Stacked III-V semiconductor diode

Abstract

Stacked III-V semiconductor diode (10) comprising or consisting of GaAs, having - a highly n-doped cathode layer (12), - a highly p-doped anode layer (16) and - a drift region (14) arranged between the cathode layer (12) and the anode layer (16), wherein, - the drift region (14) has a low n-doped drift layer (14.1) and a low p-doped drift layer (14.2), - the n-doped drift layer (14.1) is arranged between the p-doped drift layer (14.2) and the cathode layer (12), - both drift layers (14.1, 14.2) each have a layer thickness (D n , D p ) of at least 5 µm and along the respective layer thickness (D n , D p ) a dopant concentration maximum of 8·10 15 cm -3 have, - the dopant concentration maxima of the two drift layers (14.1, 14.2) have a ratio of 0.1 to 10 to each other and - a ratio of the layer thickness (D n ) of the n-doped drift layer to the layer thickness (D p ) of the p-doped drift layer is between 0.5 and 3, the anode layer (16) has a first section (16.1) with a constant dopant concentration profile and a second section (16.2) arranged between the first section (16.1) and the drift region (14) with a dopant concentration profile increasing in steps in the direction of the first section (16.1).

Description

[0001] The invention relates to a stacked III-V semiconductor diode comprising or consisting of GaAs with a highly n-doped cathode layer, a highly p-doped anode layer and a drift region arranged between the cathode layer and the anode layer.

[0002] A high-voltage-resistant semiconductor diode with a p + - n - n + Structure of gallium arsenide is known from “GaAs Power Devices” by German Ashkinazi, ISBN 965-7094-19-4, pages 8 and 9.

[0003] Further stacked III-V semiconductor diodes are known from EP 3 321 971 B1 and EP 3 321 970 B1, wherein the semiconductor diodes have an additional intermediate layer between the drift region and the cathode or anode. Further semiconductor components are known from JP H06 - 314 801 A, DE 10 2016 111 844 A1, and DE 10 2018 000 395 A1.

[0004] Against this background, the object of the invention is to provide a device that further develops the state of the art.

[0005] The object is achieved by a stacked III-V semiconductor diode having the features of patent claim 1. Advantageous embodiments of the invention are the subject of subclaims.

[0006] In the subject matter of the invention, a stacked III-V semiconductor diode comprising or consisting of GaAs is provided, comprising a highly n-doped cathode layer, a highly p-doped anode layer and a drift region arranged between the cathode layer and the anode layer.

[0007] The drift region has a low n-doped drift layer and a low p-doped drift layer, wherein the n-doped drift layer is arranged between the p-doped drift layer and the cathode layer.

[0008] Both drift layers each have a layer thickness of at least 5 µm and a dopant concentration maximum of 8 10 15 cm -3 on.

[0009] The dopant concentration maxima of the two drift layers have a ratio of 0.1 to 10.

[0010] The ratio of the layer thickness of the n-doped drift layer to the layer thickness of the p-doped drift layer is between 0.5 and 3.

[0011] It is understood that all semiconductor layers of a semiconductor diode consisting of GaAs or comprising GaAs, in particular the cathode layer, the anode layer and the drift region, each consist of GaAs or at least comprise GaAs.

[0012] In other words, each semiconductor layer of the III-V semiconductor diode contains at least the elements Ga and As.

[0013] The semiconductor layers are preferably produced by epitaxy. In a further development, the cathode layer or the anode layer can be formed by a substrate layer. Preferably, additional III-V semiconductor layers are grown epitaxially on the substrate layer to form the III-V semiconductor diode.

[0014] Alternatively, the III-V semiconductor diode comprises at least one semiconductor bond. In this case, the surfaces of two GaAs semiconductor wafers are joined together.

[0015] Preferably, the doping of the respective GaAs semiconductor layers is introduced during epitaxy. Epitaxy is preferably performed using MOVPE and / or LPE.

[0016] In a further development, doping is carried out by means of ion implantation additionally after epitaxial growth or alternatively instead of introduction during epitaxy.

[0017] Furthermore, it is understood that the semiconductor diode preferably comprises additional layers made of other materials, in particular metallic terminal contact layers. The terminal contact layers consist, for example, entirely or partially of a metal, e.g., gold, or a metal alloy, and are produced, for example, by means of electron beam evaporation or sputtering.

