JPH07326824A - Light emitting element - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent deterioration of the light-emitting element due to movement of impurities and defects. [Structure] A light emitting portion of a light emitting element such as a semiconductor laser or a light emitting diode and a portion in the vicinity thereof are formed of a multi-element mixed crystal semiconductor composed of plural kinds of binary compound semiconductors having different lattice constants of 0.1 Å or more. The composition ratio of the element having the minimum composition in this multi-element mixed crystal semiconductor is set to 5 × 10 ⁻³ or more. Alternatively, the light emitting portion of the light emitting element and the portion in the vicinity thereof should have at least 2 different lattice constants of 0.1 Å or more.
It is composed of a compound semiconductor superlattice in which a plurality of kinds of compound semiconductor layers of the original and above are laminated on each other. The number of layers of this compound semiconductor superlattice is 6 or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device, and is suitable for application to, for example, a semiconductor laser or a light emitting diode.

[0002]

2. Description of the Related Art Generally, a light emitting element such as a semiconductor laser or a light emitting diode deteriorates during use. One of the causes is considered to be that impurities contained in the semiconductor layer forming the light emitting element and defects caused by the absorption and transfer of energy released by non-radiative recombination of carriers.

The problem of deterioration of the light emitting device will be specifically described below by taking a semiconductor laser having a double hetero structure as an example. Now, let us consider a semiconductor laser having a double hetero structure in which an n-type cladding layer and a p-type cladding layer are sandwiched above and below the active layer. In this semiconductor laser, when forward current is applied by applying a forward voltage between the n-side electrode and the p-side electrode which are in ohmic contact with the n-type cladding layer and the p-type cladding layer, respectively, the current is injected into the active layer. Electrons are injected from the layer side and holes are injected from the p-type cladding layer side. And
In this way, the electrons and holes injected into the active layer are recombined to emit light, which causes laser oscillation. On the other hand, apart from such radiative recombination, as shown in FIG. 11, for example, electrons injected from the n-type cladding layer side pass through the active layer and reach the p-type cladding layer, and the electrons are injected into the p-type cladding layer. Non-radiative recombination may occur with holes in the layer (electrons and holes are indicated by black circles and white circles in FIG. 11, respectively). It is considered that the energy released during this non-radiative recombination is supplied to, for example, impurities and defects existing in the p-type clad layer to promote the movement thereof and deteriorate the semiconductor laser. .

[0004]

As can be seen from the above, if the movement of impurities or defects can be suppressed, the deterioration of the light emitting element due to the movement of impurities or defects can be suppressed. An effective means of suppressing
At present, it has not been proposed yet.

The problem of the deterioration of the light emitting element is that a semiconductor having a strong ionicity, represented by a II-VI group compound semiconductor, which has a small cohesive energy per chemical bond (bonding energy of chemical bond) is used. In the light emitting element, the movement of impurities and defects in the semiconductor is fast, which is a serious problem.

Therefore, an object of the present invention is to provide a light emitting device capable of preventing deterioration due to movement of impurities and defects.

[0007]

As a result of intensive studies to solve the above-mentioned problems, the present inventor has found that interatomic atoms are present in a light emitting portion where a light field exists at the time of light emission of a light emitting element and in the vicinity thereof. By providing regions with different bond lengths (interatomic distances) or lattice constants regularly or irregularly (randomly), in other words, the bond between atoms in the semiconductor of the light emitting part and its vicinity can be It was found that the effect of suppressing the movement of impurities and defects can be obtained by modulating the length. Here, in order to irregularly provide regions having different bond lengths or lattice constants in the light emitting portion of the light emitting element and the vicinity thereof, like the latter,
These portions may be made of a multi-element mixed crystal semiconductor in which a plurality of kinds of binary compound semiconductors having different lattice constants are mixed. Further, in order to regularly provide regions having different coupling lengths or lattice constants in the light emitting portion of the light emitting element and the portion in the vicinity thereof as in the former case, these portions may be formed of a plurality of two different lattice constants. A compound semiconductor superlattice in which layers of the original compound semiconductor are laminated may be used.

The mechanism by which the movement of impurities and defects can be suppressed by regularly or irregularly providing regions having different bond lengths or lattice constants as described above will be considered.

FIG. 9 shows the relationship between the cohesive energy E _coh per bond and the interatomic distance d. The cohesive energy E _coh is expressed by the following equation. E _coh = −E _pro −V _o (d) + E _bond (1) where E _pro is the promotion energy, V
_o (d) is the potential energy representing the overlap interaction, and E _bond is the bond formation energy.
When equation (1) is changed, δE _coh to _{−δV o} (d) + δE _bond (2) is obtained.

As shown in FIG. 9, the bond length between atoms (interatomic distance) is equal to the value of d that minimizes the total energy. On the other hand, it is known that the bond length in the mixed crystal semiconductor is locally almost equal to that in the binary compound semiconductor forming the mixed crystal semiconductor.

Considering these two things, it is considered that local cohesive energy exists even in a mixed crystal semiconductor. Then, in a multi-element mixed crystal semiconductor composed of plural kinds of binary compound semiconductors whose bond lengths or lattice constants are greatly different from each other, the variation of this local cohesive energy is also largely different. For example, from FIG. 9, the difference Δ in lattice constant between these binary compound semiconductors
When a is ~ 0.5Å (0.05 nm), δE _coh
~ 3 eV.

Therefore, according to the equation (2), −δV _o (d) + δE _bond ˜3 eV (3), and the potential energy V _o (d) of the overlap interaction and the bond formation energy E _bond also fluctuate greatly. Recognize.

