Hole Ionization Rates Research Articles

Breakdown Field Model for 3C-SiC Power Device Simulations

Modeling and simulation of 3C-SiC power devices such as MOSFETs and diodes requires a model for the breakdown field that is consistent with the Monte-Carlo-simulated ionization rates of electron and holes and supported by experimental results. The challenge one faces is the limited number of publications reporting such calculations and the limited availability of high-quality ionization breakdown data for 3C-SiC diodes. We therefore performed a series of 2D simulations of both n-type and p-type Schottky diodes and p+-n diodes that confirms the general breakdown field trend with doping density obtained from experiments. We uncovered a difference between n-type and p-type diode breakdown behavior, identified the discrepancy between the calculations and the experimental data, and extracted a simple breakdown field model, useful for further 3C-SiC device design and simulation.

Additional confirmation of a generalized analytical model based on multistage scattering phenomena to evaluate the ionization rates of charge carriers in semiconductors

This paper contains additional validations of a comprehensive analytical model based on multistage scattering phenomena to evaluate the impact ionization rates of charge carriers in semiconductors which was proposed by the authors and reported earlier. The model has been used to evaluate the ionization rates of both electrons and holes in some potential wide bandgap (WBG) semiconductors such as Wurtzite-GaN (Wz-GaN), type-IIb diamond and 6H-SiC. The numerical results obtained from the analytical model within the respective electric field ranges under consideration have been compared with the ionization rate values calculated by using the empirical relations fitted from the experimentally measured data. The calculated values of impact ionization rates of electrons and holes in all the WBG semiconductors under consideration are found to be in close agreement with the experimental results.

Influence of the anisotropy on the performance of D-band SiC IMPATT diodes

Numerical simulation has been made to predict the RF performance of direction and < $$ 11\bar{2}0 $$ > direction p+/n/n−/n+ (single drift region) 4H silicon carbide (4H-SiC) impact-ionization-avalanche-transit-time (IMPATT) diodes for operation at D-band frequencies. We observed that the output performance of 4H-SiC IMPATT diode is sensitive to the crystal direction of the one-dimensional current flow. The simulation results show that direction 4H-SiC IMPATT diode provides larger breakdown voltage for its lower electron and hole ionization rates and higher dc-to-rf conversion efficiency (η) for its higher ratio of drift zone voltage drop (VD) to breakdown voltage (VB) compared with those for < $$ 11\bar{2}0 $$ > direction 4H-SiC IMPATT diode, which lead to higher-millimeter-wave power output for direction 4H-SiC IMPATT compared to < $$ 11\bar{2}0 $$ > direction. However, the quality factor Q for the < $$ 11\bar{2}0 $$ > direction 4H-SiC IMPATT diode is lower than that of direction, which implies that the < $$ 11\bar{2}0 $$ > direction 4H-SiC IMPATT diode exhibits better stability and higher growth rate of microwave oscillation compared with direction 4H-SiC IMPATT diode.

A generalized analytical model based on multistage scattering phenomena for estimating the impact ionization rate of charge carriers in semiconductors

A generalized analytical model based on multistage scattering phenomena has been developed in this paper for estimating the impact ionization rate of charge carriers in semiconductors. The probabilities of impact ionization initiated by electrons and holes have been calculated separately by taking into account all possible combinations of optical phonon scattering and carrier-carrier collisions prior to the impact ionization. Finally the analytical expressions of impact ionization rate of electrons and holes have been developed by using the aforementioned impact ionization probabilities. The impact ionization rates of electrons and holes in 4H-SiC have been calculated within the field range of $$2.5\times 10^{8}$$2.5×108---$$6.5\times 10^{8}\hbox { V m}^{-1}$$6.5×108Vm-1 by using the analytical expressions of those developed in the present paper. Those are also calculated by using the analytical expressions developed by some other researchers earlier without considering the multistage scattering phenomena. Finally the theoretical results obtained from the analytical model proposed in this paper and the analytical model developed by earlier researchers within the field range under consideration have been compared with the ionization rate values calculated by using the empirical relations fitted from the experimentally measured data. Closer agreement with the experimental data has been achieved when the impact ionization rate of charge carriers in 4H-SiC are calculated from the proposed model as compared to the earlier one.

