JP6222684B2 - Red light emitting semiconductor device and method for manufacturing the same - Google Patents

Description

  The present invention relates to a red light emitting semiconductor element and a method for manufacturing the same, and more specifically, an active layer in which Eu or Pr is added to a specific base material (base material) such as GaN, InN, or AlN is divided into an n-type layer and a p-type layer. The present invention relates to a red light emitting semiconductor element having excellent light emission characteristics provided therebetween and a method for manufacturing the same.

  Nitride semiconductors such as gallium nitride (GaN) are attracting attention as semiconductor materials for blue light-emitting devices, and in recent years, by adding high concentrations of indium (In) to GaN, green and red light-emitting devices can be obtained. It is expected to be realized. However, as the In composition becomes higher, fluctuations in the In composition and piezo electric field effects become more prominent, so that a red light emitting device using a nitride semiconductor has not been realized.

  On the other hand, paying attention to the wide gap of nitride semiconductors, semiconductors to which europium (Eu) or praseodymium (Pr) is added with GaN as an additive base are promising as red light emitting devices.

  Under such circumstances, the present inventors succeeded in realizing a red light emitting diode (LED) having Eu or Pr-doped GaN as an active layer for the first time in the world (Patent Document 1).

  And by realizing such a red light emitting diode, it is possible to integrate light primary diodes of light using a nitride semiconductor on the same substrate together with the blue light emitting diode and the green light emitting diode that have already been developed. Therefore, application to fields such as a small and high-definition full-color display and LED lighting to which light emission in a red region not included in the current white LED is added is expected.

International Publication No. 2010/128643

  However, the light output of the red light emitting diode described above is still about 100 μW at present, and further improvement in light emission intensity (light output) is required for practical use.

  Accordingly, the present invention provides a red light emitting semiconductor element having a light emitting intensity improved as compared with the conventional red light emitting semiconductor element having a nitride semiconductor layer to which Eu or Pr is added as an active layer, and a method for manufacturing the red light emitting semiconductor element. And

  As a result of intensive studies, the present inventor has found that the above problems can be solved by the invention shown in the following claims, and has completed the present invention.

The invention described in claim 1
A method of manufacturing a red light emitting semiconductor device using GaN, InN, AlN or a mixed crystal of any two or more thereof,
Using GaN, InN, AlN, or a mixed crystal of any two or more thereof as a base material, Eu or Pr is changed to Ga, In under a temperature condition of 900 to 1100 ° C. using a metal organic vapor phase epitaxial method. Alternatively, when an active layer added to replace Al is formed between a p-type layer and an n-type layer in a series of formation steps of the p-type layer and the n-type layer, O is added together with Eu or Pr. do it,
A method for producing a red light emitting semiconductor device, comprising producing a red light emitting semiconductor device having an optical output of 100 μW or more in the active layer .

  That is, an active layer having a base material of a mixed crystal composed of two or more selected from GaN, InN, AlN, or GaN, InN, and AlN is formed at a temperature of 900 to 1100 ° C. between the p-type layer and the n-type layer. Under the conditions, using a metal organic vapor phase epitaxial method, when forming a p-type layer and an n-type layer in a series of forming steps, Ga raw material and N raw material (in the case of GaN), In raw material and N raw material A method for producing a red light emitting semiconductor device, comprising adding an Eu organic material and oxygen to (in the case of InN) or an Al material and an N material (in the case of AlN). Oxygen can be added by allowing an oxygen gas mixed in an inert gas such as argon to coexist with the raw material in the epitaxial step.

  Since light emission due to addition of Eu or Pr strongly depends on the crystal field, it is essential to increase the light emission transition probability of Eu ions and Pr ions, which are the light emission centers of the active layer, in order to improve the light output.

  However, the emission of Eu ions and Pr ions is due to the transition in the 4f shell, and the transition in the 4f shell of these rare earth elements is a forbidden transition. Therefore, in order to increase the probability of luminescence transition and obtain a high luminescence intensity, It is necessary to reduce the symmetry of the local local structure of Eu ions and Pr ions in the crystal field by incorporating Eu and Pr into the crystal.

