DE102021123907A1 - LED and manufacturing method therefor - Google Patents

Abstract

LED (1) comprising
- a base layer (2) made of doped diamond or doped silicon carbide with color centers (3) embedded therein,
- a Schottky contact (4) connected to the base layer (2),
- an ohmic contact (5) connected to the base layer (2).

Description

The invention relates to an LED and a method for producing such an LED.

LEDs are used today in a large number of applications, for example for lighting, data transmission or in biological processes. LEDs are typically formed from semiconductor materials. With known LEDs, however, considerable heat is regularly generated. This can damage the LEDs or reduce their service life, which limits the possible uses of known LEDs. In addition, the materials of known LEDs are unsuitable for many biological applications, which means that the LEDs have to be encapsulated in a complex manner. Such a cladding can affect the light emission. Known LEDs can also only achieve a modulation speed that is insufficient for many applications. In addition, the design of known LEDs is complex because the emission spectrum is primarily determined by the choice of semiconductor material.

It is the object of the present invention, based on the prior art described, to present an LED which can be used in a more versatile manner.

These objects are solved with the LED and the method for manufacturing an LED according to the independent claims. Further advantageous developments are specified in the dependent claims. The features presented in the claims and in the description can be combined with one another in any technologically meaningful way.

• - eine Grundschicht aus dotiertem Diamant oder dotiertem Siliziumkarbid mit darin eingebetteten Farbzentren,
• - einen an die Grundschicht angebundenen Schottky-Kontakt,
• - einen an die Grundschicht angebundenen ohmschen Kontakt.

According to the invention, an LED is presented which comprises:

• - a base layer of doped diamond or doped silicon carbide with embedded color centers,
• - a Schottky contact connected to the base layer,
• - an ohmic contact bonded to the base layer.

The LED described is based on the base layer of doped diamond or doped silicon carbide with color centers embedded therein. Light can be emitted through the color centers by applying an appropriate electrical voltage between the Schottky contact and the ohmic contact. In particular through the use of diamond or silicon carbide in the base layer, the LED described can be used in a variety of ways. The fact that the base layer is called the base layer and not just a layer only serves to differentiate it from other layers.

The base layer is preferably formed from diamond. Diamond is a heat-resistant material, so that the LED described can also be operated at particularly high temperatures. This is favorable both with regard to any heat development by the LED itself and with regard to external heat effects. In addition, diamond is a particularly good conductor of heat, so that heat can be dissipated from the LED correspondingly well, for example to a cooling element. The LED described is therefore particularly robust and has a particularly long service life. The LED described can therefore also be used under difficult conditions, in particular with regard to external temperature effects or limited possibilities for heat dissipation. The LED described can also withstand external forces particularly well through the use of diamond, so that the LED described can also be used in environments with high pressures, for example.

Furthermore, diamond is chemically inert. The LED can thus also be used in applications in which known LEDs have to have a casing, as can be the case in particular in biological applications. The use of diamond eliminates the expense of such a coating. In addition, with the LED described, the light emission is not impaired by such a cladding.

Silicon carbide has properties similar to diamond as far as relevant for the LED described. Even though silicon carbide is less robust than diamond, some of the advantages described above can also be achieved with silicon carbide.

The LED described can be used in all applications in which known LEDs are also used, for example for lighting or for data transmission. In particular, the LED described can be used in a motor vehicle or a mobile phone. For example, the LED described can be used in a LIDAR (“Light Detection and Ranging”) sensor. The LED described can also be used for a wide variety of purposes in the scientific field. In particular, the LED described can be used in biological applications, for example for spectroscopy or microscopy.

The base layer is formed of doped diamond or doped silicon carbide. The endowment is preferably an n-doping. The doping can be formed by phosphorus, for example. The base layer is preferably uniformly doped. This means that the dopant atoms are evenly distributed over the base layer.

Color centers are embedded in the base layer. The term "color center" is an established term in the field of solid state physics, which is used here with its usual meaning. According to this, color centers are point defects in a crystal that can emit light. Color centers can therefore also be referred to as luminescent defects. Color centers have properties similar to atoms in terms of light emission.

If an appropriate electrical voltage is applied between the Schottky contact and the ohmic contact, the color centers can be electrically excited, which can lead to the emission of light by the color centers. Thus, with the LED described, light can be emitted by electroluminescence of the color centers. In addition to the direct recombination of electrons and holes across the band gap, light emission is also possible at the color centers. Due to the large band gap of diamond and silicon carbide, color centers can be embedded particularly well in the base layer of diamond or silicon carbide.

While defects should be avoided as far as possible for many applications, the color centers are deliberately provided for in the LED described. Preferably, a multiplicity of color centers are embedded in the base layer. In particular, it is preferred that an active measure is taken in the manufacture of the LED in order to selectively increase the type and number of the color centers. Examples of this are chemical vapor deposition (CVD for short) and ion implantation.

