Carrier Removal Effects Research Articles

Effect of heavy ion radiation on low frequency noise characteristics of AlGaN/GaN high electron mobility transistors

AlGaN/GaN high election mobility transistor (HEMT) has important application prospects in satellite communication, radar, nuclear reactors and other extreme environments, owing to its excellent electrical performance and strong radiation resistance. Heavy ion radiation mainly causes single-event effect and displacement damage effect in AlGaN/GaN HEMT device. In this work, the displacement damage defects introduced by heavy ion radiation are analyzed in detail. With the increase of heavy ion radiation influence, more defects are introduced by displacement damage. These defects reduce the two-dimensional electron gas (2DEG) concentration through carrier capture and removal effect, and reduce the carrier mobility through scattering mechanism, resulting in gradual degradation of the electrical characteristics of the device. In this work, AlGaN/GaN high electron mobility transistors are irradiated by <sup>181</sup>Ta<sup>32+</sup> ions with fluences of 1×10<sup>8</sup> ions/cm<sup>2</sup>, 1×10<sup>9</sup> ions/cm<sup>2</sup> and 1×10<sup>10</sup> ions/cm<sup>2</sup>. The electrical characteristics, EMMI and low-frequency noise characteristics of the device before and after heavy ion radiation are measured. The results show that heavy ion radiation can lead to the degradation of electrical parameters. When the heavy ion radiation dose reaches 1×10<sup>10</sup> ions/cm<sup>2</sup>, the electrical characteristics of the device deteriorate seriously, the threshold voltage shifts forward by 25%, and the drain saturation current deteriorates obviously. The defect locations introduced by irradiation are analyzed by EMMI test, and it is found that the number of “hot spots” increases significantly after the having been irradiated by heavy ions with a fluence of 1×10<sup>10</sup> ions/cm<sup>2</sup>, indicating that the radiation leads to the increase of defect density and serious damage to the device. Through the noise test, it is found that with the increase of the radiation fluence, the current noise power spectral density gradually increases. When the fluence reaches 1×10<sup>10</sup> ions/cm<sup>2</sup>, the defect density increases to 3.19×10<sup>18</sup> cm<sup>–3</sup>·eV<sup>–1</sup>, and the Hooge parameter increases after having been irradiated by heavy ions. We believe that the radiation leads to the defect density and parasitic series resistance of AlGaN/GaN HEMT device to increases, resulting in larger Hooge parameters. Through analyzing the variation of the normalized power spectral density of the drain current noise with bias voltage, it is found that the defects caused by heavy ion radiation will cause the parasitic series resistance to increase.

Trap and carrier removal study of 4J InGaP/InGaAs-GaAsP MQW/InGaAsNSb/Ge high efficient space solar cell using advanced physical models

We propose a novel 4J InGaP/InGaAs-GaAsP MQW/InGaAsNSb/Ge solar cell design, which can provide optimum efficiency under the influence of space irradiation. Under 1-sun AM0 spectrum, the device efficiency is obtained to be 40 %. The impact of carrier removal and deep level traps on the device parameters (Jsc, Voc, and η) is mainly emphasized in this paper. Using APSYS from crosslight Inc, the trap related parameters are defined for each trap concentration from 1 × 1013 cm−3 to 1 × 1018 cm−3. The multiple quantum wells (MQW) inserted in the intrinsic region of the GaAs p-i-n subcell provided a strong electric field for carrier collection. The visualization of carrier removal effect on device electric field became possible using 3D surface and 2D contour plots. Finally, we present EQE of each subcell, peak efficiency value, and maximum power for the proposed device. With the inclusion of 1 × 104 cm/s surface recombination velocity, 1 × 1016 cm−3 trap concentration, 1 × 1016 cm−3 background doping in the MQW intrinsic region, the peak efficiency is obtained to be 46 % at 600 sun concentration.