Identification of Electron and Hole Ionization Rates in GaAs with reference to IMPATT Diode

A computer aided simulation study of electron and hole ionization rates in GaAs with reference to the Terahertz source of power called IMPATT diode is presented in this paper. It is based on the breakdown voltage calculation using the computer simulation method developed for the DC analysis of an IMPATT diode. The comparison of simulation results reveals that the break down voltage calculated using carrier ionization rates data reported by Pearsall et al is in good agreement with the experimental reports.

Optimization of Bipolar SiC-Diodes by Analysis of Avalanche Breakdown Performance

In this work we discuss measurements of the breakdown voltage of diodes with non-punch-through (NPT)- and punch-through (PT)-designs. From the experimental results we deduce the temperature dependent Fulop constants of the effective ionization rate. The data of this work agree very well with ionization rates for electrons and holes determined recently.

Optically modulated III–V nitride-based high-power IMPact Avalanche Transit Time oscillator at Millimeter-wave window frequency

Extensive simulation experiments are carried out for the first time, to study the optical modulation of the high- frequency characteristics of III–V GaN-(gallium nitride) based top-mounted and flip-chip IMPact Avalanche Transit Time (IMPATT) oscillators at MM-wave window frequency (140.0 GHz). It is found that the un-illuminated GaN IMPATT is capable of delivering a RF power of 5.6 W with an efficiency of 23.5% at 145.0 GHz. Frequency up-chirping of 6.0 GHz and a degradation of RF power output by almost 15.0% are further observed in case of photo-illuminated FC IMPATT. The study reveals that compared to predominate electron photocurrent in top-mounted IMPATT, photo-generated leakage current dominated by hole in flip-chip IMPATT has more pronounced effect on the GaN-based device as regards the frequency chirping and decrease of negative conductance and total negative resistance per unit area of the device. The inequality in the magnitudes of electron and hole ionization rates in the wide band gap semiconductor has been found to be correlated with the above results. The study reveals that GaN IMPATT is a potential candidate for replacing conventional IMPATTs at high-frequency operation. These results are useful for practical realization of optically controlled GaN-based high-power IMPATTs for application in MM-wave communication systems.

Optically Modulated III–V Nitride-Based Top-Mounted and Flip-Chip IMPATT Oscillators at Terahertz Regime: Studies on the Shift of Avalanche Transit Time Phase Delay Due to Photogenerated Carriers

Extensive simulation experiments are carried out to study the effects of optical illumination on the terahertz (>1.0 THz) characteristics of GaN-based IMPact Avalanche Transit Time (ATT) (IMPATT) oscillator. The shift of ATT phase delay, due to photogenerated carriers, in the top-mounted (TM) and flip-chip (FC) IMPATTs is also studied through a modified simulation scheme, for the first time. The study reveals that, compared to predominant electron photocurrent in TM IMPATT, hole-dominated photoleakage current in FC IMPATT is more important in modulating the high-frequency characteristics of the GaN-based terahertz device. Optically illuminated FC IMPATT shows more pronounced shift of avalanche phase delay, frequency chirping, as well as a decrease of negative conductance and total negative resistance of the device. The inequality in the magnitudes of electron and hole ionization rates in GaN has been found to be correlated with the aforementioned results.

Prospects of 4H-SiC Double Drift Region IMPATT Device as a Photo-Sensitive High-Power Source at 0.7 Terahertz Frequency Regime

The dynamic performance of wide-bandgap 4H-SiC based double drift region (p++ p n n++) IMPATT diode is simulated for the first time at terahertz frequency (0.7 Terahertz) region. The simulation experiment establishes the potential of SiC based IMPATT diode as a high power (2.5×1011 Wm−2) terahertz source. The parasitic series resistance in the device is found to reduce the RF power output by 10.7%. The effects of external radiation on the simulated diode are also studied. It is found that (i) the negative conductance and (ii) the negative resistance of the diode decrease, while, the frequency of operation and the quality factor shift upward under photoillumination. Holes in 4H-SiC based IMPATT are found to dominate the modulation activities. The inequality in the magnitude of electron and hole ionization rates in the semiconductors may be correlated with these findings.

