Reverse Blocking Characteristics Research Articles

On the coupled effect of a MIS-based anode and AlGaN-polarized super-junction to reduce the local electric field for AlGaN/GaN Schottky barrier diodes

This work employs advanced physical models with the help of technology computer-aided design tools to systematically design and investigate AlGaN/GaN Schottky barrier diodes (SBDs), focusing on enhancing forward conduction and reverse blocking characteristics. A recessed metal/insulator/III-nitride (MIS) anode is demonstrated to manage electric field distribution. The incorporation of a 1 nm thick Al2O3 layer enables a reduced leakage current and a significant increase in breakdown voltage (BV). Subsequently, tailored field plates (FPs) further improve the BV of the MIS SBD to ∼1650 V but strong electric field magnitude will be found at the edge of the FP. Hence, a MIS SBD with a graded AlGaN barrier layer (MIS-GA SBD) is designed, featuring a gradient decrease in Al content along the [0001] direction. The generation of negative polarization charges within the barrier functions as a super-junction, significantly homogenizing the electric field. As a result, the MIS-GA SBD achieves a remarkable BV exceeding 3500 V, highlighting its strong potential for high-voltage power electronic applications.

Elevated barrier height originated from electric dipole effect and improved breakdown characteristics in PtOx/β-Ga2O3 Schottky barrier diodes

The higher Schottky barrier height of PtOx/β-Ga2O3 Schottky barrier diode (SBD) was derived from the electric dipole effect of PtOx Schottky electrode. And the higher Schottky barrier height effectively improved the reverse breakdown characteristics of β-Ga2O3 SBD. In this work, PtOx/β-Ga2O3 and Pt/β-Ga2O3 SBDs were fabricated, and the Schottky barrier height of PtOx SBD increased with the increment of oxygen element component in PtOx electrode, which were all higher than the Schottky barrier height of Pt SBD. Kelvin probe force microscope measurement indicated that Fermi level pinning effect and the variation in work functions of Schottky electrodes were irrelevant to the higher barrier height. Moreover, with the increment of inserting PtOx layer thickness in Pt/PtOx/β-Ga2O3 SBDs, the Schottky barrier height increased from 1.32 eV to 1.82 eV. Bright-field scanning transmission electron microscopy image demonstrated that PtOx was mainly polycrystal with layer structure near the Schottky interface. The layer structure composed of Pt ions and O ions induced electric dipole effect, and the electric dipole effect led to the increase of Schottky barrier height for PtOx SBD. Lower leakage current density, higher breakdown voltages and more concentrated breakdown voltage distribution were obtained for PtOx SBDs. Furthermore, the barrier heights of PtOx SBDs gradually increased as the temperature raised, resulting in their reverse leakage current increased much more slowly with temperature than that of Pt SBD. The above results demonstrated that PtOx/β-Ga2O3 SBD had great potential in enhancing reverse blocking characteristics and high-temperature environment applications.

Current transport mechanism of AlGaN-channel Schottky barrier diode with extremely low leakage current and high blocking voltage of 2.55 kV

This Letter presents work on lateral AlGaN-channel Schottky barrier diodes (SBDs) with impressive reverse blocking characteristics and low onset voltage (VON). A low reverse current (IR) of 28 nA/mm and low VON of 0.60 V are obtained by utilizing an AlGaN back barrier layer with high Al composition and low work function metal as the anode. The fabricated AlGaN-channel SBD with an anode–cathode distance (LAC) of 30 μm achieves a high blocking voltage of 2.55 kV and a power figure-of-merit of 363 MW/cm2. Meanwhile, the current transport mechanism of AlGaN-channel SBDs goes through thermionic emission, thermionic field emission, and trap-assisted tunneling as the reverse bias is gradually increased. The thermal activation energy (EA) is calculated to be 141.3 meV at high reverse bias. IR at 475 K is only 3 μA/mm, which shows an adequate barrier height for rectifying at high temperature even with low VON. The AlGaN-channel SBDs show great promise for next-generation power electronics with balanced forward and reverse characteristics.

