JP3716395B2 - Semiconductor light emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light emitting device, and more particularly to a semiconductor light emitting device such as a short wavelength semiconductor laser in which tensile strain is introduced into an active layer made of a GaN compound semiconductor.
[0002]
[Prior art]
In recent years, short-wavelength semiconductor lasers having wavelengths from blue to the near-ultraviolet region have been actively developed. As materials for blue semiconductor lasers, ZnSe-based II-VI compound semiconductors and GaN-based III-V compound semiconductors are used. And have been studied.
[0003]
Of these, the ZnSe system is almost lattice-matched with GaAs, which has a proven track record as a high-quality substrate. Therefore, the ZnSe system is considered to be more advantageous for a long time, and the majority of researchers around the world have studied this ZnSe system. In terms of laser research, the ZnSe system is ahead of the others.
[0004]
As for this ZnSe system, room temperature continuous oscillation by injection excitation has already been reported, but since it is a material that is inherently easily deteriorated, reliability is a problem, and it has not yet been put into practical use.
[0005]
On the other hand, in the case of GaN-based, GaN high-reliability GaN has been reconsidered with respect to reliability that has become a bottleneck in the ZnSe-based system since the announcement of GaN high-brightness LED by Nichia two years ago. And see a large increase in researchers.
[0006]
Since this GaN compound semiconductor is a wurtzite compound semiconductor, it is epitaxially grown on a hexagonal sapphire substrate or 6H-SiC substrate having a similar crystal structure by using the MOVPE method (metal organic chemical vapor deposition method). Therefore, here, a conventional short wavelength light emitting device will be described with reference to FIG.
[0007]
4A. First, an n-type Al _0.1 Ga _0.9 N clad layer 23 and an n-type GaN light guide layer 24 are formed on a sapphire substrate 21 having a (0001) plane as a main surface via a GaN low-temperature buffer layer 22. The In _0.1 Ga _0.9 N active layer 25, the p-type GaN optical guide layer 26, and the p-type Al _0.1 Ga _0.9 N cladding layer 27 are epitaxially grown by the MOVPE method and then etched to form an n-type Al _0.1 Ga _0.9 N cladding layer. In addition, an n-side electrode composed of a Ti / Au electrode 28 was provided, and a p-side electrode composed of a Ni / Au electrode 29 was provided on the p-type Al _0.1 Ga _0.9 N cladding layer 27. .
[0008]
[Problems to be solved by the invention]
However, in the case of a conventional short wavelength light emitting device, it has been pointed out that the threshold current density is large from the report of oscillation by optical excitation, and the most recent report of successful laser oscillation by injection excitation (if necessary, S (See Nakamura et al., Japan Journal of Applied Physics, vol. 35, p. L74, 1996), the threshold current density is 4 kA / cm ² or more.
[0009]
Further, theoretical calculation also predicts that the threshold current density becomes very large due to the large effective mass of the band, etc. Here, referring to FIG. The band structure of the compound compound semiconductor will be described.
[0010]
In the GaN-based compound semiconductor shown in FIG. 4B, the lowest band in terms of energy in view of the holes in the valence band, that is, HH (Heavy Hole) and LH (Light Hole) are degenerate double, and the spin orbit The energy is separated by the amount of interaction, and in addition, a band called CH, which is peculiar to GaN-based compound semiconductors, appears.
[0011]
On the other hand, according to recent research, the present applicant has found that the in-plane lattice constants of the n-type Al _0.1 Ga _0.9 N cladding layer 23 to the p-type Al _0.1 Ga _0.9 N cladding layer 27 in the above-described conventional short wavelength light emitting device are as follows. It has been found that it is defined by the lattice constant of the n-type Al _0.1 Ga _0.9 N cladding layer 23 immediately above the GaN low-temperature buffer layer 22.
[0012]
Therefore, the n-type GaN light guide layer 24, the Ga _0.9 In _0.1 N active layer 25, and the p-type GaN light guide layer 26 that are coherently grown on the n-type Al _0.1 Ga _0.9 N cladding layer 23 have lattice mismatch and thermal expansion. Due to the coefficient difference, a compressive stress is received in the (0001) plane.
