High performance of high-voltage 4H-SiC Schottky barrier diodes

High performance of high-voltage rectifiers could be realized utilizing 4H-SiC Schottky barrier diodes. A typical specific on-resistance (R_on) of these devices was 1.4×10³ Ω cm³ at 24°C (room temperature) with breakdown voltages as high as 800 V. These devices based on 4H-SiC had R _on's lower than 6H-SiC based high-power rectifiers with the same breakdown voltage. As for Schottky contact metals, Au, Ni, and Ti were employed in this study. The barrier heights of these metals for 4H-SiC were determined by the analysis of current-voltage characteristics, and the reduction of power loss could be achieved by controlling the barrier heights     

P-type 4H and 6H-SiC high-voltage Schottky barrier diodes

High-voltage Schottky barrier diodes have been successfully fabricated for the first time on p-type 4H- and 6H-SiC using Ti as the barrier metal. Good rectification was confirmed at temperatures as high as 250°C. The barrier heights were estimated to be 1.8-2.0 eV for 6H-SiC and 1.1-1.5 eV for 4H-SiC at room temperature using both I-V and C-V measurements. The specific on resistance (R_on,sp) for 4H- and 6H-SiC were found to be 25 mΩ cm^-2 and 70 mΩ cm^-2 at room temperature. A monotonic decrease in resistance occurs with increasing temperature for both polytypes due to increased ionization of dopants. An analytical model is presented to explain the decrease of R_on,sp with temperature for both 4H and 6H-SiC which fits the experimental data. Critical electric field strength for breakdown was extracted for the first time in both p-type 4H and 6H-SiC using the breakdown voltage and was found to be 2.9×10⁶ V/cm and 3.3×10⁶ V/cm, respectively. The breakdown voltage remained fairly constant with temperature for 4H-SiC while it was found to decrease with temperature for 6H-SiC     

Optimized design of 4H-SiC floating junction power Schottky barrier diodes

SiC floating junction Schottky barrier diodes were simulated with software MEDICI 4.0 and their device structures were optimized based on forward and reverse electrical characteristics.Compared with the conventional power Schottky barrier diode,the device structure is featured by a highly doped drift region and embedded floating junction region,which can ensure high breakdown voltage while keeping lower specific on-state resistance,solved the contradiction between forward voltage drop and breakdown voltage.The simulation results show that with optimized structure parameter,the breakdown voltage Can reach 4 kV and the specific on-resistance is 8.3 mΩ·cm2.     

Demonstration of the first 10-kV 4H-SiC Schottky barrier diodes

This letter reports the demonstration of the first 4H-SiC Schottky barrier diode (SBD) blocking over 10 kV based on 115-/spl mu/m n-type epilayers doped to 5.6 /spl times/ 10/sup 14/ cm/sup -3/ through the use of a multistep junction termination extension. The blocking voltage substantially surpasses the former 4H-SiC SBD record of 4.9 kV. A current density of 48 A/cm/sup 2/ is achieved with a forward voltage drop of 6 V. The Schottky barrier height, ideality factor, and electron mobility for this very thick epilayer are reported. The SBD's specific-on resistance is also reported.     

浮结型碳化硅肖特基势垒功率二极管的优化设计

SiC floating junction Schottky barrier diodes were simulated with software MEDICI 4.0 and their device structures were optimized based on forward and reverse electrical characteristics. Compared with the conventional power Schottky barrier diode, the device structure is featured by a highly doped drift region and embedded floating junction region, which can ensure high breakdown voltage while keeping lower specific on-state resistance, solved the contradiction between forward voltage drop and breakdown voltage. The simulation results show that with opti- mized structure parameter, the breakdown voltage can reach 4 kV and the specific on-resistance is 8.3 mΩ·cm2.     

I-V characteristics of high-voltage 4H-SiC diodes with a 1.1-eV Schottky barrier

The I-V characteristics of high-voltage 4H-SiC diodes with a Schottky barrier ∼1.1 eV in height are measured and analyzed. The forward I-V characteristics proved to be close to “ideal” in the temperature range of 295–470 K. The reverse I-V characteristics are adequately described by the model of thermionic emission at the voltages to 2 kV in the temperature range of 361–470 K if, additionally, a barrier lowering with an increase in the band bending in the semiconductor is taken into account.     