Temperature-dependent electrical characteristics of neutron-irradiated GaN Schottky barrier diodes

Temperature-dependent electrical characteristics were explicitly investigated for a 400-μm diameter neutron-irradiated (NI) GaN Schottky barrier diode (SBD). Based on C-V measurements, a marked decrease in electron concentration has been revealed for the NI diode compared with the pristine sample, suggesting a thermal-enhanced carrier removal effect. Neutron irradiation causes noticeable Schottky barrier height inhomogeneity, which was studied by a two-barrier model. Data indicates that neutron irradiation affects a small but measurable suppression of leakage current as well as low frequency noise level. Despite a new deep-level trap was identified, the temperature-dependent electrical results specified GaN SBD's outstanding resistance to neutron irradiations and robustness in extreme operation temperatures.

A comparative study on radiation reliability of composite channel InP high electron mobility transistors* *Project supported by the National Natural Science Foundationof China (Grant No. 11775191), the Natural Science Foundation of Henan Province, China (Grant No. 202300410379), the Promotion Funding for Excellent Young Backbone Teacher of Henan Province, China (Grant No. 2019GGJS017), Key Technologies Research and Development Program of Henan

This paper proposes a reasonable radiation-resistant composite channel structure for InP HEMTs. The simulation results show that the composite channel structure has excellent electrical properties due to increased modulation doping efficiency and carrier confinement. Moreover, the direct current (DC) and radio frequency (RF) characteristics and their reliability between the single channel structure and the composite channel structure after 75-keV proton irradiation are compared in detail. The results show that the composite channel structure has excellent radiation tolerance. Mechanism analysis demonstrates that the composite channel structure weakens the carrier removal effect. This phenomenon can account for the increase of native carrier and the decrease of defect capture rate.

Enhancement of radiation hardness of InP-based HEMT with double Si-doped plane**Project supported by the National Natural Science Foundation of China (Grant Nos. 11775191, 61404115, 61434006, and 11475256) and the Promotion Funding for Excellent Young Backbone Teacher of Henan Province, China (Grant No. 2019GGJS017).

An anti-radiation structure of InP-based high electron mobility transistor (HEMT) has been proposed and optimized with double Si-doped planes. The additional Si-doped plane under channel layer has made a huge promotion in channel current, transconductance, current gain cut-off frequency, and maximum oscillation frequency of InP-based HEMTs. Moreover, direct current (DC) and radio frequency (RF) characteristic properties and their reduction rates have been compared in detail between single Si-doped and double Si-doped structures after 75-keV proton irradiation with dose of 5 × 1011 cm−2, 1 × 1012 cm−2, and 5 × 1012 cm−2. DC and RF characteristics for both structures are observed to decrease gradually as irradiation dose rises, which particularly show a drastic drop at dose of 5 × 1012 cm−2. Besides, characteristic degradation degree of the double Si-doped structure is significantly lower than that of the single Si-doped structure, especially at large proton irradiation dose. The enhancement of proton radiation tolerance by the insertion of another Si-doped plane could be accounted for the tremendously increased native carriers, which are bound to weaken substantially the carrier removal effect by irradiation-induced defects.

Response of Waveguide-Integrated Germanium-on-Silicon p-i-n Photodiodes to Neutron Displacement Damage

The effects of 14-MeV neutron displacement damage (DD) on waveguide (WG)-integrated germanium-on-silicon p-i-n photodiodes (PDs) for silicon photonics have been investigated up to the fluences of $7.5\times 10^{12}$ n/cm2 (14 MeV) or $1.4\times 10^{13}\,\,\text{n}_{1\text {-MeV}_{\mathrm{ eq}}}$ /cm2(Si). This article includes the measurements of dark current–voltage characteristics across temperature from 150 to 375 K, measurements of PD junction capacitance, spectral response measurements from 1260 to 1360 nm, and frequency-response measurements. The devices are found to be susceptible to DD-induced carrier removal effects; however, they also continue to operate without meaningful impact to performance for the DD dose levels examined. Since the PD test chips include silicon photonic integrated grating couplers and WGs, which carry the optical signal to the PD, some assessment of the impact of DD on these passive devices can also be inferred. This article does not examine the short-term annealing or transient behavior of the DD, and instead, it has only considered the lasting damage that remains after any initial period of room-temperature annealing.

