JP2004288757A - Semiconductor light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor light emitting element which is improved in luminous efficiency. <P>SOLUTION: The semiconductor light emitting element 10 is equipped with a substrate 1, an underlying layer 2 made of first nitride semiconductor epitaxially grown on the substrate 1, and a light emitting layer 5 made of second nitride semiconductor provided on the underlying layer 2. In the first nitride semiconductor, the Al content amount is 50 atom% or more against the sum of III element contents, a dislocation density is 10<SP>11</SP>/cm<SP>2</SP>or below, and the half band width of an X-ray locking curve on a (002) plane is 200 sec or below. The second nitride semiconductor contains one or more elements selected from a group composed of rare earth elements and transition metal elements as additive elements. The light emitting layer is thermally treated at a temperature above 1,300°C. In the second nitride semiconductor, an Al content amount is 20 atom% or more against the sum of III element contents. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device.
[0002]
2. Description of the Related Art In recent years, demands for light-emitting diodes (LEDs) of various colors have been increasing. LED consumes less power, since longer life, so far not only as LED for mere display, such as, reduction of power consumption, in terms of CO ₂ reduction due to energy consumption reduction, the increased demand for lighting Is expected.
As LEDs, GaAs, AlGaAs, GaP, GaAsP, InGaAlP, etc. LEDs from red to yellow-green have been put to practical use, and they have been used in various applications especially for display. Was. In recent years, blue and green LEDs have been realized in a GaN-based system, so that almost all colors can be arranged and displayed in all colors, and a full-color display can be realized. In particular, LEDs with higher efficiencies of the three primary colors are being craved all over the world as lighting devices that can solve environmental problems with low energy.
[0004] In view of such circumstances, attempts have been made to produce an ultraviolet LED and cause the phosphors of the three primary colors to emit light with the ultraviolet rays to obtain a white LED. However, the principle of this method is basically the same as that of a fluorescent lamp, in which ultraviolet light emitted by mercury discharge in a fluorescent lamp is replaced with an ultraviolet LED. Therefore, there is a disadvantage in terms of cost since phosphors of three primary colors are separately required.
[0005] The present applicant has proposed a semiconductor light emitting device which can be suitably used as an LED in Patent Document 1. In this device, the underlying layer is formed of a high-quality crystal Al-containing nitride semiconductor having a half width of an X-ray rocking curve of 90 sec or less, and a light emitting layer made of an AlGaN-based nitride semiconductor is formed thereon. .
[Patent Document 1]
JP-A-2002-261324
The present inventor has further studied this semiconductor light emitting device and has conducted research for improving the luminous efficiency thereof. This is because the improvement of the luminous efficiency is the most important for practical use of the present semiconductor light emitting device.
An object of the present invention is to provide a semiconductor light emitting device including a substrate, an underlayer made of a nitride semiconductor epitaxially grown on the substrate, and a light emitting layer made of the nitride semiconductor provided on the underlayer. Is to improve the luminous efficiency.
[0008]
SUMMARY OF THE INVENTION The present invention provides a substrate, an underlayer made of a first nitride semiconductor epitaxially grown on the substrate, and a light emitting layer made of a second nitride semiconductor provided on the underlayer. A semiconductor light emitting device comprising:
The first nitride semiconductor has an Al content of 50 atomic% or more based on the total content of the group III elements, a transition density of 10 ¹¹ / cm ² or less, and an X-ray rocking curve of a (002) plane. The half-width is 200 sec or less, the second nitride semiconductor contains at least one element selected from the group consisting of rare earth elements and transition metal elements as an additional element, and the light-emitting layer has a temperature of 1300 ° C or higher. The heat treatment is performed, and in the second nitride semiconductor, the Al content is equal to or greater than 20 atom% with respect to the total content of the group III elements.
The present inventor has proposed that when a rare earth element or a transition metal element is added as a light emitting element to a light emitting layer, the second nitride semiconductor may have an Al content of 20 atoms with respect to the total content of Group III elements. % Or more, and the heat treatment (or annealing treatment) of the light emitting layer at a temperature of 1300 ° C. or more has been considered. As a result, the inventors have found that the luminous efficiency of the device is significantly improved, and have reached the present invention.
