DE112005000222B4 - III-nitride current control device and manufacturing method - Google Patents

Abstract

A III-nitride current control device (31; 41; 56; 60; 70) comprising: - a conduction channel formed at an interface (15) between two III-nitride materials (14, 16; 74, 75) having different in-planes Have lattice constants or different band gaps; - a first electrode (19; 52; 55; 62; 55; 78) coupled to the duct to carry duct power; A second electrode (18, 30, 18, 40, 54, 50, 54, 61, 77A, 77B) coupled to the duct and operable to affect the duct to conduct the power between the first electrode (19, 52, 55 62, 55, 78) and the second electrode (18, 30, 18, 40, 54, 50, 54, 61, 77A, 77B) through the duct; wherein - said second electrode (18, 30; 18, 40; 54, 50; 54, 61; 77A, 77B) comprises an ohmic contact (18; 54; 77A) and a rectifying contact (30; 40; 50; 61; 77B ); wherein the rectifying contact (30; 40; 50; 60; 77A) lies on the ohmic contact (18; 54; 77B); and wherein - the first electrode (19; 52; 55; 62; 5; 78) comprises a further ohmic contact (19; 55; 78).

Description

The present invention generally relates to a class of field effect current regulators, and more particularly to rectifiers and current limiters constructed using III-nitride material systems.

There are currently known III-nitride semiconductors which have a large dielectric breakdown field of more than 2.2 MV / cm. Heterojunction III-nitride structures are also capable of delivering extremely high currents, making devices made of III-nitride material systems ideal for high-current applications.

The development of devices based on III-nitride materials is generally focused on high power / high frequency applications such B. Emitter for mobile base stations. The devices fabricated for this type of application are based on general device structures that have high electron mobility, and are often referred to as a heterostructure field effect transistor (HFET), high electron mobility transistors (HEMT), or modulation doped field effect transistors (MODFETs). This type of device is typically able to withstand high voltages, such as high voltages. In the range of 100 volts, operating at high frequencies, usually in the range of 2-100 GHz. This type of device can be modified for some applications, but it typically functions by the use of piezoelectric polarization fields to produce a two-dimensional electron gas (2DEG) that enables the transport of high current densities with very low resistive losses. The 2DEG is formed in these conventional III-nitride HEMT devices at the interface of the AlGaN and GaN materials. Due to the nature of the AlGaN / GaN interface and the formation of 2DEG at the interface, devices fabricated by the III-nitride system are often normally-on or junction-mode devices. The high electron mobility of the 2DEG at the interface of the AlGaN / GaN layers allows the III-nitride device such. B. a HEMT element, without the application of a gate potential as a conductor to act. Due to the fact that the previously manufactured HEMT components are normal OPEN elements, their usability for heavy current management is limited. The boundaries of the normal OPEN elements are revealed by the fact that a control circuit is needed before the current can be safely controlled by a III-nitride HEMT element. Accordingly, it is also desirable to provide a III-nitride HEMT device that is normal CLOSE to avoid powerline problems during startup and other modes of operation.

A disadvantage of the III-nitride HEMT devices that allow high current densities with low resistance losses is the limited thickness that can be achieved with the strained AlaN / GaN system. The difference in the lattice structures of these materials creates a stress that can lead to dislocation of the films forming the various layers. This leads to a high level of power losses z. B. by a barrier layer. Some earlier models focused on reducing the in-plane lattice constants of the AlGaN layer to approach the point where relaxation occurs, thus reducing the occurrence of offset and current loss. However, these models do not solve the problem of limited thickness.

US 2002/0 017 696 A1 describes a special semiconductor device with avalanche properties. In this case, the anode and cathode electrodes are formed of an n-type AlGaN layer. An undoped GaN layer is formed on the AlGaN layer between the anode and cathode electrodes. The field plate electrode prevents it from lowering the breakdown voltage between the anode and cathode electrodes.

KUMAR V describes high-transconductance AlGaN / GaN HEMT of the enhancement type on SiC substrate. See Electronic letters, Vol. 39, 2003, No. 24, 1758-1760.

Another solution is to add insulating layers to solve the problems of power loss. The addition of an insulating layer can reduce the current leakage through the barrier layer; typical layers used for these purposes are silicon oxide, silicon nitride, sapphire, or other insulators placed between the AlGaN and metal gate layers. This type of device is often called MISHFET and has several advantages over conventional devices without an insulating layer.

While additional insulating layers may allow thicker strained AlGaN / GaN systems to be built, the barrier layer formed by the additional insulation will reduce the power line capacitance due to the scattering effect created at the electrons of the GaN / insulator interface. The additional interface between the AlGaN layer and the insulator also creates an interface separation state that slows down the device's response. The additional thickness of the oxide as well as the additional interfaces between the two layers also lead to larger gate sizes. Drive voltages can be used to switch the device.

Conventional devices that use nitride materials to obtain normal OPEN elements rely on this additional insulator, which acts as an interface, and can reduce or remove the top AlGaN layer. However, due to the scattering effect at the GaN-insulator interface, these devices typically have lower power line capacitances.

Accordingly, it would be desirable to fabricate a heterostructure device or FET that has less power loss and fewer interfaces and layers, and yet can withstand high voltages and generate high current densities with low resistive losses. Planar devices with GaN and AlGaN alloys, including MOCVD (metal organic vapor deposition) and molecular beam epitaxy (MBE) and hydride gas phase epitaxy (HVPE), are currently being produced using various technologies.

Materials such as gallium nitride material systems may include gallium nitride (GaN) as well as its alloys such as aluminum gallium nitride (AlGaN), indium gallium nitride (InGaN), and indium aluminum gallium nitride (InAlGaN). These materials are semiconductor compounds that have a relatively broad direct band gap that allows high energy electronic transitions to occur. Gallium nitride materials have been deposited on a number of different substrates, including silicon carbide (SiC), sapphire, and silicon. Silicon substrates are readily available and relatively inexpensive, and the technology of silicon processing is well developed.

