JPH0654821B2 - Semiconductor light emitting element - Google Patents

Description

The present invention relates to a semiconductor light emitting device that emits light or oscillates a laser.

(Prior Art and Problems Thereof) In general, a multi-element mixed crystal compound semiconductor can change the energy gap and the refractive index in a wide range by a combination of its constituent elements. A direct transition type compound semiconductor having a desired energy gap is used as an active layer, and a compound semiconductor having a larger energy gap and a smaller refractive index than the active layer is used as a cladding layer. A semiconductor laser is constructed. Conventionally, GaAs as the active layer or _{Al x Ga 1-x As,} , Al x 'Ga 1-x' As a cladding layer (0 <x <x '< 1)
Double heterostructure using Al (called AlGaAs dh), Ga
_y In _1-y P _z As _1-z (0 <y <1, 0 <z <1) is the active layer, I
A double heterostructure with nP as a cladding layer (called InP-based dh) is a typical example widely used.

As a substrate for forming this double heterostructure, AlGa
As system uses GaAs and InP system uses InP. The former is lattice-matched with the substrate regardless of the composition of the compound, and the latter has a lattice mismatch in the active layer Ga _y In _1-y P _z As _1-z, but the active layer is thin and thick. Since the majority of InP is lattice-matched with the substrate, the problem of maintaining lattice matching is solved relatively easily. In these examples, the problem of device reliability related to lattice mismatch is minor.

Further, when operating as an element, the quality of the heat dissipation to the electrode side greatly affects the element characteristics. That is, if the thermal resistance of the clad layer on the electrode side is high, the device characteristics and device reliability will be impaired. In the above-mentioned AlGaAs-based and InP-based examples, since AlGaAs and InP are used as the cladding layer, the thermal resistance is not so high and the effect on the element is small.

However, in order to expand the emission wavelength range, compounds having other compositions have been used in recent years. For example, wavelength 0.58μm
As a visible light semiconductor light emitting device of ~ 0.68 μm, Ga
_0.5 an In _0.5 P or _{(Al x Ga 1-x)} 0.5 In 0.5 P, the cladding layer _{(Al x 'Ga 1-x} ') 0.5 In 0.5 P (0 <x
There is a double heterostructure using <x'1), which has a wavelength of 0.
Ga _0.47 In _0.53 As or active layer as the infrared light semiconductor light emitting device _{92μm~1.6μm (Al x Ga 1-x} ) 0.47 In 0.53 As, the cladding layer _{(Al x 'Ga 1-x} ') 0.47 In 0.53 As (0 <x <x '
There is a dh structure using 1), the former is GaAs and the latter is
InP is used as the substrate. AlGaInP with these configurations
The lattice constant of AlGaInAs and AlGaInAs vary greatly,
In order to be lattice-matched with the substrate, its composition must be precisely controlled. Furthermore, in the case of the double hetero structure, the cladding layer is a compound whose composition must be strictly controlled to maintain the lattice matching property, and therefore the influence of the lattice mismatch is greater than that of the AlGaAs system or the InP system. Further, since the clad layer on the electrode side is also a quaternary compound, its thermal resistance is significantly higher than that of a binary or ternary compound.

The structure of a conventional double heterostructure semiconductor laser made of AlGaInP is shown in the sectional view of FIG. 4 (Magazine “Appl. Phys. Lett.” No. 4).
3 (1983) 987-989). This configuration is for n-type substrate GaAs1
1.0 μm thick n-type GaAs buffer layer 12 with a thickness of 1.0
μmn type (Al _0.3 Ga _0.7 ) _0.5 In _0.5 P clad layer 13, thickness
0.2 μm Andove Ga _0.5 In _0.5 P Active layer 14, thickness 1.0 μ
mp type (Al _0.3 Ga _0.7 ) _0.5 In _0.5 P clad layer 15, thickness 1.0
A μmp type GaAs cap layer 7 is formed. Active layer 1
The energy gap, the refractive index, the thickness, and the device parameter of the cladding layers 13 and 15 are determined from the conditions of carrier and light confinement in the layer 4. In this conventional example, the thickness of the cladding layer cannot be made thinner without impairing the device characteristics. Due to the thickness of the clad layer, there is the effect of lattice mismatch and the effect of high thermal resistance. Therefore, there is a drawback that a high-performance and highly reliable device cannot be obtained with good reproducibility. The same was true for other combinations of compositions.

(Object of the Invention) An object of the present invention is to eliminate such drawbacks of the prior art and to provide a semiconductor light emitting device having high performance, high reliability and good reproducibility.

(Structure of the Invention) The structure of the semiconductor light emitting device of the present invention is GaInP or A.
AlGaInP active layer and AlInP having an energy gap larger than that of the active layer sandwiching the active layer.
Alternatively, a double hetero structure having a cladding layer made of AlGaInP and one or both surfaces of the double hetero structure provided on the surface of the cladding layer on the side not in contact with the active layer have a larger energy gap than that of the active layer and a refractive index. Of AlAs or AlGaAs having a small size, and the thickness of the layer including the active layer and the clad layer is thin enough to suppress thermal resistance to a sufficiently low level.