By the way, it is considered that the movement of impurities and defects is carried out by repeatedly cutting and forming bonds between atoms, so that the energy required for this cutting and generation is modulated in the order of 3 eV. Therefore, it becomes difficult for impurities and defects to move by that amount.

The difference Δa in the lattice constant between the binary compound semiconductors is preferably about 0.5 Å as described above, but this difference Δa
When a is at least 0.1 Å or more, the effect of suppressing the movement of impurities and defects can be obtained.

Next, the lower limit of the composition ratio of the elements contained in the mixed crystal semiconductor, which is necessary to obtain the effect of suppressing the movement of impurities and defects, or the minimum content ratio of the elements in the mixed crystal semiconductor. Estimating is as follows. 0.1 now
InGaAs is considered as a mixed crystal semiconductor composed of plural kinds of binary compound semiconductors having a lattice constant difference Δa of about 0.5Å. In InGaAs, InAs having a lattice constant of about 6.05Å is GaA having a lattice constant of about 5.6Å.
The strain that occurs when mixed with s is considered to extend to the range of the third to sixth adjacent atoms. In this case, InA
s is a local heteromaterial mixed in GaAs,
It is considered that the exudation of the electronic system also occurs over the range of the second to third adjacent atoms. Then, it is considered that the length of the coupling within this range can be modulated through overlap integration or the like.

Therefore, in this case, if at least one In atom is contained in a sphere having a radius equal to the thickness of six atomic layers, impurities and defects are pinned in the strain field around In. And the movement is suppressed. here,
The matrix phase GaAs has a density D _Host of -10 ²² cm ^-3 in the cubic crystal filling of one atomic layer. In addition, the density D _In of In atoms at this time is up to (1/6) ³ · 10 ²² cm ⁻³ . Therefore, D _In / D _Host ˜ (1/6) ³ ˜5 × 1
It becomes 0 ⁻³ = 0.5%.

From the above, it is derived that the minimum content of elements in the above mixed crystal semiconductor, which is necessary to suppress the movement of impurities and defects, is about 5 × 10 ⁻³ or 0.5%. On the other hand, when the light emitting portion of the light emitting element and the portion in the vicinity thereof are to be a compound semiconductor superlattice in which layers of plural kinds of binary compound semiconductors having different lattice constants are laminated, the number of layers is 6 or less. However, it is effective in suppressing the movement of impurities and defects. The present invention has been devised based on the above examination by the present inventor.

In other words, in order to achieve the above object, in the light emitting device according to the present invention, the light emitting portion and the portion in the vicinity thereof are made of at least three element compound semiconductors having lattice constants different from each other by at least 0.1 Å or more.
It is characterized in that it is composed of a compound semiconductor containing at least one element.

Here, the element compound semiconductor is typically a binary compound semiconductor. Examples of this binary compound semiconductor include those shown in FIG.
As can be seen from FIG. 10, for example, GaAs and InAs
, A combination of ZnSe and CdSe,
A combination of ZnS and MgSe and the like has a difference in lattice constant of 0.5 Å or more and is an example of a suitable combination.

The compound semiconductor containing at least three elements is typically a compound semiconductor containing at least three elements. Here, the composition ratio of the element having the minimum composition in the compound semiconductor containing at least three or more elements is preferably 5 × 10 ⁻³ or more.

Alternatively, the compound semiconductor containing at least three or more kinds of elements is a compound semiconductor superlattice composed of at least two kinds of compound semiconductor layers of at least two elements having mutually different lattice constants of at least 0.1 Å or more. is there.

In the present invention, when the compound semiconductor containing at least three or more elements is a compound semiconductor of at least ternary or more, the elements constituting the first element group are A ₁ , A ₂ , ..., A expressed in _i, B ₁ elements constituting the second element group, B _2, ..., when expressed in _{B j, (a 1) x1} (a 2) x2 ... (a i) xi (B 1) y1 (B ₂ )
_y2 ... (B _{j) yj} (where, 0 ≦ x1, x2, ... , xi ≦ 1,0 ≦ y1,
y2, ..., yj ≦ 1, x1 + x2 + ... + xi = 1, y1
+ Y2 + ... + yj = 1) is a multi-element compound semiconductor represented by the general formula. Here, in a typical example, the first group of elements is II
The second group of elements is a group consisting of group VI elements and the group of group VI elements. In another typical example, the first group of elements is a group III element and the second group of elements is a group V element.

In the present invention, when the compound semiconductor containing at least three or more elements is a compound semiconductor superlattice made of a binary compound semiconductor, it comprises elements A ₁ , A ₂ , which constitute the first element group, , A _i , and the elements constituting the second element group are B ₁ , B ₂ , ..., B _j , (A _k B _l ) _M (A _{k'B l '} ) _N (however, 1 ≦ k, k ′ ≦ i, 1 ≦ l, l ′ ≦ j, 1 ≦
A compound semiconductor superlattice represented by the general formula: M, N ≦ 3). Here, in a typical example, the first group of elements is II
The second group of elements is a group consisting of group VI elements and the group of group VI elements. In another typical example, the first group of elements is a group III element and the second group of elements is a group V element. The compound semiconductor containing at least three kinds of elements may be, for example, a compound semiconductor superlattice made of a ternary compound semiconductor.

In a typical embodiment of the present invention, the active layer has a structure in which the upper and lower sides are sandwiched by an n-type cladding layer and a p-type cladding layer. A portion within a diffusion length of electrons in the n-type cladding layer from the interface between the layer and the n-type cladding layer, and
At least two element compounds having lattice constants different from each other by at least 0.1 Å or more in a portion within the diffusion length of holes in the p-type cladding layer from the interface between the active layer and the p-type cladding layer in the p-type cladding layer. It is composed of a compound semiconductor containing at least three kinds of elements composed of a semiconductor.

