Current Gain Degradation Research Articles

Investigation on Effect of Interface Trap Charges and Temperature in Gate Overlap Graphene Source Step Shape Double Gate Tunnel FET

Abstract This work evaluates the electrical parameters of Gate Overlap Graphene source Step Shape Double Gate TFET (GO-GR-SSDG-TFET) with wide variation in interface trap charges (ITCs) and temperature. Here, both the positive interface charges (PITCs) and negative interface charges (NITCs) along with temperature ranges from 200-500 K on DC, RF/analog and linearity characteristics are analyzed using TCAD Sentaurus Simulator. It is observed that there is improvement (degradation) in current ratio, transconductance, gain, cut-off frequency, and delay with increase (decrease) in PITC (NITC), whereas, opposite trend is realized in terms of linearity parameters. The rise in temperature leads to degradation is subthreshold behaviour due to exponential characteristic of Shockley-Read-Hall (SRH) recombination with temperature. It is also seen that at high temperature there is degradation transconductance, device efficiency, cut-off frequency, current ratio, delay, and temperature sensitivity (ST) in the proposed TFET. Moreover, the linearity parameters are degraded with rise in temperature. Finally, a comparison table is highlighted in terms of various electrical parameters for proposed TFET with existing data.

Radiation hardness of bipolar transistor based integrated circuits improved by ECR hydrogen plasma treatment and Si-wafers gettering

We demonstrate significant improvement of the radiation immunity of the integrated circuits based on silicon bipolar transistors. Strong decrease of the current gain degradation and significant yield improvement after high-energy gamma irradiation are both shown. This was achieved by development of efficient hydrogenation process for the silicon bulk and the surface dielectric layer using electron cyclotron resonance (ECR) plasma, as well as implementation of effective Si-wafer gettering option. Keywords: integrated circuits, bipolar transistors, ECR-plasma, hydrogenation of semiconductor structures, trap state passivation, gettering of semiconductor wafers, γ-irradiation, radiation hardness, yield of workable transistors.

Повышение радиационной стойкости интегральных схем на основе биполярных транзисторов обработкой в водородной электронно циклотронно резонансной плазме и геттерированием Si-пластин

We demonstrate significant improvement of the radiation immunity of the integrated circuits based on silicon bipolar transistors. Strong decrease of the current gain degradation and significant yield improvement after high-energy gamma irradiation are both shown. This was achieved by development of efficient hydrogenation process for the silicon bulk and the surface dielectric layer using electron cyclotron resonance (ECR) plasma, as well as implementation of effective Si-plate gettering option.

Impact of Ring-Shaped Collector Contact on Total Ionizing Dose Susceptibility of Vertical n-p-n Bipolar Transistors

The impact of ring-shaped collector contact (RCC) on total ionizing dose (TID) susceptibility of 40-V vertical n-p-n bipolar transistors is investigated. The 60Co <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula> -ray irradiation experiment shows that the devices with RCC suffer less current gain degradation than their counterparts with conventional collector contact structure, which is independent of the emitter area and bias condition during irradiation. Technology computer-aided design (TCAD) simulation results indicate that the enhancement in radiation tolerance of the RCC devices should be attributed to the mitigation of trap-assisted carrier recombination at the Si/SiO2 interfaces near emitter–base (EB) junction rather than the concentration or distribution variations of radiation-induced traps. Moreover, the mitigation of carrier recombination in RCC devices could result from the creation of new current flow paths that suppress the diffusion of injected electrons toward the trap-enriched Si/SiO2 interfaces.

Characterizing and modeling current gain degradation in bipolar transistor exposed to heavy ion radiation

Radiation effects of 20 MeV Br on bipolar transistors are investigated in this work. A distinct different bias dependences are found for damage factors (DF) of forward and reverse current gain. For reverse current gain, DF gradually decreases with the voltage across base-collector junction (VBC) increasing, until a saturated value is reached. While an unexpected increase exists in DF of forward current gain over the high voltage across base-collector junction (VBE) region. The high injection effect is found to contribute to the observed rebound for forward current gain over high VBE region. From the device physical perspective, a physics-based analytical closed DF model for forward and reverse current gain is proposed, including the contribution of high injection effect and recombination current in junction space charge region. A good agreement is obtained between the measured and modeled data over the whole bias region.