Effect of annealing temperature on the electrical characteristics of Platinum/4H-SiC Schottky barrier diodes

Pt/4H-SiC Schottky barrier diodes have been fabricated to investigate the effect of annealing on the electrical characteristics of the fabricated devices. The parameters such as barrier height, ideality factor and donor concentration were deduced from the current–voltage (I–V) and the capacitance–voltage (C–V) measurements at room temperature. Diodes showed non-ideal behaviour like high value of ideality factor and lower value of barrier height. A barrier height of 1.82?eV was obtained from C–V measurements and it was 1.07?eV when obtained from the I–V measurements with ideality factor 1.71 for as-deposited diodes at room temperature. The diodes, therefore, were annealed in the temperature range from 25°C to 400°C to observe the effect of annealing temperature on these parameters. Schottky barrier height and ideality factors were found to be temperature-dependent. After rapid thermal annealing upto 400°C, a barrier height of 1.59?eV from C–V measurements and the value of 1.40?eV from I–V measurements with ideality factor 1.12 were obtained. Barrier heights deduced from C–V measurements were consistently larger than those obtained from I–V measurements. To come to terms with this discrepancy, we re-examined our results by including the effect of ideality factor in the expression of the barrier height. This inclusion of ideality factor results in reasonably good agreement between the values of barrier height deduced by the above two methods. We believe that these improvements in the electrical parameters result from the improvement in the quality of interfacial layer.     

Unterminated 4H-SiC Schottky barrier diodes with novel HfNxBy electrodes

4H-SiC Schottky barrier diodes (SBDs) were fabricated and characterized from room temperature to 573 K using HfN_xB_y as Schottky electrodes. The results are compared to SBDs fabricated using other electrodes that include Ni, Pt, Ti and Au. The Schottky barrier height Φ_b for as-deposited HfN_xB_y/n−/n+ diodes, determined from room temperature current-voltage characteristics, is 0.887 eV. This is lower than those of SBDs fabricated using other metals such as Au, where Φ_b is 1.79 eV. The HfN_xB_y/n−/n+ diodes studied have a much higher on-resistance R_on of around 38.24 mΩ-cm², which is about four times that of Au/n−/n+ diodes, due to the higher sheet resistance of the sputtered HfN_xB_y electrode layer. The barrier height Φ_b and ideality factor η of the HfN_xB_y/n−/n+ diodes remain almost unchanged after 400 and 750 °C anneal in N₂. This suggests excellent thermal and chemical stability of HfN_xB_y in contact with 4H-SiC.     

Gaussian distribution of inhomogeneous barrier height in tungsten/4H-SiC (000-1) Schottky diodes

The Gaussian distribution model have been used to analyze the anomalies observed in tungsten (W)/4H-SiC current voltage characteristics due to the barrier inhomogeneities that prevail at the metal-semiconductor interface. From the analysis of the forward I-V characteristics measured at elevated temperatures within the range of 303-448 K and by the assumption of a Gaussian distribution (GD) of barrier heights (BHs), a mean barrier height of 1.277 eV, a zero-bias standard deviation σ₀ = 0.092 V and a factor T₀ of 21.69 K have been obtained. Furthermore the modified Richardson plot according to the Gaussian distribution model resulted in a mean barrier height and a Richardson constant (A^∗) of 1.276 eV and 145 A/cm² K², respectively. The A^∗ value obtained from this plot is in very close agreement with the theoretical value of 146 A/cm² K² for n-type 4H-SiC. Therefore, it has been concluded that the temperature dependence of the forward I-V characteristics of the W/4H-SiC contacts can be successfully explained on the basis of a thermionic emission conduction mechanism with Gaussian distributed barriers. In addition, a comparison is made between the present results and those obtained previously assuming the pinch-off model.     

4H-silicon carbide Schottky barrier diodes for microwave applications

In this paper, physical models for vertical 4H-silicon carbide (4H-SiC) Schottky diodes are used to develop a design method, where a maximum cutoff frequency for a given punch-through is achieved. The models presented are also used to extract microwave simulator computer-aided design (CAD) models for the devices. A device process was developed and Schottky diodes were fabricated in-house. Characterization of the devices was performed and compared to the theoretical models with good agreement. A demonstrator singly balanced diode mixer was simulated using the developed models. The mixer was fabricated using the in-house developed diodes, and measurements on the mixer show good agreement with the CAD simulations. A conversion loss of 5.2 dB was achieved at 850 MHz, and an excellent IIP/sub 3/ of 31 dBm at 850-MHz RF was measured, at 30-dBm P/sub LO/. These results verify the enhanced properties of the SiC Schottky diode compared to other nonwide bandgap diodes.     