[0025]

According to the semiconductor laser of the present invention constructed as described above, at least three kinds of element compound semiconductors are used in the light emitting portion and the vicinity thereof, which are made of at least two element compound semiconductors having lattice constants different from each other by at least 0.1 Å or more. Since it is composed of a compound semiconductor containing the above elements,
The bond length locally changes in these light emitting portions and the portions in the vicinity thereof, and impurities and defects are pinned in these portions. As a result, the movement of impurities and defects can be effectively suppressed. Then, deterioration of the light emitting element due to the movement of the impurities and defects can be prevented, and the life of the light emitting element can be extended and the reliability can be improved.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a semiconductor laser according to the first embodiment of the present invention.

As shown in FIG. 1, in the semiconductor laser according to the first embodiment, the upper and lower sides of the active layer 1 are sandwiched by the n-type cladding layer 2 and the p-type cladding layer 3. Then, the n-type cladding layer 2 and the p-type cladding layer 3
The n-side electrode 4 and the p-side electrode 5 are in ohmic contact with each other.

In this case, the n-type cladding layer 2 and the p-type cladding layer 3 in the portion where the optical field exists at the time of emission of this semiconductor laser, that is, the active layer 1 and the portion in the vicinity thereof, are
It is composed of a mixed crystal semiconductor composed of at least two kinds of binary compound semiconductors having different lattice constants of at least 0.1 Å or more.

FIG. 2 shows an energy band diagram of the active layer 1, the n-type cladding layer 2 and the p-type cladding layer 3 at this time. As shown in FIG. 2, in this case, at least two kinds of 2 having lattice constants different from each other by at least 0.1 Å or more are used.
The energy band of the part composed of the mixed crystal semiconductor composed of the original compound semiconductor is modulated to reflect that the mixed crystal semiconductor is composed of plural kinds of compound semiconductors. The composition ratio of the element having the minimum composition among the elements constituting the mixed crystal semiconductor is at least 5 × 10 ⁻³ (0.0
05) Selected above.

Specific examples of combinations of the active layer 1, the n-type cladding layer 2 and the p-type cladding layer 3 are as follows. In the first example, the entire active layer 1 is Ga
It is formed of InAs, and portions of the n-type cladding layer 2 and the p-type cladding layer 3 near the active layer 1 are formed of AlGaI.
It is formed of nAs. The n-type clad layer 2 and the p-type clad layer 3 other than the part in the vicinity of the active layer 1 are made of AlG.
It is formed of aAs. In this case, GaInAs forming the active layer 1 is a mixture of InAs and 0.5% or more of InAs in GaAs, and AlGaIn forming the n-type clad layer 2 and the p-type clad layer 3 in the vicinity of the active layer 1.
As is AlGaAs, which can be regarded as a mixed crystal of AlAs and GaAs, and 0.5% or more of InAs is further mixed.

In the second example, the entire active layer 1 is Z.
The n-type cladding layer 2 and the p-type cladding layer 3 are formed of nCdSe, and a portion of the n-type cladding layer 2 and the p-type cladding layer 3 near the active layer 1 is formed by ZnSS.
e. The n-type clad layer 2 and the p-type clad layer 3 other than the portion near the active layer 1 are formed of ZnSe. In this case, ZnCd forming the active layer 1
Se is ZnSe mixed with 0.5% or more of CdSe, and ZnSSe forming the n-type clad layer 2 and the p-type clad layer 3 near the active layer 1 is ZnSe.
ZnS is mixed with 0.5% or more.

In the third example, the entire active layer 1 is Z.
Forming with nCdSe is similar to the second example, but the part of the n-type cladding layer 2 and the p-type cladding layer 3 near the active layer 1 is formed with ZnMgSSe. The n-type clad layer 2 and the p-type clad layer 3 other than the portion near the active layer 1 are formed of ZnSe.
In this case, ZnMgSSe forming the n-type clad layer 2 and the p-type clad layer 3 in the vicinity of the active layer 1 is Z
ZnSe and MgSe are each mixed in 0.5% or more with nSe.

In the fourth example, the entire active layer 1 is Z.
nSSe is formed, and portions of the n-type cladding layer 2 and the p-type cladding layer 3 near the active layer 1 are formed by ZnMgS.
It is formed of Se. The n-type clad layer 2 and the p-type clad layer 3 other than the part in the vicinity of the active layer 1 are made of ZnSe.
Formed by. In this case, ZnS forming the active layer 1
Se is ZnSe mixed with 0.5% or more of ZnS, and ZnMgSSe forming the n-type cladding layer 2 and the p-type cladding layer 3 in the vicinity of the active layer 1 is ZnS.
e is a mixture of ZnS and MgSe of 0.5% or more.

In the fifth example, the entire active layer 1 is Z.
nCdSSe, and n-type cladding layer 2 and p
The portion of the mold cladding layer 3 near the active layer 1 is ZnM.
Formed by gSSe. The n-type clad layer 2 and the p-type clad layer 3 except for the portion near the active layer 1 are made of Zn.
It is formed of Se. In this case, Z forming the active layer 1
nCdSSe is obtained by mixing ZnSe with 0.5% or more of CdSe and ZnS, and ZnMgSSe forming the n-type clad layer 2 and the p-type clad layer 3 near the active layer 1 is ZnSe and ZnS and Mg.
Se is mixed in 0.5% or more.