[0018] At least the region of the cathode layer and the anode layer adjacent to a terminal contact layer preferably has a high dopant concentration in order to form a contact with the lowest possible resistance and to keep the series resistance or the power loss of the semiconductor diode as low as possible.

[0019] The drift region is characterized by a total width of at least 10 µm. Preferably, the total width is at least 20 µm, or at least 40 µm, or at least 60 µm. The total width is divided into a lightly p-doped and a lightly n-doped region or layer.

[0020] The ratio of the layer thicknesses of the two drift layers is chosen so that the n-doped drift layer is at least half as thick as the p-doped drift layer or that the n-doped drift layer is at most three times as thick as the p-doped drift layer.

[0021] The respective dopant concentration of the two drift layers is as low as possible in a region adjacent to the other drift layer and may increase slightly in a direction away from the other drift layer. In a further development, the increase is achieved using one or more stages.

[0022] The pn junction thus forms within the drift region and in an area with very low dopant concentrations.

[0023] Due to the wide drift region consisting of two differently low-doped layers, diodes with particularly high blocking voltages of over 1100 V or even over 1200 V can be achieved and manufactured with small on-resistances and particularly low capacitances per area.

[0024] In a further development, isolelectric or isovalent centers are incorporated into the p-doped drift layer and / or the anode layer in order to increase the switching speed, i.e. the change between reverse and forward direction.

[0025] In particular, GaAs power diodes can be manufactured with a reverse recovery charge of no more than 80 nC per 1mm diode area.

[0026] In one embodiment, the layer thickness of the n-doped drift layer is greater than the layer thickness of the p-doped drift layer. In another embodiment, the n-doped drift layer and / or the p-doped drift layer have a layer thickness of at least 20 µm or at least 40 µm. The particularly high layer thickness of both drift layers makes it possible, in particular, to improve the dielectric strength of the diode.

[0027] In a further development, the n-doped drift layer has a dopant concentration profile along the layer thickness that increases in the direction of the cathode layer up to the dopant concentration maximum.

[0028] In particular, the slow reduction of the dopant concentration of the n-doped drift layer towards the p-doped drift layer makes it possible to achieve very low dopant concentrations and to create a controlled and reproducible pn junction.

[0029] In another alternative embodiment, the p-doped drift layer has a dopant concentration gradient that increases along the layer thickness toward the anode layer up to the dopant concentration maximum. As already explained, the increase can also be implemented using a stepped gradient.

[0030] In alternative embodiments, the increasing dopant concentration profile is linear, concave, or convex. A convex rise follows, for example, a Gaussian curve, while a concave rise follows, for example, an exponential function.

[0031] In another embodiment, the dopant concentration profile of the n-doped drift layer and / or the p-doped drift layer has one or more steps along the layer thickness. In alternative embodiments, one step or several steps, or each step, has a convex flank, a concave flank, or a linear flank.

[0032] In another embodiment, the dopant concentration profile of the two drift layers falls in the direction of the other drift layer to a value less than 3 10 15 cm -3 or 6·10 14 cm -3 or less than 3·10 14 cm -3 or none 2·10 14 cm -3 away.

[0033] In a further embodiment, the cathode layer has a dopant concentration of at least 1·10 18 cm -3 or of at least 5·10 18 cm -3 or at least 8·10 18 cm -3on.

[0034] In a further embodiment, the anode layer has a dopant concentration of at least 1 10 17 cm -3 or of at least 5·10 17 cm -3 or at least 8·10 18 cm -3 The low doping allows for improved turn-off behavior of the diode and reduced reverse recovery charge.

[0035] It is understood that the highest possible dopant concentration is sought, particularly in an area of ​​the cathode and anode layer adjacent to the metallic connection contacts, in order to keep the series resistance of the diode as low as possible or to produce a contact with the lowest possible resistance.

[0036] In another embodiment, the cathode layer and / or the anode layer have a layer thickness of at least 2 µm, at least 5 µm, or at least 20 µm. A thin layer thickness makes it easier to keep the series resistance of the diode low.

[0037] In a further development, the cathode layer and / or the anode layer has a first section with a constant dopant concentration profile and a second section arranged between the first section and the drift region with a dopant concentration profile that increases linearly and / or concavely and / or in a step-like manner in the direction of the first section.

