JP2007123398A - Semiconductor light emitting element, method of manufacturing the same and lighting device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light emitting element formed of a plurality of nano-columns that can simultaneously emit lights in a plurality of wavelength areas without using phosphor and establish high light emitting efficiency. <P>SOLUTION: When growing a nano-column 10 on a substrate 1, (a) an amorphous, quadrangular pyramid-like GaN2a is grown at a lower temperature than usual. When increasing temperature up to the normal growth temperature, (b) the duration is made longer than usual to make the GaN2a polycrystalline and to form a nucleation layer 2 having a large variance in height. Then, the nano-column 10 is formed thereon by the normal method. Thus, the film thickness or composition of a light emitting layer 5 (especially quantum well) varies, so that different wavelengths can be assigned to the respective nano-columns 10 and light emission can be also realized in a plurality of wavelength areas without using phosphor. In addition, (f) electrodes 7 and 8 are uniformly formed on the structure, resulting in injecting current uniformly at the same time as well as permitting high light emitting efficiency. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a semiconductor light-emitting element that emits light by combining electrons and holes in a semiconductor, a lighting device using the same, and a method for manufacturing the semiconductor light-emitting element. In particular, the semiconductor light-emitting element has a columnar shape called a nanocolumn. The present invention relates to a structure having a plurality of crystal structures.

  In recent years, using a nitride semiconductor (hereinafter referred to as nitride), a light emitting layer is formed therein, an electric current is injected from the outside, and electrons and holes are combined in the light emitting layer to emit light. The development of the light emitting element to be made is remarkable. In addition, the phosphor is excited by a part of the light emitted from the light emitting element, and the white light obtained by mixing the light generated from the phosphor and the light from the light emitting element is used as a light source to be applied to the lighting device. Is attracting attention. However, there is still no product that satisfies the high efficiency requirement. The reason for this is that there are mainly two factors that reduce the efficiency when focusing on the process of obtaining white light using a phosphor.

  First, a part of energy is lost (Stokes loss) by wavelength conversion. Specifically, the excitation light emitted from the light emitting element and absorbed by the phosphor is wavelength-converted to light having energy lower than that of the light generated from the light emitting element, and is emitted to the outside again. At that time, a loss is caused by the difference in energy between the excitation light from the light emitting element and the emission light from the phosphor, and the efficiency is lowered.

  The second is a decrease in efficiency due to non-radiative recombination in the phosphor (decrease in internal quantum efficiency of the phosphor). Specifically, the crystal defects present in the phosphor function as non-radiative recombination centers, and some of the carriers generated in the phosphor by the excitation light do not contribute to light emission and are captured by the crystal defects. This is because the luminous efficiency of the phosphor is lowered.

  Therefore, when white light is obtained through the above-described two steps using a phosphor, the efficiency is remarkably lowered, which prevents high efficiency of the light emitting element. Therefore, a semiconductor light emitting device capable of emitting light at a plurality of wavelengths without using a phosphor has been attracting attention. Non-patent document 1 is given as an example of an attempt to manufacture such a semiconductor light emitting device.

According to the prior art, after an n-type GaN layer is formed on a sapphire substrate by an MOCVD (metal organic chemical vapor deposition) apparatus, light is emitted at two different wavelengths corresponding to blue and green at different wavelengths. Two quantum wells designed in (1) are formed in the light emitting layer, and then a p-type GaN layer is formed. By adopting such a structure, it is possible to simultaneously emit the blue and green light with one light emitting element.
YD Qi, H. Liang, W. Tang, ZD Lu, Kei May Lau `` Dual Wavelength InGaN / GaN multi-quantum well LEDs grown by metalorganic vapor phase epitaxy '' (Journal of Crystal Growth 272 (2004) 333-340)

However, the above-described conventional technique has two main problems. The first is a decrease in luminous efficiency due to a high threading dislocation density. Specifically, in the above-described prior art, a thin GaN layer is used as a base on a sapphire substrate, and therefore, threading dislocations with a high density of at least about 10 ⁷ cm ⁻² are generated inside the GaN crystal, resulting in a decrease in luminous efficiency. I will let you. In particular, when trying to obtain a highly efficient red color using InGaN, the difficulty of crystal growth increases as the In composition in InGaN increases. Therefore, in order to form high-quality InGaN, it is indispensable to obtain a higher-quality base crystal, which is difficult to realize.