In the sixth example, the entire active layer 1 is formed of a (ZnSe) _M (ZnS) _N superlattice and the active layer 1 of the n-type cladding layer 2 and the p-type cladding layer 3 is formed.
Is formed of ZnMgSSe. The n-type cladding layer 2 and p in a portion other than the portion in the vicinity of the active layer 1
The mold cladding layer 3 is formed of ZnSe. in this case,
The number of layers M + N of the (ZnSe) _M (ZnS) _N superlattice forming the active layer 1 is selected to be 6 or less. In addition, the active layer 1
ZnMgSSe forming the n-type clad layer 2 and the p-type clad layer 3 in the vicinity of is a mixture of ZnSe and ZnS and MgSe of 0.5% or more, respectively.

The energy band diagram of the active layer 1, the n-type cladding layer 2 and the p-type cladding layer 3 in the first example shows that the active layer 1 is made of GaAs and the n-type cladding layer 2 and the p-type cladding layer are formed. It can be regarded as approximately the same as the energy band diagram (FIG. 3) when 3 is formed of AlGaAs. Similarly, the energy band diagrams of the active layer 1, the n-type clad layer 2 and the p-type clad layer 3 in the second and third examples show that the active layer 1 is Z
It can be regarded approximately the same as the energy band diagram in the case where the n-type cladding layer 2 and the p-type cladding layer 3 are made of nCdSe and made of ZnSe. Further, the energy band diagrams of the active layer 1, the n-type cladding layer 2 and the p-type cladding layer 3 in the fourth example, the fifth example and the sixth example show that the active layer 1 is formed of ZnSe and n The Zn-type cladding layer 2 and the p-type cladding layer 3 are made of ZnM.
It can be regarded as approximately the same as the energy band diagram when formed by gSSe.

As described above, according to the first embodiment,
A mixed crystal semiconductor in which the active layer 1 in which a light field exists at the time of light emission and the n-type clad layer 2 and the p-type clad layer 3 in the vicinity thereof are made of plural kinds of binary compound semiconductors having different lattice constants of at least 0.1 Å or more. Therefore, in the active layer 1 and the n-type cladding layer 2 and the p-type cladding layer 3 in the vicinity thereof, movement of impurities and defects due to non-radiative recombination and the like is suppressed.
Therefore, it is possible to prevent the deterioration of the semiconductor laser due to the movement of the impurities and defects. Then, the life of the semiconductor laser can be extended and the reliability can be improved.

FIGS. 4 and 5 show a semiconductor laser according to a second embodiment of the present invention, FIG. 4 is a sectional view perpendicular to the cavity length direction of this semiconductor laser, and FIG. 5 is the cavity length direction of this semiconductor laser. A cross-sectional view parallel to FIG. This semiconductor laser is a so-called SCH (Separate Confinement H
eterostructure) has a structure.

As shown in FIGS. 4 and 5, in the semiconductor laser according to the second embodiment, for example, an n-type GaAs substrate 11 having a (100) plane orientation doped with silicon (Si) as an n-type impurity is used. , N-type ZnSe buffer layer 12 doped with chlorine (Cl) as an n-type impurity, for example n doped with Cl as an n-type impurity
Type Zn _1-p Mg _p S _q Se _1-q cladding layer 13, for example, n-type ZnS _s Se doped with Cl as an n-type impurity
_1-s optical waveguide layer 14, active layer 15, for example p-type ZnS _s Se _1-s optical waveguide layer 16 doped with nitrogen (N) as a p _- type impurity, for example p doped with N as a p-type impurity
Type Zn _1-p Mg _p S _q Se _1-q cladding layer 17, for example p-type ZnS _v Se doped with N as a p-type impurity
_1-v layer 18, for example a p-type ZnSe contact layer 19 doped with N as a p-type impurity, for example a quantum well layer made of p-type ZnTe and a barrier layer made of p-type ZnSe each doped with N as a p-type impurity P-type ZnTe / ZnSe multiple quantum well (MQW) layer 2 in which and are alternately stacked
0 and, for example, a p-type ZnTe contact layer 21 doped with N as a p-type impurity is sequentially stacked. The p-type ZnTe / ZnSe MQW layer 20 will be described in detail later.

In this case, the active layer 15 is made of i-type Zn _1-z Cd.
_It has a single quantum well structure composed of _z Se quantum well layers, and the thickness of the i-type Zn _1-z Cd _z Se quantum well layer is preferably selected to be 2 to 20 nm, specifically 9 nm, for example. There is. In this case, the n-type Zn _1-p Mg _p S _q Se _1-q clad layer 13 and the p-type Zn _1-p Mg _p S _q Se _1-q clad layer 17 form a barrier layer.

In this semiconductor laser, a portion where an optical field exists when the semiconductor laser emits light, that is, i
Active layer 15 composed of a Zn _{1 -z} Cd _z Se quantum well layer
n-type ZnS _s Se _1-s optical waveguide layer 14, p-type ZnS _s Se
_{The 1-s} optical waveguide layer 16, the n-type Zn _1-p Mg _p S _q Se _1-q clad layer 13 and the p-type Zn _1-p Mg _p S _q Se _1-q clad layer 17 are all lattice _- latched. The constant is 0.1Å
It is a mixed crystal semiconductor composed of a plurality of different binary compound semiconductors. Therefore, migration of impurities and defects is suppressed in these portions.

The upper part of the p _- type ZnS _v Se _1-v layer 18, p
-Type ZnSe contact layer 19, p-type ZnTe / ZnSe
The MQW layer 20 and the p-type ZnTe contact layer 21 are patterned in a stripe shape. The width of this stripe portion is, for example, 5 μm.

