JP4264600B2 - Light emitting diode - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light emitting diode, and more particularly to a light emitting diode composed of a II-VI group compound semiconductor.
[0002]
[Prior art]
A light-emitting diode is a diode that utilizes light emission by radiative recombination of minority carriers injected by applying an electric field to a pn junction, and is widely used as one of semiconductor light-emitting elements.
[0003]
A II-VI group compound semiconductor composed of a Group II element such as Zn, Cd, Mg, Be and a Group VI element such as O, S, Se, Te is a material constituting a semiconductor light emitting device such as a semiconductor laser or a light emitting diode. As promising. In particular, the ZnMgSSe mixed crystal can be grown on a GaAs substrate, and is known to be suitable for, for example, a guide layer or a clad layer constituting a blue semiconductor laser.
[0004]
FIG. 10 is a cross-sectional view showing a configuration example of a conventional light emitting diode.
Here, a case where a light emitting diode is formed of a ZnMgSSe-based material is shown.
[0005]
As shown in FIG. 10, the light-emitting diode includes an n-type GaAs: Si first buffer layer 11, an n-type ZnSe: Cl second buffer layer 12, an n-type ZnSSe: Cl second electrode on an n-type GaAs: Si substrate 10. 3 buffer layer 13, n-type ZnMgSSe: Cl first cladding layer 14, n-type ZnSSe: Cl first guide layer 15, ZnCdSe active layer 16, p-type ZnSSe: N second guide layer 17, p-type ZnMgSSe second main cladding Layer 18, p-type ZnSSe: N second subcladding layer 19, p-type ZnSe: N intermediate layer 20, p-type (ZnSe: N / ZnTe: N) superlattice semiconductor layer (SL) 21, p-type ZnTe: N contact Layers 22 are sequentially stacked.
In the layer above the upper layer portion of the p-type ZnSSe: N second sub-cladding layer 19, a region partitioned by the insulating film 23 becomes a contact region, and a p-type electrode 24 such as a Pd / Pt / Au electrode Contact is made. On the other hand, an n-type electrode 26 such as an In electrode is formed on the back side of the n-type GaAs: Si substrate 10.
[0006]
The light emitting diode shown in FIG. 10 applies light to the p-type electrode 24 and the n-type electrode 26 to inject minority carriers, and emits light emitted by radiative recombination in the active layer, for example, from the surface on which the p-type electrode 24 is formed. It can be taken out. Here, the p-type electrode 24 is formed over the entire surface covering the upper layer of the p-type ZnTe: N contact layer 22 and the upper layer of the insulating film 23, and the region partitioned by the insulating film 23 is formed over the entire surface. In this structure, current is injected.
[0007]
[Problems to be solved by the invention]
However, the light-emitting diode having the above structure has a problem that the deterioration rate of the element is large.
In the above light emitting diode, ZnCdSe constituting the active layer 16 is a strained system. Therefore, when the amount of strain is increased, the band gap difference from the guide layer increases, but the characteristics deteriorate due to the effect of strain. Therefore, it is desirable that the composition of the ZnCdSe active layer 16 is about Cd 25% and the film thickness is about 4 nm so that the emission wavelength is about 500 nm. At this time, if the emission wavelength is increased, the amount of distortion increases.
[0008]
FIG. 11 shows τ _1/2 (light emission time of the light emitting diode until the light emission amount becomes 1/2) indicating the deterioration rate with respect to the light emission wavelength when the light emission temperature is 60 ° C. and the injection current is 100 mA. FIG. Thus, the deterioration rate of the light emitting diode having the above structure increases as the emission wavelength becomes longer.
