incomplete ionization of Al doped 4H-SiC. In particular, we perform analysis on a comprehensive list of published measurements of ionization energy, resistivity, and Hall mobility for varying Al concentration. These data are used to construct two separate models with which we calculate the fraction of mobile holes to dopant atoms p/NA. First, we create a physics-based theoretical model which includes the effects of doping-dependent ionization energy, quantum-mechanical spreading of the acceptor density of states, and density of states smearing due to disorder effects. Our second model is derived mainly from experimental Hall and resistivity data, and we use the results of this calculation to verify our results from the theoretical model. We find good agreement between the two approaches which gives confidence to our resulting p/NA calculations. At doping above 1020cm−3, we observe an increase in the p/NA ratio which is likely due to the onset of a parallel impurity conduction mechanism which does not require dopant ionization. We also provide an easily evaluated expression which predicts p/NA at higher temperatures based on our full theoretical model.

Design of Diamond Power Devices: Application to Schottky Barrier Diodes

Owing to its outstanding electro-thermal properties, such as the highest thermal conductivity (22 W/(cm∙K) at room temperature), high hole mobility (2000 cm2/(V∙s)), high critical electric field (10 MV/cm) and large band gap (5.5 eV), diamond represents the ultimate semiconductor for high power and high temperature power applications. Diamond Schottky barrier diodes are good candidates for short-term implementation in power converters due to their relative maturity. Nonetheless, diamond as a semiconductor for power devices leads to specificities such as incomplete dopant ionization at room temperature and above, and the limited availability of implantation techniques. This article presents such specificities and their impacts on the optimal design of diamond Schottky barrier diodes. First, the tradeoff between ON-state and OFF-state is discussed based on 1D analytical models. Then, 2D numerical studies show the optimal design of floating metal rings to improve the effective breakdown voltage. Both analyses show that the doping of the drift region must be reduced to reduce leakage currents and to increase edge termination efficiency, leading to better figures of merit. The obtained improvements in breakdown voltage are compared with fabrication challenges and the impacts on forward voltage drop.

Mg-Doping of (111)B GaAs Thin Films Grown by Molecular Beam Epitaxy

In this work, the influence of the growth conditions in the incorporation of Mg p-type dopant atoms in epitaxial GaAs(100) and (111)B thin films was investigated. Hall effect measurements and photoluminescence spectroscopy were used to investigate the electrical and optical properties of the films, respectively. The doping level varied between 1016 and 1019 cm–3 and increased with the inverse of the growth temperature and with the temperature of the Mg evaporation cell, with similar behavior in both crystal orientations. The analysis of the Mg incorporation at several growth temperatures and Mg arrival rates established a value of Ed(111)B = 1.6 ± 0.1 eV for the thermal desorption activation energy of Mg in the GaAs(111)B, a value 33% higher than for the (100) case. However, when a more realistic incomplete ionization model for the acceptors is considered, the value of the thermal activation energy for desorption of Mg adatoms increases to 2.7 ± 0.8 eV and equals the value for the (100) surface. Two very ...

Operation of silicon-germanium heterojunction bipolar transistors with different structures at deep cryogenic temperature

In this work, the device performances of discrete and integrated SiGe heterojunction bipolar transistors (HBTs) with different device structures from 300 to 4.8 K were investigated. The turn-on voltages of base-emitter and base-collector junctions increased non-linearly with temperature cooled to 4.8 K. Energy bandgap engineering was taken into account for the analytical model of the turn-on voltage versus temperature. Incomplete ionization occurred in the base-collector junction because of the low doping concentration. The trap-assisted tunneling current in the forward base current was clearly observed below 20 K. The ideality factor and saturation current were shown to be temperature dependence. The ideality factor was much larger than 2 below 40 K, indicating that the current is not only contributed by drift, diffusion and recombination, but also by tunneling. The peak current gain of the discrete SiGe HBTs achieved the maximum value of 3,388 at 80 K, while that of the integrated was 546 at 140 K. The transconductance in logarithm was linearly dependent on reciprocal temperature above 50 K, but flattened below 50 K. Early effect was evidently observed below 77 K in the fixed base current output characteristics of the discrete SiGe HBTs, and it was not obvious for the integrated SiGe HBTs.

