Dielectric heterojunction device

Abstract

A device is provided that comprises a first layer deposited onto a second layer. The second layer comprises a lightly doped n-type or p-type semiconductor drift layer, and the first layer comprises a high-k material with a dielectric constant that is at least two times higher than the value of the second layer. A metal Schottky contact is formed on the first layer and a metal ohmic contact is formed on the second layer. Under reverse bias, the dielectric constant discontinuity leads to a very low electric field in the second layer, while the electron barrier created by the first layer stays almost flat. Under forward bias, electrons flow through the first layer, into the metal ohmic contact. For small values of conduction band offset or valence band offset between the first layer and the second layer, the device is expected to support efficient electron or hole transport.

Claims

1. A device comprising: a first layer comprising a plurality of plugs of a first material that is a high dielectric material, wherein the plurality of plugs are without metal; a second layer comprising a second semiconductor material; and a third layer comprising a third semiconductor material, wherein a dielectric constant of the first material that is the high dielectric material is at least two times greater than a dielectric constant of the second semiconductor material; a metal Schottky contact that is formed simultaneously on the first and second layers; and an ohmic contact formed on the third layer.

2. The device of claim 1, wherein the device comprises a current rectifying device, a photodetector, or a heterojunction.

3. The device of claim 1, wherein one or more carriers are transported between the first layer and the third layer when a voltage is applied to the device.

4. The device of claim 1, wherein the plurality of plugs comprises BaTiO.sub.3.

5. The device of claim 1, wherein each plug of the plurality of plugs has a width of 2 μm, has a depth of 1 μm, and a separation distance of between 0.6 μm and 2.0 μm.

6. The device of claim 1, wherein the first layer comprises BaTiO.sub.3.

7. The device of claim 1, wherein the second layer is a drift region.

8. The device of claim 1, wherein the second layer has a doping value of 1.2e16 cm.sup.−3, and a thickness of 6.1 μm.

9. The device of claim 1, wherein a metal/Ga.sub.2O.sub.3 interface of the second layer turns on at a lower forward bias of a Schottky junction allowing current to flow through the gaps formed by the plurality of plugs of the first layer.

10. The device of claim 1, wherein a metal/Ga.sub.2O.sub.3 interface of the second layer is subject to a shield based on the plurality of plugs when a reverse bias current is applied.

11. The device of claim 10, wherein the shield reduces an electrical field at the metal/Ga.sub.2O.sub.3 interface of the second layer and pushes a peak electrical field into the second layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The foregoing summary, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the embodiments, there is shown in the drawings example constructions of the embodiments; however, the embodiments are not limited to the specific methods and instrumentalities disclosed. In the drawings:

(2) FIG. 1 is an illustration of exemplary devices;

(3) FIG. 2 is an illustration of a graph of the energy of the devices of FIG. 1;

(4) FIG. 3 is another illustration of an exemplary device;

(5) FIG. 4 is an illustration of a graph of the energy of the device of FIG. 3;

(6) FIG. 5 is another illustration of exemplary devices; and

(7) FIG. 6 is an illustration of a graph of the electrical field of the devices of FIG. 5.

DETAILED DESCRIPTION

(8) This description provides examples not intended to limit the scope of the appended claims. The figures generally indicate the features of the examples, where it is understood and appreciated that like reference numerals are used to refer to like elements. Reference in the specification to “one embodiment” or “an embodiment” or “an example embodiment” means that a particular feature, structure, or characteristic described is included in at least one embodiment described herein and does not imply that the feature, structure, or characteristic is present in all embodiments described herein.

(9) FIG. 1 is an illustration of example device 100A and a device 100B. The device 100B is a normal Schottky diode and the device 100A is an improved diode. As shown, the device 100A includes a first layer 175 and a second layer 150A. The device 100B includes a corresponding second layer 150B but does not include the first layer 175. Each device 100 may further include a substrate layer 160 (i.e., the substrate layers 160A and 160B). Depending on the embodiment, the device 100A may be a current rectifying device, a photodetector, or a heterojunction.

(10) The first layer 175 of the device 100A may be constructed of a first material and the second layer 150 may be constructed of a second material. The first material may have a dielectric constant that is at least twice of the dielectric constant of the second material. The device 100A may be a high permittivity dielectric that has a minimum permittivity equal to two times that of the drift layer (i.e., the second layer 150A).

(11) The first layer 175 may be connected to the second layer 150A by a plurality of electrodes 170. The second layer 150 may be a lightly doped material such as a doped n-type or p-type material. The first layer 175 may be high k-material with a dielectric constant that is at least twice the second layer 150. Suitable materials for the first layer 150 include BaTiO.sub.3, SrTiO.sub.3, and (BaSr)TiO.sub.3. Other materials may be used.

(12) In some embodiments, the first layer 175 may be an BaTiO.sub.3 layer to the second layer 150. The second layer 150 may be an unintentional doped (UID) β-Ga.sub.2O.sub.3 layer.

(13) A metal Schottky contact 185 (i.e., the contacts 185A and 185B) may be formed on the top of the high-k material (i.e., the first layer 170). An ohmic contact 180 (i.e., the contacts 180A and 180B) may be formed on the bottom of the lightly doped semiconductor layer (i.e., the second layer 150). The device 100B is a conventional Schottky diode for comparison.

(14) In some embodiments, the 20 nm BaTiO.sub.3 layer 175 may be deposited on the β-Ga2O.sub.3 of the second layer 150A by physical vapor deposition. The metal Schottky contact 185 may be a metal stack of Pt/Au (30 nm/100 nm) that is deposited on either the second layer 150 or the BaTiO.sub.3 layer 175. The ohmic contact 180 may be formed by applying materials such as 30 nm Ti followed by 100 nm Au on the backside of the second layer 150.

