JP2000277868A - Light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting element with high light emission efficiency and a low operation current or a low threshold current. SOLUTION: A p-type impurity is doped having in the vicinity of an interface in the [000-1] direction in a quantum well layer 8b or is doped heavily near an interface in the [000-1] direction in a barrier layer 8a. Or an n-type impurity may be doped heavily near an interface in the [0001] direction in a quantum well layer 8b or doped heavily near an interface in the [0001] direction in a barrier layer 8a. In this way, at least p-type or n-type impurity is added uniformly in the light emitting layer in the quantum well structure, so that the potential generated by piezoelectric effect in the confinement direction can be reduced in the quantum well structure. Then, the isolation between electorons and holes injected as a current can be restricted, and a decrease in luminous efficiency and the increase in operation current or threshold current can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a light emitting device formed of a material having a piezoelectric effect.

[0002]

2. Description of the Related Art GaN, GaInN, AlGaN, Al
Semiconductor light emitting devices such as a semiconductor laser device and a light emitting diode using a group III nitride semiconductor (hereinafter, referred to as a nitride semiconductor) such as GaInN are applied as light emitting devices that generate light in a range from visible to out of sight. Is expected.

[0003] Among these applications, the development of a semiconductor light emitting device using a GaInN quantum well layer as a light emitting layer has been actively conducted for practical use. Such a semiconductor light emitting device is
It is fabricated on a (0001) plane of a substrate such as sapphire or silicon carbide by MOVPE (metal organic chemical vapor deposition) or MBE (molecular beam epitaxial growth).

FIG. 37 is a schematic sectional view showing the structure of a conventional GaN-based semiconductor light emitting device. The semiconductor light emitting device of FIG. 37 is disclosed in Japanese Patent Application Laid-Open No. 6-268257.

In FIG. 37, on a sapphire substrate 61, a buffer layer 62 made of GaN, an n-contact layer 63 made of n-GaN, a light emitting layer 64 having a multiple quantum well structure, and a p-cap made of p-GaN Layer 6
5 are formed in order. The light emitting layer 64 is formed by alternately stacking a plurality of barrier layers 64a and quantum well layers 64b made of GaInN having different compositions.

In such a conventional method for manufacturing a semiconductor light emitting device, a sapphire substrate 61 having a substantially (0001) plane as a main surface is usually used, and a p-cap is formed on the sapphire substrate from a buffer layer 62 by, for example, MOVPE. Layer 65
Are sequentially formed. At this time, each of the layers from the n-contact layer 63 to the p-cap layer 65 grows in the [0001] direction of the nitride semiconductor.

[0007]

In general, crystals having no center of symmetry, such as a zinc blende structure and a wurtzite structure, may generate a piezoelectric effect due to strain. For example, in a sphalerite structure, the piezoelectric effect is greatest at strains that compress or expand about the [111] axis. In the wurtzite structure, the piezoelectric effect is maximized in strain that compresses or expands with respect to the [0001] axis.

In the above conventional semiconductor light emitting device, G
The light emitting layer 64 made of aInN has a quantum well structure having a (0001) plane as a main surface. Since the lattice constant of the quantum well layer 64b made of GaInN is larger than the lattice constant of the n-contact layer 63 made of n-GaN, the quantum well layer 64b has an in-plane direction of the quantum well (a direction parallel to the interface).
, A tensile strain is applied in the direction of confinement of the quantum well (a direction perpendicular to the interface). As a result, a potential gradient due to the piezoelectric effect occurs in the quantum well layer 64b, and the potential gradient [00
The potential on the [01-1] direction side is low, and the potential on the [000-1] direction side is high. FIG. 38 shows the energy band of the light emitting layer 64 having the quantum well structure in this case. Note that FIG.
A layer barrier layer 64a and four quantum well layers 64b are shown.

As shown in FIG. 38, since a potential gradient is generated in the quantum well layer 64b in the light emitting layer 64, as shown in FIG. 39, electrons and holes are spatially separated by the injected current. . As a result, the luminous efficiency of the semiconductor light emitting device decreases. In particular, in a semiconductor laser device, the threshold current increases.

When an impurity is added to the quantum well layer 64b of the light emitting layer 64, the effect of reducing the potential gradient due to the movement of carriers appears. However, when both the p-type impurity and the n-type impurity are added to the quantum well layer 64b, the carriers are compensated and the carrier concentration is reduced. Thus, the effect of reducing the potential gradient due to the movement of carriers is reduced.
In particular, when the concentration of the p-type impurity added to the quantum well layer 64b is substantially equal to the concentration of the n-type impurity, the effect of reducing the potential gradient due to the movement of carriers is further reduced.

Such a phenomenon is caused by other III-V compound semiconductors such as a zinc blende structure and a wurtzite structure (for example, GaI
It also occurs in nP-based semiconductors, GaAs-based semiconductors, or InP-based semiconductors), II-VI group semiconductors, and I-VII group semiconductors. In particular, since the nitride semiconductor has a large piezoelectric effect, a potential gradient generated by the piezoelectric effect becomes large, and a decrease in luminous efficiency and a rise in a threshold current and an operating current are conspicuous.

An object of the present invention is to provide a light emitting device having high luminous efficiency and low operating current or threshold current.

[0013]

According to the present invention, there is provided a light emitting device having a distortion having a piezoelectric effect.
A light emitting layer having a quantum well structure including at least one well layer and at least two barrier layers disposed so as to sandwich the well layer, wherein a p-type impurity and an n-type At least one of the impurities is added non-uniformly in the direction of confinement of the quantum well structure so as to reduce a potential gradient generated as a result of the piezoelectric effect.

In the light emitting device according to the present invention, at least one of the p-type impurity and the n-type impurity is added non-uniformly into the light emitting layer having the quantum well structure, so that the light emitting layer has a confinement direction in the quantum well structure. The potential gradient generated due to the piezoelectric effect is reduced. Thereby, the separation of electrons and holes injected as current is suppressed, so that a decrease in luminous efficiency and an increase in operating current or threshold current are suppressed.

The light emitting layer may have a multiple quantum well structure composed of two or more well layers and three or more barrier layers sandwiching the well layers. Further, the light emitting layer may have a single quantum well structure including one well layer and two barrier layers sandwiching the well layer.

In the well layer, more p-type impurities may be added to the higher potential generated as a result of the piezoelectric effect than to the lower potential.

In this case, holes move in the confinement direction of the quantum well structure, and the holes are spatially separated from ionized p-type impurities. Thereby, the potential gradient of the well layer generated due to the piezoelectric effect is reduced.

In the well layer, more n-type impurities may be added to the lower potential side generated as a result of the piezoelectric effect than to the higher potential side.

In this case, electrons move in the confinement direction of the quantum well structure, and the electrons are spatially separated from the ionized n-type impurities. Thereby, the potential gradient of the well layer generated due to the piezoelectric effect is reduced.

In the barrier layer, more p-type impurities are added to a portion in contact with the interface of the well layer on the higher potential side generated as a result of the piezoelectric effect than in a portion in contact with the interface of the well layer on the lower potential side. You may.

In this case, holes move in the direction of confinement of the quantum well structure, and the holes are spatially separated from ionized p-type impurities. Thereby, the potential gradient of the well layer generated due to the piezoelectric effect is reduced.

In the barrier layer, more n-type impurities are added to a portion in contact with the interface of the well layer on the lower potential side generated as a result of the piezoelectric effect than in a portion in contact with the interface of the well layer on the higher potential side. You may.

In this case, electrons move in the direction of confinement of the quantum well structure, and the electrons are spatially separated from the ionized n-type impurities. Thereby, the potential gradient of the well layer generated due to the piezoelectric effect is reduced.

Both a p-type impurity and an n-type impurity may be added to the light emitting layer having the quantum well layer structure. in this case,
Electrons and holes are compensated, and carriers due to doping are hardly generated, but the potential gradient generated due to the piezoelectric effect due to the ionized p-type impurities and the ionized n-type impurities is reduced.

The concentration of the p-type impurity and the concentration of the n-type impurity may be substantially equal. In this case, the carrier is easily compensated, but the effect of reducing the potential gradient is great.

The light emitting layer having the quantum well structure may have a quantum wire structure. In the light emitting layer having a quantum wire structure,
The non-uniform addition of at least one of the p-type impurity and the n-type impurity in the direction of the potential gradient reduces the potential gradient generated in the light emitting layer having the quantum wire structure.

The light emitting layer having the quantum well structure may have a quantum box structure. In the light emitting layer having the quantum box structure, at least one of the p-type impurity and the n-type impurity is added non-uniformly in the potential gradient direction, so that the potential gradient generated in the light emitting layer having the quantum box structure is reduced. I do.

