Diode with a Schottky contact including a local surface region

Abstract

In a general aspect, a diode (100) includes a substrate (102) of a first conductivity type, a semiconductor layer (104) of the first conductivity type disposed on the substrate and including a drift region (120), a shield region (110a) of a second conductivity type disposed in a semiconductor layer adjacent to the drift region, and a surface region (132a) of the first conductivity type disposed in a first portion of the drift region adjacent to the shield region. The surface region has a doping concentration higher than a doping concentration of a second portion of the drift region adjacent to the surface region. The second portion does not include the surface region. The diode includes at least a part of the shield region, a surface region of the first portion of the drift region, and a Schottky material (130) disposed in the second portion of the drift region.

Description

Technical Field

[0001] This specification relates to a Schottky diode that improves the operating characteristics of a diode by including a shallow region for locally changing the barrier height and the electric field, such as under a Schottky contact within the drift region of the diode.

Background Art

[0002] Semiconductor materials used to manufacture high-power semiconductor devices, such as silicon (Si), silicon carbide (SiC), gallium nitride (GaN), etc., are affected by the presence of high electric fields during the operation of related semiconductor devices that can operate at 400 volts (V), 600 V, 1200 V, or higher. A Schottky diode utilizing such a power semiconductor material (e.g., SiC) can experience leakage current approaching or exceeding the acceptable operating limit due to such high electric fields under reverse bias conditions. This is partially due to the fact that there is a trade-off between the forward operating characteristics of the Schottky diode and its reverse bias leakage current. That is, by improving the forward operating characteristics of the Schottky diode, such as reducing the conduction loss by reducing the forward voltage drop (V f ), the leakage current of the diode increases. Therefore, with current techniques, in order to reduce the conduction loss in the on state (e.g., reduce V f ), the designer has to sacrifice the reverse characteristics of the diode, which can result in leakage current exceeding the acceptable value. Conversely, with previous techniques, in order to improve the reverse characteristics of the diode (e.g., reduce leakage), the designer has to sacrifice the forward operating characteristics of the diode.

Summary of the Invention

[0003] In some aspects, the techniques described herein relate to a diode, the diode including a substrate of a first conductivity type, a semiconductor layer of the first conductivity type disposed on the substrate, the semiconductor layer including a drift region of the diode, a shield region of a second conductivity type disposed within a semiconductor layer adjacent to the drift region, a surface region of the first conductivity type disposed in a first portion of the drift region adjacent to the shield region, the surface region having a doping concentration higher than a doping concentration of a second portion of the drift region adjacent to the surface region, the second portion of the drift region not including the surface region, and a Schottky material disposed on at least a portion of the shield region, the surface region of the first portion of the drift region, and the second portion of the drift region.

[0004] In some aspects, the techniques described herein relate to a diode, and the surface region is disposed between the shield region and the second portion of the drift region.

[0005] In some aspects, the techniques described herein relate to a diode, the surface region being a first surface region, the diode further including a second surface region of the first conductivity type disposed in a third portion of the drift region, the second surface region being disposed adjacent to the first surface region, the second surface region having a doping concentration higher than the doping concentration of the second portion of the drift region and lower than the doping concentration of the first surface region, and the Schottky material being further disposed on the second surface region.

[0006] In some aspects, the techniques described herein relate to a diode, and the second surface region is further disposed between the first surface region and the second portion of the drift region.

[0007] In some aspects, the techniques described herein relate to a diode, the semiconductor layer including a mesa having a height, the mesa being defined by a trench formed within the semiconductor layer, the surface region being disposed on an upper portion of the mesa, and the Schottky material being disposed on the mesa.

[0008] In some aspects, the techniques described herein relate to a diode, and the surface region is further disposed on the sidewall of the mesa.

[0009] In some aspects, the techniques described herein relate to a diode, the diode includes an array of geometrically shaped cells, the widest part of the drift region does not include the surface region, and the narrowest part of the drift region includes the surface region.

[0010] In some aspects, the techniques described herein relate to a diode, the first conductivity type is n-type, and the second conductivity type is p-type.

[0011] In some aspects, the techniques described herein relate to a diode, the substrate is a silicon carbide substrate, the semiconductor layer is an epitaxial silicon carbide layer, and the substrate has a doping concentration higher than that of the epitaxial silicon carbide layer.

[0012] In some aspects, the techniques described herein relate to a diode, the semiconductor layer includes a first epitaxial semiconductor layer of a first conductivity type disposed on the substrate and a second epitaxial semiconductor layer of the first conductivity type disposed on the first epitaxial semiconductor layer, and the first epitaxial semiconductor layer has a doping concentration higher than that of the second epitaxial semiconductor layer.

[0013] In some aspects, the techniques described herein relate to a diode, at least a part of the shield region is a first part of the shield region, the diode is disposed in a second part of the shield region, and the diode further includes a metal that defines an ohmic contact to the shield region.

[0014] In some aspects, the techniques described herein relate to a diode, the metal disposed in the second part of the shield region includes at least one of a Schottky material, a metal silicide, or a deposited metal.

[0015] In some embodiments, the techniques described herein relate to a diode, and the surface region has a depth of 100 nanometers (nm) or less in the semiconductor layer.

[0016] In some embodiments, the techniques described herein relate to a diode, and the surface region is disposed in 10% to 90% of the area above the drift region.

[0017] In some embodiments, the techniques described herein relate to a diode, and the doping concentration of the surface region varies along at least one of the surface of the semiconductor layer or the depth of the surface region of the semiconductor layer.

[0018] In some embodiments, the techniques described herein relate to a diode, and the surface region is further disposed in 10% to 90% of the area above the shield region.

[0019] In some embodiments, the techniques described herein relate to a diode, and this diode includes a substrate of a first conductivity type, a semiconductor layer of the first conductivity type disposed on the substrate, the semiconductor layer including a drift region of the diode, a first shield region of the second conductivity type disposed in the semiconductor layer adjacent to the drift region, a second shield region of the second conductivity type disposed in the semiconductor layer adjacent to the drift region, the drift region being at least partially disposed between the first shield region and the second shield region, a surface region of the first conductivity type disposed in a first portion of the drift region between the first shield region and the second shield region, the surface region having a doping concentration higher than the doping concentration of a second portion of the drift region adjacent to the surface region, the second portion of the drift region not including the surface region, a surface region, at least a part of the first shield region, at least a part of the second shield region, a surface region of the first portion of the drift region, and a Schottky material disposed in the second portion of the drift region.

[0020] In some embodiments, the techniques described herein relate to a diode, and a surface region is further disposed between a first shield region and a second portion of the drift region, and between a second shield region and the second portion of the drift region.

[0021] In some embodiments, the techniques described herein relate to a diode, the surface region is a first surface region, and the diode further includes a second surface region of a first conductivity type disposed in a third portion of the drift region, and the second surface region includes a first portion disposed between the first shield region and a first portion of the first surface region, and a second portion disposed between the second shield region and a second portion of the first surface region, and the second surface region has a doping concentration higher than a doping concentration of a second portion of the drift region and lower than a doping concentration of the first surface region, and a Schottky material is further disposed on the second surface region.

