Reverse Bias Leakage Current Research Articles

Silicon ultrafast recovery diode with leakage current reduced via the combined lifetime process of gold diffusion and electron-beam irradiation

We investigated the reduction in the reverse-biased leakage current of Si ultrafast recovery diodes via a combined lifetime process involving Au diffusion and bulk electron-beam irradiation (EI). The leakage current of the combined-processed diode was significantly reduced to less than one-third of that of the diode processed solely with Au diffusion, maintaining a similar switching time of 32 ns. This reduction was not achievable with the sole use of EI. Deep-level transient spectroscopy revealed that the reduction in the leakage current was due to the coexistence of the deep trap level of Au (E c-0.51 eV) and the shallow trap level of the defects (E c-0.39 eV) generated via EI as lifetime killers. By combining the deep and shallow trap levels, the lifetime of the carriers generated in the depletion layer of the reverse-biased p-n junction becomes long and consequently, the leakage current is reduced. By maintaining the trap density ratio of defects to diffused Au above 0.28, the leakage current was reduced to less than one-third of that in the solely Au-diffused diode, while maintaining a similar switching time.

Correlations between reverse bias leakage current, cathodoluminescence intensity and carbon vacancy observed in 4H-SiC junction barrier Schottky diode

Reverse bias currents of ten commercial junction barrier Schottky diodes were measured, and the dies were studied by scanning electron microscope (SEM) and cathodoluminescence (CL) after the de-capsulation of the diodes. Defect emissions (DEs) of 2.62 eV were observed in all the CL spectra. By comparing the SEM images, the integral CL intensity spatial mappings and the reverse bias leakage currents, correlations between the leakage current, the integral CL intensity and the Al-implantation process were established. The data of reverse bias leakage current against the reverse bias voltage taken at room temperature followed the Poole Frenkel emission from the Z 1/Z 2 carbon vacancy states to the conduction band. The DE at 2.62 eV is associated with the electronic transition from Z 1/Z 2 to the valence band. The current observation also opens up the feasibility of screening off SiC diodes with large leakage current during production by inspecting the CL intensity before the device fabrication is complete.

Effects of post oxidation of SiO2/Si interfaces in ultrahigh vacuum below 450 °C

Growing SiO2 layer by wet-chemical oxidation of Si surfaces before growth of another insulating film(s) is a used method to passivate Si interfaces in applications (e.g., solar cell, photodiode) at low temperatures (LT) below 450 °C. We report on potential of LT ultrahigh-vacuum (UHV) treatments combined with the wet-chemical oxidation, by investigating effects of LT-UHV oxidation after the wet-chemical growth of SiO2 and before growing Al2O3 film on top of SiO2/Si. This method modifies the SiO2/Si and is found to (i) decrease defect-level density, (ii) increase negative fixed charge density, and (iii) increase carrier lifetime for Al2O3/SiO2/p-Si, as compared to state-of-the-art SiO2/p-Si reference interfaces without LT-UHV. X-ray photoelectron spectroscopy shows that the LT-UHV treatment decreases amount of Si+3 oxidized atoms in chemically grown SiO2 and also amount of carbon contamination. In order to pave the way for further tests of LT-UHV in silicon technology, we present a design of simple UHV instrument. The above-described benefits are reproduced for 4-inch silicon wafers by means of the instrument, which is further utilized to make LT-UHV treatments for complementary SiO2/Si interfaces of the native oxide at silicon diode sidewalls to decrease the reverse bias leakage current of the diodes.

Effects of Fermi pinning and quantum mechanisms on leakage current of 4H-SiC Schottky diodes

Reverse bias leakage current through 4H-SiC Schottky diodes was modeled using quantum transmission theory and the theoretically calculated values were compared with the measured values from fabricated Schottky diodes. To account for interface defects, energy barriers due to Fermi pinning from previously observed defects were used in place of the ideal barrier structure predicted by the Schottky–Mott rule. Incorporating barriers with energy values set due to Fermi pinning at known defect energies resulted in better experimental agreement by many orders of magnitude.

