N-type Schottky Diodes Research Articles

SiC superjunction MOSFET with Schottky diode for improving short-circuit and reverse recovery ruggedness

In this article, a novel SiC superjunction MOSFET with Schottky diode containing N- and P-type barrier is proposed to improving short-circuit and reverse recovery ruggedness, investigated by TCAD simulations. The adoption of superjunction and p-shields structure can reduce saturation current, and thus, improve short-circuit capability. A fine gate oxide providing long-term reliability of the device is obtained. Also, N-type Schottky diode for electrons is used to dampen bipolar conduction of the parasitic body diode, while P-type Schottky diode for holes is introduced to constrain the hole inflow and extraction attributed to the transient variation of the superjunction. As a result, compared with an SBD-wall-integrated trench MOSFET (SWITCH-MOS), a low on-resistance and high breakdown voltage of the proposed structure are gained. More importantly, the proposed device exhibits stronger temperature-dependent immunity. As expected, simulation results indicate that the proposed device under 10 nH stray inductance shows a 30%–50 % reduction in the peak reverse recovery current and a 50%–70 % decrease in the current rising slope of reverse recovery, compared to only a single superjunction, when the metal workfunction varies from 5.1 to 5.6 eV. Moreover, the short-circuit withstanding time of the proposed structure increases roughly 2 times longer than that of SWITCH-MOS.

A Low-Reverse-Recovery-Charge Superjunction MOSFET With P-Base and N-Pillar Schottky Contacts

A superjunction metal-oxide-semiconductor field-effect transistor (SJ-MOSFET) with P-base and N-pillar Schottky contacts is proposed and investigated in this article. The dual Schottky contacts form a p-type Schottky diode and an n-type Schottky diode on the surface of the device, respectively. During the reverse conduction stage, the operation of the body p-n junction diode is suppressed by the reverse-biased p-type Schottky diode, and the reverse current is fully conducted by the n-type Schottky diode. Therefore, the minority carrier injection is completely suppressed, leading to an ultralow reverse recovery charge. TCAD simulation results show that, in comparison with the conventional SJ-MOSFET, up to 95.7% reduction in reverse recovery charge could be achieved.

Shell thickness matters! Energy transfer and rectification study of Au/ZnO core/shell nanoparticles

In the present study we report the influence of shell thickness on fluorescence resonance energy transfer between Au/ZnO core-shell nanoparticles and Rhodamine 6G dye by steady-state and time-resolved spectroscopy and rectification behaviours. Au/ZnO core-shell nanoparticles with different shell thickness were synthesized in aqueous solution by chemically depositing zinc oxide on gold nanoparticles surface. A pronounced effect on the photoluminescence (PL) intensity and shortening of the decay time of the dye in presence of Au/ZnO core-shell nanoparticles is observed. The calculated energy transfer efficiencies from dye to Au/ZnO are 62.5%, 79.2%, 53.6% and 46.7% for 1.5nm, 3nm, 5nm and 8nm thickness of shell, respectively. Using FRET process, the calculated distances (r) are 117.8, 113.2Å 129.9Å and 136.7Å for 1.5nm, 3nm, 5nm and 8nm thick Au/ZnO core-shell nanoparticles, respectively. The distances (d) between the donor and acceptor are 71.0, 57.8, 76.2 and 81.6Å for 1.5nm, 3nm, 5nm and 8nm thick core-shell Au/ZnO nanoparticles, respectively, using the efficiency of surface energy transfer (SET). The current-voltage (I-V) curve of hybrid Au/ZnO clearly exhibits a rectifying nature and represents the n-type Schottky diode characteristics with a typical turn-on voltage of between 0.6 and 1.3V. It was found that the rectifying ratio increases from 20 to 90 with decreasing the thickness of the shell from 5nm to 3nm and with shell thickness of 8nm, electrical transport through the core-shell is similar to what is observed with pure ZnO samples nanoparticles. The results indicated that the Au/ZnO core-shell nanoparticles with an average shell thickness of 3nm exhibited the maximum energy transfer efficiencies (79.2%) and rectification (rectifying ratio 90).

