JP2009266963A - Nitride-based light emitting device, and method of manufacturing semiconductor light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light emitting device in a structure that provides the light emission of a long wavelength and indicates small blue shift. <P>SOLUTION: In a nitride-based light emitting diode 11, the main surface 13a of a nitride gallium substrate 13 indicates semi-polarity and is inclined in a prescribed direction at an angle θ ≥18 degrees and ≤28 degrees to the (000-1) surface of hexagonal nitride gallium. An active layer 19 has a quantum well structure 23, and the quantum well structure 23 includes a well layer 25a comprising In<SB>X</SB>Ga<SB>1-X</SB>N(0.2<X<1) and a barrier layer 25b comprising a nitride gallium based semiconductor. The active layer 19 generates light having a peak wavelength in a wavelength range ≥510 nm. The well layer 25a is extended along a prescribed plane (plane stipulated by an X axis and a Y axis) inclined to the (000-1) surface of the In<SB>X</SB>Ga<SB>1-X</SB>N of the well layer 25a. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nitride-based light emitting device and a method for manufacturing a semiconductor light emitting device.

Non-Patent Document 1 describes an InGaN / GaN quantum well structure on a template having N-plane GaN grown on a sapphire substrate. Non-Patent Document 2 describes a light emitting diode. The light emitting diode has an InGaN / GaN quantum well structure on a GaN film grown on an m-plane sapphire substrate. The InGaN / GaN quantum well structure is grown on a semipolar (10-1-3) plane. The semipolar (10-1-3) plane is inclined at an angle of 32 degrees with respect to the Ga plane. Non-Patent Document 3 describes a light emitting diode. The light emitting diode has an InGaN / GaN quantum well structure. This InGaN / GaN quantum well structure is grown on a semipolar (11-22) plane GaN substrate. The (11-22) plane is inclined at an angle of 58.4 degrees with respect to the Ga plane.
S. Kelier et al. Appl. Phys. Lett. Vol. 90 pp.191908, (2007) R. Sharma et al. Appl. Phys. Lett. Vol. 87 pp.231110, (2005) Mitsuru Funato et al. Jpn. J Appl. Phys. Vol. 45 No. 26, 2005, pp.L659-L662

  The light emitting elements of Non-Patent Documents 1 and 2 use a template provided on a sapphire substrate, and do not use a GaN substrate. Therefore, an epitaxial film having a low dislocation density cannot be obtained.

  When the light-emitting element is fabricated on a c-plane (polar plane) gallium nitride substrate, a large blue shift is observed regardless of whether it is a Ga plane or an N plane. One cause of the blue shift is a piezo electric field. When the light emitting element is fabricated on an m-plane or a-plane (nonpolar plane) gallium nitride substrate, a blue shift due to a piezoelectric field does not occur.

  Since the quantum well structure of Non-Patent Document 1 is formed on the N-polar plane, it exhibits a large blue shift. Further, although the light emitting diodes of Non-Patent Documents 2 and 3 are manufactured on a semipolar plane, these semipolar planes are inclined at a large angle from the c plane, and therefore a large-diameter semiconductor wafer is used. It is not suitable for making. However, there is a demand for a light emitting element that exhibits a small blue shift.

  Further, the growth of InGaN on the semipolar plane is different from the growth of InGaN on the polar plane. When InGaN is grown under the same film formation conditions, the In composition of InGaN grown on the semipolar plane is smaller than the In composition of InGaN grown on the polar plane. However, a light-emitting element that emits light having a long wavelength is required. For this purpose, it is necessary to grow an InGaN layer having a large indium composition.

  Furthermore, in consideration of manufacturing a light-emitting element, the light-emitting element preferably has a structure that can be manufactured using a large-diameter wafer. For this purpose, it is preferable to use a crystal growth technique for producing an available GaN wafer by using a wafer having a relatively small off angle.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a nitride-based light-emitting device having a structure that can provide long-wavelength light emission and exhibits a small blue shift. An object of the present invention is to provide a method of producing

A nitride-based light-emitting device according to one aspect of the present invention is a nitride-based light-emitting device that generates light having a peak wavelength in a wavelength range of 510 nm or more, and includes (a) hexagonal gallium nitride, A gallium nitride substrate having a semipolar principal surface inclined in a predetermined direction at an angle of 18 degrees to 28 degrees with respect to the (000-1) plane of crystalline gallium nitride; and (b) provided on the gallium nitride substrate. An n-type gallium nitride based semiconductor region, (c) a p-type gallium nitride based semiconductor region provided on the gallium nitride substrate, and (d) an In _X Ga _1-X N (0.2 <X) well. And an active layer provided on the semipolar main surface of the gallium nitride substrate. The active layer is provided between the n-type gallium nitride semiconductor region and the p-type gallium nitride semiconductor region, and the active layer, the n-type gallium nitride semiconductor region, and the p-type gallium nitride semiconductor region Were stacked in the direction of the axis intersecting the semipolar main surface of the gallium nitride substrate.

