PiN Rectifiers Research Articles

High-voltage GaN pin vertical rectifierswith 2 µm thick i -Layer

Gallium nitride pin rectifiers have been fabricated and characterised. The device structures were grown by metalorganic chemical vapour deposition on c-plane sapphire substrates. The pin diode epitaxial structure consisted of an n+-GaN layer, followed by a 2 µm i-GaN layer and a p-type GaN layer on top. The mesa-structure pin diodes exhibited a blocking voltage as large as Vr ≃ –410 V at a reverse current density of Ir ≃ 10 A/cm2 and a forward voltage drop of only 8 V at a forward current density of ~100 A/cm2. These values indicate that GaN-based pin rectifiers can be useful in high-voltage circuits.

Design considerations and experimental analysis for silicon carbide power rectifiers

In this paper we present the investigation of properties of silicon carbide power rectifiers, in particular Schottky, PiN and advanced hybrid power rectifiers such as the trench MOS barrier Schottky rectifier. Analysis of the forward, reverse and switching experimental characteristics are presented and these silicon carbide rectifiers are compared to silicon devices. Silicon carbide Schottky rectifiers are attractive for applications requiring blocking voltage in excess of 100 V as the use of Si is precluded by its large specific on-resistance. Analysis of power dissipation indicates that silicon carbide Schottky rectifiers offer significant improvement over silicon counterparts. Silicon carbide junction rectifiers, on the other hand, are superior to silicon counterparts only for blocking voltage greater than 2000 V. Performance of acceptor (boron) and donor (phosphorus) implanted experimental silicon carbide junction rectifiers are presented and compared. Some of the recent developments in silicon carbide rectifiers have been described and compared with theory and our experimental results. The well established silicon rectifiers theory are often inadequate to describe the characteristics of the experimental silicon carbide junction rectifiers and appropriate generalization of these theories are presented. Experimental trench MOS barrier Schottky rectifiers (TMBS) have demonstrated significant improvement in leakage current compared to planar Schottky devices. Performance of current state-of-the-art silicon carbide rectifiers are far from theoretical predictions. Availability of high-quality silicon carbide crystals is crucial to successful realization of these performance projections.

Simulation of soft recovery in Si pin rectifierswith ultra-shallow p + emitters

Ultra-shallow (<500 /spl Aring/) p/sup +/-emitters in Si pin rectifiers are shown via numerical simulation to reduce the need for lifetime killing in order to obtain soft recovery. This benefit is especially pronounced at elevated operating temperatures.

Simulation of SiC High Power Devices

The impact of SiC on high power devices and their applications is analysed using simulations in a very wide range of design voltages. First, a detailed presentation of the anisotropic form of the basic equations and of the physical models for 4H-SiC used in the simulations is given. Following that the application ranges of unipolar and bipolar devices in the domains of voltage and frequency are predicted in the case of IGBTs versus MOSFETs and PiN versus Schottky rectifiers based on comparisons of the on-state voltage and of the total losses. The application limit of the MOSFETs compared to IGBTs and of the Schottky rectifiers compared to PiN rectifiers is predicted to be about 4.5 and 2.5 kV, respectively, in the case of the 4H-SiC polytype. The impact of technological limitations of SiC is illustrated by the case of low channel mobility. The merits of SiC as compared to Si are illustrated by the case of a SiC rectifier operating together with a Si IGBT. Dramatically reduced turn-on losses are demonstrated. The superiority of SiC from the point of view of dynamic avalanche is predicted and illustrated. Finally, some novel SiC switch structures are introduced in response to the reliability problems encountered in ordinary trench MOSFETs.

Modelling and characterization of the reverse recovery of a high-power GaAs Schottky diode

The reverse recovery characteristics of high-power GaAs Schottky rectifiers are reported at various temperatures; mixed device and circuit simulations were used to study the internal plasma dynamics during the reverse recovery process. In this approach, semiconductor transport and heat generation and diffusion equations were solved self-consistently using a two-dimensional (2-D) finite element grid structure under boundary conditions imposed by the measurement circuit. The simulation results are shown to be in good agreement with the measured data at temperatures in the range of 25/spl deg/C to 125/spl deg/C. These results are compared with the reverse recovery characteristics of a commercial silicon PIN power rectifier under identical conditions and it is shown that carrier depletion is the dominant mechanism causing the reverse recovery in a GaAs Schottky diode. The reverse recovery power loss is negligible in a GaAs Schottky rectifier and is shown to decrease as the case temperature is increased, contrary to the silicon PIN rectifier behaviour.

High-voltage silicon carbide rectifiers – results of experiments and simulation

Low reverse leakage silicon carbide pin rectifier diodes with a breakdown voltage reaching 1100 V are experimentally shown to have acceptably low forward voltage drops, dominated by the built-in voltage. Numerical simulations of the experimental structure, using a measured carrier lifetime of 25 ns, validate the existence of a conductive plasma in the lowly doped base layer, despite a poor injection efficiency, related to the incomplete ionization of the aluminium acceptor. Simulation also indicates the need for a lifetime of ~ 100 ns in a 3.0 kV device.