  The second is non-uniform carrier injection into the well layer. Specifically, in the above-described prior art, quantum wells that emit light at different wavelengths with respect to current are arranged in series in one light-emitting element, and electrons and holes injected into each quantum well in contrast. This is because it is difficult to uniformly inject carriers into both quantum wells. For this reason, the density of carriers injected into each quantum well changes depending on the amount of current injection, and as a result, a phenomenon occurs in which the emission color changes. Therefore, handling of the light emitting element becomes difficult.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor light emitting element capable of simultaneously emitting light in a plurality of wavelength regions without using a phosphor and realizing high light emission efficiency at each wavelength, an illumination device using the same, and a semiconductor light emitting device. It is providing the manufacturing method of an element.

  The semiconductor light-emitting device of the present invention has a columnar shape in which an n-type nitride semiconductor layer or an n-type oxide semiconductor layer, a light-emitting layer, and a p-type nitride semiconductor layer or a p-type oxide semiconductor layer are sequentially stacked on a substrate. In the semiconductor light emitting device having a plurality of crystal structures, the plurality of columnar crystal structures are different in thickness of the light emitting layer due to different growth rates.

  The method for manufacturing a semiconductor light emitting device of the present invention includes an n-type nitride semiconductor layer or an n-type oxide semiconductor layer, a light-emitting layer, a p-type nitride semiconductor layer or a p-type oxide semiconductor layer on a substrate. In a method for manufacturing a semiconductor light emitting device comprising a plurality of columnar crystal structures laminated in sequence, a step of depositing a nucleation layer serving as a seed of the columnar crystal structure on the substrate, and a heat treatment of the nucleation layer Then, the method includes a step of providing variation in the height of the nucleus, and a step of sequentially stacking the layers of the columnar crystal structure.

  According to said structure, the columnar crystal structure which laminated | stacked the n-type nitride semiconductor layer or n-type oxide semiconductor layer, the light emitting layer, and the p-type nitride semiconductor layer or the p-type oxide semiconductor layer in order on the board | substrate. Semiconductor light emitting device having a plurality of bodies (nanocolumns), an n-type electrode formed on the substrate, and a p-type electrode formed on the p-type nitride semiconductor layer or p-type oxide semiconductor layer In the method, the variation in the height of the nuclei is increased by performing a heat treatment after depositing a nucleation layer that becomes a seed of the nanocolumn at a low temperature. Thereafter, when the layers of the columnar crystal structure are sequentially stacked at a high temperature, the formation speed of nanocolumns formed on high nuclei is preferentially increased, while the formation speed of nanocolumns formed on low nuclei is The film thickness of the light emitting layer (especially the quantum well) formed inside the nanocolumn and the composition thereof can be similarly varied.

  Therefore, different wavelengths can be assigned to each of the plurality of nanocolumns, and light can be emitted simultaneously in a plurality of wavelength regions without using a phosphor. In addition, by forming electrodes uniformly on the structure, it is possible to inject current uniformly into nanocolumns having different emission wavelengths at the same time, and achieve high emission efficiency while maintaining the respective emission wavelengths. be able to.

  Furthermore, the semiconductor light emitting device of the present invention includes an insulator filled in a gap between adjacent columnar crystal structures at least in the p-type nitride semiconductor layer or the p-type oxide semiconductor layer. It is characterized by.