  However, when Eu or Pr is simply added, the peripheral local structures of Eu ions and Pr ions are simultaneously formed with various excitation efficiencies and transition probabilities, so that many emission centers are formed. A broad emission spectrum is exhibited, and an improvement in emission intensity (light output) is suppressed.

  Therefore, during the growth of crystals such as GaN, in addition to the addition of Eu and Pr, a material capable of intentionally controlling the formation of the local local structure of Eu ions and Pr ions is co-added to selectively select the emission center. If the number of emission centers formed can be reduced and simplified, the emission wavelength can be intentionally controlled and the emission intensity can be dramatically improved. is there.

  As a result of various experiments and examinations, the inventor of the present invention co-added O (oxygen) in addition to Eu and Pr when forming an active layer using a metal organic vapor phase epitaxial method (OMVPE method). It has been found that the formation of the local local structure of ions and Pr ions can be intentionally controlled to selectively form the Eu emission center, and the Eu emission wavelength can be intentionally controlled. Furthermore, it has been found that the light emission center of Eu can be simplified, and that a red light emitting semiconductor element with a greatly increased light emission intensity can be produced.

  Specifically, Eu and Pr in the active layer are arranged to replace Ga under a predetermined growth temperature. At this time, the co-doped O has a strong binding force with Eu or Pr and is a Eu ion. Since the vicinity of the Pr ion is selected and actively entered, the peak on the short wavelength side formed in the broad emission spectrum caused by the fluctuation of the local structure around the Eu ion disappears and is sharp at the wavelength of about 621 nm. It was found that the peaks are concentrated, and it was found that the number of emission centers formed can be reduced and simplified.

Then, by appropriately controlling the co-concentration concentration of O and simplifying the formation of the emission center, the photoluminescence spectrum (Photoluminescence Spectrum: PL spectrum) is not limited to the NTSC color gamut and the HDTV color gamut, and redness is observed. The perceived peak near the wavelength of 621 nm can be sharpened, and a high emission intensity of 100 μW or more can be obtained in the active layer .

  It was also found that the active layer co-doped with O has improved surface roughness, and even when an LED or the like is produced by a pn junction, no leakage current is generated and stable characteristics can be exhibited. .

  In the present invention, the temperature condition in the OMVPE method used for forming the active layer is important. That is, if the temperature is too low, Eu ions and Pr ions in different crystal fields increase and the peak near 621 nm decreases. On the other hand, if the temperature is too high, Eu ions and Pr ions are desorbed from the surface, and Eu and Pr ions. Addition becomes difficult. A preferable temperature condition is 900 to 1100 ° C, and more preferably 950 to 1050 ° C.

  Further, the formation of the p-type layer, the active layer, and the n-type layer is a series of forming steps, that is, without taking out from the reaction vessel in the middle, the layers in the reaction vessel are arranged in the order of p-type layer, active layer, n-type layer, Alternatively, by forming the n-type layer, the active layer, and the p-type layer in this order, there is no interface state between the layers, and carriers can be injected efficiently. For these reasons, a low voltage operation of about several volts is possible.

  In addition, from the viewpoint of not taking out from the reaction container in the middle of the above, it is preferable to form the n-type layer and the p-type layer by the OMVPE method, but this does not exclude other growth methods. Further, the n-type layer and the p-type layer are not necessarily in contact with the active layer. For example, a carrier block layer may be provided between the n-type layer and the p-type layer.

  In the present invention, the base material is not limited to GaN, and the same effect as described above can be obtained even when InN, AlN, or a mixed crystal thereof (InGaN, AlGaN, etc.) is used as the base material. it can.