Reverse Blocking GaN High Electron Mobility Transistors with Stepped P-GaN Drain

In this work, a reverse-blocking high electron mobility transistor with stepped p-type GaN drain (SPD RB-HEMT) has been proposed and studied in TCAD Sentaurus. In SPD RB-HEMT, the reverse-blocking capability is achieved by employing a stepped p-type GaN (P-GaN) layer connected with the Schottky metal drain. The stepped P-GaN layer is constituted by four P-GaN steps, and the thicknesses of the first to the fourth P-GaN step are descending from the source to the drain side. Due to the P-GaN/AlGaN/GaN structure, the conduction band of the AlGaN/GaN interface is lifted up. Therefore, the two-dimensional electron gas (2-DEG) channel is depleted, and the reverse current is blocked. On the other hand, when the drain is forward biased, the 2-DEG channel is recovered, and the drain induced barrier lowering (DIBL) effect in stepped P-GaN drain structure can lead to a lower on-resistance of the device. The SPD RB-HEMT exhibits a reverse breakdown voltage of −2209 V and on-resistance of 3.01 mΩ·cm2 in TCAD Sentaurus simulation. Compared with the conventional Schottky barrier drain and planar P-GaN drain RB-HEMTs, the SPD RB-HEMTs have shown the balanced and improved forward and reverse-blocking characteristics.

A low turn-on voltage AlGaN/GaN lateral field-effect rectifier compatible with p-GaN gate HEMT technology

In this paper, we designed a low turn-on voltage (V On) AlGaN/GaN lateral field-effect rectifier (LFER) compatible with p-GaN gate high-electron-mobility transistor (HEMT) technology (PG-LFER). We also established an analytical model on the gated control two-dimensional-electron-gas density (n S) distributions and V On to investigate the underlying mechanism. The designed PG-LFER features a p-GaN charge storage layer (CSL) under the anode terminal. Net negative charge density in the p-GaN CSL (σ p-GaN) is associated with the activated doping concentration of p-GaN CSL (N p-GaN) and p-GaN CSL thickness (t p-GaN). V On of the PG-LFER is significantly lowered due to the low σ p-GaN caused by reducing the N p-GaN and t p-GaN. Meanwhile, the low V On PG-LFER also preserves recognizable reverse blocking and capacitance characteristics. Verified by the calibrated simulation, the designed PG-LFER shows 70% lower V On compared with the non-optimized LFER with a high σ p-GaN. Compatible with p-GaN gate HEMT technology, the designed PG-LFER with improved performance is a promising candidate for power integrated applications.

High-voltage vertical Ga2O3 power rectifiers operational at high temperatures up to 600 K

This work presents the temperature-dependent forward conduction and reverse blocking characteristics of a high-voltage vertical Ga2O3 power rectifier from 300 K to 600 K. Vertical β-Ga2O3 Schottky barrier diodes (SBDs) were fabricated with a bevel-field-plated edge termination, where a beveled sidewall was implemented in both the mesa and the field plate oxide. The Schottky barrier height was found to increase from 1.2 eV to 1.3 eV as the temperature increases from 300 K to 600 K, indicating the existence of barrier height inhomogeneity. The net donor concentration in the drift region shows little dependence on the temperature. The reverse leakage current up to 500 V was found to be limited by both the thermionic-field electron injection at the Schottky contact and the electron hopping via the defect states in the depletion region. At 300–500 K, the leakage is first limited by the electron injection at low voltages and then by the hopping in depleted Ga2O3 at high voltages. At temperatures above 500 K, the thermionic field emission limits the device leakage over the entire voltage range up to 500 V. Compared to the state-of-the-art SiC and GaN SBDs when blocking a similar voltage, our vertical Ga2O3 SBDs are capable of operating at significantly higher temperatures and show a smaller leakage current increase with temperature. This shows the great potential of Ga2O3 SBDs for high-temperature and high-voltage power applications.