An investigation of recombination in gold-doped pin rectifiers

End region recombination in gold-doped PIN diodes has been investigated using a laser probe technique. It is found that, in contrast to undoped diodes, it is necessary to introduce a linear term to describe this recombination. The magnitude of the linear term increases markedly with the degree of gold doping. Linear end region recombination is indistinguishable from base recombination during an open circuit voltage decay and the base lifetime deduced by this technique has to be corrected. Theories for diode switching and forward voltage have been tested against experimental results on a large number of diodes with different base widths and base lifetimes. It is found that the device behaviour can be accurately predicted if the base and end region recombination parameters are known.

On the influence of recombination centers on the electrical performance of silicon power rectifiers

The use of gold, platinum and electron irradiation induced defects as recombination centers in silicon devices is studied. Results are presented concerning the variations of carrier lifetime with the concentration of both deep and shallow level impurities, for different bias conditions. The influence of carrier lifetime on the electrical performance of power PIN rectifiers is considered in order to compare the relative advantages of the lifetime controlling techniques.

Extension of Gummel's charge control relation

Gummel's charge control relation for bipolar transistors is extended to be valid for the base region of thyristors and pin rectifiers. The modified relationship is derived under the assumption of one dimensional current flow and includes the effects of recombination and majority carrier flow in the base region.

The influence of auger recombination on the forward characteristic of semiconductor power rectifiers at high current densities

It has previously been shown that the recombination of carriers in silicon and germanium at high carrier concentrations is dominated by Auger recombination (impact recombination). Carrier concentrations of 10 18 cm −3 and higher may occur in high-current devices such as power rectifiers and thyristors. The present paper analyzes the influences of the Auger recombination on the forward characteristic of pin and psn rectifiers at high current densities. It is an extension of the theory developed by Herlet, Spenke et al. for such devices, and does not take into account the concentration dependence of the carrier mobilities. It shows that the Auger recombination is important for the understanding of the current-voltage characteristic at high forward current densities.

Eine spezielle lösung für instationäre vorgänge im pin—gleichrichter

Time-dependent carrier concentrations in a pin rectifier operated by a (temporally varying) forward current are investigated. An especially clear limiting case may appear soon after switch-on. It results for the Hall case (i.e. recombination solely in the i region) in a current density rising as an arbitrarily fast exponential function of time, and in a temporarlly constant voltage drop over the i region. Especially this voltage drop has its current-independent stationary value if the current density rises slowly enough. The notion of a “slow process” is generalized for a nonexponential dependence of current density on time, and a criterion for “slowness” is given for any kind of temporal current dependence.

Influence of the doping concentration on switching processes in psn rectifiers—I: Theory

The theory, formerly developed for switching power rectifiers into the reverse state, which was limited to pin rectifiers, is extended to a noticeable homogeneous doping concentration of the middle region ( psn rectifier). In this case the swept-out zones originating at the boundaries of the middle region are qualitatively different. While at the side of the pn junction a Schottky space-charge zone with a quadratic voltage vs. time increase forms passing over into the stationary reverse state, at the other side of the middle region finally a zone develops that shows an approximative equilibrium concentration of the majority carriers. This zone is essentially free of space charge. its voltage drop becomes important at most in a medium period of the sweeping-out process (but only in the case of the ps p n rectifier because of the unequal mobilities of the charge carriers), but later on it is always negligible compared with the voltage across the Schottky zone at the pn junction. The temporal development of the swept-out zones is treated more accurately than in the pin case, i.e. we consider the difference between the points of time when the building up of swept-out zones begins at the respective sides. One finds that the sweeping-out at the n side proceeds not only more slowly but also later than at the p side. Some technical conclusions for the switching behaviour of rectifiers and thyristors are drawn up. p rectifiers have a shorter reverse recovery time than n rectifiers (and n thyristors).

Forward characteristics of thyristors in the fired state

The forward voltage of thyristors in the fired state is discussed from points of view which are especially relevant for power thyristors. With big forward currents, i.e. with high level injection in both base regions, the forward voltage of a thyristor should become identical with that of a pin rectifier of equal dimensions. This is verified by experiment; it is furthermore shown that the forward voltage is independent of the doping level in the base regions. For the difference of the forward voltages of both devices found with low current densities a simple approximate relation is derived and substantiated by experiment. The carrier lifetime with high injections is found to be independent of the doping level in these experiments; this was affirmed, too, by former measurements.

Switching processes in alloyed pin rectifiers

A theory for the switching of power rectifiers from forward to reverse state is derived, and confirmed by measurements. In cases interesting especially in application, one may confine oneself to strong injection in the forward state, and to strong reverse currents during the switching process. Under these circumstances, the reverse voltage is built up during the switching by the space charges of the flowing off charge carriers. The following results, which contradict a conception frequently voiced, may be pointed out: ( a) The flowing off of the charge carriers is not limited by “reverse-biased” doping junctions. ( b) For that reason, the duration of the switching process is not determined by the finite carrier lifetime if the sweeping out current is strong enough. It follows from the theory that during switching processes the rectifier can be destroyed by essentially smaller voltages than by those it resists under stationary conditions.

The voltage step at the switching of alloyed pin rectifiers

The voltage step at the switching of alloyed pin rectifiers

Switching processes in alloyed pin rectifiers

Switching processes in alloyed pin rectifiers