[0009]
As a cause of the deterioration of the above light emitting diode, a dark line is generated linearly in the active layer surface starting from stacking faults in the active layer, and the dark line extends with time and expands thickly over time. It has been clarified that the dark line becomes a starting point of another dark line, a new dark line is generated, the entire light emitting region becomes dark, and the light emission amount decreases. FIG. 12 is a schematic diagram for explaining this situation. In FIG. 12A, the entire region of the p-type electrode 24 formed on the entire surface is a light emitting region. Here, the dark line Z is generated starting from the stacking fault Za or the like. As shown in FIG. 12 (b), these dark lines Z are stretched and thickened with time, and the stretched dark lines become the starting point of another dark line, and a new dark line is generated. It's getting darker.
[0010]
The present invention has been made in view of such circumstances, and an object of the present invention is to have n-type and p-type cladding layers formed on both sides of the active layer and the active layer, and to generate radiation in the active layer. An object of the present invention is to provide a light-emitting diode that emits light by recombination and that reduces the deterioration by suppressing the extension of dark lines, which is a cause of deterioration.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a light emitting diode according to the present invention includes a first conductivity type first cladding layer, an active layer, and a second conductivity type second cladding layer. Radial recombination that occurs in the active layer when a first electrode is connected, a second electrode is connected to the second cladding layer, and current is injected by applying a voltage to the first electrode and the second electrode The current injection structure from the second electrode is divided into a plurality of current non-injection regions.
[0012]
In the light emitting diode of the present invention, the current injection structure from the second electrode is divided into a plurality of current non-injection regions, and the current non-injection regions generate in the active layer which causes the deterioration of the light emitting diode. The extension of the dark line is suppressed, and deterioration of the light emitting diode can be reduced.
[0013]
In the light emitting diode of the present invention, preferably, the current injection structure is divided by a width of 10 μm or more by the current non-injection region. The extension of the dark line generated in the active layer to the current non-injection region is about 10 μm, and the current injection structure is divided by the current non-injection region with a width of 10 μm or more to effectively suppress the extension of the dark line. Can do.
[0014]
In the light emitting diode of the present invention, preferably, the current injection structure is divided by an insulating film. Alternatively, preferably, the current injection structure is divided by a region into which an impurity for inactivating carriers is introduced. Thereby, it can be set as the electric current non-injection area | region which suppresses extending | stretching of a dark line. The second cladding layer is composed of a laminate of two or more layers, and at least the second cladding layer on the second electrode side is divided by an insulating film, or at least in the second cladding layer on the second electrode side The above structure can be obtained by a structure in which impurities for inactivating carriers are introduced.
[0015]
In the light emitting diode of the present invention, it is preferable that the first cladding layer, the active layer, and the second cladding layer each include at least one element selected from Be, Zn, Hg, Cd, and Mg. It is formed of a II-VI group compound semiconductor containing at least one element of O, S, Se, and Te. For example, even in a light-emitting diode composed of a strained semiconductor layer such as ZnCdSe, the present invention can suppress the extension of dark lines that cause deterioration.
[0016]
In the light emitting diode of the present invention, preferably, the current injection structure is divided into regions having an area of 3 × 10 ⁴ μm ² or less by the current non-injection region, and more preferably, It is divided into regions each having an area of 1 × 10 ⁴ μm ² or less. Stacking faults in the crystal can be suppressed to about 1 × 10 ³ pieces / cm ⁻² . This will have one defect per 1 × 10 ⁵ μm ² . Therefore, by dividing each region having an area of 3 × 10 ⁴ μm ² or less, the probability that the active layer in each region includes the origin of dark lines such as stacking faults becomes 1/3 or less, and the remaining 2 / The region 3 does not include the starting point of the dark line, and the dark line can be confined in the region corresponding to 1/3 of the whole, so that the extension of the dark line can be effectively suppressed. By dividing each region having an area of 1 × 10 ⁴ μm ² or less, the probability that the active layer in each region includes the origin of dark lines such as stacking faults becomes 1/10 or less, and the extension of dark lines is further effective. Can be suppressed.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment FIG. 1 is a plan view showing a first embodiment of a light emitting diode according to the present invention, and FIG. 2 is a cross-sectional view taken along the line XX ′ of FIG.