Effects of post-growth annealing on InGaAs quantum posts embedded in Schottky diodes

We study effects of rapid thermal annealing on photoluminescence and electron confinement of InGaAs quantum posts by means of photoluminescence experiments and capacitance–voltage spectroscopy. The quantum posts are embedded in n-type Schottky diodes grown by molecular beam epitaxy on GaAs(1 0 0). The observed photoluminescence spectra arise from the quantum posts as well as from a contribution of a wetting-layer superlattice. With increasing annealing temperatures, the quantum-post photoluminescence blueshifts toward the wetting-layer superlattice, and upon the highest annealing step, the wetting-layer superlattice luminescence dominates. In capacitance–voltage experiments, we clearly observe a charge accumulation in the quantum-post layer as well as from the wetting-layer superlattice. Capacitance–voltage spectra and carrier-density profiles only experience slight changes upon annealing treatments. We suggest that the main electron accumulation takes place in the wetting-layer superlattice.

Deep-level transient spectroscopy of low-energy ion-irradiated silicon

During electron-gun deposition of metal layers on semiconductors, the semiconductor is bombarded with low-energy metal ions creating defects in the outermost surface layer. For many years, it has been a puzzle why deep-level transient spectroscopy spectra of the as-deposited, electron-gun evaporated, n-type Schottky diodes are so simple displaying only one peak consisting of the merged E center and single-acceptor divacancy peaks, and no A center and double-acceptor divacancy peaks. With reference to a recent publication, we demonstrate that this is not due to a reduced production of divacancies and A centers in this situation but to the localization of these defects in highly defected regions.

Exact solutions for the capacitance of space charge regions at semiconductor interfaces

General mathematical expressions on capacitance behavior of space charge regions at semiconductor interfaces are presented. They lead to an analytical solution for the capacitance of a n-type Schottky diode.

Barrier height determination of SiC Schottky diodes by capacitance and current–voltage measurements

Extractions of barrier heights of 6H and 4H-SiC Schottky diodes have been performed on structures with various gate metallization, using both capacitance–voltage (C–V) and current–voltage (I–V) measurements. The sum of the two barriers extracted by C–V measurements on both n-type and p-type materials is found to be higher than the band gap energy EG, whereas the one extracted by I–V is less than EG. However, above room temperature, temperature variations of barrier heights are in agreement with the variations of EG. We have also computed theoretical I–V characteristics using a two-barrier height model. By taking account of temperature variations of a large number of parameters, e.g., the carrier mobility, free carrier concentration, and barrier height, we have achieved a good fit with experimental data. The model is shown to be valid for n-type Schottky diodes over a wide range of temperatures (from 100 to 500 K).

Study of electrically active defects in n-GaN layer

Deep level defects in both p +/n junctions and n-type Schottky GaN diodes are studied using the Fourier transform deep level transient spectroscopy. An electron trap level was detected in the range of energies at E c− E t=0.23–0.27 eV with a capture cross-section of the order of 10 −19–10 −16 cm 2 for both the p +/n and n-type Schottky GaN diodes. For one set of p +/n diodes with a structure of Au/Pt/p +–GaN/n–GaN/n + –GaN/Ti/Al/Pd/Au and the n-type Schottky diodes, two other common electron traps are found at energy positions, E c− E t=0.53–0.56 eV and 0.79–0.82 eV. In addition, an electron trap level with energy position at E c− E t=1.07 eV and a capture cross-section of σ n=1.6×10 −13 cm 2 are detected for the n-type Schottky diodes. This trap level has not been previously reported in the literature. For the other set of p +/n diodes with a structure of Au/Ni/p +–GaN/n–GaN/n +–GaN/Ti/Al/Pd/Au, a prominent minority carrier (hole) trap level was also identified with an energy position at E t− E v=0.85 eV and a capture cross-section of σ n=8.1×10 −14 cm 2. The 0.56 eV electron trap level observed in n-type Schottky diode and the 0.23 eV electron trap level detected in the p +/n diode with Ni/Au contact are attributed to the extended defects based on the observation of logarithmic capture kinetics.

