JP2005259827A - Nitride semiconductor light emitting device and method of growing nitride semiconductor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor light emitting device for emitting a light at a high brightness in a range from UV rays to near IR rays, and a nitride semiconductor growing method which grows the nitride semiconductor having a wide percentage range of In and a controlled composition on the atomic level to obtain an active layer having a high emission efficiency. <P>SOLUTION: The nitride semiconductor light emitting device has an n-type nitride semiconductor, a light emitting layer and a p-type nitride semiconductor grown in this order on a crystal growing substrate. The light emitting layer has an InN well layer and a barrier layer of In<SB>x</SB>Ga<SB>1-x</SB>N(0≤x≤0.3) or aluminum gallium nitride (Al<SB>y</SB>Ga<SB>1-y</SB>N:0≤y≤0.3), and the well layer and the barrier layer are each 10 nm or less, thus forming a superlattice structure. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a nitride semiconductor light emitting device that emits light with high luminance from ultraviolet to near infrared and a method for growing a nitride semiconductor.

As a gallium nitride semiconductor used in a blue light emitting diode or the like, for example, Patent Document 1 “Growth method of indium gallium nitride semiconductor” is disclosed. In Patent Document 1, a light emitting layer of indium gallium nitride (In _x Ga _1-x N: 0 <x ≦ 1, hereinafter simply referred to as “InGaN”) is grown at a growth temperature higher than 600 ° C. The In ratio x in InGaN obtained by the method of Patent Document 1 is 0.25, and the emission wavelength is blue of about 450 nm.

  On the other hand, FIG. 6 shows the relationship between the In ratio x and the photon energy (Photon energy: eV) in the InGaN light-emitting layer, and the emission wavelength varies depending on the In ratio x, and around x = 0.25. It is known that blue light having a wavelength of about 450 nm, near infrared light having a wavelength of about 830 nm near x = 0.5, and red light having a wavelength of about 650 nm in the middle can be emitted.

  Furthermore, Non-Patent Document 2 shows that the forbidden band width of InN is 0.7 to 0.8 eV. As a result, the range of application of nitride semiconductors as optical devices ranges from 6.2 eV for AlN to InN. It is shown that it extends from 200 nm of deep ultraviolet rays to 1550 nm of optical communication wavelength.

Other documents related to the present invention include Patent Documents 2 and 3 and Non-Patent Documents 3 to 5.
The “nitride semiconductor laser device” of Patent Document 2 is a gallium nitride semiconductor having a well layer made of In _x Ga _1-x N (0 ≦ x ≦ 1) and an active layer made of multiple quantum wells including a barrier layer. In the laser element, the difference in band gap energy between the well layer and the barrier layer is 0.20 eV or more and 0.30 eV or less.

JP-A-6-196757 JP 2001-148546 A Japanese Patent Application Laid-Open No. 2003-60237, “Method of Growing Semiconductor Crystal Film”

M.M. HORI et al. "Optical Properties of InxGa1-xN with Endier Alloy Composition on InN Buffer Layer Grown by RF-MBE", phys. stat. sol. (B) 234, no. 3, 750-754 (2002). Menishi, Araki, Miyajima, “InN and InGaN crystal growth, structure and evaluation of properties”, Applied Physics Vol.72, No.5, p565-571 (2003) D. Doppalupdi et al. "Phase separation and ordering in InGaN allies grown by molecular beam epitaxy", Journal of applied physics, vol. 84, no. 3, 1389-1395 (1998). Mori, Ito, Samukawa, Kaoru, “Natural superlattice structure in InGaN thin film”, Journal of Crystal Growth Society, vol. 30 No. 3 p97 (2003). Takashi Katoda, “Evaluation of Semiconductors by Laser Raman Spectroscopy”, University of Tokyo Press, P167-169.

As described above, the application range of nitride semiconductors as an optical device can cover from 6.2 eV of AlN to 0.8 eV of InN, and can emit light from 200 nm of deep ultraviolet light to 1550 nm of optical communication wavelength. I have a secret.
However, in the nitride semiconductor device disclosed in the conventional example, the ratio x of In in indium gallium nitride (In _x Ga _1-x N: 0 <x ≦ 1) is at most only about 0.25. In addition, when the x value is 0.5 or more, it is difficult to obtain indium gallium nitride excellent in crystallinity, and a light emitting diode or laser emitting yellow to near infrared light cannot be realized.