[0022] In some embodiments, the techniques described herein relate to a diode, and a second portion of the drift region is disposed between a first portion of the first surface region and a second portion of the first surface region.

[0023] In some embodiments, the techniques described herein relate to a method for forming a diode, the method including forming a semiconductor layer of a first conductivity type disposed on a substrate of the first conductivity type, the semiconductor layer including a drift region of the diode, forming a shield region of a second conductivity type in the semiconductor layer adjacent to the drift region, forming a surface region of the first conductivity type in a first portion of the drift region adjacent to the shield region, the surface region having a doping concentration higher than a doping concentration of a second portion of the drift region adjacent to the surface region, and the second portion of the drift region not including the surface region, and disposing a Schottky material on at least a portion of the shield region, the surface region of the first portion of the drift region, and the second portion of the drift region.

[0024] In some embodiments, the techniques described herein relate to a method, and the doping concentration of the surface region varies along at least one of the surface of the semiconductor layer or the depth of the surface region of the semiconductor layer.

[0025] In some embodiments, the techniques described herein relate to a method, the surface region is a first surface region, and the method further includes forming a second surface region of a first conductivity type in a third portion of the drift region, the second surface region being disposed adjacent to the first surface region, the second surface region having a doping concentration that is higher than the doping concentration of a second portion of the drift region and lower than the doping concentration of the first surface region, and the Schottky material being further disposed in the second surface region. BRIEF DESCRIPTION OF THE DRAWINGS

[0026]

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[0027] In drawings that are not necessarily drawn to a fixed scale, the same reference numerals in different figures may indicate the same and / or similar components (elements, structures, etc.). The drawings generally illustrate, by way of example and not limitation, the various implementations discussed in this disclosure. Reference numerals shown in one drawing may not be repeated for the same and / or similar elements in related drawings. Reference numerals that are repeated in multiple drawings may not be specifically discussed for each of those drawings, but are provided for the context between related drawings. Also, when multiple examples of an element are shown, not all of the same elements in the drawing are necessarily specifically referenced by one reference numeral.

DETAILED DESCRIPTION OF THE INVENTION

[0028] The present disclosure is directed to diodes including Schottky contacts (e.g., Schottky diodes), and related methods of manufacturing such diodes. In the approach described herein, a local surface region (e.g., a surface region having a depth of 100 nanometers or less) is used to locally modify the area of the Schottky interface in the underlying semiconductor material (e.g., on top of the drift region of a diode). That is, such a surface region can be included in the Schottky interface (e.g., Schottky contact) of a diode to locally modify the barrier height and the associated electric field of the Schottky interface. In some implementations, such a surface region can be formed by ion implantation, in situ doping, or by using other techniques. By positioning the surface region at a portion of the Schottky contact of a diode having a lower electric field, the effective turn-on voltage or forward voltage drop V f (and thus the on-state loss) of the diode can be reduced without significantly affecting the reverse blocking ability of the diode (e.g., without significantly increasing the reverse bias leakage current). In some implementations, both the forward and reverse operating characteristics of a Schottky diode can be improved.

[0029] FIG. 1 is a cross-sectional view of a Schottky diode 100 (diode) including a surface region (formed, for example, by local surface implants) according to one implementation. In some implementations, the diode 100 may have a linear (strip) cell layout (e.g., having the same structure and dimensions within and / or outside a page). In some implementations, the diode 100 may have a cell layout such as the example shown in FIG. 5. The diode 100 shows a cross-section of a single diode cell perpendicular to the stripe of the linear cell layout, which can be interconnected with other diode stripes or diode cells to form a larger diode (e.g., by electrically connecting respective anodes to each other and by electrically connecting respective cathodes to each other). Depending on the specific implementation, the element spacing, size, and arrangement of the diode 100 may vary.

[0030] As shown in FIG. 1, the diode 100 includes a substrate 102 and a semiconductor layer 104 (semiconductor region). The substrate 102 and the semiconductor layer 104 may be of a first conductivity type, for example, n-type conductivity. The substrate 102 may have a doping concentration higher than that of the semiconductor layer 104. In some implementations, the semiconductor layer 104 may be an epitaxial semiconductor layer or may include a plurality of epitaxial semiconductor layers having different doping concentrations. That is, in FIG. 1, the upper portion of the semiconductor layer 104 may have a doping concentration higher than that of the lower portion of the semiconductor layer 104, or may gradually increase along the depth of the semiconductor layer 104, for example, from the upper surface of the semiconductor layer 104 to the bottom of the semiconductor layer 104. In some implementations, the substrate 102 and the semiconductor layer 104 may include silicon carbide or other semiconductor materials. In some implementations, n-type doping may be provided by incorporating nitrogen, phosphorus, etc.

[0031] Diode 100 includes shield regions 110a and 110b disposed within semiconductor layer 104. Shield regions 110a and 110b are disposed adjacent to drift region 120 of diode 100. Shield regions 110a and 110b of diode 100 have a second conductivity type opposite to the first conductivity type, for example, p-type conductivity. In some implementations, the first conductivity type and the second conductivity type can be reversed. In some implementations, p-type doping can be provided by incorporating aluminum, boron, etc.

[0032] Diode 100 also includes a Schottky material 130 that defines a Schottky contact 140 with drift region 120, for example, along the surface of drift region 120 between shield region 110a and shield region 110b. In an exemplary implementation, Schottky material 130 can include a metal, an alloy, a semiconductor material, and / or other materials that define a Schottky barrier with drift region 120. Drift region 120 includes surface regions 132a and 132b that are disposed at respective first upper and second upper portions of drift region 120 and are included in the interface (Schottky interface) of Schottky contact 140. As shown in FIG. 1, surface regions 132a and 132b, as well as other surface regions described herein, can have a depth D. In some implementations, depth D can be, as described above, 100 nanometers or less.

[0033] Surface regions 132a and 132b are, in this example, of the first conductivity type and can be formed simultaneously (e.g., using the same implantation process). As shown in FIG. 1, the central (third) upper portion of drift region 120 along the interface of Schottky contact 140 does not include a surface region. In this example, surface regions 132a and 132b have a higher doping concentration than portions of drift region 120 that do not include such implants, such as the central portion.

[0034] As shown in FIG. 1, with respect to the interface of the Schottky contact 140, the surface regions 132a, 132b are disposed at the respective upper portions (e.g., the first portion and the second portion respectively) of the drift regions 120 adjacent to (and in contact with) the shield regions 110a and 110b. The third central upper portion of the drift region 120 disposed between the surface regions 132a and 132b does not include local surface implants and may have, for example, the original doping concentration of the semiconductor layer 104.

[0035] In this example, during reverse bias operation, the surface regions 132a and 132b locally change (lower) the barrier height of the Schottky contact 140 and locally change (increase) the associated electric field in the portion of the drift region 120 including the surface regions 132a and 132b. Thus, in this example, the Schottky contact 140 corresponding to the central portion of the drift region 120 will have a barrier height greater than that of each portion of the Schottky contact 140 corresponding to the surface regions 132a and 132b.