However, the application of gallium nitride materials to silicon substrates for semiconductor fabrication presents challenges stemming from the differences in lattice constant, thermal expansion, and bandgap between silicon and gallium nitride. The problems associated with the non-matching grating structures between GaN and the traditional substrate materials also prevail in the material layer structures containing GaN and GaN alloys. For example, GaN and AlGaN materials have lattice structures that differ significantly enough to create interfacial tension between the layers, which contributes to piezoelectric polarization. In many prior devices, the fields generated by the piezoelectric polarization are controlled to improve the features of the devices. Deviations in the aluminum content of the AlGaN / GaN layer structures lead to a change in the lattice inequality between the materials and thus to different features of the device, such. B. improved conductivity or isolation barriers.

A particular application that would benefit from a semiconductor structure with a low on-resistance or voltage drop is a rectifier. Conventionally, in high power applications, rectifiers are often controlled as a synchronous rectifier, with a diode performing the voltage blocking function of the rectifier and a synchronous switch in the diode taking over the power line when the diode is forward biased to provide an on resistance and a voltage drop of the forward voltage of the diode to avoid. This type of arrangement requires switching control for the switch so that it is turned on when the diode is to be operated in forward conduction. This type of conventional synchronous rectifier is often used in heavy current applications to avoid the disadvantages of the diodes used as rectifiers, such as. B. a drop in the forward voltage, which reduces the energy efficiency and also can contribute to thermal operating problems. However, because the synchronous switch used with the diode to form a synchronous rectifier is normally a power switch, a drive unit is used to service the switch in heavy current applications. It would therefore be desirable to obtain a rectifier that does not require additional control operations while still maintaining a low drop in forward voltage.

Another device that can limit the amount of current flowing through is a pinch resistor. A pinch resistor is typically made in a semiconductor material with two different types of conductive materials. So z. For example, a positive conductive material is placed in a negative zone and an N ⁺ zone is partially formed over the P material. The resistance of the pinch resistor is determined by the sheet resistance of the P-material under the overlapping N ⁺ -zone and the dimensions of the overlapped P-material. The current in the device is conducted in a channel that is "pinched off" by the opposing semiconductor material. By this arrangement, a very high resistance can be formed in a very small area to effectively limit the current in a given current range. However, due to the technology used during their manufacture, this type of device is often inaccurate. In some arrangements, the current through the device is effectively limited by a voltage generator in the device that may serve to control the current limiting channel. In conventional components are the currents that can be transmitted in pinch resistors are relatively low, so that heavy current applications tend to be somewhat complicated.

It would be desirable to have a high current rectifier such. As a diode or a pinch resistor to provide that can block significant voltages, thereby achieving a low drop in the forward voltage.

According to the present invention, a device for current control such. As a rectifier is provided, which is realized by means of a III-nitride material system, which is able to pass a high amperage and a high voltage can block with a reduced ON resistance. The device serves to influence the 2DEG between the two III-nitride materials by means of ohmic contacts and Schottky or insulated contacts.

According to one of the embodiments of the present invention, a rectifier is provided with a reduced turn-on voltage for the pass-line. The rectifier is formed with two III-nitride material layers, with one of the III-nitride material layers having a larger in-plane lattice constant than the other, thereby forming a 2DEG at the interface. The high carrier mobility in the 2DEG allows a low forward voltage to turn on the rectifier. The current through the devices is shunted through the 2DEG channel and out of the ohmic contact to avoid the Schottky barrier. Under reverse voltage conditions, the Schottky contact interrupts the 2DEG and opens the channel to prevent current drain in the reverse bias condition.

According to a feature of the present invention, the Schottky contact is formed in a recess of a III-nitride layer so that the device is nonconductive until a forward voltage is applied. Conveniently, the recess has the walls chamfered so that it is easily possible to control the parameters of the device.

In accordance with another embodiment of the present invention, a pinch resistor is provided in the III-nitride material system, which is a bidirectional device formed by a plurality of ohmic contacts and a plurality of Schottky or insulated contacts. The Schottky or insulated contacts are between the ohmic contacts and are connected to the corresponding ohmic contacts to regulate the formation of the 2DEG so that the current formed by the 2DEG in the channel is controlled according to the voltage applied to the contacts. The device is bidirectional to allow current limiting in either direction.

In accordance with another feature of the present invention, the pinch resistance can be adjusted to provide unbalanced current limiting characteristics similar to a rectifier and a varying ON resistance. The device can also be adjusted so that there is a high current carrying capacity in both directions.

In accordance with another embodiment of the present invention, a Schottky rectifier is provided in a III-nitride material system where the device carries current through a channel containing 2DEG formed by the interface of two different layers of III-nitride materials. The device includes a Schottky contact and an ohmic contact for the line in the direction of the ohmic contact, as well as a blocking voltage in the other direction, towards the Schottky contact. The voltage applied to the Schottky contact allows the current to flow through the channel formed by the 2DEG and out of the ohmic contact, while an oppositely applied voltage depletes the 2DEG under the Schottky contact to maintain the voltage during the reverse deviation to block. When GaN is used as one of the III-nitride layers, the high-resistance nature of a GaN layer prevents current leakage in the device. The device may be constructed with little or no doping of the III-nitride layers to achieve a low field during the reverse deviation that allows for high spacing voltages. This pleasant feature is achieved without sacrificing the rise in the forward biased resistance.

According to another feature of the present invention, there is provided a method of forming the devices described above wherein a III-nitride layer is deposited on an insulating or high resistance substrate. Optionally, a buffer layer may be provided between the substrate and the III-nitride layer, which should preferably be GaN. An AlGaN layer is deposited over the ohmic GaN layer, followed by a protective insulating layer to limit surface degradation of the AlGaN during annealing. In the protective insulating layer, a window is recessed to have access to the underlying AlGaN layer. In this window there is an ohmic metal contact, which represents an ohmic contact for the device. After starting the ohmic contact, another window will open in the protective insulating layer is inserted through which a Schottky metal is introduced to complete the device.

