JP2013115277A - Hetero-junction light-emitting element manufacturing method - Google Patents

Abstract

Provided is a method capable of manufacturing a light emitting element even if a pn junction interface of a nitride semiconductor is open to the atmosphere without a post process requiring a long time and a large amount of power.
A composition or a mixture containing zinc and oxygen as main component elements and at least one selected from the group consisting of aluminum, gallium, and indium as subcomponent elements is used on a p-type nitride semiconductor layer. Thus, a method of manufacturing a heterojunction light-emitting element including a step of forming an n-type zinc oxide layer by a sputtering method or a vacuum evaporation method is provided.
[Selection] Figure 4

Description

  The present invention relates to a method for manufacturing a heterojunction light-emitting element.

  Conventionally, nitride-based compound semiconductors such as gallium nitride (GaN), indium nitride (InN), and aluminum nitride (AlN) directly have the minimum point of the conduction band and the maximum point of the valence band at close wave positions. Since it is a transition type compound semiconductor and has a wide energy gap, it is attracting attention as a short wavelength light source and an environmental resistant device. GaN has a wide energy gap of about 3.4 eV and can be used as a light emitting element that emits light ranging from blue to ultraviolet. In recent years, blue light-emitting diodes (LEDs) mainly composed of gallium nitride have been put into practical use, and the wavelength of blue is converted to yellow using phosphors, and ultra-high efficiency white LEDs exceeding 100 lm / W by blue and yellow light emission. Has started to spread, and is mainly used as a backlight for lighting equipment and liquid crystal displays (LCD).

  Advantages of the gallium nitride LED include that it has a very long life compared to white light bulbs and white organic EL, and can emit light at a very low voltage of about 3 to 6V. The structure and manufacturing method of a conventional typical surface mount type gallium nitride LED will be described below.

  A conventional gallium nitride LED has a light emitting layer in which an n-type gallium nitride semiconductor layer and a p-type gallium nitride semiconductor layer are pn-junction on a semiconductor substrate on which a buffer layer is formed (Patent Document 1). A material such as sapphire, spinel, SiC, Si, or ZnO is used for the semiconductor substrate, and a sapphire substrate is particularly used when forming gallium nitride with good crystallinity. The buffer layer is a GaN layer, an AlN layer, or the like. The gallium nitride semiconductor exhibits n-type conductivity without being doped with impurities. When forming a desired n-type gallium nitride semiconductor layer, for example, to improve luminous efficiency, Si, Ge, Se, Te, C, or the like is appropriately introduced as an n-type dopant. On the other hand, the p-type gallium nitride semiconductor layer is doped with p-type dopants such as Zn, Mg, Be, Ca, Sr, and Ba. Since a gallium nitride compound semiconductor is difficult to be converted into a p-type simply by doping with a p-type dopant, it may be converted into a p-type by heating in a furnace, low-energy electron beam irradiation, plasma irradiation, or the like after introduction of the p-type dopant. After the exposed surfaces of the p-type semiconductor and the n-type semiconductor are formed by etching or the like, each electrode having a desired shape is formed on the semiconductor layer by using a sputtering method, a vacuum evaporation method, or the like.

A metal organic vapor phase epitaxy method (hereinafter referred to as MOVPE method) is generally used to manufacture the n-type gallium nitride semiconductor layer and the p-type gallium nitride semiconductor layer. In the MOVPE method, a raw material containing Ga and a raw material containing nitrogen are supplied to a growth furnace using a carrier gas such as hydrogen. In many cases, trimethylgallium (Ga (CH ₃ ) ₃ ) is used as a raw material containing Ga, and ammonia (NH ₃ ) is used as a raw material containing nitrogen. In the growth furnace, Ga obtained by decomposing trimethylgallium and nitrogen obtained by decomposing ammonia adhere to the sapphire single crystal substrate, and a GaN crystal film grows.

  In the case of forming the p-type gallium nitride semiconductor layer, in addition to the above, a compound containing a p-type dopant element is further supplied as an organometallic gas stream using a carrier gas. As the compound containing a p-type dopant element, bis (cyclopentadienyl) magnesium or the like is typically used.