This nitride-based light emitting device, _{In X Ga 1-X} N well layer is provided on the semipolar primary surface inclined at an angle of less than 18 degrees 28 degrees, the _{In X Ga 1-X} N well The layer extends along a predetermined plane inclined with respect to the (000-1) plane of the In _X Ga _1-X N well layer. Therefore, the blue shift of the light emitting element can be reduced. Further, since the semipolar plane is inclined from the N plane rather than the Ga plane, the amount of In composition taken in can be increased as compared to the semipolar plane provided by the inclination from the Ga plane. Furthermore, since a semipolar surface having a small inclination angle with respect to the c-plane is used, this light-emitting element can be manufactured using a large-diameter wafer.

The nitride-based light emitting device according to the present invention may further include an Al _Y Ga _1-Y N (0 <Y <1) layer that covers the semipolar main surface of the gallium nitride substrate. According to this nitride-based light emitting device, since the Al _Y Ga _1-Y N layer covers the semipolar surface having a thermally unstable property as compared with the Ga surface, epitaxial growth for the light emitting device is performed on the N surface. It is not performed on the semipolar plane of the natural property but on the Al _Y Ga _1-Y N layer.

  The nitride-based light emitting device according to the present invention may further include an n-type InGaN layer provided between the active layer and the n-type gallium nitride semiconductor region. According to this nitride-based light emitting device, the influence of the difference in lattice constant between the active layer having a high In composition and the GaN substrate can be reduced.

  In the nitride-based light-emitting element according to the present invention, the predetermined direction can be either the a-axis or m-axis direction of the hexagonal gallium nitride. According to this nitride-based light emitting device, crystal growth on the semipolar plane is good.

  In the nitride-based light emitting device according to the present invention, the active layer may be provided on the semipolar main surface of the gallium nitride substrate so as to generate light having a peak wavelength in a range of 540 nm or less. According to the nitride-based light emitting device, a light emitting device that generates light in a so-called green wavelength region can be provided.

In the nitride-based light emitting device according to the present invention, an indium composition of the In _X Ga _1-X N well layer may be 0.35 or less. In the nitride-based light emitting device according to the present invention, the width of the In _X Ga _1-X N well layer may be 5 nm or more and 10 nm or less. According to the nitride-based light emitting device, since the piezoelectric field is small, the width of the In _X Ga _1-X N well layer can be increased. If the width of the In _X Ga _1-X N well layer is 20 nm or less, lattice relaxation does not occur.

Another aspect of the present invention is a method for generating light having a peak wavelength in a wavelength range of 510 nm or more. In this method, (a) a step of preparing a gallium nitride substrate having a semipolar main surface inclined at an angle of 10 degrees to 28 degrees from the (000-1) plane; and (b) In _X Ga _1-X N (0.2 <X) growing an active layer having a well layer on the semipolar main surface. A growth temperature for the well layer is included in a range of 600 degrees Celsius or more and 700 degrees Celsius or less.

According to this method, an In _X Ga _1-X N well layer is formed on a semipolar main surface inclined at an angle of 18 degrees to 28 degrees, and the In _X Ga _1-X N well layer is formed into the In _X Ga _1-X N well layer. _X Ga extending along a predetermined plane which is inclined with respect to _1-X N-well layer (000-1) plane. Therefore, the blue shift of the light emitting element can be reduced. Further, since the semipolar plane is inclined from the N plane rather than the Ga plane, the amount of In composition taken in can be increased as compared to the semipolar plane provided by the inclination from the Ga plane. Furthermore, since a semipolar surface having a small inclination angle with respect to the c-plane is used, this light-emitting element can be manufactured using a large-diameter wafer.

  The above and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings.

  As described above, according to the present invention, a nitride-based light-emitting element having a structure that can provide long-wavelength light emission and exhibits a small blue shift is provided.

  The knowledge of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown as examples. Subsequently, embodiments of the nitride-based light emitting device of the present invention will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals. Examples of the nitride-based light emitting device include a light emitting diode and a semiconductor laser.