(Example) The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view of an embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are an energy band diagram and a refractive index diagram of the present embodiment. The structure of a red visible semiconductor laser oscillating at a wavelength of 605 nm. Indicates. In this embodiment, an n-type Al having a thickness of 1.0 μm is formed on the n-type GaAs substrate 1 by an epitaxial growth method.
_0.8 Ga _0.2 As layer 2, thin 0.1 μm n-type (Al _0.7 Ga _0.3 )
_0.5 In _0.5 P layer 3, 0.2 μm thick Andove (Al _0.2 Ga _0.8 ).
_0.5 In _0.5 P layer 4, thin 0.1 μm p-type (Al _0.7 Ga _0.3 )
_0.5 In _0.5 P layer 5, 1.0 μm thick p-type Al _0.8 Ga _0.2 As layer 6,
A p-type GaAs cap layer 7 having a thickness of 1.0 μm is sequentially grown.
As the epitaxial growth method, any of the vapor phase growth method (organometallic decomposition method [MOCVD], halogen transport method [HT / VPE]), molecular beam method (MBE), and liquid phase method (LPE) may be used. The laser active layer of each layer was undoped (Al _0.2 Ga _0.8 ) _0.5 I.
Injected carriers and emitted light are confined in the n _0.5 P layer 4 to cause laser oscillation.

After each layer is formed by the epitaxial method, a SiO ₂ film 8 having a stripe-shaped window 11, a p-electrode 9 made of an Au / Zn alloy, and an n-electrode 10 made of an Au / Ge alloy are formed and undoped.
(Al _0.2 Ga _0.8 ) _0.5 In _0.5 P Current injection is excited in the stripe-shaped portion of the active layer 4 to enable efficient oscillation.

In the energy band diagram with respect to the distance in the growth layer direction in FIG. 2 (a), (Al _0.2 Ga _0.8 ) _0.5 In _0.5 P has a larger energy gap than the active layer 4 (Al _0.7 Ga _0.3 ) _0.5 In
_The electrons 21 and holes 22 injected from the cladding layers 3 and 5 of _0.5 P are confined in the active layer 4. (Al _0.7
Ga _0.3 ) _0.5 In _0.5 P 3,5 and (Al _0.2 Ga _0.8 ) _0.5 In _0.5 P (4)
Has a sufficient energy gap difference as shown in the figure, and
(Al _0.7 Ga _0.3 ) _0.5 In _0.5 P Clad layers 3 and 5 have a thickness of 0.1 μm
Since it is sufficiently larger than the de Broglie wavelength of electrons, electrons and holes are almost completely confined in the active layer 4.

Also, as shown in FIG. 2 (b), the distribution of the refractive index n is (Al
_0.7 Ga _0.3 ) _0.5 In _0.5 P layers 3, 5 or Al adjacent to it
The refractive index of the active layer 4 is higher than that of the _0.8 Ga _0.2 As layers 2 and 6. Therefore, the thickness of the cladding layers 3 and 5 is 0.1 μm
Is not a sufficient value for confining light in the active layer 4, but Al
Due to the presence of the _0.8 Ga _0.2 As layers 2 and 6, an optical confinement effect similar to that of a normal double hetero structure can be obtained.

Further, as shown in FIG. 2 (a), the energy gap of the Al _0.8 Ga _0.2 As layers 2 and 6 is larger than that of the active layer 4, so that the Al _0.8 Ga _0.2 As layer 2 passes over the cladding layers 3 and 5. The light oozing out into 6 is not absorbed here.

As described above, the structure of the present embodiment does not impair the function of the normal double hetero structure with respect to the confinement of light and injected carriers, and overcomes the problems of the prior art as described below. There is.

(Al _x Ga _1-x ) _0.5 In _0.5 P is the GaAs of the substrate when [(molar ratio of Al) + (molar ratio of Ga)]: (molar ratio of In) = 0.5: 0.5
However, if it deviates from this value, a lattice mismatch will occur and a lattice defect will occur in the epitaxial crystal, so that the crystal quality will deteriorate and the element characteristics will deteriorate. Therefore, in order to obtain good quality crystals, the composition of the crystals must be strictly controlled,
Strict control conditions are imposed on the crystal growth, and the yield rate for obtaining good quality crystals is significantly reduced. However, even if some lattice mismatch occurs, the crystal quality deterioration can be reduced if the layer is thin.

For example, even if the lattice constant of (Al _x Ga _1-x ) _0.5 In _0.5 P differs from that of GaAs by about 3 × 10 ^-3 , (Al _x Ga _1-x )
The total thickness of the _0.5 In _0.5 P layers (that is, the total thickness of the cladding layers 3, 5 and the active layer 4) is 0.4 μ as in this embodiment.
GaAs whose other layers are lattice-matched to the GaAs substrate 1 at about m
Alternatively, with Al _x Ga _1-x As (0x1), quality deterioration that affects the device characteristics did not occur.