  Here, Mg adheres and remains on the piping for flowing the organic metal flow into the growth furnace, the piping for discharging and removing the organic metal flow from the growth furnace, and the inner surface of the growth furnace. Such residual Mg is desorbed into the atmosphere when the Si-doped n-type gallium nitride semiconductor layer is formed, and is taken into the n-type layer to cause carrier compensation.

  Furthermore, when nitride-based compound semiconductors are exposed to the p-layer interface or n-layer interface before the pn junction, the state of the junction interface changes, resulting in a significant decrease in the amount of emitted light and a longer emission wavelength. It is known to shift to the side. Therefore, after setting the sapphire substrate in the apparatus, it is necessary to produce an n-type gallium nitride semiconductor layer and a p-type gallium nitride semiconductor layer without opening the bonding surface to the atmosphere. In addition, dividing the film forming chamber into two types, n-type and p-type, has the problem that the equipment area is enlarged and the amount of capital investment is simply doubled. Realistic. In order to suppress carrier compensation of the n-type gallium nitride semiconductor layer due to residual Mg, and to suppress an increase in capital investment cost and an expansion of the equipment area, the n-type gallium nitride semiconductor layer is formed before the p-type gallium nitride semiconductor layer. The method to do is common. This method involves a post-process for heating and evacuating to remove residual Mg adhering to the piping and the growth furnace before the next batch is charged. This post-heating vacuum evacuation process between batches requires a lot of time for production and involves a great amount of power consumption, which is a problem.

  In response to these problems, LED manufacturers have devised methods such as increasing the substrate size from 2 inches to 6 inches and further increasing the growth furnace to install a plurality of substrates in one batch. However, the time and power consumed for manufacturing are still large, and while the demand for gallium nitride-based LEDs increases, there is a strong demand for significant reduction in manufacturing time and power consumption.

Japanese Patent No. 2927279

  In view of the above-mentioned problems of the prior art, the present invention eliminates the need for a post-process that requires a long time and a large amount of power, and allows a light-emitting element to be manufactured even when the pn junction interface of a nitride semiconductor is opened to the atmosphere. The purpose is to provide.

  The present invention uses a composition or mixture containing, on a p-type nitride semiconductor layer, zinc and oxygen as main component elements and at least one selected from the group consisting of aluminum, gallium and indium as subcomponent elements. And a method of manufacturing a heterojunction light-emitting element including a step of forming an n-type zinc oxide layer by a sputtering method or a vacuum evaporation method.

  According to the manufacturing method of the present invention, a light emitting device can be manufactured even when the pn junction interface of a nitride semiconductor is opened to the atmosphere, and residual Mg, which is essential in manufacturing a conventional gallium nitride LED, is removed. Therefore, it is possible to omit the post-heating vacuum evacuation process, and to significantly reduce the time and power consumption required for manufacturing.

2 is a cross-sectional view of a substrate having a p-type nitride semiconductor layer used in Embodiment 1. FIG. Sectional drawing of the heterojunction type light emitting element of Embodiment 1 in which the n-type zinc oxide layer was formed. Schematic which shows an example of a heat treatment process. Sectional drawing of the heterojunction type light emitting element of Embodiment 1 which formed the electrode. The photoluminescence spectrum of the mixed powder for sputtering targets used in the examples. The electron micrograph before the crucible baking of the n-type zinc oxide film | membrane formed into a film on the quartz substrate by the method similar to an Example. The electron micrograph after the crucible baking of the n-type zinc oxide film | membrane formed into a film on the sapphire + i-GaN board | substrate by the method similar to an Example. The electroluminescence spectrum of the heterojunction type light emitting element produced in the Example when the electric current which flows into an element is made constant.

  One embodiment and example of the present invention will be described below, but the present invention is naturally not limited to these forms, and can be appropriately modified and implemented without departing from the technical scope of the present invention. can do.

  One embodiment of the present invention includes, on the p-type nitride semiconductor layer, at least one selected from the group consisting of zinc and oxygen as main component elements and aluminum, gallium, and indium as subcomponent elements, This is a method for manufacturing a heterojunction light-emitting element, which includes a step of forming an n-type zinc oxide layer by sputtering or vacuum vapor deposition using a composition or a mixture.

  In a preferred aspect of the embodiment, the p-type nitride semiconductor layer is formed by metal organic vapor phase epitaxy.

