Reverse Current-voltage Characteristics Research Articles

Ski S. V. Influence of gamma irradiation on the reverse current-voltage characteristics of silicon photomultipliers

The study investigated the effect of Co60 gamma-quanta on the reverse current-voltage characteristic (IV) of silicon photomultiplier (SiPMs) with 1004 cells, which themselves were optically isolated from each other n+ –p–p+ -structures. The cells were optically isolated from each other by trenches filled with tungsten after passivation of the walls with SiO2 and Si3N4 layers. Two variants of structural design of SiPMs were studied. Two variants were tested for the trench metal connection in the SiPMs: variant BI connected the trench metal to the n+-region of the cell through a quenching polysilicon resistor, while variant BII connected it to the p+-region. The breakdown voltage of the investigated SiPMs was Ubr = 34 ± 1.0 V. The samples were irradiated in both the active electrical mode (avalanche breakdown mode) and the passive mode (reverse bias Ub = 0 V). It was discovered, that at dose of D = 106 rad, the dark current for SiPM (BI) and (BII) increased by 6–7 times when irradiated in passive mode and by 15–16 times for SiPM (BII) when irradiated in active mode. For SiPM (BI) irradiated in the avalanche breakdown mode, the dark current increased by 104 times at D = 105 rad. The research demonstrates that the radiation-induced degradation of the dark current in the SiPMs under study is due to an increase in the generation and, primarily, surface components. This is a result of the accumulation of positive charge in the insulating layer of the separating trenches.

Rational Doping Strategy to Build the First Solution‐Processed p‐n Homojunction Architecture toward Silicon Quantum Dot Photodetectors

Semiconductor p‐n homojunction is a requisite building block of operating transistors and diodes which make up the modern electronic circuits and optoelectronic applications. However, it has been so far limited to bulk form of single crystals such as silicon (Si) or gallium arsenide. Herein, a brand‐new method of constructing p‐n homojunction architectures that breaks through the limitation is presented. Colloidal inks of p‐type and n‐type Si quantum dots (QDs) are synthesized by thermal disproportionation of (HSiO1.5)n doped with boron or phosphorus, followed by surface ligand engineering. Analysis combining UV photoelectron spectroscopy, electron spin resonance, and current–voltage characteristics confirms that an orthogonal solvent trick makes clean interfaces between n‐type and p‐type SiQD layers without disruption on film formation. The forward and reverse current–voltage characteristics of the diode, along with various spectroscopic characterizations, demonstrate the formation of the first p‐n homojunction of SiQDs. The self‐powered photodiode provides a tunable response specific to the wavelength.

Analysis of barrier inhomogeneities in Ti/p–type strained Si0.95Ge0.05 Schottky diodes using reverse current-voltage characteristics

Extracting electrical parameters such as barrier height inhomogeneities (BHi) from the forward bias can be very challenging in metal/semiconductor (M/Sc) contacts characterized by low barrier height and high series resistance. In this work we demonstrate that the reverse bias characteristics can be used as an efficient alternative method to investigate the inhomogeneity of low barrier height in M/Sc contacts. In particular, the BHi in Ti/p-strained Si0.95Ge0.05 Schottky barrier diodes (SBD) has been investigated using reverse current–voltage-temperature (IR-VR-T) characteristics over the temperature range of 100–300 K. The temperature dependence of the measured barrier heights (ΦRBp) using reverse-bias is successfully explained in terms of a thermionic emission (TE) current transport associated with Gaussian distribution of the barrier height due BHi. The mean homogeneous barrier height (Ф‾RBp) and its corresponding standard deviation (σRs) were determined for different reverse voltages. A decrease in Ф‾RBp and an increase in σRs with increasing reverse bias are observed, indicating a large barrier height distribution upon high applied reverse bias. The deduced average zero-field barrier height (ФFBp≈0.59eV) from IR-VR agrees well with the corresponding value determined from the forward characteristics. Moreover, the reverse bias extracted values for Richardson constant A* based on BHi model, are found in fair agreement with the reported theoretical value of 32 A cm−2 K−2 for our p-type strained Si0.95Ge0.05 alloy. Finally, the results obtained on Pd/n-type Si0.90Ge0.10 structure shown in this work fully support the utilization of such reverse bias method.