FIG. 1 is a drawing schematically showing a structure of a nitride-based light emitting diode according to an embodiment of the present invention. In FIG. 1, an orthogonal coordinate system S is shown. Are shown vectors V _C indicating the direction of the c axis of the hexagonal gallium nitride, also typical c-plane C is illustrated in broken lines. Further, in order to show the direction of the crystal axis, a crystal coordinate system CR is shown, and an a axis, an m axis, and a c axis that are orthogonal to each other are drawn. The nitride-based light emitting diode 11 includes a gallium nitride substrate 13, an n-type gallium nitride-based semiconductor region 15, a p-type gallium nitride-based semiconductor region 17, and an active layer 19. The gallium nitride substrate 13 is made of hexagonal gallium nitride. The main surface 13a of the gallium nitride substrate 13 exhibits semipolarity, and is in a predetermined direction at an angle θ of 18 degrees or more and 28 degrees or less with respect to the (000-1) plane of the hexagonal gallium nitride. Inclined. With this inclination, a semiconductor light emitting device capable of reducing the influence of the piezoelectric field can be manufactured. The angle θ is defined by, for example, (θ _M ² + θ _A ² ) ^1/2 . The angle component θ _A is a tilt angle component with respect to the a-axis direction of hexagonal gallium nitride, and the angle component θ _M is a tilt angle component with respect to the m-axis direction of hexagonal gallium nitride. Preferably, the predetermined direction can be either the a-axis or m-axis direction. According to the nitride-based light emitting diode 11, crystal growth on the semipolar plane is improved. The inclination in the a-axis direction has the advantage that the steps are arranged in the m-axis direction, and the inclination in the m-axis direction has the advantage that the steps are arranged in the a-axis direction. The n-type gallium nitride semiconductor region 15, the active layer 19, and the p-type gallium nitride semiconductor region 17 are provided on the main surface 13 a of the gallium nitride substrate 13. The n-type gallium nitride based semiconductor region 15, the active layer 19, and the p-type gallium nitride based semiconductor region 17 are arranged in the direction of an axis (for example, the Z axis shown in FIG. 1) intersecting the main surface 13a. The active layer 19 is provided so as to generate light having a peak wavelength in a wavelength range of 510 nm or more. The active layer 19 is provided between the n-type gallium nitride semiconductor region 15 and the p-type gallium nitride semiconductor region 17. The active layer 19 has a quantum well structure 23, the quantum well structure _{23, In X Ga 1-X N} (0.2 <X <1) consisting of well layers 25a and the gallium nitride-based semiconductor consisting of a barrier layer 25b. The well layers 25a and the barrier layers 25b are alternately arranged in the Z-axis direction. The well layer 25a extends along a predetermined plane (a plane defined by the X-axis and the Y-axis) that is inclined with respect to the (000-1) plane of In _X Ga _1-X N of the well layer 25a.

According to the nitride-based light emitting diode 11, the well layer 25a is provided on the main surface 13a inclined at an angle of 18 degrees or more and 28 degrees or less, and the well layer 25a is made of the In _X Ga _1-X N ( 000-1) extends along the XY plane inclined with respect to the plane. Therefore, the blue shift of the light emitting diode 11 can be reduced. Further, since the inclination angle θ is defined from the N plane rather than the Ga plane, the amount of In composition taken in can be increased compared to the semipolar plane provided by the inclination from the Ga plane. Furthermore, since a semipolar surface having a small inclination angle with respect to the c-plane is used, this light-emitting element has a structure that can be manufactured using a large-diameter wafer.

In the active layer 19, the indium composition X of the In _X Ga _1-X N well layer 25 a can be 0.20 or more, which can increase the emission wavelength. The indium composition X of the In _X Ga _1-X N well layer 25a can be 0.35 or less, whereby the emission wavelength can be extended to the green range. Further, the width _DW of the In _X Ga _1-X N well layer 25a is preferably 5 nm or more, which can increase the emission intensity. Further, the width D _W can be 20 nm or less, which can suppress lattice relaxation due to distortion while increasing the emission intensity. Since the light emitting diode 11 uses the semipolar surface 13a, the piezoelectric field in the In _X Ga _1-X N well layer 25a is small. Therefore, the width of the In _X Ga _1-X N well layer 25a can be increased. If the width _{DW of the} In _X Ga _1-X N well layer 25a is 20 nm or less, lattice relaxation does not occur.

In the active layer 19, the barrier layer 25b can be made of a gallium nitride based semiconductor such as GaN, InGaN, InAlGaN or the like. Width _{D B} of the barrier layer 25b can be for example at 5nm or more and is 20nm or less.

The nitride-based light emitting diode 11 can further include an Al _Y Ga _1-Y N (0 <Y <1) layer 27 that covers the main surface 13 a of the gallium nitride substrate 13. Since the Al _Y Ga _1-Y N layer 27 covers the semipolar surface 13a, which is thermally unstable compared to the Ga surface, the epitaxial growth for the light emitting diode 11 is thermally unstable N-surface. It is performed on the Al _Y Ga _1-Y N layer 27 without being performed on the semipolar surface 13a having a special property. The aluminum composition Y of the Al _Y Ga _1-Y N layer 27 is preferably 0.01 or more, and preferably 0.1 or less. Further, the film thickness D _Al of the Al _Y Ga _1-Y N layer 27 is preferably 5 nm or more, and the film thickness D _Al is preferably 20 nm or less, which causes a decrease in crystallinity. The initial surface can be flattened.