Further, p of the portion other than the above-mentioned stripe portion is
On the type ZnS _v Se _1-v layer 18, for example, a thickness of 300
An insulating layer 22 made of an alumina (Al ₂ O ₃ ) film having a thickness of ₂ nm is formed. And stripe-shaped p-type ZnT
The p-side electrode 23 on the e-contact layer 21 and the insulating layer 22
Are formed. A portion of the p-side electrode 23 in contact with the p-type ZnTe contact layer 21 serves as a current passage. Here, as the p-side electrode 23, for example, Pd / P having a structure in which a Pd film having a thickness of 10 nm, a Pt film having a thickness of 100 nm, and an Au film having a thickness of 300 nm are sequentially stacked.
A t / Au electrode is used. On the other hand, n-type GaAs substrate 1
An n-side electrode 24 such as an In electrode is in contact with the back surface of the No. 1 substrate.

In this semiconductor laser, so-called end face coating is applied. That is, as shown in FIG. 5, of the pair of resonator end faces perpendicular to the cavity length direction, the front end face from which laser light is extracted is Al.
_A multilayer film composed of the ₂ O ₃ film 25 and the Si film 26 is coated, and of the pair of resonator end faces perpendicular to the cavity length direction, the rear end face from which laser light is not extracted is Al ₂
A multi-layer film in which the O ₃ film 25 and the Si film 26 are laminated in two cycles is coated. Here, the Al ₂ O ₃ film 25 and S
The thickness of the multilayer film including the i film 26 is selected so that the optical distance obtained by multiplying the refractive index of the i film 26 is equal to 1/4 of the oscillation wavelength of the laser light. By applying such end face coating, for example, the reflectance of the front end face can be 70% and the reflectance of the rear end face can be 95%.

In this case, the S composition ratio s of the n-type ZnS _s Se _1-s optical waveguide layer 14 and the p-type ZnS _s Se _1-s optical waveguide layer 16 is at least 5 × 10 ^-3 (0.005) or more. Has been selected for. The Mg composition ratio p of the n-type Zn _1-p Mg _p S _q Se _1-q clad layer 13 and the p-type Zn _1-p Mg _p S _q Se _1-q clad layer 17 is 0.09, and the S composition ratio is, for example. For example, q is 0.18, and the energy gap E _{g at} that time is about 2.94 eV at 77K. These M
An n-type Zn _1-p Mg _p S _q Se _1-q cladding layer 13 and a p-type Zn _1-p Mg _p S _q Se ₁ -with a g composition ratio p = 0.09 and an S composition ratio q = 0.18. _{The q} clad layer 17 lattice-matches GaAs. The Cd composition ratio z of the i-type Zn _1-z Cd _z Se quantum well layer forming the active layer 15 is, for example, 0.19, and the energy gap E at that time is E.
_g is about 2.54 eV at 77K. In this case, n-type Z
n _1-p Mg _p S _q Se _1-q cladding layer 13 and p-type Z
n _1-p Mg _p S _q Se _1-q clad layer 17 and active layer 15
The difference ΔE _{g in} the energy gap E _g with the i-type Zn ₁ -z Cd _z Se quantum well layer that constitutes the _element is 0.40 eV. The value of the energy gap E _g at room temperature is 7
It can be determined by subtracting 0.1 eV from the value of the energy gap E _g at 7K.

The thickness of the n-type Zn _1-p Mg _p S _q Se _1-q cladding layer 13 is, for example, 0.8 μm, and the impurity concentration is N _D -N _A (N _D : donor concentration, N _A : Acceptor concentration) is, for example, 5 × 10 ¹⁷ cm ⁻³ . n-type ZnS
_s The thickness of the Se _1-s optical waveguide layer 14 is 60nm for example, an impurity concentration N _D -N _A, for example, 5 × 10 ¹⁷ cm ^-3
Is. The thickness of the p-type ZnS _s Se _1-s optical waveguide layer 16 is 60nm for example, an impurity concentration is N _A -N _D, for example, 5 × 10 ¹⁷ cm ^-3. p-type Zn _1-p Mg _p S
The thickness of the _q Se _1-q cladding layer 17 is 0.6μm example, an impurity concentration N _A -N _D, for example, 2 × 10 ¹⁷ cm
^-3 . The p-type ZnS _v Se _1-v layer 18 has a thickness of, for example, 0.6 μm, and has an impurity concentration of N _A -N _D , for example, 8 μm.
It is × 10 ¹⁷ cm ^-3 . p-type ZnSe contact layer 19
Has a thickness of, for example, 45 nm, and the impurity concentration is N _A -N
For example, _D is 8 × 10 ¹⁷ cm ⁻³ . The thickness of the p-type ZnTe contact layer 21 is 70nm for example, an impurity concentration is N _A -N _D, for example, 1 × 10 ¹⁹ cm ^-3.

Since the n-type ZnSe buffer layer 12 has a slight lattice mismatch between ZnSe and GaAs, this n-type ZnSe buffer layer is caused by this lattice mismatch. In order to prevent dislocation from occurring during the epitaxial growth of the layer 12 and each of the layers thereon, the thickness is selected to be sufficiently smaller than the critical film thickness of ZnSe (up to 100 nm), but here, for example, 33 nm is selected.