From the viewpoint of improving the luminous efficiency of the device, the maximum temperature during the heat treatment of the light emitting layer is more preferably 1350 ° C. or higher, more preferably 1400 ° C. or higher, and more preferably 1450 ° C. or higher. Is most preferred. In addition, from the same viewpoint, it is more preferable that the maximum temperature during the heat treatment of the light emitting layer be 1550 ° C. or less.
In the heat treatment of the light emitting layer, the holding time at the highest temperature is preferably 1 second or more from the viewpoint of improving the luminous efficiency. From the viewpoint of crystallinity deterioration, the holding time at the highest temperature is preferably 5 minutes or less.
From the viewpoint of further improving the luminous efficiency of the device, the Al content relative to the total content of the group III elements in the light emitting layer is preferably at least 30 atomic%, more preferably at least 40 atomic%. More preferred.
[0013]
FIG. 1 is a sectional view schematically showing one example of a semiconductor light emitting device of the present invention. The element 10 includes a substrate 1, an underlayer 2 formed on the substrate 1, a conductive layer 3 made of a nitride semiconductor formed on the underlayer 2, a cladding layer 4 made of a nitride semiconductor, a light emitting layer 5, A cladding layer 6 made of a nitride semiconductor and a conductive layer 7 made of a nitride semiconductor are provided. A part of the conductive layer 3 is exposed without being covered by the cladding layer 4. An n-electrode 8 is formed on an exposed surface of conductive layer 3. A p-electrode 9 is formed on conductive layer 7.
The substrate is made of an oxide single crystal such as sapphire single crystal, ZnO single crystal, LiAlO ₂ single crystal, LiGaO ₂ single crystal, MgAl ₂ O ₄ single crystal, MgO single crystal, etc., a Si single crystal, a SiC single crystal or the like. group IV or IV-IV monocrystalline, GaAs single crystal, AlN single crystal, GaN single crystal, and III -V group single crystal such as AlGaN single crystal, such as boride single crystal such as ZrB _2, a known substrate materials Can be configured.
Further, on the above-mentioned single crystal substrate, a single crystal of oxides such as ZnO single crystal and MgO, a single crystal of Group IV or IV-IV such as a single crystal of Si, a single crystal of SiC, a single crystal of GaAs, It is also possible to use an epitaxial substrate provided with an epitaxially grown film made of a group III-V single crystal such as an InP single crystal or a mixed crystal thereof.
Each layer constituting the semiconductor light emitting device is formed by various thin film formation methods such as a metal organic chemical vapor deposition method (MOCVD method), a CVD method such as a hydride vapor phase epitaxy method (HVPE method), and a molecular beam epitaxy method (MBE method). It can be manufactured according to technology.
The rare earth element and the transition metal element added to the light emitting layer emit light having a wavelength specific to these elements when excited by obtaining energy from the outside. Therefore, by including such a rare earth element and / or transition metal element as an additional element in the light emitting layer, the additional element is excited by light emission from the light emitting layer, and emits light having a specific wavelength.
Therefore, the kind of the additive element to be added to the light emitting layer is appropriately selected from the rare earth element and the transition metal element as needed, and the light emission of an arbitrary chromaticity is obtained by utilizing the light emission from this additive element. Can be easily generated. Further, two or more kinds of additive elements can be used in combination.
The following are particularly preferred as such additional elements.
Tm, Er, Cr, Eu, Pr.
The nitride semiconductor constituting each layer of the semiconductor light emitting device contains one or more elements selected from the group consisting of Al, Ga and In, and may contain two or more kinds. Each layer may contain one or more elements selected from the group consisting of Mg, Be, Zn, Si, P, As, O and B. Further, trace impurities or unavoidable impurities contained in the film forming conditions, the raw materials, and the material of the reaction tube may be contained.
The underlayer 2 contains 50 atomic% or more of Al, has a transition density of 10 ¹¹ / cm ² or less, and has a half value width of the X-ray rocking curve on the (002) plane of 200 seconds or less. Forming the light emitting layer 5 on the underlayer 2 having such a good crystal quality is a prerequisite for improving the luminous efficiency of the device.
From the viewpoint of improving the luminous efficiency of the device, the transition density is preferably 5 × 10 ¹⁰ / cm ² or less, more preferably 1 × 10 ¹⁰ / cm ² or less. More preferably, the half width of the X-ray rocking curve on the (002) plane is 100 seconds or less.