Study of 14.9 MeV Neutron Irradiation Effects on Ni/GaN Schottky Contacts Using Low‐Frequency Noise Spectroscopy

A thorough study of 14.9 MeV neutron irradiation effects on Ni/GaN Schottky contacts is reported. The electrical characteristics and low‐frequency noise (LFN) spectra of the irradiated devices are measured and analyzed. The fast neutron irradiation shows an obvious carrier removal effect on the n−‐GaN with a carrier removal rate of ≈5.5 cm−1, resulting in significantly decreased forward currents of the irradiated devices. The irradiation also increases the inhomogeneity of the Schottky barrier by creating extra trap states at the Ni/GaN interface, according to the temperature–dependent current–voltage (I–V–T) measurements. The LFN analysis reveals an appearance of Lorentzian noise in the irradiated devices, suggesting that one dominant type of trap states located at around 0.52 eV below the conduction band is generated by the 14.9 MeV fast neutron irradiation in the Ni/GaN Schottky contacts.

Modeling of InGaP/InGaAs-GaAsP/Ge multiple quantum well solar cell to improve efficiency for space applications

Multiple quantum wells (MQWs) are incorporated in the current limiting middle subcell of standard InGaP/InGaAs/Ge multi-junction solar cell (MJSC). Considering a realistic radiation dose in geo-stationary orbits (1 MeV electron irradiation-1 × 1016 cm−2 fluence), carrier lifetime is calculated and defined in the top cell and middle subcell region. The thermionic emission and recombination lifetimes are taken into consideration while defining lifetime in the middle MQW region. The physical thickness of quantum well (QW) and quantum barrier (QB) are slightly adjusted to numerically satisfy the strain balancing condition and to achieve higher efficiency at 1-sun (AM0 spectrum). In addition to interface recombination, carrier removal effects were taken into consideration by changing the intrinsic region in the PiN middle subcell into n-type. With the nonidealities taken into consideration, the proposed device exhibits an efficiency of 32% at 1-sun AM0 radiation and a peak efficiency of 37.63% at concentrated sunlight. Trap concentration of 1 × 1017 cm−3 in top cell with 10 ns lifetime defined in the middle cell emitter, base and MQW region is obtained as threshold point beyond which the device exhibits significant degradation.

Study of deep level defects in InGaP/InGaAs-GaAsP/InGaAsN quantum well based multi-junction solar cell using finite element analysis

Degradation analysis of a quantum well-dilute nitride based multi-junction solar cell is presented using a 2D numerical device simulator: APSYS. By taking carrier removal effects into consideration, the proposed device exhibits strong electric field uniformity within the intrinsic region of the p-i-n middle cell. The electron traps are defined in the top InGaP and bottom InGaAsN base region considering 1 MeV electron irradiation in geostationary orbits. Considering thermionic emission, tunneling and SRH lifetime an effective lifetime value of 16.7 ps is considered in the middle MQW region. A record efficiency value of 38% and 44% is obtained at 1-sun and 500-sun AM0 spectrum respectively. The same efficiency value dropped by 4% by introducing a realistic SRV (1 × 104 cm s−1) and trap concentration values (1 × 1016 cm−3). Finally, we illustrate the influence of traps and lifetime on overall cell Jsc, Voc, η, and power density.

Electron Radiation Effects on the 4H-SiC PiN Diodes Characteristics: An Insight From Point Defects to Electrical Degradation

Silicon carbide (SiC) devices have shown substantial promise in realizing ultrahigh-voltage and high power, and have been usually considered as a potential candidate for high radiation levels applications. However, in this work it is found that the SiC P-intrinsic-N (PiN) diodes are sensitive to the electron irradiation, which exerts significant influence on the device characteristics. The physical mechanisms behind these behaviors are studied by probing the production of point defects and the evolution of carrier lifetime in the SiC epilayers after irradiation. It is found that the forward current is significantly reduced by irradiation and the specific on-resistance monotonously increases with the increasing electron fluences, which is resulted from the deteriorated conductivity modulation effects in the epilayer due to the enhanced carrier recombination from the radiation induced deep-level defects, such as the carbon vacancy (VC), silicon vacancy (VSi) and VC+VSi complexes. Inversely, no significant change is observed in the reverse leakage current of 4H-SiC PiN diodes, and the breakdown voltage even slightly increases after electron irradiation, which are ascribed to the suppressed carrier generation arising from the point defects in 4H-SiC with a wide bandgap and the carrier-removal effects caused by the acceptor like point defects generated during irradiation, respectively.