Vertical β‐Ga2O3 Schottky Barrier Diodes with Enhanced Breakdown Voltage and High Switching Performance

Herein, vertical Schottky barrier diodes (SBDs) based on a bulk β‐Ga2O3 substrate are developed. The devices feature an ion‐implanted planar edge termination (ET) structure, which can effectively smoothen the electric field peak and reduce the electric field crowding at the Schottky junction edge. Greatly enhanced reverse blocking characteristics including ≈103× lower reverse leakage current and 1.5× higher breakdown voltage (VB) are achieved, whereas good forward conduction such as a reasonably high on‐state current density and near‐unity ideality factor is maintained. In addition, the switching performance of the fabricated vertical β‐Ga2O3 SBDs is investigated using a double‐pulse test circuit. When switching from an on‐state current of 350 mA to a reverse‐blocking voltage of −100 V, the vertical β‐Ga2O3 SBDs exhibit fast reverse recovery with a reverse recovery time (trr) of ≈14.1 ns and reverse recovery charge (Qrr) of ≈0.34 nC, outperforming the Si fast recovery diode (FRD) of similar ratings. The results indicate a great promise of vertical β‐Ga2O3 SBDs for high‐voltage fast switching applications.

1230 V β-Ga2O3 trench Schottky barrier diodes with an ultra-low leakage current of <1 μA/cm2

β-Ga2O3 vertical trench Schottky barrier diodes (SBDs) are realized, demonstrating superior reverse blocking characteristics than the co-fabricated regular SBDs. Taking advantage of the reduced surface field effect offered by the trench metal-insulator-semiconductor structure, the reverse leakage current in the trench SBDs is significantly suppressed. The devices have a higher breakdown voltage of 1232 V without optimized field management techniques, while having a specific on-resistance (Ron,sp) of 15 mΩ cm2. An ultra-low leakage current density of <1 μA/cm2 is achieved before breakdown, the lowest among all reported Ga2O3 Schottky barrier diodes. Fast electron trapping and slow de-trapping near the Al2O3/Ga2O3 interface are observed by repeated C-V measurements, which show an interface state ledge and positive shifts of flat-band voltages with increasing voltage stress. By comparison between pulsed and DC measurements, the device self-heating effect and the trapping effect are uncoupled. It is found that the trapping effect at the trench sidewall affects the on-resistance of the trench SBDs, even under pulsed conditions. With reduced trapping effect and better field management technique, the trench SBDs could further harvest the promising material properties of β-Ga2O3.

A novel AlGaN/GaN hybrid-anode current regulating diode (CRD) with step-graded Schottky-Ohmic cathode

In this work, a novel AlGaN/GaN lateral current regulating diode was proposed and studied. The diode features a MIS-Gated hybrid anode enabling flexibly tailor the forward turn-on voltage and reverse blocking characteristics of the diode. Meanwhile, instead of utilizing the conventional Ohmic cathode, the cathode of the proposed CRD consists a step-graded Schottky extension connecting with the Ohmic contact, which endows the CRD with excellent current regulation capability. The drive current capability, knee voltage and current steadiness can be precisely modulated by tailoring the gradient and length of the Schottky extension at the cathode. The proposed CRD with such a new functionality is of great potential to expand the applications of AlGaN/GaN electronic devices.

Numerical analysis of the reverse blocking enhancement in High-K passivation AlGaN/GaN Schottky barrier diodes with gated edge termination

We conducted a numerical analysis on high-K dielectric passivated AlGaN/GaN Schottky barrier diodes (HPG-SBDs) with a gated edge termination (GET). The reverse blocking characteristics were significantly enhanced without the stimulation of any parasitic effect by varying the dielectric thickness dge under the GET, thickness TP, and dielectric constant εr of the high-K passivation layer. The leakage current was reduced by increasing εr and decreasing dge. The breakdown voltage of the device was enhanced by increasing εr and TP. The highest breakdown voltage of 970 V and the lowest leakage current of 0.5 nA/mm were achieved under the conditions of εr = 80, TP = 800 nm, and dge = 10 nm. C-V simulation revealed that the HPG-SBDs induced no parasitic capacitance by comparing the integrated charges of the devices with different high-K dielectrics and different dge.