Simulation of Transient Processes in 4H-SiC Based Semiconductor Devices (Taking into Account the Incomplete Ionization of Dopants in the ATLAS Module of the SILVACO TCAD Software Package)

Transient process in a resistor–capacitor (RC) circuit with a reverse-biased 4H-SiC p–n diode as the capacitive element is simulated. Simulation is performed with the ATLAS software module from the SILVACO TCAD system for technology computer-aided design (TCAD). An alternative way, to that in ATLAS, to set the parameters of doping impurities partly ionized in 4H-SiC at room temperature is suggested. (The INCOMPLETE physical model available in the ATLAS module, which describes the incomplete ionization of doping impurities in semiconductors, is unsuitable for simulating the dynamic characteristics of devices.) The simulation results are discussed in relation to previously obtained experimental results.

Моделирование переходных процессов в полупроводниковых приборах на основе 4H-SiC (учет неполной ионизации легирующих примесей в модуле ATLAS программного пакета SILVACO TCAD)

AbstractTransient process in a resistor–capacitor (RC) circuit with a reverse-biased 4 H -SiC p – n diode as the capacitive element is simulated. Simulation is performed with the ATLAS software module from the SILVACO TCAD system for technology computer-aided design (TCAD). An alternative way, to that in ATLAS, to set the parameters of doping impurities partly ionized in 4 H -SiC at room temperature is suggested. (The INCOMPLETE physical model available in the ATLAS module, which describes the incomplete ionization of doping impurities in semiconductors, is unsuitable for simulating the dynamic characteristics of devices.) The simulation results are discussed in relation to previously obtained experimental results.

Analytical Models of Breakdown Voltage and Specific On-Resistance for Vertical GaN Unipolar Devices

In this paper, the analytical models of breakdown voltage design parameters and minimum specific on-resistance in vertical gallium nitride unipolar devices are proposed. Considering the discrepancy of the impact ionization coefficients (IIC) reported in previous literatures from the Monte Carlo simulations and experiments, the analytical models of avalanche breakdown of gallium nitride devices both in punch-through and non-punch-through conditions are presented, i.e., the relationship between the breakdown voltage, drift doping concentration, drift thickness and critical electric field, which shows high accuracy with the results from numerical simulations. The comparison with the reported experimental results demonstrates the comparatively higher accuracy of the IIC data from Baliga. Taking into account the incomplete ionization in dopant impurities in GaN, the tradeoff between specific on-resistance and breakdown voltage is also given, demonstrating the optimized punch-through design has minimum specific on-resistance, which can be reduced by up to 12% for breakdown voltage from 1 kV to 15 kV. Meanwhile, the corresponding drift thickness can be reduced by from 18% to 20%, which can largely reduce the fabrication cost of epitaxial growth. The proposed optimized relationship is in good accordance with the results from MEDICI simulations.

Static and Dynamic Effects of the Incomplete Ionization in Superjunction Devices

The incomplete ionization of impurity atoms affects the free carrier concentration of several wide-bandgap (WBG) semiconductor materials even at room temperature, thus modifying the electrical properties of power devices. In this paper, the influence of the partial ionization of the dopants on the static and dynamic behaviors of WBG semiconductor-based superjunction (SJ) devices has been numerically investigated through extensive 2-D finite-element simulations. While this physical effect has only a minor impact on the static device characteristics, if a reverse bias pulse with a rise time comparable or smaller than the ionization time constant is applied to the structure, a “dynamic ionization” phenomenon can take place. The onset of this time-dependent ionization is the cause of charge unbalance effects in the device structure, due to the temporal dependence of the activated number of dopants. Electrothermal simulations, which have been carried out for a 4H-silicon carbide SJ diode, show a nonuniform temperature distribution during the transients which leads, in turn, to the self-heating of the device. Through an accurate redesign of the cross-sectional view of the device, the drawbacks of the incomplete ionization have been mitigated and the device performance enhanced.