A unified thermionic and thermionic-field emission (TE–TFE) model for ideal Schottky reverse-bias leakage current

We present a unified thermionic emission (TE) and thermionic-field emission (TFE) model for the ideal reverse-bias leakage current in Schottky junctions. The unified TE–TFE analytical model advances upon previous analytical TFE models by Murphy–Good and Padovani–Stratton, which are the two most widely adopted models by the community, in two major aspects: (i) the applicability of the TFE expression therein is extended to near-zero surface electric fields by an error-function correction, allowing for the calculation of the total current by a nontrivial sum of TE (over-the-barrier current) and TFE (below-the-barrier current) contributions; therefore, an accurate description of the TE-to-TFE transition region is captured analytically for the first time; (ii) image-force lowering is considered with much-simpler correction terms. Comparisons with the reference numerical model show that the unified TE–TFE model has excellent accuracy, as well as a 10 000× reduction in computation time. The unified model is further tested against experimental data from Schottky barrier diodes based on Si, 4H-SiC, GaN, and β-Ga2O3, revealing accurate extractions of barrier heights and correct descriptions of the ideal reverse leakage characteristics. With the extended applicable range, improved accuracy, and computational efficiency, the unified TE–TFE model is highly valuable for the design and analysis of devices based on Schottky junctions, as well as for potential integration in technology computer-aided design (TCAD) tools.

Effect of GaN Substrate Properties on Vertical GaN PiN Diode Electrical Performance

Present GaN technology consists primarily of heteroepitaxial, lateral high electron mobility transistors; however, high-power devices would be much more efficiently manufactured with a vertical geometry due to better blocking voltage scaling. This technology has yet to be realized due to the inconsistency of GaN wafer properties. These inconsistencies can be detected with several long-range, non-destructive techniques including Raman spectroscopy, optical profilometry, and photoluminescence mapping. In particular, Raman spectroscopy is an effective tool for determining the carrier concentration of GaN substrates and whether the wafers are uniform or inhomogeneous. In this work, vertical p-i-n GaN diodes are fabricated using both uniform and inhomogeneous wafers determined by using the A1 Raman peak position to monitor carrier concentration. The inhomogeneous samples have regular patterns of varying conductivity as a result of electron-donating defects brought about by changes in crystal stress. By avoiding these defects, we have found that diode performance improves by increasing the +/− 10 V rectification ratio by up to a factor of 5X and reducing the 200 V reverse bias leakage current by several orders of magnitude. Using the higher quality substrates with uniform electron carrier concentrations can improve the rectification ratio by another order of magnitude.

Improved rectification and transport properties of hybrid PEDOT:PSS/Ge/Si heterojunctions with Ge nanoclusters

The electrical characteristics and deep-level transient spectroscopy of a hybrid poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/GeNCs/Si heterojunction with Ge nanoclusters grown by molecular beam epitaxy on a p-type Si(001) substrate are investigated. The heterostructure shows good rectifying J–V characteristics, the dark current exhibits an activation energies of 280 meV and 550 meV, while the reverse bias leakage current is suppressed due to the coating of Ge nanoclusters with PEDOT:PSS. We show that recombination via deep hole states close to grain boundaries can be partly suppressed by the PEDOT:PSS thin films, leading to a decrease in the saturation current and an improvement of the rectification without deterioration of forward current.

AlGaN/GaN Schottky-Gate HEMTs With UV/O₃-Treated Gate Interface

The surface condition under gate of AlGaN/GaN heterostructure plays a critical role in high-electron mobility transistor (HEMT). In this study, the effects of ultraviolet/ozone (UV/O3) treatment applied to Al0.3 Ga0.7 N/GaN heterostructure on the electrical performance of AlGaN/GaN Schottky-gate HEMT were investigated. The reverse-bias leakage current of Schottky diode was reduced by three orders after the treatment. X-ray photoelectron spectroscopy confirms the formation of the Ga2O x layer which serves as an interface passivation layer and thus suppresses trap-assisted electron tunneling. Capacitance–voltage measurements of AlGaN/GaN HEMT show shifts of threshold and on-set voltages, indicating decreased surface states as a result of the treatment. The electrical characteristics of AlGaN/GaN HEMT exhibit improved transconductance and subthreshold swing values after the treatment.

Leakage Current in Fast Recovery Diode Suppressed by Low Temperature Supercritical Fluid Treatment Process

Fast recovery diodes (FRD) are widely used in transformer circuits for fast switching. Generally, in order to reduce forward voltage to achieve fast switching, the doping concentration is increased to reduce on-state resistance (Ron). This, however, will also increase reverse bias leakage as well as recovery time, resulting in a large amount of excess power consumption. In this letter, we use a unique low temperature supercritical fluid treatment process (LTSCF) to reduce this reverse bias leakage current, without affecting the on-state characteristics or switching characteristics. Experimental results show that the device’s average reverse bias leakage was reduced by 65% after LTSCF.