  According to the invention of this claim, it is possible to provide a large economic effect as described above. In other words, the realization of a red light-emitting diode with simplified light emission center and high light output device characteristics enables the integration of light-emitting diodes of the three primary colors of “red, green, and blue” at a practical level. Therefore, a full-color display using a small, high-definition, high-output light emitting diode can be realized.

  In addition, by adding high-intensity light emission in the red region that is not included in current white LEDs, the emission wavelength does not change depending on the ambient temperature as well as an alternative to AlGaInP-based LEDs currently used as red LEDs. High-intensity LED lighting that makes use of the characteristics of rare earth elements can be realized.

The invention described in claim 2
2. The method for manufacturing a red light emitting semiconductor device according to claim 1, wherein the element added to the base material is Eu.

  Any of Eu and Pr may be used because the outer shell electrons are shielded by the inner shell electrons and emit light that feels red without being limited to the NTSC color gamut or the HDTV color gamut. However, it is preferable to use Eu with higher red emission efficiency. Eu also has a track record as a red phosphor for color televisions, and is easier to obtain than Pr.

The invention according to claim 3
Eu is supplied by (bis (tetramethylmonoalkylcyclopentadienyl) europium). The method for manufacturing a red light emitting semiconductor element according to claim 2, wherein Eu is supplied by (bis (tetramethylmonoalkylcyclopentadienyl) europium).

The Eu raw material for supplying Eu (Eu organic raw material) is preferably an Eu compound that has a high vapor pressure and can be efficiently added. Eu [C ₅ (CH ₃ ) ₄ R] ₂ (R: alkyl) (Bis (tetramethylmonoalkylcyclopentadienyl) europium) represented by the group) is more preferred, and among these, bis (normalpropyltetramethylcyclopentadienyl) europium (EuCp ^pm ₂ ) is preferred.

That is, for example, since compounds such as Eu (C ₁₁ H ₁₉ O ₂ ) ₃ and Eu (C ₅ H ₇ O ₂ ) ₃ have a relatively high vapor pressure, they have been generally used as Eu sources (Eu organic raw materials). However, since it is a solid even in the vicinity of the use temperature of 150 ° C., there is often a problem in stability at the time of supply. Further, since oxygen is contained in the structure, deterioration of the base material due to oxygen can be considered during the addition of Eu. In addition, when co-adding O, it is necessary to consider the amount of oxygen in the structure. Therefore, it is not easy to control the addition concentration in the co-addition of O.

In contrast, (bis (tetramethylmonoalkylcyclopentadienyl) europium) has a relatively low melting point (for example, EuCp ^pm ₂ is 49 ° C.) and is liquid at the use temperature, so it is more stable by bubbling. Can be supplied. Further, since oxygen is not included in the structure, film formation without oxygen is possible, and control in co-addition of O can be performed reliably and easily.

The invention according to claim 4
A red light emitting semiconductor device using GaN, InN, AlN or a mixed crystal of any two or more thereof as a base material,
An active layer sandwiched between a p-type layer and an n-type layer on the substrate;
The active layer is formed by adding Eu or Pr to GaN, InN, AlN, or a mixed crystal of any two or more thereof so as to replace Ga, In, or Al, and together with Eu or Pr. An active layer to which O is added;
The red light-emitting semiconductor device is characterized in that the light output in the active layer is 100 μW or more.

As described above, in the red light-emitting semiconductor element to which O is co-doped, the formation of local structures around Eu ions and Pr ions is intentionally controlled, the emission center is simplified, and the surface of the active layer is roughened. Due to the improvement, the emission intensity is greatly improved, and a red light emitting semiconductor element having a high emission intensity of 100 μW or more in the active layer can be provided.

  The substrate on which the active layer is formed is usually sapphire, but is not limited to this. For example, Si, GaN, GaAs or the like can be used.

The invention described in claim 5
5. The red light emitting semiconductor device according to claim 4, wherein the active layer has an addition concentration of O of 1 × 10 ¹⁷ to 1 × 10 ²⁰ cm ⁻³ .