The Effects of Thermal Neutron Irradiation on Current-Voltage and Capacitance-Voltage Characteristics of Au/n-Si/Ag Schottky Barrier Diodes

To observe the neutron transmutation and displacement damage effects, Au/n-Si/Ag Schottky barrier diodes were exposed to thermal neutron irradiation. Irradiation induced changes in Schottky barrier height, saturation current, and donor concentration were investigated by using current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the diodes. The irradiation for 10 s caused a little change in the Schottky diode parameters which were obtained from I-V and C-V measurements. Observable changes in the parameters occurred after the second irradiation of 30 s duration. After the total dose, an increase in saturation current and barrier height inhomogeneties took into place and a decrease in carrier concentration was observed due to the carrier removal effect of thermal neutron-induced damages. Whereas the values of zero bias barrier height have little change after irradiations, the values of ideality factor increased after irradiations. The values of zero-bias barrier height for all diodes was also calculated from reverse bias current characteristics. After second dose, the values of zero-bias barrier height decreased for all diodes. The values of series resistance were determined by Cheung functions before and after irradiations. Before irradiations, the values were found between 2.10 kΩ and 2.76 kΩ. After second dose, the values of series resistance of all diodes decreased and were found between 1.59 kΩ and 2.20 kΩ. Furthermore, the proof of thermal neutron transmutation of elements in the devices was given via energy dispersive spectroscopy (EDS) mapping.

Multiple Angle Analysis of 30-MeV Silicon Ion Beam Radiation Effects on InGaN/GaN Multiple Quantum Wells Blue Light-Emitting Diodes

High-resolution X-ray diffraction, temperature-dependent photoluminescence (PL), time-resolved PL, and positron annihilation spectroscopy are employed to investigate the degradation mechanism of InGaN/GaN multiple quantum wells (MQWs) light-emitting diodes (LEDs) under silicon ion irradiation. Reduction of the quantum-confined Stark effect due to crystalline strain relaxation, enhancement of indium localization due to thermal spike, generation of nonradiative recombination centers (NRCs), and carrier removal effect due to atom displacement are revealed to be critical factors in LEDs postirradiation performance. New NRCs are proven to be the main reason for the degradation of the internal quantum efficiency of MQWs. The increase of the threshold voltage and leakage current in LEDs are caused by the carrier removal effect and new defects in bandgap induced by radiation. In addition, new NRCs are found to appear earlier than indium localization and carrier removal effect with increasing silicon ion fluence. Atom displacement defects are revealed to be located mainly in p-type GaN and MQWs layers. Radiation-induced nitrogen vacancies are considered compensation donors in p-type GaN, whereas all other nitrogen and gallium-related defects are NRCs in MQWs.

Characterization of bulk traps and interface states in AlGaN/GaN heterostructure under proton irradiation

This paper provides a systematic study on the bulk traps and interface states in a typical AlGaN/GaN Schottky structure under proton irradiation. After 3 MeV proton irradiation with a dose of 5 × 1014 H+/cm2, a positive flat band voltage shift of 0.3 V is observed according to the capacitance-voltage (C-V) measurements. Based on this, the distribution of electrons across AlGaN and GaN layers is extracted. Associated with the numerical calculation, direct experimental evidences demonstrate that the bulk traps within the AlGaN layer dominate the carrier removal effect under proton irradiation. Furthermore, the effects of proton irradiation on AlGaN/GaN interface states were investigated by utilizing the frequency dependent conductance technique. The time constants are extracted, which increase from 1.10–2.53 μs to 3.46–37 μs after irradiation. Meanwhile, it shows that the density of interface states increases from 9.45 × 1011–1.70 × 1013 cm−2·eV−1 to 1.8 × 1012–1.8 × 1013 cm−2·eV−1 with an increase in trap activation energy from 0.34 eV–0.32 eV to 0.41 eV–0.35 eV after irradiation. The Coulomb scattering effect of electron trapping at interface states with deeper energy levels is utilized to explain the mobility degradation in this paper.