Conveniently, the coating and contact layers may be applied over or under the active zone. Other known methods of constructing electrodes, insulating layers, etc. may also be used for the present invention.

According to a feature of the present invention, instead of additional insulating layers or structures on the active layer, a good GaN insulating layer is provided to improve the current carrying capacity. Without additional insulating layers, the epitaxial character of the hetero-interface described here leads to an overall order of magnitude greater mobility of the electrons in the 2DEG.

According to another embodiment of the present invention, a normal-to-ZU control implemented in a III-nitride material system provides an AlGaN / GaN interface at which formation of a 2DEG occurs. The zone in the AlGaN layer around a Schottky contact is back-etched to locally remove the 2DEG and thus achieve a device in enhancement mode. According to a feature of the present invention, the current control element comprises two Schottky contacts mounted adjacent to the respective ohmic contacts, the Schottky contacts being equidistant from the respective ohmic contacts and thus forming the current carrying element.

According to a feature of the present invention, the AlGaN layer in the zone around the Schottky contact is back-etched to form a device in the pruning operation with the 2DEG locally eliminated between the AlGaN / GaN layers.

The large dielectric breakdown field in the III-nitride semiconductor material system allows the construction of normal-to-ZU devices with smaller size spacing zones. The material system also allows for the fabrication of devices having similar lower resistances compared to known devices of similar voltage ranges. In the case of the GaN / AlGaN devices discussed here, a planar device has an approximately 100-fold improvement in specific on-resistance in a voltage range of approximately 300 volts compared to its vertical geometric counterpart.

Heterostructure III nitride current control elements can exploit the symmetrical properties to allow the fabrication of a normal-to-device that can block voltage in both directions without sacrificing the wafer area. Because of this advantage over the conventional devices that block the voltage in one direction only, a device that operates in two directions can replace a number of unidirectional devices.

The device is also characterized by a low loss of contacts and a high breakdown field from the boundary layer. This results in that the component compared to conventional insulators, such. As SiO ₂ and SiN, a larger dielectric constant. The high critical fields of the GaN material enable thin layers that can withstand high voltages without dielectric breakdown. The dielectric constant of the GaN materials is around 10, which is about 2.5 times better than that of SiO ₂ .

Other features and advantages of the present invention will become apparent from the following description of the invention, which refers to the accompanying drawings.

The 1A Figure 3 illustrates graphically the relationship between the thickness of the AlGaN and the density of the 2DEG in a heterostructure AlGaN / GaN device.

The 1B Illustrates as a graphical representation of the stromabschnürende effect in the device according to the present invention.

2A FIG. 12 is a cross-sectional view of a partially formed III-nitride current control element according to the present invention. FIG.

2 B shows an etched contact zone in the device 2A ,

2C illustrates a method for forming the in 2 B shown depressions.

3A illustrates a device according to the first embodiment.

3B shows a part of another variant of the device of the present invention as z. In 3A ,

3C shows a part of another variant of the device of the present invention as z. In 3A ,

3D shows a part of another variant of the device of the present invention as z. In 3A ,

4 shows a device according to another embodiment of the present invention.

5 FIG. 12 is a cross-section of a Schottky contact type pinch resistor made in accordance with one embodiment of the present invention. FIG.

6 FIG. 12 is a cross-section of a pinch resistor with insulated contacts made in accordance with one embodiment of the present invention. FIG.

7 is a cross section of a rectifier, as an illustrative example.

8th is a top view of the rectifier 7 which illustrates the interdigitated electrodes.

The 9A - 9E illustrate the operation in the arrangement of the device of 7 as an illustrative example.

10 is another variant of the device 7 ,

11 shows a plan view of a variant of the device according to the present invention.

When building devices made of GaN materials, several factors come into play that affect the performance and functionality of the devices. Large lattice mismatch in III nitride materials and the strong effects of piezoelectricity and polarization in these materials significantly affect the electrical properties of heterojunction III nitride devices.

A significant number of currently reported GaN-based devices use strained GaN-AlGaN transitions with alloys designed to maximize strain but avoid exceeding the relaxation threshold, which would lead to dislocations or long-term instabilities in the devices. In general, such devices are designed to maximize stretch within the relaxation limit. With increasing thickness of the AlGaN layer or increasing Al content in the AlGaN, the elongation also increases, which leads to an increase in the 2DEG density and the carrier mobility. However, if the AlGaN layer increases in thickness or the Al content is too large, the whole layer relaxes and loses all the desirable properties mentioned above. Various devices and systems have been proposed for the construction of heterojunction devices to control the lattice mismatch and strain of the GaN-AlGaN junctions. These devices are specifically designed to take advantage of the effects of piezoelectricity and spontaneous polarization, and to minimize long-term instabilities.

GaN / AlGaN devices typically have one or more ports for controlling the flow of electrical current in a given device. An electrical potential applied to a terminal controls the flow of current in an electrically conductive channel to which the terminal is coupled. The electrically conductive channel is determined by at least one heterointerface between two different semiconductor materials.

When semiconductor materials of a heterojunction device are composed of AlGaN / GaN materials and AlGaN is used as a boundary layer, polarization charges resulting from the AlGaN properties of spontaneous polarization and strain-induced features known as piezoelectric polarization fields are present. In the construction of a III-nitride device, the control of the formation of these fields leads to various features that cause GaN-based devices to be suitable for a wide range of applications, depending on how the device is characterized.

Heterojunction devices designed with GaN materials typically include an AlGaN barrier layer overlaying the GaN layer to induce a 2DEG (two-dimensional electron gas) that generates a high concentration of electrons in the channel to thereby provide electrical conductivity properties to improve the channel.

Due to the presence of the 2DEG induced in the interface between the AlGaN and GaN layers, fundamentally designed III-nitride devices are in the target state because, for example, the presence of the channel allows current to flow between electrodes.

The current in the 2DEG can be cut off when the charge depletes in the 2DEG. According to the present invention, the charge in a selected area of the channel is reduced to reduce the maximum amount of current that can flow through the channel. As a result, the current can be "pinched off" at a certain maximum level. Preferably, the selected range is small, so that the total resistance of the device can remain low until the pinch-off state is achieved.