The light emitting diode 11 can further include an In _Z Ga _1-Z N (0 <Z <1) layer 29 provided between the active layer 19 and the n-type gallium nitride based semiconductor region 15. According to the InGaN layer 29, the influence of the lattice constant difference between the active layer 19 having a high average In composition and the GaN substrate 13 can be reduced. An In _Z Ga _1-Z indium composition Z of the N layer 29 is preferably 0.25 or more and 0.35 or less. _The thickness _{D an In} of In _{Z Ga 1-Z} N layer 29 is preferably 5nm or more. The film thickness D _In is preferably 20 nm or less, whereby the emission intensity can be increased while increasing the emission wavelength without relaxing the lattice.

The n-type gallium nitride based semiconductor region 15 may include an n-type gallium nitride based semiconductor layer to provide electrons to the active layer 19.
The p-type gallium nitride based semiconductor region 17 can include, for example, an electron block layer 31 and a p-type contact layer 33. A first electrode 35 is provided on the p-type contact layer 33. The first electrode 35 makes a good ohmic contact with the p-type contact layer 33. A second electrode 37 is provided on the back surface 13 b of the GaN substrate 13. The second electrode 37 makes a good ohmic contact with the GaN substrate 13.

  In the light emitting diode 11, the light L from the active layer 19 is emitted through the first electrode 35. Therefore, the first electrode 35 is provided so that light from the active layer 19 can be transmitted. The active layer 19 is provided on the semipolar main surface 13a of the gallium nitride substrate 13 so as to generate light having a peak wavelength in the range of 540 nm or less. According to the light emitting diode 13, light in a so-called green wavelength region is generated.

An example light emitting diode has the following structure.
Gallium nitride substrate 13: off angle 18 degrees, thickness 400 μm AlGaN layer 27: Si-added Al _0.1 Ga _0.9 N, thickness 10 nm
n-type gallium nitride based semiconductor region 15: Si-doped GaN, 2000 nm
Active layer 19: In _0.3 Ga _0.7 N / In _0.05 Ga _0.95 N, thickness 3 nm / 15 nm
p-type gallium nitride semiconductor region 17: electron block layer 31 and p-type contact layer 33
Electron blocking layer 31: Mg-added Al _0.15 Ga _0.85 N, thickness 20 nm
p-type contact layer 33: Mg-doped GaN, thickness 50 nm.

FIG. 2 is a drawing showing main steps of a method for manufacturing a light emitting diode according to the present embodiment. In step S101, as shown in FIG. 3A, a GaN wafer 40 having a main surface inclined from the N plane _SN is prepared. The main surface 40a of the GaN wafer 40 is inclined at an angle in the range of 18 degrees to 28 degrees with respect to the N-plane. In step S102, as shown in FIG. 3B, the GaN wafer 40 is placed in the growth reactor R, and the GaN wafer 40 is heat-treated. The heat treatment is performed in an atmosphere containing ammonia and hydrogen. The heat treatment temperature for the N plane is, for example, 900 degrees Celsius.

  In step S103, as shown in FIG. 3C, the n-type AlGaN layer 41 is epitaxially grown so as to cover the main surface 40a of the n-type GaN wafer 40. The growth temperature is, for example, 1000 degrees Celsius, and can range from 950 degrees Celsius to 1050 degrees Celsius. The thickness of the n-type AlGaN layer 41 is, for example, about 10 nm, and can be in the range of 5 nm to 20 nm.

  In step 104, as shown in FIG. 3D, the n-type GaN layer 42 is epitaxially grown so as to cover the main surface 41a of the n-type AlGaN layer 41. The growth temperature is, for example, 950 degrees Celsius, and can be in the range of 900 degrees Celsius or more and 1050 degrees Celsius or less. The thickness of the n-type GaN layer 42 is, for example, about 2000 nm, and can be in the range of not less than 500 nm and not more than 4000 nm.

  In step 105, as shown in FIG. 3E, the n-type InGaN layer 43 is epitaxially grown so as to cover the main surface 42a of the n-type GaN layer 42. The growth temperature is, for example, 750 degrees Celsius, and can be in the range of 700 degrees Celsius or more and 850 degrees Celsius or less. The thickness of the n-type InGaN layer 43 is, for example, about 50 nm, and can be in the range of 10 nm to 100 nm.