In the nitride semiconductor constituting the underlayer 2, the Al content relative to the total content of the group III elements is at least 50 atomic%. The Al content with respect to the total content of the group III elements is more preferably 80 atomic%, and the nitride semiconductor is most preferably AlN. In addition to Al, In or Ga may be contained.
In order to obtain an underlayer having the above-mentioned half width and transition density, the substrate is heated to preferably 1100 ° C. or higher, more preferably 1150 ° C. or higher by MOCVD using a predetermined raw material supply gas.
The upper limit of the formation temperature of the underlayer is not particularly limited, but is preferably 1250 ° C. As a result, it is possible to effectively suppress surface roughness depending on the material composition of the nitride semiconductor constituting the underlayer, and further, diffusion of a composition component in the underlayer. Note that the “forming temperature” does not mean a temperature for controlling the heater, but means a substrate temperature when the base film is formed.
The thickness of the underlayer 2 is preferably 0.5 μm or more, more preferably 1 μm to 3 μm. In order to improve the crystallinity of the conductive layer, the cladding layer, and the light-emitting layer formed on the base layer, it is preferable that the base layer be formed thick. However, if the underlayer is too thick, cracks or peeling may occur.
The nitride semiconductor constituting the light emitting layer 5 is particularly preferably i-AlGaN. The above-mentioned additional element is added to the light emitting layer. The content of the additional element is not particularly limited. However, by setting the content of the additional element to 0.01 atomic% or more, the luminous efficiency of the device can be improved. On the viewpoint, the content of the additional element may more preferably be 0.1 atomic% or more. In addition, from the viewpoint of improving the crystallinity of the nitride semiconductor forming the light emitting layer, the content of the additional element is preferably set to 7 atomic% or less, more preferably 3 atomic% or less.
A buffer layer can be provided between the underlayer and the substrate. It is preferable that the buffer layer contains Al, and the Al content increases continuously or stepwise from the substrate side toward the base layer side.
[0029]
Example (Example 1)
A 2-inch diameter 630 μm thick sapphire substrate was ultrasonically cleaned with acetone and isopropyl alcohol, washed with water and dried, and then placed in a metal organic chemical vapor deposition (MOCVD) apparatus. Each gas system of NH ₃ , TMA, TMG, Cp ₂ Mg, and SiH ₄ is attached to the MOCVD apparatus as a gas system. The pressure in the apparatus was set to 50 mBar, and the temperature of the substrate 1 was increased to 1200 ° C. while flowing H ₂ at a flow rate of 1 m / sec. Thereafter, NH ₃ gas was flowed together with the hydrogen carrier gas for 5 minutes to nitride the main surface of the substrate. As a result of the analysis by ESCA, it was found that a nitrided layer was formed on the main surface of the substrate 1 by this surface nitriding treatment, and the nitrogen content at a depth of 1 nm from the main surface was 7 atomic%.
Next, TMA and NH ₃ were combined and flowed at a flow rate of 5 m / sec to epitaxially grow the AlN layer as the underlayer 2 to a thickness of 1 μm. The dislocation density of this AlN layer 2 was 2 × 10 ¹⁰ / cm ² , and the half-width of the X-ray diffraction rocking curve on the (002) plane was 60 seconds, indicating that the AlN layer was a good quality AlN layer. Further, when the surface flatness was confirmed, it was found that Ra in the range of 5 μm was 1.5 angstroms, and that the surface had an extremely flat surface.
Next, the pressure was set to 100 mBar, the temperature of the substrate was raised to 1150 ° C., and TMA, TMG, NH ₃ , SiH ₄ and H ₂ and N ₂ as carrier gases were flowed at a flow rate of 5 m / sec. Then, n-Al _0.45 Ga _0.65 N layers 3 and 4 were epitaxially grown to a thickness of 2 μm. The dislocation density of the n-Al _0.45 Ga _0.65 N layers 3 and 4 was 1 × 10 ⁹ / cm ² , and the half-width of the X-ray rocking curve on the (002) plane was 100 seconds.
[0032] Here, once the substrate is removed from the MOCVD apparatus, using the sputtering apparatus were placed _Al 0.4 _{Ga 0.6} N target containing 1% Eu, _Al 0.4 _{Ga 0} containing 1% _{Eu. 6} N layer (light-emitting layer 5) was 10nm deposited. Thereafter, the apparatus was set in an annealing apparatus, and an annealing treatment was performed for 1 minute at 1500 ° C. in dry air to activate the rare earth element.