[0013]
In the case of this compressive stress, the energy seen from the hole in the CH band is merely higher than the HH band and the LH band, and the lowest band in terms of energy in the valence band is doubled. In order to cause laser oscillation in such a GaN-based compound semiconductor, it is necessary to fill the two degenerated bands HH and LH with carriers, and a threshold value for causing laser oscillation. There was a problem that the current density was high.
[0014]
Accordingly, an object of the present invention is to reduce a threshold current density required for laser oscillation in a semiconductor light emitting device using a GaN-based compound semiconductor, particularly in a short wavelength semiconductor laser.
[0015]
[Means for Solving the Problems]
FIG. 1 is an explanatory diagram of the principle configuration of the present invention, and FIG. 2 is an explanatory diagram of the strain dependence of the band structure of the valence band of GaN. With reference to FIG. 1 and FIG. Means for solving the problems described in FIG.
See Figure 1. (1) The present invention, in the semiconductor light emitting device, only setting the low-temperature buffer layer 2 made of GaN or AlN on the substrate 1, InGaN growth layer 3 provided directly on the low temperature buffer layer 2, AlInN, or, with either a AlGaInN, AlGaN on the growth layer 3, AlInN, or to form a barrier layer 4, 6 consisting of either AlGaInN, and constitute a double heterojunction structure by an active layer 5 made of GaN Thus, a tensile strain is introduced into the active layer 5 .
[0016]
As described above, when the GaN-based compound semiconductor is grown using the substrate 1 with the (0001) plane of sapphire as the main surface, the present applicant provides the lattice constant of each layer directly above the low-temperature buffer layer 2. The growth layer 3 provided immediately above the low temperature buffer layer 2 is either InGaN, AlInN, or AlGaInN, and the lattice constant of the growth layer 3 is By making it larger than the lattice constant of the active layer 5, tensile strain can be introduced into the active layer 5 having a forbidden band width suitable for blue light emission.
[0017]
On the other hand, from the theoretical calculation of the strain dependence of the band structure, since the band edge is formed only by the CH band by introducing the tensile strain, the threshold current is obtained by introducing the tensile strain to the active layer 5. The density can be reduced.
[0018]
As is clear from FIG. 2, in the case of no strain or compression strain as in the conventional case, the lowest HH band and LH band viewed from the hole are in a degenerated state, but tensile strain is introduced. As a result, the CH band drops in energy and forms a band edge only by the CH band. In order to oscillate the laser, only the CH band needs to be filled with carriers. To reduce.
[0019]
In FIG. 2, in the region indicated by the broken-line circle, the coupling of the wave functions becomes large, the wave functions of the LH band and the CH band are interchanged, and the CH band has the lowest energy level (as shown in the drawing). Will move to the top).
[0021]
In particular, by forming the barrier layers 4 and 6 separately from the growth layer 3, a clad layer having a specific lattice constant can be formed of a GaN-based compound semiconductor having an arbitrary band gap.
[0024]
( 2 ) Further, according to the present invention, in the semiconductor light emitting device, the low temperature buffer layer 2 is provided on the substrate 1, the barrier layer 4 having a lattice constant larger than that of GaN is formed immediately above the low temperature buffer layer 2, and By forming a double heterojunction structure with the active layer 5, a tensile strain is introduced into the active layer 5.
[0025]
Thus, the manufacturing process is simplified by using the growth layer 3 itself as the barrier layer 4, that is, the cladding layer.
[0026]
( 3 ) Further, in the above (1) or (2) , the present invention is characterized in that the tensile strain introduced into the active layer 5 is 1.0% or less.
[0027]
As described above, tensile strain is necessary to reduce the threshold current density. However, if the strain is too large, that is, if the lattice constant is too different, dislocations are likely to occur and the crystallinity deteriorates. Therefore, it is appropriate that the tensile strain is 1.0% or less.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to FIG.
Refer to FIG. 3. First, on a sapphire substrate 11 having a (0001) plane as a main surface, TMGa (trimethylgallium) is 10 to 100 μmol / min, for example, 45 μmol / min, ammonia is 0.02 to 0.2 mol / min, For example, 0.1 mol / min, 300 to 3000 sccm of hydrogen as a carrier gas, for example, 1000 sccm is flowed, the growth pressure is 70 to 760 Torr, for example, 100 Torr, and the growth temperature is 400 to 800 ° C., for example, 500 ° C. In this state, a GaN low-temperature buffer layer 12 having a thickness of 100 to 1000 mm, for example, 500 mm is grown.
