Carrier Removal Rate Research Articles

On the ?-Particle Irradiation Effects in MESFETs

α-particle irradiation investigations have been carried out on various structure GaAs metal-semiconductor field-effect transistors. The device characteristics were measured before irradiation and after α-particle irradiation with fluences ranging from 5×1010 to 3×1012 cm-2. The carrier removal rate was found to be independent of the doping level as determined from Schottky diodes and device parameters. Five traps were found to be introduced by irradiation. Two of them were found to determine the temperature dependence of drain current. The threshold voltage shift was modeled taking into account the degradation of the channel carrier removal, the gate barrier height and the channel-substrate space charge region width.

Variation of Carrier Removal Rate with Irradiation Dose in Fast-Pile Neutron Irradiated n-Si

Variation of Carrier Removal Rate with Irradiation Dose in Fast-Pile Neutron Irradiated n-Si

Effect of Electron Irradiation on Properties of CuInSe2 Thin Films

Effects of 2MeV electron irradiation on electrical properties of CuInSe2 thin films have been investigated, n-type CuInSe2 films in which carrier concentration were about 2×1017cm-3, were epitaxially grown on GaAs(001) substrate by RF diode sputtering. No significant change in the electrical properties was observed under the electron fluence less than 1016cm-2. As the electron fluence exceeded 1017cm-2, both carrier concentration and Hall mobility slightly decreased. The carrier removal rate was determined to be about 1cm-1, which is lower, compared to III-V compound materials.

Demonstration of an SiC neutron detector for high-radiation environments

Neutron response studies have been performed on Schottky diodes fabricated using 4H-SiC material. These studies indicate that neutron detection using SiC diodes is possible without significant degradation in the energy resolution, noise characteristics or, most importantly, the neutron counting rate even after exposure to neutron fluences of 3.4/spl times/10/sup 17/ n/sub th//cm/sup 2/ (1/spl times/10/sup 17/ n/sub fast//cm/sup 2/; E/sub n.fast/>1 MeV), the highest yet examined. The results represent orders of magnitude increased device lifetime in neutron fields compared to commercial silicon based detectors. Additionally, detector response was found to be linear up to thermal neutron fluxes of 2000 n/sub th//cm/sup 2//s. However, degradation in the charge collection efficiency due to neutron damage-induced defects prevented self-biased operation after exposures above /spl sim/5.7/spl times/10/sup 16/ n/sub th//cm/sup 2/. A carrier removal rate of 9.7/spl plusmn/0.7 cm/sup -1/ was calculated from C-V doping profile measurements on neutron irradiated samples. These results demonstrate the viability of SiC-based detectors for a variety of radiation monitoring applications.

A detailed model to improve the radiation-resistance of Si space solar cells

An accurate radiation degradation model, based on measured radiation damage to devices and physical principles on radiation-induced defects in Si, has been established to improve the radiation-resistance of the Czochralski (CZ)-grown and floating-zone (FZ)-grown single-crystal Si space solar cells. We have successfully carried out the optimization of radiation-resistant Si space solar cells by taking into account the effective base carrier concentration dependence of the most important analytical parameters, damage coefficient K/sub L/, for the minority-carrier diffusion length and carrier removal rate R/sub c/ for majority-carriers. The model can be used to adequately predict the radiation degradation of the Si solar cells irradiated with a complete spectrum of electron fluence. It has been established that the radiation-resistance of the silicon solar cell is very dependent on effective carrier concentration in the high fluence range and irradiation tolerance can be improved further by varying the base carrier concentration upon irradiation.

Carrier removal in p-type InP

Electron and proton carrier removal rates due to 1 MeV electrons, 3 and 10 MeV protons, and 2 MeV alpha particles in p-type InP are found to be linearly proportional to nonionizing energy loss and independent of the initial carrier concentration over the range from 10/sup 16/ to 4/spl times/10/sup 17/ cm/sup -3/.