Experimental analysis of the electric field distribution in semi-insulating GaAs detectors via alpha particles

Semi-insulating gallium arsenide (SI GaAs) detectors offer a promising alternative to commercially available silicon detectors. They demonstrate superior radiation hardness and provide improved efficiency for gamma and X-ray detection, primarily attributed to their higher density. In this study, we examined 350 μm thick SI GaAs detectors featuring front-side Ti/Pt/Au Schottky contacts with varying contact areas, complemented by back-side Ni/AuGe/Au ohmic contacts spanning the entire area. First, the reverse current-voltage characteristics of the prepared detectors were measured. The dependence of the reverse current and the breakdown voltage on the Schottky contact area was revealed. As the contact area decreases, the reverse current decreases and the breakdown voltage increases. The detection performance of the detectors was evaluated by alpha spectrometry using an 241Am source. After irradiation of the detectors from the Schottky electrode, the measured alpha spectra show an increasing CCE with decreasing Schottky contact area. Finally, the correlation between the applied bias voltage and the extent of the active detector area from the edge of the detector contact was investigated.

Ultrawide bandgap vertical β-(AlxGa1−x)2O3 Schottky barrier diodes on free-standing β-Ga2O3 substrates

Ultrawide bandgap β-(AlxGa1−x)2O3 vertical Schottky barrier diodes on (010) β-Ga2O3 substrates are demonstrated. The β-(AlxGa1−x)2O3 epilayer has an Al composition of 21% and a nominal Si doping of 2 × 1017 cm−3 grown by molecular beam epitaxy. Pt/Ti/Au has been employed as the top Schottky contact, whereas Ti/Au has been utilized as the bottom Ohmic contact. The fabricated devices show excellent rectification with a high on/off ratio of ∼109, a turn-on voltage of 1.5 V, and an on-resistance of 3.4 mΩ cm2. Temperature-dependent forward current-voltage characteristics show effective Schottky barrier height varied from 0.91 to 1.18 eV while the ideality factor from 1.8 to 1.1 with increasing temperatures, which is ascribed to the inhomogeneity of the metal/semiconductor interface. The Schottky barrier height was considered a Gaussian distribution of potential, where the extracted mean barrier height and a standard deviation at zero bias were 1.81 and 0.18 eV, respectively. A comprehensive analysis of the device leakage was performed to identify possible leakage mechanisms by studying temperature-dependent reverse current-voltage characteristics. At reverse bias, due to the large Schottky barrier height, the contributions from thermionic emission and thermionic field emission are negligible. By fitting reverse leakage currents at different temperatures, it was identified that Poole–Frenkel emission and trap-assisted tunneling are the main leakage mechanisms at high- and low-temperature regimes, respectively. Electrons can tunnel through the Schottky barrier assisted by traps at low temperatures, while they can escape these traps at high temperatures and be transported under high electric fields. This work can serve as an important reference for the future development of ultrawide bandgap β-(AlxGa1−x)2O3 power electronics, RF electronics, and ultraviolet photonics.

Characteristics of leakage currents in InGaN/AlGaN nanowire-based red microLEDs.

III-nitride nanowire (NW) LEDs have been intensively studied for several emerging applications. However, the performance of these LEDs is still limited due to many factors. A leakage current may cause idle power consumption and affect the reliability and luminescence efficiency of the devices. Hence, it is one of the most important limiting factors from an application point of view. In this context, we have experimentally observed temperature-dependent forward and reverse leakage current-voltage characteristics of InGaN/AlGaN NW-based red microLEDs. The characteristic curves are fitted using different constant parameters such as the space charge term, zero bias current, and the characteristic energy. They are found to have error bars of less than 10%. The extra space charge term is believed to be due to inherent space charges trapped with the NWs and presents at every instance of the operation of the diode. The characteristic energy and ideality factors are compared to the reported values. An Arrhenius plot is used to calculate the thermal activation energy in the high- and low-temperature regions for both bias conditions. Our results show that the voltage-dependent activation energy is found to be about double in the case of the forward bias compared to that of the reverse bias in all voltage ranges. However, in a high voltage regime, the magnitudes of these parameters are almost four and six times greater for the forward and reverse biases, respectively, compared to those in the lower voltage regions. This study presents vital insight into the design and fabrication of high-performance NW-based LEDs.

From a single silicon carbide detector to pixelated structure for radiation imaging camera

Abstract In this work, Schottky detectors based on a high-quality 4H-SiC epitaxial layer with a thickness of 50 µm were prepared. The Schottky contact of Ni/Au metallization with a 3 mm diameter was made. Reverse current-voltage characteristics were measured up to a voltage of 300 V with a leakage current of 40 pA at room temperature. Using an α-particle radiation source, the spectrometric characteristics of the 4H-SiC detector were tested. The best energy resolution in the FWHM (Full Width and Half Maximum) about 15 keV for 5.5 MeV α-particles was observed. Furthermore, a 4H-SiC pixel sensor (256 × 256) for the Timepix3 reading chip was prepared. The spectrometric and imaging properties of the new Timepix3 detector based on the 4H-SiC sensor were tested. The results showed high energy resolution and also high-quality X-ray imaging of the biological object.