The crystal structure of the material forming the well layer may be a wurtzite structure. In a crystal having a wurtzite structure, a piezoelectric effect occurs due to strain. Therefore, when at least one of the p-type impurity and the n-type impurity is non-uniformly added to the light emitting layer having the quantum well structure, the potential gradient of the well layer generated due to the piezoelectric effect is reduced.

The confinement direction of the quantum well structure is substantially <00
01> direction. In wurtzite crystals,
Since the piezoelectric effect due to the strain that compresses or expands with respect to the <0001> axis is maximized, the effect of reducing the potential gradient by adding the impurities unevenly appears.

The crystal structure of the material forming the well layer may be a zinc blende structure. In a sphalerite structure crystal, a piezoelectric effect occurs due to strain. Therefore, when at least one of the p-type impurity and the n-type impurity is non-uniformly added to the light emitting layer having the quantum well structure, the potential gradient of the well layer generated due to the piezoelectric effect is reduced.

The confinement direction of the quantum well structure is approximately <11
1> direction. In crystals with sphalerite structure,
Since the piezoelectric effect due to the strain that compresses or expands with respect to the <111> axis is maximized, the effect of reducing the potential gradient by adding impurities unevenly appears.

The strain accompanying the generation of the piezoelectric effect may include a strain that extends the well layer in the confinement direction of the quantum well structure.
In this case, a piezoelectric effect occurs due to strain that extends the well layer in the confinement direction of the quantum well structure. Therefore, the potential gradient generated due to the piezoelectric effect is reduced by non-uniformly adding at least one of the p-type impurity and the n-type impurity to the light emitting layer having the quantum well structure.

The distortion accompanying the generation of the piezoelectric effect may include a distortion that compresses the well layer in the confinement direction of the quantum well structure.
In this case, a piezoelectric effect occurs due to strain compressing the well layer in the confinement direction of the quantum well structure. Therefore, the potential gradient generated due to the piezoelectric effect is reduced by non-uniformly adding at least one of the p-type impurity and the n-type impurity to the light emitting layer having the quantum well structure.

The material forming the well layer may be a group III-V compound semiconductor. Further, the group III-V compound semiconductor may be a nitride semiconductor containing at least one of boron, gallium, aluminum and indium. In particular, the nitride semiconductor has a large piezoelectric effect,
The potential gradient generated by the piezoelectric effect increases. Therefore, the effect of reducing the potential gradient due to the non-uniform addition of the impurity is remarkably exhibited.

The material forming the well layer may be a II-VI compound semiconductor or an I-VII compound semiconductor. Also in this case, the potential gradient can be reduced due to the piezoelectric effect by adding the impurities unevenly.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (A) First Embodiment A light emitting device according to a first embodiment has a (0001) plane composed of a quantum well layer made of GaInN and a barrier layer made of GaN as a main surface. And an MQW light emitting layer having a wurtzite structure (a light emitting layer having a multiple quantum well structure). The quantum well layer has a compressive strain in an in-plane direction of the quantum well (a direction parallel to the interface) and a strain that extends in a confinement direction of the quantum well (a direction perpendicular to the interface). A potential gradient is formed in the quantum well layer made of GaInN by the piezoelectric effect.

In the case of a group III-V compound semiconductor, the potential in the [000-1] direction is high in this potential gradient, and
01] direction potential is low. In order to reduce the potential gradient generated due to the piezoelectric effect, a p-type impurity is heavily doped into the [000-1] direction side portion in the quantum well layer, or [000-1] of the quantum well layer in the barrier layer. -1] Dope heavily into the portion in contact with the interface on the direction side. Alternatively, the n-type impurity is heavily doped in the [0001] direction side portion of the quantum well layer, or heavily doped in the barrier layer in contact with the [0001] direction interface of the quantum well layer.

FIG. 1 is a schematic perspective view showing the structure of a semiconductor laser device according to the first to seventh embodiments of the present invention.
In the semiconductor laser device of FIG. 1, an MQW light emitting layer made of GaInN is used.

In FIG. 1, (00) of the sapphire substrate 1
A buffer layer 2 made of AlGaN having a thickness of about 15 nm is formed on the (01) plane. On this buffer layer 2,
Undoped GaN layer 3 having a thickness of about 0.5 μm and a thickness of 4 μm
n-contact layer 4 of n-GaN of about m, n-crack prevention layer 5 of n-GaInN of about 0.1 μm thickness, n-first cladding of n-AlGaN of about 0.45 μm thickness Layer 6, n-G about 50 nm thick
n-second cladding layer 7 made of aN, and GaInN
Are formed in order.

On the MQW light emitting layer 8, a p-first cladding layer 9 of p-GaN having a thickness of about 40 nm, a thickness of 0.4
A p-second cladding layer 10 made of p-AlGaN having a thickness of about 5 μm and a p-cap layer 11 made of p-GaN having a thickness of about 50 nm are formed in this order.

The p-cap layer 11 has a thickness of 0.2 μm.
A current confinement layer (current block layer) 14 of about m silicon nitride is formed. The current confinement layer 14 has a stripe-shaped opening having a width of about 2 μm, and the stripe-shaped opening serves as the current path 13.

A p-contact layer 12 of p-GaN having a thickness of 3 to 5 μm is formed in the stripe-shaped opening of the current confinement layer 14, on the p-cap layer 11, and on the current confinement layer 14. Each layer from the undoped GaN layer 3 to the p-contact layer 12 has a wurtzite structure, and grows in the [0001] direction of these nitride semiconductors.

Part of the region from p-contact layer 12 to n-contact layer 4 is removed, and the surface of n-contact layer 4 is exposed. Thereby, a mesa shape having a width of about 10 μm is formed. A p-electrode 15 is formed on p-contact layer 12, and an n-electrode 16 is formed on the exposed surface of n-contact layer 4.

FIG. 2 shows M in the semiconductor laser device of FIG.
FIG. 4 is an energy band diagram of the QW light emitting layer 8.

As shown in FIG. 2, the MQW light emitting layer 8 has a multiple quantum well structure in which barrier layers 8a made of GaN having a thickness of about 4 nm and quantum well layers 8b made of GaInN having a thickness of about 4 nm are alternately stacked. Having a structure. For example, GaN
The number of barrier layers 8a made of is five, and the number of quantum well layers 8b made of GaInN is four.

Here, the lattice constant of the quantum well layer 8b made of GaInN is compared with the lattice constant of the undoped GaN layer 3 having a thickness of about 0.5 μm and the n-contact layer 4 of n-GaN having a thickness of about 4 μm. Is large, compressive strain is generated in the in-plane direction of the quantum well (direction parallel to the interface),
A strain is generated that extends in the direction of confinement of the quantum well (direction perpendicular to the interface). As a result, a potential gradient accompanying the piezoelectric effect is formed in the quantum well layer 8b in the MQW light emitting layer 8, and the MQW
The energy band in the light emitting layer 8 has the structure shown in FIG.

In the following first to seventh embodiments, in order to reduce the potential gradient formed in the quantum well layer 8b, the MQW
At least one of a p-type impurity and an n-type impurity is non-uniformly added to the light emitting layer 8.

(1) First Embodiment FIGS. 3 and 4 are energy band diagrams of the MQW light emitting layer 8 in the semiconductor laser device of the first embodiment.

As shown in FIG. 3, for example, Mg as the p-type impurity is heavily doped in the [000-1] direction side, that is, the n-second cladding layer 7 side in the quantum well layer 8b. Specifically, only the portion of the quantum well layer 8b having a thickness of about 2 nm on the n-second cladding layer 7 side is doped with Mg, and the thickness of the quantum well layer 8b on the p-first cladding layer 9 side is reduced. The portion of about 2 nm is not doped with Mg.

The doping amount of Mg is 1 × 10 ¹⁷ to 1
× 10 ²¹ cm ^-3 is preferred. As a method of non-uniform doping of the p-type impurity, other methods may be used. For example, the n-second cladding layer 7 in the quantum well layer 8b
2 × 10 ¹⁰ to 2 × 1 at a depth of about 1 nm from the side interface
Delta doping may be performed with a p-type impurity to a concentration of about 0 ¹⁴ cm ⁻² . Be, C other than Mg as p-type impurities
a, Sr, Ba, Zn, Cd, Hg or the like may be used.