Radiation response of heteroepitaxial n+p InP/Si solar cells

The effect of 1 MeV electron and 3 MeV proton irradiation on the performance of n+p InP solar cells grown heteroepitaxially on Si (InP/Si) substrates is presented. The radiation response of the cells was characterized by a comprehensive series of measurements of current versus voltage (I–V), capacitance versus voltage (C–V), quantum efficiency (QE), and deep level transient spectroscopy (DLTS). The degradation of the photovoltaic response of the cells, measured under simulated 1 sun, AM0 solar illumination, is analyzed in terms of displacement damage dose (Dd) which enables a characteristic degradation curve to be determined. This curve is used to accurately predict measured cell degradation under proton irradiation with energies from 4.5 down to 1 MeV. From the QE measurements, the base minority carrier diffusion length is determined as a function of particle fluence, and a diffusion length damage coefficient is calculated. From the C–V measurements, the radiation-induced carrier removal rate in the base region of the cells is determined. The DLTS data show the electron and proton irradiations to produce essentially the same defect spectra, and the spectra are essentially the same as observed in irradiated homoepitaxial n+p InP. From the DLTS data, the introduction rate of each defect level is determined. From the dark I–V curves, the effect of irradiation on the various contributions to the dark current are determined. The data are analyzed, and a detailed description of the physical mechanisms for the radiation response of these cells is given. The results enable a model to be developed for the radiation response of the cells.

Electron and proton irradiation-induced degradation of epitaxial InP solar cells

The degradation of epitaxial, shallow homojunction n +p InP solar cells under 1 MeV electron and 3 MeV proton irradiation is presented. The data measured under 3 MeV proton irradiation are analyzed in terms of displacement damage dose which is the product of the particle fluence and the calculated non-ionizing energy loss (NIEL)[1]. A characteristic proton degradation curve is derived from which the cell degradation under any energy proton irradiation can be calculated. The data measured under 1 MeV electron irradiation is also analyzed in terms of displacement damage dose. The electron irradiation-induced degradation is correlated with the proton degradation curve by determining electron to proton dose ratios for each of the photovoltaic (PV) parameters. A comparison of the characteristic degradation curves for InP and GaAs/Ge solar cells, which was determined previously, shows InP to be intrinsically more resistant to displacement energy deposition. The base carrier concentration was measured during the irradiations, and significant carrier removal was observed. When analyzed as a function of displacement damage dose, the reduction in carrier concentration under both the 1 MeV electron and the 3 MeV proton irradiation is shown to follow the same degradation curve. From this common degradation curve, a characteristic carrier removal rate is calculated for InP under any irradiation. The junction dark current was also measured during both irradiations, and the data were fit to a three-term diode dark current equation. From the fits, the diffusion current is determined as a function of particle fluence. Changes in the diffusion current under electron and proton irradiation are shown to correlate in terms of displacement damage dose in the same way as the cell maximum power. The junction recombination current is also determined from the dark current data, and the results show the energy level of the dominant radiation-induced recombination center to be approximately the same in both the electron and proton irradiated samples. In addition, the dark current analysis indicates that the relative changes in the hole and electron lifetimes are essentially the same under both the electron and the proton irradiations. Based on these results and the overall correlation between the electron and proton damage, a detailed description of the mechanism of the radiation response of InP is developed which describes the cell degradation under any particle irradiation.

Implantation isolation in n-type InP bombarded with He + and B +

An extensive study has been carried out to investigate the changes in the electrical properties of n-type InP, doped in the range 2.5 × 10 16–1 × 10 18 cm −3, and bombarded with 55 keV He + and 125 keV B +. The carrier concentration initially decreases with ion dose and reaches a minimum at a dose of ∼ 5 × 10 13 cm −2 for He + and 1 × 10 13 cm −2 for B + irradiation. The dose where the minimum occurs for each ion and the magnitude of the minimum carrier concentration is independent of the initial carrier concentration. However, at doses below this minimum the carrier removal rate is directly dependant on the carrier concentration. At higher doses the electrical properties are dominated by radiation defects and are independent of initial doping. These results are discussed in terms of the production of defects and defect/dopant interactions.

Deep level defects in alpha particle irradiated 6H silicon carbide

A deep level transient spectroscopy study of native and radiation induced defects in metal organic chemical vapor deposition n on p 6H-SiC diodes has been conducted. Three majority carrier levels were found, at Ev+0.50, +0.55, and +0.69 eV, and three minority carrier deep levels were found, at Ec −0.38, −0.48, and −0.58 eV. These six levels were initially observed in the unirradiated materials. Their concentration increased 2 to 13-fold after irradiation to a fluence of 2×1011 cm−2 of 5.5 MeV alpha particles. In addition the carrier removal was monitored during irradiation, and a carrier removal rate of 7.8×104 cm−1 for 5.5 MeV alpha particles was measured. When compared with a similar study of alpha particle irradiation of InP, the results suggest that SiC has radiation resistance comparable to that of InP, another highly radiation resistant semiconductor.