[0036] As shown in FIG. 1, the portion of the drift region 120 that does not include surface regions (e.g., implants) may have a width W1. In some implementations, the width W1 may be 10 percent to 90 percent of the width of the upper portion of the drift region 120 disposed between the shield regions 110a and 110b. In other words, the surface regions 132a and 132b may occupy 90 percent to 10 percent of the upper portion of the drift region 120. In an exemplary implementation, the width W1 may be selected based on the electric field distribution at the surface of the drift region 120 (e.g., the electric field distribution along the Schottky contact 140 under reverse bias conditions) to achieve a desired relationship between the on-state operating characteristics and the off-state operating characteristics of the diode 100. In the following description, references to the electric field and the electric field distribution refer to the electric field and the electric field distribution under reverse bias conditions, respectively, unless otherwise specified.

[0037] In this example, as W1 changes (widens or narrows), the associated surface area of drift region 120, which does not include the surface region where the Schottky material 130 is disposed, changes (increases or decreases, respectively). Similarly, as W1 changes, the respective surface areas of surface regions 132a and 132b where the Schottky material 130 is disposed also change accordingly. That is, when W1 is increased, the respective surface areas of surface regions 132a and 132b included in the Schottky contact 140 become smaller, and when W1 is decreased, the respective surface areas of surface regions 132a and 132b included in the Schottky contact 140 become larger.

[0038] In diode 100, in the absence of surface regions 132a and 132b, the electric field distribution in drift region 120 (e.g., directly under the Schottky contact 140 (e.g., 5 nanometers or less)) is highest at the midpoint between shield region 110a and shield region 110b, and decreases (e.g., has a bell-shaped curve distribution) towards shield region 110a and shield region 110b, respectively, as the distance from the midpoint increases. Thus, when appropriately designed, the central portion of drift region 120, which does not include the surface region, will have the highest electric field for diode 100, while surface regions 132a and 132b are disposed in portions of drift region 120 that originally have a lower electric field.

[0039] In this example, the portion of Schottky contact 140 corresponding to the portion of the drift region that does not include the surface region will have a higher barrier height than the barrier heights of the portions of Schottky contact 140 corresponding to surface regions 132a and 132b. Thus, the trade-off between the forward operating characteristics and the reverse operating characteristics of diode 100 can be improved, for example, as compared to having a uniformly doped surface of drift region 120 under Schottky contact 140.

[0040] For example, in some implementations, the diode 100, the width W1, and the doping of the surface regions 132a and 132b are configured such that the leakage current density (e.g., the total leakage through a particular device portion divided by the area of that portion) and / or the on-state current density of each of the portion of the Schottky contact 140 corresponding to the central portion of the drift region and the portion of the Schottky contact 140 corresponding to the surface regions 132a and 132b are the same or substantially the same (e.g., having the same design goals). In other implementations, the width W1 and the doping of the surface regions 132a and 132b are such that the leakage current density through the portion of the Schottky contact 140 corresponding to the surface regions 132a and 132b is lower than the current density through the portion of the Schottky contact 140 corresponding to the central portion of the drift region 120, but the corresponding device still has a lower barrier height and a lower Vf associated with the more highly doped surface regions 132a and 132b. Such an implementation can reduce the total leakage current of the diode 100 and achieve specific forward operating characteristics, as compared to having a uniformly more highly doped Schottky contact 140. Further, in the diode 100, the lower barrier height of the Schottky contact 140 associated with the more highly doped surface regions 132a and 132b reduces the Vf of the diode 100 (e.g., reduces the on-state conduction loss) and achieves specific reverse operating characteristics, as compared to a diode having a uniformly less highly doped surface under the Schottky contact 140. Thus, the implementation of the diode 100 can achieve an improved trade-off between the on-state operating characteristics and the off-state operating characteristics of the Schottky diode.

[0041] Also, as shown in FIG. 1, diode 100 includes a metal that includes portions 134a and 134b. Portions 134a and 134b form ohmic contacts 144a with shield region 110a and ohmic contacts 144b with shield region 110b, respectively. In some implementations, portions 134a and 134b may include the Schottky material 130 of diode 100. In some implementations, portions 134a and 134b may include different materials that can be deposited, annealed, and / or silicided to form ohmic contacts 144a and 144b.

[0042] FIG. 2 is a cross-sectional view of another diode 200 that includes a more highly doped surface region, according to one implementation. Similar to diode 100, in some implementations, diode 200 may have a linear (strip) cell layout (i.e., into and / or out of the page). In some implementations, the cell layout of diode 200 may be, for example, a cell type (e.g., an array of geometric cells such as squares, hexagons, etc.) as shown in the example of FIG. 5. Diode 200 shows a single diode stripe or a single diode cell, which can be interconnected with other diode stripes or diode cells to form a larger diode. Depending on the particular implementation, the element spacing, size, and arrangement of diode 200 may vary.

[0043] As shown in FIG. 2, the diode 200 includes a substrate 202 and a semiconductor layer 204 (semiconductor region). The substrate 202 and the semiconductor layer 204 can be of a first conductivity type, for example, n-type conductivity. The substrate 202 can have a doping concentration higher than that of the semiconductor layer 204. In some implementation forms, the semiconductor layer 204 can be an epitaxial semiconductor layer or can include a plurality of epitaxial semiconductor layers having different doping concentrations. That is, looking at FIG. 2, the upper part of the semiconductor layer 204 can have a doping concentration higher than that of the lower part of the semiconductor layer 204 or a doping concentration that changes along the depth of the semiconductor layer 204. In some implementation forms, the substrate 202 and the semiconductor layer 204 can include silicon carbide or other semiconductor materials.

[0044] The diode 200 includes a shield region 210a and a shield region 210b disposed in the semiconductor layer 204. The shield region 210a and the shield region 210b are disposed adjacent to the drift region 220 of the diode 200. The shield region 210a and the shield region 210b of the diode 200 are of a second conductivity type opposite to the first conductivity type, for example, p-type conductivity. In some implementation forms, the first conductivity type and the second conductivity type can be reversed.

[0045] Similar to diode 100, diode 200 includes, for example, a Schottky material 230 (e.g., a Schottky metal layer or other Schottky material) that defines a Schottky contact 240 with the drift region 220 along the surface of the drift region 220 between the shield regions 210a and 210b. The drift region 220 includes a surface region 232a (e.g., formed by ion implantation) and a surface region 232b (e.g., formed by ion implantation), which are disposed in the first and second portions of the drift region 220, respectively, and define a Schottky contact 240 with the Schottky material 230. The diode further includes a surface region 236a (e.g., a local surface implant) and a surface region 236b (e.g., a local surface implant) that are disposed in the third and fourth portions of the drift region 220, respectively, and define a Schottky contact 240 with the Schottky material 230.