In the present embodiment, as shown in FIG. 3, for example, Mg as the p-type impurity is [000-1] in the quantum well layer 8b.
Since the doping is heavily doped in the direction side, that is, on the side of the n-second cladding layer 7, holes move in the [0001] direction as shown in FIG. 4, and the holes and the ionized p-type impurities are spatially separated. To separate. Thus, the potential gradient of the quantum well layer 8b generated due to the piezoelectric effect decreases, and the gradient of the energy band also decreases. As a result, the separation of electrons and holes injected as current is suppressed, so that a decrease in luminous efficiency and an increase in threshold current are suppressed.

(2) Second Embodiment FIGS. 5 and 6 are energy band diagrams of the MQW light emitting layer 8 in the semiconductor laser device of the second embodiment.

As shown in FIG. 5, for example, Si is heavily doped as an n-type impurity on the [0001] direction side in the quantum well layer 8b, that is, on the p-first cladding layer 9 side. Specifically, only the portion of the quantum well layer 8b having a thickness of about 2 nm on the p-first cladding layer 9 side is doped with Si, and the thickness of the quantum well layer 8b on the n-second cladding layer 7 side is reduced. About 2 nm portion is not doped with Si.

The doping amount of Si is 1 × 10 ¹⁷ to 1
× 10 ²¹ cm ^-3 is preferred. As a method of non-uniform doping of the n-type impurity, other methods may be used. For example, the p-first cladding layer 9 in the quantum well layer 8b
2 × 10 ¹⁰ to 2 × 1 at a depth of about 1 nm from the side interface
An n-type impurity may be delta-doped to a concentration of about 0 ¹⁴ cm ^-2 . Ge and P other than Si as n-type impurities
b, S, Se, Te, etc. may be used.

In the present embodiment, as shown in FIG. 5, for example, Si as the n-type impurity is [0001] in the quantum well layer 8b.
Since a large amount is doped on the direction side, that is, on the side of the p-first cladding layer 9, electrons move in the [000-1] direction as shown in FIG. 6, and the electrons and the ionized n-type impurities are spatially separated. To separate. Thereby, the potential gradient of the quantum well layer 8b generated due to the piezoelectric effect decreases. As a result, the separation of electrons and holes injected as current is suppressed, so that a decrease in luminous efficiency and an increase in threshold current are suppressed.

(3) Third Embodiment FIGS. 7 and 8 are energy band diagrams of the MQW light emitting layer 8 in the semiconductor laser device of the third embodiment.

As shown in FIG. 7, for example, Mg as a p-type impurity in the barrier layer 8a has the [000-1] of the quantum well layer 8b.
It is heavily doped on the direction side, that is, on the portion in contact with the interface on the n-second cladding layer 7 side. Specifically, only a portion of the barrier layer 8a having a thickness of about 2 nm which is in contact with the interface of the quantum well layer 8b on the side of the n-second cladding layer 7 is doped with Mg, and the quantum well layer 8b in the barrier layer 8a is doped with Mg. Mg is not doped in a portion having a thickness of about 2 nm in contact with the interface on the p-first cladding layer 9 side.

The doping amount of Mg is 1 × 10 ¹⁷ to 1
× 10 ²¹ cm ^-3 is preferred. As a method of non-uniform doping of the p-type impurity, other methods may be used. For example, in the barrier layer 8a, the n-second
2 × 1 at a depth of about 1 nm from the interface on the side of the cladding layer 7
Delta doping with a p-type impurity may be performed at a concentration of about 0 ^{10 to} 2 × 10 ¹⁴ cm ⁻² . Be, Ca, Sr, Ba, Zn, Cd, Hg or the like may be used as the p-type impurity in addition to Mg.

In this embodiment, as shown in FIG. 7, for example, Mg as a p-type impurity in the [000-1] direction side of the quantum well layer 8b in the barrier layer 8a, that is, the interface with the n-second cladding layer 7 side. Since the contact portion is heavily doped, holes move in the [0001] direction as shown in FIG. 8, and the holes are spatially separated from the ionized p-type impurity. Thereby, the potential gradient of the quantum well layer 8b generated due to the piezoelectric effect decreases. As a result, the separation of electrons and holes injected as current is suppressed, so that a decrease in luminous efficiency and an increase in threshold current are suppressed.

(4) Fourth Embodiment FIGS. 9 and 10 are energy band diagrams of the MQW light emitting layer 8 in the semiconductor laser device of the fourth embodiment.

As shown in FIG. 9, for example, Si is used as an n-type impurity in the barrier layer 8a in the [0001] of the quantum well layer 8b.
It is heavily doped on the direction side, that is, on the portion in contact with the interface on the p-first cladding layer 9 side. Specifically, only a portion of the barrier layer 8a having a thickness of about 2 nm in contact with the interface between the quantum well layer 8b and the p-first cladding layer 9 is doped with Si. The portion having a thickness of about 2 nm in contact with the interface on the n-second cladding layer 7 side is not doped with Si.

The doping amount of Si is 1 × 10 ¹⁷ to 1
× 10 ²¹ cm ^-3 is preferred. As a method of non-uniform doping of the n-type impurity, other methods may be used. For example, in the barrier layer 8a, the p-first
2 × 1 at a depth of about 1 nm from the interface on the side of the cladding layer 9
The n-type impurity may be delta-doped to a concentration of about 0 ^{10 to} 2 × 10 ¹⁴ cm ⁻² . Ge, Pb, S, Se, Te, or the like may be used as the n-type impurity in addition to Si.

In this embodiment, as shown in FIG. 9, for example, Si as an n-type impurity in the barrier layer 8a is in contact with the [0001] direction side of the quantum well layer 8b, that is, the interface in contact with the interface on the p-first cladding layer 9 side. 10, electrons move in the [000-1] direction as shown in FIG. 10, and the electrons are spatially separated from the ionized n-type impurities. Thereby, the potential gradient of the quantum well layer 8b generated due to the piezoelectric effect decreases. As a result, the separation of electrons and holes injected as current is suppressed, so that a decrease in luminous efficiency and an increase in threshold current are suppressed.

Although the doping methods in the first to fourth embodiments can be used alone, the effects can be obtained.
Two or more embodiments of the doping method may be combined. For example, the first and third embodiments may be combined, the first, second, and third embodiments may be combined, and the first, second, third, and fourth embodiments may be combined. Is also good.

(5) Fifth Embodiment FIGS. 11 and 12 are energy band diagrams of the MQW light emitting layer 8 in the semiconductor laser device of the fifth embodiment.

The fifth embodiment is a combination of the first embodiment and the second embodiment, as shown in FIG. This embodiment shows a case where the doping concentrations of Mg as a p-type impurity and Si as an n-type impurity are substantially equal.

In this embodiment, as shown in FIG. 12, electrons and holes are compensated, and almost no carriers are generated by doping. However, the piezoelectric effect due to the ionized p-type impurity and the ionized n-type impurity is reduced. Therefore, the generated potential gradient decreases. As a result, the separation of electrons and holes injected as current is suppressed, so that a decrease in luminous efficiency and an increase in threshold current are suppressed.

Therefore, particularly, the pW
When both the p-type impurity and the n-type impurity are added, even if carriers are compensated by adding the p-type impurity and the n-type impurity unevenly, the effect of reducing the potential gradient is large. When the concentration of the p-type impurity and the concentration of the n-type impurity added to the MQW light emitting layer 8 are substantially equal, the carrier is more easily compensated, but the effect of reducing the potential gradient is large.

For example, when the first and fourth embodiments are combined, even when the second and third embodiments are combined, an effect equivalent to that of the fifth embodiment is produced.

(6) Sixth Embodiment FIGS. 13 and 14 are energy band diagrams of the MQW light emitting layer 8 in the semiconductor laser device of the sixth embodiment.

The sixth embodiment is a combination of the third embodiment and the fourth embodiment, as shown in FIG. This embodiment shows a case where the doping concentrations of Mg as a p-type impurity and Si as an n-type impurity are substantially equal.

In this embodiment, as shown in FIG. 14, electrons and holes are compensated, and almost no carriers are generated by doping. However, the p-type impurity ionized and the n-type impurity ionized cause the piezoelectric effect to be reduced. Therefore, the generated potential gradient decreases. As a result, the separation of electrons and holes injected as current is suppressed, so that a decrease in luminous efficiency and an increase in threshold current are suppressed.

In this embodiment, the p-type impurity and the n-type impurity are not doped in the quantum well layer 8b. Therefore, in addition to the effect of the fifth embodiment, the effect that the impurity level due to the doping of the quantum well layer 8b or the light emission by the light emitting center can be reduced is obtained. Thereby,
When the MQW light-emitting layer 8 of the present embodiment is applied to a light-emitting diode, the emission spectrum width can be narrowed.
As a result, color purity can be improved.