Current Gain Enhancement for Silicon-on-Insulator Lateral Bipolar Junction Transistors Operating at Liquid-Helium Temperature

Conventional homojunction bipolar junction transistors (BJTs) are not suitable for cryogenic operation due to heavy doping-induced emitter band-gap narrowing and strong degradation in current gain (β) at low temperature. In this letter, we show that, on lateral version of the BJTs (LBJTs) fabricated on silicon-on-insulator (SOI) substrate, such β degradation can be mitigated by applying a substrate bias (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sub</sub> ), and a β over unity is achieved in a base current (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ) range over 5 orders of magnitudes at 4.2 K, with a peak β ~ 100 demonstrated. The β improvement is explained by the enhanced electron tunneling through base region as a result of base barrier lowering and thinning by a positive Vsub, which leads to dramatic increase of collector current (IC) while IB is negligibly affected.

Effect of protons located at different region in SiO2 layer on GLPNP transistors degradation

Based on 100-keV, 130-keV and 170-keV proton irradiations, the contribution of ionization damage to the electrical property degradation of gate controlled lateral PNP (GLPNP) transistors is investigated. The key electrical parameters are measured in-situ during irradiations. The radiation-induced defects are characterized by deep level transient spectroscopy (DLTS). Experimental results show that the same ionization dose of various energy protons caused different degradation of current gain in GLPNP transistors. The current gain of the irradiated transistors by 170-keV protons degrades obviously, while that of the irradiated transistors by 100-keV protons does not almost change. As the ionization dose increases, the excess base currents of the irradiated transistors by 170-keV and 130-keV protons increase. The ideality factor of the irradiated transistor by 170-keV protons changes, while that of the transistor irradiated by 130-keV protons does not change. The gate sweep (GS) curves show that the main ionization defects induced by different protons are the interface traps. Compared with the irradiated transistors by 100-keV and 130-keV protons, the irradiated transistors by 170-keV protons has a high gate sweep peak at the same dose indicating that the 170-keV protons induced more interface traps. Therefore, the protons located at different region in SiO2 of GLPNP transistors can induce different degree of degradation, and the location of the proton is closer to the Si/SiO2 interface, the number of the radiation-induced interface traps is the more.

Correlation Between High Dose Rate Irradiation and Low Dose Rate Irradiation for Switched Dose Rate Technique

Based on gated lateral p-n-p (GLp-n-p) transistors, the correlation between the high dose rate (HDR) and low dose rate (LDR) irradiations during the switched dose rate experiments is investigated. Experimental results show that a significant deviation of the current gain degradation caused by switching dose rate irradiations from that by individual LDR ones is found. It is also observed that, after the switching of dose rate from HDR to LDR, the positive oxide-trapped charges induced by the HDR irradiations would influence the recombination of interface traps produced by the LDR irradiations, leading to an abnormal evolution of the excess base current and excess collector current for the GLp-n-p transistors. The decrease in the positive oxide-trapped charges from HDR to LDR is not caused by an annealing effect. The evolution of positive oxide-trapped charges could influence the formation of interface traps during switched dose rate experiments. All the experimental results indicate that the degradations in the GLp-n-p caused by the HDR and LDR irradiations are not two independent processes for the switched dose rate technique.

Evolution of radiation defects in NPN bipolar junction transistors irradiated by 3 MeV protons

In space, energetic proton irradiation produces both ionization and displacement damage in semiconductors and devices served in spacecraft. In order to separate the ionization and displacement damage in bipolar junction transistor (BJT), the electrical degradation and radiation-induced defects were studied during 3 MeV proton irradiation and the annealing process. The current gain degradation shows a nonlinear relationship with the increasing fluence during irradiation. It can be deduced that the proton irradiation produces the ionization/displacement combined damage in NPN BJTs. Ionization and displacement-induced defects are measured by deep level transient spectroscopy (DLTS) during the isochronal annealing. During the isochronal annealing, the ionization-induced defects annealed at a relatively low temperature (400 K), while the displacement-induced defects recovered at a higher temperature (higher than 500 K). According to the comparison between the DLTS analysis and current gain recovery, the accepter-like defects (V-O and V2(−/0)) act an important role in irradiated NPN BJTs.

