JP2015162631A - Light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure to efficiently perform a heat treatment of activating Mg in a p-type nitride semiconductor layer in a light emitting element in which an n-type nitride semiconductor is joined on the p-type nitride semiconductor layer by tunnel junction to be used as a current diffusion layer (window layer).SOLUTION: A light emitting element comprises: a substrate; a first n-type nitride semiconductor layer 13 arranged on the substrate; an active layer arranged on the first n-type nitride semiconductor layer 13; a p-type nitride semiconductor layer arranged on the active layer; and a second n-type nitride semiconductor layer 16 which is arranged on a top face of the p-type nitride semiconductor layer and forms tunnel junction with the p-type nitride semiconductor layer. In any region on a top face of the p-type nitride semiconductor layer, a distance to an end face of a mesa formed by at least by the second n-type nitride semiconductor layer 16 is equal to or less than 100 μm.

Description

  The present invention mainly relates to a light emitting device having a nitride semiconductor material.

In recent years, a nitride semiconductor material is often used as a semiconductor material for a semiconductor light emitting device (LED). The nitride semiconductor material is made of Si, SiC, sapphire, oxide, or II I-V group compound as a substrate, and is formed thereon by MOCVD or MBE.
However, since the p-type nitride semiconductor material has low mobility, current diffusion in the lateral direction is small. For this reason, even if a voltage is applied to the semiconductor light emitting element, the light emitting region is limited to a position immediately below the electrode, and current is difficult to diffuse across the entire surface of the semiconductor light emitting element. Therefore, for an electrode used in such a semiconductor light emitting device, for example, ITO (Indium-Tin) can be used as a material that can make ohmic contact with a p-type nitride semiconductor material and is transparent to light emitted from the semiconductor light emitting device. -Oxide), ZnO (Zinc-Oxide), or the like (see Patent Document 1).

On the other hand, as shown in FIG. 1, as a next-generation LED structure, an LED that uses an n-type nitride semiconductor as a current diffusion layer (window layer) by joining a p-type nitride semiconductor layer with a tunnel junction has been developed. Has been.

JP2011-243615A

Since the p-type nitride semiconductor layer is in an inactive state (no supply of Hall) due to residual hydrogen immediately after epitaxial film formation, it is usually necessary to activate Mg by annealing in an atmosphere that does not contain hydrogen. There is. At this time, since the film thickness of the p-type nitride semiconductor layer is usually 200 nm or less, hydrogen in the p-type nitride semiconductor layer is desorbed from the surface to the outside and removed.
However, in the structure according to the conventional example as shown in FIG. 1, when the n-type nitride semiconductor layer is formed on the p-type nitride semiconductor layer, the hydrogen in the p-type nitride semiconductor layer is changed to the n-type nitride. It is very difficult to go outside through the semiconductor layer. Although this phenomenon is not fully understood, the hydrogen in the p-type nitride semiconductor layer does not come out through the n-type nitride semiconductor layer, but is a mesa end face (of the p-type nitride semiconductor layer 15 in FIG. 1). From the side) to be removed mainly to the outside.

At this time, the movement (diffusion) distance of hydrogen in the p-type nitride semiconductor layer until hydrogen in the p-type nitride semiconductor layer is eliminated is larger than that of an LED not using an n-type nitride semiconductor layer as a window layer. Become longer. That is, in an LED in which an n-type nitride semiconductor layer is not formed on a p-type nitride semiconductor layer, the upper surface of the p-type nitride semiconductor layer is exposed to the outside during annealing. Residual hydrogen is desorbed. However, if an n-type nitride semiconductor layer is formed on the upper surface of the p-type nitride semiconductor layer, as described above, the residual hydrogen is desorbed only from the mesa end surface of the p-type nitride semiconductor layer. is there.

Therefore, in the structure according to the conventional example of FIG. 1, a long-time heat treatment is required for annealing. However, the heat treatment temperature needs to be about 400 ° C. or higher because hydrogen moves, and if the heat treatment is performed at that temperature for a long time, the structure of the light emitting layer formed of the superlattice containing InGaN is deteriorated. Specifically, the light emission efficiency decreases, the change in the light emission wavelength due to the current increases, and the reliability (deterioration characteristics due to energization) deteriorates.

Therefore, the present invention provides an LED in which an n-type nitride semiconductor layer is joined to a p-type nitride semiconductor layer by a tunnel junction (tunnel junction) and used as a current diffusion layer (window layer). A structure for efficiently performing heat treatment for activating Mg is proposed.