(7) Seventh Embodiment FIGS. 15 and 16 are energy band diagrams of the MQW light emitting layer 8 in the semiconductor laser device of the seventh embodiment.

In the seventh embodiment, as shown in FIG.
In the quantum well layer 8b of the first embodiment in which, for example, Mg is non-uniformly doped as a p-type impurity, for example, Si is uniformly doped as an n-type impurity. The doping concentration of Si is 5 × 10 ^{16 to} 5 × 10 ²⁰ cm ⁻³ .

In the present embodiment, as shown in FIG. 15, for example, Mg as the p-type impurity is [000−] in the quantum well layer 8b.
1], that is, the n-second cladding layer 7 side is heavily doped, and, for example, Si is uniformly doped in the quantum well layer 8b as an n-type impurity. The carrier is compensated and almost no carriers are generated by doping, but the potential gradient generated due to the piezoelectric effect due to the ionized p-type impurity and n-type impurity is reduced. As a result, the separation of electrons and holes injected as current is suppressed, so that a decrease in luminous efficiency and an increase in threshold current are suppressed.

The quantum well layer 8 of the third embodiment, for example,
When the n-type impurity is uniformly doped in b and the p-type impurity is uniformly doped in the quantum well layer 8b of the second or fourth embodiment, the same effect as in the seventh embodiment can be obtained. Occurs.

FIGS. 17 to 21 are schematic process sectional views showing a method of manufacturing the semiconductor laser device of FIG.

Each nitride semiconductor layer of the semiconductor laser device of FIG. 1 is formed on a sapphire substrate 1 by MOVPE. As the raw material gas, for example, trimethyl aluminum (TMAl), trimethyl gallium (TMGa),
Trimethyl indium (TMIn), NH ₃ , Si
H ₄ , cyclopentadienyl magnesium (Cp ₂ M
g) is used.

First, as shown in FIG.
A buffer layer 2 having a thickness of about 15 nm is formed on the sapphire substrate 1 while maintaining the temperature at 00 ° C. Next, the substrate temperature was set to 1150
While maintaining the temperature, the undoped GaN layer 3 having a thickness of about 0.5 μm and the n-contact layer 4 made of Si-doped GaN having a thickness of about 4 μm are formed. Further, the substrate temperature is set to 880 ° C.
And a Si-doped Ga _0.95 In layer having a thickness of about 0.1 μm
_An n-crack preventing layer 5 made of 0.05N is formed. Next, while maintaining the substrate temperature at 1150 ° C., the n-first cladding layer 6 made of Al-doped Al _0.15 Ga _0.85 N having a thickness of about 0.45 μm, and the Si-doped Ga having a thickness of about 50 nm
An n-second cladding layer 7 made of N is formed.

Further, the substrate temperature is maintained at 880 ° C., and five barrier layers 8 made of undoped GaN having a thickness of about 4 nm are formed.
a and undoped Ga _0.85 In _0.15 n about 4 nm thick
N four quantum well layers 8b are alternately stacked, and Ga
An MQW light emitting layer 8 made of InN is formed. At this time, according to the first to seventh embodiments, the MQW light emitting layer 8 is doped with a p-type impurity or an n-type impurity.

Finally, the substrate temperature is kept at 1150 ° C., the p-first cladding layer 9 made of Mg-doped GaN having a thickness of about 40 nm, and the Mg-doped AlG having a thickness of about 0.45 μm.
A p-second cladding layer 10 made of aN and a p-cap layer 11 made of Mg-doped GaN having a thickness of about 50 nm are formed. Each layer from the buffer layer 2 to the p-cap layer 11 is formed by the atmospheric pressure MOVPE method.

Thereafter, as shown in FIG. 18, a silicon nitride such as Si ₃ N ₄ having a thickness of about 0.2 μm is formed on the entire surface of the p-cap layer 11 by, for example, ECR (electron cyclotron resonance) plasma CVD. Current confinement layer 1 made of
4 is formed. Next, photolithography and BHF
2μm width by wet etching with (buffered hydrofluoric acid)
Removing the silicon nitride in the striped area
The p-cap layer 11 is exposed. Thus, a stripe-shaped current path 13 is formed.

Next, as shown in FIG.
The n-current confinement layer 14 is formed by a reduced pressure MOVPE method of orr.
Above and on the p-cap layer 11 in the stripe opening
A p-constant made of Mg-doped GaN having a thickness of 3 to 5 μm
The tact layer 12 is formed. At this time, the p-cap layer 11
P-GaN grows selectively on the exposed part of
In addition, the growth conditions are appropriately adjusted. For example, reduce the substrate temperature to about
100 ° C, NH _ThreeAbout three times the flow rate of
You.

When growth is performed under such conditions, p
-P-GaN grows on the exposed portion of the cap layer 11 to form a portion corresponding to the current path 13. On the other hand, p-GaN does not grow on the current confinement layer 14. When the crystal growth is continued, p-GaN becomes
P- grown on the current path 13
Crystal growth starts laterally from the side surface of GaN, and p-contact layer 12 made of p-GaN is formed on current confinement layer 14. For example, the p-contact layer 12 is formed with a width of about 8 μm around a portion corresponding to the current path 13.

As a result, the p-cap layer 11 and the p-con
The tact layer 12 is a stripe-shaped current passage having a width of about 2 μm.
The p-cap layer 11 and the p-contact
Between the gate layer 12 and the current path 13 except for the current path 13.
Si of about 0.2μm_ThreeN _FourCurrent confinement layer 14 made of
Is formed.

Next, as shown in FIG. 20, a metal mask and EB (electron beam) vapor deposition are used to form a stripe having a width of about 10 μm and a thickness of 3 to 5 μm on the region including the p-contact layer 12. Deposit the film. This N
Using the i-film as a mask, for example, using CF ₄ as an etching gas, reactive ion etching (RIE) is performed until the n-contact layer 4 is exposed from the p-contact layer 12 to the n-crack prevention layer 5. Etch in a mesa shape. Thereafter, the Ni film used as the mask is removed using hydrochloric acid or the like.

Further, as shown in FIG. 21, Si ₃ N ₄
The insulating film 17 such as a p-contact layer 12 is formed by ECR plasma CVD, photolithography and etching.
To the n-contact layer 4 excluding the side surfaces from the substrate to the n-crack prevention layer 5 and the electrode formation region. Then, on the exposed surface of the n-contact layer 4, for example, A
An n-electrode 16 made of u / Ti is formed, and a p-electrode 15 made of Au / Pd is formed on the p-contact layer 12.

Finally, a cavity structure having a cavity length of 300 μm is formed in the direction along the stripe-shaped current path 13 by cleavage, for example. Thus, a semiconductor laser device having the structure shown in FIG. 1 is manufactured.

It should be noted that Si was applied to the cavity surface of the semiconductor laser device.
An end face high reflection film or a low reflection film such as a dielectric multilayer film in which ₃ N ₄ , SiO ₂ , Al ₂ O ₃ , TiO _{2 and the} like are laminated may be formed.

(8) Eighth Embodiment The semiconductor laser device of the eighth embodiment has the same structure as the semiconductor laser device of FIG. 1, and the crystal growth method of the nitride-based semiconductor layer is as follows. different.

In the structure of the semiconductor laser device shown in FIG.
After crystal growth of at least the buffer layer 2 and the undoped GaN layer 3 at a low temperature and at a high temperature on the (0001) plane of the sapphire substrate 1 by the MOVPE method,
For example, MBE (molecular beam epitaxy) or H
The crystal is grown by a crystal growth method other than MOVPE such as VPE (halide vapor phase epitaxy). The structure of the MQW light emitting layer 8 is the same as in the first to seventh embodiments.

In this embodiment, the undoped GaN layer 3
To p-contact layer 12 have a wurtzite structure and grow in the [0001] direction of the nitride-based semiconductor. Therefore, the same effects as those of the first to seventh embodiments can be obtained.

Thus, the (000) of the sapphire substrate 1
1) After the buffer layer 2 is grown on the surface by MOVPE at a low temperature and subsequently the crystal growth of the nitride-based semiconductor layer is performed at a high temperature, the nitride-based semiconductor layer grows in the [0001] direction. Even if the crystal growth method is changed, the crystal growth direction does not change and the crystal continues to grow in the [0001] direction.

(9) Ninth Embodiment A semiconductor laser device according to a ninth embodiment has the same structure as the semiconductor laser device shown in FIG. 1, and a method for growing a nitride-based semiconductor layer will be described below. Are different.

