Effect of annealing on the electrical performance of N-polarity GaN Schottky barrier diodes

A nitrogen-polarity(N-polarity)GaN-based high electron mobility transistor(HEMT)shows great potential for high-fre-quency solid-state power amplifier applications because its two-dimensional electron gas(2DEG)density and mobility are mini-mally affected by device scaling.However,the Schottky barrier height(SBH)of N-polarity GaN is low.This leads to a large gate leakage in N-polarity GaN-based HEMTs.In this work,we investigate the effect of annealing on the electrical characteristics of N-polarity GaN-based Schottky barrier diodes(SBDs)with Ni/Au electrodes.Our results show that the annealing time and tem-perature have a large influence on the electrical properties of N-polarity GaN SBDs.Compared to the N-polarity SBD without annealing,the SBH and rectification ratio at±5 V of the SBD are increased from 0.51 eV and 30 to 0.77 eV and 7700,respec-tively,and the ideal factor of the SBD is decreased from 1.66 to 1.54 after an optimized annealing process.Our analysis results suggest that the improvement of the electrical properties of SBDs after annealing is mainly due to the reduction of the inter-face state density between Schottky contact metals and N-polarity GaN and the increase of barrier height for the electron emis-sion from the trap state at low reverse bias.

Improvement of Ga_(2)O_(3)vertical Schottky barrier diode by constructing NiO/Ga_(2)O_(3)heterojunction

The high critical electric field strength of Ga_(2)O_(3)enables higher operating voltages and reduced switching losses in power electronic devices.Suitable Schottky metals and epitaxial films are essential for further enhancing device performance.In this work,the fabrication of vertical Ga_(2)O_(3)barrier diodes with three different barrier metals was carried out on an n--Ga_(2)O_(3)homogeneous epitaxial film deposited on an n+-β-Ga_(2)O_(3)substrate by metal-organic chemical vapor deposition,excluding the use of edge terminals.The ideal factor,barrier height,specific on-resistance,and breakdown voltage characteristics of all devices were investigated at room temperature.In addition,the vertical Ga_(2)O_(3)barrier diodes achieve a higher breakdown volt-age and exhibit a reverse leakage as low as 4.82×10^(-8)A/cm^(2)by constructing a NiO/Ga_(2)O_(3)heterojunction.Therefore,Ga_(2)O_(3)power detailed investigations into Schottky barrier metal and NiO/Ga_(2)O_(3)heterojunction of Ga_(2)O_(3)homogeneous epitaxial films are of great research potential in high-efficiency,high-power,and high-reliability applications.

High frequency doubling efficiency THz GaAs Schottky barrier diode based on inverted trapezoidal epitaxial cross-section structure

A high-performance terahertz Schottky barrier diode(SBD)with an inverted trapezoidal epitaxial cross-sectional structure featuring high varactor characteristics and reverse breakdown characteristics is reported in this paper.Inductively coupled plasma dry etching and dissolution wet etching are used to define the profile of the epitaxial layer,by which the voltage-dependent variation trend of the thickness of the metal-semiconductor contact depletion layer is modified.The simulation of the inverted trapezoidal epitaxial cross-section SBD is also conducted to explain the physical mechanism of the electric field and space charge region area.Compared with the normal structure,the grading coefficient M increases from 0.47 to 0.52,and the capacitance modulation ratio(C^(max)/C_(min))increases from 6.70 to 7.61.The inverted trapezoidal epitaxial cross-section structure is a promising approach to improve the variable-capacity ratio by eliminating the accumulation of charge at the Schottky electrode edge.A 190 GHz frequency doubler based on the inverted trapezoidal epitaxial cross-section SBD also shows a doubling efficiency of 35%compared to that 30%of a normal SBD.

