4H-SiC Diodes Research Articles

Sub-nanosecond semiconductor opening switches based on 4H–SiC p +p on +-diodes

4H–SiC p +n on +- and p +p on +-type diodes have been fabricated and evaluated as opening switch devices which are known in Si to employ the effect of fast reverse current break after switching the diodes from forward to reverse bias conditions. The recovery properties of p +p on +-diodes were found to be drastically differ from those of p +n on +-type ones. In p +n on +-diodes, recombination processes predetermine soft recovery behavior in a time of approximately 16 ns. In p +p on +-type diodes, purely drift mechanism was found to be responsible, under proper conditions, for the very fast reverse current break in a time less than 1 ns. p +p on +-Diodes were utilized in a pulse generator which was fabricated with an inductive energy storing unit. The rise time of 400-V pulses generated, about 4 ns, was found to be equal to the quarter of the oscillation period of the LC-tank consisting of 2-μH storing inductance and 2-pF 4H–SiC diode capacitance.

Carrier lifetime measurements in 10 kV 4H-SiC diodes

The minority carrier lifetime τp has been measured by open circuit voltage decay (OCVD) and current recovery time (CRT) (or Lax-Neustadter's) techniques in high-voltage (10 kV) 4H-SiC p+n0n+ diodes. The τp value measured by OCVD is 1.55 µs at room temperature, which is the highest reported value for 4H-SiC diodes. CRT measurements indicate a homogeneous distribution of carrier lifetime across the diode base without any deteriorated layer between the p+-emitter and the n0-base. Some limitations of lifetime measurements by CRT are discussed.

Characterization of hard- and soft-switching performance of high-voltage Si and 4H-SiC PiN diodes

This paper presents a study of the performance of high-voltage Si and 4H-SiC diodes in a DC-DC buck converter. Device operation in both hard- and zero-voltage switching conditions is presented with the help of measurements and two-dimensional (2-D) mixed device-circuit simulations. Experimental results show that SiC PiN diodes have a strong potential for use in high-speed high-voltage power electronics applications operating at high temperature. A combination of low excess carrier concentration and low carrier lifetime results in superior switching performance of the 4H-SiC diode over ultrafast Si diodes. Soft switching is shown to minimize the switching loss and allow operation at higher switching frequencies using Si diodes. The power loss of 4H-SiC diodes is dominated by conduction loss. Consequently, soft-switching techniques result in a marginal reduction in power loss. However, the low overall power loss implies that SiC diodes can be used at very high switching frequencies even in hard-switching configurations.

Multiplication and excess noise characteristics of thin 4H-SiC UV avalanche photodiodes

The avalanche multiplication and excess noise characteristics of thin 4H-SiC avalanche photodiodes with an i-region width of 0.1 /spl mu/m have been investigated. The diodes are found to exhibit multiplication characteristics which change significantly when the wavelength of the illuminating light changes from 230 to 365 nm. These multiplication characteristics show unambiguously that /spl beta/>/spl alpha/ in 4H-SiC and that the /spl beta///spl alpha/ ratio remains large even in thin 4H-SiC diodes. Low excess noise, corresponding to k=0.1 in the local model where k=/spl alpha///spl beta/ for hole injection, was measured using 325-nm light. The results indicate that 4H-SiC is a suitable material for realizing low-noise UV avalanche photodiodes requiring good visible-blind performance.

On the possibility of creating a superfast-recovery silicon carbide diode

The possibility of a superfast (<1 ns) termination of the reverse current during the recovery of a 4H-SiC diode with a p+p0n+ structure is experimentally demonstrated for the first time. It is shown that the gate recovery process is much like that taking place in inverse-recovery silicon diodes.

Measurement and Device Simulation of Avalanche Breakdown in High-Voltage 4H-SiC Diodes Including the Influence of Macroscopic Defects

Measurement and Device Simulation of Avalanche Breakdown in High-Voltage 4H-SiC Diodes Including the Influence of Macroscopic Defects

Material quality improvements for high voltage 4H-SiC diodes

The influence of thin 4H-SiC buffer layers grown by liquid phase epitaxy (LPE) on structural quality of 4H-SiC low-doped epitaxial layers, grown by chemical vapor deposition (CVD) was investigated in detail. A dramatic defect density reduction in CVD epitaxial layers grown on commercial wafers with buffer LPE layer was detected. P +n junctions were formed on these CVD layers by high dose Al ion implantation followed by rapid thermal anneal. It was shown that both the increase of diffusion lengths of minority carriers (Lp) in CVD layers and the forming of p +-layers after Al ion implantation and high temperature anneal lead to superior device characteristics.