  The method for manufacturing a semiconductor light-emitting device according to the present invention includes: a columnar crystal structure adjacent to at least a portion of the p-type nitride semiconductor layer or p-type oxide semiconductor layer after the layers of the columnar crystal structure are stacked; A step of filling the gap between the insulator and a step of continuously forming a p-type electrode on the tip surface of the p-type nitride semiconductor layer or the p-type oxide semiconductor layer exposed from the insulator. It is characterized by that.

  According to the above configuration, the p-type electrode to be provided on the tip side of the nanocolumn is not a continuous film of the p-type nitride semiconductor layer or the p-type oxide semiconductor layer, but a p-type electrode (the p-type electrode). (Including a transparent conductive film when the electrode side is the light extraction surface). However, when forming the p-type electrode, at least the p-type nitride semiconductor layer or the p-type oxide semiconductor layer is filled with an insulator in the gap between adjacent nanocolumns.

  Therefore, even if the p-type electrode is continuously formed by a technique such as normal vapor deposition, the n-type nitride semiconductor layer or the n-type oxide semiconductor layer and the p-type nitride semiconductor layer or the p-type layer straddle the light emitting layer. It is possible to prevent the type oxide semiconductor layer from being short-circuited with the material for the p-type electrode. As a result, a highly efficient semiconductor light emitting device can be realized that takes advantage of the fact that the nanocolumn does not have threading dislocations inside.

  Furthermore, the lighting device of the present invention is characterized by using the semiconductor light emitting element.

  According to the above configuration, by using a semiconductor light emitting element that can simultaneously emit light in a plurality of wavelength regions without using a phosphor and can realize high light emission efficiency while maintaining the respective emission wavelengths. In order to obtain the same luminous flux (brightness and illuminance), a small and low power consumption lighting device can be realized.

  As described above, the semiconductor light-emitting device and the method for manufacturing the same according to the present invention include an n-type nitride semiconductor layer or n-type oxide semiconductor layer, a light-emitting layer, and a p-type nitride semiconductor layer or p-type oxide on a substrate. A plurality of columnar crystal structures (nanocolumns) sequentially stacked with a semiconductor layer; an n-type electrode on the substrate; and a p-type electrode on the p-type nitride semiconductor layer or the p-type oxide semiconductor layer, respectively In the formed semiconductor light-emitting device and the method for manufacturing the same, the dispersion of the height of the nuclei is increased by performing a heat treatment after depositing a nucleation layer that becomes a seed of the nanocolumn at a low temperature, and then the columnar crystal structure By laminating each layer of the body in order at a high temperature, the film thickness and composition of the light emitting layer (particularly the quantum well) formed inside the nanocolumn can be varied.

  Therefore, different wavelengths can be assigned to each of the plurality of nanocolumns, and light can be emitted simultaneously in a plurality of wavelength regions without using a phosphor. In addition, by forming electrodes uniformly on the structure, it is possible to inject current uniformly into nanocolumns having different emission wavelengths at the same time, and achieve high emission efficiency while maintaining the respective emission wavelengths. be able to.

  Furthermore, as described above, the illuminating device of the present invention can simultaneously emit light in a plurality of wavelength regions without using a phosphor, and can achieve high light emission efficiency while maintaining the respective emission wavelengths. The semiconductor light-emitting element that can be used is used.

  Therefore, it is possible to realize a small-sized and low power consumption lighting device for obtaining the same luminous flux (brightness and illuminance).

  FIG. 1 is a cross-sectional view schematically showing a manufacturing process of a light-emitting diode that is a semiconductor light-emitting element according to an embodiment of the present invention. In the present embodiment, it is assumed that the growth of the nanocolumn 10 is performed by metal organic chemical vapor deposition (MOCVD), but the growth method of the nanocolumn 10 is not limited to this, and molecular beam epitaxy (MBE). It is well known that nanocolumns can be produced even using an apparatus such as hydride vapor phase epitaxy (HVPE). Hereinafter, an MOCVD apparatus is used unless otherwise specified.