The addition concentration of O is preferably about the same as Eu, and is preferably 4 times or less of Eu at the maximum, but if it is 1 × 10 ¹⁷ to 1 × 10 ²⁰ cm ⁻³ , The number is preferred because it is appropriately controlled and simplified. More preferably, it is 1 × 10 ¹⁹ to 1 × 10 ²⁰ cm ⁻³ .

The invention described in claim 6
6. The red light emitting semiconductor device according to claim 4, wherein the number of light emitting centers formed in the active layer is 2 to 6.

  If the number of emission centers is simplified to 2 to 6 by intentionally co-adding O, higher emission intensity can be obtained.

  The red light-emitting semiconductor element co-doped with O has a dramatic change in the peripheral local structure of Eu ions, and the Eu emission center is simplified. Thus, the emission intensity is greatly improved, and an unprecedented 100 μW or more is achieved. A red light emitting semiconductor element having high light output can be provided.

The invention described in claim 7
A red light emitting semiconductor device using GaN, InN, AlN, or a mixed crystal of any two or more thereof,
An active layer sandwiched between a p-type layer and an n-type layer on the substrate;
The active layer is formed by adding Eu or Pr to GaN, InN, AlN, or a mixed crystal of any two or more thereof so as to replace Ga, In, or Al, and together with Eu or Pr. , O is an active layer added with a concentration of 1 × 10 ¹⁷ to 1 × 10 ²⁰ cm ⁻³ ,
A red light-emitting semiconductor device, wherein the light output in the active layer is 100 μW or more.

In the red light emitting semiconductor device as described above, since the emission center is simplified by appropriately co-adding O, the emission intensity is greatly improved as described above, and the red light having a high light output of 100 μW or more in the active layer. A light-emitting semiconductor element can be provided.

  ADVANTAGE OF THE INVENTION According to this invention, in the red light emitting semiconductor element which uses the nitride semiconductor layer to which Eu or Pr was added as an active layer, the red light emitting semiconductor element which improved the emitted light intensity conventionally, and its manufacturing method can be provided. .

It is a figure which shows the basic structure of the red light emitting semiconductor element which concerns on one embodiment of this invention. It is a figure which shows PL spectrum of a red light emitting semiconductor element. It is a CEES mapping image of a Eu addition GaN layer. It is a differential interference microscope photograph which shows the surface morphology of Eu addition GaN layer.

  Hereinafter, the present invention will be described based on embodiments. Note that the present invention is not limited to the following embodiments. Various modifications can be made to the following embodiments within the same and equivalent scope as the present invention.

(Structure of red light emitting semiconductor element)
FIG. 1 shows a basic structure of a red light emitting semiconductor element in the present embodiment. In FIG. 1, 20 is an Eu-doped GaN layer (Eu-doped GaN layer) in which O is co-doped (doped) with Eu on a GaN base material, 30 is an undoped GaN layer, 40 is a low-temperature GaN buffer layer, and 50 is a sapphire substrate. is there.

  In this experimental example, the red light emitting semiconductor elements of Experimental Examples 1 to 3 in which Eu-doped GaN layers having different co-addition amounts of O were formed as active layers were manufactured, and the emission center and emission intensity were measured.

1. Production of Red Light-Emitting Semiconductor Element First, a low-temperature GaN buffer layer (thickness 30 nm) 40 was grown on the sapphire substrate 50 by metal organic vapor phase epitaxy (OMVPE method).

  Next, an undoped GaN layer (thickness 1700 nm) 30 was grown on the low-temperature GaN buffer layer 40 in the same manner using the OMVPE method.

  Next, an unillustrated n layer (thickness 2500 nm) was formed on the undoped GaN layer 30.

  Next, an Eu-doped GaN layer (thickness 300 nm) 20 in which O was co-added to the GaN base material was laminated on the n layer as an active layer.

  Next, a p layer (thickness: 70 nm) (not shown) was formed on the Eu-doped GaN layer 20.