The base layer preferably has between 10 ¹¹ and 10 ¹¹ color centers per cubic centimeter, in particular between 10 ¹³ and 10 ¹⁹ color centers per cubic centimeter. This applies in particular if the color centers are generated by means of CVD. It has been found that such a light output can be achieved that is suitable for many applications.

If color centers are generated by means of ion implantation, it is preferred that between 10 ⁶ and 10 ¹⁶ ions per square centimeter are used, in particular between 10 ⁸ and 10 ¹⁴ ions per square centimeter. This applies in particular to silicon vacancy color centers. It has been found that in this way a base layer can be obtained with which a light output can be achieved which is suitable for many applications.

It is also conceivable to reduce the number of color centers to such an extent that the LED described can be regarded as an electrically driven single-photon source. The base layer can also have fewer than 10 ¹¹ color centers per cubic centimeter. In the limit case, even only individual color centers can be provided.

The LED can emit light with an emission spectrum that is determined in particular by the color centers. There are a multitude of possible configurations of the color centers. In particular, the color centers can be formed by atoms of a wide variety of elements. The emission spectrum of the LED can therefore be designed via the type and number of color centers. In particular, the width and position of the emission spectrum of the LED can be influenced by the configuration of the color centers. For example, the color centers can be chosen to give a narrow emission spectrum with a width of 1 nm or a broad emission spectrum with a width of 200 nm, as well as an emission spectrum from the UV to the infrared. By combining different color centers, the LED described can be designed as a white light source. Since there are many different color centers, the LED described can be designed particularly flexibly and adapted to a wide variety of requirements through the choice of color centers. It is not necessary to deviate from diamond or silicon carbide as the basic material. In the case of known semiconductor-based LEDs, on the other hand, it may be necessary to resort to a different semiconductor material as a whole in order to design an LED with a different emission spectrum, so that a specific technology platform only offers limited possibilities with regard to the emission spectra.

The configuration of one of the two contacts as a Schottky contact also simplifies the production of the LED described. In particular, the Schottky contact makes it possible to dispense with the formation of a p-n junction or a p-i-n junction, which is usually used in semiconductor-based LEDs. In contrast, the contacts of the described LED can be obtained by applying metal to the surface of the base layer.

In a preferred embodiment, the LED further comprises a substrate, wherein the Schottky contact and the ohmic contact abut a first side of the base layer and wherein the substrate abuts a second side of the base layer opposite the first side.

In the present embodiment, the LED described can be manufactured from intrinsic diamond, for example. For this purpose, a top layer of the intrinsic diamond can be doped and provided with color centers, so that this layer becomes the base layer. The remaining intrinsic diamond becomes the mentioned substrate. The same applies to silicon carbide. The substrate is preferably formed from intrinsic diamond, particularly in the case where the base layer is formed from doped diamond. Alternatively, the substrate is preferably formed from intrinsic silicon carbide, particularly in the case where the base layer is formed from doped silicon carbide.

In a further preferred embodiment of the LED, at least some of the color centers are silicon vacancy color centers (SiV color centers for short) and/or at least some of the color centers are nitrogen Vacancy color centers and/or at least some of the color centers are H3 centers.

Silicon vacancy color centers are negatively charged and can emit light with a narrow near-infrared emission spectrum. If the LED described has silicon vacancy color centers, the LED can be used, for example, for data transmission or in biological sensors.

Nitrogen vacancy color centers have a neutral charge and can emit light with a broad emission spectrum (broad band light source). If the LED described has nitrogen vacancy color centers, the LED can therefore be used particularly well for experiments in plasmonics, for example.

H3 centers can emit light in the lower visible wavelength range of, for example, 520 nm.

The color centers discussed above are only examples. Alternatively or additionally, a wide variety of other color centers can be embedded in the base layer of the LED described.

In a further preferred embodiment of the LED, the Schottky contact is formed by a metal layer and a hydrogen passivation layer lying on it, the hydrogen passivation layer lying on the base layer.

The surface potential of the base layer can be influenced by the hydrogen passivation layer in such a way that the injection of minority charge carriers into the base layer is facilitated. This enables efficient excitation of the color centers. The metal layer is preferably made of gold.

1. a) Bereitstellen einer Grundschicht aus dotiertem Diamant oder dotiertem Siliziumkarbid mit darin eingebetteten Farbzentren,
2. b) Erzeugen eines an die Grundschicht angebundenen Schottky-Kontakts und eines an die Grundschicht angebundenen ohmschen Kontakts.

As a further aspect of the invention, a method for producing an LED is presented, which comprises the following steps, which are carried out in the order given:

1. a) providing a base layer of doped diamond or doped silicon carbide with color centers embedded therein,
2. b) creating a Schottky contact attached to the base layer and an ohmic contact attached to the base layer.