[0046] The surface regions 232a and 232b are, in this example, of the first conductivity type and can be formed simultaneously using an ion implantation process. The surface regions 236a and 236b are also of the first conductivity type and can be formed simultaneously using another ion implantation process. In diode 200, the surface regions 232a and 232b have a higher doping concentration than the portion of the drift region 220 that does not include such surface regions, e.g., the central portion, and the surface regions 236a and 236b have a higher doping concentration compared to the doping concentration of the surface regions 232a and 232b. As shown in FIG. 2, the central (fifth) portion of the drift region 220 along the interface of the Schottky contact 240 does not include a surface region and can have, for example, the original doping concentration of the semiconductor layer 204.

[0047] As shown in FIG. 2, the surface region 232a is disposed adjacent to the upper central portion of the drift region 220, and the surface region 232b is disposed adjacent to the upper central portion of the drift region 220 and, for example, symmetrically to the surface region 232a with respect to the upper central portion of the drift region 220. Further, the surface region 236a is disposed between the shield region 210a and the surface region 232a, and the surface region 236b is disposed between the shield region 210b and the surface region 232b.

[0048] The surface regions 232a, 232b, 236a, and 236b, in this example, locally change (lower) the barrier height of the Schottky contact 240 respectively, and locally change (increase) the associated electric field in the portions of the drift region 220 that include those surface regions. Thus, in this example, the Schottky barrier is higher at the Schottky interface above the central upper part of the drift region 220 that does not include the surface regions than at each part of the Schottky contact above the portion of the drift region 220 that includes the surface regions 232a, 232b, 236a, and 236b. Further, the Schottky 240 at the interface between the Schottky material 230 and the portion of the drift region that includes the surface regions 232a and 232b will have a higher barrier height than the barrier height of the Schottky contact at the interface above the portion of the drift region 220 that includes the surface regions 236a and 236b. That is, the part of the Schottky contact 240 corresponding to the central part of the drift region 220 will have a larger barrier height than the barrier height of each part of the Schottky contact 240 corresponding to the surface regions 232a and 232b. Also, the barrier height of the part of the Schottky contact 240 corresponding to the surface regions 232a and 232b will be higher than the barrier height of each part of the Schottky contact 240 corresponding to the surface regions 236a and 236b.

[0049] As shown in FIG. 2, the portion of the drift region 220 that does not include the surface regions (e.g., local surface implants) may have a width W1. Further, the portion of the drift region 220 that does not include the surface regions, together with the portion of the drift region 220 that includes the surface regions 232a and 232, has a width W2. In an exemplary implementation, the widths W1 and W2, and the doping concentrations of the surface regions 232a, 232b, a36a, 236b may be selected based on the electric field distribution at the surface of the drift region 220 (e.g., the electric field distribution under reverse bias conditions) so as to achieve a desired relationship between the on-state operating characteristics and the off-state operating characteristics of the diode 200.

[0050] In this example, as W1 changes (widens or narrows), the associated surface area of the drift region 220 that does not include the surface region where the Schottky material 230 is disposed changes (increases or decreases, respectively). Similarly, as W1 changes, the respective surface areas of the drift region 220 where the surface regions 232a, 232b, 236a, and 236b are disposed also change accordingly. That is, when W1 is increased, the total surface area of the drift region 220 where the surface regions 232a, 232b, 236a, and 236b are disposed decreases, and when W1 is reduced, the total surface area of the drift region 220 where the portions 232a, 232b, 236a, and 236b are disposed increases. Also, as W2 changes, the respective surface areas of the drift region 220 where the surface regions 236a and 236b are disposed also change accordingly. That is, when W2 is increased, the surface area of the drift region 220 where the surface regions 236a and 236b are disposed decreases, and when W2 is reduced, the surface area of the drift region 220 where the surface regions 236a and 236b are disposed increases.

[0051] In the diode 200, in the absence of the regions 232a, 232b, 236a, and 236b, similar to the diode 100, the electric field in the drift region 220 (e.g., directly below the Schottky contact 240) is highest at the midpoint between the shield region 210a and the shield region 210b and decreases (e.g., has a bell-shaped curve distribution) towards the shield region 210a and the shield region 210b, respectively, as it moves away from the midpoint. Therefore, the central portion of the drift region 220 that does not include the surface region will have the highest electric field with respect to the diode 200, but the electric field in the upper portion of the drift region 220 that includes the surface regions 232a, 232b, 236a, and 236b will be similar or lower.

[0052] In this example, the portion of the Schottky contact 240 corresponding to the portion of the drift region that does not include surface implants will have a barrier height higher than the barrier height of the portion of the Schottky contact 240 corresponding to the surface regions 232a, 232b, 236a, and 236b. Further, the barrier height of the portion of the Schottky contact 240 corresponding to the surface regions 232a, 232b will be higher than the barrier height of the portion of the Schottky contact 240 corresponding to the surface regions 236a and 236b. Thus, the trade-off between the forward operating characteristics and the reverse operating characteristics of the diode 200 can be improved, for example, as compared to the case of having a Schottky contact with a uniform doping concentration at the upper part of the drift region.

[0053] For example, in the diode 200, the widths W1 and W2 can be adjusted such that the respective leakage current densities (e.g., the leakage current passing through a specific device portion divided by the corresponding area) and / or the respective on-state current densities of the portion of the Schottky contact 240 corresponding to the central portion of the drift region and the portions of the Schottky contact 240 corresponding to the surface regions 232b, 232a, 236a, and 236b are the same or substantially the same (e.g., having the same design goals). Such an implementation can reduce the total leakage current of the diode 200 and achieve specific forward operating characteristics as compared to the case of having a uniformly and more highly doped upper part of the drift layer under the Schottky contact 240. Further, in the diode 200, the lower barrier height of the Schottky contact 240 associated with the surface regions 232a, 232b, 236a, and 236b reduces the Vf of the diode 200 (e.g., reduces the on-state conduction loss) and achieves specific reverse operating characteristics as compared to a diode having a uniformly and less highly doped upper part of the drift layer under the Schottky contact 240. Thus, the implementation of the diode 200 can achieve an improved trade-off between the on-state operating characteristics and the off-state operating characteristics of the Schottky diode.

[0054] Also, as shown in FIG. 2, diode 200 includes a metal that includes portions 234a and 234b. Portions 234a and 234b can respectively define ohmic contacts 244a with shield region 210a and ohmic contacts 244b with shield region 210b. In some implementations, portions 234a and 234b can include the Schottky material 230 of diode 200. In some implementations, portions 234a and 234b can include different materials (e.g., metals such as Cu, AlCu, etc.) that can be deposited, annealed, and / or silicided to form ohmic contacts 244a and 244b.

[0055] FIG. 3 is a cross-sectional view of yet another Schottky diode 300 including a surface region, according to one implementation. Diode 300 is a variation of diode 100 of FIG. 1 and includes similar and / or like elements referenced by 300-series reference numbers corresponding to the 100-series reference numbers of FIG. 1. For example, diode 300 includes a substrate 302, a semiconductor layer 304, shield regions 310a and 310b, a drift region 320, surface regions 332a and 332b, a Schottky material 330, Schottky contacts 340, and metal portions 334a and 334b. For the sake of brevity, aspects and details of diode 300 that are similar to diode 100 are not described again here.