Energy band offsets and charge transport process in an InAsSb based nBn structure: A numerical simulation

We report on the valence energy band offset (ΔEvC-A) between the InAsSb contact (C) and the InAsSb absorber (A) layers, in the C–InAsSb/B–AlAsSb/A-InAsSb nBn structure. ΔEv(C-A) is analyzed, numerically, for different thicknesses of the AlAsSb barrier (B) layer and different doping levels of the barrier and the contact layers, under equilibrium and at room temperature. A value of ΔEv(C-A) around 0,331 meV, corresponding to a near flat band situation, was obtained with donor's concentration of about 1016 cm−3 in the contact. First, simulations were carried at room temperature, under reverse bias, and for a 50 nm and a 100 nm barrier's thicknesses. The temperature dependence of ΔEv(C-A), under reverse bias, was analyzed between 150 K and 300 K. Finally, the reverse current-voltage characteristics of the structure were simulated in the dark and under illumination. Our results are compared to experimental results encountered in the literature and for the same system.

Modification of contact properties in Pt/n-GaN Schottky junctions with ZnO and TiO2/ZnO interlayers

In this study, ZnO (10 nm) and TiO2 (2 nm) were grown on a GaN substrate via atomic layer deposition, and the modified properties of Pt/GaN Schottky diodes with ZnO and ZnO/TiO2 interlayers (ILs) were electrically investigated. The barrier height increased with the ZnO and ZnO/TiO2 ILs; however, the ideality factor increased with the ZnO/TiO2 IL. The reverse-current–voltage characteristics were associated with the Poole–Frenkel emission for all the three junctions. Compared with the Pt/GaN junction, the density of the surface states decreased for the Pt/ZnO/GaN junction but increased for the Pt/ZnO/TiO2/GaN junction. An increase in the ideality factor and a decrease in the barrier height with decreasing temperature were observed at the Pt/GaN and Pt/ZnO/TiO2/GaN junctions. In general, the diode characteristics of the Pt/GaN junction improved owing to the ZnO IL, whereas it degraded owing to the ZnO/TiO2 IL. However, both ZnO and ZnO/TiO2 ILs demonstrate worse diode characteristics at higher temperatures. A thicker ZnO layer (>10 nm) is suggested for improved thermal stability.

Influence of formation conditions of silicon diodes on their reverse currents

In this work, a study was made of the influence of silicon diode manufacturing technology on the emergence of generation and recombination centers. The electrical characteristics of p-n junctions formed in different ways on n-type silicon substrates were compared: a) the p-type layer was created by the diffusion method; b) the p-type layer was formed by ion implantation into an epitaxial n-layer preliminarily grown on the substrate; c) two n- and p-type epitaxial layers were successively deposited on the substrate. It has been established that for diodes based on a double epitaxial layer, the direct and reverse current-voltage characteristics (CVC) are due to the diffusion mechanism, and the structures themselves have a low concentration of recombination centers. At the same time, in diodes based on the diffusion method and ion implantation, the CVCs are due to the generation-recombination mechanism. With reverse bias, electron-phonon processes play a significant role in the formation of the CVC, and with forward bias, carrier recombination in the region of the space charge of the p-n junction. The concentrations and energies of recombination centers have been determined. Keywords: forward and reverse current-voltage characteristic, p-n junction, diffusion, ion implantation, epitaxy, recombination centers, the Poole--Frenkel effect, electron-phonon interaction.

Влияние условий формирования кремниевых диодов на их обратные токи

In this work, a study was made of the influence of silicon diode manufacturing technology on the emergence of generation and recombination centers. The electrical characteristics of p-n junctions formed in different ways on n-type silicon substrates were compared: a) the p-type layer was created by the diffusion method; b) the p-type layer was formed by ion implantation into an epitaxial n-layer preliminarily grown on the substrate; c) two n- and p-type epitaxial layers were successively deposited on the substrate. It has been established that for diodes based on a double epitaxial layer, the direct and reverse current-voltage characteristics (CVC) are due to the diffusion mechanism, and the structures themselves have a low concentration of recombination centers. At the same time, in diodes based on the diffusion method and ion implantation, the CVCs are due to the generation-recombination mechanism. With reverse bias, electron-phonon processes play a significant role in the formation of the CVC, and with forward bias, carrier recombination in the region of the space charge of the p-n junction. The concentrations and energies of recombination centers have been determined.