Comparison of the radiation resistance of electron irradiated indium phosphide grown by metal-organic chemical-vapor deposition and liquid encapsulated Czochralski

Electrical characterization has been carried out on electron irradiated InP grown by metal-organic chemical-vapor deposition (MOCVD) and liquid encapsulated Czochralski (LEC), through I–V (–T), C–V, deep level transient spectroscopy (DLTS) and admittance spectroscopy measurements and the resistance to electron radiation for these two materials has been compared. It was found that MOCVD-InP was more resistant to electron radiation than LEC-InP, as demonstrated by the lower carrier removal rate and change of series resistance in the MOCVD-InP diodes as a result of electron radiation. The introduction rates for the dominant hole defects H3 and H4 and for additional electron defect states were found to be similar for both materials, but were insufficient to explain the degree of degradation of solar cell efficiency incurred by these known defects. A new defect, HD1, has been found to be responsible for the high carrier removal rate and the introduction of a large series resistance which accounts for the difference of radiation hardness between these two materials. The results again show that the dominant irradiation defects in InP are not the defects H3 and H4 as is usually accepted, but the new found defect HD1, which was undetected by the DLTS technique.

Analysis of neutron damage in high-temperature silicon carbide JFETs

Neutron-induced displacement damage effects in n-channel, depletion-mode junction-field-effect transistors (JFETs) fabricated on 6H-silicon carbide are reported as a function of temperature from room temperature (RT) to 300/spl deg/C. The data are analyzed in terms of a refined model that folds in recently reported information on the two-level ionization energy structure of the nitrogen donors. A value of 5/spl plusmn/1 cm/sup -3/ per n/cm/sup 2/ is obtained for the deep-level defect introduction rate induced by the neutron irradiation. Due to partial ionization of the donor atoms at RT, the carrier removal rate is a function of temperature, varying from 3.5 cm/sup -1/ at RT to 4.75 cm/sup -1/ at 300/spl deg/C. The relative neutron effect on carrier mobility varies with temperature approximately as T/sup -7/2/, dropping by an order of magnitude at 300/spl deg/C compared with the RT effect. The results offer further support for the use of SiC devices in applications which combine high-temperature and severe radiation environments, where the use of Si and GaAs technologies is limited. >

Deep level defects and carrier removal due to proton and alpha particle irradiation of InP

Deep level transient spectroscopy and capacitance voltage measurements of the defect introduction rates and carrier removal rates for 2 MeV proton and 2 MeV alpha particle irradiations in p-type InP have been performed. The carrier removal rate for 2 MeV protons was 6500 cm−1 and for 2 MeV alpha particles was 73 400 cm−1, or 12 times higher. The defect introduction rates for H4, the predominant radiation induced defect in p-type InP, were 229 per 2 MeV proton and 9000 per 2 MeV alpha particle, or 39 times higher for alpha irradiation. The very large rates of carrier removal and high defect introduction rates in the latter case may limit the usefulness of InP in a radiation environment containing high energy alpha particles.

Silicon carbide JFET radiation response

Total dose and neutron-induced displacement damage effect studies are reported for n-channel, 2- mu m channel length, depletion mode junction-field-effect-transistors (JFETs) fabricated on 6H-silicon carbide. Very little effect was observed on device characteristics for total dose ionizing radiation for doses up to 100 Mrads(Si), but the devices were significantly degraded after a neutron fluence of 10/sup 16/ n/cm/sup 2/. A value of 4.5+or-0.5 carriers/cm/sup 3//neutrons/cm was obtained for the carrier removal rate from neutron irradiation. The results offer promise for SiC devices to be used in applications which combine high-temperature and radiation environments, where the use of Si and GaAs technologies is limited.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Positron Annihilation and Electron Spin Resonance of Electron-Irradiated 3C-SiC

ABSTRACTPositron annihilation and electron spin resonance (ESR) have been used to study defects introduced by lMeV electron irradiation in n-type cubic silicon carbide (3C-SiC) epitaxially grown on Si by chemical vapor deposition. Positron annihilation measurements by using variable-energy positron beams indicated the narrowing of the Doppler-broadened energy spectrum of annihilation gamma-rays and the decrease in the effective diffusion length of positrons with increasing the electron fluence. These results show the formation of vacancy-type defects in 3C-SiC. An ESR spectrum labeled T1, which has an isotropie g-value of 2.0029±0.0001, was observed in electron irradiated 3C-SiC. The T1 spectrum is interpreted by hyperfine interactions of paramagnetic electrons with 13C at four carbon sites and 29Si at twelve silicon sites, leads that the Tl center results from a point defect at a silicon sublattice site. The production rate of the Tl center was in good agreement with the carrier removal rate, indicating that the Tl center captures an electron from the conduction band. All these results are accounted for by the introduction of negatively charged vacancies at silicon sublattice sites in 3C-SiC by the irradiation.