Hydrogen soaking irradiation acceleration method: application to and damage mechanism analysis on 3DG111 transistors

Bipolar devices are extremely sensitive to ionization effects, and their low dose rate radiation damage is more serious than their high dose rate radiation damage, which phenomenon is especially named enhanced low dose rate sensitivity. In the actual space radiation environment, the radiation dose rate of the device is extremely low. Currently, the enhanced low dose rate sensitivity effect has become a key factor of evaluating the reliability of spacecraft and its electronic systems, due to the fact that the low dose rate irradiation test needs longer time. The method to speed up the test on the ground is one of the hottest topics in this research area. In recent years, some researches have suggested that the use of hydrogen immersion irradiation for accelerating the test can simulate low dose rate radiation damage to some extent, but the damage mechanism has not been analyzed in detail. In this paper, the mechanisms of electrical properties and deep level defects for the 3DG111 transistor by &lt;sup&gt;60&lt;/sup&gt;Co gamma ray under high and low dose rates in the cases with and without hydrogen are investigated. In order to analyze the damage mechanism of bipolar junction transistor, the excess base current and deep level transient spectrum are measured by using semiconductor parameter analyzer and deep level transient spectroscopy. The experimental results show that the current gain degradation of 3DG111 transistor is more serious under low dose rate radiation than under high dose rate radiation, at the same time, the excess base current of transistor increases significantly. This shows that in the device there appears the enhanced low dose rate sensitivity. Under both high dose rate radiation and low dose rate irradiation, the radiation damage defects are the traps for both oxide positive charge and interface state. Under the low dose rate irradiation, there are two main reasons for the increase in transistor damage. First, the oxide charge concentration increases under low dose rate irradiation, and the oxide charge and interface state energy levels move toward the middle band. Eventually, the space charge region recombination of the transistor is intensified, and thus causing the excessive base current of the transistor to increase and transistor performance to degrade. The comparison shows that the number and type of defects under the high dose rate irradiation are the same as those under the low dose rate irradiation. Based on the analysis, the hydrogen treatment can be used as an effective method of accelerating the assessment of radiation damage enhancement effect at low dose rates.

Extraction and Analysis of Gamma Irradiated Si BJT SPICE Model

The Simulation Program with Integrated Circuit Emphasis (SPICE) model parameters of pre and post-irradiated silicon bipolar junction transistor (Si BJT) were extracted with the use of Altium Designer (AD)/SPICE model wizard. The percentage changes (Δ%) between forward and reverse-bias parameters of existing BJT (ZETEX BCW72) SPICE model were estimated and also the degradation Δ% between the experimental data of pre and post-irradiated Si BJT were calculated. Then the new measured results by comparison were imported into AD/SPICE model wizard to extracts forward-bias parameters. The extracted forward-bias parameters were used to generate reverse-bias parameters through Δ%. The final extracted Si BJT SPICE model parameters were implemented in SPICE simulator to obtained forward and reverse Gummel plots. As expected, base current (IB) increases, the collector current (IC) increases slightly at low bias base-emitter voltage, leading to current gain degradation due to positive charge trapped in the oxide and interface of the BJT device. In addition, the results of the IB in the forward Gummel flows in parallel with base-emitter junction, while the IB in the reverse Gummel flows across the base-collector junction down to the back side collector contact through the collector region. Finally, the compared results of Si BJT forward Gummel simulation and experimental data showed good agreement.

Experimental studies of collector-emitter voltage bias influence on the total ionization dose effects in NPN Si BJTs

The voltage VCE, bias influence studies on total ionizing dose (TID) in bipolar junction transistors (BJTs) were investigated. The BJTs were set at forward active mode of base-emitter voltage (VBE) swept from 0 to 1.0 V at different biased conditions of VCE, ranging from 1 V to 2 V at an interval of 0.25 V during 60Co γ irradiation. The damage mechanism of TID in BJTs at different VCE bias conditions were analysed by forward Gummel characteristics, forward current gain (βf), normalized excess base current (ΔIB/IBpre), normalized excess collector current (ΔIC/ICpre), normalized current gain (βfpost/βfpre), ideality factor (n) and power dissipation (Pd). The results show that the increments of base current (IB) and collector current (IC) are slightly different in various VCE bias conditions which also effects slight changes in their current gain (Δβf) degradation. The current gain degradation (βf) at high bias VCE degraded more slightly than low bias VCE. The ΔIB/IBpre, ΔIC/ICpre and βfpost/βfpre estimated shows similar trend of different VCE bias conditions resulting into varying distribution of performance degradation of the BJT. The ideality factors (n) for excess base current (ΔIB) were ∼2 for VBE from 0.35 V to 0.6 V at different VCE bias conditions. Thus, ideality factor (n) slightly increases as the VCE bias rises and decreases with the increased accumulated total dose level after the n peak value was obtained at TID equals to 130 krad (Si) for irradiated BJTs. Finally, the power dissipated (Pd) by BJTs were compared as VCE = 2 V > 1.75>1.5 V > 1.25>1 V and were noted to be more effective at VBE>0.6 V which also concur with temperature rise TR. The TR in BJTs resulted into self-heating effects.