Reverse blocking characteristics and mechanisms in Schottky-drain AlGaN/GaN HEMT with a drain field plate and floating field plates**Project supported by the National Natural Science Foundation of China (Grant Nos. 61204085, 61334002, 61306017, 61474091, 61574112, and 61574110).

In this paper, a novel AlGaN/GaN HEMT with a Schottky drain and a compound field plate (SD-CFP HEMT) is presented for the purpose of better reverse blocking capability. The compound field plate (CFP) consists of a drain field plate (DFP) and several floating field plates (FFPs). The physical mechanisms of the CFP to improve the reverse breakdown voltage and to modulate the distributions of channel electric field and potential are investigated by two-dimensional numerical simulations with Silvaco-ATLAS. Compared with the HEMT with a Schottky drain (SD HEMT) and the HEMT with a Schottky drain and a DFP (SD-FP HEMT), the superiorities of SD-CFP HEMT lie in the continuous improvement of the reverse breakdown voltage by increasing the number of FFPs and in the same fabrication procedure as the SD-FP HEMT. Two useful optimization laws for the SD-CFP HEMTs are found and extracted from simulation results. The relationship between the number of the FFPs and the reverse breakdown voltage as well as the FP efficiency in SD-CFP HEMTs are discussed. The results in this paper demonstrate a great potential of CFP for enhancing the reverse blocking ability in AlGaN/GaN HEMT and may be of great value and significance in the design and actual manufacture of SD-CFP HEMTs.

High-voltage 4H-SiC trench MOS barrier Schottky rectifier with low forward voltage drop using enhanced sidewall layer

In this paper, a 4H-SiC trench MOS barrier Schottky (TMBS) rectifier with an enhanced sidewall layer (ESL) is proposed. The proposed structure has a high doping concentration at the trench sidewall. This high doping concentration improves both the reverse blocking and forward characteristics of the structure. The ESL–TMBS rectifier has a 7.4% lower forward voltage drop and a 24% higher breakdown voltage. However, this structure has a reverse leakage current that is approximately three times higher than that of a conventional TMBS rectifier owing to the reduction in energy barrier height. This problem is solved when ESL is used partially, since its use provides a reverse leakage current that is comparable to that of a conventional TMBS rectifier. Thus, the forward voltage drop and breakdown voltage improve without any loss in static and dynamic characteristics in the ESL–TMBS rectifier compared with the performance of a conventional TMBS rectifier.

Various Schottky Contacts of AlGaN/GaN Schottky Barrier Diodes (SBDs)

We have proposed and fabricated high performance of AlGaN/GaN Schottky Barrier Diodes (SBDs) with various Schottky contact. The breakdown voltage of proposed SBDs with the TaN and ITO Schottky contact deposited by RF sputtering method was increased compared to the widely used Ni/Au Schottky contact. The extracted Schottky barrier height (SBH) of TaN and ITO was 0.62 eV and 0.54 eV respectively while that of Ni/Au was 0.51 eV. The reverse blocking characteristics such as the leakage current and breakdown voltage was improved by TaN and ITO Schottky contact due to its high SBH. However, forward current of TaN and ITO Schottky contact was less than that of Ni/Au Schottky contact. The TaN Schottky SBDs achieved highest breakdown voltage of 605 V and ITO Schottky SBDs achieved 472 V. On the contrary, the breakdown voltage of Ni/Au Schottky SBDs exhibits 335 V.