  According to one aspect of the present invention, a substrate, a first n-type nitride semiconductor layer disposed on the substrate, an active layer disposed on the first n-type nitride semiconductor layer, A p-type nitride semiconductor layer disposed on the active layer and a second n-type nitride disposed on the upper surface of the p-type nitride semiconductor layer and having a junction with the p-type nitride semiconductor layer as a tunnel junction A semiconductor layer; a p-side electrode disposed on the second n-type nitride semiconductor layer and electrically connected to the p-type nitride semiconductor layer; and the first n-type nitride semiconductor layer electrically N-side electrode connected to each other, and in any region of the upper surface of the p-type nitride semiconductor layer, at least the second in the substrate direction from the upper surface of the second n-type nitride semiconductor layer The distance to the end face of the mesa formed at a depth penetrating the n-type nitride semiconductor layer is 100 μm Emitting device is provided that equal to or less than.

  According to the present invention, in an LED that uses an n-type nitride semiconductor layer as a current diffusion layer (window layer) by joining an n-type nitride semiconductor layer on a p-type nitride semiconductor layer with a tunnel junction, the light emission efficiency is improved and the current of the emission wavelength is increased. An LED with little change and high reliability can be provided.

It is sectional drawing of the light emitting element which concerns on a prior art example. It is a top view of the light emitting element concerning a 1st embodiment of the present invention. It is sectional drawing in the AA of FIG. It is a top view of the light emitting element which concerns on the modification of the 1st Embodiment of this invention. It is sectional drawing in the BB line of FIG. It is a top view of the light emitting element concerning other modifications of the 1st embodiment of the present invention. It is sectional drawing of the light emitting element which concerns on the 2nd Embodiment of this invention.

  Next, an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic and ratios of thicknesses of the respective regions are different from actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

(First embodiment)
FIG. 2 is a plan view of the light emitting device 1 according to the first embodiment of the present invention. When the light emitting element 1 is viewed from the top, it is configured by a horizontally long rectangle. FIG. 3 shows a cross-sectional structure taken along line AA in FIG. The light emitting device 1 according to the present embodiment includes a buffer layer 12, a first n-type nitride semiconductor layer 13, an active layer 14, a p-type nitride semiconductor layer 15, on a substrate 11 formed of silicon carbide or silicon. The second n-type nitride semiconductor layer 16 is laminated in this order, and is formed by dicing or cleaving it. The active layer 14 has, for example, a general multi-quantum well (MQW) structure. In order to make the light-emitting element 1 highly efficient, it is formed by laminating thin films of several nm to several tens of nm. In order to achieve high efficiency, it is necessary to obtain excellent optical crystallinity and crystallinity, and metal organic chemical vapor deposition (MOCVD) is used for the production of the active layer 14.

A second n-type nitride semiconductor layer 16 is disposed on the upper surface of the p-type nitride semiconductor layer 15, and the p-type nitride semiconductor layer 15 and the second n-type nitride semiconductor layer 16 are connected to a tunnel junction. Is configured to be formed. For example, as the p-type nitride semiconductor layer 15, a 5 nm p-type InGaN layer is formed on a 170 nm p-type GaN layer. The doping density of the p-type GaN layer and the p-type InGaN layer is preferably 1E + 19 cm −2 or more. Then, on the p-type InGaN layer, a second n-type nitride semiconductor layer 16 in which a 1000 nm n-type GaN layer is formed on a 5 nm n-type InGaN layer is disposed. The doping density of the n-type InGaN layer and the n-type GaN layer is preferably 1E + 19 cm −2 or more.

A p-side electrode 17 that is electrically connected to the p-type nitride semiconductor layer 15 is formed on the second n-type nitride semiconductor layer 16. The n-side electrode 18 is formed so as to expose a part of the upper surface of the first n-type nitride semiconductor layer 13 and to be electrically connected to the exposed surface.

L shown in FIG. 2 indicates the distance from the line AA (the center line in the short direction of the light emitting element 1) to the mesa end surface 21 formed by the peripheral portion of the second n-type nitride semiconductor layer 16. . Here, L is 100 μm or less. With this configuration, in any region on the upper surface of the p-type nitride semiconductor layer 15 in a plan view, the mesa end surface 21 formed by the peripheral portion of the second n-type nitride semiconductor layer 16 is connected at the shortest distance. In this case, it is 100 μm or less. What is important here is that when the shortest distance is formed from any region on the upper surface of the p-type nitride semiconductor layer 15 in plan view to the mesa end surface 21 formed by the peripheral portion of the second n-type nitride semiconductor layer 16, 100 μm. There should be at least one passage that: For this reason, although the light emitting element 1 is a horizontally long rectangle in FIG. 2, the length in the longitudinal direction is not limited.