Hydrogen Soaking, Displacement Damage Effects, and Charge Yield in Gated Lateral Bipolar Junction Transistors

The effects of 70-keV and 1-MeV electron irradiations on gate-controlled lateral PNP (GLPNP) transistors are evaluated with and without molecular hydrogen (H2) soaking. At a given ionization dose, 1-MeV electron irradiation causes more degradation of current gain in GLPNP transistors that have not been soaked in H2 than 70-keV electrons. This is because linear bipolar transistors are sensitive to both ionization and displacement damage effects, and because 1-MeV electrons induce significant displacement damage in Si-based bipolar junction transistors and 70-keV electrons do not. In H2-soaked transistors, the degradation is much larger than in unsoaked devices, and similar amounts of degradation are observed for 70-keV electron irradiation and 1-MeV electron irradiation. This occurs because ionization–induced release, transport, and reactions of hydrogen in the bipolar-base oxide greatly enhance interface-trap buildup and dominate device response in H2-soaked devices, and because charge yield ratios for 70-keV and 1-MeV electron irradiations differ by less than ~20%.

60Co gamma radiation total ionizing dose combined with conducted electromagnetic interference studies in BJTs

The influence of combined 60Co gamma radiation total ionization dose (TID) and conducted electromagnetic interference (EMI) in bipolar transistors was studied. The BJTs were set at forward active bias during the entire irradiation processes to investigate the current gain degradation. The experimental results demonstrated that the base current increases under the influence of EMI, TID and combined TID with EMI due to the recombination currents in the emitter-base spacer of the transistor. The ideality factor n investigated showed that TID was approximately equal to 2 and the combination of TID and EMI was greater than 2. Meanwhile, the degradation quantity of the device current gain βTID+EMI tested with combined TID and EMI irradiation was observed to be more severe than that of βTID or βEMI tested only with TID or EMI at low bias VBE region (<0.65 V). However, the degradation trends of the dc characteristics of the tested devices at high VBE region (>0.6 V) became smaller under different experimental conditions (EMI, TID, TID + EMI). Finally, the current gain degradation levels of the tested devices were compared (βTID+EMI > βTID > βEMI).

Synergistic effects of NPN transistors caused by combined proton irradiations with different energies

There are a large number of protons with different energies from the dozens of keV to hundreds of MeV in space environment, which simultaneously act on the bipolar junction transistors (BJTs), and induce different irradiation effect and damage defects. Moreover, interaction between displacement defects and ionization defects occurs. In the paper, the interaction mechanisms between oxide charge and displacement defects in 3DG112 NPN BJTs caused by the combined 70 keV and 170 keV protons with 5 MeV proton irradiation are studied. Experimental results show the degradation of current gain increases linearly with increasing the irradiation fluence of the 170 keV and 5 MeV protons, but increases nonlinearly for the 70 keV protons, implying that the 170 keV and 5 MeV protons mainly induce displacement damage on the NPN BJTs, while the 70 keV protons cause ionization damage. It can be seen from the Geant4 calculation that 70 keV and 170 keV protons cause almost the same ionization damage on the 3DG112 transistors, while have significant difference in displacement damage ability, which is favorable to analyze the effect of displacement damage in oxide layer of NPN BJTs induced by 170 keV and 70 keV protons on ionization damage caused by the subsequent 5 MeV protons. DLTS analyses show that 5 MeV protons produce mainly displacement defect centers in based-collector junction of 3DG112 transistors, and 170 keV and 70 keV protons only induce almost the same number of the oxide trapped charges. While the combined irradiation can produce the more oxide trapped charges, except displacement defects, showing that displacement damage in oxide layer caused by 170 keV and 70 keV protons can increase the oxide trapped charges during the subsequent 5 MeV exposures. Moreover, the more displacement defects in oxide layer will induce more oxide trapped charges, and give more enhanced synergistic effects. These results will help to assess the reliability of BJTs in the space radiation environment.