[0038] The second layer section makes it possible, in particular, to design the transition of the dopant concentration from the low level in the region of the drift region to a significantly higher level of the second section of the anode and / or cathode layer.

[0039] By avoiding a sudden transition by means of a gradual or stepwise increase over a transition region, i.e. the second section, the turn-off behavior of the diode is significantly improved.

[0040] In a first embodiment, the second section has a layer thickness of at least 0.5 µm and at most 10 µm. Preferably, the second section of the cathode layer has a layer thickness of 3 µm to 5 µm, while the second section of the anode layer preferably has a layer thickness of 2 µm to 4 µm.

[0041] In another embodiment, the cathode layer or the anode layer is formed as a substrate. Typical layer thicknesses of an anode or cathode layer formed as a substrate are 100 µm to 250 µm.

[0042] The invention will be explained in more detail below with reference to the drawings. Similar parts are labeled with identical designations. The illustrated embodiments are highly schematic, ie the distances and the lateral and vertical extensions are not to scale and, unless otherwise stated, do not have any deducible geometric relationships to one another. Fig. 1 a view of a first embodiment of a stacked III-V semiconductor diode, Fig. 2 a view of a second embodiment of the stacked III-V semiconductor diode, Fig. 3 a view of a third embodiment of the stacked III-V semiconductor diode, Fig. 4 a dopant concentration profile along the stacked III-V semiconductor diode In a further embodiment Fig. 5 shows a further embodiment of the dopant concentration profile along the stacked III-V semiconductor diode.

[0043] The illustration of the Fig. Figure 1 shows a view of a first embodiment of a stacked III-V semiconductor diode 10 comprising GaAs or consisting of GaAs. A highly n-doped substrate layer forms a cathode layer 12, on which the drift region 14 with a total thickness D D followed by a highly p-doped anode layer 16 with a layer thickness D A is arranged.

[0044] The drift region 14 is divided into a weakly n-doped drift layer 14.1 adjacent to the cathode layer 12 with a layer thickness D n and a weakly p-doped drift layer 14.2 arranged between the n-doped drift layer 14.1 and the anode layer 16 with a layer thickness D p on.

[0045] The cathode layer 12 formed by a substrate accordingly has a somewhat larger layer thickness D k from 50 µm to 250 µm. The dopant concentration of the cathode layer is preferably at least 8 10 18 cm -3 and is constant or at least essentially constant along the layer thickness.

[0046] The additional layers are preferably epitaxially grown on the cathode layer 12. The doping can be generated during epitaxy or subsequently by ion implantation. The layer thickness D n of the n-doped drift layer 14.1 is at least 5 µm, preferably at least 40 µm. A dopant concentration decreases from a dopant concentration maximum of at most 8 10 15 cm -3 , preferably not more than 2·10 15 cm -3 , towards the p-doped drift layer 14.2.

[0047] The layer thickness D pof the p-doped drift layer 14.2 is at least 5 µm, preferably at least 20 µm. Preferably, the layer thickness D p the p-doped drift layer 14.2 half or one third of the layer thickness D n the n-doped drift layer 14.1. A dopant concentration of the p-doped drift layer 14.2 decreases towards the anode layer 16 up to a dopant concentration maximum of at least 1 10 17 cm -3 or at least 1·10 18 cm -3 to.

[0048] In the illustration of the Fig. 2 shows another embodiment. In the following, only the differences to the illustration of the Fig. 1 explained.

[0049] The stacked III-V semiconductor diode 10 has a cathode layer 12 with a first section 12.1 with a constant dopant concentration of at least 1·10 18 cm -3 , preferably at least 8·10 18 cm -3and a second section 12.2. The second section 12.2 is arranged between the first section 12.1 and the drift region 14 and has a relatively small layer thickness D k2 from 0.5 µm to 10 µm, preferably from 3 µm to 5 µm.

[0050] The second layer section serves to shape the dopant concentration transition from the highly doped first section 12.1 of the cathode layer to the lightly n-doped drift layer 14.1. For this purpose, the second section 12.2 has a dopant concentration profile that increases in the direction of the first section 12.1 from a dopant concentration minimum to a dopant concentration maximum. The dopant concentration profile is linear, concave, convex, or stepped with one step or multiple steps. In a stepped profile, the flank of one step, multiple steps, or all steps is preferably convex, concave, or linear.