How out As can be seen, calculations have shown that the density of the 2DEG can be dependent on the thickness of the AlGaN layer ( . ). According to one aspect of the present invention, the AlGaN layer is thinned in a small area of the device to locally reduce the density of the 2DEG, thereby allowing the pinch-off effect, as will be seen below. How out As can be seen, the pinch-off current is reduced when the AlGaN layer is thinned. If the AlGaN layer is thinned until the 2DEG is eliminated below the gate, the pinch current of the device is reduced to 0 or nearly zero. Under such conditions, the device is effectively a power converter, because the pinching takes place in one direction only.

With reference to becomes a device with heterojunction according to the present invention in the early development phase as a device 10 shown. device 10 comprises a support 12 , a non-conductive GaN layer 14 and an active AlGaN layer 16 , The galvanically conductive connections 18 and 19 be on the AlGaN layer 16 created to serve as connection points or connections in the resulting device. The GaN / AlGaN interface 15 forms a conductive channel with a 2DEG, which conducts a current between the galvanically conductive connections 18 and 19 allows.

The GaN layer 14 of the device 10 has a larger lattice constant on the same plane than the AlGaN layer 16 , It should be apparent that other III nitride materials can be used to device 10 as long as an interface enables the formation of a channel for the flow of current. The support 12 is nonconductive, but may prove to be highly resistive or present as an n- or p-doped substrate and is typically formed from known materials such as silicon carbide, silicon, sapphire, and other known support materials.

With reference to here is a depression 20 shown in the AlGaN layer 16 next to connection 18 is etched. The deepening 20 includes the slanted sidewalls 22 but does not have to be designed according to a specific geometry. Preferably, to minimize the resistance of the device, the beveled sidewalls 22 to be available. In addition, the separation distance L _S and the gate length L _{g can} also be used to control the level of pinch-off current. The deepening 20 Allows placing a contact in the immediate vicinity of the interface between AlGaN layer 16 and GaN layer 14 , It should be noted, however, that the device will stall the current even without an etched recess at maximum level. As will be seen below, such a device would also be considered as pinch resistance.

With reference to becomes a technique for manufacturing a device 60 shown, the design of device 56 can be further processed. An opaque layer 62 is via the III-nitride interface 16 laid and the openings 64 and 65 become in the opaque layer 62 brought in. The openings 64 and 65 have sloped sidewalls to allow for an etching step to tilt the inclined geometry to the III-nitride interface 16 transferred to. In the shown inclined side walls can be designed according to this technique. Typically, the III-nitride boundary layer settles 16 AlGaN together and a suitable etching process is used for the opaque layer 62 and the openings 64 and 65 used to layer the recesses with sloped sidewalls 16 stake.

With reference to owns a device 31 a contact 30 which is composed of a Schottky metal. With reverse bias or in the off state device is conducting 31 no current between the galvanically conductive connections 18 and 19 because the current-carrying channel established by the 2DEG is under contact 30 is interrupted. With forward bias (when the contacts 18 and 30 are more positive than contact 19 ) is device 31 capable of removing the current between the galvanically conductive connections 18 and 19 respectively. This is due to the filling of the channel under contact 30 due.

Contact 30 can be composed of a Schottky metal and is located on AlGaN layer 16 , is in depression 20 inserted and covers contact 18 ,

As mentioned above, AlGaN layer 16 be replaced by each layer of a III-nitride material, as long as the lattice constant at the same level of the layer 16 is smaller than the lattice constant at the same level of the layer 14 or as long as the band gap of the layer 16 is greater than the band gap of the layer 14 ,

device 31 can work with several different geometries for the electrically conductive connections 18 and 19 and contact 30 be constructed. For example, it can be in contact 30 to act a Schottky contact, which is the electrically conductive connection 18 surrounds. Contact 30 can also be a part of the galvanically conductive connection 18 where gaps or etched areas are formed to accommodate the flow of current in particular directions or areas device 31 to restrict. The galvanically conductive connection 18 and contact 30 , designed as Schottky contact, may also be located at different distances from one another to increase or decrease the breakdown voltage and the pinch current and to change on-resistance parameters.

The combination of Schottky diode and Abschnürstrom results in a unique device. In fact, the etch has changed the pinch-off voltage for the device. After the pinch has occurred, another voltage on the second contact is lowered through the etched area of the device. Due to the reduced pinch-off stress achieved by the etch-in of the recess, the Schottky contact need only block the pinch-off voltage. This pinch-off voltage can be reduced to within the 1-2 volt range, allowing a device with very low creep loss, even if the Schottky diode has poor quality or low barrier height.

According to the present invention causes a recess 20 a local change in the density of the 2DEG. Although recessing is preferred, it is not the only way to reduce the local density of the 2DEG. The change in the density of the 2DEG may be created for localized oxidation of AlGaN to form AlGaO or AlGaON by locating a dopant for p-type doping under the pinch site or locally changing the orientation of the interface.

With reference to, for example can be an area 20A instead of a recess 20 be oxidized to reduce the density of the 2DEG locally. The area 20A can be formed by first covering the AlGaN layer with SiN or another anti-oxidation layer, then opening a window in the SiN over the region to be oxidized and then performing the oxidation.

The oxidation can be achieved by a high temperature effect on H ₂ O, O ₂ , oxygen plasma or other known chemical substances. Gases containing H ₂ can be helpful in catalyzing the process when working carefully with H ₂ and high temperature oxygen.

With reference to can be an area 20B in the AlGaN layer instead of the recess 20 be doped. Thus, for example, the AlGaN layer may be covered with SiN or another suitable protective layer, and then a window in the SiN may overshadow the desired location 20 be opened. Thereafter, the AlGaN layer is exposed to a gas containing Mg, Fe or Cr in a high-temperature environment. Alternatively, one of the dopants can be inserted or used at the bottom of the window in the SiN layer over the AlGaN layer and be diffused in a curing step. The exact time and temperature will depend on the desired doping level and diffusivity of the dopant in the AlGaN layer.