Analysis and simulation of a 4H-SiC semi-superjunction Schottky barrier diode for softer reverse-recovery

In this paper, a 4H-SiC semi-superjunction （S J） Schottky barrier diode is analysed and simulated. The semi-SJ structure has an optimized design and a specific on-resistance lower than that of conventional SJ structures, which can be achieved without increasing the process difficulty. The simulation results show that the specific on-resistance and the softness factor depend on the aspect and thickness ratios, and that by using the semi-SJ structure, specific on-resistance can be reduced without decreasing the softness factor. It is observed that a trade-off exists between the specific on-resistance and the softness of the diode.

Study and optimal simulation of 4H-SiC floating junction Schottky barrier diodes' structures and electric properties

This paper stuides the structures of 4H SiC floating junction Schottky barrier diodes. Some structure parameters of devices are optimized with commercial simulator based on forward and reverse electrical characteristics. Compared with conventional power Schottky barrier diodes, the devices are featured by highly doped drift region and embedded floating junction layers, which can ensure high breakdown voltage while keeping lower specific on-state resistance, and solve the contradiction between forward voltage drop and breakdown voltage. The simulation results show that with optimized structure parameter, the breakdown voltage can reach 4.36 kV and the specific on-resistance is 5.8 mΩ.cm2 when the Baliga figure of merit value of 13.1 GW/cm2 is achieved.

A simulation study of field plate termination in Ga2O3 Schottky barrier diodes

In this work, the field plate termination is studied for Ga2O3Schottky barrier diodes(SBDs) by simulation. The influence of field plate overlap, dielectric material and thickness on the termination electric field distribution are demonstrated.It is found that the optimal thickness increases with reverse bias increasing for all the three dielectrics of SiO2, Al2O3, and HfO2. As the thickness increases, the maximum electric field intensity decreases in SiO2and Al2O3, but increases in HfO2.Furthermore, it is found that SiO2and HfO2are suitable for the 600 V rate Ga2O3SBD, and Al2O3is suitable for both600 V and 1200 V rate Ga2O3SBD. In addition, the comparison of Ga2O3SBDs between the SiC and GaN counterpart reveals that for Ga2O3, the breakdown voltage bottleneck is the dielectric. While, for SiC and GaN, the bottleneck is mainly the semiconductor itself.

Lateralβ-Ga_(2)O_(3)Schottky barrier diode fabricated on(-201)single crystal substrate and its temperature-dependent current-voltage characteristics

Lateralβ-Ga_(2)O_(3)Schottky barrier diodes(SBDs)each are fabricated on an unintentionally doped(-201)n-typeβ-Ga_(2)O_(3)single crystal substrate by designing L-shaped electrodes.By introducing sidewall electrodes on both sides of the conductive channel,the SBD demonstrates a high current density of 223 mA/mm and low specific on-resistance of4.7 mΩ·cm^(2).Temperature-dependent performance is studied and the Schottky barrier height is extracted to be in a range between 1.3 eV and 1.35 eV at temperatures ranging from 20℃to 150℃.These results suggest that the lateralβ-Ga_(2)O_(3)SBD has a tremendous potential for future power electronic applications.

Degradation of β-Ga_(2)O_(3) Schottky barrier diode under swift heavy ion irradiation

The electrical characteristics and microstructures ofβ-Ga_(2)O_(3) Schottky barrier diode(SBD)devices irradiated with swift heavy ions(2096 MeV Ta ions)have been studied.It was found thatβ-Ga_(2)O_(3) SBD devices showed the reliability degradation after irradiation,including turn-on voltage Von,on-resistance Ron,ideality factor n,and the reverse leakage current density Jr.In addition,the carrier concentration of the drift layer was decreased significantly and the calculated carrier removal rates were 5×10^(6)-1.3×10^(7)cm^(-1).Latent tracks induced by swift heavy ions were observed visually in the wholeβ-Ga2O3 matrix.Furthermore,crystal structure of tracks was amorphized completely.The latent tracks induced by Ta ions bombardments were found to be the reason for the decrease in carrier mobility and carrier concentration.Eventually,these defects caused the degradation of electrical characteristics of the devices.In terms of the carrier removal rates,theβ-Ga_(2)O_(3) SBD devices were more sensitive to swift heavy ions irradiation than SiC and GaN devices.