  In step S106, the active layer 44 is formed on the n-type InGaN layer 43 as shown in FIG. The active layer 44 has one or more group III nitride semiconductor layers containing In. In step S107, a barrier layer 44a is grown on the n-type InGaN layer 43. The growth temperature is, for example, 750 degrees Celsius, and can be in the range of 700 degrees Celsius or more and 800 degrees Celsius or less. In step S108, a well layer 44b is grown on the barrier layer 44a. The growth temperature is, for example, 650 degrees Celsius, and can be in the range of 550 degrees Celsius to 700 degrees Celsius. In step S109, the growth of the barrier layer 44a and the well layer 44b is repeated until the active layer is completed. The well layer 44b of the active layer 44 can be made of InGaN, and the barrier layer 44a can be made of InGaN or GaN. The thickness of the well layer is 20 nm or less, and can be 5 nm or more. The thickness of the barrier layer is, for example, 15 nm. Since the low-temperature grown InGaN buffer layer 43 is provided on the n-type GaN semiconductor layer 42, the influence of distortion of the InGaN well layer 44b in the active layer 44 is reduced. Further, as described above, the c-plane of the well layer 44b is also inclined at an off angle in the range of 18 degrees to 28 degrees from the N-plane.

  In step S110, as shown in FIG. 4B, the p-type AlGaN semiconductor layer 45 is epitaxially grown on the active layer 44. The p-type AlGaN semiconductor layer 45 is, for example, an electron block layer. The thickness of the p-type AlGaN semiconductor layer 45 is, for example, 20 nm, and Mg is added to the p-type AlGaN semiconductor layer 45.

  In step S111, as shown in FIG. 4C, the p-type contact layer 46 is epitaxially grown on the p-type AlGaN semiconductor layer 45. The thickness of the p-type contact layer 46 is, for example, 50 nm. The p-type contact layer 46 can be, for example, p-type GaN or p-type AlGaN, and Mg is added to the p-type contact layer 46. By these processes. An epitaxial wafer E is produced.

  Next, a first electrode (anode electrode) is formed on the p-type contact layer 46 of the epitaxial wafer E, and a second electrode (cathode electrode) is formed on the back surface 40 b of the GaN wafer 40. The first electrode can be, for example, a translucent electrode.

(Example)
A semipolar substrate is used to reduce the piezo electric field due to the lattice distortion contained in the InGaN active layer. In the experiment by the inventor, in the range of the combined angle off angle of 18 degrees to 28 degrees, the semipolar plane inclined from the (000-1) N polar plane is more even by the inclination from the (0001) Ga polar plane. A lot of In can be taken in. This is considered to be due to the difference in bonds appearing on the semipolar surface. As the off angle approaches 90 degrees, it approaches the nature of a nonpolar surface (no difference between the front and back). For this reason, the influence by the difference in the surface bond is reduced, and the difference in In incorporation is reduced.

  In addition, the above-described semipolar surface with an off angle has improved the thermal and chemical stability of the wafer surface and the surface roughness of the epitaxial film compared to the just N surface where nitrogen bonds appear on the entire surface. Reduced.

  Furthermore, the generation of hillocks on the surface of the epitaxial film can be reduced by covering the semipolar surface with a gallium nitride based semiconductor layer containing Al at the start of growth. This is understood as follows: aluminum having a strong binding force is bonded to the nitrogen (N) step end, and step-flow-like growth continues with the bonded aluminum as a starting point, so that the flatness of the epitaxial film is improved. Improved.

An InGaN epitaxial film was grown on a GaN wafer having an off angle from the N plane. On the gallium nitride surface inclined with a small off angle from the (000-1) N plane, the indium uptake amount was small under the growth conditions, and in the larger off angle range, the indium uptake amount was further reduced. For example, on the (000-1) plane, the growth temperature of the InGaN active layer was 760 degrees Celsius and the growth rate was 0.15 μm / h. Under this growth condition, an In _0.23 Ga _0.77 N epitaxial film is obtained, and blue light green P emission is possible with this indium composition. However, using the same growth conditions, an InGaN epitaxial film was grown on a GaN wafer having an off angle from the N plane. The indium composition was 14% at an off angle of 18 degrees, and the indium composition was 11% at an off angle of 28 degrees. On the other hand, in the growth on the (0001) Ga plane, the indium composition was 10% at an off angle of 18 degrees, and the indium composition was 7% at an off angle of 28 degrees. The use of a GaN wafer inclined from the N-plane has been effective in increasing the amount of indium that can be incorporated.

  A light emitting diode (LED) was fabricated. A GaN wafer inclined at an off angle of 18 degrees in the a-axis direction was prepared. The GaN wafer was heat-treated at 1000 degrees Celsius in an atmosphere containing ammonia and hydrogen. Thereafter, trimethylgallium (TMG), trimethylaluminum (TMA) and ammonia were supplied in a growth furnace to grow an n-type AlGaN film on the GaN wafer. The n-type AlGaN film has a thickness of 10 nm. Under the growth conditions, the flow rate of TMG was 4.9 sccm, the flow rate of TMA was 11.5 sccm, and the flow rate of ammonia was 24 slm.