[0056] As shown in FIG. 3, diode 300 is different from diode 100 in that surface regions 332a and 332b extend over respective portions of shield regions 310a and 310b. In some implementations, surface regions 332a and 332b can extend over 10 percent to 90 percent of shield regions 310a and 310b, respectively. Such implementations can provide further improvement in forward conduction characteristics by increasing the total area of Schottky contacts 340, for example, compared to diode 100, for the same active area of the device, etc.

[0057] FIG. 4 is a cross-sectional view of yet another Schottky diode 400 that includes a local drift region implant according to one implementation. Similar to diode 300, diode 400 is a variation of diode 100 of FIG. 1 and includes similar and / or like elements that are referenced by 400-series reference numbers corresponding to the 100-series reference numbers of FIG. 1. For example, diode 400 includes a substrate 402, a semiconductor layer 404, shield regions 410a and 410b, a drift region 420, surface regions 432a and 432b, a Schottky material 430, a Schottky contact 440, and metal portions 434a and 434b. For the sake of brevity, aspects and details of diode 400 that are similar to diode 100 are not described again here.

[0058] As shown in FIG. 4, diode 400 is different from diode 300 in that the interface of the Schottky contact 440 is mounted on the mesa 450 of the semiconductor layer 404, and the mesa 450 is included in the drift region 420. Such an implementation can improve the forward conduction characteristics by increasing the area of the associated Schottky interface (e.g., the area of the Schottky contact 440), similar to diode 300.

[0059] In some implementations, the mesa 450 can be defined by forming a shallow trench in which ohmic contacts are formed by the metal portions 434a and 434b. The shape and dimensions of the mesa 450 in FIG. 4 are shown by way of example and are not necessarily to scale. For example, the mesa 450 can have a height H that is 5 microns or less. In diode 400, the additional resistance of the mesa 450 can be compensated by including the surface regions 432a and 432b on the sidewalls of the mesa 450 (within the sidewalls, along the sidewalls, etc.) in addition to the portion on the top surface of the mesa 450.

[0060] FIG. 5 is a (planar) view showing another diode 500 including a local surface area, as viewed from above according to one implementation form. The diagram of the diode 500 shown in FIG. 5 is part of a diode having a cell type design. For the sake of explanation, the diode 500 is shown without a Schottky material layer and / or a metallization layer, such as a Schottky metal and / or an ohmic contact metal, so as not to obscure the underlying structure.

[0061] In the example of FIG. 5, the diode 500 includes hexagonal diode cells, each cell includes a shield region 510, and the drift region 520 of the diode 500 has intersections of the drift region 520 between the hexagonal shield regions 510, and is disposed, for example, as segments, streets, etc. between the hexagonal shield regions. That is, a hexagonal drift region surrounds each shield region 510. In the diode 500, the highest electric field is shown as region 540 in FIG. 5 and occurs at these intersections of the drift region part 520 that is the widest in the drift region 520. The diode 500 also includes an ohmic contact region 534 disposed within the shield region 510. In this example, a Schottky material (for example, a metal, an alloy, a semiconductor material, etc.) is disposed in the drift region 520 including region 540 and can form a Schottky contact with the drift region 520. The Schottky material can also be disposed in a part of the shield region 510, as in the diodes of FIGS. 1-4. The ohmic contact in the ohmic contact region 534 can be formed using a Schottky material or another material such as the materials described herein.

[0062] In diode 500, a segment of the drift region 520 between regions 540 (e.g., a narrower or narrowest portion of the drift region 520) can include one or more surface regions that can provide a respective Schottky barrier height as described herein, and regions 540 can be free of such surface regions. Thus, the portion of the Schottky contact within region 540 will have a higher barrier height than the portion of the Schottky contact within the region (segment) of the drift region 520 that includes one or more surface regions. The width W1 of region 540 (similar to the width W1 of diode 100) can be varied to achieve the desired operating characteristics of diode 500. For example, increasing W1 of diode 500 decreases the area of the drift region 520 of diode 500 where one or more surface regions are disposed, and decreasing W1 of diode 500 increases the area of the drift region 520 of diode 500 where one or more surface regions are disposed. In some implementations, the width W1 of region 540 can be selected such that the leakage current density of region 540 is the same as or substantially the same as (e.g., has the same design goal as) the respective leakage current density of the segments of the drift region 520 between each of the regions 540. In some implementations, the width W1 of region 540 can be selected such that the leakage current density of region 540 is lower than the respective leakage current density of the segments of the drift region 520 between each of the regions 540.

[0063] FIG. 6 is a cross-sectional view showing the doping profile of a diode portion 600 (e.g., half of a cell of a diode in a linear / stripe design) that includes a surface region, such as can be used to implement a diode as described herein. In an exemplary implementation, diode portion 600 can be mirrored to the right and / or left to build a complete and / or additional diode stripe or cell.

[0064] As shown in FIG. 6, the diode portion 600 includes a semiconductor layer 604 of a first conductivity type (e.g., n-type conductivity) and a shield region 610 of a second conductivity type (e.g., p-type conductivity). In some implementations, these conductivity types can be reversed. The Schottky material 630 is disposed in the drift region 620 to form a Schottky contact 640 with the drift region and is also disposed on a part of the shield region 610. The diode portion 600 also includes a surface region 632 adjacent to the shield region 610. As shown in FIG. 6, the portion of the drift region 620 that does not include the surface region 632 has a width of 0.5 W1, for example, half of the width W1 in FIG. 1, since the diode portion 600 is a half-diode segment or cell. Similar to the diode 100 in FIG. 1, the portion of the Schottky contact 640 corresponding to the portion of the drift region 620 that does not include the surface region 632 will have a barrier height greater than the barrier height of the portion of the Schottky contact corresponding to the surface region 632. Note that in FIG. 6, the metal defining the ohmic contact with the shield region 610 is omitted.

[0065] FIG. 6 shows the relative doping concentrations of both the first conductivity type (e.g., n-type) and the second conductivity type (e.g., p-type) of the diode portion 600. For example, for the semiconductor layer 604 and the surface region 632 including the drift region 620 of the diode portion 600, regions of the relative doping concentration of the first conductivity type are shown. In this example, the region of the relative doping concentration of the second conductivity type is shown in the shield region 610. In some implementations, the doping concentration of the surface region 632 (e.g., at the interface of the Schottky contact 640) can be 10 to 1000 times higher than the doping concentration of the drift region 620 (e.g., at the interface of the Schottky contact 640 that does not include the surface region 632). In this example, the doping concentration within the shield region 610 can be higher at the surface of the semiconductor layer 604 and decrease with depth within the semiconductor layer 604. Such doping concentrations depend on the particular implementation.