[0051] In a first embodiment, the dopant concentration maximum of the second section 12.2 corresponds to the dopant concentration of the first section 12.1, while the dopant concentration minimum of the second section 12.2 corresponds to the dopant concentration maximum of the n-doped drift region. In other embodiments, a dopant concentration jump forms at the interface between the first and second sections 12.1, 12.2 and / or between the second section 12.2 and the drift region 14. Due to the dopant concentration profile of the second section 12.2, the dopant concentration jump is smaller than in an embodiment of the semiconductor diode 10 without a second cathode section 12.2.

[0052] In the illustration of the Fig. 3 shows another embodiment. In the following, only the differences to the illustration of the Fig. 2 explained.

[0053] The stacked III-V semiconductor diode 10 has an anode layer 16 with a first section 16.1 with a constant dopant concentration of at least 1 10 17 cm -3 and a second section 16.2 with a dopant concentration profile increasing in the direction of the first section 16.1 and a layer thickness D A2 from 0.5 µm to 10 µm, preferably from 2 µm to 4 µm.

[0054] Like the second section 12.2 of the cathode layer 12, the second section 16.2 of the anode layer 16 serves to shape the dopant concentration transition. The dopant concentration profile of the second section 16.2 is linear, concave, convex, or stepped with one or more steps. In a stepped profile, the flank of one step, several steps, or all steps is preferably convex, concave, or linear.

[0055] In a further embodiment not shown here, the stacked III-V semiconductor diode 10 has the above-described anode layer 16 with the two sections 16.1 and 16.2 as well as a drift layer 14 In the first embodiment of the Fig. 1, i.e. without the second section 12.2.

[0056] In the illustration of the Fig. 4 shows another embodiment. In the following, only the differences to the illustration of the Fig. 1 explained.

[0057] In Fig. 4 are different dopant concentration profiles along the stacked III-V semiconductor diode 10 with a Fig. 1. In alternative embodiments, the dopant concentration profile of the n-doped drift layer 14.1 is convex or concave or linearly increasing toward the cathode layer 12.

[0058] In alternative embodiments, the dopant concentration profile of the p-doped drift layer 14.2 is constant or increasing in the direction of the anode layer 16, wherein the increase is step-shaped or convex or linear or concave.

[0059] In a first embodiment, the convex rise of the n-doped and / or p-doped drift layer 14.1 or 14.2 is Gaussian-shaped.

[0060] Alternatively, the concave rise of the n-doped and / or p-doped drift layer 14.1 or 14.2 follows an exponential curve in one embodiment.

[0061] In the illustration of the Fig. 5 shows another embodiment. In the following, only the differences to the illustration of the Fig. 3 explained.

[0062] In Fig. 5 shows various dopant concentration profiles along the stacked III-V semiconductor diode 10 as examples.

[0063] The dopant concentration profile begins with a constant, high dopant concentration of n-dopants over the first section 12.1 of the cathode layer 12, followed by a dopant concentration drop over the second section 12.2 of the cathode layer, wherein the drop is convex and begins at the dopant concentration level of the first section 12.2 or at a significantly lower level.

[0064] Subsequently, the dopant concentration continues to decrease across the n-doped drift layer 14.1. The decrease occurs more slowly and with or without steps.

[0065] A change of the dopant takes place between the n-doped drift layer 14.1 and the p-doped drift layer 14.2, wherein the p-doped drift layer 14.2 in the illustrated embodiment has a constant or linearly increasing or step-like concentration of p-dopants.

[0066] In the second section 16.2 of the anode layer 16 adjacent to the drift region, the dopant concentration of p-dopants increases in a stepped manner over several rectangular steps. The adjoining first section 16.1 of the anode layer 16 has a constant dopant concentration level of at least 1 10 17 cm -3 on.

[0067] In addition, the anode layer 16 has a third section 16.3 following the first section 16.1, so that the first section 16.1 is arranged between the second section 16.2 and the third section 16.3. The third section 16.3 has a higher dopant concentration than the first section 16.1, preferably a constant dopant concentration of at least 5 10 18 cm -3 or of at least 1·10 19 cm -3 .