In the structure of the semiconductor laser device shown in FIG.
On the (0001) plane of the sapphire substrate 1, at least the buffer layer 2 is formed at a low temperature and undoped by MBE.
After crystal growth of the aN layer 3 at a high temperature, the other layers 4 to 12,
14 with another crystal growth method (for example, HVPE method, MOVP
E) etc. or crystal growth by MBE.

In this embodiment, the undoped GaN layer 3
To p-contact layer 12 have a wurtzite structure and grow in the [000-1] direction of the nitride-based semiconductor. For this reason, the direction of the potential gradient of the MQW light emitting layer 8 is the first direction.
-It is the opposite of the eighth embodiment.

FIGS. 22 and 23 are energy band diagrams of the MQW light emitting layer 8 in the semiconductor laser device of the ninth embodiment.

As shown in FIG. 22, for example, Si as an n-type impurity has a thickness of [000] in the quantum well layer 8b in the barrier layer 8a.
1] direction side, that is, a portion in contact with the interface on the side of the n-second cladding layer 7 is heavily doped, and, for example, Mg as a p-type impurity in the barrier layer 8a in the [000-1] direction side of the quantum well layer 8b, that is -A portion in contact with the interface on the first cladding layer 9 side is heavily doped to form a modulation doping structure. This embodiment shows a case where the doping concentrations of the n-type impurity and the p-type impurity are substantially equal.

In this embodiment, as shown in FIG. 23, electrons and holes are compensated, and almost no carriers are generated by doping. However, due to an ionized p-type impurity and an ionized n-type impurity, a piezoelectric effect is generated. The potential gradient generated at the time decreases. As a result, the separation of electrons and holes injected as current is suppressed, so that a decrease in luminous efficiency and an increase in threshold current are suppressed.

Therefore, in particular, pW
When both the p-type impurity and the n-type impurity are added, even if carriers are compensated by adding the p-type impurity and the n-type impurity unevenly, the effect of reducing the potential gradient is large. When the concentration of the p-type impurity and the concentration of the n-type impurity added to the MQW light emitting layer 8 are substantially equal, the carrier is more easily compensated, but the effect of reducing the potential gradient is large.

The structure of the MQW light-emitting layer 8 includes first to seventh
When the structure of the embodiment is used, the same effects as those of the first to seventh embodiments can be obtained.

In the first to ninth embodiments, the sapphire substrate 1 is used as the substrate. However, if the nitride semiconductor layer has a wurtzite structure, spinel, SiC, Si, Ga
A substrate of As, GaP, InP, GaN, or the like may be used.

In the first to ninth embodiments, the MQW light emitting layer 8 having a wurtzite structure having a strain extending in the direction of confining the quantum well (perpendicular to the interface) has been described. MQ including a quantum well layer made of AlGaN and a barrier layer made of AlGaInN on a substrate
When the W light emitting layer is formed, strain compressing in the direction of confining the quantum well (direction perpendicular to the interface) occurs. In this case, the potential gradient due to the piezoelectric effect is [0001]
The potential on the direction side becomes higher, and the potential on the [000-1] direction side becomes lower. Therefore, the distribution position of the doping of the p-type impurity or the n-type impurity is (0) at the center of the quantum well layer.
The (001) plane may be reversed from the first to ninth embodiments.

The same effect can be obtained if the semiconductor has a wurtzite structure or a hexagonal structure, such as a II-VI compound semiconductor represented by wurtzite ZnSe. However, in the case of the II-VI compound semiconductor and the I-VII compound semiconductor represented by CuCl, the potential gradient is reversed.

In addition, the plane orientation of the quantum well layer is not limited to the (0001) plane as long as the potential well is confined in the direction in which a potential gradient occurs due to strain. As long as the plane orientation of the strained quantum well is other than the plane orientation including the [0001] axis in the plane, the potential causes a potential gradient in the confinement direction of the quantum well in any plane orientation. That is, as long as the plane orientation of the strained quantum well is other than the plane orientation represented by the general formula (HKL0), the piezoelectric effect is generated in any plane orientation. Here, H, K and L are H + K + L
= 0 and any number except H = K = L = 0. The (HKL0) plane is, for example, a (1-100) plane and a (11-20) plane. In particular, in a strained quantum well having a (0001) plane as a main surface, the piezoelectric effect of generating a potential gradient in the direction of confinement of the quantum well is the largest. In addition,
The plane orientation of the quantum well layer in which a potential gradient occurs due to strain will be described later.

(B) Second Embodiment The light emitting device of the second embodiment has an MQW light emitting layer having a zinc blende structure with a (111) plane having a strain in a quantum well layer. If the quantum well has a strain in the confinement direction (direction perpendicular to the interface), a potential gradient is formed by the piezoelectric effect.

The III-V compound semiconductor has a tensile strain in the in-plane direction of the quantum well (direction parallel to the interface),
In the case where the strain compresses in the direction of confinement of the quantum well (direction perpendicular to the interface), the potential in the [111] direction is high in the potential gradient generated due to the piezoelectric effect, and the potential in the [-1-1-1] direction is high. Is low. In order to reduce this potential gradient, p-type impurities are heavily doped in the [111] direction side of the quantum well layer, or [1] of the quantum well layer in the barrier layer.
11] A large amount of doping is applied to a portion in contact with the interface on the direction side. Alternatively, an n-type impurity is heavily doped into the [-1-1-1] direction portion of the quantum well layer, or is connected to the [-1-1-1] direction interface of the quantum well layer in the barrier layer. Heavily dope the contacting parts.

Conversely, in a III-V group compound semiconductor,
When the strain has a compressive strain in the in-plane direction of the quantum well (direction parallel to the interface) and a strain that extends in the confinement direction of the quantum well (direction perpendicular to the interface), the potential gradient generated due to the piezoelectric effect is The potential on the [-1-1-1] direction side is high,
1] The potential on the direction side is low. In order to reduce this potential gradient, p-type impurities are heavily doped into the [-1-1-1] direction part of the quantum well layer, or [-1-1] of the quantum well layer is formed in the barrier layer. -1] Dope heavily into the portion in contact with the interface on the direction side. Alternatively, an n-type impurity is added to [111] in the quantum well layer.
The portion on the direction side is heavily doped, or the portion in the barrier layer that contacts the interface on the [111] direction side of the quantum well layer is heavily doped.

On the other hand, II-VI compound semiconductors and I-VI
When a group I compound semiconductor has tensile strain in the in-plane direction of the quantum well (direction parallel to the interface) and compressive strain in the confinement direction of the quantum well (direction perpendicular to the interface),
[-1-1-1] in the potential gradient generated due to the piezoelectric effect
The potential on the direction side is high, and the potential on the [111] direction side is low.
In order to reduce this potential gradient, p-type impurities are heavily doped into the [-1-1-1] direction part of the quantum well layer, or [-1-1] of the quantum well layer is formed in the barrier layer. -1] Dope heavily into the portion in contact with the interface on the direction side. Alternatively, an n-type impurity is heavily doped into a portion of the quantum well layer on the [111] side, or a portion of the barrier layer which is in contact with an interface of the quantum well layer on the [111] side.

Conversely, II-VI compound semiconductors and I-VI
In the case of a Group I compound semiconductor that has a compressive strain in the in-plane direction of the quantum well (direction parallel to the interface) and a strain that extends in the confinement direction of the quantum well (direction perpendicular to the interface), the piezoelectric effect occurs. The potential in the [111] direction is high and the potential in the [-1-1-1] direction is low. In order to reduce this potential gradient, a p-type impurity is heavily doped into the [111] direction side portion of the quantum well layer, or a portion of the barrier layer which is in contact with the [111] direction interface of the quantum well layer. Dope a lot. Alternatively, a large amount of an n-type impurity is doped in the [-1-1-1] direction side of the quantum well layer,
Alternatively, a portion of the barrier layer that is in contact with the interface on the [-1-1-1] direction side of the quantum well layer is heavily doped.

The direction of confinement of the quantum well is not limited to the plane orientation equivalent to the (111) plane as long as the potential gradient is generated due to strain. If the plane orientation of the strained quantum well is other than the plane orientation including the [100] axis in the plane and its equivalent plane orientation, the potential gradient is generated in the confinement direction of the quantum well due to the strain in any plane orientation. That is, as long as the plane orientation of the strained quantum well is other than the plane orientation represented by the general formula (0MN) and its equivalent plane orientation, the piezoelectric effect is generated in any plane orientation. Here, M and N are arbitrary numbers except M = N = 0. The (0MN) plane is, for example, a (001) plane and a (011) plane. In particular, in a strained quantum well having a (111) plane as a main surface, the piezoelectric effect of generating a potential gradient in the direction of confinement of the quantum well is the largest. The plane orientation of the quantum well layer where a potential gradient occurs due to strain will be described later.