Crystal Defects as Source of Anomalous Forward Voltage Increase of 4H-SiC Diodes

Crystal Defects as Source of Anomalous Forward Voltage Increase of 4H-SiC Diodes

X-band Silicon Carbide IMPATT Oscillator

ABSTRACTPulsed X-band (8.2 - 12.4 GHz) IMPATT oscillators have been fabricated and characterized. They utilized 4H-SiC diodes with single drift p+-n-n+ structures and avalanche breakdown voltages of about 290 V. The microwave oscillations appeared at a threshold current of 0.3 A. The maximum measured output power was about 300 mW at input pulse current of 0.35 A and pulse duration of 40 ns.

An improved technology of 6H-SiC power diodes

A refined technology of SiC p–n junctions is proposed. Usage of boron to compensate the high doping of n layers on structures with different continuous areas is primarily experimentally demonstrated. A comparison between the electrical characteristics of boron compensated and uncompensated diodes is presented. Then a technology using cellular structure for 6H-SiC large area p–n devices is designed and optimized. For these split area structures the micropipes effect is avoided. Based on a matrix structure with 0.16mm2 cell area a medium power (600V breakdown voltage and 1A at forward voltage of 5V) p–n diode has been fabricated and tested.

Dynamic Avalanche and Trapped Charge in 4H-SiC Diodes

A dynamically reduced breakdown voltage from more than 2 kV under static conditions to 300 V during reverse recovery was measured for 4H-SiC p(+)nn(+) diodes. Device simulation indicates that deep ...

6H-SiC Diodes with Cellular Structure to Avoid Micropipe Effects

6H-SiC Diodes with Cellular Structure to Avoid Micropipe Effects

Fabrication and Characterization of 4H-SiC GTOs and Diodes

Fabrication and Characterization of 4H-SiC GTOs and Diodes

Dynamic and Steady-State Description of Incomplete Ionization in 4H-SiC Power Diodes under Turn-Off

Dynamic and static description of incomplete ionization in 4H-SiC power diodes under turn-off

Simulation and Fabrication of High-Voltage 4H-SiC Diodes with Multiple Floating Guard Ring Termination

Simulation and Fabrication of High-Voltage 4H-SiC Diodes with Multiple Floating Guard Ring Termination

The Temperature Dependent Breakdown Voltage For 4H- and 6H-SiC Diodes

ABSTRACTThe breakdown voltages of 6H- and 4H-SiC rectifiers as function of temperature were modeled analytically in both non-reachthrough diode and reachthrough diode. The breakdown voltage was derived by the ionization integral employing accurate hole impact ionization coefficient. The breakdown voltage of SiC rectifiers was increased with increasing temperature and the positive temperature coefficient of breakdown voltage indicates that SiC rectifiers are suitable for high temperature applications. The breakdown voltages of both 6H- and 4H-SiC diodes were increased by M(T)-1/4 in NRDs and M(T)-1/8 in RDs.

High voltage SiC diodes with small recovery time

4H-SiC diodes with 6 kV blocking capability, low forward voltage drop (4.2 V at 100 A/cm2, 5.8 V at 500 A/cm2), and very small recovery time (≤ 7 ns) have been demonstrated for the first time. Experimental results can be explained by the combination of high lifetime across the major part of the base and the presence near the metallurgical boundary of the p+n junction of a thin layer with a very small carrier lifetime.

Capacitance measurements for diodes in the case of strong dependence of the diode-base series resistance on the applied voltage

Epitaxial-diffused 6H-SiC diodes incorporating a high-resistivity interlayer in the base were studied; the resistance of this interlayer varied when the forward-bias voltage was applied. It is shown that, in spite of the absence of direct indications of the effects of the series resistance (the capacitance is independent of frequency and the value of capacitive cutoff voltage is small), the capacitance measurements for such structures may be incorrect.

High hole lifetime (3.8 µs) in 4H-SiC diodeswith 5.5 kV blocking voltage

The hole lifetime τp in the n-base of 4H-SiC diodes with 5.5 kV blocking voltage has been measured in the temperature range 300–550 K. The τp increases monotonically in this temperature range from 0.6 to 3.8 µs. Forward current-voltage characteristics demonstrate a very high level of base modulation by minority carriers.

Direct observation of excess carrier distribution in 4H-SiC power diodes

The first direct measurements of electrically injected carrier distributions in the base of 4H-SiC power diodes are reported. A novel approach of combining micron-resolution free-carrier absorption technique with optical imaging of e-h recombination radiation was applied to study the spatial and temporal plasma build-up. The excess carrier distributions both along and across the base region were examined during forward biasing within a 50-250 A/cm/sup 2/ range. The revealed local deviations of carrier density and lifetimes are attributed to inherent structural imperfections of the epilayer. Numerical device simulation demonstrated a good agreement with experiment and validated the importance of actual lifetime, contact, and emitter injection parameters to the overall plasma formation.