(15) The design principle of the device 100 is as follows. When a reverse bias is applied to the device 100B, the β-Ga.sub.2O.sub.3 Schottky barriers display reverse breakdown due to tunneling across the Schottky barrier at fields (typically ˜3 MV/cm) that are significantly lower than breakdown field of β-Ga.sub.2O.sub.3 (>7 MV/cm). In the case of the device 100A, when the reverse bias is applied, the dielectric constant discontinuity (ratio ˜29) leads to a very low electric field in BaTiO.sub.3 (i.e., the BaTiO.sub.3 layer 175). The BaTiO.sub.3 electron barrier stays almost flat under reverse bias. Therefore, the BaTiO.sub.3/Ga.sub.2O.sub.3 dielectric heterojunction maintains a barrier to electron tunneling at much higher voltages than the metal/semiconductor junction of the device 100B.

(16) Under forward bias, electrons must flow from the semiconductor, through the high dielectric constant layer, into the metal. For small values of conduction band offset between BaTiO.sub.3/Ga.sub.2O.sub.3 (as predicted from the electron affinity difference), dielectric heterojunction is expected to support efficient electron transport. An example conduction band offset or valence hand offset between the first layer 175 and the second layer 150 is less than 0.2 eV.

(17) A graph 200 of the energy of the device 100A (dielectric heterojunction) and the device 100B (Schottky junction) at different depths and biases is shown in FIG. 2. For the device 100A, the line 201A represents the energy at different depths while a reverse bias is applied, and the line 203A represents the energy at different depths while a forward bias is applied. For the device 100B, the line 201B represents the energy at different depths while a reverse bias is applied, and the line 203B represents the energy at different depths while a forward bias is applied.

(18) FIG. 3 is an illustration of an example device 300. Similar to the devices 100, the device 300 includes a first layer 175, a second layer 150, a contact 180, and a contact 185. Depending on the embodiment, the device 300 may be a current rectifying device, a photodetector, or a heterojunction.

(19) Unlike the devices 100, the device 300 may further include an electron/hole barrier 190 between the low dielectric material of the second layer 150 and the high dielectric material of the first layer 175. Suitable materials for the electron/hole barrier 190 include SiO.sub.2, Al.sub.2O.sub.3, and SiN.sub.x. Other material may be used.

(20) A graph 400 of the energy of the device 300 at different depths is shown in FIG. 4. The line 401A represents the energy at different depths while a reverse bias is applied to the device 300. The line 401B represents the energy at different depths while a forward bias is applied to the device 300.

(21) FIG. 5 is an illustration of an example devices 500 (i.e., the devices 500A and 500B). Similar to the device 100A, the devices 500 include a first layer 175, a second layer 150, a substrate layer 160, a plurality of electrodes 170 connecting the first layer 175 to the second layer 150, a contact 180, and a contact 185. Depending on the embodiment, the devices 500 may each be a current rectifying device, a photodetector, or a heterojunction.

(22) As shown, the devices 500 include the BaTiO.sub.3 layer 175. However, rather than a continuous layer, in the devices 500 the BaTiO.sub.3 layer 175 comprises a plurality of BaTiO.sub.3 plugs inserted into the second layer 150. Depending on the embodiment, each BaTiO.sub.3 plug may have a width (i.e., ΔW.sub.BTO) of approximately 2 μm, may have a depth ((i.e., ΔT.sub.BTO) of approximately 1 μm, and a separation distance or gap (i.e., ΔW.sub.JBS) of between 0.6 μm and 2.0 μm. Note that the plugs may be made of BaTiO.sub.3 or any high k material.

(23) In some embodiments, the second layer 150 (i.e., the drift region) may have a doping value (i.e., N.sub.d) of approximately 1.2e16 cm .sup.3, and thickness (i.e., T.sub.drift) of approximately 6.1 μm. Other values and dimensions may be used.

(24) The device 500A shows a current path 195 through the first layer 175A and into the second layer 150A when a forward bias current is applied. The metal/Ga.sub.2O.sub.3 of the second layer 150A turns on at the lower forward bias of a Schottky junction allowing current to flow through the gaps formed by the plugs of the BaTiO.sub.3 layer 175.

(25) In contrast, the device 500B shows a depletion region 197 caused when a reverse bias current is applied. The metal/Ga.sub.2O.sub.3 interface of the second layer 150B is shielded due to the lateral depletion of the plugs of the BaTiO.sub.3 layer 175. This shielding reduces the field seen at the interface and pushes the peak electric field into the bulk of the second layer 150B.

(26) FIG. 6 is a graph 600 of the electrical field versus distance for devices including the device 500. The line 601 corresponds to measured electrical field values for devices such as the device 100A or the device 300. The line 603 corresponds to the device 500. As can be seen, the plugs of the BaTiO.sub.3 layer 175 push the peaks of the electrical field a further distance into the bulk of the device 500.

(27) As used herein, the singular form “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise.

(28) As used herein, the terms “can,” “may,” “optionally,” “can optionally,” and “may optionally” are used interchangeably and are meant to include cases in which the condition occurs as well as cases in which the condition does not occur.

(29) Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed.

(30) Although exemplary implementations may refer to utilizing aspects of the presently disclosed subject matter in the context of one or more stand-alone computer systems, the subject matter is not so limited, but rather may be implemented in connection with any computing environment, such as a network or distributed computing environment. Still further, aspects of the presently disclosed subject matter may be implemented in or across a plurality of processing chips or devices, and storage may similarly be effected across a plurality of devices. Such devices might include personal computers, network servers, and handheld devices, for example.

(31) Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.