Then, the substrate was set in a MOCVD apparatus, the pressure was set to 100 mBar, the temperature of the substrate was raised to 1000 ° C., and TMA, TMG, NH ₃ , Cp 2 Mg, and H ₂ and N ₂ as carrier gases were added in total. At a flow rate of 5 m / sec, the p-Al _0.45 Ga _0.65 N layer 6 was epitaxially grown to a thickness of 5 nm and the p-Al _0.05 Ga _0.95 N layer 7 to a thickness of 0.2 μm. Finally, annealing was performed at 750 ° C. for 5 minutes in a nitrogen atmosphere to activate the p-type layer.
After the growth is completed, a part of the multilayer film formed as described above is removed until the AlGaN layers of the n-type conductive layers 3 and 4 are exposed. N-electrode 8 was formed. A p-electrode 9 made of Au / Ni was formed on p-GaN layers as the conductive layers 6 and 7.
Next, when a voltage of 5 V was applied between the p-electrode 9 and the n-electrode 8 and a current of 20 mA was passed, highly efficient red light emission was confirmed. That is, it was confirmed that the semiconductor light emitting device of the present invention can operate as a practical red light emitting device.
(Comparative Example 1)
A semiconductor light emitting device was manufactured in the same manner as in Example 1. However, the condition of the annealing treatment of the light emitting layer for activating the rare earth was changed to 1200 ° C. for 5 minutes. As a result, although red light emission was confirmed, the light emission luminance could be secured only 1/10 or less of Example 1.
(Comparative Example 2)
A semiconductor light emitting device was manufactured in the same manner as in Example 1. However, the compositions of the n-type layers 3 and 4 were changed to Al _0.2 Ga _0.8 N. The composition of the light emitting layer 5 was changed to Al _0.15 Ga _0.85 N containing 1% Eu. The compositions of the p-type layers 6 and 7 were changed to Al _0.2 Ga _0.8 N and Al 0.05 Ga 0.95 N, respectively. As a result, although red light emission was confirmed, the light emission luminance could be secured only 1/10 or less of Example 1.
(Comparative Example 3)
After performing the pretreatment of the substrate in the same manner as in Example 1, the substrate was placed in an MOCVD apparatus, the pressure was set to 200 mBar, and the temperature of the substrate was raised to 550 ° C. while flowing H 2 at a flow rate of 1 m / sec. . Thereafter, TMG and NH3 were combined and flowed at a flow rate of 5 m / sec to grow a GaN layer as a buffer layer to a thickness of 20 nm. Next, the temperature of the substrate was raised to 1080 ° C., and TMG, NH ₃ , and H ₂ and N ₂ as carrier gases were combined and flowed at a flow rate of 1 m / sec, and the GaN layer as the underlayer 2 was formed to a thickness of 3 μm. It was epitaxially grown. The dislocation density of this GaN layer was 1 × 10 ⁹ / cm ² , and the half-width of the X-ray rocking curve on the (002) plane was 250 seconds.
Next, the pressure was set to 100 mBar, the temperature of the substrate was raised to 1150 ° C., and TMA, TMG, NH ₃ , SiH ₄ and H ₂ and N ₂ as carrier gases were flowed at a flow rate of 5 m / sec. Then, n-Al _0.45 Ga _0.65 N layers 3 and 4 were epitaxially grown to a thickness of 2 μm. The dislocation density of the n-Al _0.45 Ga _0.65 N layers 3 and 4 was 1 × 10 ₁₀ / cm ² , and the half-width of the X-ray rocking curve on the (002) plane was 350 seconds.
Thereafter, in the same manner as in Example 1, the substrate was once taken out of the MOCVD apparatus, and Eu was used as the light emitting layer 5 using a sputtering apparatus in which an Al _0.4 Ga _0.6 N target containing 1% of Eu was installed. Al _0.4 Ga _0.6 N containing 1% was deposited to a thickness of 10 nm. After that, it was set in an annealing apparatus, and an annealing treatment was performed at 1500 ° C. for 1 minute in dry air to activate the rare earth element. However, the underlying layer GaN was decomposed, and the grown AlGaN layer was removed. Peeling was observed occasionally, and the device structure could not be manufactured with high yield.
