The present disclosure concerns the field of optoelectronic devices with a PN junction such as light-emitting diodes (LED) or photodiodes.
Patent application EP2960951 (DD14957) previously filed by the applicant describes PN junction optoelectronic devices provided with an insulated conductive gate coating a lateral side of at least one of the semiconductor regions forming the PN junction.
The application of a potential on the conductive gate creates an electric field enabling to improve the injection of charge carriers into the junction, and accordingly the conversion efficiency of the device.
It would be desirable to at least partly improve certain aspects of optoelectronic devices of this type.
For this purpose, an embodiment provides an optoelectronic device comprising:
According to an embodiment, the conductive spacer is made of a material different from that of the third layer.
According to an embodiment, the conductive spacer is made of metal.
According to an embodiment, the conductive spacer is made of a metal from the group comprising platinum, nickel, and tungsten.
According to an embodiment, the third layer is made of aluminum or of silver.
According to an embodiment, the device further comprises a connection metallization in contact with the first semiconductor layer.
According to an embodiment, the connection metallization is electrically insulated from the conductive gate.
According to an embodiment, the connection metallization is electrically connected to the insulated conductive gate.
According to an embodiment, the device further comprises an emissive semiconductor layer between the first and second semiconductor layers, the peripheral trench crosses the emissive semiconductor layer, the trench laterally delimiting a portion of the emissive semiconductor layer, and the insulated conductive gate extending against a lateral side of said portion of the emissive semiconductor layer.
According to an embodiment, each of the first and second semiconductor layers is made of a III-N compound.
Another embodiment provides a method of manufacturing an optoelectronic device such as defined hereabove, comprising the successive steps of:
According to an embodiment, the method further comprises, after step d) and before step e), a step of chemical cleaning of the exposed surfaces of the first layer inside of the trench.
According to an embodiment, the chemical cleaning step is carried out by means of a solution based on potassium hydroxide or of a solution based on tetramethylammonium hydroxide or of a solution based on tetraethylammonium hydroxide.
The foregoing and other features and advantages will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings, in which:
Like features have been designated by like references in the various figures. In particular, the structural and/or functional features that are common among the various embodiments may have the same references and may dispose identical structural, dimensional and material properties.
For the sake of clarity, only the steps and elements that are useful for an understanding of the embodiments described herein have been illustrated and described in detail.
Unless specified otherwise, when reference is made to two elements connected together, this signifies a direct connection without any intermediate elements other than conductors, and when reference is made to two elements coupled together, this signifies that these two elements can be connected or they can be coupled via one or more other elements.
In the following description, when reference is made to terms qualifying absolute positions, such as terms “front”, “rear”, “top”, “bottom”, “left”, “right”, etc., or relative positions, such as terms “above”, “under”, “upper”, “lower”, etc., or to terms qualifying directions, such as terms “horizontal”, “vertical”, etc., unless otherwise specified, it is referred to the orientation of the drawings, it being understood that, in practice, the described devices may be oriented differently.
Unless specified otherwise, the expressions “around”, “approximately”, “substantially” and “in the order of” signify within 10%, and preferably within 5%.
The device 100 of
Each of semiconductor layers 101 and 105 may be made of a III-N compound, for example, of the same III-N compound respectively N-type doped for layer 101 and P-type doped for layer 105. The term III-N compound here designates a composite semiconductor material comprising nitrogen (N), associated with one or a plurality of elements of column III of the periodic table of elements, for example, gallium (Ga), aluminum (Al), and/or indium (In). As an example, the term III-N compound here designates a semiconductor material from the group comprising gallium nitride (GaN), indium gallium nitride (InGaN), aluminum nitride (AlN), aluminum-gallium nitride (AlGaN), and indium gallium aluminum nitride (InGaAlN). As an example, pads 101 and 105 are made of AlGaN.
Emissive layer 103 may comprise confinement means corresponding to multiple quantum wells. As an example, layer 103 comprises an alternation of semiconductor layers of a first III-N compound and of semiconductor layers of a second III-N compound, each layer of the first compound defining a quantum well and being sandwiched between two layers of the second compound, the first compound having a band gap different from that of the second compound.