A perspective on leakage current induced by threading dislocations in 4H-SiC Schottky barrier diodes

This study compared the influences of threading edge and screw dislocation (TED and TSD) defects and their work functions on electrical property of leakage current statistically through the reverse current–voltage characteristics of dozens of pieces of 4H-SiC Schottky barrier diodes (SBDs). The experimental results indicated that TEDs correlated strongly more than TSDs to the leakage current in 4H-SiC SBDs under the soft-breakdown regime. Furthermore, Kelvin probe force microscopy revealed that the work function at TED site was about 15 meV lower than that at TSD site. We proposed a possible mechanism based on band-structure near the Schottky barrier, which illustrated that TED site possesses the larger degree of band bending and therefore increases the tunneling transmission probability in contrast to TSD site.

Silicon carbide of 4H-SiC type Schottky diode current-voltage characteristics in small-sized type metal-polymeric package SOT-89

The forward and reverse current–voltage characteristics of Ti/Al/4H-SiC Schottky diode type DDSH411A91 in modern small-sized (SOT-89) type metal-polymeric package have been obtained. In forward direction (current up to 2 A) on the basis of analysis it is shown that Schottky diode corresponds to the "ideal" diode with ideality factor n=1.12 and effective Schottky barrier height φB =1.2 eV. It is shown that reverse current-voltage characteristics (breakdown voltage 1200 V) can be well approximated by mechanism of field dependence of barrier height lowering by the presence of the intermediate layer in the form of oxide on the 4H-SiC surface.

Schottky diodes based on 4H-SiC epitaxial layers

Forward and reverse current-voltage (IV) characteristics of Cr-SiC (4H) Schottky diodes based on epitaxial layers with doping (1-3)· 1015 cm-3 were studied in the temperature range of 300-550 K. It is shown that in many cases the IV characteristics are close to ideal, but a significant spread of the forward IV characteristics of diodes manufactured in the same way on the same epitaxial layer was found, probably due to the spread of the Schottky barrier heights reaching 0.3 eV. Heating of the diode, as well as packaging, can also change the Schottky barrier height. An alternative explanation suggests the presence of a powerful shunt.

Effects of silicon surface defects on the graphene/silicon Schottky characteristics

Distinct characteristics and yet adverse in some cases have been widely reported in the graphene/silicon Schottky junction under DC biasing, for biological and chemical sensing, or as a photodetector. The explanations to these observations are often attributed to the nature of the graphene layer but are still far from satisfactorily for many cases. In this work, we conducted a detailed analysis on both the forward and reverse current-voltage characteristics under different temperatures and we proposed that the silicon surface defects, which had been well-known as Pb0 centers or ≡Si, should play an important role in the adverse characteristics observed in the Gr/Si junction. Compared with the metal/Si and oxide/Si interface, the graphene-isolated Pb0 centers at the Gr/Si interface are chemically inactive but are still electrically active and that modify the carrier transportation over the junction barrier. Without efficient chemical passivation, the graphene-covered Si surface should maintain the most native Si surface such that it preserves a much higher amount of Pb0 centers as compared with other Si junctions or interfaces. This should be the main origin for the reported adverse current-voltage characteristics.

Effects of Downstream Plasma Exposure on β-Ga2O3 Rectifiers

The effects of downstream plasma exposure with O2, N2 or CF4 discharges on Si-doped Ga2O3 Schottky diode forward and reverse current-voltage characteristics were investigated. The samples were exposed to discharges with rf power of 50 W plasma at a pressure of 400 mTorr and a fixed treatment time of 1 min to simulate dielectric layer removal, photoresist ashing or surface cleaning steps. Schottky contacts were deposited through a shadow mask after exposure to avoid any changes to the surface. A Schottky barrier height of 1.1 eV was obtained for the reference sample without plasma treatment, with an ideality factor of 1.0. The diodes exposed to CF4 showed a 0.25 V shift from the I–V of the reference sample due to a Schottky barrier height lowering around 14%. The diodes showed a decrease of Schottky barrier height of 2.5 and 6.5% with O2 or N2 treatments, respectively. The effect of plasma exposure on the ideality factor of diodes treated with these plasmas was minimal; 0.2% for O2 and N2, 0.3% for CF4, respectively. The reverse leakage currents were 1.2, 2.2 and 4.8 μA cm−2 for the diodes treated with O2, and CF4, and N2 respectively. The effect of downstream plasma treatment on diode on-resistance and on-off ratio were also minimal. The changes observed are much less than caused by exposure to hydrogen-containing plasmas and indicate that downstream plasma stripping of films from Ga2O3 during device processing is a relatively benign approach.