Neutron and proton irradiation of shallow channel GaAs direct-coupled field-effect-transistor logic devices and circuits

Neutron and proton irradiations have been performed on self-aligned GaAs metal-semiconductor field-effect transistors (MESFETs) and resistors utilizing shallow ion-implanted channels. FET threshold voltage shifts during irradiation were lower than reported elsewhere (less than 115 mV for a −0.85 V threshold FET irradiated by 4.3×1014 neutron cm−2). This is shown to be explained by the shallow active layers used. A neutron carrier removal rate between 20 and 25 cm−1 is necessary to fit the FET data. Carrier removal rates derived from resistor damage were 150 cm−1 for peak doping levels of 4×1017 cm−3, greatly in excess of those derived from epitaxial or bulk GaAs resistors, and inconsistent with values obtained from threshold shifts of FETs with identical active layers. Resistor and FET threshold voltage changes for 52 MeV proton irradiation were nearly an order of magnitude greater than for an equivalent dose of 1 MeV (Si) neutrons. The extrapolated worst-case failure dose of direct-coupled FET logic inverters was better than 1.8×1015 neutron cm−2 despite the limited noise margins of this logic scheme.

The efficiency of direct annihilation of resistivity silicon primary radiation defects in high-resistivity silicon

Abstract The change of charge-carrier concentration and lifetime in high-resistivity float-zone n- and p-Si with equilibrium concentrations of electrons n0=(2 to 30)× 1012 cm−3 and holes p0=(5 to 30)× 1011 cm−3 when irradiating by 60Co γ-rays (T= 330 K) is studied. There is a drastic increase of the initial charge- carrier removal rate and the coefficient for the radiation variation of their lifetime. The results obtained are explained on the assumption of the dependence of the annihilation probability of Frenkel pairs on the charge state of vacancy (V) and interstitial Si atom (I).The energetic position of the levels separating the states I0/I++ and V−/V0 which are at Ec −(0.43−0.45) eV and Ec −(0.47−0.54) eV, respectively, is estimated.

Neutron radiation effects in GaAs ion-implanted metal-semiconductor field-effect transistors

Neutron radiation investigations have been carried out on ion-implanted GaAs metal-semiconductor field-effect transistors (MESFETs). Device characteristics were measured before irradiation and following neutron irradiations with fluences from 5×1013 to 2×1015 n/cm2. At 5×1013 n/cm2, the device degradation is negligible, while at 2×1015 n/cm2 the threshold voltage shift was 0.7 V and the device transconductance was 30% of its original value. Degradation parameters needed to explain these results are larger than what has been previously reported; this discrepancy is, in part, due to the nonuniform doping profiles in the FET channel. The details of a new model applicable to nonuniform carrier distributions and to density dependent carrier removal rates are presented and results compared to those in the literature. A carrier removal rate of approximately 20 cm−1 is required to explain the degree of observed device degradation.

AC conductivity measurements for electron-irradiated InSb

Extensive irradiations were carried out on n-type crystalline InSb with 2 MeV electrons at 0 degrees C. The carrier removal rate was estimated from changes in the barrier capacitance and found to be 0.8 cm-1. The introduction of a sufficient quantity of radiation damage allowed the observation of variable-range hopping which obeyed Mott's law sigma varies as exp(-b/T14/). Evidence of electron-electron interaction is presented. For heavy doses of irradiation the value of b increased considerably (b=18) and became comparable with corresponding values for amorphous InSb. The frequency dependence of the hopping conductivity was of the form sigma varies as omega s with s decreasing from s=0.6 as the number of charged defects increased.

Neutron radiation effects in GaAs junction field effect transistors

The effect of high-energy neutrons on GaAs junction field-effect transistors (JFETs) was investigated. The device threshold voltage, transconductance, and saturation current were measured before irradiation and following neutron irradiations with fluences from 6*10/sup 13/ n/cm/sup 2/ to 2*10/sup 15/ n/cm/sup 2/. At 6*10/sup 13/ n/cm/sup 2/ the device degradation was negligible while at 2*10/sup 15/ n/cm/sup 2/ the threshold voltage shift was 0.410 V, and the transconductance and saturation current were degraded to 49% and 17% of their original values, respectively. The threshold voltage shift was successfully modeled by applying nonuniform carrier removal to a Gaussian approximation of the p- and n-type doping profiles of the JFET. An average carrier removal rate of 19 cm/sup -1/ in the n region of the JFET resulted in calculated threshold voltage shifts consistent with those observed experimentally. >