Local defect-enhanced anodic oxidation of reformed GaN nanowires

Understanding formation and distribution of defects in GaN substrates and device layers is needed to improve device performance in rf and power electronics. Here we utilize conductive atomic force microscopy (c-AFM) for studying defect-related leakage paths in an unintentionally doped GaN film formed by nanowire reformation. A nanoscopic Schottky contact is formed between the c-AFM probe and the GaN surface, which, under reverse-bias conditions, reveals local leakage currents at the positions of the nanowires. Cathodoluminescence shows these areas to be dominated by yellow-band luminescence, in contrast to the surrounding GaN matrix, which mainly shows near-band-gap luminescence. These results are attributed to a high density of native and residual defects, confined to the nanowires. In addition, we use anodic oxidation to map defect-related conductive paths through locally induced growth of gallium oxide. The oxide yield, which is known to depend on the local electric field strength between the AFM tip and the sample, correlates well with the level of reverse-bias leakage current. Local irregularities in oxide height reveal extended oxidation attributed to defect-related deep-level states. Thisis confirmed by controlled dissolution of the oxide in NaOH, showing that a deeper oxide film is grown over areas where defect-related conductive paths are formed. Finally, we demonstrate how this approach can be used as a quick and easy diagnostic tool for evaluating the influence of specific growth conditions and process steps on defect-induced leakage current levels and defect distribution in GaN structures, demonstrating its potential for accelerated test of leakage degradation at critical positions in GaN-based devices. (Less)

Evidence of Poole-frenkel and Fowler-Nordheim tunneling transport mechanisms in leakage current of (Pd/Au)/Al0.22Ga0.78N/GaN heterostructures

In this report, the gate leakage mechanism for AlGaN/GaN high electron mobility transistors (HEMTs) is consistently analyzed by means of temperature-dependent reverse gate current–voltage characteristics in the temperature range of 60–320 K. The gate leakage current of the AlGaN/GaN HEMT is studied by adjusting the experimental data using Poole–Frenkel (PF), and Fowler–Nordheim (FN) tunneling. In the temperature range of 200–325 K, the reverse bias leakage current is well dominated by a Frenkel-Poole emission model. The scenario describing the PF mechanism assumes that a defect level at φt = 0.45eV could be considered as an intermediate level through which carriers can transit to reach another level attributed to dislocations closer to conduction band. On the other hand, the FN mechanism seems to operate over the entire temperature range of 60–320 K and starts to dominate the gate leakage current due to triangular barrier formation.

A Novel High Schottky Barrier Based Bilateral Gate and Assistant Gate Controlled Bidirectional Tunnel Field Effect Transistor

In this article, we propose a high Schottky barrier source/drain contacts based bilateral gate and assistant Gate controlled bidirectional tunnel field Effect transistor (HSB-BTFET). Different from Schottky barrier (SB) MOSFET which use lower Schottky barrier to produces the thermionic emission current, the proposed HSB -BTFET utilizes higher Schottky barrier to minimize the thermionic emission current and adopts bilateral gate to generate a strong band-to-band tunneling (BTBT) current which works as the conduction mechanism of the forward current. An assistant gate is introduced which efficiently blocks the reverse biased leakage current. Compared to SB MOSFET, HSB-BTFET can realize lower subthreshold swing, much smaller leakage current, higher $\text{I}_{\mathrm{ on}}-{\mathrm{ I}}_{\mathrm{ off}}$ ratio, compared to TFET, it can realize larger forward current. Besides the device symmetry, it's more compatible with MOSFET technology. The function and influence of the Schottky barrier height have been analyzed.