With reference to can be a doped area 20C according to another variation in GaN layer 14 instead of AlGaN layer 16 be formed. A standard setting and curing step can be performed to range 20C either through the AlGaN layer 16 to form or area 20C can in the GaN layer 14 formed and by another GaN layer and then by an AlGaN layer 16 to be covered. The dopant for p-type doping may be Mg, Fe, Cr or Zn. Mg or Zn would be the preferred dopants.

With reference to becomes an alternative embodiment of the present invention as a device 41 shown. device 41 is device 31 essentially similar, except that contact 40 consists of a conductive material and on an insulating layer 42 is set. Accordingly, it is in contact 40 rather, a nonconductive contact than a Schottky contact and may include a metal conductor of some sort to device 41 to operate. In addition to metal conductors, other conductive materials such as Si, GaN or Ge can be used. The operation of device 41 is essentially the same as that of device 31 where the 2DEG is under contact 40 interrupted or reduced in density. The application of an electrical potential to contact 18 (and thus also to contact 40 ), which is greater than the electrical potential that is connected to the electrically conductive connection 19 is created, causing the formation of a 2DEG under contact 40 , and contact 41 can generate electricity between the galvanically conductive connections 18 and 19 conduct.

With reference to Will be another embodiment according to the present invention as a device 56 shown. At device 56 it is a pinch resistance with two electrodes 50 and 52 , As with the devices 31 and 41 can the electrodes 50 and 52 in a recess in AlGaN layer 16 be formed to reduce the density of the 2DEG below the recess to change the Abschnürstrom without switching off the device, wherein device 56 can become a pinch resistance and used to control the current level. However, device represents 56 another configuration that is good for that Abschnürwiderstands device as a power control unit works.

That through Device shown works as follows: When a voltage between the galvanic conductive connections 54 and 55 is applied, electrons from the electrically conductive connection 54 fed into the channel by AlGaN layer 16 and GaN layer 14 is formed. The charge flows laterally into the channel under Schottky contact 50 across the drift area under Schottky contact 52 and from the galvanically conductive connection 55 , Due to the resistance in each of these areas, the voltage drops as the current flows. As a result, the voltage of the channel changes laterally from one end of the device to the other. The more current that flows, the greater the voltage drop across the device. Especially the voltage in the channel directly under the Schottky contact will change with the amount of current. When the voltage difference between this point in the channel and the Schottky contact reaches a certain value, referred to as the "V-pinch" or V-threshold, the density of the electrons in the channel is depleted and no further increase in current occurs with added voltage connected to the galvanically conductive connection 55 is created, enter.

A device according to is symmetrical, making it a bidirectional device, but a unidirectional device could be created when the second Schottky contact 52 Will get removed. In this case, the constriction would only take place in one direction. In the above description it was assumed that the galvanically conductive connection 54 has a bias of 0 and the electrically conductive connection 55 relative to contact 54 positively biased. To the Schottky contacts 50 and 52 All kinds of materials including Au, Ni and Pt can be used. It should be noted that the Abschnürstrom can be tuned by the work function of the formation of the Schottky contacts 50 and 52 Changed selected metal.

Another variation is to use p-type GaN instead of a Schottky metal. The introduction of a Schottky contact 50 / 52 is important to determine the current at which the device pinches off. Since the voltage in the channel changes across the device, a greater distance from the electrically conductive connection to the edge of the Schottky contact results in a lower pinch current. Field plates can also be included in the design to increase the breakdown voltage. For a device according to is it the edge? 50A such Schottky contacts 50 and 52 , which determines the Abschnürstrom.

If one of the contacts 54 or 55 has a forward bias with respect to the other contact (when contact 54 for example, a higher potential than contact 55 and vice versa), current flows between the two contacts. Thus, it is in the in shown device to a bidirectional device. According to the principles of operation of the previous devices described herein, the current is pinched off regardless of the direction of current flow. Therefore, it is device 60 a bidirectional pinch resistance.

The constriction occurs because it is at the potential among the contacts 50 and 52 due to the current flow is a different potential. Thus, the current itself justifies the differences in potential and limits the line level.

device 56 is a nominal bidirectional device and provides a balanced current flow between the electrodes 54 and 55 if the distance to the respective Schottky contacts 50 and 52 stays the same. This means that the same distance between electrode 54 and Schottky contact 50 and between electrode 55 and Schottky contact 52 As a result, the breakdown voltage, the on-resistance and other switching characteristics can be compensated, so that device 56 works in essentially the same way, whether at current flow of electrode 54 to electrode 55 or the other way around. It should be understood that several parameters may be modified to alter the device characteristics, such as: B. on-resistance, Abschnürstrom, breakdown voltage, etc.

As electricity enters the channel of the device 56 flows, builds a voltage potential with respect to the Schottky contacts 50 and 52 and the AlGaN layer 16 on.

Due to the voltage build-up with increasing current, a point is reached where the voltage potential depletes the interface area 15 causing it to pinch off the 2DEG duct. As the current in the channel increases from one electrically conductive connection to another, the voltage on the 2DEG under the Schottky contacts will change with respect to the voltage across the Schottky contacts. Finally, the voltage difference between the Schottky contact and the 2DEG will cause depletion of the 2DEG and stall the current to a saturation value. Because it is the device 56 Being a bi-directional device, the pinch-off works in any direction and can be tailored to specific applications through the structure and content of the layers and contacts. It can, for example be desirable to produce a device that has a higher Abschnürstrom in one direction than in the other direction, which can be achieved by manipulating the relationship between the Schottky contacts and the electrically conductive connections. By its current limitation function represents device 56 a useful component for power applications where overcurrent conditions can cause damage to power network components.

The operational design goals of device 56 can by placing a contact between the two ohmic contacts 54 . 55 be achieved in order to limit the flow of current.