  In a preferred aspect of the embodiment, the p-type nitride semiconductor layer is a p-type gallium nitride layer.

  In a preferred aspect of the embodiment, the n-type zinc oxide layer is formed by a high-frequency magnetron sputtering method or an electron beam evaporation method.

  In a preferred aspect of the embodiment, the amount of the subcomponent element is 0.03 at% or more and 3.0 at% or less with respect to zinc.

  One preferable aspect of the embodiment further includes a step of heat-treating the n-type zinc oxide layer in a non-oxidizing atmosphere in which zinc oxide and gallium oxide and / or phosphorus oxide coexist. At this time, it is preferable that the temperature of the said heat processing is the range of 700 to 1000 degreeC.

(Embodiment 1)
First, a p-type nitride semiconductor layer is prepared. FIG. 1 shows a substrate having a p-type nitride semiconductor layer used in this embodiment. An i-GaN layer 2 is formed on the sapphire substrate 1 as a buffer layer, and a p-GaN layer 3 is further formed thereon. Is formed. The sapphire substrate 1 is about 5 mm square, the thickness of the i-GaN layer 2 is 1.70 μm, and the thickness of the p-GaN layer 3 is 1.85 μm, but the dimensions are not limited thereto.

  The substrate is not limited to a sapphire substrate, and a quartz substrate, a silicon substrate, a gallium nitride substrate, a zinc oxide single crystal substrate, a SiC substrate, a spinel substrate, or the like can be used.

  The buffer layer is not limited to the GaN layer but may be an AlN layer or the like. Alternatively, the p-type nitride semiconductor layer may be formed directly on the substrate without the buffer layer.

  For the nitride semiconductor of the p-type layer, GaN is used. As the nitride semiconductor, for example, a nitride of at least one metal selected from the group consisting of aluminum, gallium, and indium can be used. GaN is preferred from the viewpoint of light emission characteristics.

  The p-GaN layer is doped with a p-type dopant. Examples of the p-type dopant include Zn, Mg, Be, Ca, Sr, Ba and the like, and Mg is preferable from the viewpoint of practicality.

  The p-type nitride semiconductor layer can be produced according to a known method, and is preferably produced by the MOVPE method.

  Next, an n-type zinc oxide layer 4 is formed on the p-GaN layer 3 by sputtering as shown in FIG. The n-type zinc oxide layer 4 is formed of a composition including at least one selected from the group consisting of zinc and oxygen as main component elements and aluminum, gallium, and indium as subcomponent elements.

  The sputtering method is not particularly limited as long as the n-type zinc oxide layer is formed, but a high-frequency magnetron sputtering method is preferable.

  Corresponding to the composition of the n-type zinc oxide layer 4, the sputtering target contains at least one selected from the group consisting of zinc and oxygen as main component elements and aluminum, gallium, and indium as subcomponent elements, A composition or mixture is used.

  The composition or mixture containing zinc as a main component means that zinc is 80% or more, more desirably 90% or more of the cation component element, and the composition or mixture contains oxygen as a main component. The term “oxygen” means that oxygen is 80% or more, more preferably 90% or more of the anion component element.

  In the composition of the n-type zinc oxide layer 4, at least one subcomponent element (first subcomponent element) selected from the group consisting of aluminum, gallium, and indium is essential. When zinc oxide contains the first subcomponent element, the green emission of zinc oxide is suppressed, and the ultraviolet emission is improved. In addition, the presence of the first subcomponent reduces the electrical resistivity of zinc oxide and exhibits remarkable n-type conductivity. This is presumably because a part of the divalent zinc site of zinc oxide is replaced with trivalent aluminum, gallium, and indium, whereby a donor level is formed in the forbidden band directly under the conductor.

  Correspondingly, the composition or mixture used for the target contains at least one selected from the group consisting of aluminum, gallium, and indium as the first subcomponent element.

  Of these three types of first subcomponent elements, gallium is the easiest to replace zinc, and aluminum and indium are not easily replaced. Accordingly, gallium is most likely to exhibit the brightness enhancement effect of zinc oxide, and gallium is most desirable in terms of characteristics. On the other hand, aluminum is the cheapest in terms of cost, and gallium and indium are rare and expensive compared to aluminum. Therefore, aluminum is most desirable in terms of cost. Compared to gallium and aluminum, using indium has less merit.