The p-type ZnS _v Se _1-v layer 1 laminated on the p-type Zn _1-p Mg _{p Sq} Se _1-q clad layer 17
8 is p-type Zn _1-p Mg _p S _q Se _1-q depending on the case.
Function as a second p-type clad layer added to the clad layer 17, p-type Zn _1-p Mg _{p Sq} Se _1-q clad layer 17
It has one or more of the following functions: a lattice matching function with and a function as a spacer layer to prevent a short circuit due to solder creep-up at the chip end surface when mounting a laser chip on a heat sink. . p
There is a trade-off between the Mg composition ratio p and the S composition ratio q of the type Zn _1-p Mg _p S _q Se _1-q cladding layer 17, but this p
The S composition ratio v of the ZnS _v Se _1-v layer 18 is 0 <v ≦
0.1, preferably 0.06 ≦ v ≦ 0.08, and is most suitable for achieving lattice matching with the p-type Zn _1-p Mg _p S _q Se _1-q cladding layer 17. The S composition ratio v is 0.06.

The above-mentioned p-type ZnTe / ZnSe MQW layer 2
0 is provided for the p-type ZnSe contact layer 1
9 is directly bonded to the p-type ZnTe contact layer 21, a large discontinuity occurs in the valence band at the bonding interface,
This is from the p-side electrode 23 to the p-type ZnTe contact layer 21.
This is to effectively eliminate this barrier because it becomes a barrier to holes injected into the.

That is, the upper limit of the carrier concentration in p-type ZnSe is usually about 5 × 10 ¹⁷ cm ^-3.
The carrier concentration in the type ZnTe can be 10 ¹⁸ cm ⁻³ or more. In addition, p-type ZnSe / p-type ZnTe
The valence band discontinuity at the interface is about 0.5 eV
Is. The valence band of such a p-type ZnSe / p-type ZnTe junction, the junction is assumed to be a step junction, W = the p-type ZnSe side ^{_{(2εφ T / qN A) 1/2}} (4) Width The band is bent over. Here, ε is the dielectric constant of ZnSe, and φ _T is p-type ZnSe / p-type ZnTe.
Size of discontinuity in valence band at interface (about 0.5e
V) is represented.

When W is calculated in this case using the equation (4), W = 32 nm. FIG. 6 shows how the top of the valence band changes along the direction perpendicular to the p-type ZnSe / p-type ZnTe interface at this time. However, it is approximated that the Fermi levels of p-type ZnSe and p-type ZnTe coincide with the top of the valence band. As shown in FIG. 6, in this case, the valence band of p-type ZnSe is p-type Zn
Turns downward (toward the lower energy side) toward Te. This downward convex valence band change acts as a potential barrier for holes injected from the p-side electrode 13 into the p-type ZnSe / p-type ZnTe junction.

This problem is caused by the p-type ZnSe contact layer 1
9 and the p-type ZnTe contact layer 21 between the p-type ZnT
This can be solved by providing the e / ZnSe MQW layer 20. This p-type ZnTe / ZnSe MQW layer 2
0 is specifically designed as follows, for example.

FIG. 7 shows the width L _W of the quantum well made of p-type ZnTe in a single quantum well having a structure in which both sides of the quantum well layer made of p-type ZnTe are sandwiched by barrier layers made of p-type ZnSe. The results obtained by quantum mechanical calculation for the well-type potential of the finite barrier show how the one quantum level E ₁ changes. However, in this calculation, the effective mass m of holes in p-type ZnSe and p-type ZnTe is defined as the mass of electrons in the quantum well layer and the barrier layer.
Assuming _h , 0.6 m ₀ is used, and the depth of the well is 0.5 eV.

From FIG. 7, the first quantum level E ₁ formed in the quantum well is reduced by reducing the width L _W of the quantum well.
It turns out that can be raised. p-type ZnTe /
The ZnSe MQW layer 20 is designed by utilizing this fact.

In this case, the band bending generated over the width W from the p-type ZnSe / p-type ZnTe interface to the p-type ZnSe side is a quadratic function of the distance x from the p-type ZnSe / p-type ZnTe interface (FIG. 6). φ (x) = φ _T {1- (x / W) ² } (5) Therefore, p-type ZnTe / ZnSeMQW
The layer 20 is designed based on the equation (5) such that the first quantum level E ₁ formed in each of the quantum well layers made of p-type ZnTe is at the top of the valence band of p-type ZnSe and p-type ZnTe. This can be done by stepwise changing L _W so that it matches the energy and is equal to each other.

FIG. 8 shows the width L _{B of the} barrier layer made of p-type ZnSe in the p-type ZnTe / ZnSe MQW layer 20 to be 2
An example of designing the quantum well width L _w in the case of nm is shown. Here, the acceptor concentration N of the p-type ZnSe contact layer 19 is N.
_A is 5 × 10 ¹⁷ cm ^−3, and the acceptor concentration N _A of the p-type ZnTe contact layer 21 is 1 × 10 ¹⁹ cm ⁻³ . As shown in FIG. 8, in this case, the width L _w of the total of seven quantum wells is set so that the first quantum level E ₁ is p-type Zn.
L _w = 0.3 nm, 0.4 n from the p-type ZnSe contact layer 19 toward the p-type ZnTe contact layer 21 so as to match the Fermi levels of Se and p-type ZnTe.
m, 0.5 nm, 0.6 nm, 0.8 nm, 1.1n
m, 1.7 nm.

In designing the width L _w of the quantum well, strictly speaking, since the levels of the respective quantum wells are mutually coupled, it is necessary to consider their interaction, and the quantum Although the effect of strain due to the lattice mismatch between the well layer and the barrier layer must be taken into consideration, setting the quantum level of the multiple quantum well flat as shown in FIG.
It is possible in principle.