Next, a p ⁺ -GaN contact layer (thickness 20 nm) (not shown) was stacked on the p layer.

  In each experimental example, trimethylgallium (TMGa) was used as a Ga raw material, and the supply amount was 0.55 sccm.

Further, ammonia (NH ₃ ) was used as the N raw material, and the supply amount was 4.0 slm.

Further, EuCp ^pm ₂ bubbled with a carrier gas (hydrogen gas: H ₂ ) was used as the Eu raw material, and the supply amount was 1.5 slm (supply temperature: 115 ° C.).

In addition, the co-addition of O was performed by changing the oxygen gas O ₂ diluted with Ar gas to a concentration of 10 ppm to supply amounts of 100 sccm (Experimental Example 1), 300 sccm (Experimental Example 2), and 1000 sccm (Experimental Example 3). It was performed by supplying together with a carrier gas having a flow rate of 40 slm.

  The Eu-added GaN layer 20 co-doped with O was formed at a growth rate of 0.8 μm / h under growth conditions of a temperature of 1030 ° C. and a pressure of 100 kPa.

  At this time, the supply temperature of the Eu raw material is kept at a sufficiently high temperature of 115 to 135 ° C. by changing the piping valve of the OMVPE device from the normal specification (heat resistant temperature 80 to 100 ° C.) to the high temperature special specification. Thus, a sufficient amount of Eu was supplied to the reaction tube.

  The formation of each layer was performed in a series of steps so that the sample was not taken out from the reaction tube and the growth was not interrupted.

2. Preparation of Comparative Test Specimens Separately, for comparison, a red light-emitting semiconductor element (comparative example) was prepared by stacking an Eu-doped GaN layer as an active layer under the same conditions as above except that O was not co-added. .

3. Next, the photoluminescence spectrum (PL spectrum) from each active layer was measured for the red light emitting semiconductor elements obtained in each experimental example and comparative example using a helium / cadmium laser (measurement temperature: room temperature). .

  The results are shown in FIG. In FIG. 2, the vertical axis represents the PL intensity (arbitrary unit, au), and the horizontal axis represents the wavelength (nm).

As can be seen from FIG. 2, the peak on the short wavelength side disappears and the peak concentrates in the vicinity of the wavelength of 621 nm as the supply amount of O ₂ increases, and the emission spectrum is simplified.

4). Eu emission center Next, the Eu emission center was identified using the red light emitting semiconductor element obtained in Experimental Example 1 and Comparative Example.

  Specifically, the Eu emission center was identified by using Combined Excitation-Emission Spectroscopy (CEES) measurement.

When using this measuring method, ⁵ D ₀ of Eu without crystal field splitting - by exciting between ⁷ F ₀ level can be directly identify the number and type of luminescent center.

  FIG. 3 shows a CEES mapping image obtained by mapping measurement results at a temperature of 10K. In FIG. 3, (a) is a comparative example, (b) is a CEES mapping image in Experimental Example 1, the horizontal axis is emission energy, and the vertical axis is excitation energy.

  As shown in FIG. 3 (a), in the absence of co-addition of O, the emission center identified so far of Eu-doped GaN produced by OMVPE method, that is, identified by Woodward et al. and sample dependent electron-phonon coupling of Euions in epitaxy-growth GaN layers Optical ", Optical Materials of 33 (2011), 1050-1054, and 8 light emitting OMVPE. The emission center shown is observed. These correspond to the broad emission spectrum in the comparative example shown in FIG.

  On the other hand, when O is added together, as shown in FIG. 3B, only OMVPE4 and OMVPE7 are significantly observed, and it is understood that the emission center is simplified. This result corresponds to simplification of the emission spectrum in Experimental Example 1 shown in FIG.

  From the measurement of the above emission spectrum and the identification result of the Eu emission center, by intentionally adding O, the emission center containing Eu and O is preferentially formed, and the emission center is simplified. It could be confirmed.