  The amount of the first subcomponent (the total amount of aluminum, gallium, and indium) is desirably 0.03 at% or more and 3.0 at% or less with respect to zinc. The amount of the first subcomponent is desirably 0.03 at% or more and 3.0 at% or less with respect to zinc. If the amount is less than 0.03 at%, the luminance enhancement effect of zinc oxide by the subcomponent is not remarkable. This is because even if the amount exceeds 0 at%, the brightness of the obtained n-type zinc oxide layer is not further improved and is wasted. However, even if it is less than 0.03 at% or more than 3.0 at%, the luminance is higher than when not used.

  Further, when the n-type zinc oxide layer 4 contains phosphorus as the second subcomponent, the luminance is increased. This is because the addition of phosphorus tends to promote the replacement of aluminum, gallium, and indium with Zn sites, so the electrical neutrality that occurs when aluminum, gallium, and indium replace the Zn sites. It is considered that the breakage is prevented by substituting phosphorus with an oxygen site of ZnO as an anion, and as a result, the substitution of aluminum, gallium, and indium is promoted, and the ultraviolet emission luminance is improved. Therefore, the composition or mixture used for the target may further contain phosphorus as the second subcomponent element. The desirable amount of phosphorus is 0.03 at% or more and 3.0 at% or less with respect to zinc, and the reason why this range is desirable is the same as that of the first subcomponent element.

  Further, the n-type zinc oxide layer 4 can emit light even if it contains a component other than zinc, oxygen, the first subcomponent, and the second subcomponent. For example, magnesium oxide dissolves in a small amount in zinc oxide and has the effect of increasing its band gap (that is, shifting the emission wavelength to the short wavelength side), but this zinc oxide-magnesium oxide solid solution system is also effective. By using the above-mentioned subcomponent, there is an effect of suppressing the green light emission and improving the ultraviolet light emission intensity. Therefore, the n-type zinc oxide layer 4 may contain magnesium instead of a part of zinc. Therefore, the composition or mixture used for the target may contain magnesium instead of a part of zinc, and at this time, a cation component combining zinc and magnesium is the main component.

  When the target is a mixture, as long as the target n-type zinc oxide layer 4 is obtained, there is no particular limitation on the type of compound to be mixed. For example, zinc oxide, aluminum oxide, gallium oxide, indium oxide, etc. These oxides can be used.

  When the target is a composition, zinc oxide, zinc hydroxide, zinc carbonate or the like is used as a zinc source, and oxides, hydroxides or carbonates of the respective metal elements are used as the first subcomponent element source. The composition of the target can be produced by firing these mixtures using the above.

  When phosphorus is used, a phosphorus compound can be used as the phosphorus source. For example, phosphorus oxide, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, or the like can be used as a safer compound.

  In view of ease of handling, when the target is a mixture, it is preferably a compression molded body, and when the target is a composition, it is preferably a sintered body.

  As the sputtering conditions, known conditions for forming a zinc oxide film by sputtering can be employed.

  By forming the n-type zinc oxide layer 4 on the p-GaN layer 3 by a sputtering method, the heterojunction light-emitting element 10 shown in FIG. 2 is obtained. In FIG. 2, an n-type zinc oxide layer 4 having a thickness of 360 to 380 nm is formed on a part of the p-GaN layer 3, and the light emitting element 10 has an L-shaped structure. The structure of the light emitting element 10 is not limited to the L-shaped structure, and the n-type zinc oxide layer 4 may be formed on the entire surface of the p-GaN layer 3. Note that the thickness of the n-type zinc oxide layer 4 is not limited to the above as long as it matches the carrier balance corresponding to the mobility and carrier density.

  In the present embodiment, the n-type zinc oxide layer 4 is formed by sputtering, but it can also be formed by vacuum deposition. The vacuum deposition method is not particularly limited as long as the n-type zinc oxide layer is formed, but is preferably an electron beam deposition method. As the vapor deposition material, the same composition and mixture as the sputtering target can be used.