RF-Sputtered HfO2 Gate Insulator in High-Performance AlGaN/GaN MOS-HEMTs

We have proposed and fabricated AlGaN/GaN metal-oxide-semiconductor-high-electron-mobility transistors (MOS-HEMTs) on Si substrate employing RF-sputtered HfO2 gate insulator for a high breakdown voltage. The HfO2 sputtering conditions such as a sputtering power and working pressure have been optimized in order to improve reverse blocking characteristics. We obtained the high breakdown voltage of 1524 V, the low drain leakage current of 67 pA/mm when VDS= 100 V and VGS= –10 V, and on/off current ratio of 2.37×1010 at sputtering power of 50 W and working pressure of 3 mTorr. In addition, we also discussed the mechanism of breakdown voltage improvement and investigated HfO2/GaN interface in the proposed devices by measuring the leakage current, capacitance-voltage characteristics, and X-ray diffraction (XRD).

High-performance AlGaN/GaN High-electron-mobility transistors employing H2O annealing

We have proposed and fabricated high performance AlGaN/GaN high-electron-mobility transistors (HEMTs), of which the breakdown voltage is considerably high and the leakage current is efficiently suppressed employing H2O annealing. We also investigated the effects of H2O annealing on the formation of GaOx film on the surface of AlGaN/GaN HEMT as well as reverse blocking characteristics including the breakdown voltage and the leakage current. We compared the reverse blocking characteristics of the AlGaN/GaN HEMTs fabricated by the proposed H2O annealing treatment with those of the HEMT by widely used O2 annealing method. Also, we investigated the reverse blocking characteristics of HEMT fabricated without any annealing treatment. We used the smaller molecular size, higher permeation probability, and the lower activation energy of H2O than O2. The breakdown voltage of AlGaN/GaN HEMT with the LGD of 20μm employing H2O and O2 annealing was 1674 and 1512V, respectively. The drain leakage current of these devices using H2O and O2 annealing was 13.1 and 60.1nA/mm under VDS of 100V and VGS of −10V, respectively. A conventional device without any annealing process exhibited the breakdown voltage of 598V and the leakage current of 666.0μA/mm. In order to investigate the amounts of deep traps in the interface of AlGaN/GaN HEMT, we measured the pulsed I–V. A low drain current of the device under pulsed bias indicated that the GaOx, which was formed by H2O annealing, induced the deeper level and longer emission time of traps compared to the shallow ones. These may be related to the surface leakage current in the AlGaN/GaN HEMTs.

Simulation study on 4H–SiC power devices with high-k dielectric FP terminations

The reverse blocking characteristics of 4H–SiC power devices with high dielectric constant (k) materials field plate (FP) terminations have been investigated by numerical simulations in this paper. The study makes a comparison between the breakdown characteristics of 4H–SiC power devices with different FP dielectrics comprising silicon oxide (SiO2), silicon nitride (Si3N4) and hafnium oxide (HfO2). The results show that the high-k dielectrics FP can significantly relieve the electric field enhancement at the junction corners and enhance the breakdown voltage of devices. The breakdown voltage as high as 2249V, which reaches about close to more than 90% of theoretical value, is achieved in HfO2 FP terminated 4H–SiC Schottky barrier diode. The maximum electric field in the dielectric layer can be greatly reduced from 7MV/cm for SiO2 FP to 5.7MV/cm for Si3N4 FP and 3.6 MV/cm for HfO2 FP. Meanwhile, it also implies that the high-k dielectrics FP terminations can efficiently suppress the sensitivity of the breakdown voltage to the interface states and improve the devices reliability compared with the conventional SiO2 FP termination.

The Field Modulation Effect of a Fluoride Plasma Treatment on the Blocking Characteristics of AlGaN/GaN High Electron Mobility Transistors

We designed and fabricated aluminium gallium nitride (AlGaN)/GaN high electron mobility transistors (HEMTs) with stable reverse blocking characteristics established by employing a selective fluoride plasma treatment on the drainside gate edge region where the electric field is concentrated. Implanted fluoride ions caused a depolarization in the AlGaN layer and introduced an extra depletion region. The overall contour of the depletion region was expanded along the drift region. The expanded depletion region distributed the field more uniformly and reduced the field intensity peak. Through this field modulation, the leakage current was reduced to 9.3 nA and the breakdown voltage (<TEX>$V_{BR}$</TEX>) improved from 900 V to 1,400 V.