The analysis on simulation and invalidation of hot-spot temperature distribution in micro-defective crystalline silicon solar cells

According to the distribution of reverse biased leakage current of micro-defective solar cells, the mathematic models of the hot spot thermal power of photovoltaic (PV) modules are established. The uniform and non-uniform distribution of thermal power in hot spot solar cell are theoretically calculated and experimentally analyzed in different shading conditions. Based on the model, the hot spot temperature distribution of different defective cells is simulated by ANSYS software. Then a novel experimental platform is set up to validate the simulation results in outdoor conditions. The mechanism of hot spot failure and the worst hot spot condition are analyzed. According to the results of experiment and simulation, the relative deviation between simulation and experimental data is less than 10% through the model proposed in this paper. Furthermore, in the normal modules, according to the result of simulation and experiment, the worst case of hot spots happens when the heat power is maximum and the shading ratio is about 10–20%. In the defective modules, it happens when the heat power is not maximum and the shading ratio is about 50–60%.

Performance Improvement of GaN-Based Light-Emitting Diodes With a Microhole Array, 45° Sidewalls, and a SiO2 Nanoparticle/Microsphere Passivation Layer

The characteristics of GaN-based light-emitting diodes (LEDs) with a hybrid structure incorporating a microhole array, 45 sidewalls, and an appropriate SiO2 nanoparticle (NP)/microsphere (MSs) passivation layer are studied and reported. The use of a SiO2 NP/MSs passivation layer causes a remarkable reduction in reverse-biased leakage current. The employment of this hybrid structure leads to substantial enhancements in optical properties without any degradation in electrical performance. In addition, a lower content of SiO2 NP in the mixed SiO2 NP/MSs solution leads to enhanced optical behavior due to the improved transmittance. Experimentally, as compared with a conventional LED (Device A), the studied Device E shows 50.6%, 50.9%, 48.4%, and 49.9% enhancements in light output power, luminous flux, luminous efficacy, and wall-plug efficiency, respectively. These advantages are mainly attributed to the increased scattering probability and the opportunity to find photon escape cones as well as the reduced total internal reflection and Fresnel reflection effects. Therefore, the studied hybrid structure provides a promise for high-performance GaN-based LED applications.

Core-shell p-i-n GaN nanowire LEDs by N-polar selective area growth.

GaN nanowire LEDs with radial p-i-n junctions were grown by molecular beam epitaxy using N-polar selective area growth on Si(111) substrates. The N-polar selective area growth process facilitated the growth of isolated and high-aspect-ratio n-type NW cores that were not subject to self-shadowing effects during the subsequent growth of a conformal low-temperature Mg:GaN shell. LED devices were fabricated from single-NW and multiple-NW arrays in their as-grown configuration by contacting the n-type core through an underlying conductive GaN layer and the p-type NW shell via a metallization layer. The NW LEDs exhibited rectifying I-V characteristics with a sharp turn-on voltage near the GaN bandgap and low reverse bias leakage current. Under forward bias, the NW LEDs produced electroluminescence with a peak emission wavelength near 380 nm and exhibited a small spectral blueshift with increasing current injection, both of which are consistent with electron recombination in the p-type shell layer through donor-acceptor-pair recombination. These core-shell NW devices demonstrate N-polar selective area growth as an effective technique for producing on-chip nanoscale light sources.

Effect of Green Quantum Well Number on Properties of Green GaN-Based Light-Emitting Diodes**Supported by the National Key Research and Development Program of China under Grant No 2016YFB0400601, and the National Natural Science Foundation of China under Grant Nos 61704069, 11674147, 61604066, 51602141 and 11604137.

InGaN-based green light-emitting diodes (LEDs) with different green quantum well numbers grown on Si (111) substrates by metal organic chemical vapor deposition are investigated. It is observed that V-shaped pits appear in the AFM images with the green quantum well number increasing from 5 to 9, and results in larger reverse-bias leakage current. Meanwhile, in the case of the sample with the number from 5 to 7 then to 9, the external quantum efficiency increases firstly, and then decreases. These phenomena may be related to the size of V-shaped pits in the active area and the distribution of electrons and holes in the active area caused by V-shaped pits. The optimal number of green quantum wells is determined to be 7.