Accordingly, both are Schottky contacts 50 . 52 not required to device 56 to operate, in accordance with the current invention. For example, in terms of illustrates a power control device 31 the concept of the invention described in in a nominally off-nominal device with a single contact between two ohmic contacts 18 and 19 , It should be understood that a device similar to that used in is shown in accordance with device 56 can be designed to provide a nominally on, acting as a pinch resistor with a single Schottky contact.

Therefore, a pinch resistance according to another variation of the current invention may include two ohmic contacts 54 . 55 include two current flow restricting contacts 50 . 52 and an etched recess under each current flow restrictive contact 50 . 52 , like under contact 40 in and under contact 30 in you can see. In a device according to the current invention, current flows between the ohmic contacts 54 . 55 while the current-limiting contacts 50 . 52 behave in such a way that they bring the surface potential to a constant value corresponding to the potential of the ohmic contact to which they are connected. The function of the etched depressions in a pinch resistance according to the current invention may be to reduce the density of 2DEG, but not to eliminate it. By changing the depth, the width of the etched recesses and the shape of the maximum allowable current flow, the device can be controlled. Accordingly, the depressions in a pinch resistance attached to the current invention can change the current current value at which the device pinches off.

Now re Another embodiment of a pinch resistance according to the current invention is as a device 60 shown. contraption 60 includes isolated contacts 61 . 62 instead of the Schottky contacts 50 . 52 from , The isolated contacts have the additional advantage of allowing voltage blockages to a greater degree without device failure. contraption 60 works in the same way as device 56 that is, as a pinch resistor that pinches off the channel passing through the 2DEG at the interface 15 is generated when a sufficient amount of power is conveyed through the duct. However, isolated contacts can 61 . 62 be formed of each conductive material. The isolated contacts 61 . 62 are in electrical contact with the ohmic contacts 54 . 55 in the device 60 so that the pinch-off control is influenced by the current passing through the ohmic contacts 54 . 55 is passed, and so a voltage difference between the isolated contacts 61 . 62 and the 2DEG at interface 15 generated. contraption 60 is virtually the same as the device in every way 56 in the way that a single insulated contact would suffice to device 60 to allow to act as pinch resistance; Modifications in laminate contents and configurations of the various contacts provide certain parametric properties for the device, and device 60 can act as a current sensor device. contraption 60 but also contains an insulating layer 64 that precede the formation of the isolated contacts 61 . 62 is shaped to allow that contacts 61 . 62 from the AlGaN layer 16 be isolated.

The ohmic contacts 54 . 55 can be generated in various ways, such as by the implantation of donors such as Si or Ge, prior to deposition, by the deposition of heavily doped III-nitride material on the AlGaN layer 16 before the Ohmic deposition, the formation of a III-nitride supragitter structure under the ohmic contacts 54 . 55 , etching the AlGaN layer 16 in conjunction with the above deposits, and so on.

Both devices 60 and 56 are bidirectional, which improves their flexibility and the number of applications. devices 56 and 60 can also be generated with HFETs, with the gate electrode shorted to the source electrode. The separations between the ohmic and Schottky contacts are variable to increase or decrease the pinched current flow. The geometry of the Schottky contacts can be realized by various configurations, such as when Schottky material encloses an ohmic contact, or when two Schottky contacts enclose each ohmic contact, or through an etch-sealed Schottky non-enclosing Regions to limit the flow of electricity to specific regions on the device, and so on.

Now regarding : This is an explanatory illustration as a device 70 shown. contraption 70 includes a substrate 72 composed of insulating or highly resistant material such as sapphire, silicon, silicon carbide or other suitable materials. A durable III-nitride material layer 74 superimposed substrate 72 and optionally includes a buffer layer 73 , positioned between layer 74 and layer 72 , buffer layer 73 can between buffers 74 and 72 be positioned to the strain forces associated with the lattice mismatch between the layers 72 and 74 to reduce or mitigate. Another III-nitride material layer 75 is over layer 74 stored, so layer 75 a smaller in-plane lattice constant has as a layer 74 , According to the behavior of III-nitride materials, a 2DEG forms between the layers 74 and 75 which is able to transport high amounts of electricity.

contraption 70 also contains an insulating layer 76 which protects the underlying layer and also provides a means of configuring the device to form contacts and electrodes.

contraption 70 also contains contacts 77B . 78 where contact 77B a schottky contact and contact 78 an ohmic contact is. The contacts 77B . 78 are mounted in a field plate design, with part of the contacts through the insulating layer 76 to the contact layer 75 run. That means Schottky contact 77B includes a field plate part 77A , The resulting device is a nominally active rectifier due to the formation of the high-density high-mobility 2DEG at the interface between the layers 74 . 75 , The 2DEG is formed by the combination of piezoelectric and spontaneous polarization forces, creating an extremely thin but highly conductive and highly resistant layer. A channel that is at the interface between the layers 74 and 75 can carry a very high current flow without the use of a strong, doped region. Accordingly, in a forward voltage direction, with the device conducting, high amounts of current may be transported through the channel. Under conditions of reverse bias, the channel is deprived of mobile charge, so that no current flows into the channel, and the strong resistance of the underlying layer 74 Also prevents the charge from flowing into this layer. Because layers 74 and 75 are not doped, the reverse bias voltage of the device produces weak electric fields. Since the fields have a low value, the device can withstand high voltages and still produce a weak forward voltage resistance. The high, critical fields as well as the teeth improve the RA product for a certain breakdown voltage. Another feature of the device 70 is the ability to damage the device by etching the layer 75 due to the resistance qualities of Schicht 74 , This means that the 2DEG can be etched through layer 75 to be interrupted. As the continuity of 2DEG by the etching of a part or the entire layer 75 interrupted, multiple devices can form on a single substrate, but are electrically isolated from each other. represents regions 200 which pits may be, or implanted regions, or any other characteristics that may interrupt the 2DEG at certain positions to allow the formation of multiple electrically separated devices on a wafer. All of these features and advantages enable the integration of a number of devices on a single chip, with only a few associated space compromises, so that the high performance device can be manufactured in a smaller space than usual with relative complexity.