  Thus, in the present invention, an n-type zinc oxide layer is formed as an n-type semiconductor layer in place of the n-type nitride semiconductor layer. Even if the n-type zinc oxide layer is formed on the p-type nitride semiconductor layer after being opened to the atmosphere, the light-emitting element exhibits good light-emitting characteristics. Therefore, according to the present invention, the p-type nitride semiconductor layer and the n-type zinc oxide layer can be formed in separate devices, respectively, thereby requiring a long time and a great amount of power required in the prior art. A process becomes unnecessary. In addition, as described above, even if Mg is mixed in the n-type zinc oxide layer, the characteristics as a light-emitting element can be exhibited. Therefore, the p-type nitride semiconductor layer and the n-type can be formed in the same device without performing a post-process. It is also possible to continue production of the zinc oxide layer. In the case where the p-type nitride semiconductor layer and the n-type zinc oxide layer are formed in separate apparatuses, existing sputtering apparatuses and vacuum deposition apparatuses can be used, and these apparatuses have already been enlarged for mass production. Therefore, mass production of the light emitting element is very easy and the productivity is very excellent. In addition, since the n-type zinc oxide layer is formed instead of the n-type nitride semiconductor layer, the amount of rare metal used can be greatly reduced, which is advantageous in terms of the stability and cost of obtaining raw materials.

  In the present invention, in order to further improve the ultraviolet emission luminance of the n-type zinc oxide layer, the n-type zinc oxide layer is heat-treated in a non-oxidizing atmosphere in which zinc oxide and gallium oxide and / or phosphorus oxide coexist. You may perform the process to do. (Hereinafter, zinc oxide and gallium oxide and / or phosphorus oxide may be referred to as coexisting substances.)

The reason why the ultraviolet emission luminance of the n-type zinc oxide layer is improved by the heat treatment in the presence of these is not necessarily clear,
(1) Suppressing sublimation / evaporation of ZnO from the composition (2) Suppressing desorption of oxygen from ZnO of the composition (3) Suppressing sublimation / evaporation of P ₂ O ₅ from the composition ( 4) The effect of reducing the influence of residual oxygen in the system on the composition is conceivable. Here, since gallium oxide is expensive and phosphorus oxide has high hygroscopicity, it is desirable to use zinc oxide as a main component and mix it with a small amount. From the viewpoint of luminance, it is preferable to use zinc oxide, gallium oxide, and phosphorus oxide.

  Next, as the form of these coexisting substances, the effect is recognized in any form, whether it is a powder or a sintered body, but it is desirable that the surface area be large as can be estimated from the above (1) to (4). Usually, it is good to use as a powder or a molded body obtained by hardening the powder.

  When the heat treatment is performed in a state where the surroundings are open, evaporation and sublimation are more likely to occur. Therefore, it is most effective to perform the heat treatment in a sealed space (for example, an airtight heating container, heating chamber, heating furnace, etc.).

  Next, the non-oxidizing atmosphere at the time of heat treatment refers to heat treatment in a neutral or reducing atmosphere such as nitrogen gas, argon gas or helium gas, not in an oxygen-containing oxidizing atmosphere. Usually, heat treatment may be performed in an inexpensive nitrogen gas. The residual oxygen concentration contained in the non-oxidizing atmosphere (particularly nitrogen gas) is preferably 100 ppm or less, more preferably 10 ppm or less, and even more preferably 1 ppm or less.

  Furthermore, in order to reduce the oxygen partial pressure of the non-oxidizing atmosphere, it is preferable to mix hydrogen gas with a neutral atmosphere such as nitrogen gas to form a reducing atmosphere. When the n-type zinc oxide layer is heat-treated in a reducing atmosphere, the emission intensity can be further improved.

  Hydrogen gas is mixed in order to further reduce the concentration of trace oxygen remaining in a neutral atmosphere gas such as nitrogen gas. Here, the degree of reduction of the oxygen concentration due to the mixing of hydrogen gas depends only on the temperature as long as the concentration of hydrogen gas is not extremely small, so the concentration is not limited. However, if hydrogen gas leaks into the atmosphere, if its concentration exceeds 4% by volume, there is a risk of explosion, so it is desirable to make it less than 4% by volume. On the other hand, the lower limit of the hydrogen concentration may be about 0.1% by volume since the amount of oxygen remaining in a neutral atmosphere gas such as nitrogen gas is usually small, but in reality it is used for heat treatment. Considering the case where oxygen adsorbed on the material inside the atmosphere furnace or the case where there is a slight leak in the furnace and oxygen enters from the outside, it is better to be higher within the explosion limit range. Therefore, the preferable oxygen concentration is preferably as high as possible at less than 4% by volume, and in reality, it is preferably 0.5% by volume or more and less than 4% by volume.