(Experiment for Changing Heat Treatment Conditions)
A semiconductor light emitting device was manufactured in the same manner as in Example 1. However, the annealing time of the light emitting layer for activating rare earth was set to 1 minute. Further, the maximum temperature during the annealing process was variously changed as shown in FIG. 2 (1000, 1100, 1200, 1300, 1400, 1500, 1600 ° C.). As a result, the emission intensity was significantly improved at a processing temperature of 1300 ° C. or higher.
(Experiment for Changing Al Composition)
A semiconductor light emitting device was manufactured in the same manner as in Example 1. At this time, as shown in FIG. 3, the Al composition of the light emitting layer 5 was changed to 0, 10, 20, 40, and 100%. Note that the Al compositions of the n-type layers 3 and 4 and the p-type layer 6 are changed to a value of (composition of light emitting layer−5)%. The annealing time of the light emitting layer for rare earth activation was fixed at 1500 ° C. for 1 minute. As a result of performing a cathodoluminescence measurement and evaluating the light-emitting characteristics from the light-emitting layer, the light-emitting intensity was significantly improved when the Al composition was 20% or more.
Although the present invention has been described in detail with reference to the embodiments of the present invention by giving specific examples, the present invention is not limited to the above contents and does not depart from the scope of the present invention. All modifications and changes are possible as far as possible.
For example, as a method of forming the light emitting layer, sputtering is exemplified. However, the light emitting layer may be formed by simultaneously flowing a material containing Eu by a CVD method, or Eu may be implanted by ion implantation. It is. In addition, it is also possible to appropriately mix In with the light emitting layer.
Further, in the device shown in FIG. 1, the function as a conductive layer can be given to the cladding layer 4 and the conductive layer 3 can be omitted. Similarly, the function as a conductive layer may be given to the cladding layer 6 and the conductive layer 7 may be omitted.
In the semiconductor light emitting device shown in FIG. 1, the lower layer around the light emitting layer 5 is made n-type and the upper layer is made p-type. However, they can be formed by reversing both layers.
Further, in the above embodiment, the AlGaN layer as the conductive layer 3 was directly formed on the AlN underlayer 2. However, a multilayer structure such as a buffer layer or a strained superlattice can be formed between them.
[0048]
As described above, according to the present invention, there are provided a substrate, an underlayer made of a nitride semiconductor epitaxially grown on the substrate, and a light emitting layer made of the nitride semiconductor provided on the underlayer. In such a semiconductor light emitting device, the luminous efficiency of the device can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a semiconductor light emitting device 10 according to the present invention.
FIG. 2 is a graph showing a relationship between a heat treatment temperature of a light emitting layer and a light emission intensity of a device.
FIG. 3 is a graph showing a relationship between a change in Al composition and a light emission intensity of the device.
[Description of Signs] 1 Substrate 2 Underlayer 3, 7 Conductive layer 4, 6 Cladding layer 5 Light emitting layer 10 Semiconductor light emitting element

Claims (5)

A semiconductor light emitting device comprising a substrate, an underlayer made of a first nitride semiconductor epitaxially grown on the substrate, and a light emitting layer made of a second nitride semiconductor provided on the underlayer,
The first nitride semiconductor has an Al content of 50 atomic% or more based on the total content of the group III elements, a transition density of 10 ¹¹ / cm ² or less, and an X-ray rocking curve of a (002) plane. The half width is 200 seconds or less, the second nitride semiconductor contains at least one element selected from the group consisting of rare earth elements and transition metal elements as an additional element, and the light-emitting layer has a temperature of 1300 ° C. or more. Wherein the Al content in the second nitride semiconductor is at least 20 atomic% based on the total content of the group III elements. 2. The semiconductor light emitting device according to claim 1, wherein the content of the additional element in the light emitting layer is 0.01 to 7 atomic%. 3. The semiconductor light emitting device according to claim 1, wherein the first nitride semiconductor has an Al content of 80 atomic% or more based on the total content of the group III elements. 4. The semiconductor light emitting device according to claim 3, wherein the first nitride semiconductor is aluminum nitride. 5. The semiconductor light emitting device according to claim 1, wherein the first nitride semiconductor is formed at a deposition temperature of 1100 ° C. or higher by a metal organic chemical vapor deposition method. 6. element.

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