The described features and advantages of the LED are applicable and transferable to the method, and vice versa. The LED described is preferably obtained using the method described.

In step a) the base layer of doped diamond or doped silicon carbide with color centers embedded therein is provided. The color centers are preferably generated in step a). In this case, the color centers are deliberately generated as part of the process. In particular, the following configuration of step a) is preferred: providing a base layer made of doped diamond or doped silicon carbide with color centers embedded therein, the color centers being generated by an active measure. In particular, chemical vapor deposition (CVD for short) or ion implantation can be considered as such an active measure. In this respect in particular, the method described differs from methods in which diamond or silicon carbide is produced with the aim of obtaining as few defects as possible.

In a preferred embodiment of the method, the base layer is grown in step a), at least some of the color centers being produced by means of chemical vapor deposition (CVD for short) during the growth of the base layer.

In this embodiment, the base layer is made as part of the described process. To this end, the base layer is grown in step a). This can be the case, for example, insofar as intrinsic diamond is grown in step a) and is at least doped in an upper layer. This layer is the base layer, while the remainder of the diamond can be viewed as the intrinsic diamond substrate described above. As the diamond grows, some or all of the color centers become embedded in the material that ultimately forms the base layer. In the present embodiment, this is done by means of chemical vapor deposition. This is particularly useful for nitrogen vacancy color centers. The same applies to silicon carbide.

In a further preferred embodiment of the method, at least some of the color centers are produced in step a) by means of ion implantation in the base layer.

Using ion implantation, some or all of the color centers are embedded in the base layer after it has been grown. In this case, the growth of the base layer can be completed before the start of the process. Alternatively, it is also preferred in this embodiment that the base layer is grown as part of step a). In this respect, what was described for the previous embodiment also applies here.

In this embodiment some or all of the color centers are created by ion implantation in the final base layer. This is particularly suitable for silicon vacancy color centers. By means of ion implantation, color centers can be embedded in the base layer in a region lying at the surface of the base layer, in particular on the first side of the base layer. For example, the energy of an ion beam used for ion implantation can be set to a few 10 keV so that color centers are formed at a depth of up to 200 nm from the surface of the base layer. During ion implantation, vacancies are formed in the base layer, which recombine with silicon atoms or nitrogen atoms in the diamond or silicon carbide and thus form silicon vacancy color centers or nitrogen vacancy color centers. This is favored by increased temperature, so that annealing is preferably carried out after the ion implantation.

It is preferred to combine the two previously described embodiments with one another. Thus, the base layer can be grown in step a), with part of the color centers being generated by chemical vapor deposition during the growth of the base layer, and with another part of the color centers being generated by ion implantation in the base layer after the base layer has been grown. Preferably, the color centers generated by chemical vapor deposition during growth of the base layer are nitrogen vacant color centers and the color centers generated by ion implantation after growth of the base layer are silicon vacant color centers or nitrogen vacant color centers.

In a further preferred embodiment of the method, the type and/or number of color centers in the base layer are selected for step a) depending on a desired emission spectrum of the LED.

As an alternative to the selection of the color centers, properties of the emission spectrum can also be set by the electrical voltage applied between the Schottky contact and the ohmic contact and/or by the temperature of the LED. These two setting options also exist after the LED has been completed.

• b1) Erzeugen des ohmschen Kontakts an einer ersten Seite der Grundschicht,
• b2) Erzeugen einer Wasserstoff-Passivierungs-Schicht an der ersten Seite der Grundschicht mittels eines Wasserstoff-Plasmas,
• b3) Erzeugen einer Metallschicht auf der in Unterschritt b2) erzeugten Wasserstoff-Passivieru ngs-Sch icht,

wobei der Schottky-Kontakt aus der in Unterschritt b2) erzeugten Wasserstoff-Passivierungs-Schicht und der in Unterschritt b3) erzeugten Metallschicht durch Maskierung vor Unterschritt b2) und/oder durch Ätzen nach Unterschritt b3) erhalten wird.In a further preferred embodiment of the method, step b) comprises the following sub-steps, which are carried out in the order given:

• b1) creating the ohmic contact on a first side of the base layer,
• b2) creating a hydrogen passivation layer on the first side of the base layer by means of a hydrogen plasma,
• b3) producing a metal layer on the hydrogen passivation layer produced in sub-step b2),

wherein the Schottky contact is obtained from the hydrogen passivation layer produced in sub-step b2) and the metal layer produced in sub-step b3) by masking before sub-step b2) and/or by etching after sub-step b3).

In sub-step b1), the ohmic contact can be produced, for example, by means of optical lithography and sputtering. For example, the ohmic contact can be formed from chromium, titanium, or other carbide forming metals and gold.

Sub-step b2) preferably takes place in a CVD reactor. In this, the hydrogen passivation layer is created on the base layer. Annealing of the ohmic contact can also be achieved by the temperature prevailing in sub-step b2).