In addition, the light emitting diode of this embodiment is comprised by the material of ZnMgSSe type | system | group.
[0018]
As shown in FIG. 2, this light emitting diode has the following structure, for example. On the substrate 10 made of n-type GaAs: Si or the like, a first buffer layer 11 made of n-type GaAs: Si or the like, a second buffer layer 12 made of n-type ZnSe: Cl or the like having a thickness of about 10 nm, and n-type ZnSSe: A third buffer layer 13 made of Cl or the like (this layer can be omitted), a first cladding layer 14 made of n-type ZnMgSSe: Cl such as Zn _0.88 Mg _0.12 S _0.18 Se _0.82 : Cl and having a thickness of about 1 μm. First guide layer 15 having a thickness of about 100 nm made of n-type ZnSSe: Cl such as ZnS _0.06 Se _0.94 : Cl, Active layer 16 having a thickness of about 3 to 4 nm made of ZnCdSe, etc., ZnS _0.06 Se _0.94 : N p-type, such as ZnSSe: second guide layer 17 having a film thickness of about 300nm made of _{N, Zn 0.75 Mg 0.25 S 0.28} Se 0.72: p -type ZnMg such N Second main cladding layer 18 made of Se: N or the like with a thickness of about 1 μm, second sub-cladding layer 19 made of p-type ZnSSe: N or the like with a thickness of about 2 μm, and a thickness of about 150 nm made of p-type ZnSe: N or the like. An intermediate layer 20, a superlattice semiconductor layer (SL) 21, which is a layer in which p-type ZnSe: N and ZnTe: N are alternately stacked, and a contact layer 22 made of p-type ZnTe: N are sequentially stacked. .
[0019]
In the layer above the upper layer portion of the second sub-cladding layer 19, a region divided and partitioned by the insulating film 23 becomes a contact region, and is a transparent p-type made of Au having a thickness of about 10 nm. Contact with the electrode 24 is made. Further, a pad electrode 25 is formed in the upper layer portion of the insulating film 23 connected to the p-type electrode 24, for example, by forming the same conductive material as the p-type electrode 24 to a thickness of about 200 nm. Ti, Pd, or the like may be formed between Au and the insulating film 23. On the other hand, an n-type electrode 26 such as an In electrode is formed on the back side of the n-type GaAs: Si substrate 10.
[0020]
The light emitting diode shown in FIG. 1 and FIG. 2 applies light to the p-type electrode 24 and the n-type electrode 26 to inject minority carriers, and emits light emitted by radiative recombination in the active layer, for example, the p-type electrode 24. It can be taken out from the forming surface. Here, for example, as shown in FIG. 1, the p-type electrode 24 is divided by the insulating film 23 region (and the pad electrode 25 region formed thereon), so that the insulating film 23 region is not subjected to current injection. Thus, the current injection structure from the p-type electrode 24 is divided into a plurality of regions by the current non-injection region. In the drawing, the current injection structure is divided into regions each having an area of about 250 μm × 100 μm with a width of 10 μm or more (corresponding to the width of the insulating film) by a current non-injection region. The width of dividing the current injection structure by the current non-injection region may be 10 μm or more, and preferably 20 μm or more.
[0021]
The defect that becomes the starting point of the dark line can be suppressed to several stacking faults per 1 mm ² (1 mm × 1 mm) as the area of the light emitting region in addition to the end portion of the chip. In the region including these starting points, The dark line is enlarged and darkened, but in other areas where there is no initial defect, there is almost no propagation of the dark line from other areas, so that deterioration hardly occurs. Since the current injection structure is divided into a plurality of current non-injection regions in this manner, the extension of the dark line generated in the active layer, which causes the deterioration of the light emitting diode, is suppressed. Can be reduced.
[0022]
The light emitting diode having the above structure is manufactured by a well-known general method. Below, the outline of a manufacturing method is demonstrated easily.