Impact of nitride passivation layer on ionizing irradiation damage on LPNP bipolar transistors

Bipolar junction transistors (BJTs) are generally employed in spacecraft, due to their current drive capability, linearity and excellent matching characteristics. High-energy particles and cosmic rays in space environment remarkably affect electronic devices, especially in BJTs producing total ionizing dose, displacement damage or single event effect. Among them, ionizing irradiation effects on BJTs dominates. For BJTs, ionization damage can induce the oxide trapped charges in SiO2 layer and interface traps in Si/SiO2, resulting in more recombination base current and the degradation of current gain. Consequently, the accumulation of both oxide charges and interface traps causes an increase in the base current.#br#Passivation layer is also an important factor of the irradiation effects of BJTs. Previous works only studied the degradation of electrical properties of the devices with/without passivation layer induced by irradiation, and did not give an influence mechanisms of passivation layer on the irradiation respond of devices. Therefore, the irradiation damage mechanisms of the BJTs with or without nitride passivation layer are not clear so far.#br#In this paper, the impact of Si3N4 passivation layer on ionizing irradiation damage on lateral PNP bipolar transistors (LPNP) was studied by using 60Co gamma irradiation source. The KEITHLEY 4200-SCS semiconductor parameter analyzer was used to measure the relationship between the electrical properties of LPNP transistors and ionization dose, including the Gummel characteristics, the degradation of current gain, etc. The irradiation defects of the LPNP transistors with/without passivation layer structure were analyzed by the deep level transient spectroscopy (DLTS). The experimental results show that the electrical properties of the LPNP transistors with and without passivation layer exhibit similar characteristics. For all samples, the base current increases with increasing the total dose, while the collector current does not almost change. Compared with the LPNP transistors without Si3N4 passivation layer, the degradation of LPNP transistor with Si3N4 passivation layer is severe.#br#Based on the excess base current as a function of base-emitter voltage for the LPNP transistors with/without nitride passivation layer, the degradation of bipolar transistors with nitride passivation layer is severe under the same irradiation conditions. The DLTS analyses show that compared with the bipolar transistors without nitride passivation layer, the signal peak located at about 300 K is shifted to low temperature for the bipolar transistors with nitride passivation layer. The above results show that the LPNP transistors with nitride passivation could produce a large number of interface states with the energy level is closer to the middle of the forbidden band during the irradiation, which is attributed to a large number of hydrogen presence during the processing of fabricated passivation layer.

Radiation Degradation of Bipolar Transistor Current Gain

Radiation Degradation of Bipolar Transistor Current Gain

Suppressed Self-Heating in Multi-Finger InP-Based DHBTs with Au Subcollector Fabricated on SiC Substrate by Surface-Activated Bonding