[0066] In FIG. 6, the distance in arbitrary unit (A.U.) is shown on the x-axis, and the depth in A.U. is shown on the y-axis. The distance and depth in FIG. 6 are shown for reference and vary according to specific implementation forms. In the example of FIG. 6, the distance along the x-axis indicates the left-right distance along the diode portion 600, corresponding to the distance A.U. in the graph of the electric field distribution of the implementation form of the diode portion 600 shown in FIG. 7 and the distance A.U. in the doping concentration profile of FIG. 8. The depth A.U. in FIG. 6 indicates the depth of the semiconductor layer 604, which can be a part of the epitaxial semiconductor layer as described in this specification. The depth A.U. in FIG. 6 corresponds to the depth A.U. in FIG. 8.

[0067] FIGS. 7 to 10 are graphs showing various operating characteristics and aspects of the implementation forms of diodes including Schottky contacts having a surface region, such as the implementation form of the diode 100 in FIG. 1 (for example, using the diode portion 600). However, the aspects of FIGS. 7 to 10 described below can be similarly applied to other diodes, such as the exemplary diode implementation forms described in this specification.

[0068] FIG. 7 is a graph 700 showing the electric field distribution of various implementation forms of the diode portion 600 in FIG. 6 (or the diode 100 in FIG. 1) under reverse bias conditions having various widths W1. FIG. 8 is a graph 800 showing examples of the doping concentration (for example, trace 810 and trace 820) versus the depth in the surface region (formed, for example, using ion implantation) for a diode implementation form having a surface region. FIG. 9 is a graph 900 showing the IV curve (for example, forward operating characteristics) of the implementation form of the diode in FIG. 1 based on, for example, the diode portion 600, compared with a conventional diode implementation form. FIG. 10 is a graph 1000 showing the forward voltage drop of the diode implementation form shown in FIG. 9.

[0069] Referring to FIG. 7, under reverse bias conditions, the electric field distributions along the semiconductor surface under the Schottky contact are shown for various implementations of the diode portion 600 where the width W1 varies. The applied reverse bias voltage varies depending on the particular implementation. In some implementations, the reverse bias voltage can be 500 volts (V) or more. Trace 710 shows an implementation of the diode having no surface region (e.g., W1 is equal to the width of the drift region bounded by the shield region), and trace 760 shows an implementation of the diode portion 600 where the width W1 is 0 (e.g., the entire drift region has a high doping concentration surface region). Traces 720, 730, 740, and 750 show implementations of the diode portion 600 where the width W1 is greater than 0 and less than the width of the upper portion of the drift region bounded by the shield region. The specific value of the width W1 depends on the particular implementation, such as the width of the drift region of the diode. That is, the specific value of the width W1 shown in FIG. 7 can be proportional to the width of the upper portion of the drift region of the corresponding diode.

[0070] Traces 710 - 760 shown in FIG. 7 show the electric fields in various implementations of the diode portion 600 directly below the upper surface of the semiconductor layer 604 (e.g., 5 nm below the upper surface). As described above, the distance A.U. along the x - axis in FIG. 7 corresponds to the distance A.U. along the x - axis in FIG. 6 of the diode portion 600. The electric field is shown in A.U. on the y - axis as a function of distance.

[0071] As shown by trace 710, the implementation form of the diode without a surface region has the lowest or similar electric field along the y direction, which may exhibit higher conduction losses than the diode implementation form with a surface region shown in FIG. 7 by, for example, traces 720 to 760. However, the peak 770 of the electric field of trace 710 may indicate the upper limit of the electric field of a given diode structure (regardless of the presence or absence of a surface region). Therefore, traces 720 and 730 show diodes with a surface region that have a higher (e.g., lower conduction loss) electric field than that shown by trace 710 at some positions along the y-axis but do not exceed peak 770. The electric fields shown by traces 740 to 770 all exceed peak 770 (e.g., at their respective peak electric fields), which may result in high leakage current and potentially excessive power loss during reverse bias operation, causing degradation of device characteristics and / or sudden failure. Therefore, such electric field distribution information can be used to select an appropriate value of width W1 in a corresponding diode implementation form such as diode 100, and improvement of the on-state performance characteristics can be achieved without degrading the reverse direction / blocking characteristics of the corresponding diode.

[0072] Referring to FIG. 8, graph 800 shows an exemplary doping concentration profile of a local surface implant that can be used in the diode implementation forms described herein. As described above, the distance A.U. along the x-axis in FIG. 8 corresponds to the distance A.U. in FIG. 6, and the depth A.U. along the y-axis in FIG. 8 corresponds to the depth A.U. in FIG. 6. In FIG. 8, trace 810 shows the doping concentration distribution of a surface region formed by ion implantation through a film (layer) of another material disposed on the surface of the semiconductor layer or by a diffusion method, and trace 820 shows an example of the doping concentration distribution of a surface region formed using ion implantation without such a film on the surface of the semiconductor layer. In an implementation form such as the example shown by trace 810, the film can be removed after the formation of the implant. The film can be a screen oxide such as a thermal oxide, a deposited oxide, or a layer of another implant screen material. The choice of surface region formation depends on device design specifications and process compatibility.

[0073] Referring to FIG. 9, a graph 900 showing the IV curves (forward operating characteristics) of various Schottky diode implementation forms, such as the implementation form of the diode 100 having the diode portion 600, is shown. In graph 900, the voltage (forward voltage) is shown in A.U. along the x-axis, and the current is shown in A.U. along the y-axis. In graph 900, trace 910 shows the forward IV characteristics of a Schottky diode having no surface region (for example, the width W1 is equal to the width of the upper part of the drift region).

[0074] In FIG. 9, traces 920, 930, 940, 950, and 960 show the forward operating characteristics (IV characteristics) of the implementation form of the diode 100. The width W1 is smaller than the width of the upper part of the drift region, and as the width W1 decreases in different designs (as shown in FIG. 9), the area of the drift region 120 where the surface regions 132a and 132b are disposed increases. The diode implementation forms shown by traces 910 to 960 may correspond to the diode implementation forms shown by traces 710 to 760 in FIG. 7 in this example. As shown in FIG. 9, as W1 decreases, the current for a given forward voltage increases, indicating the advantage of the method described herein of using the surface region within the drift region of the Schottky diode to improve the trade-off between the forward operating characteristics and the reverse operating characteristics.

[0075] Referring to FIG. 10, graph 1000 shows the dependence of the forward voltage drop V (at a constant forward current density) on the width W1 of the implementation form of the diode 100, such as an implementation form that may correspond to the implementation forms shown by traces 920 to 960 in FIG. 9. In FIG. 10, the width W1 is shown in A.U. along the x-axis, and the corresponding V f value is shown in A.U. along the y-axis. As shown in FIG. 10, as W1 decreases, V f fIt also decreases. In graph 1000, in this example, points 1020 and 1030 respectively correspond to traces 720 and 730 of FIG. 7 and traces 920 and 930 of FIG. 9. In this example, point 1020 represents a reduction in V, for example, of about 4 percent compared to the diode implementation form (for example, a diode without a surface area) indicated by trace 910. f It can represent a reduction, and point 1030 can represent a reduction in V, for example, of about 8 percent compared to the diode implementation form indicated by trace 910. f Such a reduction in V f enables reducing the overall size of the Schottky diode to achieve the desired forward operating current density and can reduce the total manufacturing cost.