Optical pumping in ferromagnet-semiconductor heterostructures: Magneto-optics and spin transport

Epitaxial ferromagnetic metal - semiconductor heterostructures are investigated using polarization-dependent electroabsorption measurements on GaAs p-type and n-type Schottky diodes with embedded In1-xGaxAs quantum wells. We have conducted studies as a function of photon energy, bias voltage, magnetic field, and excitation geometry. For optical pumping with circularly polarized light at energies above the band edge of GaAs, photocurrents with spin polarizations on the order of 1 % flow from the semiconductor to the ferromagnet under reverse bias. For optical pumping at normal incidence, this polarization may be enhanced significantly by resonant excitation at the quantum well ground-state. Measurements in a side-pumping geometry, in which the ferromagnet can be saturated in very low magnetic fields, show hysteresis that is also consistent with spin-dependent transport. Magneto-optical effects that influence these measurements are discussed.

Comparison of current-voltage characteristics of n- and p-type 6H-SiC Schottky diodes

Current-voltage (I–V) characteristics of n- and p-type 6H−SiC Schottky diodes are compared in a temperature range of room temperature to 400°C. While the room temperature I–V characteristics of the n-type Schottky diode after turn-on is more or less linear up to ∼100 A/cm2, the I–V characteristics of the p-type Schottky diode shows a non-linear behavior even after turn-on, indicating a variation in the on-state resistance with increase in forward current. For the first time it is shown that at high current densities (>125 A/cm2) the forward voltage drop across p-type Schottky diodes is lower than that across n-type Schottky diodes on 6H−SiC. High temperature measurements indicate that while the on-state resistance of n-type Schottky diodes increases with increase in temperature, the on-state resistance of p-type Schottky diodes decreases with increase in temperature up to ∼330 K.

Comparison of Current – Voltage Characteristics of N and P Type 6H-SiC Schottky Diodes

ABSTRACTForward and reverse current – voltage (I–V) characteristics of N and P-type Schottky diodes on 6H-SiC are compared in a temperature range of room temperature to 550K. While the room temperature I–V characteristics of the N-type Schottky diode after turn-on is more or less linear up to ∼ 100 A/cm2, the I–V characteristics of the P-type Schottky diode shows a non-linear behavior even after turn-on, indicating a variation in the on-state resistance with increase in forward current. For the first time it is shown that at high current densities (> 210 A/cm2) the forward voltage drop across P type Schottky diodes is lower than that across N type Schottky diodes on 6H-SiC. High temperature measurements indicate that while the on-state resistance of N type Schottky diodes increases with increase in temperature, the on-state resistance of P type Schottky diodes decreases with increase in temperature until a certain temperature. While the N-type diodes seem to have soft breakdown characteristics, the P-type diodes exhibit more or less abrupt breakdown characteristics.

Effect of grown-in biaxial strain on deep level defects in Si1−yCy/Si epitaxial heterostructures

We report the first study of traps in strained Si1−yCy random alloys grown on Si 〈100〉 substrates using chemical vapor deposition. Deep level transient spectroscopy (DLTS) measurements of n-type Schottky diodes fabricated on Si/Si1−yCy/Si heterostructures (y<0.02) were used to study the impact of carbon and grown-in strain on the formation of deep levels. The observed deep level activation energies were found to vary with carbon fraction, and ranged between 0.175 and 0.225eV, measured with respect to the conduction band. The systematic variation in the measured activation energies with carbon fraction suggests the splitting of a single deep level due to strain in the Si1−yCy alloy layer. The DLTS peaks exhibit anomalous broadening which increases with increasing carbon fraction and can be explained using an alloy broadening model.