The influence of high energy electron irradiation on the Schottky barrier height and the Richardson constant of Ni/4H-SiC Schottky diodes

The influence of high energy electron (HEE) irradiation from a Sr-90 radio-nuclide on n-type Ni/4H–SiC samples of doping density 7.1×10¹⁵ cm⁻³ has been investigated over the temperature range 40–300 K. Current–voltage (I–V), capacitance–voltage (C–V) and deep level transient spectroscopy (DLTS) were used to characterize the devices before and after irradiation at a fluence of 6×10¹⁴ electrons-cm⁻². For both devices, the I–V characteristics were well described by thermionic emission (TE) in the temperature range 120–300 K, but deviated from TE theory at temperature below 120 K. The current flowing through the interface at a bias of 2.0 V from pure thermionic emission to thermionic field emission within the depletion region with the free carrier concentrations of the devices decreased from 7.8×10¹⁵ to 6.8×10¹⁵ cm⁻³ after HEE irradiation. The modified Richardson constants were determined from the Gaussian distribution of the barrier height across the contact and found to be 133 and 163 A cm⁻² K⁻² for as-deposited and irradiated diodes, respectively. Three new defects with energies 0.22, 0.40 and 0.71 eV appeared after HEE irradiation. Richardson constants were significantly less than the theoretical value which was ascribed to a small active device area.     

Intrinsic 4H-SiC parameters study by temperature behaviour analysis of Schottky diodes

The main intrinsic parameters in silicon carbide material are not exhaustively studied up to now. An experimental study of the behaviour of electrical parameters of Schottky barrier diodes (SBD) fabricated on the Si face of 4H-SiC epitaxial layers with respect to temperature is shown. Analysed devices present an electrical behaviour in accordance to thermoionic emission and a good metal-semiconductor interface uniformly confirmed by capacitance/voltage measurements (C-V). Current/voltage measurements (I-V) have been performed in a large temperature range and lead to an evaluation of the Richardson constant.     

Fabrication and characteristics of a 4H-SiC junction barrier Schottky diode

4H-SiC junction barrier Schottky(JBS)diodes with four kinds of design have been fabricated and characterized using two different processes in which one is fabricated by making the P-type ohmic contact of the anode independently,and the other is processed by depositing a Schottky metal multi-layer on the whole anode.The reverse performances are compared to find the influences of these factors.The results show that JBS diodes with field guard rings have a lower reverse current density and a higher breakdown voltage,and with independent P-type ohmic contact manufacturing,the reverse performance of 4H-SiC JBS diodes can be improved effectively. Furthermore,the P-type ohmic contact is studied in this work.     

4H-SiC结型势垒肖特基二极管的制作与特性研究

本文设计制作了两种具有不同结构参数的4H-SiC结型势垒肖特基二极管,在制作过程中采用了两种制作方法：一种是对正电极上的P型欧姆接触进行单独制作,然后制作肖特基接触的工艺过程;另一种是通用的通过一次肖特基接触制作就完成正电极制作的工艺过程。器件制作完成后,通过测试结果比较了采用场限环作为边界终端与未采用边界终端的器件的反向特性,结果显示采用场限环有效地提高了该器件的击穿电压,减小了其反向电流。另外,测试结果还显示采用独立制作P型欧姆接触的工艺过程有效提高了4H-SiC结型势垒肖特基二极管的反向特性,其中P型欧姆接触的制作过程和结果也在本文中做出了详细叙述。     

不同退火温度下金属/4H-SiC Schottky势垒高度的研究

采用磁控溅射的方法在4H-SiC样品上分别沉积四种金属薄膜(Ag,Cu,Ni,Cr)形成Schottky接触,研究了不同温度退火对Schottky势垒高度的影响.通过对样品的I-V测试结果的拟合,得到各金属/4H-SiC Schottky接触的势垒高度以及理想因子.在反向偏压100V下,样品的反向漏电流小于10-10A,说明样品的反向特性良好.样品经过不同温度的退火后,发现Cu、Ni与4H-SiC的势垒高度(SBH)随退火温度的升高而提高,超过某一温度,其整流特性变差;Ag、Cr的SBH在退火后降低.SBH与金属功函数呈线性关系(Cr金属除外),斜率为0.11.     

Gallium arsenide dual Schottky barrier diodes

Gallium arsenide diodes were made which had Schottky-barriers for both contacts. Devices which were too thick for space change reach-through to occur at breakdown showed microwave oscillations, while thin diodes did not oscillate. Additionally, the structures could be distinguished on the basis of the noise accompanying breakdown. The performance was analysed in terms of transistor theory in which there is avalanche multiplication in the collector space charge region. It was concluded that there is a smooth transition between the reachthrough breakdown characteristic of the BARITT and true avalanche breakdown. The nature of the breakdown depends on the base width and the emitter efficiency.     

Thermally oxidized mesa Schottky barrier diodes

Schottky barriers with a thermally oxidized mesa structure have been fabricated. The fabrication process is described. The mesa structure averts electric field crowding at the barrier periphery. The reverse diode characteristic shows a sharp breakdown at the voltage expected for an ideal, abrupt diode of semi-infinite extent and identical doping concentration.