[0029]
Subsequently, TMGa is 2.5 to 25 μmol / min, such as 10 μmol / min, TMIn (trimethylindium) is 25 to 250 μmol / min, such as 100 μmol / min, ammonia is 0.02 to 0.2 mol / min, such as , 0.1 mol / min, and N ₂ as a carrier gas of 300 to 3000 sccm, for example, 1000 sccm, a growth pressure of 70 to 760 Torr, for example, 100 Torr, and a growth temperature of 550 to 800 ° C., for example, 650 ° C. In this state, an In _0.08 Ga _0.92 N buffer layer 13 having a thickness of 0.1 to 2.0 μm, for example, 0.5 μm is grown.
[0030]
Subsequently, TMAl (trimethylaluminum) is 10 to 100 μmol / min, such as 45 μmol / min, TMGa is 10 to 100 μmol / min, such as 45 μmol / min, ammonia is 0.02 to 0.2 mol / min, such as 0 .1 mol / min, dopant, Si ₂ H ₆ 0.0001 to 0.002 μmol / min, for example 0.0007 μmol / min, and H ₂ as a carrier gas to flow 300 to 3000 sccm, for example 1000 sccm In the state where the growth pressure is 70 to 760 Torr, for example, 100 Torr and the growth temperature is 850 to 1100 ° C., for example, 950 ° C., the n-type Al _0.1 having a thickness of 0.5 to 2.5 μm, for example, 1.0 μm. A Ga _0.9 N cladding layer 14 is grown.
[0031]
Subsequently, TMGa is 10 to 100 μmol / min, such as 45 μmol / min, ammonia is 0.02 to 0.2 mol / min, such as 0.1 mol / min, and hydrogen as a carrier gas is 300 to 3000 sccm, such as , And a growth pressure of 70 to 760 Torr, for example, 100 Torr, and a growth temperature of 800 to 1050 ° C., for example, 930 ° C., to grow the GaN active layer 15 having a thickness of 3 to 100 nm, for example, 30 nm. Let
[0032]
Subsequently, TMAl is 10 to 100 μmol / min, for example 45 μmol / min, TMGa is 10 to 100 μmol / min, for example 45 μmol / min, ammonia is 0.02 to 0.2 mol / min, for example 0.1 mol / min. In addition, 0.01 to 0.5 μmol / min of biscyclopentadienyl magnesium, for example, 0.05 μmol / min, and H ₂ as a carrier gas are allowed to flow at 300 to 3000 sccm, for example, 1000 sccm, and the growth pressure is set to 70 to The p-type Al _0.1 Ga _0.9 N cladding layer 16 having a thickness of 0.5 to 2.0 μm, for example, 1.0 μm, at 760 Torr, for example, 100 Torr and a growth temperature of 850 to 1100 ° C., for example, 950 ° C. Grow.
[0033]
Next, a part of the p-type Al _0.1 Ga _0.9 N cladding layer 16 to the n-type Al _0.1 Ga _0.9 N cladding layer 14 is etched by reactive ion etching (RIE) to expose the exposed n-type Al _0.1 Ga _0.9 N cladding layer. 14 is provided with a Ti / Au electrode 17 as an n-side electrode, while a Ni / Au electrode 18 is provided as a p-side electrode on the p-type Al _0.1 Ga _0.9 N cladding layer 16.
[0034]
Next, similarly, the end face is etched by reactive ion etching to form a pair of parallel etching end faces to form a resonator mirror.
[0035]
In this case, since the in-plane atomic spacing of each layer is defined by the a-axis lattice constant of 3.218 の of the In _0.08 Ga _0.92 N buffer layer 13, the GaN active layer 14 having an a-axis lattice constant of 3.189Å. 0.9% tensile strain is introduced, and the CH band comes to the top, and laser oscillation occurs due to the transition between the CH band and the conduction band, and the threshold current density Will be reduced.
[0036]
In the above embodiment, the GaN low-temperature buffer layer is used as the low-temperature buffer layer, but other nitride-based compound semiconductors such as AlN may be used.