This cause can be explained as follows.
The first cause is the relationship between the molar fraction x of In in indium gallium nitride and the equilibrium temperature shown in FIG. As shown in this figure, when the molar fraction x of In in In _x Ga _1-x N is increased to about 0.5 or more, the equilibrium temperature becomes about 600 ° C. or less at normal pressure. Therefore, in the process of growing an InGaN semiconductor film on the surface of the sapphire substrate, if the sapphire substrate or the formed InGaN is heated to about 600 ° C. or higher, the InGaN is thermally decomposed.
On the other hand, in order to obtain indium gallium nitride which is a high-quality light emitting layer by the conventional metal organic vapor phase epitaxy method, it was necessary to produce the substrate at a substrate temperature exceeding 600 ° C. Therefore, InGaN containing a high concentration of indium causes phase separation, and as a practical problem, InGaN that emits light having a wavelength exceeding red has never been successfully grown. That is, it is difficult to grow a high-quality nitride semiconductor at 600 ° C. or lower.

  As described in Non-Patent Document 3, the second cause is that InN and GaN constituting a mixed crystal of indium gallium nitride differ in bond length by about 11%, even if macroscopically uniform. At the atomic level, the composition of the mixed crystal semiconductor is not controlled, so it is difficult to obtain a uniform mixed crystal, and when the In concentration increases, phase separation and indium droplets occur, and high quality InGaN can be obtained. It was difficult.

  The present invention has been made to solve such problems. That is, an object of the present invention is to grow a nitride semiconductor light emitting device that emits light with high luminance from ultraviolet to near infrared, and to grow the nitride semiconductor with a composition having a wide In ratio range and controlled even at the atomic level. An object of the present invention is to provide a method for growing a nitride semiconductor capable of obtaining a high active layer.

According to the present invention, there is provided a nitride semiconductor light-emitting device in which an n-type nitride semiconductor, a light-emitting layer, and a p-type nitride semiconductor are sequentially grown on a crystal growth substrate,
The light emitting layer includes a well layer made of InN and In _x Ga _1-x N (0 ≦ x ≦ 0.3) or aluminum gallium nitride (Al _y Ga _1-y N: 0 ≦ y ≦ 0.3). There is provided a nitride semiconductor light emitting device characterized in that the well layer and the barrier layer each have a thickness of 10 nm or less, thereby forming a superlattice structure.

Further, according to the present invention, there is provided a nitride semiconductor growth method for sequentially growing an n-type nitride semiconductor, a light emitting layer, and a p-type nitride semiconductor on a crystal growth substrate,
The substrate for crystal growth is maintained at a temperature of about 600 ° C. or less in the reaction vessel, precursors are sequentially supplied into the reaction vessel, the surface of the substrate is irradiated with a pulsed laser, a well layer made of InN is formed on the irradiated portion, and In _{x Ga 1-x N (0} ≦ x ≦ 0.3) or aluminum gallium nitride _{(Al y Ga 1-y N} : 0 ≦ y ≦ 0.3) alternately by organometallic vapor phase epitaxy and a barrier layer made of In addition, a method for growing a nitride semiconductor is provided, in which each is grown to a thickness of 10 nm or less, thereby forming a superlattice structure.

According to the above means of the present invention, the crystal growth substrate is maintained at a temperature of about 600 ° C. or less in the reaction vessel, so that the thermal decomposition is performed in the process of growing the InGaN (or AlGaN) semiconductor film on the surface of the substrate. Can be prevented.
Further, precursors are sequentially supplied into the reaction vessel, the surface of the substrate is irradiated with a pulse laser, and a well layer made of InN is formed on the irradiated portion, and In _x Ga _1-x N (0 ≦ x ≦ 0.3) or nitriding A barrier layer made of aluminum gallium (Al _y Ga _1-y N: 0 ≦ y ≦ 0.3) is grown by metal organic vapor phase epitaxy. A bond (N—H bond, C-amine bond, etc.) can be broken, and InGaN (or AlGaN) can be grown there.
Furthermore, since the well layers and the barrier layers are alternately grown to a thickness of 10 nm or less, a superlattice structure with less strain controlled at the atomic level can be formed.
Therefore, since a superlattice structure with less strain is formed, an active layer having a wide In ratio range and high luminous efficiency can be obtained, and a nitride semiconductor light emitting device that emits light with high luminance from ultraviolet to near infrared can be obtained. it can.

According to a preferred embodiment of the present invention, the light emitting layer has a quantum well structure in which well layers and barrier layers are alternately stacked.
With this configuration, it is possible to form superlattice structures each having a thickness of 10 nm or less and to arbitrarily set the total thickness to control the emission intensity.