In the shown example, layers 101, 103, and 105 rest on a support substrate 10, for example, made of sapphire, a buffer layer 12 forming an interface between support substrate 10 and the lower surface of layer 101. Buffer layer 12 and layers 101, 103, and 105 are for example successively formed by epitaxy from the upper surface of substrate 10.
In this example, the active portion of LED 100 is laterally delimited by a peripheral trench 110 vertically extending from the upper surface of layer 105 down to layer 101. In the shown example, trench 110 extends vertically down to an intermediate level in layer 101. As a variant, trench 110 stops on the upper surface of layer 101. Thus, the active portion of LED 100 forms, in the stack of layers 105, 103, and optionally 101, a pad-shaped island or mesa laterally delimited by trench 110.
The LED 100 of
In the example of
The LED 100 of
The LED 100 of
In the example of
In this example, LED 100 further comprises, opposite its active portion, a connection metallization 115 arranged in an opening crossing layers 113, 111, and 109, metallization 115 being in contact, by its lower surface, with the upper surface of anode contact metallization 107. Metallization 115 is insulated from conductive gate layer 113 by an insulating spacer 117 and enables to take an electric contact on metallization 107.
To emit light, a positive voltage is applied between anode contact metallization 107 and the cathode contact metallization (not shown) of the LED. Further, in this example, a negative potential with respect to the potential of the cathode contact metallization is applied to gate 113. This results in an accumulation of holes at the level of the sides of the P-type layer 105 of the LED, resulting in the forming of a hole channel in the vicinity of the sides of the P layer. This enables to ease the injection of holes into the emissive layer 103 of the LED, and thus to improve the light conversion efficiency of the LED.
The manufacturing of the LED 100 of
Gate insulator layer 111 is preferably deposited by a conformal deposition method, for example, by deposition in successive atomic layers or ALD (“Atomic Layer Deposition”). As an example, gate insulator layer 111 is selected to resist to an electric field of at least 10 MV/cm. As an example, layer 111 is made of alumina (Al2O3). As an example, the thickness of layer 111 is in the range from 2 to 100 nm.
A step of local removal of layers 113, 111, and 109 opposite at least a portion of anode contact metallization 107 may further be provided to allow the taking of an electric contact on metallization 107, via connection metallization 115.
In this example, the forming of the cathode contact metallization of the LED has not been detailed. As an example, a local removal of layers 111 and 113 from the bottom of trench 110 may be provided to allow the taking of an electric contact on the upper surface of cathode layer 101, via a metallization, not shown. As a variant, the cathode contact metallization may be formed before the deposition of layers 111 and 113.
In practice, a plurality of identical or similar LEDs may be simultaneously formed inside and on top of the active LED stack formed by layers 101, 103, and 105, for example to form a LED emissive micro-display.
The etching of semiconductor layers 105, 103, and optionally 101 to form trench 110 is a dry etching, for example, a plasma etching. A problem which is posed is that, at the end of this etching, the sides of semiconductor layers 105, 103, and optionally 101, of the active portion of the LED may be superficially damaged. This may result in significantly degrading the conductivity of the hole channel induced by the application of a negative potential on conductive gate 113.
To overcome this disadvantage, a possibility is to provide, after the dry etch step, a cleaning of the sides of semiconductor layers 101, 103, and 105, by means of a wet chemical etch solution, for example, a solution based on potassium hydroxide (KOH) or of a solution based on tetramethylammonium hydroxide (TMAH), or of a solution based on tetraethylammonium hydroxide (TEAH), or any other solution capable of etching the III-N compound(s) forming layers 101, 103, and 105.
However, this chemical cleaning may result in damaging the sides of the anode contact metallization 107 of the LED, which may in particular result in decreasing the contact surface area between metallization 107 and anode layer 105, and thus in decreasing the efficiency of the LED.
The device 200 of
The manufacturing of the LED 200 of
As in the example of
Similarly to what has been described in relation with
Further, the cathode contact metallization of the LED (not shown in
In the example of
Thus, a good quality interface is obtained between gate insulator layer 111 and the sides of the semiconductor layers of the active portion of the LED, while preserving the integrity of the sides of the anode contact metallization 107 of the LED.