Modeling of 4H-SiC multi-floating-junction Schottky barrier diode

This paper develops a new and easy to implement analytical model for the specific on-resistance and electric field distribution along the critical path for 4H-SiC multi-floating junction Schottky barrier diode. Considering the charge compensation effects by the multilayer of buried opposite doped regions, it improves the breakdown voltage a lot in comparison with conventional one with the same on-resistance. The forward resistance of the floating junction Schottky barrier diode consists of several components and the electric field can be understood with superposition concept, both are consistent with MEDICI simulation results. Moreover, device parameters are optimized and the analyses show that in comparison with one layer floating junction, multilayer of floating junction layer is an effective way to increase the device performance when specific resistance and the breakdown voltage are traded off. The results show that the specific resistance increases 3.2 mΩ.cm2 and breakdown voltage increases 422 V with an additional floating junction for the given structure.

4H-SiC trench MOSFET with an integrated Schottky barrier diode and L-shaped P^+shielding region

A novel 4H-SiC trench MOSFET is presented and investigated by simulation in this paper.The device features an integrated Schottky barrier diode and an L-shaped P^+shielding region beneath the gate trench and aside one wall of the gate trench(S-TMOS).The integrated Schottky barrier diode works as a free-wheeling diode in reverse recovery and reverse conduction,which significantly reduces reverse recovery charge(Q_(rr))and reverse turn-on voltage(VF).The L-shaped P^+region effectively shields the coupling of gate and drain,resulting in a lower gate–drain capacitance(C_(gd))and date–drain charge(Q_(gd)).Compared with that of conventional SiC trench MOSFET(C-TMOS),the V_F and Q_(rr)of S-TMOS has reduced by 44%and 75%,respectively,with almost the same forward output current and reverse breakdown voltage.Moreover,the S-TMOS reduces Q_(gd)and C_(gd)by 32%and 22%,respectively,in comparison with C-TMOS.

High energy electron radiation effect on Ni and Ti/4H-SiC Schottky barrier diodes at room temperature

This paper reports that Ni and Ti/4H-SiC Schottky barrier diodes （SBDs） were fabricated and irradiated with 1 MeV electrons up to a dose of 3.43 × 10^14 e/cm2. After radiation, the Schottky barrier height φB of the Ni/4H-SiC SBD increased from 1.20 eV to 1.21 eV, but decreased from 0.95 eV to 0.94 eV for the Ti/4H-SiC SBD. The degradation of φB could be explained by interface states of changed Schottky contacts. The on-state resistance Rs of both diodes increased with the dose, which can be ascribed to the radiation defects. The reverse current of the Ni/4H-SiC SBD slightly increased, but for the Ti/4H-SiC SBD it basically remained the same. At room temperature, φB of the diodes recovered completely after one week, and the RS partly recovered.

Device topological thermal management of β-Ga_(2)O_(3) Schottky barrier diodes

The ultra-wide bandgap semiconductor β gallium oxide(β-Ga_(2) O_(3)) gives promise to low conduction loss and high power for electronic devices. However, due to the natural poor thermal conductivity of β-Ga_(2) O_(3), their power devices suffer from serious self-heating effect. To overcome this problem, we emphasize on the effect of device structure on peak temperature in β-Ga_(2) O_(3) Schottky barrier diodes(SBDs) using TCAD simulation and experiment. The SBD topologies including crystal orientation of β-Ga_(2) O_(3), work function of Schottky metal, anode area, and thickness, were simulated in TCAD, showing that the thickness of β-Ga_(2) O_(3) plays a key role in reducing the peak temperature of diodes. Hence, we fabricated β-Ga_(2) O_(3) SBDs with three different thickness epitaxial layers and five different thickness substrates. The surface temperature of the diodes was measured using an infrared thermal imaging camera. The experimental results are consistent with the simulation results. Thus, our results provide a new thermal management strategy for high power β-Ga_(2) O_(3) diode.