In order to control the emission wavelength, the film thickness ratio between the well layer and the barrier layer is preferably set within a predetermined range.
By this means, the In ratio of the entire light emitting layer can be freely adjusted over a wide range while maintaining the well layer and the barrier layer with high quality.

In order to control the emission wavelength, the thickness of the well layer may be set within a predetermined range not exceeding 1 nm.
By this means, the emission wavelength can be controlled by controlling the well width (well layer thickness).

The n-type nitride semiconductor is preferably gallium nitride or aluminum gallium nitride.
The pulse laser is preferably a YAG laser, an excimer laser, or the like.

  As described above, the nitride semiconductor light emitting device of the present invention can emit light with high brightness from ultraviolet to near infrared, and the nitride semiconductor has a wide In ratio range and is controlled even at the atomic level by the growth method of the present invention. It is possible to obtain an active layer having a high luminous efficiency and the like.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the common part in each figure, and the overlapping description is abbreviate | omitted.

In the “semiconductor crystal film growth method” of Patent Document 3, we have shown that non-doped, high-quality InGaN can be grown at a temperature of 650 ° C. or less by growing while irradiating with a pulse laser.
Further, in “Natural superlattice structure in InGaN thin film” of Non-Patent Document 4, it has been reported that a superlattice structure of InN layer / InGaN layer can be formed and strain energy can be relaxed thereby.
Furthermore, “Evaluation of superlattice structure and disorder” in Non-Patent Document 5 shows that it is possible to use a superlattice of GaAs and AlAs instead of the mixed crystal semiconductor Ga _1-x Al _x As. Has been.

The present invention has been made in view of the above. That is, if the means of Patent Document 3 is used, high-quality indium gallium nitride (In _x Ga _1-x N) can be grown when the In ratio x is in the range of 0 ≦ x ≦ 0.3. By forming a superlattice structure having a thickness of 10 nm or less in combination with a well layer made of InN, an active layer with high luminous efficiency capable of emitting light with high luminance from ultraviolet to near infrared can be easily obtained.

  FIG. 1 is a schematic view of an apparatus for growing a nitride semiconductor by the method of the present invention. A pulse laser 10 is generated and emitted by a laser device 11 (for example, an excimer laser) controlled by a laser controller 12. The pulse laser 10 has its energy distribution made uniform by the beam shaping optical system 13, reflected downward by the mirror 14, and passed through an opening (not shown) provided in the reaction vessel 6 on the upper surface of the crystal growth substrate 1. Irradiated. The substrate 1 may be silicon, SiC or sapphire.

  The pulse laser 10 scans on the substrate by swinging the mirror 14 or moving the beam shaping optical system 13. The stage controller 16 can move the substrate 1 two-dimensionally. Further, the inside of the reaction vessel 6 (chamber) is controlled to a predetermined gas atmosphere by the pump system 15 and the gas introduction part 17.

  In the method of the present invention, the substrate 1 is maintained in the reaction vessel 6 at a temperature at which InGaN is not thermally decomposed by temperature adjusting means (not shown) such as a heater. In addition, In, Ga, and N precursors are sequentially or simultaneously supplied into the reaction vessel 6 from the gas introduction unit 17. The temperature at which InGaN does not thermally decompose is preferably about 600 ° C. or less. In addition, it becomes easy to thermally decompose at the temperature over about 600 degreeC. In addition, if it is less than about 500 ° C., it becomes difficult to form InGaN crystals.

FIG. 2A is a configuration example of a nitride semiconductor to be grown according to the present invention. In this figure, a nitride semiconductor 5 is manufactured by sequentially growing an n-type nitride semiconductor 2, an indium gallium nitride light emitting layer 3, and a p-type nitride semiconductor on a crystal growth substrate 1.
FIG. 2B shows a configuration example in which a part of FIG. 2A is removed by etching, an electrode 7 is attached to the n-type nitride semiconductor 2 and the p-type nitride semiconductor 4, and a light emitting diode is formed.