Proton Irradiation Effect on InP‐Based High Electron Mobility Transistor by Numerical Simulation with Non‐Uniform Induced Acceptor‐Like Defects

In this paper, an improved charge control model is proposed to investigate the effect of proton irradiation on InP‐based high electron mobility transistor (HEMT) with fluence varying among 0, 1 × 1011, 5 × 1011, 1 × 1012, and 2 × 1012 cm−2. The non‐uniform acceptor‐like defects in InAlAs/InGaAs hetero‐junction layers have been taken into account in the charge control model of the device after proton irradiation. The simulated characteristics by the charge control model have shown compatible trend with experimental data. The calculated results show that the channel current, transconductance, and current gain cutoff frequency depict a decline trend with the increase of proton fluence, and the pinch‐off voltage drifts toward positive value. Moreover, the performances gradually begin to degrade after the proton fluence reaches 5 × 1011 cm−2, and deteriorate dramatically with proton fluence up to 2 × 1012 cm−2. The observed obvious variation of electrical properties with different proton fluence could be accounted for by the carrier sheet density reduction, which is a result of the carrier removal effect from induced As acceptor‐like defects.

Effect of 60Co γ-ray irradiation on electrical properties of Ti/Au/GaAs1−xNx Schottky diodes

Current-voltage (I-V), capacitance-voltage-frequency (C-V-f) and conductance-voltage-frequency (G/ω-V-f) measurements at room temperature are used to study 50 kGy 60Co γ-ray electrical properties irradiation dependence of Ti/Au/GaAs1−xNx Schottky diodes with 0.2%; 0.4%; 0.8% and 1.2% nitrogen dilution. This γ-ray irradiation induces a permanent damage that has increased ideality factor and series resistance for all samples. It was accompanied by a decrease in Schottky barrier height with nitrogen content up to 0.4%N and remained constant thereafter. Radiation was also found to degrade the reverse leakage current.At high frequency (1 MHz), capacitance and conductance decreased after radiation due to a decrease in net doping concentration. Interface state density and series resistance were determined from C-V-f and G/ω-V-f characteristics using Hill-Coleman methods. Interface states density exponentially decreased with increasing frequency confirming the behavior of interface traps response to ac signal.Series resistance increases after irradiation is attributed to carrier's removal effect and mobility degradation. It has two peaks in the accumulation and inversion region for some diodes (0.4%N, 0.8%N). γ-ray irradiation produced traps levels and recombination centers that reduce relaxation time. An increase in %N content can impede irradiation damage with even some compensation when the percent of diluted nitrogen is high (1.2%N).

Quantum-Well Solar Cells for Space: The Impact of Carrier Removal on End-of-Life Device Performance

In this paper, a detailed analysis on the radiation response of solar cells with multi quantum wells (MQW) included in the quasi-intrinsic region between the emitter and the base layer is presented. While the primary source of radiation damage of photovoltaic devices is minority carrier lifetime reduction, we found that in the case of MQW devices, carrier removal (CR) effects are also observed. Experimental measurements and numerical simulations reveal that with increasing radiation dose, CR can cause the initially quasi-intrinsic background doping of the MQW region to become specifically n- or p-type. This can result in a significant narrowing and even the collapse of the electric field between the emitter and the base where the MQWs are located. The implications of the CR-induced modification of the electric field on the current-voltage characteristics and on the collection efficiency of carriers generated within the emitter, the MQW region, and the base are discussed for different radiation dose conditions. This paper concludes with a discussion of improved radiation hard MQW device designs.