  Next, TMG and ammonia were supplied in a growth furnace to grow an n-type GaN film on the AlGaN film. The n-type GaN film had a thickness of 2000 nm. Under the growth conditions, the flow rate of TMG was 40 sccm and the flow rate of ammonia was 24 slm.

  Thereafter, TMG, trimethylindium (TMI) and ammonia were supplied in a growth furnace to grow an n-type InGaN film on the n-type GaN film. The n-type InGaN film has a thickness of 50 nm. Under the growth conditions, the flow rate of TMG was 3.0 sccm, the flow rate of TMI was 1.8 sccm, and the flow rate of ammonia was 29.6 slm.

  In the growth of the active layer, the growth conditions of the InGaN well layer are as follows: the growth temperature is 650 degrees Celsius, the flow rate of TMG is 6.0 sccm, the flow rate of TMI is 3.2 sccm, and ammonia The flow rate of was 100 slm. The growth rate was 0.08 μm / h. The indium composition was 0.3. The growth conditions of the InGaN barrier layer were as follows: the growth temperature was 750 degrees Celsius, the TMG flow rate was 4.9 sccm, the TMI flow rate was 7.4 sccm, and the ammonia flow rate was 14. 7 slm.

  On the active layer, TMG, TMA and ammonia were supplied in a growth furnace to grow a p-type AlGaN film for an electron blocking layer. The p-type AlGaN film has a thickness of 20 nm. Under the growth conditions, the flow rate of TMG was 3.4 sccm, the flow rate of TMA was 3.9 sccm, and the flow rate of ammonia was 19.6 slm.

  On the p-type AlGaN film, TMG and ammonia were supplied in a growth furnace to grow a p-type GaN film for the contact layer. The p-type GaN film had a thickness of 50 nm. Under the growth conditions, the flow rate of TMG was 27 sccm, and the flow rate of ammonia was 19.4 slm. As a result, an epitaxial wafer was completed.

  After forming an electrode on the epitaxial wafer, an electroluminescence (EL) spectrum was measured. FIG. 5 is an example of current-EL (electroluminescence) characteristics of the semiconductor light emitting device obtained by the manufacturing method according to the above embodiment, the horizontal axis indicates the supply current value (mA), and the vertical axis indicates the EL intensity (μW). Is shown. FIG. 6 is an example of the emission spectrum of the semiconductor light emitting device obtained by the manufacturing method according to the above embodiment, the horizontal axis indicates the wavelength (nm), and the vertical axis indicates the light intensity (the output of the spectrometer, the unit is mV). ). The peak wavelength was 520 nm green light emission. The blue shift of the emission wavelength was 6 nm at an applied current of 20 mA to 200 mA. On the other hand, an epitaxial wafer was similarly fabricated on an N-plane GaN wafer. After forming the electrode on the epitaxial wafer, the EL spectrum was measured. The peak wavelength was 511 nm. The blue shift of the emission wavelength was 27 nm at 20 mA to 200 mA.

  As described above, according to the method for manufacturing a semiconductor light emitting device according to the present embodiment, in the active layer having a small piezo electric field and a high In composition compared to the case of using a GaN wafer having a c-plane as a main surface. A green light-emitting semiconductor light-emitting element in which blue shift is suppressed can be manufactured. In addition, a green LED can be manufactured using a semipolar GaN wafer having a large diameter of 2 inches.

  FIG. 5 is a diagram for explaining a specific example of the growth of the active layer in detail. Referring to FIG. 5A, the temperature transition of the GaN wafer 40 when the active layer 44 is grown is shown. Referring to FIG. 5B, a supply gas supply profile is shown. First, an InGaN crystal that becomes a well layer is grown in a period T1. In the step of growing the well layer, the growth temperature of the well layer can be 550 degrees Celsius or higher, and can be 700 degrees Celsius or lower. Generally, the temperature for growing an InGaN crystal on a polar surface is set to about 780 degrees Celsius in order to obtain a sufficient crystal quality. However, a lower temperature is used for the growth of the well layer in the present embodiment. A suitable growth temperature is, for example, 650 degrees Celsius.

In the step of growing the well layer, the flow rate _Q In of the flow rate _Q V (mol / min) and In source gas of the material gas of the V group element (e.g., ammonia) (such as trimethyl indium) (mol / min) The molar flow rate ratio (Q _V / Q _In ) is preferably 9000 or more, and preferably 30000 or less. Generally, the molar flow rate ratio when growing an InGaN crystal is adjusted to about 40000 in order to prevent generation of droplets. The molar flow rate ratio in this embodiment is lower than this. That is, the molar flow rate ratio has a large proportion of In source gas. A suitable molar flow ratio is, for example, 24000.