[0076] FIGS. 11A - 11C are diagrams showing cross - sectional views of an exemplary method for forming a surface area within a Schottky diode. For the sake of explanation, the techniques of FIGS. 11A - 11C will be described with reference to the structure of the diode portion 600 of FIG. 6. Referring to FIG. 11A, a mask 1115 can be formed on the surface of the semiconductor layer 604. After the formation of the mask 1115, a deep, high - energy implantation (for example, p - type implantation) can be performed to form a shield region 610. Then, the mask 1115 can be removed and an implantation mask 1125 can be formed. The mask 1125 can be used for the formation of local surface (drift region) implants 1132 (which can correspond to implants 632 of FIG. 6). Then, the implantation mask 1125 can be removed and the Schottky material 630 and / or metal 634 can be formed to define the Schottky contact and the ohmic contact. In some implementations, the mask 1125 can be formed from the mask 1115 using self - aligning techniques such as, for example, an etch - back process and / or a spacer process.

[0077] Figures 12A - 12D are diagrams showing cross - sectional views of another exemplary method for forming a surface region within a Schottky diode. Similar to Figures 11A - 11C, for the sake of explanation, the techniques of Figures 12A - 12D will be described with reference to the structures of diode 300 in Figure 3 and diode portion 600 in Figure 6. Referring to Figure 12A, a mask 1215 can be formed on the surface of 604. After the formation of mask 1215, a deep, high - energy implantation (e.g., p - type implantation) can be performed to form an embedded portion 610a of the shield region 610. Then, mask 1215 can be removed, and mask 1225 can be formed. Mask 1225 can be used to form local surface (drift region) implants 1232 (which can correspond to surface regions 332a and 332 in Figure 3, shield regions 310a and 310a respectively, or extend over shield region 610 in Figure 6). Then, mask 1225 can be removed, mask 1235 can be formed, and mask 1235 can be used to form the upper portion 610b of the shield region 610. Then, mask 1225 can be removed, and Schottky metal 630 and / or metal 634 can be formed to define Schottky contacts and ohmic contacts. In this example, mask 1225 and / or mask 1235 can be formed using a self - aligned semiconductor process. For example, in some implementations, mask 1225 can be formed from mask 1215 using, for example, an etch - back process. Also, in some implementations, mask 1235 can be formed from mask 1225 using, for example, a spacer process.

[0078] Figures 13A - 13C are diagrams showing cross - sectional views of yet another exemplary method for forming a surface region within a Schottky diode. Similar to Figures 11A - 11C and Figures 12A - 12D, for purposes of explanation, the method of Figures 13A - 13C will be described with reference to the structure of the diode portion 600 of Figure 6. Referring to Figure 13A, a mask 1315 may be formed on the surface of the semiconductor layer 604. After the formation of the mask 1315, a deep, high - energy implantation (e.g., p - type implantation) may be performed to form a shield region 610. Then, the implantation mask 1315 may be removed, and a mask 1325 may be formed. The mask 1325 may be an inclined mask and may be used for the formation of the surface region 1332. The doping concentration of the implant 1332 may vary gradually along the surface and / or depth of the implant 1332 within the semiconductor layer 604. Then, the implantation mask 1325 may be removed, and a Schottky metal 630 and / or a metal 634 may be formed to define a Schottky contact and an ohmic contact. In some implementations, the mask 1325 may be formed using a photoresist re - flow process and / or a gray - scale photolithography process.

[0079] In the methods described herein, such as the processing methods of Figures 11A - 11C, Figures 12A - 12D, and Figures 13A - 13C, the surface region may be formed using ion implantation at an implantation dose (e.g., p - type dose) of 50 keV or less and 1×10 12 cm -2 ~1×10 14 cm -2 . In some implementations, different beam energies, implantation doses, masking techniques, doping techniques (e.g., diffusion), etc. may be used. The specific beam energy and dose used may depend, at least in part, on the semiconductor material used, such as silicon, SiC, etc.

[0080] In the foregoing description, when an element such as a layer, region, substrate, or component is said to be on, connected to, electrically connected to, coupled to, or electrically coupled to another element, it will be understood that this can be directly placed on, connected to, or coupled to the other element, or that one or more intervening elements may be present. On the other hand, when an element is said to be directly on, directly connected to, or directly coupled to another element or layer, no intervening element or layer is present. Although the terms directly on, directly connected, or directly coupled may not be used throughout the detailed description of the present invention, elements illustrated as being directly on, directly connected, or directly coupled may be referred to as such. The claims (if included) of the present application may be amended to recite the exemplary relationships described herein or shown in the drawings.

[0081] As used in this specification and the claims, the singular forms may include the plural forms unless the context clearly dictates otherwise. Terms indicating spatial relativity (e.g., throughout, on, above, below, underneath, beneath, lower, etc.) are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the drawings. In some implementations, the relative terms above (or upper) and below may each include vertically above and vertically below, respectively. In some implementations, the term adjacent may refer to regions that are adjacent to each other laterally or horizontally, e.g., in contact, in semiconductor materials, semiconductor layers, and / or semiconductor regions.

[0082] Some implementations may be implemented using various semiconductor processing and / or packaging techniques. Some implementations may be implemented using various types of semiconductor processing techniques associated with semiconductor substrates including, but not limited to, for example, silicon (Si), gallium arsenide (GaAs), gallium nitride (GaN), silicon carbide (SiC), and / or combinations thereof.

[0083] While specific features of the described embodiments have been illustrated as described herein, those skilled in the art will envision many modifications, substitutions, changes, and equivalents. Therefore, it will be understood that the appended claims are intended to cover all such modifications and changes as fall within the scope of the embodiments. These are presented by way of example only and not by way of limitation, and it should be understood that various changes may be made in form and detail. Any part of the apparatus and / or method described herein may be combined in any combination, except mutually exclusive combinations. The embodiments described herein may include various combinations and / or partial combinations of functions, components, and / or features of the different embodiments described.

[0084] While specific features of the described embodiments have been illustrated as described herein, those skilled in the art will envision many modifications, substitutions, changes, and equivalents. Therefore, it will be understood that the appended claims are intended to cover all such modifications and changes as fall within the scope of the embodiments.