The light emitting layer 3 of indium gallium nitride grown according to the present invention includes a well layer 3a made of InN and a barrier layer made of In _x Ga _1-x N (0 ≦ x ≦ 0.3) located above and below the well layer 3a. 3b. In this case, InN and In _x Ga _1-x N (including GaN) in the range of 0 ≦ x ≦ 0.3 can be easily formed with a defect-free thin film by the method of the present invention. An active layer having higher luminous efficiency can be obtained more easily than a crystal semiconductor.
In the present invention, the film thicknesses of the well layer 3a and the barrier layer 3b are each set to 10 nm or less to form a superlattice structure. The light emitting layer 3 is not limited to a single well layer 3a, and may have a quantum well structure in which a plurality of well layers 3a and a plurality of barrier layers 3b are alternately stacked.

Further, the emission ratio is controlled by controlling the In ratio of the entire light emitting layer by the film thickness ratio of the well layer and the barrier layer.
For example, when the well layer 3a made of InN and the barrier layer 3b made of GaN are stacked at a film thickness ratio of 1: 1, the In ratio x of the entire light emitting layer 3 becomes 0.5, and In _x Ga _1-x N (x = 0.5) can emit near infrared light having a wavelength of about 830 nm.
Similarly, for example, when a well layer 3a made of InN and a barrier layer 3b made of In _x Ga _1-x N (x = 0.3) are stacked at a film thickness ratio of 2: 1, In _x Ga _1-x N ( A light emitting layer of x = 0.77) can be formed.

In FIGS. 2A and 2B, the In ratio of the entire light emitting layer is preferably 0.5 or more, so that it is possible to grow a light emitting element having a red or near infrared wavelength, which has been difficult in the past.
Note that the present invention is not limited to this, and the ratio of In, Ga, and N can be changed to change the ratio of In in the range of 0 <x ≦ 1. It can be used not only as a laser diode but also as a light emitting element of near infrared wavelength.

It is also known that photoluminescence with weak excitation in superlattices without interaction between quantum wells is caused by recombination of electrons at the lowest level in the quantum well with heavy and light holes. Yes. Assuming such a recombination process, the relationship between the width of the well layer and the emission peak is as shown in FIG. As can be seen from this figure, the emission wavelength is controlled by the well width (well layer thickness) by setting the thickness of the well layer 3a within a predetermined range not exceeding 1 nm so as to control the emission wavelength. be able to.
Further, the same effect can be obtained even when the barrier layer is made of Al _y Ga _1-y N (0 ≦ y ≦ 0.3).

  Using the apparatus shown in FIG. 1, InGaN was grown on the gallium nitride substrate 2 while irradiating the pulse laser 10 at a growth temperature of 600 ° C. under the following experimental conditions. The gallium nitride substrate 2 was heated to 1000 ° C., lowered to 600 ° C., and kept at this temperature during growth.

(Experimental conditions)
1. Reaction gas Trimethylgallium (TEG): 1.2 × 10 ⁻⁵ atm
Trimethylindium (TMI): 3.0 × 10 ⁻⁵ atm
Ammonia: 0.4 atm
Nitrogen gas: 850 ml / min
2. Substrate temperature 600 ° C
3. Laser device Nd: YAG laser output 1mW
Repeat frequency 1Hz
Wavelength 532nm
4). Growth time 2Hr

The In ratio x in the grown indium gallium nitride (In _x Ga _1-x N: 0 <x ≦ 1) was 0.53. Hereinafter, this InGaN is represented as In _0.53 Ga _0.47 N.

FIG. 4 is a comparison diagram of ω-scan X-ray diffraction vibration curves of In _0.53 Ga _0.47 N with and without laser irradiation. In this figure, A is the case with irradiation and B is the case without irradiation. From this figure, it can be seen that the FWHM of the film grown by laser irradiation is smaller than that in the case of no laser irradiation.
FIG. 5 shows a surface image (A) and a cross-sectional image (B) of In _0.53 Ga _0.47 N observed by SEM. From this figure, it can be seen that even though a high concentration of In is grown at a low temperature, no phase separation or dislocation occurs and a uniform film is formed. In the cross-sectional image (B), GaN and InGaN are stacked in contact with each other, and it is predicted that a superlattice structure can be formed by setting the thicknesses of the well layer 3a and the barrier layer 3b to 10 nm or less, respectively. it can.
FIG. 6 shows the result of photoluminescence measurement of In _0.53 Ga _0.47 N, which is the active layer grown. In this figure, the horizontal axis indicates the wavelength [nm], and the vertical axis indicates the light emission intensity in photoluminescence.
In the figure, the solid line indicates light emission at room temperature (RT), and the broken line indicates light emission at 77K.