Ion-induced changes in semiconductor properties of hydrogenated amorphous silicon

Undoped, phosphorus doped (n-type), and boron doped (p-type) hydrogenated amorphous silicon (a-Si:H) thin films are irradiated with 3.0MeV protons, 100keV protons, and 2.8MeV silicon ions, and the electric conductivity variations as a function of ion fluence are investigated. The Seebeck coefficient variations as a function of ion fluence are also investigated and are compared to the electric conductivity variations. As a result, a systematic interpretation of radiation effects on a-Si:H semiconductors is obtained. In the fluence regime of below 10−6dpa, the increase in electric conductivity and the emergence of negative Seebeck effect are observed in the undoped a-Si:H because of donor-center generation. In the fluence regime from 10−6dpa to 10−4dpa, the decrease in electric conductivity and the decrease in absolute value of Seebeck coefficient are observed in the doped a-Si:H, since the carrier removal effect is caused by radiation defects, which are thought to be mainly dangling bonds. In the fluence regime of above 10−4dpa, the increase in electric conductivity caused by the enhancement of hopping transport via localized states is observed. The absolute value of Seebeck coefficient of doped a-Si:H decreases in this fluence regime, whereas no Seebeck effect is observed in the undoped a-Si:H.

Electronic Transport Transition of Hydrogenated Amorphous Silicon Irradiated With Self Ions

Electric conductivity variations of hydrogenated amorphous silicon due to self-ion irradiation, i.e. irradiation with Si or H ions, are comprehensively investigated. The anomalous enhancement of dark conductivity (DC) and photoconductivity (PC) are firstly observed due to proton irradiation in the cases of undoped and n-type a-Si:Hs, and after that both decrease with increasing the irradiation fluence. However, Si ion irradiation does not induce the anomalous enhancement and induce a monotonic decrease in DC and PC in the low fluence regime. It is shown from the Seebeck effect analysis that the anomalous enhancement is caused by generation of donor-centers which have metastable nature at room temperature. The decrease in DC and PC is ascribed to the carrier removal effect and the carrier lifetime decrease accompanied by accumulation of dangling bonds, respectively. However, further irradiation causes the loss of photoconduction and the drastic increase in DC. This indicates that the dominant conduction mechanism changes from the band transport to the hopping transport due to excessive accumulation of dangling bonds. The change in the dominant conduction mechanism occurs at above about 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> dpa (displacement per atom) and is independent of the majority carrier concentration before irradiation. It is concluded that the conductivity variations caused by self-ion irradiation can be systematically categorized according to the ratio of the nuclear energy deposition to the electronic energy deposition of incident ions.

Electric properties of undoped hydrogenated amorphous silicon semiconductors irradiated with self-ions

This paper reports dark conductivity (DC), photoconductivity (PC), and Seebeck coefficient variations of undoped hydrogenated amorphous silicon semiconductors irradiated with protons and Si ions. Both the DC and PC values show nonmonotonic variations with increasing a fluence in the case of proton irradiation, whereas the monotonic decreases are observed in the case of Si ion irradiation. From results of the Seebeck coefficient variation due to proton irradiation, it is shown that the increase in DC and PC in the low fluence regime is caused by donor-center generation. Also, it is shown by analyzing the proton energy dependence and the energy deposition process that the donor-center generation is based on the electronic excitation effect. On the other hand, the decrease in DC and PC in the high fluence regime is attributed to the carrier removal effect and the carrier lifetime decrease due to the accumulation of dangling bonds, respectively. The dangling bond generation due to ion irradiation is mainly caused by the displacement damage effect and therefore it is different from the generation process in the Staebler–Wronski effect.

Irradiation induced degradation of high-speed response of Si p/sup +/-i-n/sup +/ photodiodes studied by pulsed laser measurements

High-speed photodetectors such as Si p/sup +/-i-n/sup +/ photodiodes are the primary components responsible for bit error rate reduction in optical links used in radiation-hard environments. In this paper, we examine degradation in the high-speed characteristics of a 1.5-GHz Si p/sup +/-i-n/sup +/ photodiode subjected to 2-MeV electron irradiation. IV, CV, and pulsed laser measurements are all performed as a function of electron fluence. Degradation in the pulsed operation is explained in terms of carrier removal effects on depletion width and base resistivity. Trapping and lifetime effects are also briefly discussed.