An On-Chip CMOS Temperature Sensor Using Self-Discharging P-N Diode in a <inline-formula> <tex-math notation="LaTeX">$\Delta$ </tex-math> </inline-formula>-<inline-formula> <tex-math notation="LaTeX">$\Sigma$ </tex-math> </inline-formula> Loop

A CMOS temperature sensor to monitor on-chip distributed thermal profile of high-performance system-on-chips (SoCs) is presented. The architecture of this sensor utilizes a self-discharging p-n diode to implement a first-order delta-sigma ( $\Delta$ - $\Sigma$ ) loop. To determine the on-chip temperature, the temperature-dependent reverse-bias leakage current of the diode is measured. The sensor is implemented in a 0.18- $\mu \text{m}$ CMOS process and it occupies a small area of $550\mu \text{m}^{2}$ . Performance measurements demonstrate the on-chip sensor inaccuracies of ±0.1 °C ( $3\sigma$ ) with calibration, and ±0.5 °C ( $3\sigma$ ) without any calibration, over 35 °C–100 °C, which is the functional temperature range of current high-performance SoCs. The sensor, excluding the digital and any reference generators, consumes $4\mu \text{W}$ from a single 1.8-V supply. The worst case resolution of the sensor is 75 mK at 2-Hz bandwidth with the overall sensor figure of merit of 11 nJ°K2.

Analysis of screw dislocation mediated dark current in Al0.50Ga0.50N solar-blind metal-semiconductor-metal photodetectors

We report on a billion-fold reduction in reverse-bias leakage current density (11.3 A/cm2 to 8.5 nA/cm2 at 20 V) across Schottky contacts made to Al0.50Ga0.50N epilayers grown on sapphire. Interdigitated back-to-back Ni/Au Schottky contacts were made to unintentionally doped Al0.50Ga0.50N epilayers grown by metal organic chemical vapor deposition to realize photodetectors with metal-semiconductor-metal geometry. Testing on a self-consistent series of samples grown under different conditions revealed that a two-order reduction in screw dislocation density is primarily responsible for the significant reduction in the lateral leakage (dark) current. This observation is validated by conductive atomic force microscopy experiments. Analytical modelling by temperature-dependent current-voltage measurements confirm a screw dislocation mediated carrier transport mechanism. The anomalously high reverse-bias leakage current (μA-mA) in the highly defective samples is found to be dominated by thermionic field emission (TFE) at low biases and Poole-Frenkel emission (PFE) from a deep donor level at high biases. With a significant improvement in the crystalline quality, a solar-blind photodetector with an EQE of 47%, photo/dark current ratio of 1.4 × 105 and transient characteristics of <20 ms is demonstrated. This study towards understanding the leakage in Al0.50Ga0.50N is expected to benefit the development of various deep-UV devices and GaN-AlGaN based power transistors.

Significant improvement in the electrical characteristics of Schottky barrier diodes on molecularly modified Gallium Nitride surfaces

III-Nitride semiconductors face the issue of localized surface states, which causes fermi level pinning and large leakage current at the metal semiconductor interface, thereby degrading the device performance. In this work, we have demonstrated the use of a Self-Assembled Monolayer (SAM) of organic molecules to improve the electrical characteristics of Schottky barrier diodes (SBDs) on n-type Gallium Nitride (n-GaN) epitaxial films. The electrical characteristics of diodes were improved by adsorption of SAM of hydroxyl-phenyl metallated porphyrin organic molecules (Zn-TPPOH) onto the surface of n-GaN. SAM-semiconductor bonding via native oxide on the n-GaN surface was confirmed using X-ray photoelectron spectroscopy measurements. Surface morphology and surface electronic properties were characterized using atomic force microscopy and Kelvin probe force microscopy. Current-voltage characteristics of different metal (Cu, Ni) SBDs on bare n-GaN were compared with those of Cu/Zn-TPPOH/n-GaN and Ni/Zn-TPPOH/n-GaN SBDs. It was found that due to the molecular monolayer, the surface potential of n-GaN was decreased by ∼350 mV. This caused an increase in the Schottky barrier height of Cu and Ni SBDs from 1.13 eV to 1.38 eV and 1.07 eV to 1.22 eV, respectively. In addition to this, the reverse bias leakage current was reduced by 3–4 orders of magnitude for both Cu and Ni SBDs. Such a significant improvement in the electrical performance of the diodes can be very useful for better device functioning.

Improvement in reverse bias leakage current of Ni/4H-nSiC Schottky barrier diodes via MeV selective ion irradiation

Present work deals with enhancement in reverse bias leakage current of Ni/4H-nSiC schottky barrier diode (SBD) via irradiating with 200 MeV 107Ag14+ ions at a fluence of 1013 ions/cm2 in selective way. Compared to pristine SBD, the reverse bias I-V characteristics of selectively irradiated SBD show significant improvement in leakage current. Role of quodons have been discussed to rationalize the performance of irradiated SBD.