  From this figure, despite the high indium composition and non-doping, the emission at the puddle edge is seen, and high-quality InGaN is obtained, and high-quality InGaN can be obtained even at 600 ° C. or lower by irradiation with a pulse laser. It became clear. Since high-quality InGaN can be obtained even without being doped, it is clear that doping with n-type, p-type or both dopants can provide InGaN with higher light emission.

As described above, since growth is possible at 600 ° C. or lower, InGaN having the entire indium composition can be manufactured without causing phase separation. Similarly, a high-quality crystal can be obtained for p-type (Al _y Ga _1-y N: 0 ≦ y ≦ 1) grown on top of InGaN.
Further, by using an optical system that makes the beam uniform, for example, a (In _x Ga _1-x N: 0 <x <1) light-emitting layer necessary for a light-emitting device on the entire surface of a 2-inch size such as a sapphire substrate, and p-type _{(Al y Ga 1-y N} : 0 ≦ y ≦ 1) can be a grown at a low temperature.

  In addition, this invention is not limited to the Example and embodiment mentioned above, Of course, it can change variously in the range which does not deviate from the summary of this invention.

1 is a schematic view of an apparatus for growing a semiconductor crystal film according to the present invention. It is a structural example of the nitride semiconductor grown by the method of the present invention. It is a relationship figure of the width | variety of a well layer, and a light emission peak. It is a comparison figure of the ω-scan X-ray diffraction vibration curve of In0.53Ga0.47N with and without laser irradiation. It is the surface image (A) and cross-sectional image (B) of In0.53Ga0.47N observed by SEM. It is a diagram showing a photoluminescence measurement result of the grown _In 0.53 _{Ga 0.47} N with the present invention. FIG. 4 is a relationship diagram between the molar fraction x of In in indium gallium nitride and the equilibrium temperature.

Explanation of symbols

1 substrate, 2 n-type nitride semiconductor, 3 light emitting layer, 4 p-type nitride semiconductor,
5 Nitride semiconductors, 6 reaction vessels, 7 electrodes,
10 pulse laser, 12 laser controller,
11 excimer laser, 13 beam shaping optics,
14 mirror, 15 pump system, 16 stage controller,
17 Gas introduction part

Claims (9)

A nitride semiconductor light-emitting device in which an n-type nitride semiconductor, a light-emitting layer, and a p-type nitride semiconductor are sequentially grown on a crystal growth substrate,
The light emitting layer includes a well layer made of InN and In _x Ga _1-x N (0 ≦ x ≦ 0.3) or aluminum gallium nitride (Al _y Ga _1-y N: 0 ≦ y ≦ 0.3). A nitride semiconductor light emitting device, wherein the well layer and the barrier layer each have a thickness of 10 nm or less, thereby forming a superlattice structure. 2. The nitride semiconductor light emitting device according to claim 1, wherein the light emitting layer has a quantum well structure in which well layers and barrier layers are alternately stacked. 2. The nitride semiconductor light emitting device according to claim 1, wherein a film thickness ratio between the well layer and the barrier layer is set in a predetermined range so as to control an emission wavelength. 2. The nitride semiconductor light emitting device according to claim 1, wherein the thickness of the well layer is set in a predetermined range not exceeding 1 nm so as to control an emission wavelength. The nitride semiconductor light emitting device according to claim 1, wherein the n-type nitride semiconductor is gallium nitride or aluminum gallium nitride. A method for growing a nitride semiconductor, comprising sequentially growing an n-type nitride semiconductor, a light emitting layer, and a p-type nitride semiconductor on a crystal growth substrate,
The substrate for crystal growth is maintained at a temperature of about 600 ° C. or less in the reaction vessel, precursors are sequentially supplied into the reaction vessel, the surface of the substrate is irradiated with a pulsed laser, a well layer made of InN is formed on the irradiated portion, and In _{x Ga 1-x N (0} ≦ x ≦ 0.3) or aluminum gallium nitride _{(Al y Ga 1-y N} : 0 ≦ y ≦ 0.3) alternately by organometallic vapor phase epitaxy and a barrier layer made of And growing a film thickness of 10 nm or less to form a superlattice structure, respectively. The method for growing a nitride semiconductor according to claim 6, wherein a film thickness ratio between the well layer and the barrier layer is set in a predetermined range so as to control an emission wavelength. 7. The method for growing a nitride semiconductor according to claim 6, wherein the film thickness of the well layer is set to a predetermined range not exceeding 1 nm so as to control the emission wavelength. The nitride semiconductor growth method according to claim 6, wherein the pulse laser is a YAG laser, an excimer laser, or the like.

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