  Further, silicon carbide (SiC) is used for the substrate 1, so that it can be taken out of the light emitting diode without absorbing light emitted from the blue to long wavelength side. Further, since SiC can ensure conductivity by adding impurities, the n-type electrode 8 can be directly formed on the substrate 1. However, the board | substrate 1 is not limited to SiC, What is necessary is just to have electroconductivity and translucency with respect to light emission wavelength. For example, gallium nitride, gallium oxide, or the like that has conductivity and is transparent in the visible light region can be used.

  In the light-emitting diode according to the present embodiment, the nanocolumn 10 composed of an n-type nanocolumn GaN layer 3, a light-emitting layer 5, and a p-type nanocolumn GaN layer 4 is formed on an n-type conductive substrate 1, A p-type electrode 7 is formed on the tip of the p-type nanocolumn GaN layer 4, and the n-type electrode 8 is formed on the back surface of the substrate 1. It should be noted that in the present embodiment, when the nanocolumn 10 is grown, as shown in FIG. 1B, the nucleation layer 2 having a large variation is formed on the substrate 1.

For the formation of the nucleation layer 2, the pressure of the MOCVD reactor is set to a reduced pressure of, for example, 76 Torr, and the substrate temperature is set to 500 ° C. lower than the growth temperature of the normal nanocolumn 10. Thus, by setting the conditions different from the normal GaN growth conditions, the GaN layer grows in the plane direction and grows in an amorphous and quadrangular pyramid shape. Then, hydrogen gas (H ₂ ) as a carrier gas, trimethyl gallium (Ga (CH ₃ ) ₃ ) as a Ga raw material, and ammonia (NH ₃ ) as a nitrogen raw material are supplied for 5 minutes, so that in FIG. As shown, amorphous GaN 2a is formed to a thickness of approximately 25 nm. Thereafter, the substrate temperature is raised to about 1050 ° C., which is the normal growth temperature of the n-type nanocolumn GaN layer 3, and the amorphous GaN 2a is polycrystallized. At this time, the heating time is usually about 2 minutes for the above temperature rise, but for example, by extending it to about 30 minutes, the amorphous GaN 2a is condensed, and in FIG. As shown, the nucleation layer 2 having a large variation in height is formed. The degree of variation can be controlled by controlling the length of the heat treatment time.

Subsequently, the nanocolumn 10 is formed on the nucleation layer 2 formed as described above by a usual method. First, the growth temperature is maintained at 1070 ° C. and the furnace pressure is maintained at 76 Torr. Then, by supplying silane (SiH ₄ ) while supplying the hydrogen gas, trimethylgallium and ammonia, Si is added as an impurity, and the n-type nanocolumn GaN layer 3 having n-type conductivity is grown. At this time, the height of the nanocolumns 10 formed on the nucleation layer 2 varies depending on the height variation of the nucleation layer 2. Specifically, the height of nanocolumns formed on high nuclei is high, while the height of nanocolumns on low nuclei is low. However, the material of the nanocolumn 10 is not limited to GaN. For example, InN, InGaN, AlGaN, AlN, ZnO, MgZnO, and the like can be listed as candidates.

Next, the growth temperature is lowered to 700 ° C., and trimethylindium (In (CH ₃ ) ₃ ) is supplied while supplying the hydrogen gas, trimethylgallium and ammonia while maintaining the columnar structure, whereby InGaN / GaN. A light emitting layer 5 having a multiple quantum well structure is formed. The number of well layers was five. At this time, the growth rate of the nanocolumns with a high height is faster than that with the nanocolumns with a low height. Consequently, the thickness of the well layer and the barrier layer is inevitably increased, which is influenced by the quantum confined Stark effect. A light emitting layer that emits light on the long wavelength side can be formed. On the other hand, in the light emitting layer formed on the nanocolumn having a low height, the thickness of the well layer and the barrier layer is reduced, and the light emitting layer emitting light on the short wavelength side is formed by the quantum effect.