In relation to showing a diagram of the design of the rectifier with toothed fingers as a device 80 represents. By the equipment of layer 80 with toothed fingers for the various contacts represents device 80 an improvement in the RA product. Schottky contact rotor 81 provides a common connection for the Schottky contact fingers 83 while the Ohmic contact runner 82 a common contact for the ohmic contact fingers 84 prepares. In the rectifier device 80 current flows from ohmic contacts 84 to the Schottky contacts 83 , with very low resistance and high current capacity under forward voltage conditions. With reverse bias, an electrical potential on the Schottky contacts is depleted 83 the 2DEG region to interrupt the channel, located at the interface between the layers 74 . 75 shaped. Since the schottky and ohmic contacts 83 . 84 interlinked, results in a series of current paths that enhance the RA product.

A device according to and conducts and blocks the tension laterally. In addition, and in contrast to the previous figure is a device according to and a Schottky device using a high density (high density) 2DEG.

It should be mentioned that the high degree of gearing also improves the space utilization.

In a device according to the illustrative example is insulating layer 76 very thin (10-200 Å), while the width of the field plate 77A is very large (1-3 μm), which is the size of a Schottky contact 101 (3-10 microns) is comparable. In a device according to conventional design, the contact area is much larger than the plate width. The reason for having a larger than ordinary field plate is that the Schottky contact in this type of heterojunction device is very transparent at high electric fields. The big field plate 77A shifts the field to the end of the Schottky metal, which is located on an insulator where no permeability occurs. This protects the Schottky contact from high fields.

In terms of - where a technique for making a device 90 is shown according to the current invention. In becomes device 90 after forming a series of layers over a substrate 92 shown. substratum 92 may consist of an insulator or of highly resistant material, such as sapphire, silicon, silicon carbide or the like material.

A resistant III nitride layer such as a GaN layer 94 is the substrate 92 superimposed, with an intermediate buffer layer 93 , buffer layer 93 is provided to reduce the strain caused by the lattice mismatch between the substrates 92 and 94 is induced. About shift 94 there is another III nitride layer 95 shown in device 90 as an AlGaN layer. layer 94 has a larger in-plane lattice constant as a layer 95 What the training of a 2DEG 97 at the interface of the layers 94 . 95 causes.

In terms of , a contact window 98 is in insulator layer 96 for the formation of an ohmic contact on shift 95 open. describes the deposition of the ohmic contact 99 to connect to the AlGaN layer 94 to prepare a path for the current carried in the channel created by 2DEG 97 is formed.

Now in terms of where a Schottky contact window 101 in insulating layer 96 is opened to AlGaN layer 95 expose. In relation to where a Schottky contact 103 over and in contact with AlGaN layer 96 through contact window 101 is appropriate. Schottky contact 103 is also able to carry electricity that is powered by 2DEG 97 formed channel is provided.

By the formation of device 90 which functions as a rectifier as described above becomes insulating layer 96 first over layer 95 deposited to decomposition of AlGaN layer 95 during the healing process. When the ohmic metal contact 99 through the insulating layer 96 in is attached, takes place an annealing process to the formation of the ohmic contact 99 to finish. During the annealing process insulator layer prevents 96 a substantial decline of the AlGaN layer 94 , Note that none of the layers, which device 90 forms, doped or exposed to typical processes used in the formation of doped semiconductor materials. The absence of a doped current-carrying layer and the use of the highly conductive 2DEG 97 dramatically improves the RA product for a given breakdown voltage. The resistant GaN layer 94 also allows the separation of device 90 by etching the AlGaN layer 94 , This ability of separation of device 97 enables the integration of many devices on a single chip, so that a complete network can be realized in the manufacture of an integrated circuit.

Note that, for example, Schottky contact window 101 can be formed with sloping sides, according to the illustrative example.

The fabrication of ohmic contacts, Schottky contacts, insulating layers and metallized contacts can be accomplished by known techniques. In addition, passivation layers and cladding may be used with the devices described herein, as well as techniques for forming contacts to current carrying electrodes and gates to produce a complete package.

The III-nitride materials used in the construction of the devices 31 . 41 . 56 . 60 and 70 have much better blocking characteristics than conventional materials, allowing the devices to be made smaller than conventional materials while retaining operational parametric values. Because the devices 31 . 41 . 56 . 60 and 70 can be realized in a smaller form than conventional devices to perform comparable functions, a reduced on-resistance can be realized in order to obtain a better degree of performance.

In addition, the electrodes described herein can be formed with a low-resistance contact process, which further improves the operational characteristics of the devices described.

Now in terms of where the Schottky part 77B the device in with the P-type GaN Body 103 can be replaced. P-Type GaN Body 103 can within opening 101 held or could protrude beyond the insulator if it had been generated by regrowth.

Claims (28)