  Further, by simplifying the emission center in this way, it is possible to improve the emission intensity, and it is possible to provide a red light emitting semiconductor element having an excellent light output of 100 μW or more.

5. Surface State Next, the surface morphology (roughness state) of the Eu-doped GaN layer formed in Experimental Example 1 and Comparative Example was observed using a differential interference microscope.

  The observation results are shown in FIG. In FIG. 4, (a) is a comparative example, and (b) is a differential interference micrograph in Experimental Example 1.

  As shown in FIG. 4, the surface is roughened in the absence of co-addition of O, but the occurrence of roughening is mitigated by the co-addition of O, and the co-addition of O reduces the surface morphology of Eu-doped GaN. It turns out that it is improving.

  When an LED or the like is fabricated by pn-junction of a red light-emitting semiconductor element formed with a Eu-doped GaN layer having a rough surface morphology, the junction surface is rough, so that leakage current is likely to occur, and stable output characteristics are obtained. Can't get.

  On the other hand, when the present invention is applied, since the surface morphology is improved by co-addition of O, generation of leakage current can be suppressed and stable output characteristics can be exhibited.

  As described above, in the present invention, it is possible to manufacture and provide a red light emitting semiconductor element having excellent light output of 100 μW or more by controlling the formation of the light emission center by appropriately co-adding O. It becomes.

  As a result, it is possible to realize a full-color display using a small, high-definition, high-output light emitting diode as described above and high-luminance LED illumination.

20 Eu-doped GaN layer 30 Undoped GaN layer 40 Low-temperature GaN buffer layer 50 Sapphire substrate

Claims (7)

A method of manufacturing a red light emitting semiconductor device using GaN, InN, AlN or a mixed crystal of any two or more thereof,
Using GaN, InN, AlN, or a mixed crystal of any two or more thereof as a base material, Eu or Pr is changed to Ga, In under a temperature condition of 900 to 1100 ° C. using a metal organic vapor phase epitaxial method. Alternatively, when an active layer added to replace Al is formed between a p-type layer and an n-type layer in a series of formation steps of the p-type layer and the n-type layer, O is added together with Eu or Pr. do it,
A method for producing a red light emitting semiconductor device, comprising producing a red light emitting semiconductor device having an optical output of 100 μW or more in the active layer .   2. The method for manufacturing a red light emitting semiconductor element according to claim 1, wherein the element added to the base material is Eu.   The method for producing a red light emitting semiconductor element according to claim 2, wherein Eu is supplied by (bis (tetramethylmonoalkylcyclopentadienyl) europium). A red light emitting semiconductor device using GaN, InN, AlN or a mixed crystal of any two or more thereof as a base material,
An active layer sandwiched between a p-type layer and an n-type layer on the substrate;
The active layer is formed by adding Eu or Pr to GaN, InN, AlN, or a mixed crystal of any two or more thereof so as to replace Ga, In, or Al, and together with Eu or Pr. An active layer to which O is added;
A red light-emitting semiconductor device, wherein the light output in the active layer is 100 μW or more. 5. The red light emitting semiconductor device according to claim 4, wherein the concentration of O in the active layer is 1 × 10 ¹⁷ to 1 × 10 ²⁰ cm ⁻³ .   6. The red light emitting semiconductor device according to claim 4, wherein the number of light emitting centers formed in the active layer is 2 to 6. A red light emitting semiconductor device using GaN, InN, AlN, or a mixed crystal of any two or more thereof,
An active layer sandwiched between a p-type layer and an n-type layer on the substrate;
The active layer is formed by adding Eu or Pr to GaN, InN, AlN, or a mixed crystal of any two or more thereof so as to replace Ga, In, or Al, and together with Eu or Pr. , O is an active layer added with a concentration of 1 × 10 ¹⁷ to 1 × 10 ²⁰ cm ⁻³ ,
A red light-emitting semiconductor device, wherein the light output in the active layer is 100 μW or more.