Low electric field hole impact ionization coefficients in GaInAs and GaInAsP

The electric field dependence of the hole impact ionization coefficients in Ga/sub 0.47/In/sub 0.53/As and Ga/sub 0.28/In/sub 0.72/As/sub 0.61/P/sub 0.39/ was obtained from the electrical characteristics of p-n-p heterojunction bipolar transistors. The anomalous low field behavior of the electron impact ionization coefficients in these materials was not observed for the case of holes. Within the accuracy of our measurements me observed no change in the hole ionization rates in the temperature range of 20 to 120/spl deg/C.

Characteristics of impact ionization rates in direct and indirect gap semiconductors

Impact ionization rates for electrons and holes in three semiconductors with particular band structure characteristics are examined to determine underlying factors influencing their qualitative behavior. The applicability of the constant matrix element approximation is investigated, and found to be good for the indirect gap material studied, but overestimates threshold softness in the direct gap materials. The effect that final states in the Γ valley have in influencing characteristics of the rate in the direct gap materials is investigated, and it is found that they play a significantly greater role than the low density of Γ valley states would suggest. The role of threshold anisotropy in affecting threshold softness is examined, and it is concluded that it plays only a small part, and that softness is controlled mainly by the slow increase in available phase space as the threshold energy is exceeded.

Study of avalanche breakdown and impact ionization in 4H silicon carbide

Epitaxial p-n diodes in 4H SiC are fabricated with uniform avalanche multiplication and breakdown. Photomultiplication measurements were performed to determine electron and hole ionization rates. Theoretical values of critical fields and breakdown voltages in 4H SiC are calculated using the ionization rates obtained. We discuss ionization mechanisms in 4H SiC and make a comparison between silicon carbide and gallium nitride.

Ionization rates and critical fields in 4H silicon carbide

Epitaxial p-n diodes in 4H SiC are fabricated showing a good uniformity of avalanche multiplication and breakdown. Peripheral breakdown is overcome using the positive angle beveling technique. Photomultiplication measurements were performed to determine electron and hole ionization rates. For the electric field parallel to the c-axis impact ionization is strongly dominated by holes. A hole to electron ionization coefficient ratio of up to 50 is observed. It is attributed to the discontinuity of the conduction band of 4H SiC for the direction along the c axis. Theoretical values of critical fields and breakdown voltages in 4H SiC are calculated using the ionization rates obtained.

Theory of hole initiated impact ionization in bulk zincblende and wurtzite GaN

In this article, the first calculations of hole initiated interband impact ionization in bulk zincblende and wurtzite phase GaN are presented. The calculations are made using an ensemble Monte Carlo simulation including the full details of all of the relevant valence bands, derived from an empirical pseudopotential approach, for each crystal type. The model also includes numerically generated hole initiated impact ionization transition rates, calculated based on the pseudopotential band structure. The calculations predict that both the average hole energies and ionization coefficients are substantially higher in the zincblende phase than in the wurtzite phase. This difference is attributed to the higher valence band effective masses and equivalently higher effective density of states found in the wurtzite polytype. Furthermore, the hole ionization coefficient is found to be comparable to the previously calculated electron ionization coefficient in zincblende GaN at an applied electric field strength of 3 MV/cm. In the wurtzite phase, the electron and hole impact ionization coefficients are predicted to be similar at high electric fields, but at lower fields, the hole ionization rate appears to be greater.

Theoretical Prediction of Zinc Blende Phase GaN Avalanche Photodiode Performance Based on Numerically Calculated Electron and Hole Impact Ionization Rate Ratio

AbstractIn this paper, we present the first calculations of the electron and hole initiated interband impact ionization rate in zinc blende phase GaN as a function of the applied electric field strength. The calculations are performed using an ensemble Monte Carlo simulator including the full details of the conduction and valence bands along with a numerically determined, wave-vector dependent interband ionization transition rate determined from an empirical pseudopotential calculation. The first four conduction bands and first three valence bands, which fully comprise the energy range of interest for device simulation, are included in the analysis. It is found that the electron and hole ionization rates are comparable over the full range of applied electric field strengths examined. Based on these calculations an avalanche photodiode, APD, made from bulk zinc blende GaN then would exhibit poor noise and bandwidth performance. It should be noted however, that the accuracy of the band structure employed and the scattering rates is presently unknown since little experimental information is available for comparison. Therefore, due to these uncertainties, it is difficult to unequivocally conclude that the ionization rates are comparable.