As described above, in a light-emitting device that uses an n-type nitride semiconductor bonded to a p-type nitride semiconductor layer by a tunnel junction as a current diffusion layer (window layer), Mg in the p-type nitride semiconductor layer is activated. In order to achieve this, it is necessary to desorb hydrogen. However, since hydrogen is desorbed mainly from the end face of the mesa, hydrogen diffuses and moves in the direction in which the p-type nitride semiconductor layer is stacked (in the plane perpendicular to the growth direction of the semiconductor layer). In a conventional light emitting device that does not form an n-type nitride semiconductor on a p-type nitride semiconductor layer, there is no n-type nitride semiconductor that blocks hydrogen desorption on the upper surface of the p-type nitride semiconductor layer. Hydrogen can also be desorbed from the upper surface of the type nitride semiconductor layer. Therefore, a light-emitting element that is used as a current diffusion layer (window layer) in which an n-type nitride semiconductor layer is joined to a p-type nitride semiconductor layer by a tunnel junction is also desorbed from the top surface of the p-type nitride semiconductor layer. Since the diffusion movement distance is longer than that of the conventional light emitting element, the heat treatment time required for activation becomes longer.

Here, in any region of the p-type nitride semiconductor layer 15, the distance to the mesa end face 21 is formed to be 100 μm or less, so that the diffusion movement distance of residual hydrogen in the p-type nitride semiconductor layer 15 can be reduced. Since it can be 100 um or less, the heat treatment time during annealing can be made within 30 minutes. As a result, it was found that heat treatment can be performed without degrading the quality of the active layer 14. At this time, in the case of an active layer formed by a quantum well structure, the light emitting function is reduced by diffusion of In or Ga by heat treatment in a thin stacked structure, and therefore the thickness of the well layer is preferably 2 nm or more.

4 and 5 are modifications of the light emitting device according to the first embodiment. FIG. 4 is a plan view of a light-emitting element according to a modification of the first embodiment. 5 is a cross-sectional view taken along line BB in FIG. That is, when the light-emitting element 1 is large, the distance from the central region to the mesa end surface (first mesa end surface) 21 at the periphery of the second n-type nitride semiconductor layer 16 is increased. In that case, a hole 20 is formed in a region inside the periphery of the second n-type nitride semiconductor layer 16. The hole 20 penetrates the p-type nitride semiconductor layer 15 and the active layer 14 from the upper surface of the second n-type nitride semiconductor layer 16 and is deep enough to expose the upper surface of the first n-type nitride semiconductor layer 13. It is formed. By forming the hole 20 in this way, a mesa end face (second mesa end face) 22 deeper than the p-type nitride semiconductor layer 15 is formed in a region inside the periphery of the second n-type nitride semiconductor layer 16. From which residual hydrogen is effectively desorbed by annealing. Therefore, the heat treatment can be performed without degrading the quality of the active layer 14. Therefore, the hole 20 is desirably formed to a depth that penetrates the p-type nitride semiconductor layer 15.

Thus, by forming the hole 20, a mesa end surface (second mesa end surface) 22 by the hole 20 is formed in a region inside the periphery of the second n-type nitride semiconductor layer 16. Therefore, as in FIG. 2, the shortest distance to the first mesa end surface 21 or the second mesa end surface 22 is L (100 μm) or less in any region on the upper surface of the p-type nitride semiconductor layer 15 in plan view. Become.

Further, as shown in FIG. 6, a plurality of holes 20 may be formed in a region inside the periphery of the second n-type nitride semiconductor layer 16. The hole 20 is not limited to a circular shape, but the hole 20 is substantially circular when viewed from the top surface of the light emitting element 1, and the distance between the substantially circular holes 20 (that is, the plurality of second mesa end surfaces 22 is different). And the distance between the hole 20 and the mesa end surface 21 at the periphery of the second n-type nitride semiconductor layer 16 (that is, from the second mesa end surface closest to the first mesa end surface to the first mesa end surface). In the case of a structure having a distance to the mesa end face) of 150 μm or less, more preferably 50 μm or less, an LED having the highest luminous efficiency was obtained. When the holes 20 have a substantially circular shape as shown in FIG. 6, the area of the mesa end surface formed by each hole 20 is smaller than the holes 20 formed in the light emitting device 1 shown in FIG. 4. Therefore, in order to make it easy to desorb residual hydrogen from the p-type nitride semiconductor layer 15, the distance between the holes 20 shown in FIG. 6 and the mesa end surface of the periphery of the hole 20 and the second n-type nitride semiconductor layer 16 are shown. The distance to 21 is preferably shorter than the distance (2L) shown in FIG. Further, rather than forming a large hole 20 between the p-side electrode and the n-side electrode as shown in FIG. 4, a plurality of relatively small holes 20 are formed so as to provide a constant interval as shown in FIG. This improves the current spreading effect and the light extraction efficiency of the light emitting element 1. This is because when a large hole 20 is formed between the p-side electrode and the n-side electrode, the current path is blocked by the hole 20, and the current needs to be detoured to avoid the hole. However, as shown in FIG. 6, by forming a plurality of relatively small holes 20 at regular intervals, a current path flowing between the p-side electrode and the n-side electrode is formed through the plurality of holes 20. This is because the current can be uniformly diffused in the plane when viewed from the upper surface of the light emitting element 1. Furthermore, since the light from the active layer 14 is extracted from the holes 20, the light extraction efficiency of the light-emitting element 1 is improved by forming a plurality of relatively small holes 20 so as to be spaced apart as shown in FIG. Will be improved.