[0023]
FIG. 3 is a schematic diagram showing the configuration of the molecular beam epitaxial crystal growth apparatus. A substrate holder 2 is provided in the vacuum chamber 1, and an rf cell 4 and a molecular beam source (K cell) 5 are arranged so as to face the surface thereof. A GaAs: Si substrate 3 is fixed to the substrate holder 2, the inside of the vacuum chamber 1 is evacuated to a high vacuum state, and a molecular beam MB is irradiated from the molecular beam source 5 toward the surface of the substrate 3. Thus, the first buffer layer 11 to the contact layer 22 as described above are sequentially grown on the substrate 3. The rf cell 4 is used when nitrogen is used as a raw material.
Next, after forming a resist pattern on the contact layer 22 so that the electrode pattern shown in FIG. 1 is obtained, the resist layer is used as an etching mask, and the contact layer 22 is formed by wet etching or dry etching. The lattice semiconductor layer 21, the intermediate layer 20, and the second sub-cladding layer 19 are etched to a predetermined depth in the thickness direction of the second sub-cladding layer 19.
[0024]
Next, an insulating film such as silicon oxide is deposited using the resist pattern used as an etching mask as a growth mask, and lift-off treatment is performed, so that an insulating film is formed in a region corresponding to the gap portion of the electrode pattern shown in FIG. 23 is formed.
Next, an electrode material such as Au is deposited on the entire surface so as to be connected to the contact layer 22, and a transparent p-type electrode 24 is formed. Further, an electrode material is formed in a thick film of about 200 nm on the upper layer portion of the insulating film 23 to form the pad electrode 25. On the other hand, an electrode material such as In is also formed on the back side of the GaAs: Si substrate 3 to form the n-type electrode 26. Through the above steps, the light emitting diode shown in FIGS. 1 and 2 can be formed.
[0025]
(Example 1)
In the light emitting diode of the present embodiment, when the p-type electrode 24 has the width W _E as the shape of the p-type electrode 24, dark lines that cause deterioration extend from the end of the p-type electrode 24 to the insulating film 23 region. The result of observing the situation is shown in FIG. The dark line Z spreads from the end of the p-type electrode 24 to the region of the insulating film 23, but its width W _Z is about 10 μm and has not been extended to a region beyond that.
[0026]
(Example 2)
FIG. 5 shows the result of observing the extension of the dark line Z that causes deterioration when the shape of the p-type electrode 24 in the light emitting diode of this embodiment is the shape shown in FIG. The dark line Z extends in the p-type electrode 24a region on the left side of the drawing, but does not propagate to the p-type electrode region 24b on the right side of the drawing, and passes through the insulating film 23 having a width W _I (here, 50 μm). By providing, the extension of the dark line Z could be suppressed.
[0027]
(Example 3)
In a light emitting diode having a light emitting region of 1 mm × 1 mm, a light emitting diode (D1) having electrodes over the entire surface of the light emitting region and a light emitting diode (D2) in which a p-type electrode is divided by an insulating film in the pattern shown in FIG. . FIG. 6 is a graph plotting the change in relative light output over time when each diode (D1, D2) emits light at a temperature of 60 ° C. and an injection current of 100 mA (20 Acm ⁻² ). As described above, it was confirmed that the degradation can be suppressed by dividing the p-type electrode by the insulating film in the pattern shown in FIG.
[0028]
Second embodiment The light-emitting diode of this embodiment is substantially the same as the light-emitting diode of the first embodiment, except that the pattern of the p-type electrode 24 and the insulating film 23 (and the gap portion corresponding thereto) The only difference is that the pattern of the pad electrode 25) formed in the upper layer is the pattern shown in FIGS. 7A and 7B. The pattern shown in FIG. 7 is a pattern in which an electrode region having an area of 30 μm × 80 μm is repeatedly formed across an insulating film region having a width of 20 μm. The pattern in FIG. 7A is an enlarged view of a portion corresponding to the region A in FIG. 7B, and the pattern in FIG. 7B can be obtained by repeating this pattern.