Vertical structure Schottky barrier diode fabrication using insulating diamond substrate

To obtain high current operation of the diamond SBDs, the device should be designed in a vertical type structure in order to minimize the device on-resistance. In this research, we have designed and developed the technology for fabrication of diamond vertical structure Schottky barrier diodes (vSBD) by utilizing Inductively Coupled Plasma etching technique. Free standing CVD grown epilayers (p +/p − = 100 μm/5 μm) were obtained by removing the base Ib substrate on which the epi-layers were grown, using ICP etching process. After ICP etching, ohmic contact (Ti/Pt/Au) was made at the bottom of p + layer, and Schottky contact (Mo) was made at top side on oxidized surface of p − layer, to realize Diamond/Mo vSBDs and were analyzed for their electrical characteristics. The SBDs showed a reproducible ideality factor close to 1.0, and a barrier height of 1.4 eV, with a small standard deviation of 0.06 and 0.12 eV respectively. Diodes in the vertical structure exhibited R on with a battery uniformity irrespective of their location on the wafer, compared the diodes in a pseudo-vertical structure. Room temperature I– V analysis of the fabricated vSBDs (70 μm size) exhibited a high forward current density of 2980 A/cm 2 (= 0.115 A) with a low R onS of 8 mΩ cm 2, which could be attained due to the vertical geometry of the diodes. At the high temperature operation, still higher current density could be obtained. Satisfactory reverse blocking characteristics also could be achieved with a breakdown field of 2.7 MV/cm for small size diodes.

Influence of Shockley Stacking Fault Generation on Electrical Behavior of 4H-SiC 10 kV MPS Diodes

The influence of stacking fault (SF) generation on the reverse blocking characteristics has been investigated on SiC 10 kV, 5 A Merged PiN (MPS) diodes. For the first time, we have observed that the generation of SFs under forward biased stress increases the reverse leakage current. In addition, the presence of a secondary diode formed by the electrical stress was observed and attributed to the breakdown voltage failure on certain devices.

Static and Dynamic Characterization of High-Speed Silicon Carbide (SiC) Power Transistors

This paper describes the operating characteristics of NPN 4H-SiC (a polytype of silicon carbide) bipolar junction transistor (BJT) and 4H-SiC Darlington Pairs. A large amount of experimental data was collected. The wafer BJTs were able to block over the rated 600 V in the common-emitter configuration and the TO-220 BJTs were able to block over the 1200 V rated voltage. In the thermal analysis, it is found out that at higher temperatures the forward and reverse (blocking) characteristics were stable at 100°C and 200°C. The transistors show positive temperature coefficients of forward voltage (Vf). In general the current gain (β) characteristics obtained (with VCE = 6 V) were approximately as expected for the BJTs. The β‘s were very low (2 to 5 for wafer BJTs, 5 to 20 for the wafer Darlington Pairs, and 5 to 30 for TO-220 BJTs). The large amount of experimental data collected confirms some of the superior properties of the Silicon carbide material when used to fabricate power semiconductor devices, namely high thermal conductivity and high temperature operability. The data presented here will establish the trends and the performance of silicon carbide devices. The silicon carbide BJT has fast switching and recovery characteristics. From the analysis, silicon carbide power devices will be smaller (about 20 times) than a similar silicon power device and with reduced power losses. Silicon carbide will also be very useful for device integration in high densities, as found in integrated chips for current handling capabilities, for applications in instrumentation and measurements. Presently, most of the research is on improving the basic silicon carbide material quality, power device optimization, and applications engineering using devices that have been developed to date.