(Second Embodiment)
FIG. 7 is a cross-sectional view of the light emitting device 1 according to the second embodiment of the present invention. The difference from the first embodiment is the depth of the hole 20. As described with reference to FIG. 5, the hole 20 formed in the light emitting device 1 in the first embodiment is formed to a depth at which the upper surface of the first n-type nitride semiconductor layer 13 is exposed. The hole 20 formed in the light emitting device 1 according to the embodiment is formed to a depth at which the upper surface of the p-type nitride semiconductor layer 15 is exposed. With such a configuration, residual hydrogen can be desorbed from the upper surface of the p-type nitride semiconductor layer 15 exposed to the outside through the holes 20 by annealing. The other structure of the present invention is the same as the modification of the first embodiment. For example, the structure shown in FIGS. 4 and 6 is adopted as the planar structure. The light-emitting element 1 according to the second embodiment can obtain the same effects as those of the light-emitting element according to the modification of the first embodiment.

As described above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

DESCRIPTION OF SYMBOLS 1 ... Light emitting element 11 ... Substrate 12 ... Buffer layer 13 ... 1st n-type nitride semiconductor layer 14 ... Active layer 15 ... p-type nitride semiconductor layer 16 ... Second n-type nitride semiconductor layer (window layer)
17 ... p-side electrode 18 ... n-side electrode 20 ... hole 21 ... mesa end face (first mesa end face)
22 ... mesa end face (second mesa end face)

Claims (7)

A substrate,
A first n-type nitride semiconductor layer disposed on the substrate;
An active layer disposed on the first n-type nitride semiconductor layer;
A p-type nitride semiconductor layer disposed on the active layer;
A second n-type nitride semiconductor layer disposed on an upper surface of the p-type nitride semiconductor layer and having a junction with the p-type nitride semiconductor layer as a tunnel junction;
A p-side electrode disposed on the second n-type nitride semiconductor layer and electrically connected to the p-type nitride semiconductor layer;
An n-side electrode electrically connected to the first n-type nitride semiconductor layer;
With
In any region of the upper surface of the p-type nitride semiconductor layer,
The distance from the upper surface of the second n-type nitride semiconductor layer to the mesa end surface formed at least at a depth penetrating the second n-type nitride semiconductor layer in the substrate direction is 100 μm or less. Light emitting element. The mesa end face is
In the peripheral portion on the upper surface of the second n-type nitride semiconductor layer,
A first mesa end surface formed by a side surface portion of the second n-type nitride semiconductor layer and the p-type nitride semiconductor layer;
At least one hole formed at a depth penetrating at least the second n-type nitride semiconductor layer from the upper surface of the second n-type nitride semiconductor layer toward the substrate;
A second mesa end surface formed on the inner surface of the hole;
The light emitting device according to claim 1, comprising: A plurality of the second mesa end faces are formed, and the distance between the second mesa end faces is 150 μm or less, and the first mesa end faces closest to the first mesa end faces are the first mesa end faces. The light emitting device according to claim 2, wherein the distance to the end face of the mesa is 150 µm or less. 4. The light emitting device according to claim 2, wherein the hole is formed to a depth at which an upper surface of the p-type nitride semiconductor layer is exposed. 4. The light emitting device according to claim 2, wherein the hole is formed to a depth at which an upper surface of the first n-type nitride semiconductor layer is exposed. The light-emitting element according to claim 2, wherein the hole is formed in a substantially circular shape. 7. The light emitting device according to claim 1, wherein a film thickness of the well layer forming the active layer is 2 nm or more.

Images