  As a specific heat treatment method, in FIG. 3, a coexisting substance 6 is added under a dry nitrogen 7 in a heatable container 5 that can be sealed, and a light emitting element 10 is placed thereon, and the coexisting substance is in the vicinity of the n-type zinc oxide layer. 6 is heat-treated. In addition to this, the coexisting material 6 may be placed on the n-type zinc oxide layer of the light emitting element 10 and heat-treated, or the n-type zinc oxide layer may be embedded in the coexisting material 6 powder and heat-treated.

  In the present invention, a compound that is converted into zinc oxide, gallium oxide, or phosphorus oxide by heat treatment may be used so that the n-type zinc oxide layer and coexisting substances coexist during heat treatment.

  About heat processing temperature, it is 700 to 1000 degreeC normally. This is because the effect is not significant when the heat treatment temperature is outside this range. The heat treatment temperature is preferably 775 ° C to 950 ° C.

  As for the heat treatment time, it is sufficient that the local disorder of the atomic arrangement reaches the thermal equilibrium state at the set temperature, and a few minutes is sufficient. Depending on the size of the furnace, the time required for the entire furnace to reach a uniform temperature varies, so it may be determined appropriately according to the productivity.

  Although there is a concern about thermal carrier diffusion near the pn junction interface due to heat treatment and contamination or alteration of the surface of the p-type nitride semiconductor layer that is exposed in the case of an L-shaped device, The main component Zn of the coexistent used in the n-type zinc oxide layer or heat treatment is an element having the same valence number as Mg as the p-type dopant, and carrier compensation does not occur even if it is thermally diffused and incorporated into the p-GaN layer. Absent.

  Further, the luminance of the light-emitting element can be further improved by performing the heat treatment at least twice. When heat treatment is performed a plurality of times in the range of 700 ° C. to 1000 ° C., the first time is preferably performed at a temperature near 950 ° C. close to 1000 ° C., and the second and subsequent heat treatments are preferably performed near 775 ° C. lower than the first time. . At this time, the temperature may be returned to around room temperature once between the first heat treatment and the second heat treatment. This is because the disorder of the atomic arrangement and the lattice defect after the film formation are gradually alleviated by repeating the heating and cooling. In general, when the heating and cooling steps are repeated, it is preferable to lower the temperature of each processing step from a high temperature having a long diffusion length to a low temperature having a short diffusion length.

  In FIG. 4, Ni and Au are vapor-deposited in this order on the p-GaN layer 3 with respect to the obtained light emitting element 10 to form an anode 8 of 1550 μm × 800 μm × 300 nm (Ni: 100 nm, Au: 200 nm). Then, Al was vapor-deposited on the n-type zinc oxide layer 4 to form a cathode 9 of 1550 μm × 500 μm × 300 nm (distance between electrodes 710 μm). The material of the anode 8 is not limited to Ni / Au, and may be Pt / Pd. The material of the cathode 9 is not limited to Al but may be Ta. Moreover, the dimension of each electrode and the distance between electrodes are not restricted above. By energizing between these electrodes, the heterojunction light-emitting element can emit light, and the light-emitting element has high emission luminance.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to the said Example.

(Examination of sputtering target composition)
5N purity ZnO powder (product of high purity chemical, particle size 0.6 μm), 3N purity Ga ₂ O ₃ powder (product of high purity chemical, particle size 0.5 μm) and reagent-grade (NH ₄ ) ₂ HPO ₄ ( Kanto Chemical Co., Ltd.) were mixed at various ratios using a ball mill and heat-treated at 775 ° C. in a dry nitrogen stream to prepare a sputtering target powder. One preparation amount was 100 g. Hereinafter, the mixed powder containing Zn, Ga, and P is referred to as ZGP powder.