Monte Carlo simulation of impact ionization rates in InAlAs-InGaAs square and graded barrier superlattice

The Monte Carlo method is used to analyze impact ionization rates for electrons and holes in a <100> crystal direction In/sub 0.52/Al/sub 0.48/As-In/sub 0.53/Ga/sub 0.47/As square and graded barrier superlattice. The calculated impact ionization rate ratio /spl alpha///spl beta/ is enhanced to more than 10 in a wide barrier and narrow-well square barrier superlattice. This is because the hole ionization rate /spl beta/ is greatly reduced in the narrower well superlattice, while the electron ionization rate /spl alpha/ is less sensitive to well and barrier layer thickness. These results are explained by a combination of the ionization dead space effect for the barrier layer and the electron ionization rate enhancement in the well layer due to large conduction band edge discontinuity. Furthermore, it is found that in a graded barrier superlattice, the impact ionization rate ratio /spl alpha///spl beta/ is smaller than that for a square barrier superlattice having the same barrier and well thickness. This is due to the occurrence of hole ionization in the narrow bandgap region in graded barriers. The band structure effects on hot carrier energy distribution, as well as impact ionization, are also discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of electron- and hole-dominant photocurrent on the millimetre wave properties of an indium phosphide IMPATT diode at a 94 GHz window under optical illumination

The effect of photogenerated predominant electron or hole components of the leakage current on the admittance and negative resistance properties of a 94 GHz p+nn+ indium phosphide IMPATT diode under optical illumination is presented in this paper. A computer modelling and simulation technique has been used to study the above effect. The results show that the photogenerated leakage current dominated by holes is more important than that dominated by electrons in modulating the millimetre wave properties of the device and shifting its oscillation frequency. The magnitudes of electron or hole ionization rates in the semiconductor have been found to be correlated with the above effect.

Studies on the high-frequency properties of ?111?, ?110? and ?100? oriented GaAs IMPATT diodes

High-frequency analysis has been carried out to predict the rf performance of 〈111〉, 〈110〉 and 〈100〉 oriented p+nn+, n+pp+ (single drift region) and n+npp+ (double drift region) GaAs IMPATT diodes for opertion at 35 and 60 GHz. The microwave performance is observed to be highly sensitive to crystal orientation in case of p+nn+ and n+npp+ diodes whereas orientation of the substrate has negligible effect on n+pp+ avalanche diodes. The calculation shows that 〈111〉 oriented GaAs IMPATT diode would provide the largest magnitude of negative resistance and negative conductance for both SDR p+nn+ and DDR n+npp+ diodes which indicates that high microwave power with high conversion efficiency can be realised from these 〈111〉 oriented GaAs devices. This result can be explained from the experimental data of electron and hole ionization rates for different orientations in GaAs.

New doped multiple-quantum-well avalanche photodiode: The doped barrier Al0.35Ga0.65As/GaAs multiple-quantum-well avalanche photodiode

The performance of doped barrier, multiple-quantum-well avalanche photodiodes (MQW APDs) is reported for the first time. Investigations are presented for a 800 Å/200 Å MQW Al0.35Ga0.65As/GaAs undoped structure with a p-n junction in each barrier. The devices exhibit low dark currents, low breakdown voltages (−10 V), and gains up to 20 for electron injection. Noise measurements show an enhancement of the electron to hole ionization rates ratio, α/β, to values between 50 and 12.5 for gains up to 5, and to 5 for gains above 5. α/β is enhanced by a factor of 6 over the bulk GaAs, and a factor of at least 2 over the simple MQW APD. The particular design we report provides medium gain and very-low-noise characteristics at low bias voltage. These experimental noise results are the best reported so far for AlGaAs/GaAs MQW APD structures.

Impact ionization rates of holes in AlxGa1−xSb

This paper discusses the impact ionization rates of holes in AlxGa1−xSb near x=0.06, where resonance impact ionization is expected. Resonance impact ionization did not occur in a range of the electric field we studied. We evaluate the impact ionization of holes at the spin-split-off band theoretically, and show that our measured result is reasonable.