Next, by supplying cyclopentadienylmagnesium (Mg (C ₅ H ₅ ) ₂ ) while supplying hydrogen gas, trimethylgallium and ammonia under the same conditions as those for forming the n-type nanocolumn layer 3, Mg is added as an impurity to grow the p-type nanocolumn GaN layer 4 having p-type conductivity. Similar to the n-type nanocolumn layer, the material of the p-type nanocolumn layer is not limited to GaN. Thus, the nanocolumn 10 can be formed as shown in FIG.

Subsequently, as shown in FIG. 1D, the insulator 6 is embedded in the gap between the adjacent nanocolumns 10. The insulator 6 is filled with SOG (Spin on Glass), liquid SiO ₂ or the like (hereinafter described as SOG). When the SOG is spin-coated, it is in a liquid state, so that it penetrates into the gaps between the nanocolumns 10 and controls the spacing between the nanocolumns 10, the viscosity of the SOG, etc. It is easy to enter the substrate 1 side.

  Thereafter, the SOG is solidified by baking at 400 ° C., and the SOG is etched on the entire surface using buffered hydrofluoric acid so that only the p-type nanocolumn GaN layer 4 of the nanocolumn 10 is exposed, as shown in FIG. As described above, the SOG buried layer as the insulator 6 is formed so as to cover at least the p-type nanocolumn GaN layer 4 and the light emitting layer 5.

  Further, as shown in FIG. 1 (f), a transparent electrode made of, for example, Ni / Au and capable of making ohmic contact with the p-type nanocolumn GaN layer 4 at the tip of the nanocolumn 10 is continuously formed by vapor deposition or the like. The p-type electrode 7 is formed, and an n-type electrode 8 made of, for example, Ti / Au and capable of being in ohmic contact with the substrate 1 is continuously formed on the back surface of the substrate 1 by vapor deposition or the like. The structure of the light emitting diode of the form is completed.

  By manufacturing in this way, the film thickness of the light emitting layer 5 (especially quantum well) formed in the nanocolumn 10 and also the composition can be varied, and the plurality of nanocolumns 10 can be red, green, blue. It becomes a monochromatic light source which radiates | emits one of these, and can be light-emitted simultaneously in a several wavelength range, without using fluorescent substance. Further, by forming the electrodes 7 and 8 uniformly on the structure, it is possible to inject current uniformly into the nanocolumns 10 having different emission wavelengths at the same time. Efficiency can be realized.

  Furthermore, when growing the nanocolumns 10 having different heights as described above, the nucleation layer 2 is formed and only the heat treatment time is adjusted, so that the existing manufacturing equipment is used as it is. Can do.

  Here, when forming the p-type electrode 7 on the p-type nanocolumn GaN layer 4, for example, Reference 1 (Reference 1: Kikuchi, Nomura, Kishino “Development of a new functional device material using a nitride semiconductor nanocolumn crystal” ( When the p-type electrode is formed after epitaxially growing the p-type nanocolumn GaN layer while expanding the nanocolumn diameter, as described in the 2004 Fall Meeting of the Japan Society of Applied Physics (1st volume 4P-W-1)) When the diameter of the nanocolumns is increased and crystals with different plane orientations are mixed and grown, even if there are no threading dislocations in the nanocolumns, a large number of threading dislocations are generated in the expanded part. Therefore, much of the light generated in the light emitting layer is absorbed by the threading dislocation.

  On the other hand, by embedding the insulator 6 as described above, the n-type nanocolumn GaN layer 3 straddles the light emitting layer 5 even if the p-type electrode 7 is continuously formed by a technique such as ordinary vapor deposition. And the p-type nanocolumn GaN4 can be prevented from being short-circuited by the material for the p-type electrode 7, and high-efficiency light emission can be performed taking advantage of the nanocolumn 10 without threading dislocations. The insulator 6 does not need to be filled over the entire length of the nanocolumn 10 (up to the base end side), at least a part of the p-type nanocolumn GaN layer 4 is blocked, and the metal of the p-type electrode 7 is n It is sufficient that the mold nanocolumn GaN layer 3 cannot be penetrated.