InP-based double-heterojunction bipolar transistors (DHBTs) have demonstrated excellent high-frequency performance suitable for submillimeter-wave ICs and wideband-communication’s ICs. For these ICs, increasing the operation current density of the transistor is effective for improving the high-frequency performance. Multi-finger transistor design is very useful in reducing the IC chip size because it reduces the required number of transistors. However, it results in the increased power dissipation per unit area, leading to an increase in junction temperature and thus to the degradation of current gain of DHBTs. In order to suppress these undesirable effects, we propose the multi-finger DHBT on a highly thermal-conductive SiC substrate fabricated by surface-activated bonding (SAB). The measured thermal resistance, R th, shows the significant impact of the proposed DHBT structure on suppressing device self-heating thanks to the highly thermal-conductive SiC substrate and a simultaneously introduced highly thermal-conductive Au subcollector. Figure 1 shows a cross-sectional view of a fabricated multi-finger DHBT. The DHBT structure is formed on a SiC substrate (thermal conductivity κ = 490 W/m/K) through an Au subcollector (κ = 320 W/m/K). For single-finger devices, we have demonstrated the marked improvement in heat dissipation [1]. Epitaxial layer structures are designed for high-current-density operation (> 10 mA/μm2). The emitter is 20-nm-thick InP. The InGaAsSb base is 20-nm thick and highly C-doped at 7 x 1019 cm-3. The collector is 60-nm-thick InP. For the contact to the Au subcollector, 10-nm-thick, highly Si-doped InGaAs is employed. Emitter fingers and base electrodes are formed on one Au subcollector. We prepared twelve types of multi-finger DHBTs with combinations of four to six emitter fingers and emitter-finger spacing of 0.9, 1.4, and 3.4 μm. The device fabrication started with the epitaxial growth of DHBT layers on a 3-inch InP substrate by metal-organic chemical vapor deposition as shown in Fig. 2. After Au had been deposited as an adhesive and subcollector material both on the DHBT layers and a 3-inch SiC substrate, they were bonded by SAB. This bonding technique can prevent thermal degradation of the epitaxial layers because of its low bonding temperature (~150oC) [2]. After the removal of the InP substrate, DHBTs with emitter widths of 0.25 μm and 0.5 μm were fabricated using the self-aligned process [3]. Figure 3 shows a scanning electron microscope image of a fabricated four-finger DHBT with an emitter finger size of 0.5 μm x 4.0 μm. DHBTs were successfully fabricated on the SiC without any serious problems associated with the bonding process. Figure 4 plots the R th for the fabricated DHBTs as a function of the emitter-finger spacing and finger number. For comparison, the R th for the conventional DHBTs without an Au subcollector fabricated on an InP substrate is also plotted. Here, the R th was estimated by following Ref. [4] and normalized by the total emitter junction area. For the conventional DHBTs on the InP, decreasing the emitter-finger spacing or increasing the emitter-finger number markedly increases the R th due to increased heat density. On the other hand, such abrupt increases are not observed for the Au-subcollector DHBTs on the SiC. These results clearly show the combination of the Au subcollector and the SiC substrate efficiently transfers the generated heat from the inside of the device to the substrate. The proposed DHBTs exhibit 68% reduction in the R th, compared with the conventional ones when the emitter-finger spacing is reduced to 0.9 μm. Consequently, the multi-finger DHBTs on the SiC possibly operate even at much higher current density. Figure 5 shows collector I-V curves for the four-finger DHBT with a 0.25-μm-wide emitter. As expected, the DHBT on the SiC successfully suppresses the current-gain lowering in the high-V C and high-I C bias regions (~20 mW/μm2). In summary, we fabricated multi-finger InP DHBTs with an Au subcollector on a SiC using the SAB technique. The DHBTs show that the R th is almost independent of the emitter-finger spacing or emitter-finger number. In addition, the fabricated DHBTs exhibit a 68% reduction of R th compared with the conventional ones. The proposed multi-finger DHBT with the SAB technique is very useful in increasing the operation speed and decreasing the chip size of ICs.

The effects of gamma irradiation on neutron displacement sensitivity of lateral PNP bipolar transistors

The effects of gamma irradiation on neutron displacement sensitivity of four types of lateral PNP bipolar transistors (LPNPs) with different neutral base widths, emitter widths and the doping concentrations of the epitaxial base region are studied. The physical mechanisms of the effects are explored by defect analysis using deep level transient spectroscopy (DLTS) techniques and numerical simulations of recombination process in the base region of the lateral PNP bipolar transistors, and are verified by the experiments on gate-controlled lateral PNP bipolar transistors (GCLPNPs) manufactured in the identical commercial bipolar process with different gate bias voltage. The results indicate that gamma irradiation increases neutron displacement damage sensitivity of lateral PNP bipolar transistors and the mechanism of this phenomenon is that positive charge induced by gamma irradiation enhances the recombination process in the defects induced by neutrons in the base region, leading to larger recombination component of base current and greater gain degradation.

Improved Model for Increased Surface Recombination Current in Irradiated Bipolar Junction Transistors

Current gain degradation in irradiated bipolar junction transistors is primarily due to excess base current caused by enhanced carrier recombination in the emitter-base space-charge region (SCR). Radiation-induced traps at the interface between silicon and the bipolar base oxide facilitate the recombination process primarily above the sensitive emitter-base junction. This leads to an increase in surface recombination current in the SCR, which is a non-ideal component of the BJT's base current characteristic under active bias conditions. In this paper, we derive a precise analytical model for surface recombination current that captures bias dependencies typically omitted from traditional models. This improved model is validated by comparisons to these traditional approaches.