(10) Tenth Embodiment FIG. 24 is a sectional view showing the structure of an AlGaInP semiconductor laser device having a buried ridge structure according to a tenth embodiment of the present invention. FIGS. 25 and 26 are energy band diagrams of the MQW light emitting layer in the semiconductor laser device of the tenth embodiment.

In FIG. 24, n-GaAs substrate 21
Has a crystal growth plane with a plane orientation of (111) A. n-
Consisting n-Ga _0.51 In _0.49 P on the GaAs substrate 21 n-buffer layer _{22, n- (Al 0.7 Ga 0.3} ) 0.51 I
An n-cladding layer 23 made of n _0.49 P and an MQW light emitting layer 24 are sequentially formed.

[0115] MQW light-emitting layer 24, as shown in FIG. _{25, (Al 0.5 Ga 0.5)} 0.51 In 0. 49 to the light guide layer 24c made of _{P (Al 0.5 Ga 0.5) 0.45} In 0.55 P
Of five compression-strain barrier layers 24a and Ga _0.6 In
Four tensile strain well layers 24b of _0.4 P are alternately stacked.

On the MQW light emitting layer 24, (Al_0.57Ga
_0.43)_0.51In_0.49The light guide layer 25 made of P
Quantum barrier layers 26 are sequentially formed. Multiple quantum barrier
Layer 26 comprises Ga_0.51In_0.4910 well layers of P
And (Al_0.7Ga_0.3) _0.51In_0.491 consisting of P
Zero barrier layers are alternately stacked. This multiple quantum disorder
The wall layer 26 is provided for improving temperature characteristics.

On the multiple quantum barrier layer 26, p- (Al
_A p-cladding layer 27 made of _0.7 Ga _0.3 ) _0.51 In _0.49 P is formed. The upper region of the p-cladding layer 27 is formed in a stripe-shaped ridge portion by mesa etching or the like. The width of the ridge is 5 μm. A p-contact layer 28 of p-Ga _0.51 In _0.49 P is formed on the ridge of the p-cladding layer 27.

On both sides of the p-cladding layer 27, n-Ga
An n-current blocking layer 29 made of As is formed,
On the contact layer 28 and the n-current blocking layer 29, a p-cap layer 30 made of p-GaAs is formed. An n-electrode 32 is formed on the lower surface of the n-GaAs substrate 21, and a p-electrode 31 is formed on the upper surface of the p-cap layer 30.

Table 1 shows the material and thickness of each layer in the semiconductor laser device of FIG.

[0120]

[Table 1]

In this semiconductor laser device, n-Ga
The layers 22 to 30 on the As substrate 21 are formed by MOCVD (metal organic chemical vapor deposition) or the like.

The lattice constant of the compressive strain barrier layer 24a is n-Ga
It is set larger than the lattice constant of the As substrate 21.
As a result, the compressive strain barrier layer 24a becomes the n-GaAs substrate 2
1 has a compressive strain. The lattice constant of the tensile strain well layer 24b is set smaller than the lattice constant of the n-GaAs substrate 21. Thereby, the tensile strain well layer 24b has a tensile strain with respect to the n-GaAs substrate 21.

As shown in FIG. 25, for example, Se as an n-type impurity is formed in the tensile strain well layer 24 in the compressive strain barrier layer 24a.
b is heavily doped in the [1-1-1] direction side, that is, the portion in contact with the interface on the light guide layer 24c side, and Zn as a p-type impurity is included in the tensile strain well layer 24b in the compressive strain barrier layer 24a.
Is heavily doped in the [111] direction side, that is, the portion in contact with the interface on the light guide layer 25 side, to form a modulation doping structure. This embodiment shows a case where the doping concentrations of the n-type impurity and the p-type impurity are substantially equal.

In this embodiment, since the well layer 24b has a tensile strain and the barrier layer 24a has a compressive strain in the plane of the quantum well in the MQW light emitting layer 24, the barrier layer 24a
Generates a potential gradient opposite to that of the well layer 24b.

In this embodiment, as shown in FIG. 26, electrons and holes are compensated, and almost no carriers are generated by doping. However, the tensile strain well layer 24b is formed by ionized p-type impurities and ionized n-type impurities. Of the electric potential decreases. As a result, the separation of electrons and holes injected as current is suppressed, so that a decrease in luminous efficiency and an increase in threshold current are suppressed.

(11) Eleventh Embodiment FIG. 27 is a sectional view showing the structure of a ZnSe-based semiconductor laser device according to an eleventh embodiment of the present invention. FIGS. 28 and 29 are energy band diagrams of the MQW light emitting layer in the semiconductor laser device of the eleventh embodiment.

In FIG. 27, on the (111) B plane of the n-GaAs substrate 41, an n-first buffer layer 42 made of n-GaAs, an n-second buffer layer 43 made of n-ZnSe, and n-Zn _An n-cladding layer 44 made of _0.9 Mg _0.1 S _0.15 Se _0.85 and an MQW light emitting layer 45 are sequentially formed.

As shown in FIG. 28, the MQW light emitting layer 45 has five tensile strain barrier layers 45a made of ZnS _0.1 Se _0.9 and four compressive strain well layers 45b made of Zn _0.7 Cd _0.3 Se alternately stacked. Be done.

On the MQW light emitting layer 45, p-Zn _0.9 M
A p-cladding layer 46 made of g _0.1 S _0.15 Se _0.85 is formed. The upper region of the p-cladding layer 46 is a stripe-shaped ridge.

On the ridge portion of the p-cladding layer 46, p
A p-contact layer 48 made of -ZnSe is formed;
SiO ₂ films 47 are formed on both sides of the ridge portion of the p-cladding layer 46 and the p-contact layer 48. n-
An n-electrode 50 is formed on the lower surface of the GaAs substrate 41, and a p-
P electrode 4 on contact layer 48 and SiO ₂ layer 47
9 are formed.

Table 2 shows the material and thickness of each layer in the semiconductor laser device of FIG.

[0132]

[Table 2]

As shown in FIG. 28, for example, Cl is compressed as an n-type impurity in the compressive strain well layer 45 in the tensile strain barrier layer 45a.
b is heavily doped in the [-1-1-1] direction side, that is, the portion in contact with the interface on the p-cladding layer 46 side, and, for example, nitrogen as a p-type impurity is formed in the tensile strain barrier layer 45a.
A large portion is doped in the [111] direction side of b, that is, the portion in contact with the interface on the n-cladding layer 44 side, thereby forming a modulation doping structure. This embodiment shows a case where the doping concentrations of the n-type impurity and the p-type impurity are substantially equal.

In the present embodiment, the well layer 45b has a compressive strain in the plane of the quantum well in the MQW light emitting layer 45,
Since the barrier layer 45a has a tensile strain, a potential gradient opposite to that of the well layer 45b is generated in the barrier layer 45a.

In this embodiment, as shown in FIG. 29, electrons and holes are compensated and almost no carriers are generated by doping. However, the compressive strain well layer 45b is formed by ionized p-type impurities and ionized n-type impurities. Of the electric potential decreases. As a result, the separation of electrons and holes injected as current is suppressed, so that a decrease in luminous efficiency and an increase in threshold current are suppressed.

(C) Third Embodiment The light emitting device of the third embodiment has an MQW light emitting layer having a quantum wire structure or a quantum box structure.

(12) Twelfth Embodiment FIGS. 30 to 33 show a method of manufacturing a semiconductor laser device according to a twelfth embodiment. FIG. 30 is a schematic sectional view of a process, and FIG. 31 is an enlarged sectional view of an MQW light emitting layer. FIG. 32, FIG.
(B) is an enlarged sectional view and a schematic plan view of the MQW light emitting layer on which the quantum wire is formed, FIG. 33 is an enlarged sectional view of the MQW light emitting layer having the quantum wire structure, and FIG. 34 is a schematic process sectional view.

First, as shown in FIG. 30, the buffer layer 2 and the undoped G layer are formed on the (0001) plane of the sapphire
The aN layer 3, the n-contact layer 4, the n-crack preventing layer 5, the n-first cladding layer 6, the n-second cladding layer 7, and the MQW light emitting layer 8 are grown.

As shown in FIG. 31, the MQW light emitting layer 8
A plurality of barrier layers 8a and a plurality of quantum well layers 8b are alternately stacked. The method of doping the MQW light emitting layer 8 with impurities is the same as in the first to seventh embodiments.