A Physics-Based Compact Model of SiC Junction Barrier Schottky Diode for Circuit Simulation

A physics-based compact model of silicon carbide (SiC) junction barrier Schottky diode for circuit simulation is developed in this paper. The semiconductor physics mechanism in SiC, such as temperature-dependent mobility and incomplete ionization, are considered. The detailed device parameters, including drift region concentration, drift thickness, active area, and Schottky barrier height, are modeled. Then, a datasheet-oriented parameter extraction procedure for the device parameters is presented for three kinds of commercial SiC Schottky diodes with junction barrier structure. The model is implemented in the circuit simulator PSpice. In order to verify this model, the Technology Computer-Aided Design Sentaurus simulation is conducted with the device parameters and physical models, which shows a good agreement with the PSpice simulation.

Electrical Properties of Schottky-Diodes Based on B Doped Diamond

Schottky diodes fabricated on free-standing B doped monocrystalline diamond substrate have been investigated. As expected, reverse leakage current due to Schottky barrier lowering has been observed due to the high electric field at the metal-semiconductor interface. Forward current is highest under operating temperatures between 400 and 450K due to incomplete ionization hole mobility dependence on temperature. It is demonstrated that the static device characteristics in the temperature range from 300K to 450K can be modelled by parametrizing an analytical introduced for unipolar SiC and Si diodes.

Influence of Dopant Incomplete Ionization on the Capacitance of a Reverse-Biased 4H-SiC p+−i−n+ Diode

The transient process in an RC circuit with a reverse-biased 4H-SiC p+−i−n+ diode serving as a capacitor has been numerically simulated using the SILVACO TCAD software environment. The model experiment has shown that the charge time of an optimally designed 4H-SiC p+−i−n+ capacitor with dopant incomplete ionization is roughly an order of magnitude shorter than in the hypothetical case of complete ionization. The potential effect of the dopant ionization dynamics on the transient process has been found.

Electron Transport in PHEMT AlGaAs/InGaAs/GaAs Quantum Wells at Different Temperatures: Influence of One-Side δ-Si Doping

The influence of the concentration of δ doping with Si on the electron transport properties of Al0.25Ga0.75As/In0.2Ga0.8As/GaAs pseudomorphic quantum wells is studied in a broad temperature range of 4.2–300 K. A decrease in the doping efficiency at an electron concentration of >1.8 × 1012 cm–2 is found. This is caused by the effects of incomplete impurity ionization, which is also reflected on the temperature dependence of the electron concentration. A nonmonotonic variation in the electron mobility with increasing donor concentration, which is not associated with filling of the upper subband of size quantization, is observed. An increase in the mobility is associated with a rise in the Fermi momentum and screening, while its subsequent drop with increasing Si concentration is caused by the tunnel degradation of the spacer layer with a decrease in the conduction-band potential in the region of the δ-Si layer.

Электронный транспорт в квантовых ямах AlGaAs/InGaAs/ GaAs РНЕМТ при различных температурах: влияние одностороннего дельта-легирования Si

AbstractThe influence of the concentration of δ doping with Si on the electron transport properties of Al_0.25Ga_0.75As/In_0.2Ga_0.8As/GaAs pseudomorphic quantum wells is studied in a broad temperature range of 4.2–300 K. A decrease in the doping efficiency at an electron concentration of >1.8 × 10^12 cm^–2 is found. This is caused by the effects of incomplete impurity ionization, which is also reflected on the temperature dependence of the electron concentration. A nonmonotonic variation in the electron mobility with increasing donor concentration, which is not associated with filling of the upper subband of size quantization, is observed. An increase in the mobility is associated with a rise in the Fermi momentum and screening, while its subsequent drop with increasing Si concentration is caused by the tunnel degradation of the spacer layer with a decrease in the conduction-band potential in the region of the δ-Si layer.