  By using the light emitting diode configured as described above for the lighting device, it is possible to emit light simultaneously in a plurality of wavelength regions without using a phosphor, and to obtain the same luminous flux (luminance, illuminance), it is small. A lighting device with low power consumption can be realized. In addition, since the light-emitting diode can be wired in the same manner as a conventional light-emitting diode, a highly efficient lighting device can be realized by simply exchanging elements without requiring a large change in the lighting device. .

  Although the above embodiment has been described using a nitride semiconductor, the present invention can also be applied to an oxide semiconductor. ZnO which is an oxide semiconductor has extremely excellent characteristics as a light-emitting element. The exciton binding energy is 60 meV, 2 to 3 times that of GaN, the internal quantum efficiency may be higher than that of GaN, and the refractive index is about 2. It is small compared to the above, and is overwhelmingly advantageous in terms of light extraction. It is also attractive from a commercial basis that the materials themselves are inexpensive.

  Therefore, although the above-described embodiment describes a GaN-based nanocolumn that is a nitride semiconductor, the same structure of a semiconductor light-emitting element is similarly applied to ZnO that is an oxide semiconductor that is similar in crystal structure. Can be produced. The details are as follows.

  Both GaN and ZnO have a hexagonal crystal structure, and the lattice constants of the crystals are close. The band gap is also close to 3.4 for GaN and 3.3 for ZnO. Both are direct transition semiconductors. Therefore, if a nanocolumn is formed of GaN, a nanocolumn can be formed of ZnO. In fact, in Document 2, ZnO nanocolumns (called nanorods in this document) are formed on a sapphire substrate using MOCVD (Reference 2: WIPark, YHJun, SWJung and Gyu-Chul). Yi Appl. Phys. Lett. 964 (2003)).

It is sectional drawing which shows typically the manufacturing process of the light emitting diode which is a semiconductor light-emitting device concerning one Embodiment of this invention.

Explanation of symbols

1 n-type conductive substrate 2 nucleation layer 2a amorphous GaN
3 n-type nanocolumn GaN layer 4 p-type nanocolumn GaN layer 5 light emitting layer 6 insulator 7 p-type electrode 8 n-type electrode 10 nanocolumn

Claims (5)

A plurality of columnar crystal structures in which an n-type nitride semiconductor layer or an n-type oxide semiconductor layer, a light emitting layer, and a p-type nitride semiconductor layer or a p-type oxide semiconductor layer are sequentially stacked on a substrate; In a semiconductor light emitting device comprising:
The plurality of columnar crystal structures have different growth rates, and thus the thickness of the light emitting layer is different.   2. The semiconductor light emitting device according to claim 1, wherein at least a portion of the p-type nitride semiconductor layer or the p-type oxide semiconductor layer includes an insulator filled in a gap between adjacent columnar crystal structures. element.   An illumination device using the semiconductor light emitting device according to claim 1. A plurality of columnar crystal structures in which an n-type nitride semiconductor layer or an n-type oxide semiconductor layer, a light emitting layer, and a p-type nitride semiconductor layer or a p-type oxide semiconductor layer are sequentially stacked on a substrate; In a method for manufacturing a semiconductor light emitting device comprising:
Depositing a nucleation layer to be a seed of the columnar crystal structure on the substrate;
Heat treating the nucleation layer to vary the height of the nuclei; and
And a step of sequentially stacking the layers of the columnar crystal structure. After laminating each layer of the columnar crystal structure, filling a gap between the columnar crystal structure and an insulator in at least a portion of the p-type nitride semiconductor layer or p-type oxide semiconductor layer;
5. The semiconductor light emitting device according to claim 4, wherein a step of continuously forming a p-type electrode on a tip surface of the p-type nitride semiconductor layer or the p-type oxide semiconductor layer exposed from the insulator is performed. Manufacturing method.

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