Hole Impact Research Articles

Characteristics and Ionization Coefficient Extraction of 1kV 4H-SiC Implanted Anode PiN Rectifiers with Near Ideal Performance Fabricated Using AlN Capped Annealing

4H-SiC PiN rectifiers with implanted anode and single-zone JTE were fabricated using AlN capped anneal. The surface damage during the high temperature activation anneal is significantly reduced by using AlN capped anneal. The forward drop of the PiN rectifiers at 100A/cm2 is 3.0V while the leakage current is less than 10-7A/cm2 up to 90% breakdown voltage at room temperature. With 6μm thick and 2×1016cm-3 doped drift layer, the PiN rectifiers can achieve near ideal breakdown voltage up to 1050V. Hole impact ionization rate was extracted and compared with previously reported results.

Temperature dependence of electron ionization coefficients of InGaP measured in InGaP/GaAs/InGaP DHBT's

Accurate characterization of carrier impact ionization coefficients in InGaP is important for the prediction of the avalanche breakdown characteristics of GaAs-based heterojunction bipolar transistors and high electron mobility transistors, which is an important design parameter for device structures using InGaP layers. Recently, room temperature electron and hole impact ionization coefficients, α and β in InGaP have been reported using photocurrent multiplication techniques on p–i–n photodiodes. However, the information on the temperature dependence of impact ionization coefficient in InGaP is still lacking. In this work, the measurements of electron impact ionization coefficient for InGaP at elevated temperatures ( T=300–450 K) are reported. As the temperature increases, the measured multiplication is found to be weakly reduced. An empirical expression is obtained for the temperature dependence of the ionization coefficients.

Temperature dependence of impact ionization in GaAs

The temperature dependence of electron and hole impact ionization in gallium arsenide (GaAs) has been determined from photomultiplication measurements at temperatures between 20 K and 500 K. It is found that impact ionization is suppressed by increasing temperature because of the increase in phonon scattering. Temperature variations in avalanche multiplication are shown to decrease with decreasing avalanching region width, and the effect is interpreted in terms of the reduced phonon scattering in the correspondingly reduced ionization path length. Effective electron and hole ionization coefficients are derived and are shown to predict accurately multiplication characteristics and breakdown voltage as a function of temperature in p/sup +/in/sup +/ diodes with i-regions as thin as 0.5 /spl mu/m.

Monte Carlo simulations of Hg0.7Cd0.3Te avalanche photodiodes and resonance phenomenon in the multiplication noise

Monte Carlo simulations of Hg0.7Cd0.3Te avalanche photodiodes are presented. The simulated very low excess noise and exponential gain curve are consistent with those that have been experimentally observed and are consistent with the speculated large ratio of electron and hole impact ionization rates. The simulations suggest that there is a large difference between the scattering rates of electrons and holes, a direct consequence of the band structure. A resonance behavior in the excess noise factor at gain values near 2, 4, 8, and 16 is also revealed in the simulations. This effect is explained by comparing to the gain and noise of a photomultiplier tube.

Estimates of Impact Ionization Coefficients in Superlattice-Based Mid-Wavelength Infrared Avalanche Photodiodes

ABSTRACTWe describe band engineering strategies to either enhance or suppress electron-initiated impact ionization relative to hole-initiated impact ionization in type II superlattice mid-wavelength infrared avalanche photodiodes. The strategy to enhance electron-initiated impact ionization involves placing a high density of states at approximately one energy gap above the bottom of the conduction band and simultaneously removing valence band states from the vicinity of one energy gap below the top of the valence band. This gives the electrons a low threshold energy and the holes a high one. The opposite strategy enhances hole-initiated impact ionization. Estimates of the electron (α) and hole (β) impact ionization coefficients predict that α/β>>1 in the first type of superlattice and α/β<<1 in the second type.

Modelling of the hole-initiated impact ionization current in the framework of hydrodynamic equations

Several research papers have shown the feasibility of the hydrodynamic transport model to investigate impact ionization in semiconductor devices by means of mean-energy-dependent generation rates. However, the analysis has been usually carried out for the case of the electron-initiated impact ionization process and less attention has been paid to the modelling of the generation rate due to impact ionization events initiated by holes. This paper therefore presents an original model for the hole-initiated impact ionization in silicon and validates it by comparing simulation results with substrate currents taken from p-channel transistors manufactured in a 0.35 μm CMOS technology having three different channel lengths. The experimental data are successfully reproduced over a wide range of applied voltages using only one fitting parameter. Since the impact ionization of holes triggers the mechanism responsible for the back-bias enhanced gate current in deep submicron nMOS devices, the model can be exploited in the development of non-volatile memories programmed by secondary electron injection.