Next, as shown in FIG. 32, a part of the MQW light emitting layer 8 is n-typed by a focused ion beam (FIB) or the like.
The MQW light emitting layer 8 is linearly cut until it reaches the second cladding layer 7 and is processed linearly. The width of the remaining portion of the MQW light emitting layer 8 is, for example, about 5 nm, and the width of the portion cut by the FIB is, for example, about 20 nm.

Thereafter, as shown in FIG. 33, the MQW light emitting layer 8 is embedded with an undoped GaN layer 8c. Thus, an MQW light emitting layer 80 having a quantum wire structure is formed.

Further, as shown in FIG. 34, the p-first cladding layer 9 and the p-second cladding layer 1 are formed on the MQW light-emitting layer 80 by MOVPE in the same manner as in the step of FIG.
The 0 and p-cap layers 11 are grown in sequence. Subsequent steps are the same as the steps shown in FIGS.

In the semiconductor laser device of this example, a potential gradient is generated in the MQW light emitting layer 80 having the quantum wire structure in the crystal growth direction on the substrate. Therefore, the first to seventh
In the same manner as in the first embodiment, impurities are non-uniformly doped in the crystal growth direction on the substrate. Thus, the potential gradient generated in the MQW light emitting layer 80 having the quantum wire structure is reduced. As a result, the separation of electrons and holes injected as current is suppressed, so that a decrease in luminous efficiency and an increase in threshold current are suppressed.

(13) Thirteenth Embodiment FIG. 35 is an enlarged sectional view and an enlarged plan view of an MQW light emitting layer having a quantum box structure of a semiconductor laser device according to a thirteenth embodiment. A method for manufacturing a semiconductor laser device according to the thirteenth embodiment will be described with reference to FIGS. 30, 31, 33, and 34.

First, as shown in FIG. 30, a buffer layer 2, an undoped GaN layer 3, and an n-contact layer are formed on the (0001) plane of the sapphire substrate 1 by MOVPE in the same manner as in the step of FIG. 4. The n-crack preventing layer 5, the n-first cladding layer 6, the n-second cladding layer 7, and the MQW light emitting layer 8 are grown.

As shown in FIG. 31, the MQW light emitting layer 8
A plurality of barrier layers 8a and a plurality of quantum well layers 8b are alternately stacked. The method of doping the MQW light emitting layer 8 with impurities is the same as in the first to seventh embodiments.

Next, as shown in FIG. 35, a part of the MQW light emitting layer 8 is n-typed by a focused ion beam (FIB) or the like.
The MQW light-emitting layer 8 is cut into a box shape until the first clad layer 7 is reached. The width of the remaining portion of the MQW light emitting layer 8 is, for example, about 6 nm, and the width of the portion cut by the FIB is, for example, about 20 nm.

Thereafter, as shown in FIG. 33, the MQW light emitting layer 8 is embedded with an undoped GaN layer 8c. Thus, an MQW light emitting layer 80 having a quantum box structure is formed.

Further, as shown in FIG. 34, the p-first cladding layer 9 and the p-second cladding layer 1 are formed on the MQW light emitting layer 80 by MOVPE in the same manner as in the step of FIG.
The 0 and p-cap layers 11 are grown in sequence. Subsequent steps are the same as the steps shown in FIGS.

In the semiconductor laser device of this embodiment, a potential gradient is generated in the MQW light emitting layer 80 having the quantum box structure in the crystal growth direction on the substrate. Therefore, as in the first to seventh embodiments, the impurity is non-uniformly doped in the crystal growth direction on the substrate. Thereby, the MQ of the quantum box structure
The potential gradient generated in the W light emitting layer 80 decreases. As a result, the separation of electrons and holes injected as current is suppressed, so that a decrease in luminous efficiency and an increase in threshold current are suppressed.

In the light emitting layer 80 having the quantum wire structure and the quantum box structure, the direction in which the potential gradient occurs is not limited to the crystal growth direction on the substrate. Depending on the plane orientation of the substrate, the orientation of the quantum wire or quantum box, the shape of the quantum wire or quantum box, a potential gradient may be generated in the in-plane direction of the substrate. In such a case, doping may be made non-uniform in the in-plane direction of the substrate by a method such as ion implantation.

Although the first to thirteenth embodiments have described the case where the present invention is applied to a semiconductor laser device, the present invention can be applied to other light emitting devices such as light emitting diodes. .

The plane orientation of the quantum well layer in which a potential gradient is generated due to strain The polarization in the confinement direction of the quantum well is determined by PIEZOELECTRICITY V
ol. 1 (New Revised Edition) by WGCADY Dover Publi
According to literature such as cations, Inc. New York 1964,
Can be calculated.

In FIG. 36, the z-axis is the direction of confinement of the quantum well. The XYZ coordinate system is rotated by an angle α using the Z axis as a rotation axis. As for the coordinate axes after rotation, the X axis moves to the ξ axis,
The Y axis moves to the y axis.

Ξ The y β coordinate system is defined as an angle β with the y axis as a rotation axis.
Rotate. After the rotation, the 回 転 axis moves to the x axis,
The axis moves to the z-axis.

In the wurtzite-type crystal, the X axis is defined as [2-1] of the crystal.
-10] axis, the Y axis is [01-10] axis, and the Z axis is [0
001] axis. In the zinc blende type crystal, the X axis is the [100] axis of the crystal, the Y axis is the [010] axis, and the Z axis is the Z axis.
Let the axis be the [001] axis.

Here, the polarization in the z-axis direction is P_zAnd distortion
Ε_xx, Ε_yy, Ε_yz, Ε_xz, Ε_xyAnd the piezoelectric coefficient
(Piezoelectric stress coefficients)₃₁,
e₃₃, E ₁₅, E₁₄And

In the ordinary quantum well structure as in the first to eleventh embodiments, the potential gradient is proportional to the polarization P _z in the z-axis direction.
ε _xx = ε _yy , ε _yz = ε _xz = ε _xy = 0, and ε _xx and ε _zz
Are different.

In a wurtzite crystal, the polarization P _{z in the} z-axis direction is
Is represented by the following equation. P _z = ε _xx cos β (e ₃₁ cos ² β + e ₃₃ sin ² β-e ₁₅ sin ² β) + ε _yy e ₃₁ cos β + ε _zz cos β (e ₃₁ sin ² β + e ₃₃ cos ² β + e ₁₅ sign ² β) + ε _xz sin β (2e ₃₁ cos ² β-2e ₃₃ cos ² β + e ₁₅ sin ² β) (1) The electrode P _{z in the} z-axis direction is independent of α. From the above equation (1), in the wurtzite crystal, for example, when the angle β is 90 °, the polarization P _z in the z-axis direction becomes 0. That is, when the z-axis in FIG. 36 is on the XY plane, no potential gradient occurs due to strain in the confinement direction of the quantum well. Therefore,
As described above, the plane (H, K, and L) of the general formula (HKL0) satisfies H + K + L = 0, and H = K = L = 0.
In the plane orientation represented by (arbitrary number excluding), no potential gradient occurs in the confinement direction of the quantum well, and in other plane orientations, a potential gradient occurs in the confinement direction of the quantum well.

In the zinc blende type crystal, the polarization P _{z in the} z-axis direction is expressed by the following equation. _{P z = ε xx e 14 sinαcosαcosβ} (cos 2 β-sin 2 β) -ε yy e 14 sinαcosαcosβ + 3ε zz e 14 sinαcosαsin 2 βcos β + 2ε yz e 14 (cos 2 α-sin 2 α) sinβcosβ + 2ε xz e 14 si nαcosαsinβ (2cos from ^{2 β-sin 2 β) +} 2ε xy e 14 (cos 2 α -sin 2 α) (cos 2 β-sin 2 β) ··· (2) equation (2), the zinc blende type crystal, for example, When the angle α is 0 ° or 90 ° or when the angle β is 0 ° or 90 °, the polarization P _z in the z direction becomes 0. Therefore, as described above, in the plane orientation represented by the general formula (0MN) plane (M and N are any numbers except M = N = 0) and the plane orientation equivalent thereto, the confinement direction of the quantum well is No potential gradient is generated in other regions, and a potential gradient is generated in the confinement direction of the quantum well in other plane orientations.

The value of the piezoelectric coefficient is the value of LANDOLT-BORNSTEIN Nume.
rical Data and Functional Relationships in Science
and Technology New Series Group III; Crystal and
Solid State Physics Vol. 17a, Edited by O. Madelun
g, springer-Verlag Berlin-Heidelberg 1982 and the like.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing a configuration of a semiconductor laser device according to first to seventh embodiments of the present invention.

FIG. 2 is an energy band diagram of an MQW light emitting layer in the semiconductor laser device of FIG.