In FIG. 8, the holes injected into the p-type ZnTe are resonantly tunneled through the first quantum level E ₁ formed in each quantum well of the p-type ZnTe / ZnSe MQW layer 20 to cause p-type ZnSe. Since it can flow to the side, the potential barrier at the p-type ZnSe / p-type ZnTe interface effectively disappears.

Next, a method of manufacturing the semiconductor laser shown in FIGS. 4 and 5 configured as described above will be described.

That is, in order to manufacture the semiconductor lasers shown in FIGS. 4 and 5, first, on the n-type GaAs substrate 11, an n-type GaAs substrate 11 is formed by an MBE method using a growth material as described below.
Type ZnSe buffer layer 12, n-type Zn _1-p Mg _p S _q S
e _1-q clad layer 13, n-type ZnS _s Se _1-s optical waveguide layer 14, i-type Zn _1-z Cd _z Se quantum well layer active layer 15, p-type ZnS _s Se _1-s optical waveguide layer 16, p-type Zn
_1-p Mg _p S _q Se _1-q clad layer 17, p-type ZnS _v
The Se _1-v layer 18, the p-type ZnSe contact layer 19, the p-type ZnTe / ZnSe MQW layer 20, and the p-type ZnTe contact layer 21 are sequentially epitaxially grown.

In the above epitaxial growth by the MBE method, for example, the Zn raw material has a purity of 99.99.
99% of Zn is used, and the purity of Mg is 99.9%.
Of Mg and 99.9999% Zn as the S raw material
S is used, and Se having a purity of 99.9999% is used as the Se raw material.
e is used. Further, C as an n-type impurity of the n-type ZnSe buffer layer 12, the n-type Zn _1-p Mg _{p Sq} Se _1-q cladding layer 13, and the n-type ZnS _s Se _1-s optical waveguide layer 14 is used.
The doping of l is, for example, Zn with a purity of 99.9999%.
It is performed using Cl ₂ as a dopant. On the other hand, p-type Zn
S _s Se _1-s optical waveguide layer 16, p-type Zn _1-p Mg _p S _q S
e _1-q clad layer 17, p-type ZnS _v Se _1-v layer 18,
p-type ZnSe contact layer 19, p-type ZnTe / ZnS
The doping of N as a p-type impurity in the eMQW layer 20 and the p-type ZnTe contact layer 21 is performed by irradiating N ₂ plasma generated by electron cyclotron resonance (ECR).

Next, a stripe-shaped resist pattern (not shown) having a predetermined width is formed on the p-type ZnTe contact layer 21, and the p-type ZnS _v Se _1-v layer 18 is formed using this resist pattern as a mask. Etching is performed by a wet etching method in the middle of the thickness direction. As a result, the upper layer portion of the p _- type ZnS _v Se _1-v layer 18 and the p-type Zn
Se contact layer 19, p-type ZnTe / ZnSeMQW
Layer 20 and p-type ZnTe contact layer 21 are patterned in stripes.

Next, an Al ₂ O ₃ film was vacuum-deposited on the entire surface while leaving the resist pattern used for the above-mentioned etching, and then this resist pattern was formed on top of this.
It is removed together with the l ₂ O ₃ film (lift-off). As a result, p-type ZnS _v Se _{1-v in the} part other than the stripe part
An insulating layer 22 made of an Al ₂ O ₃ film is formed only on the layer 18.

Next, a Pd film, a Pt film, and an Au film are sequentially vacuum-deposited on the entire surface of the stripe-shaped p-type ZnTe contact layer 21 and the insulating layer 22 to form a p-side electrode 23 composed of a Pd / Pt / Au electrode. Then, heat treatment is performed as necessary to bring the p-side electrode 23 into ohmic contact with the p-type ZnTe contact layer 21. On the other hand, an n-side electrode 24 such as an In electrode is formed on the back surface of the n-type GaAs substrate 11.

After that, the n-type GaAs substrate 11 having the laser structure formed as described above is cleaved into a bar shape to form both resonator end faces, and then Al ₂ is formed on the end face on the front side by vacuum deposition. A multi-layered film including the O ₃ film 25 and the Si film 26 is formed, and a multi-layered film in which the Al ₂ O ₃ film 25 and the Si film 26 are repeated for two cycles is formed on the rear end surface. After the end face coating is applied in this manner, the bar is cleaved to form chips, and packaging is performed.

As described above, according to this second embodiment,
Impurities and defects can be pinned in these portions because the portions where the light field exists at the time of emission of the semiconductor laser are composed of plural kinds of binary compound semiconductors having different lattice constants of 0.1 Å or more. It is possible to effectively prevent their movement. Therefore, it is possible to prevent the semiconductor laser from deteriorating due to the movement of the impurities and defects, and it is possible to extend the life of the semiconductor laser and improve its reliability.

According to the second embodiment, it is possible to realize a semiconductor laser which can emit light with a short wavelength and has a low threshold current density. More specifically, for example, it is possible to realize a green-emitting semiconductor laser capable of continuous oscillation at room temperature. It is also possible to reduce the applied voltage required for laser oscillation.

The embodiments of the present invention have been specifically described above, but the present invention is not limited to the above-mentioned embodiments, and various modifications can be made based on the technical idea of the present invention.

For example, in the second embodiment described above, S
The case where the present invention is applied to the manufacture of a semiconductor laser having a CH structure has been described, but the present invention can also be applied to the manufacture of a semiconductor laser having a DH structure (Double Heterostructure).

Although the GaAs substrate is used as the compound semiconductor substrate in the second embodiment, a GaP substrate or the like may be used as the compound semiconductor substrate.