Measurements of the InGaAs hole impact ionization coefficient in InAlAs/InGaAs pnp HBTs

The hole multiplication factor in pnp InAlAs/InGaAs single heterojunction bipolar transistors (HBTs) has been measured as a function of the base-collector bias. The hole impact ionization coefficient /spl beta//sub p/ has been estimated taking into account the Early effect, I/sub CBO/, and thermal effects. Numerical corrections for dead space were made. The importance of considering second order effects is highlighted, showing that rough approximations can lead to an overestimation of the coefficient /spl beta//sub p/. At low electric fields, the extracted coefficient agrees with the most recent photomultiplication measurements available in the literature. At high electric fields, hole impact ionization coefficient is estimated up to values previously not reported in the literature (/spl beta//sub p//spl ap/10/sup 4/ cm/sup -1/).

Avalanche multiplication and ionization coefficient in AlGaAs/InGaAs p-n-p heterojunction bipolar transistors

The hole-initiated impact ionization multiplication factor Mp−1 and the ionization coefficient αp in AlGaAs/InGaAs p-n-p heterojunction bipolar transistors (HBTs) are presented. A large discrepancy is observed at low electric field when the measured data from the p-n-p HBTs are compared with those given from avalanche photodiode. The results show that the conventional impact ionization models, based on local electric field, substantially overestimate the hole impact ionization multiplication factor Mp−1. We believe that the hole ionization coefficient in p-n-p HBTs where significant dead space effects occur in the collector space charge region.

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.

Monte Carlo simulation of 4H-SiC IMPATT diodes

A Monte Carlo particle (MCP) bipolar model for 4H-SiCconsisting of three electron and two hole bands is developedto simulate the millimetre wave power generation by 4H-SiCIMPATT diodes. Validation of the model is provided by comparing(i) carrier transport properties with full band simulationresults and (ii) hole impact ionization coefficients with themost recent experimental results. MCP simulation results arereported for a low-voltage 4H-SiC IMPATT diode connecteddirectly in a parallel resonant circuit with a standard50 O load resistor. The detailed evolution of carriergeneration, accumulation and drift are presented to confirm thedesign of an efficient hi-lo IMPATT diode structure. Criticalperformance parameters investigated include bias and frequencydependences of millimetre wave output power, generationefficiency, conduction current and frequency stability at anoperating frequency around 200 GHz. It is predicted that veryhigh-power millimetre waves at around 200 GHz can be generated atpulse mode.

Hydrodynamic modeling of avalanche breakdown in a gate overvoltage protection structure

The breakdown of an overvoltage protection structure is analyzed in the temperature range from 298 to 523 K. The avalanche generation rates are modeled as a function of the carrier and lattice temperature. The generation rates are proportional to the carrier concentration. Careful attention is given to the pre-breakdown regime and to the breakdown process. The importance of various generation processes to the impact process is studied as well as the influence on variations of the ionization threshold energy and of the energy loss during the impact process. It is shown that the carrier generation inside the junction causes adiabatic carrier cooling, which leads to different carrier heating effects at low and high lattice temperature. The behavior of carrier heating at room temperature is strongly affected by the asymmetric field distribution inside the junction. The reason for this is the field dependence of the used trap assisted band to band tunneling model and of the direct band to band tunneling model. It is shown that at room temperature, the onset of hole impact ionization plays an important role for the electron heating. This is different at a temperature of 523 K, where the electrons dominate the onset of impact ionization.

Numerical analysis of surface-state effects on kink phenomena of GaAs MESFETs

Effects of surface states on the (or an abnormal increase in output conductance with the drain voltage) in GaAs MESFETs are studied by two-dimensional (2-D) simulations. It is shown that the kink could arise due to a space-charge effect originated from impact ionization of holes and the following hole trapping by the surface states. The onset voltage for current rise depends on the nature of surface states, which strongly affects the potential profiles. Transient or dynamic simulation indicates that the trap-related kink phenomenon should be a rather slow process. Substrate-related kink dynamics are also analyzed.

The Temperature Dependent Breakdown Voltage For 4H- and 6H-SiC Diodes

ABSTRACTThe breakdown voltages of 6H- and 4H-SiC rectifiers as function of temperature were modeled analytically in both non-reachthrough diode and reachthrough diode. The breakdown voltage was derived by the ionization integral employing accurate hole impact ionization coefficient. The breakdown voltage of SiC rectifiers was increased with increasing temperature and the positive temperature coefficient of breakdown voltage indicates that SiC rectifiers are suitable for high temperature applications. The breakdown voltages of both 6H- and 4H-SiC diodes were increased by M(T)-1/4 in NRDs and M(T)-1/8 in RDs.