III-nitride current control device ( 31 ; 41 ; 56 ; 60 ; 70 ), comprising: - a duct formed at an interface ( 15 ) between two III-nitride materials ( 14 . 16 ; 74 . 75 ) having different in-plane lattice constants or different band gaps; A first electrode ( 19 ; 52 ; 55 ; 62 ; 55 ; 78 ) coupled to the duct to carry duct power; A second electrode ( 18 . 30 ; 18 . 40 ; 54 . 50 ; 54 . 61 ; 77A . 77B coupled to the duct and operative to affect the duct to connect the power line between the first electrode (12) 19 ; 52 ; 55 ; 62 ; 55 ; 78 ) and the second electrode ( 18 . 30 ; 18 . 40 ; 54 . 50 ; 54 . 61 ; 77A . 77B ) through the duct; wherein - the second electrode ( 18 . 30 ; 18 . 40 ; 54 . 50 ; 54 . 61 ; 77A . 77B ) an ohmic contact ( 18 ; 54 ; 77A ) and a rectifying contact ( 30 ; 40 ; 50 ; 61 ; 77B ); where the rectifying contact ( 30 ; 40 ; 50 ; 60 ; 77A ) on the ohmic contact ( 18 ; 54 ; 77B ) lies; and wherein - the first electrode ( 19 ; 52 ; 55 ; 62 ; 5 ; 78 ) another ohmic contact ( 19 ; 55 ; 78 ). Device according to claim 1, wherein the first electrode ( 52 . 55 ; 62 . 55 ) also has a rectifying contact ( 52 ; 62 ). The device of claim 1, wherein the first electrode comprises a p-type semiconductor. The device of claim 1, wherein the first electrode comprises an n-type semiconductor. Device according to claim 1, wherein the III-nitride materials ( 14 . 16 ; 74 . 75 ) GaN- ( 14 . 74 ) or AlGaN layers ( 16 . 75 ), the electrodes ( 19 ; 52 ; 55 ; 62 ; 55 ; 78 ; 18 . 30 ; 18 . 40 ; 54 . 50 ; 54 . 61 ; 77A . 77B ) on the AlGaN layer ( 16 ; 75 ) are formed. Device according to claim 1, wherein the rectifying contact of the second electrode ( 18 . 30 ; 18 . 40 ; 54 . 50 ; 54 . 61 ; 77A . 77B ) a Schottky contact ( 30 ; 50 ; 77B ). Device according to claim 1, wherein the second electrode ( 77A . 103 ) a p-type semiconductor ( 103 ). Apparatus according to claim 1, further comprising an insulating layer ( 42 ; 64 ) between the rectifying contact ( 40 ; 61 ) of the second electrode ( 18 . 40 ; 54 . 61 ) and one of the two III-nitride materials ( 14 ; 16 ). Apparatus according to claim 5, further comprising an insulating layer ( 42 ; 64 ) between the rectifying contact ( 40 ; 61 ) of the second electrode ( 18 . 40 ; 54 . 61 ) and the AlGaN layer ( 16 ). Device according to claim 8, wherein the rectifying contact ( 40 ; 61 ) of the second electrode ( 18 . 40 ; 54 . 61 ) comprises a conductive material comprising Si, GaN or Ge. Device according to claim 9, wherein the rectifying contact ( 40 ; 61 ) of the second electrode is a conductive material with Si, GaN or Ge. Device according to claim 8, wherein the rectifying contact ( 40 ; 61 ) of the second electrode ( 18 . 40 ; 54 . 61 ) comprises a semiconductor material. Device according to claim 9, wherein the rectifying contact ( 40 ; 61 ) of the second electrode is a semiconductor material. Apparatus according to claim 1, wherein the duct is formed with a two-dimensional electron gas. Apparatus according to claim 1, further comprising a recess ( 20 ) contained in one of the III-nitride materials ( 16 ) under a part of the rectifying contact ( 30 ; 40 ) of the second electrode ( 18 . 30 ; 18 . 40 ) is formed. Device according to claim 15, wherein the recess ( 20 ) is arranged to charge carriers under the second electrode ( 18 . 30 ; 18 . 40 ) to eliminate. Device according to claim 15, wherein the recess ( 20 ) is arranged to increase the charge density under the second electrode ( 18 . 30 ; 18 . 40 ), which causes the reduction of pinch current. Device according to claim 15, wherein the recess ( 20 ) oblique pages ( 22 ) Has. Device according to claim 1, wherein the first electrode ( 52 . 55 ), a Schottky contact ( 52 ) coupled to the duct and operative to affect the duct to control the power line in the duct. Device according to claim 1, wherein the first electrode ( 52 . 55 ) and the second electrode ( 54 . 50 ) continue to use Schottky contacts ( 52 . 50 ), which are coupled to the duct and operable to affect the duct to control the power line in the duct. Apparatus according to claim 20, wherein each Schottky contact ( 52 . 50 ) from a corresponding Ohmic contact ( 55 . 54 ) and connected to it, in a corresponding electrode ( 52 . 55 ; 54 . 50 ). Apparatus according to claim 21, wherein the distances between each Schottky contact ( 52 . 50 ) and the corresponding ohmic contact ( 55 . 54 ) are substantially the same. Process for forming a selective, current-carrying III-nitride device ( 31 ; 41 ), comprising: providing a substrate ( 12 ); Forming a III-nitride layer ( 14 ) above the substrate ( 12 ) with a first in-plane lattice constant; Forming another III-nitride layer ( 16 ) over the first III nitride layer ( 14 ), wherein the second III-nitride layer ( 16 ) has a second in-plane lattice constant which is smaller than the first in-plane lattice constant; Forming a first electrode ( 19 ) on the second III-nitride layer ( 16 ), the first electrode ( 19 ) comprises an ohmic contact; - forming a depression ( 20 ) in the second III-nitride layer ( 16 ); - forming an ohmic contact ( 18 ) a second electrode ( 18 . 30 ; 18 . 40 ); - forming a rectifying contact ( 30 ; 40 ) of the second electrode ( 18 . 30 ; 18 . 40 ) in the depression ( 20 ) and on ohmic contact ( 18 ) lying in such a way that a duct between the first electrode ( 19 ) and the second electrode ( 18 . 30 ; 18 . 40 ) under the rectifying contact ( 30 ; 40 ) is interrupted to obtain a normally inactive device. The method of claim 23, wherein said forming the rectifying contact ( 30 ; 40 ) in the depression ( 20 ) forming a Schottky contact ( 30 ) in the depression ( 20 ). The method of claim 23, further comprising preparing a mask ( 62 ) over the second III-nitride layer ( 16 ) to positions ( 64 . 65 ) of the depressions ( 20 ), the mask ( 62 ) has there sloping sides where the wells must be determined. A method according to claim 23, further comprising producing the recess ( 20 ) with sloping sides ( 22 ). The method of claim 23, further comprising forming the rectifying contact ( 30 . 40 ), which with the ohmic contact ( 18 ) of the second electrode ( 18 . 30 ; 18 . 40 ) connected is. A method according to claim 23, further comprising preparing an insulating layer ( 42 ) in the depression ( 20 ), prior to the formation of the rectifying contact ( 40 ).

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