[0037]
Further, the buffer layer provided immediately above the GaN low-temperature buffer layer 12 does not need to be the In _0.08 Ga _0.92 N buffer layer 13, and an InGaN buffer layer of another composition, an AlInN buffer layer, or an AlInGaN buffer layer may be used. However, the lattice constant of the GaN or InGaN active layer suitable for blue light emission needs to be larger than the lattice constant of the active layer in order to give an appropriate tensile strain of 1.0% or less.
[0038]
In the above embodiment, GaN is used as the active layer, but the mixed crystal ratio is changed to Al _x Ga _{1 -xy} In _y N (0 ≦ x ≦ 1, 0 ≦ y depending on the required wavelength. ≦ 1), and accordingly, the mixed crystal ratio of the light guide layer and the clad layer is changed to Al _a Ga _1-ab In _b N (0 ≦ a ≦ 1, 0 ≦ You may change within the range of b <= 1).
[0039]
For example, a combination of an Al _0.4 Ga _0.3 In _0.3 N cladding layer and an In _0.1 Ga _0.9 N active layer may be used. In this case, the a-axis lattice constant of the Al _0.4 Ga _0.3 In _0.3 N cladding layer is 3. 266Å, which is larger than the Ga _0.9 In _0.1 N active layer having an a-axis lattice constant of 3.225Å.
Note that the energy gaps of Ga _0.9 In _0.1 N and Al _0.4 Ga _0.3 In _0.3 N are 3.15 eV and 3.6 eV, respectively.
[0040]
In the above embodiment, the light guide layer is not used, but may be provided if necessary, and a GaN-based compound semiconductor having a forbidden band width between the cladding layer and the active layer may be used. .
[0041]
Furthermore, although the above-described embodiment is a semiconductor laser, it is not limited to a semiconductor laser but is also intended for a normal light emitting diode (LED). In this case, it is necessary to form an etching end face. There is no.
[0042]
【The invention's effect】
According to the present invention, the short wavelength semiconductor light emitting device made of a GaN-based compound semiconductor is provided via the growth layer in which the lattice constant provided immediately above the low-temperature buffer layer is larger than the lattice constant of the active layer. Alternatively, an appropriate tensile strain is introduced into the InGaN active layer, and the CH band becomes the band edge, so that the threshold current density can be reduced, and it can be used as a light source for an optical information recording apparatus or the like. The place to contribute is great.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a basic configuration of the present invention.
FIG. 2 is an explanatory diagram of the strain dependence of the band structure of the valence band of GaN.
FIG. 3 is an explanatory diagram of an embodiment of the present invention.
FIG. 4 is an explanatory diagram of a conventional short wavelength light emitting device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Substrate 2 Low-temperature buffer layer 3 Growth layer 4 Barrier layer 5 Active layer 6 Barrier layer 7 Electrode 8 Electrode 11 Sapphire substrate 12 GaN Low-temperature buffer layer 13 In _0.08 Ga _0.92 N buffer layer 14 n-type Al _0.1 Ga _0.9 N cladding layer 15 GaN Active layer 16 p-type Al _0.1 Ga _0.9 N clad layer 17 Ti / Au electrode 18 Ni / Au electrode 21 Sapphire substrate 22 GaN low-temperature buffer layer 23 n-type Al _0.1 Ga _0.9 N clad layer 24 n-type GaN light guide layer 25 In _0.1 Ga _0.9 N active layer 26 p-type GaN light guide layer 27 p-type Al _0.1 Ga _0.9 N cladding layer 28 Ti / Au electrode 29 Ni / Au electrode

Claims (3)

Only set a low-temperature buffer layer of GaN or AlN on a substrate, InGaN growth layer provided directly on the low-temperature buffer layer, AlInN, or with either a AlGaInN, AlGaN on the growth layer, AlInN, or, A semiconductor light emitting device , wherein a barrier layer made of any one of AlGaInN is formed, and a double heterojunction structure is formed with an active layer made of GaN, whereby tensile strain is introduced into the active layer .   A low-temperature buffer layer is provided on the substrate, a barrier layer having a lattice constant larger than that of GaN is formed immediately above the low-temperature buffer layer, and a double heterojunction structure is formed by the active layer made of GaN. A semiconductor light emitting device characterized by introducing tensile strain into a layer. Tensile strain introduced into the active layer, the semiconductor light-emitting device according to claim 1 or 2, characterized in that 1.0% or less.

Images