Investigation of lateral spreading current in the 4H-SiC Schottky barrier diode chip

Lateral current spreading in the 4H-SiC Schottky barrier diode(SBD)chip is investigated.The 4H-SiC SBD chips with the same vertical parameters are simulated and fabricated.The results indicate that there is a fixed spreading resistance at on-state in current spreading region for a specific chip.The linear specific spreading resistance at the on-state is calculated to be 8.6Ω/cm in the fabricated chips.The proportion of the lateral spreading current in total forward current(Psp)is related to anode voltage and the chip area.Psp is increased with the increase in the anode voltage during initial on-state and then tends to a stable value.The stable values of Psp of the two fabricated chips are 32%and 54%.Combined with theoretical analysis,the proportion of the terminal region and scribing trench in a whole chip(Ksp)is also calculated and compared with Psp.The Ksp values of the two fabricated chips are calculated to be 31.94%and 57.75%.The values of Ksp and Psp are close with each other in a specific chip.The calculated Ksp can be used to predict that when the chip area of SiC SBD becomes larger than 0.5 cm2,the value of Psp would be lower than 10%.

Design and simulation of AlN-based vertical Schottky barrier diodes

The key parameters of vertical AlN Schottky barrier diodes(SBDs) with variable drift layer thickness(DLT) and drift layer concentration(DLC) are investigated. The specific on-resistance(R_(on,sp)) decreased to 0.5 mΩ · cm^(2) and the breakdown voltage(V_(BR)) decreased from 3.4 kV to 1.1 kV by changing the DLC from 10^(15) cm^(-3) to 3×10^(16) cm^(-3). The VBRincreases from 1.5 kV to 3.4 kV and the Ron,sp also increases to 12.64 mΩ · cm^(2) by increasing DLT from 4-μm to 11-μm. The VBRenhancement results from the increase of depletion region extension. The Baliga's figure of merit(BFOM) of3.8 GW/cm^(2) was obtained in the structure of 11-μm DLT and 10^(16) cm^(-3) DLC without FP. When DLT or DLC is variable,the consideration of the value of BFOM is essential. In this paper, we also present the vertical AlN SBD with a field plate(FP), which decreases the crowding of electric field in electrode edge. All the key parameters were optimized by simulating based on Silvaco-ATLAS.

Characterization of ion-implanted 4H-SiC Schottky barrier diodes

Ion-implantation layers are fabricated by multiple nitrogen ion-implantations （3 times for sample A and 4 times for sample B） into a p-type 4H-SiC epitaxial layer. The implantation depth profiles are calculated by using the Monte Carlo simulator TRIM. The fabrication process and the I-V and C V characteristics of the lateral Ti/4H-SiC Schottky barrier diodes （SBDs） fabricated on these multiple box-like ion-implantation layers are presented in detail. Measurements of the reverse I V characteristics demonstrate a low reverse current, which is good enough for many SiC-based devices such as SiC metal-semiconductor field-effect transistors （MESFETs）, and SiC static induction transistors （SITs）. The parameters of the diodes are extracted from the forward I-V and C-V characteristics. The values of ideality factor n of SBDs for samples A and B are 3.0 and 3.5 respectively, and the values of series resistance Rs are 11.9 and 1.0 kf~ respectively. The values of barrier height φB of Ti/4H-SiC are 0.95 and 0.72 eV obtained by the I-V method and 1.14 and 0.93 eV obtained by the C-V method for samples A and B respectively. The activation rates for the implanted nitrogen ions of samples A and B are 2% and 4% respectively extracted from C V testing results.