FIG. 3 shows MQ in the semiconductor laser device of the first embodiment.
FIG. 3 is an energy band diagram of a W light emitting layer.

FIG. 4 shows MQ in the semiconductor laser device of the first embodiment.
FIG. 3 is an energy band diagram of a W light emitting layer.

FIG. 5 shows an MQ in the semiconductor laser device of the second embodiment.
FIG. 3 is an energy band diagram of a W light emitting layer.

FIG. 6 shows an MQ in the semiconductor laser device of the second embodiment.
FIG. 3 is an energy band diagram of a W light emitting layer.

FIG. 7 shows an MQ in a semiconductor laser device according to a third embodiment.
FIG. 3 is an energy band diagram of a W light emitting layer.

FIG. 8 shows an MQ in the semiconductor laser device of the third embodiment.
FIG. 3 is an energy band diagram of a W light emitting layer.

FIG. 9 shows an MQ in the semiconductor laser device of the fourth embodiment.
FIG. 3 is an energy band diagram of a W light emitting layer.

FIG. 10 shows M in the semiconductor laser device of the fourth embodiment.
It is an energy band diagram of a QW light emitting layer.

FIG. 11 shows M in the semiconductor laser device of the fifth embodiment.
It is an energy band diagram of a QW light emitting layer.

FIG. 12 shows M in the semiconductor laser device of the fifth embodiment.
It is an energy band diagram of a QW light emitting layer.

FIG. 13 shows M in the semiconductor laser device of the sixth embodiment.
It is an energy band diagram of a QW light emitting layer.

FIG. 14 shows M in the semiconductor laser device of the sixth embodiment.
It is an energy band diagram of a QW light emitting layer.

FIG. 15 shows M in the semiconductor laser device of the seventh embodiment.
It is an energy band diagram of a QW light emitting layer.

FIG. 16 shows M in the semiconductor laser device of the seventh embodiment.
It is an energy band diagram of a QW light emitting layer.

FIG. 17 is a schematic process sectional view illustrating the method of manufacturing the semiconductor laser device of FIG. 1;

18 is a schematic process sectional view illustrating the method for manufacturing the semiconductor laser device of FIG. 1.

FIG. 19 is a schematic process sectional view illustrating the method of manufacturing the semiconductor laser device of FIG. 1;

20 is a schematic process sectional view illustrating the method of manufacturing the semiconductor laser device of FIG. 1;

FIG. 21 is a schematic process sectional view showing the method of manufacturing the semiconductor laser device of FIG. 1;

FIG. 22 shows M in the semiconductor laser device of the ninth embodiment.
It is an energy band diagram of a QW light emitting layer.

FIG. 23 shows M in the semiconductor laser device of the ninth embodiment.
It is an energy band diagram of a QW light emitting layer.

FIG. 24 is a schematic sectional view showing the structure of an AlGaInP-based semiconductor laser device having a buried ridge structure according to a tenth embodiment of the present invention.

FIG. 25 is an energy band diagram of an MQW light emitting layer in the semiconductor laser device according to the tenth embodiment.

FIG. 26 is an energy band diagram of an MQW light emitting layer in the semiconductor laser device of the tenth embodiment.

FIG. 27 is a schematic sectional view showing the structure of a ZnSe-based semiconductor laser device according to an eleventh embodiment of the present invention.

FIG. 28 is an energy band diagram of an MQW light emitting layer in the semiconductor laser device of the eleventh embodiment.

FIG. 29 is an energy band diagram of the MQW light emitting layer in the semiconductor laser device of the eleventh embodiment.

FIG. 30 is a schematic process sectional view showing the method of manufacturing the semiconductor laser device in the twelfth embodiment.

FIG. 31 is an enlarged sectional view of an MQW light emitting layer of a semiconductor laser device according to a twelfth embodiment.

FIG. 32 is an enlarged cross-sectional view and a schematic plan view of an MQW light emitting layer in which a quantum wire structure of a semiconductor laser device according to a twelfth embodiment is formed.

FIG. 33 is an enlarged cross-sectional view of an MQW light emitting layer having a quantum wire structure of a semiconductor laser device according to a twelfth embodiment.

FIG. 34 is a schematic process sectional view illustrating the method of manufacturing the semiconductor laser device in the twelfth embodiment.

FIG. 35 is an enlarged cross-sectional view and a schematic plan view of an MQW light emitting layer in which a quantum box structure of a semiconductor laser device according to a thirteenth embodiment is formed.

FIG. 36 is a diagram illustrating a plane orientation of a quantum well layer in which a potential gradient is generated due to strain.

FIG. 37 is a schematic sectional view showing a configuration of a conventional GaN-based semiconductor light emitting device.

FIG. 38 is an energy band diagram of an MQW light emitting layer in a conventional semiconductor light emitting device.

FIG. 39 is an energy band diagram of an MQW light emitting layer in a conventional semiconductor light emitting device.

[Explanation of symbols]

 Reference Signs List 1 sapphire substrate 6 n-first cladding layer 7 n-second cladding layer 8, 24, 45, 80 MQW light emitting layer 9 p-first cladding layer 10 p-second cladding layer 8a, 24a, 45a barrier layer 8b quantum Well layer 23,45 n-cladding layer 27,46 p-cladding layer 24b, 45b well layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) H01S 5/347 H01S 3/18 678 F term (Reference) 5F041 AA03 CA04 CA05 CA34 CA35 CA40 CA41 CA43 CA44 CA46 CA65 5F073 AA04 AA13 AA51 AA71 AA74 AA75 CA07 CA14 CA22 CB02 CB05 CB17 DA05 EA23 EA29

Claims (18)

[Claims] 1. A light emitting layer having a quantum well structure comprising one or more well layers having strain accompanied by generation of a piezoelectric effect and two or more barrier layers arranged so as to sandwich said well layer. Wherein at least one of a p-type impurity and an n-type impurity in the light emitting layer of the quantum well structure is non-uniform so as to reduce a potential gradient generated as a result of a piezoelectric effect in a confinement direction of the quantum well structure. A light-emitting element, which is added. 2. In the well layer, a higher potential generated as a result of the piezoelectric effect has a higher p than a lower potential.
The light emitting device according to claim 1, wherein a large amount of type impurities are added. 3. In the well layer, the lower side of the potential generated as a result of the piezoelectric effect is n more than the higher side of the potential.
3. The light emitting device according to claim 1, wherein a large amount of type impurities are added. 4. In the barrier layer, a portion which is in contact with the interface of the well layer on the higher potential side generated as a result of the piezoelectric effect is more p-type than a portion in contact with the interface of the well layer on the lower potential side. The light emitting device according to claim 1, wherein a large amount of impurities are added. 5. In the barrier layer, a portion in contact with the interface of the well layer on the lower potential side generated as a result of the piezoelectric effect is more n-type than a portion in contact with the interface of the well layer on the higher potential side. The light emitting device according to claim 1, wherein a large amount of impurities are added. 6. The light emitting device according to claim 1, wherein both a p-type impurity and an n-type impurity are added to the light emitting layer having the quantum well structure. 7. The light emitting device according to claim 6, wherein the concentration of the p-type impurity is substantially equal to the concentration of the n-type impurity. 8. The light emitting device according to claim 1, wherein the light emitting layer having the quantum well structure has a quantum wire structure. 9. The light emitting device according to claim 1, wherein the light emitting layer having the quantum well structure has a quantum box structure. 10. The light emitting device according to claim 1, wherein a crystal structure of a material forming the well layer is a wurtzite structure. 11. The confinement direction of the quantum well structure is substantially the <0001> direction.
The light-emitting element according to any one of the preceding claims. 12. The light emitting device according to claim 1, wherein a crystal structure of a material forming said well layer is a zinc blende structure. 13. The light emitting device according to claim 12, wherein a confinement direction of the quantum well structure is substantially a <111> direction. 14. The light emitting device according to claim 1, wherein the strain accompanying the generation of the piezoelectric effect includes a strain that extends the well layer in a direction in which the quantum well structure is confined. . 15. The light emitting device according to claim 1, wherein the strain accompanying the generation of the piezoelectric effect includes a strain for compressing the well layer in a direction in which the quantum well structure is confined. . 16. The material forming the well layer is III-V.
16. A group compound semiconductor.
The light emitting device according to any one of the above. 17. The light emitting device according to claim 16, wherein said III-V compound semiconductor is a nitride semiconductor containing at least one of boron, gallium, aluminum and indium. 18. The light emitting device according to claim 1, wherein a material forming said well layer is a II-VI compound semiconductor or an I-VII compound semiconductor.