  This ZGP powder was molded by a rubber press. The shape of the molded body was a disk shape having a diameter of 12 mm and a thickness of 1 mm. The ZGP powder compact was subjected to PL spectrum measurement at an excitation wavelength of 350 nm using an absolute PL quantum yield measuring apparatus for near ultraviolet rays (C9920-02G manufactured by Hamamatsu Photonics). FIG. 5 shows the measurement results when the element ratio of Zn / Ga / P is 100: 1: 1 and 100: 1: 3. Although ZGP powder having any phosphorus element ratio has a PL peak at 385 nm, PL having the strongest phosphorus element ratio of 1 was observed. The quantum yield measured from the spectrum was 10.6% for an element ratio of 100: 1: 1 and 5.4% for an element ratio of 100: 1: 3. Based on these results, in the next experiment, ZGP powder having an element ratio of Zn / Ga / P of 100: 1: 1 was used for the sputtering target.

(Preparation of heterojunction light-emitting element and EL light emission evaluation)
Regarding electrical characteristics such as carrier number density and mobility of n-type zinc oxide, it is not possible to expect electrical characteristics in the epitaxial growth by the conventional method. Therefore, considering the carrier balance, Mg-doped p-type gallium nitride has an Mg doping amount of It was decided to use about 1E + 18 cm ⁻³ which is one digit smaller than a normal gallium nitride LED. Therefore, commercially available Technologies and Devices International, Inc. 2 "C-plane sapphire substrate p-GaN: Mg 2 μm (11VS1599-2) manufactured by Furuuchi Chemical Co., Ltd. According to the data provided by the manufacturer, the Mg doping amount is 2E + 18 cm ⁻³ without being activated by Mg. When the various thicknesses of the purchased substrate were measured with SEM (S-4200 manufactured by Hitachi High-Technology), the i-GaN layer was 1.70 μm on the sapphire substrate, and the p-GaN layer was 1.85 μm on top. The structure was

  Next, using an RTA (Rapid Thermal Annealing) firing furnace (ULVAC SSA-P610CP), in a dry nitrogen atmosphere, at a set temperature of 750 ° C., the temperature was raised to the set temperature in 30 seconds, and held for 10 minutes. Mg activation heat treatment was performed by a method of allowing to cool to ° C.

  Next, using a high-frequency magnetron sputtering apparatus (SPF-312H manufactured by ANELVA), a ZGP powder having an element ratio Zn / Ga / P of 100: 1: 1 formed into a disk shape having a diameter of 12 mm and a thickness of 1 mm is used as a target. Then, an n-type zinc oxide was partially formed on the p-type gallium nitride substrate subjected to the Mg activation treatment using a metal mask. The film forming conditions were set to an output of 100 W, a substrate temperature Tsub = 300 ° C., a pressure of 1 Pa, an argon flow rate of 15 sccm, and an oxygen flow rate of 1.5 sccm.

Next, ZnO powder having a purity of 5N (manufactured by high purity chemical, particle size 0.6 μm), Ga ₂ O ₃ powder having a purity of 3N (manufactured by high purity chemical, particle size 0.5 μm), and reagent-grade (NH ₄ ) ₂ Two types of ZGP powder obtained by ball mill mixing HPO ₄ (manufactured by Kanto Chemical Co., Inc.) with Zn / Ga / P element ratios of 100: 1: 1 and 100: 1: 3 were prepared for crucible firing.

  A sample in which 18 g of the prepared ZGP powder for firing the crucible and the n-type zinc oxide was partially formed was placed in the crucible in the positional relationship shown in FIG. The diameter of the alumina crucible was 30 mm. The thickness of the powder was 1 mm, and the height from the spread powder to the lid was 5 mm.

  At this time, care was taken so that the n-type zinc oxide layer was not in direct contact with the ZGP powder. After the installation, the crucible was covered from above and a dry nitrogen stream was passed, and the first firing was performed at 950 ° C. and the second 775 ° C. (the temperature was once returned to room temperature between the first and second rounds). ). A total of four types of prototypes were made: two types of ZGP powders for the crucible firing, with only the phosphorus element ratio being changed, one taken out in the first firing and two taken out after the second firing. Sample numbers, element ratios and firing conditions are as follows.

  For reference, an electron micrograph of an n-type zinc oxide film formed on a quartz substrate by a high-frequency magnetron sputtering method using a ZGP powder as a sputtering target before firing in a crucible is shown in FIG.