In sub-step b3), the metal layer is produced on the hydrogen passivation layer produced in sub-step b2), for example by metal deposition.

The hydrogen passivation layer formed in sub-step b2) and the metal layer together form the Schottky contact. The hydrogen passivation layer and the metal layer are preferably locally limited and, in particular, do not extend as far as the ohmic contact. This can be achieved by masking before sub-step b2) and/or by etching after sub-step b3). Before the production of the hydrogen passivation layer in sub-step b2), a mask can be applied to the first side of the base layer and to the ohmic contact, which mask has a recess at the point provided for the Schottky contact. After sub-step b3), the mask can be removed together with the hydrogen passivation layer and metal layer possibly formed thereon. Alternatively, the hydrogen passivation layer and the metal layer can be grown without a mask on the first side of the base layer and on the ohmic contact and, after sub-step b3), be locally removed by etching such that only the Schottky contact remains.

• 1: eine erfindungsgemäße LED.

The invention is explained in more detail below with reference to the figure. The figure shows a particularly preferred embodiment to which the invention is not limited. The figure and the proportions shown therein are only schematic. It shows:

• 1 : an LED according to the invention.

1 shows an LED 1 comprising a base layer 2 made of doped diamond with color centers 3 embedded therein. These color centers 3 are distributed uniformly in the base layer 2 and are indicated in the figure by the fact that the base layer 2 is additionally provided with reference number 3 . Another part of the color centers 3 are silicon vacancy color centers that have been implanted into the base layer 2 by ion implantation after the growth of the base layer 2 . These are indicated as an area of silicon 11 implanted. Furthermore, the LED 1 has a Schottky contact 4 connected to the base layer 2 and an ohmic contact 5 connected to the base layer 2 . In addition, the LED 1 has a substrate 6 made of intrinsic diamond. The Schottky contact 4 and the ohmic contact 5 bear against the base layer 2 on a first side 7; the substrate 6 is in contact with the base layer 2 on a second side 8 opposite the first side 7 . The Schottky contact 4 is formed by a metal layer 10 and a hydrogen passivation layer 9 lying thereon. The hydrogen passivation layer 9 is in contact with the base layer 2 .

Reference List

1

LEDs

2

base layer

3

color centers

4

Schottky contact

5

ohmic contact

6

substrate

7

first page

8th

second page

9

hydrogen passivation layer

10

metal layer

11

implanted silicon

Claims (9)

LED (1) comprising - a base layer (2) made of doped diamond or doped silicon carbide with color centers (3) embedded therein, - a Schottky contact (4) connected to the base layer (2), - an ohmic contact (5) connected to the base layer (2). LED (1) after claim 1 , further comprising a substrate (6), wherein the Schottky contact (4) and the ohmic contact (5) abut on a first side (7) of the base layer (2) and wherein the substrate (6) on one of the first side ( 7) opposite second side (8) of the base layer (2). LED (1) according to one of the preceding claims, wherein at least some of the color centers (3) are silicon vacancy color centers and/or wherein at least some of the color centers (3) are nitrogen vacancy color centers and/or wherein at least some of the color centers (3) are H3 centers. LED (1) according to one of the preceding claims, wherein the Schottky contact (4) is formed by a metal layer (10) and a hydrogen passivation layer (9) lying thereon, and wherein the hydrogen passivation layer (9) on the base layer (2). A method for producing an LED (1), comprising the following steps, which are carried out in the order given: a) providing a base layer (2) of doped diamond or doped silicon carbide with color centers (3) embedded therein, b) creating a a Schottky contact (4) bonded to the base layer (2) and an ohmic contact (5) bonded to the base layer (2). procedure after claim 5 , wherein the base layer (2) is grown in step a), and wherein at least part of the color centers (3) is produced by means of chemical vapor deposition during the growth of the base layer (2). procedure after claim 5 or 6 , wherein in step a) at least some of the color centers (3) are generated by means of ion implantation in the base layer (2). Procedure according to one of Claims 5 until 7 , wherein for step a) type and / or number of color centers (3) in the base layer (2) depending on a desired emission spectrum of the LED (1) are selected. Procedure according to one of Claims 5 until 8th , wherein step b) comprises the following sub-steps, which are carried out in the order given: b1) creating the ohmic contact (5) on a first side (7) of the base layer (2), b2) creating a hydrogen passivation layer ( 9) on the first side (7) of the base layer (2) by means of a hydrogen plasma, b3) producing a metal layer (10) on the hydrogen passivation layer (9) produced in sub-step b2), the Schottky contact ( 4) is obtained from the hydrogen passivation layer (9) produced in sub-step b2) and the metal layer (10) produced in sub-step b3) by masking before sub-step b2) and/or by etching after sub-step b3).

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