[0029]
In the above light emitting diode, even if there is a stacking fault in one of the regions divided by the insulating film and the region is darkened, in other regions where there is no initial defect, the other regions are different from other regions. Since there is almost no propagation of dark lines, the deterioration is extremely difficult to occur. Since the current injection structure is divided into a plurality of current non-injection regions in this manner, the extension of the dark line generated in the active layer, which causes the deterioration of the light emitting diode, is suppressed. Can be reduced. In particular, each region having a smaller area of 30 μm × 80 μm than that of the first embodiment is divided, and the probability that an initial defect exists in each region is further reduced. Therefore, the deterioration is reduced as compared with the first embodiment. be able to.
[0030]
The pattern of the p-type electrode 24 and the pattern of the insulating film 23 (and the pad electrode 25 formed thereon) corresponding to the gap are 30 μm × 30 μm as shown in FIG. A pattern in which an electrode region having an area is repeatedly formed across an insulating film region having a width of 20 μm, and an electrode region having an area of 60 μm × 60 μm as illustrated in FIG. 8B is spaced from an insulating film region having a width of 40 μm. Or a pattern in which an electrode region having an area of 70 μm × 90 μm as shown in FIG. 8C is repeatedly formed across an insulating film region having a width of 10 to 30 μm. it can.
[0031]
Third embodiment The light-emitting diode of this embodiment is substantially the same as the light-emitting diode of the first embodiment, but the current non-injection region that divides the current injection structure inactivates carriers. The only difference is that the region 23a is implanted with, for example, oxygen ions as impurities.
[0032]
In the light emitting diode of the present embodiment, the contact layer 22 is stacked in the same manner as in the first embodiment, and then a resist film is patterned in the p-type electrode formation region, and oxygen ions are ion-implanted to deactivate the carrier. Then, the p-type electrode 24, the pad electrode 25, and the n-type electrode 26 are formed in the same manner as in the first embodiment.
[0033]
Similarly to the first embodiment, the light emitting diode according to the present embodiment is divided into a plurality of current injection structures by the current non-injection region, so that the active layer that causes the deterioration of the light emitting diode is included in the active layer. Since the extending | stretching of the dark line to generate | occur | produce is suppressed, deterioration of a light emitting diode can be reduced.
[0034]
In addition, as a pattern of the p-type electrode of the light emitting diode according to the present embodiment, it is also preferable to form a pattern similar to that of the second embodiment.
[0035]
The present invention is not limited to the above embodiment. For example, in the embodiment, a II-VI group compound semiconductor (ZnMgSSe-based) light emitting diode is described. However, the present invention can be applied to various semiconductor light emitting elements, and a part of the light emitting region is deteriorated. In the case of occurrence in a chain, a great effect can be obtained by using the present invention. The light emitting material can be applied to various light emitting diodes such as nitride-based, AlGaAs-based, AlInGaP-based, AlGaAsP-based III-V group compound semiconductors, or organic EL elements. In addition, the n-type electrode can be divided by an insulating film or the like instead of the p-type electrode. In addition, various modifications can be made without departing from the scope of the present invention.
[0036]
【The invention's effect】
As described above, according to the present invention, the active layer and the active layer have n-type and p-type cladding layers connected to both surfaces, and emit light by radiative recombination generated in the active layer. There can be provided a light emitting diode which is a light emitting diode and which suppresses the extension of a dark line which is a cause of deterioration and reduces the deterioration.
[Brief description of the drawings]
FIG. 1 is a plan view showing a pattern of a p-type electrode of a light emitting diode according to a first embodiment.
FIG. 2 is a cross-sectional view of the light-emitting diode according to the first embodiment taken along the line XX ′ in FIG.
FIG. 3 is a schematic diagram showing a configuration of a molecular beam epitaxial crystal growth apparatus.