Study of Different Edge Terminations Used for 6H-SiC Power Diodes

Silicon Carbide is a wide bandgap semiconductor (3 eV for 6H-SiC at 300 K) suitable for high voltage, high temperature, high frequency and power devices. Its drift velocity is high (2 x 10 7 cm s -1 ), its thermal conductivity is similar to that of copper (5 Wm -1° C- 1 ) and its critical electric field is almost 10 times higher than that of silicon. In the field of power devices, many publications refer to PN structures (4.5 kV), Schottky diodes (1.3 kV) as well as MOSFET and JFET. PN junction diodes have been designed and characterized with two different peripheral protections to achieve high breakdown voltage. The first protection is the MESA structure. In this approach, the curvature region of the main junction where the electric field is higher than in the bulk, is etched off. The efficiency of a P + NN + MESA structure can be increased by decreasing the doping level of the N-type layer. For this purpose compensation by boron atoms is used for P + NN + MESA structures. The second peripheral protection is a planar structure in which equipotential lines are spread around the lateral P-type low-doping implanted zones for P+N junction or N-type Schottky diodes. The experimental breakdown voltage of these diodes lies between 600 and 1500 V.

Spatial confinement and saturation of substitutional platinum by diffusion into ion-beam damaged silicon

The diffusion of platinum into lightly damaged regions of ion-implanted silicon has been investigated using deep-level transient spectroscopy and capacitance-voltage profiling. The samples consisted of PtSi/Si n-type Schottky diodes which had been implanted with O, F, or Cl to an intermediate depth between the zero-bias and reverse-bias depletion boundaries, and subsequently annealed at a temperature of 700 °C. The distribution of in-diffused Pt was obtained by monitoring the electron emission from the acceptor level (EC−ET=0.23 eV) previously assigned to Pt in a distorted substitutional configuration. The Pt was found to be distributed approximately congruous with the vacancy distribution generated during implantation. For a typical implantation dose (≊1011 cm−2) we recorded an enhanced accumulation of Pt by about two orders of magnitude as compared to diffusion into nonimplanted material. This apparent decoration of the primary damage profile occurs without the simultaneous introduction of other electrically active defects on a comparable scale. We infer that the residual damage present during annealing is sufficient to promote accumulation to saturation of substitutional Pt in the region of primary implantation damage. This rather remarkable property of guided in-diffusion, a kind of gettering phenomenon, may have potential applications in Si-device engineering.

Auger regeneration of the EL2 defect induced by the Debye tail in the space-charge region of a junction: Application to the so-called "optical regeneration"

We have studied the regeneration of the EL2 defect, i.e., the transition from its metastable to its stable state, in n-type Schottky diode under zero bias. We show that this transition is induced by the so-called ``Auger regeneration,'' which occurs normally under injection of electrons in a junction. In our case, the regeneration is attributed to the free carriers of the Debye tail. A numerical simulation of the mechanism is proposed, in good agreement with the experimental data. Finally, we discuss the observed optical regeneration of EL2, which can be explained, at least in some cases, by an Auger mechanism, triggered by optically induced carriers.

Defects in single-crystal silicon induced by hydrogenation

It is demonstrated that hydrogenation induces microdefects and electronic deep levels in single-crystal silicon, which are unrelated to either plasma or radiation damage. After hydrogenation of either n-type or p-type silicon, transmission electron microscopy reveals defects that can be described as hydrogen-stabilized platelets or microcracks which appear within 0.1 \ensuremath{\mu}m of the exposed surface and are predominantly oriented along {111} crystallographic planes. These defects correlate with high concentrations of hydrogen or deuterium as measured by secondary-ion mass spectrometry and with the appearance of Si---H bonds as revealed by Raman spectroscopy. The concomitant introduction of electrically active gap states is demonstrated with both photoluminescence spectroscopy (PL) and deep-level transient spectroscopy (DLTS). In PL several H-induced radiative transitions are observed, with the dominant peak at 0.98 eV, which had previously been ascribed to plasma damage. In n-type Schottky diodes, DLTS detects two H-induced levels with thermal activation energies for electron emission of approximately 0.06 and 0.51 eV. These defects are detected at depths greater than the surface layer, are in low concentrations (${&lt;10}^{13}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$), are acceptorlike, and anneal with an activation energy of \ensuremath{\sim}0.3 eV.