However, a disadvantage of the LED of
The device 300 of
In operation, spacer 301 is at the same potential as anode contact metallization 107, which favors the forming of a hole conduction channel towards emissive layer 103 with respect to a structure of the type described in relation with
The manufacturing of the LED 300 of
As in the example of
Similarly to what has been described in relation with
Further, the cathode contact metallization of the LED (not shown in
In the example of
The step of chemical etching of the exposed surfaces of semiconductor layers 105, 103, and 101 inside of trench 110 enables to remove the semiconductor material surface film possibly damaged during the step of dry etching of trench 110. Spacer 301 enables to protect the sides of anode contact metallization 107 during the chemical cleaning step. Preferably, the etching time is adapted so that the thickness of semiconductor material removed from the sides of the active portion of the LED is smaller than the thickness of spacer 301, to avoid reaching layer 107.
Spacer 301 may be made of a metal different from that of anode contact metallization 107. As an example, spacer 301 is a metal from the group comprising platinum, nickel, and tungsten, these metals having the advantage of not being, or of being little, etched by cleaning solutions based on KOH, on TMAH, or on TEAH. Preferably, spacer 301 is made of platinum, which has the additional advantage of forming a good electric contact with layer 105.
As a variant, the material of hard mask layer 109 may be a conductive material. In this case, connection metallization 115 does not need crossing the hard mask 109. As an example, connection metallization 115 only crosses layers 113 and 111 and is in contact, by it lower surface, with the upper surface of layer 109, the lower surface of layer 109 being in contact with the upper surface of metallization 107. As an example, hard mask 109 is made of the same conductive material as spacer 301.
Various embodiments and variants have been described. It will be understood by those skilled in the art that certain features of these various embodiments and variations may be combined, and other variations will occur to those skilled in the art. In particular, the described embodiments are not limited to the examples of materials and of dimensions mentioned in the present disclosure. More particularly, semiconductor layers 101, 103, and/or 105 may be made of semiconductor materials other than III-N compounds.
Further, although only examples of LED-type photo-emitting devices have been described hereabove, the described embodiments may also apply to PN junction photodetector devices, for example, photodiodes.
Further, the described embodiments are not limited to the specific example described in relation with
Further, embodiments where conductive gate 113 is electrically insulated not only from anode contact metallization 115, but also from the cathode contact metallization (not shown) have been described hereabove. As a variant, conductive gate 113 may be electrically insulated from anode contact metallization 115 but electrically connected to the cathode contact metallization. A field effect similar to what has been described hereabove can then be obtained, particularly for relatively high operating voltages, for example, beyond 5 volts.
Number | Date | Country | Kind |
---|---|---|---|
1873672 | Dec 2018 | FR | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/FR2019/053175 | 12/18/2019 | WO |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2020/128340 | 6/25/2020 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
20090184337 | Fan et al. | Jul 2009 | A1 |
20130161705 | Disney et al. | Jun 2013 | A1 |
20160322538 | Einfeldt et al. | Nov 2016 | A1 |
20170288050 | Ueno | Oct 2017 | A1 |
20170309676 | Odnoblyudov et al. | Oct 2017 | A1 |
20170309713 | Hirler | Oct 2017 | A1 |
Number | Date | Country |
---|---|---|
2642533 | Sep 2013 | EP |
Entry |
---|
Translation of the Written Opinion of the International Search Authority for International Application No. PCT/FR2019/053175, 5 pages. |
International Search Report for International Application No. PCT/FR2019/053175 dated Feb. 25, 2020, 2 pages. |
Translation of the Written Opinion of the International Search Authority for International Application No. PCT/FR2019/053174 dated Mar. 3, 2020, 5 pages. |
International Search Report for International Application No. PCT/FR2019/053174 dated Mar. 3, 2020, 2 pages. |
Number | Date | Country | |
---|---|---|---|
20220059725 A1 | Feb 2022 | US |