The impact of parasitic inductance on the dV/dt ruggedness of 4H-SiC Schottky diodes

In this study, the dV/dt ruggedness of commercial 4H-SiC Schottky diodes C3D02060A (Wolfspeed) with DC blocking voltage of 600 V and continuous forward current of 2 A was investigated. The quasi-static reverse current-voltage characteristics of the diodes were measured in the recoverable avalanche breakdown regime up to currents of about 7 A. The mature avalanche breakdown voltage was measured to be 1180 V which is almost twice the rated blocking voltage of 600 V. The dV/dt tests were performed with the use of a pulse current generator capable of generating short (3 ns), high-current (up to 80 A), high-voltage (up to 4 kV at 50-ohm load) pulses. The dV/dt limit was found to be 1260 V/ns, in combination with the value of diode terminal voltage of 750 V. Based on TCAD simulations, the impact of unavoidable lead inductance of TO-220A package on the dV/dt limit is pointed out. It is shown that a high voltage is induced on semiconductor structure being higher than the voltage on diode external terminals. As a result, diode failure occurs, although the diode terminal voltage is significantly lower than the mature avalanche breakdown voltage of semiconductor structure.

High-Voltage 4H-SiC Schottky Diodes with Field-Plate Edge Termination

High-voltage (2000V) 4H-SiC Schottky diodes are fabricated. To suppress the premature breakdown at the edge of diode structures, a field plate is formed as the edge termination. In this plate, an insulator layer is formed via the self-aligned implantation of high-energy (53 MeV) argon ions into 4H-SiC. To mask the active region of the diodes, 10–12-μm-thick nickel columns with vertical walls are grown on Schottky contacts by local electrochemical deposition. A comparison of the current–voltage characteristics of terminated and nonterminated diodes shows that the forward current–voltage characteristics barely degrade after implantation, whereas the reverse current–voltage characteristics are greatly improved. Both the forward and reverse current–voltage characteristics of terminated diodes are well described in terms of the classical thermionic emission model if lowering of the Schottky-barrier height with increasing bending of energy bands is taken into account.

The reverse bias current–voltage–temperature (I–V–T) characteristics of the (Au/Ti)/Al2O3/n-GaAs Schottky barrier diodes (SBDs) in temperature range of 80–380 K

We analyzed current conduction mechanisms (CCMs) of the (Au/Ti)/Al2O3/n-GaAs (MIS) type SBDs in the wide temperature range (80–380 K) by 30 K steps using reverse bias current-voltage (IR–VR) characteristics. In general, the values of barrier-height (BH) obtained from the forward bias current–voltage (IF–VF) and reverse bias current-voltage (IR–VR) characteristics increase with increasing temperature and this change is in-agreement with the reported negative-temperature coefficient bandgap of semiconductor (α = ΔEg/ΔT) or BH for ideal SDs. However, the change in BH at lower temperatures becomes more pronounced. The value of BH obtained from the IR–VR data is lower than that obtained from IF–VF especially under room temperatures. The necessary barrier height (Φt) for electron emission from the trap state was obtained from the ln (IR) − E0.5, (E = VR/d), plot as 1.25 eV to (at 80 K) 0.91 eV (at 380 K), respectively. This change in the Φt with temperature is in agreement with the reported α value of the Eg for GaAs. The reverse leakage current mechanism in this study was assessd for various temperatures using Schottky emission (SE), Poole–Frenkel emission (PFE), Trap-Assisted Tunneling (TAT), and ohmic conduction mechanisms. The evaluation of the IR–VR characteristics shows that the ohmic and TAT are the most dominant conduction mechanisms rather than others.

Effect of Electron–Phonon Interaction and γ-Ray Irradiation on the Reverse Currents of Silicon Photodiodes

The current–voltage characteristics of silicon photodiodes before and after irradiation by γ-quanta with an energy of 1.25 MeV and an irradiation dose of 0.5 mrad are investigated. It is established that the reverse currents are determined by the Poole–Frenkel mechanism in a strong electric field with the influence of electron–phonon interaction. A procedure is developed and the parameters of the electron–phonon interaction described by the single-coordinate configuration model are calculated from the reverse current–voltage characteristics. It is assumed that divacancy-oxygen centers in silicon, which determine the reverse photodiode currents, are formed due to γ-ray irradiation.