  In the step of growing the well layer, the growth rate of the well layer is preferably 0.01 (μm / hour) or more, and preferably 0.1 (μm / hour) or less. Generally, the growth rate of InGaN crystal is adjusted to about 0.15 (μm / hour). The growth rate of the well layer in this embodiment is slower than this. A suitable growth rate is, for example, 0.08 (μm / hour).

  Subsequently, in the period T2, a barrier layer made of a GaN crystal is grown. In the step of growing the barrier layer, the supply of trimethylindium, which is an In source gas, is stopped, and the temperature of the GaN wafer 40 is raised to, for example, 800 degrees Celsius, and then a GaN crystal is grown. When the barrier layer is made of InGaN, it is preferable to raise the temperature of the GaN wafer 40 to, for example, 750 degrees Celsius while reducing the supply amount of trimethylindium from the period T1.

  In the growth of the active layer 44, the well layers and the barrier layers are alternately grown in the periods T3 to T6 after the period T2. That is, in the period T3 and the period T5 after the period T2, the well layer is grown using the same growth conditions as in the period T1. In the period T4 after the period T3 and the period T6 after the period T5, the barrier layer is grown using the same growth conditions as in the period T2.

  The effects obtained by the manufacturing method described above will be described together with the process in which the present inventor obtained a solution problem and reached the solution. First, InGaN crystals were grown under the same growth conditions on a plurality of GaN wafers having different inclination angles with respect to the N plane in order to determine the conditions for InGaN growth enabling green light emission in the active layer including the InGaN well layer. At this time, the In composition ratio in InGaN was different depending on the off angle of the c-plane with respect to the N-plane. In the off-angle range where the tilt angle is relatively small, the In composition ratio decreased as the off-angle increased. However, this decrease was found to be small compared to InGaN growth on a semipolar plane inclined from the c-plane Ga plane. That is, the semipolar plane inclined from the N plane is easier to incorporate In than the semipolar plane inclined from the Ga plane.

  The present inventor examined a method for increasing the In composition ratio in order to further shift the photoluminescence spectrum of the group III nitride semiconductor layer containing In grown on the semipolar plane of the GaN wafer to a longer wavelength. . As a result, the growth temperature and growth rate of the group III nitride semiconductor layer are lowered and the molar flow ratio of the In source gas is increased as compared with the conventional growth conditions, and the off-angle from the N plane is also obtained. It has been found that by using a GaN wafer, light having a longer wavelength can be obtained.

The present inventor uses a GaN wafer having a semipolar main surface with an off angle in the range of 18 degrees or more and 28 degrees or less in inclination from the N plane instead of the Ga plane, and uses conventional growth conditions to increase the In adhesion rate. As compared with the above, the In incorporation ratio is increased by lowering the growth temperature of the group III nitride semiconductor layer and lowering the growth rate. Specifically, the following conditions were used when the group III nitride semiconductor layer was grown on the GaN wafer having the off angle.
Growth temperature: 600 degrees Celsius or more and 700 degrees Celsius or less,
Molar flow rate ratio (Q _V / Q _In ): 9000 to 30000,
The flow rate Q _V (mol / min) of the source gas of the group V element (for example, ammonia) and the flow rate Q _In (mol / min) of the source gas of _In
Group III nitride semiconductor layer growth rate: 0.01 (μm / hour) or more and 0.1 (μm / hour)] or less.
As a result, the In incorporation ratio can be increased while maintaining good crystallinity.

  In this embodiment, the active layer 44 has a multiple quantum well structure, and the growth temperature of the GaN barrier layer grown on the InGaN well layer is 800 degrees Celsius, which is higher than the growth temperature of the InGaN well layer. Thereby, an annealing effect on the InGaN well layer can be obtained when the GaN barrier layer is grown.

  In order to investigate the In composition of the group III nitride semiconductor layer obtained by the above method, an InGaN single layer having a thickness of 50 (nm) was grown on the GaN wafer by the above method. At this time, a granular material having a diameter of several tens of nm was observed on the surface of the layer. As a result of specifying this granular material by X-ray diffraction and composition analysis, it was found to be an In droplet. However, when an InGaN well layer having a thickness of 3 nm is grown on a GaN wafer by the above method, no In droplet is generated according to TEM observation. When the thickness of the InGaN layer grown by the above method is extremely thin (for example, 20 nm or less), it is considered that the growth is completed before the In droplet is generated.

  As described above, the growth condition according to the above method is that a large InGaN layer having a thickness of, for example, 50 nm is grown, and a large amount of In source gas is supplied to the extent that In droplets are formed. On the main surface of the GaN wafer having an off-angle, the surface step density is large and the c-plane terrace width is small, so that In acts as a surfactant due to the large amount of supply of In source gas, and a large amount is taken into the InGaN crystal. It is thought that it came to be. In addition, since In atoms migrate using the main surface of the GaN wafer having a small terrace width as a surfactant, it is considered that the deterioration of the crystal quality is suppressed even when the growth temperature of the InGaN crystal is low.