Breakdown characteristics of AlGaN/GaN Schottky barrier diodes fabricated on a silicon substrate

In this work, the breakdown characteristics of AlGaN/GaN planar Schottky barrier diodes （SBDs） fabricated on the silicon substrate are investigated. The breakdown voltage （BV） of the SBDs first increases as a function of the anodeto-cathode distance and then tends to saturate at larger inter-electrode spacing. The saturation behavior of the BV is likely caused by the vertical breakdown through the intrinsic GaN buffer layer on silicon, which is supported by the post-breakdown primary leakage path analysis with the emission microscopy. Surface passivation and field plate termination are found effective to suppress the leakage current and enhance the BV of the SBDs. A high BV of 601 V is obtained with a low on-resistance of 3.15 mΩ·cm^2.

Influence of dry-etching damage on the electrical properties of an AlGaN/GaN Schottky barrier diode with recessed anode

The influences of dry-etching damage on the electrical properties of an AlGaN/GaN Schottky barrier diode with ICPrecessed anode was investigated for the first time. It was found that the turn-on voltage is decreased with the increase of dry-etching power. Furthermore, the leakage currents in the reverse bias region above pinch-off voltage rise as radio frequency（RF） power increases, while below pinch-off voltage, leakage currents tend to be independent of RF power.Based on detailed current–voltage–temperature（I–V –T） measurements, the barrier height of thermionic-field emission（TFE） from GaN is lowered as RF power increases, which results in early conduction. The increase of leakage current can be explained by Frenkel–Poole（FP） emission that higher dry-etching damage in the sidewall leads to the higher tunneling current, while below pinch-off voltage, the leakage is only related to the AlGaN surface, which is independent of RF power.

The Cu Based AlGaN/GaN Schottky Barrier Diode

The electrical characteristics of Cu and Ni/Al AlGaN/GaN Schottky barrier diodes on Si su bstrates are compared. The onset voltage of Cu Schottky diodes is about 0.4 V less than the Ni/Al contact. For the Cu/Ni Schottky contact, the leakage current is 4.7 × 10^-7 A/mm at -10 V. After annealing, the leakage current is decreased to 3.7 × 10^-7 A/mm for 400℃ or 4.6 × 10^-8 A/mm for 500℃, respectively. The electrical property is affected by the thickness ratio of Cu to Ni. The Cu/Ni for 80/20 nm shows a low onset voltage, while the Cu/Ni for 20/80 nm shows a low leakage current. Both breakdown voltages are above 720 V.

Design of vertical diamond Schottky barrier diode with junction terminal extension structure by using the n-Ga_(2)O_(3)/p-diamond heterojunction

A novel junction terminal extension structure is proposed for vertical diamond Schottky barrier diodes(SBDs) by using an n-Ga_(2)O_(3)/p-diamond heterojunction. The depletion region of the heterojunction suppresses part of the forward current conduction path, which slightly increases the on-resistance. On the other hand, the reverse breakdown voltage is enhanced obviously because of attenuated electric field crowding. By optimizing the doping concentration, length, and depth of n-Ga_(2)O_(3), the trade-off between on-resistance and breakdown voltage with a high Baliga figure of merit(FOM)value is realized through Silvaco technology computer-aided design simulation. In addition, the effect of the work functions of the Schottky electrodes is evaluated. The results are beneficial to realizing a high-performance vertical diamond SBD.

Hybrid-anode structure designed for a high-performance quasi-vertical GaN Schottky barrier diode

A quasi-vertical Ga N Schottky barrier diode with a hybrid anode structure is proposed to trade off the on-resistance and the breakdown voltage.By inserting a Si N dielectric between the anode metal with a relatively small length,it suppresses the electric field crowding effect without presenting an obvious effect on the forward characteristics.The enhanced breakdown voltage is ascribed to the charge-coupling effect between the insulation dielectric layer and Ga N.On the other hand,the current density is decreased beneath the dielectric layer with the increasing length of the Si N,resulting in a high on-resistance.Furthermore,the introduction of the field plate on the side wall forms an metal-oxide-semiconductor(MOS)channel and decreases the series resistance,but also shows an obvious electric field crowding effect at the bottom of the mesa due to the quasi-vertical structure.