FIG. 4 is a schematic diagram showing a result of observing how dark lines are stretched according to Example 1;
FIG. 5 is a schematic diagram showing a result of observing a state in which dark lines according to Example 2 are stretched.
FIG. 6 is a diagram comparing temporal changes in light output of light emitting diodes of the present invention and a comparative example in Example 3.
FIG. 7 is a plan view showing a pattern of a p-type electrode of a light emitting diode according to a second embodiment.
FIG. 8 is a plan view showing a pattern of a p-type electrode of a light emitting diode according to a second embodiment.
FIG. 9 is a cross-sectional view of the light emitting diode according to the third embodiment taken along the line XX ′ in FIG.
FIG. 10 is a cross-sectional view of a light emitting diode according to a conventional example.
FIG. 11 is a graph plotting the deterioration rate (τ _1/2 ) of the light emitting diode according to the conventional example against the emission wavelength.
FIG. 12 is a schematic diagram showing a result of observing the deterioration of a light emitting diode according to a conventional example, and changes from (a) to (b).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Vacuum chamber, 2 ... Substrate holder, 3 ... Substrate, 4 ... rf cell, 5 ... Molecular beam source, 10 ... Substrate, 11 ... 1st buffer layer, 12 ... 2nd buffer layer, 13 ... 3rd buffer layer, DESCRIPTION OF SYMBOLS 14 ... 1st clad layer, 15 ... 1st guide layer, 16 ... Active layer, 17 ... 2nd guide layer, 18 ... 2nd main clad layer, 19 ... 2nd sub clad layer, 20 ... Intermediate layer, 21 ... Super Lattice semiconductor layer (SL), 22 ... contact layer, 23 ... insulating film, 23a ... region doped with impurities for inactivating carriers, 24 ... p-type electrode, 25 ... pad electrode, 26 ... n-type electrode, MB ... molecular beam, Z ... dark line, Za ... starting point of dark line.

Claims (7)

A first conductivity type first cladding layer; an active layer; and a second conductivity type second cladding layer. A first electrode is connected to the first cladding layer, and a second electrode is connected to the second cladding layer. Electrodes are connected to emit light by radiative recombination that occurs in the active layer when a voltage is applied to the first electrode and the second electrode to inject current,
The second clad layer is formed of a laminate of two or more layers, and the second clad layer on the second electrode side is divided by an insulating film that becomes a current non-injection region up to an intermediate depth, and the current from the second electrode A light-emitting diode in which the injection structure is divided into multiple pieces. A first conductivity type first cladding layer; an active layer; and a second conductivity type second cladding layer. A first electrode is connected to the first cladding layer, and a second electrode is connected to the second cladding layer. Electrodes are connected to emit light by radiative recombination that occurs in the active layer when a voltage is applied to the first electrode and the second electrode to inject current,
A current non-injection region in which the second clad layer is formed of a laminate of two or more layers, and an impurity that inactivates carriers is introduced into the second clad layer on the second electrode side to a midpoint; A light emitting diode in which a current injection structure from the second electrode is divided into a plurality of parts. The light emitting diode according to claim 1, wherein the current injection structure is divided by the current non-injection region with a width of 10 μm or more. Each of the first cladding layer, the active layer, and the second cladding layer is composed of at least one element selected from Be, Zn, Hg, Cd, and Mg and at least one selected from O, S, Se, and Te. The light emitting diode according to claim 1 or 2, wherein the light emitting diode is formed of a II-VI group compound semiconductor containing the above elements. The light emitting diode according to claim 1, wherein the current injection structure is divided into regions each having an area of 3 × 10 ⁴ μm ² or less by the current non-injection region. The light emitting diode according to claim 5 , wherein the current injection structure is divided into regions having an area of 1 × 10 ⁴ μm ² or less by the current non-injection region. The light emitting diode according to claim 1, wherein the first electrode is an n-side electrode, and the second electrode is a p-side electrode.

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