Claims

1. A diode (100, 200, 300, 400, 500), comprising: a substrate (102, 202, 302, 402) of a first conductivity type; a semiconductor layer (104, 204, 304, 404) of the first conductivity type disposed on the substrate, the semiconductor layer including a drift region (120, 220, 320, 420, 520) of the diode; a shield region (110a, 110b, 210a, 210b, 310a, 310b, 410a, 410b, 510) of a second conductivity type disposed in the semiconductor layer adjacent to the drift region; a surface region (132a, 132b, 232a, 232b, 332a, 332b, 432a, 432b, 540) of the first conductivity type disposed in a first portion of the drift region adjacent to the shield region, the surface region having a doping concentration higher than a doping concentration of a second portion of the drift region, the surface region being disposed between the shield region and the second portion of the drift region, and the second portion of the drift region not including the surface region; a Schottky material (130, 230, 330, 430), comprising: at least a part of the shield region; the surface region of the first portion of the drift region; and the Schottky material (130, 230, 330, 430) disposed in the second portion of the drift region.

2. The surface region is a first surface region, and the diode further comprises: a second surface region (236a, 236b) of the first conductivity type disposed in a third portion of the drift region, the second surface region being disposed adjacent to the first surface region, the second surface region having a doping concentration higher than the doping concentration of the second portion of the drift region and lower than the doping concentration of the first surface region; The Schottky material is further disposed in the second surface region. The diode (200) according to claim 1.

3. The second surface region is further disposed between the first surface region and the second portion of the drift region. The diode according to claim 2.

4. The semiconductor layer includes a mesa (450) having a height, and the mesa is defined by a trench formed in the semiconductor layer. The surface regions (432a, 432b) are disposed on top of the mesa. The Schottky material is disposed on the mesa. The diode (400) according to claim 1.

5. The surface region is further disposed on the sidewall of the mesa. The diode according to claim 4.

6. The diode includes an array of cells having a geometric shape. The widest part of the drift region (540) does not include the surface region. The narrowest part of the drift region (520) includes the surface region. The diode (500) according to claim 1.

7. The first conductivity type is n-type. The second conductivity type is p-type. The diode according to claim 1.

8. The substrate is a silicon carbide substrate. The semiconductor layer is an epitaxial silicon carbide layer. The substrate has a doping concentration higher than that of the epitaxial silicon carbide layer. The diode according to claim 1.

9. The semiconductor layer is a first epitaxial semiconductor layer of the first conductivity type, and the first epitaxial semiconductor layer is disposed on the substrate. The first epitaxial semiconductor layer and a second epitaxial semiconductor layer of the first conductivity type, and the second epitaxial semiconductor layer is disposed on the first epitaxial semiconductor layer. The second epitaxial semiconductor layer. The first epitaxial semiconductor layer has a doping concentration higher than that of the second epitaxial semiconductor layer. The diode according to claim 1.

10. At least a part of the shield region is a first part of the shield region, and the diode is further provided with metals (134a, 134b, 234a, 234b, 334a, 334b, 434a, 434b) disposed in a second part of the shield region and defining an ohmic contact to the shield region. The diode according to claim 1.

11. The metal disposed in the second part of the shield region is the Schottky material metal silicide, or The diode according to claim 10, comprising at least one of the deposited metals.

12. The diode according to claim 1, wherein the surface region has a depth of 100 nanometers (nm) or less in the semiconductor layer.

13. The diode according to claim 1, wherein the surface region is disposed in 10% to 90% of the area of the upper part of the drift region.

14. The doping concentration of the surface region is at the surface of the semiconductor layer, or varies along at least one of the depths of the surface region of the semiconductor layer. The diode according to claim 1.

15. The diode according to claim 1, wherein the surface region is further disposed in 10% to 90% of the area of the upper part of the shield region.

16. A diode (100, 200, 300, 400, 500), comprising a substrate (102, 202, 302, 402) of a first conductivity type, and a semiconductor layer (104, 204, 304, 404) of the first conductivity type disposed on the substrate, the semiconductor layer including a drift region (120, 220, 320, 420, 520) of the diode, the semiconductor layer (104, 204, 304, 404), and a first shield region (110a, 210a, 310a, 410a, 510) of a second conductivity type disposed in the semiconductor layer adjacent to the drift region, and a second shield region (110b, 210b, 310b, 410b, 510) of the second conductivity type disposed in the semiconductor layer adjacent to the drift region, wherein the drift region is at least partially disposed between the first shield region and the second shield region, the second shield region (110b, 210b, 310b, 410b, 510), and a surface region (132a, 132b, 236a, 236b, 332a, 332b, 432a, 432b, 540) of the first conductivity type disposed in a first portion of the drift region between the first shield region and the second shield region, the surface region having a doping concentration higher than a doping concentration of a second portion of the drift region adjacent to the surface region, and the second portion of the drift region not including the surface region, the surface region (132a, 132b, 236a, 236b, 332a, 332b, 432a, 432b, 540). A Schottky material (130, 230, 330, 430), at least a part of the first shield region, at least a part of the second shield region, the surface region of the first part of the drift region, and a Schottky material (130, 230, 330, 430) disposed in the second part of the drift region, and a diode (100, 200, 300, 400, 500).

17. The surface region is between the first shield region and the second part of the drift region, and further disposed between the second shield region and the second part of the drift region. The diode according to claim 16.

18. The surface region is a first surface region (236a, 236b), and the diode is a second surface region (232a, 232b) of the first conductivity type disposed in a third part of the drift region, and the second surface region is a first part (232a) disposed between the first shield region and a first part of the first surface region, and a second part (232b) disposed between the second shield region and a second part of the first surface region, and the second surface region further includes a second surface region (232a, 232b) having a doping concentration higher than that of the second part of the drift region and lower than that of the first surface region, The Schottky material is further disposed in the second surface region. The diode (200) according to claim 16.

19. The second part of the drift region is disposed between the first part of the first surface region and the second part of the first surface region. The diode according to claim 18.

20. A method of forming a diode (100, 200, 300, 400), the method comprising: forming a semiconductor layer (104, 204, 304, 404) of the first conductivity type on a substrate (102, 202, 302, 402) of the first conductivity type, the semiconductor layer including a drift region (120, 220, 320, 420) of the diode, forming a shield region (110a, 110b, 210a, 210b, 310a, 310b, 410a, 410b) of the second conductivity type in the semiconductor layer adjacent to the drift region, Forming the surface regions (132a, 132b, 236a, 236b, 332a, 332b, 432a, 432b) of the first conductivity type in a first portion of the drift region adjacent to the shield region, the surface regions having a doping concentration higher than a doping concentration of a second portion of the drift region, the surface regions being disposed between the shield region and the second portion of the drift region, the second portion of the drift region not including the surface regions, and depositing a Schottky material (130, 230, 330, 430) on at least a part of the shield region, the surface regions of the first portion of the drift region, and the second portion of the drift region, a method comprising.

21. The doping concentration of the surface regions is the surface of the semiconductor layer, or varies along at least one of depths of the surface regions of the semiconductor layer, the method according to claim 20.

22. The surface regions are first surface regions (236a, 236b), and the method comprises forming second surface regions (232a, 232b) of the first conductivity type in a third portion of the drift region, the second surface regions being disposed adjacent to the first surface regions, the second surface regions having a doping concentration higher than the doping concentration of the second portion of the drift region and lower than the doping concentration of the first surface regions, further comprising the Schottky material being further disposed on the second surface regions, the method according to claim 20.

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