Claims

[1] Stacked III-V semiconductor diode (10) comprising or consisting of GaAs, having - a highly n-doped cathode layer (12), - a highly p-doped anode layer (16) and - a drift region (14) arranged between the cathode layer (12) and the anode layer (16), wherein, - the drift region (14) has a low n-doped drift layer (14.1) and a low p-doped drift layer (14.2), - the n-doped drift layer (14.1) is arranged between the p-doped drift layer (14.2) and the cathode layer (12), - both drift layers (14.1, 14.2) each have a layer thickness (D n , D p ) of at least 5 µm and along the respective layer thickness (D n , D p ) a dopant concentration maximum of 8·10 15 cm -3 have, - the dopant concentration maxima of the two drift layers (14.1, 14.2) have a ratio of 0.1 to 10 to each other and - a ratio of the layer thickness (D n ) of the n-doped drift layer to the layer thickness (D p ) of the p-doped drift layer is between 0.5 and 3, the anode layer (16) has a first section (16.1) with a constant dopant concentration profile and a second section (16.2) arranged between the first section (16.1) and the drift region (14) with a dopant concentration profile increasing in steps in the direction of the first section (16.1). [2] Stacked III-V semiconductor diode (10) according to claim 1, wherein the layer thickness (D n ) of the n-doped drift layer (14.1) is greater than the layer thickness (D p ) of the p-doped drift layer (14.2). [3] Stacked III-V semiconductor diode (10) according to claim 1 or 2, wherein the n-doped drift layer (14.1) and / or the p-doped drift layer (14.2) has a layer thickness (D n , D p ) of at least 20 µm or at least 40 µm. [4] Stacked III-V semiconductor diode (10) according to one of the preceding claims, wherein the n-doped drift layer (14.1) is arranged along the layer thickness (D n ) has a dopant concentration profile increasing in the direction of the cathode layer (12) up to the dopant concentration maximum. [5] Stacked III-V semiconductor diode (10) according to one of the preceding claims, wherein the p-doped drift layer (14.2) is arranged along the layer thickness (D p ) has a dopant concentration profile increasing in the direction of the anode layer (16) up to the dopant concentration maximum. [6] Stacked III-V semiconductor diode (10) according to one of claims 4 or 5, wherein the increasing dopant concentration profile is linear or concave or convex. [7] Stacked III-V semiconductor diode (10) according to one of claims 4 or 5, wherein the dopant concentration profile of the n-doped drift layer (14.1) and / or the p-doped drift layer (14.2) along the layer thickness (D n , D p ) has one or more stages. [8] A stacked III-V semiconductor diode (10) according to claim 7, wherein one or more stages or each stage has a convex flank or a concave flank or a linear flank. [9] Stacked III-V semiconductor diode (10) according to one of claims 4 to 8, wherein the dopant concentration profile of the two drift layers (14.1, 14.2) in each case in the direction of the other drift layer (14.1, 14.2) is set to a value of less than 9 10 14 cm -3or less than 6·10 14 cm -3 or less than 3·10 14 cm -3 or less than 2·10 14 cm -3 falls. [10] Stacked III-V semiconductor diode (10) according to one of the preceding claims, wherein the cathode layer (12) and / or the anode layer (16) have a dopant concentration of at least 1·10 17 cm -3 or at least 5·10 18 cm -3 or at least 8·10 18 cm -3 has. [11] Stacked III-V semiconductor diode (10) according to one of the preceding claims, wherein the cathode layer (12) and / or the anode layer (16) has a layer thickness (D k , D A ) of at least 2 µm or at least 5 µm or at least 20 µm. [12] Stacked III-V semiconductor diode (10) according to one of the preceding claims, wherein the cathode layer (12) has a first section (12.1) with a constant dopant concentration profile and a second section (12.2) arranged between the first section (12.1) and the drift region (14) with a dopant concentration profile that increases linearly and / or concavely and / or in a step-like manner in the direction of the first section (12.1). [13] Stacked III-V semiconductor diode (10) according to claim 12, wherein the second section (12.2) has a layer thickness (D K2 , D A2 ) of at least 0.5 µm and not more than 10 µm or of at least 2 µm and not more than 4 µm. [14] Stacked III-V semiconductor diode (10) according to one of the preceding claims, wherein the cathode layer (12) or the anode layer (16) is formed as a substrate.

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