3 (a) and 3 (b) are the materials (Al _x Ga _1-x ) constituting the present embodiment.
Shows a characteristic diagram for _0.5 an In _0.5 P and _{Al x Ga 1-x As (} 0x1) Al composition ratio x of the thermal resistance of about. Fig. 3
(b) is shown in the magazine "Journal of Applied Physics", Vol. 44, p. 1292, 1973, and its thermal resistivity is binary compounds GaAs and AlAs.
Is small, and is large in ternary mixed crystal AlGaAs. Also,
The thermal resistivity of (Al _x Ga _1-x ) _0.5 In _0.5 P in FIG. 3 (a) was measured by the present inventors. The quaternary compound AlGaInP is a ternary compound Al _0.5 In _0.5 P Ga _0.5 Its thermal resistivity is higher than that of In _0.5 P, and that of Al _x Ga _1-x As based binary or ternary compounds is higher. According to this fact, in this embodiment, the p-side quaternary cladding layer (Al _0.7 Ga) having a thin thickness of 0.1 μm is used.
_0.3 ) _0.5 In _0.5 P5 with a thickness of 1.0 μm p-Al _0.8 Ga _0.2 As layer 6
By adjoining, the thermal resistance can be reduced to one third or less as compared with the case of the conventional double hetero structure requiring a thickness of about 1.0 μm. Therefore, it has a great effect on heat dissipation of the element, and has an effect of reducing the oscillation threshold of the element and improving the life of the element.

As described above, in this embodiment, the confinement of light and carriers does not impair the function of the conventional double hetero structure, the lattice mismatch greatly reduces the adverse effect on the crystal quality, and the thermal resistance of the conventional double hetero structure is reduced. We were able to reduce it to less than one-third. Therefore, it was possible to improve the productivity of the device and obtain a high-performance and highly reliable device.

The parameters such as the compound composition and layer thickness of this example are as follows.
The values of the present invention are not limited to the values described here, and the effects of the present invention can be obtained as long as they satisfy the claims. Also,
If the semiconductor layer 6 adjacent to the p-type cladding layer 5 in this example is a binary AlAs layer, the thermal resistance thereof can be further reduced to about 1/5. The present invention can also be applied to combinations of other compounds, for example, 1 μm for an n-type InP substrate.
m-thick n-type InP, 0.1 μm-thick n-type Al _0.47 In _0.53 As clad layer, 0.2 μm-thick undoped (Al _0.7 Ga _0.3 ) _0.47 I
It can be applied to a near-infrared emitting semiconductor laser with a wavelength of 950 nm having a multilayer structure in which an n _0.53 As active layer and a p-type Al _0.47 In _0.53 As clad layer having a thickness of 0.1 μm are sequentially formed.

(Effects of the Invention) As described above, according to the present invention, the confinement of light and carriers does not impair the function of the ordinary double hetero structure at all, and significantly reduces the adverse effect of lattice mismatch on the crystal quality. Further, by lowering the heat resistance, a semiconductor light emitting device with improved device productivity and characteristics can be obtained. .

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 (a),
(b) is an energy band diagram of this embodiment and its refractive index diagram. FIGS. 3 (a) and 3 (b) are (Al _x Ga _1-x ) _0.5 In _0.5 P and Al _x Ga used in this embodiment. FIG. 4 is a sectional view of an example of a conventional semiconductor light emitting device, which is a characteristic diagram corresponding to an Al composition having a thermal resistivity of _1-x As. In the figure, 1 ... n-GaAs substrate, 2 ... n-Al _0.8 Ga _0.2 As layer, 3,
13 ... n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer, 4 ...
... Undoped (Al _0.2 Ga _0.8 ) _0.5 In _0.5 P active layer, 5, 15
…… p− (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer, 6 …… p
-Al _0.8 Ga _0.2 As layer, 7 ... p-GaAs layer, 8 ... SiO ₂ film,
9 ... p electrode, 10 ... n electrode, 11 ... stripe window, 12 ... n-GaAs buffer layer, 14 ... undoped
Ga _0.5 In _0.5 P active layer, 21 ... injection electron, 22 ... injection hole, 23 ... conduction band, 24 ... valence band.

Claims (1)

[Claims] 1. An active layer made of GaInP or AlGaInP and AlInP or AlGaInP having an energy gap larger than that of the active layer sandwiching the active layer.
And a double hetero structure having a cladding layer made of, and provided on one surface or both surfaces of the double hetero structure on a surface not in contact with the active layer and having a larger energy gap and a smaller refractive index than the active layer. AlA
and a semiconductor layer made of AlGaAs, and the thickness of the layer including the active layer and the clad layer is formed thin enough to suppress thermal resistance to a sufficiently low level.