  Moreover, the electron micrograph after the crucible baking of the n-type zinc oxide film | membrane formed on the sapphire + i-GaN board | substrate with the method similar to an Example is shown in FIG.

  It can be seen that the n-type zinc oxide layer before firing the crucible is grown in a granular form. On the other hand, the n-type zinc oxide layer after firing the crucible loses the grain growth observed before firing, the thickness of the n-type zinc oxide layer is reduced by about 10% before and after firing at the crucible 950 ° C., and changes into a dense film. I can see that

  Next, electrodes were formed by electron beam evaporation using a metal mask with an EB vapor deposition machine (ANELVA-made EVC-500A) for the four types of light-emitting elements that were prototyped. The thickness of the cathode Al was 3000 mm, and the thickness of the anode was 1000 mm for Ni and 2000 mm for Au.

  In the EL spectrum measurement this time, since the fiber is arranged on the sapphire substrate side opposite to the electrode side of the L-shaped structure shown in FIG. 4, light shielding by the electrode is not particularly problematic.

  FIG. 8 shows the measurement results of the EL spectrum when the amount of current flowing through the four light-emitting elements manufactured is fixed at 23 mA. It can be seen that the EL spectrum intensity is increased by firing twice for both the phosphorus element ratio of 1 and the phosphorus element ratio of 3. As the reason, the following firing mechanism is assumed. Since the melting temperature of both zinc oxide and gallium oxide is 1800 ° C or higher, and the decomposition temperature of diammonium hydrogen phosphate is 100 ° C or lower, it affects the n-type zinc oxide layer via the gas phase at 950 ° C. It affects only phosphorus compounds. By the first firing at 950 ° C., only a small amount of group V phosphorus is incorporated into the film, and the group III gallium atoms irregularly arranged in the zinc oxide crystal serve to correct the stable atomic arrangement. By performing the second firing at 775 ° C., which is lower than ℃, phosphorus taken in by the first firing at 950 ° C. is released from the film, and when using n-type zinc oxide, the group V phosphorus that causes carrier compensation is reduced. The EL characteristics are considered to be improved.

  According to the present invention, it is possible to mass-produce heterojunction light-emitting elements with high productivity. The heterojunction light-emitting elements obtained by the present invention are not only used as backlights for liquid crystal monitors of liquid crystal televisions and personal computers, It is also very useful as a lighting fixture or a self-luminous small image display device.

DESCRIPTION OF SYMBOLS 1 Sapphire substrate 2 i-GaN layer 3 p-GaN layer 4 n-type zinc oxide layer 5 Heating vessel 6 Coexistence 7 Dry nitrogen 8 Anode 9 Cathode 10 Heterojunction type light emitting element

Claims (7)

  Sputtering method using a composition or a mixture containing, on the p-type nitride semiconductor layer, at least one selected from the group consisting of zinc and oxygen as main component elements and aluminum, gallium and indium as subcomponent elements Or the manufacturing method of the heterojunction type light emitting element which has the process of forming an n-type zinc oxide layer by a vacuum evaporation method.   The method for manufacturing a heterojunction light-emitting element according to claim 1, wherein the p-type nitride semiconductor layer is formed by metal organic vapor phase epitaxy.   The method for manufacturing a heterojunction light-emitting element according to claim 1, wherein the p-type nitride semiconductor layer is a p-type gallium nitride layer.   The method for producing a heterojunction light-emitting element according to any one of claims 1 to 3, wherein the n-type zinc oxide layer is formed by a high-frequency magnetron sputtering method or an electron beam evaporation method.   The method for manufacturing a heterojunction light-emitting element according to any one of claims 1 to 4, wherein an amount of the subcomponent element is 0.03 at% or more and 3.0 at% or less with respect to zinc.   The heterojunction type according to any one of claims 1 to 5, further comprising a step of heat-treating the n-type zinc oxide layer in a non-oxidizing atmosphere in which zinc oxide and gallium oxide and / or phosphorus oxide coexist. Manufacturing method of light emitting element.   The method for manufacturing a heterojunction light-emitting element according to claim 6, wherein a temperature of the heat treatment is in a range of 700 ° C. to 1000 ° C.