[0071]

As described above, according to the present invention,
Since the light emitting portion and the portion in the vicinity thereof are made of a compound semiconductor containing at least three kinds of elements composed of at least two kinds of element compound semiconductors having lattice constants different from each other by at least 0.1Å or more, these light emitting parts and It is possible to suppress the movement of impurities and defects in the vicinity thereof, thereby preventing the deterioration of the light emitting element due to the movement of the impurities and defects. Further, the life of the light emitting element can be extended and the reliability can be improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing a semiconductor laser according to a first embodiment of the present invention.

FIG. 2 is an energy band diagram of the active layer, the n-type cladding layer and the p-type cladding layer of the semiconductor laser according to the first embodiment of the present invention.

FIG. 3 is an energy band diagram for explaining the semiconductor laser according to the first embodiment of the present invention.

FIG. 4 is a sectional view perpendicular to the cavity length direction of a semiconductor laser according to a second embodiment of the present invention.

FIG. 5 is a sectional view parallel to the cavity length direction of the semiconductor laser according to the second embodiment of the present invention.

FIG. 6 is an energy band diagram showing a valence band near a p-type ZnSe / p-type ZnTe interface.

FIG. 7 is a graph showing changes in the first quantum level E ₁ of the quantum well with respect to the width L _w of the quantum well made of p-type ZnTe.

FIG. 8 is a schematic diagram showing a design example of a p-type ZnTe / ZnSe MQW layer in a semiconductor laser according to a second embodiment of the present invention.

FIG. 9 is a graph showing the relationship between cohesive energy and interatomic distance.

FIG. 10 is a graph showing the relationship between the band gap energy and the lattice constant of some binary compound semiconductors.

FIG. 11 is an energy band diagram for explaining a problem of a conventional semiconductor laser.

[Explanation of symbols]

1, 15 active layer 2 n-type clad layer 3 p-type clad layer 4, 24 n-side electrode 5, 23 p-side electrode 11 n-type GaAs substrate 12 n-type ZnSe buffer layer 13 n-type Zn _1-p Mg _p S _q Se _1-q clad layer 14 n-type ZnS _s Se _1-s optical waveguide layer 15 active layer 16 p-type ZnS _s Se _1-s optical waveguide layer 17 p-type Zn _1-p Mg _p S _q Se _1-q clad layer 18 p-type ZnS _v Se _1-v layer 19 p-type ZnSe contact layer 20 p-type ZnTe / ZnSe MQW layer 21 p-type ZnTe contact layer 22 insulating layer

Claims (10)

[Claims] 1. The light emitting portion and a portion in the vicinity thereof have at least two lattice constants different from each other by at least 0.1 Å or more.
1. A light emitting device comprising a compound semiconductor containing at least three or more kinds of element compound semiconductors. 2. The light emitting device according to claim 1, wherein the element compound semiconductor is a binary compound semiconductor. 3. The light emitting device according to claim 1, wherein the compound semiconductor containing at least three or more elements is at least a ternary or more compound semiconductor. 4. The composition ratio of the element having the minimum composition of the compound semiconductor containing at least three or more elements is 5 × 10.
^-3 or more, The light emitting element of Claim 1 characterized by the above-mentioned. 5. A compound semiconductor superlattice composed of at least two kinds of compound semiconductor layers of at least two elements having mutually different lattice constants of at least 0.1 Å or more, wherein the compound semiconductor containing at least three elements is laminated. The light emitting device according to claim 1 or 2, wherein 6. The compound semiconductor containing at least three or more kinds of elements, wherein the elements constituting the first element group are A ₁ and A 2.
₂ , ..., A _i , the elements constituting the second element group are represented by B
_1, B _2, ..., when expressed in _{B j, (A 1) x1} (A 2) x2 ... (A i) xi (B 1) y1 (B 2)
_y2 ... (B _{j) yj} (where, 0 ≦ x1, x2, ... , xi ≦ 1,0 ≦ y1,
y2, ..., yj ≦ 1, x1 + x2 + ... + xi = 1, y1
+ Y2 + ... + yj = 1) The light emitting device according to claim 1, which is a multi-element compound semiconductor represented by the general formula: 7. The compound semiconductor containing at least three or more kinds of elements, wherein the elements constituting the first element group are A ₁ and A 2.
₂ , ..., A _i , the elements constituting the second element group are represented by B
When represented by ₁ , B ₂ , ..., B _j , (A _k B _l ) _M (A _{k ′} B _{l ′} ) _N (where 1 ≦ k, k ′ ≦ i, 1 ≦ l, l ′ ≦ j 1 ≦
The light emitting device according to claim 1, which is a compound semiconductor superlattice represented by the general formula: M + N ≦ 6). 8. The light emitting device according to claim 6, wherein the first element group is a group consisting of a group II element and the second element group is a group consisting of a group VI element. . 9. The light emitting device according to claim 6, wherein the first element group is a group III group element and the second element group is a V group element. . 10. The active layer has a structure sandwiched between an n-type cladding layer and a p-type cladding layer, and the active layer among the n-type cladding layer and the n-type cladding layer and the n-type cladding layer. At least within the diffusion length of electrons in the n-type clad layer from the interface with and from the interface between the active layer and the p-type clad layer in the p-type clad layer, at least in the p-type clad layer. A part within the diffusion length of holes in the above is composed of a compound semiconductor containing at least three kinds of elements consisting of at least two kinds of element compound semiconductors having lattice constants different from each other by at least 0.1 Å or more. The light emitting device according to claim 1.