  When growing the InGaN single layer with a thickness of 50 nm, if the molar flow ratio of the In source gas was lowered, In droplets were gradually not observed, but the In composition ratio was lowered, the emission wavelength was shortened, and the green emission Could not be realized. For comparison, when an InGaN crystal was grown under the growth conditions according to the above method using a GaN wafer having a c-plane as a main surface, the occurrence of In droplets was observed when a GaN wafer having an off angle was used. It became equivalent. However, sufficient light emission intensity could not be obtained under the growth conditions where the molar flow rate ratio of the In source gas was reduced to such an extent that In droplets were not generated even when the thick film was grown.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

FIG. 1 is a drawing schematically showing a structure of a nitride-based light emitting diode according to an embodiment of the present invention. FIG. 2 is a flowchart showing main steps of the method for manufacturing the light emitting diode according to the present embodiment. FIG. 3 is a diagram showing products in main steps of the method for manufacturing the light emitting diode according to the present embodiment. FIG. 4 is a drawing showing products in the main steps of the method for manufacturing a light emitting diode according to the present embodiment. FIG. 5 is a diagram showing current-EL characteristics of the semiconductor light emitting device obtained by the manufacturing method according to the embodiment. FIG. 6 is a view showing an emission spectrum of the semiconductor light emitting device obtained by the manufacturing method according to the embodiment. FIG. 7 is a drawing showing the temperature transition of the GaN wafer and the supply state of the source gas during the growth of the active layer.

Explanation of symbols

11 ... light-emitting diode, 13 ... gallium nitride substrate, 15 ... n-type gallium nitride based semiconductor region, 17 ... p-type gallium nitride based semiconductor region, 19 ... active layer, 23 ... quantum well _{structure, 25a ... In X Ga 1-} X N well layer, 25b ... barrier layer made of gallium nitride semiconductor, 27 ... AlGaN layer, 31 ... electron block layer, 33 ... p-type contact layer, 40 ... GaN wafer, 41 ... n-type AlGaN layer, 42 ... n-type GaN layer,
43 ... n-type InGaN layer, 44 ... active layer, 44a ... barrier layer, 44b ... well layer, 45 ... p-type AlGaN semiconductor layer, 46 ... p-type contact layer

Claims (8)

A nitride-based light emitting device that generates light having a peak wavelength in a wavelength range of 510 nm or more,
A gallium nitride substrate made of hexagonal gallium nitride and having a semipolar principal surface inclined in a predetermined direction at an angle of 18 degrees to 28 degrees with respect to the (000-1) plane of the hexagonal gallium nitride;
An n-type gallium nitride based semiconductor region provided on the gallium nitride substrate;
A p-type gallium nitride based semiconductor region provided on the gallium nitride substrate;
An active layer provided on the semipolar main surface of the gallium nitride substrate, including an In _X Ga _1-X N (0.2 <X) well layer and a gallium nitride based semiconductor barrier layer;
The active layer is provided between the n-type gallium nitride semiconductor region and the p-type gallium nitride semiconductor region,
The active layer, the n-type gallium nitride based semiconductor region, and the p-type gallium nitride based semiconductor region are stacked in a direction of an axis intersecting the semipolar main surface of the gallium nitride substrate. Physical light emitting device. The nitride _- based light-emitting element according to claim 1, further comprising an Al _Y Ga _1-Y N (0 <Y <1) layer covering the semipolar main surface of the gallium nitride substrate. 3. The nitride-based light emitting device according to claim _1, wherein an indium composition of the In _X Ga _1-X N well layer is 0.35 or less. 4. The nitride-based light-emitting element according to claim 1, wherein a width of the In _X Ga _1-X N well layer is 5 nm or more and 20 nm or less. 5.   5. The active layer according to claim 1, wherein the active layer is provided on the semipolar main surface of the gallium nitride substrate so as to generate light having a peak wavelength in a range of 540 nm or less. The nitride-based light emitting device according to one item.   The nitride according to any one of claims 1 to 5, further comprising an n-type InGaN layer provided between the active layer and the n-type gallium nitride based semiconductor region. System light emitting element.   The nitride system according to any one of claims 1 to 6, wherein the predetermined direction is one of an a-axis direction and an m-axis direction of the hexagonal gallium nitride. Light emitting element. A method of manufacturing a semiconductor light emitting device that generates light having a peak wavelength in a wavelength range of 510 nm or more,
A step of preparing a gallium nitride substrate having a semipolar principal surface inclined at an angle of not less than 10 degrees and not more than 28 degrees from the (000-1) plane;
And growing an active layer having an In _X Ga _1-X N (0.2 <X) well layer on the semipolar main surface,
The growth temperature for the well layer is in the range of 600 degrees Celsius or more and 700 degrees Celsius or less.

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