First principles modeling of high field transport in wide-band-gap materials

In the present work, we have theoretically investigated the electronic and transport properties of three wide-band-gap materials, ZnS, SrS, and GaN, using full-band ensemble Monte Carlo (EMC) simulation. We show a suppression of the hole impact ionization rate for ZnS and SrS in particular, and GaN to a lesser extent, due to the narrowness of the upper valence bands. The resulting impact ionization coefficient for electrons in ZnS simulated using the EMC with microscopically calculated phonon scattering rates is in good agreement with the re-interpreted data of Thompson and Allen (J. Phys. C: Solid State Phys. 20 (1987) L499).

Near infrared avalanche photodiodes with bulk Al0.04Ga0.96Sb and GaSb/AlSb superlattice gain layers

We demonstrate the use of bulk Al0.04Ga0.96Sb and GaSb/AlSb superlattice as the gain material in a separate absorption/multiplication avalanche photodiode with sensitivity up to 1.74 μm. Both gain schemes were implemented in a molecular-beam epitaxy grown structure with a selectively doped InAs/AlSb superlattice as the n-type layer. Hole impact ionization enhancement was observed in Al0.04Ga0.96Sb by using a two wavelength injection scheme. The superlattice gain layer device exhibited multiplication factors in excess of 300, and surface limited dark current at a level comparable to InGaAs/InAlAs devices of similar design. The superlattice gain layer was found to be more promising than its bulk counterpart due to its inherent lower dark current.

MBE growth of HgCdTe avalanche photodiode structures for low-noise 1.55 μm photodetection

Molecular-beam epitaxy (MBE) has been utilized to fabricate HgCdTe heterostructure separate absorption and multiplication avalanche photodiodes (SAM-APD) sensitive to infrared radiation in the 1.1–1.6 μm spectral range, as an alternative technology to existing III–V APD detectors. Device structures were grown on CdZnTe(211)B substrates using CdTe, Te, and Hg sources with in situ In and As doping. The composition of the HgCdTe alloy layers was adjusted to achieve both efficient absorption of IR radiation in the 1.1–1.6 μm spectral range and low excess-noise avalanche multiplication. The Hg 1− x Cd x Te alloy composition in the gain region of the device, x=0.73, was selected to achieve equality between the bandgap energy and spin–orbit splitting to resonantly enhance the impact ionization of holes in the split-off valence band. The appropriate value of this alloy composition was determined from analysis of the 300 K bandgap and spin–orbit splitting energies of a set of calibration layers, using a combination of IR transmission and spectroscopic ellipsometry measurements. MBE-grown APD epitaxial wafers were processed into passivated mesa-type discrete device structures and diode mini-arrays using conventional HgCdTe process technology. Device spectral response, dark current density, and avalanche gain measurements were performed on the processed wafers. Avalanche gains in the range of 30–40 at reverse bias of 85–90 V and array-median dark current density below 2×10 −4 A/cm 2 at 40 V reverse bias have been demonstrated.

Measurement of collector-base junction avalanche multiplication effects in advanced UHV/CVD SiGe HBT's

This paper presents measurements of the avalanche multiplication factor (M-1) in SiGe HBTs using a new technique capable of separating the avalanche multiplication and Early effect contributions to the increase of collector current with collector-base bias, as well as allowing safe measurements at practical current densities. The impact of collector doping, current density, Ge profile, and operation temperature are reported for the first time using measured and simulated results from a production quality UHV/CVD SiGe HBT technology. Limitations of the technique in the presence of significant self-heating are discussed. By turning on the secondary hole impact ionization, we revealed the difference in impact ionization between strained SiGe and Si in the presence of the dead space effect. Despite its smaller bandgap, the compressively strained SiGe layer shows an apparent decrease in the secondary hole impact ionization rate compared to Si.

Temperature dependence of hole impact ionization coefficients in 4H and 6H-SiC

Hole impact ionization coefficients have been accurately measured as a function of temperature in both 4H and 6H-SiC using the pulsed electron beam induced current (P-EBIC) technique. For Chynoweth's equation ( α=a e − b/ E ), our measurements gave an a p value of (2.6±0.12)×10 6/cm and a b p value of (1.5±0.01)×10 7 V/cm for 6H-SiC at room temperature while the values of a p and b p for 4H-SiC were found to be (3.25±0.3)×10 6/cm and (1.71±0.04)×10 7 V/cm, respectively, at room temperature. The coefficient a p was found to decrease with increasing temperature for both polytypes while the coefficient b p remained constant. Based upon this data, the breakdown voltage of the 4H and 6H-SiC devices is predicted to increase with temperature which is an important desirable characteristic for power devices.

Temperature dependence of impact ionization coefficients in p-Si

An efficient full-band Monte Carlo program for high-energy carrier transport is employed to investigate hole impact ionization in p-Si for a range of electric fields up to 800 kV/cm and lattice temperatures between 77 and 450 K. An empirical expression is developed for the temperature dependence of ionization coefficients. The results are compared with those obtained from existing models. The empirical model agrees well with experiments and other numerically intensive models, providing a means to incorporate these effects into other device simulators and reliability models.

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.