JPH04218994A - Semiconductor light emitting device - Google Patents

Abstract

PURPOSE:To improve emission efficiency by implanting carriers efficiently to an active layer. CONSTITUTION:On an n-type InP substrate 21 are stacked in order, through an n-type InP buffer layer 12, an InGaAs/InGaAsP multiple quantum well active layer 13, an In0.5218Ga0.0875Al0.3907As carrier overflow preventive layer 14, an In0.77Ga0.23As0.5P0.5 optical wave layer 15. And in the light wave guide pipe 15 is made a primary phase shift structure refractive grating 26, 1.55mum in Bragg wavelength. Thereon, further, are stacked a p-type Inp clad layer 17 and an InGaAsP contact layer 28. And a p-type ohmic electrode 213 is formed on the InGaAsP contact layer 28 and the p-type InGaAsP contact layer 212, while an n-type ohmic electrode 214 is made at the bottom of the substrate 21. This contact layer 212 and the electrode 214 work in a body as carrier implantation means.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to semiconductor light emitting devices, such as semiconductor lasers and light emitting diodes, which have improved reactive current prevention layers.

0002

2. Description of the Related Art Hitherto, attempts have been made to improve the characteristics of semiconductor light emitting devices by eliminating reactive currents that do not contribute to light emission, such as overflow currents and leakage currents flowing out of active layers. FIG. 11 shows a perspective view of a conventional semiconductor laser.

On a substrate 111 are an N-type InP buffer (cladding layer) 112, an InGaAs/InGaAsP multi-quantum well active layer 113, and an InGaAsP optical waveguide layer 1.
15. A P-type InP cladding layer 117 is formed, and the injected electrons (e) and holes (h) recombine in the active layer 113 to emit light. Here, in order to prevent electrons (e) from overflowing to the optical waveguide layer 115 without being recombined in the active layer 113, InP carriers having a wider forbidden band width than these are placed between the active layer 113 and the optical waveguide layer 115. An overflow prevention layer 114 is interposed.

FIG. 12 shows a band diagram of this semiconductor laser taken along the line AA'. 112-11 in the figure
7 corresponds to 112 to 117 in FIG. As shown in FIG. 12, such a structure is effective in preventing electrons (e) from overflowing into the optical waveguide layer 115, but holes (
h) was a barrier to injection into the active layer. As a result, luminous efficiency was not improved, leading to problems such as property deterioration due to heat generation.

[0005]

As described above, conventional semiconductor light emitting devices have had the problem of not being able to effectively reduce the reactive current that does not contribute to light emission.

The present invention has been developed in consideration of the above-mentioned circumstances, and its purpose is to provide good characteristics that can generate more light and improve luminous efficiency by efficiently injecting carriers into the active layer. The object of the present invention is to provide a semiconductor light emitting device having the following characteristics. [Structure of the invention]

[0007]

[Means for Solving the Problems] In order to achieve the above object, the first invention includes an active layer consisting of a first semiconductor layer, and an N-type second semiconductor layer formed so as to sandwich the active layer. and a P-type third semiconductor layer; means for injecting electrons into the active layer through the second semiconductor layer and injecting holes through the third semiconductor layer; a carrier overflow prevention layer consisting of a fourth semiconductor layer formed between the third semiconductor layer, and the carrier overflow prevention layer has an energy level of the lowest quantum level of the conduction band for electrons in the active layer and the carrier overflow prevention layer. A semiconductor characterized in that the energy level of the lowest level of the valence band for holes is higher than that of the third semiconductor layer, and is higher than the active layer and substantially equal to or lower than that of the third semiconductor layer. A light emitting device is provided.

[0008] A second invention also provides an active layer comprising a first semiconductor layer, an N-type second semiconductor layer and a P-type third semiconductor layer, which are formed to sandwich the active layer. injecting electrons into the active layer via the second semiconductor layer,
means for injecting holes through the third semiconductor layer; and a fourth semiconductor layer formed between the active layer and the third semiconductor layer.
a carrier overflow prevention layer consisting of a semiconductor layer of A semiconductor characterized by having a quantum well structure in which the energy level of the energy level is set and a pseudomorphic strained semiconductor layer having a wider forbidden band width than the active layer acts as a barrier layer for electrons. A light emitting device is provided.

[0009] A third aspect of the present invention also provides an active layer comprising a first semiconductor layer, a second N-type semiconductor layer and a third P-type semiconductor layer, which are formed to sandwich the active layer. means for injecting electrons and holes into the active layer through the second semiconductor layer and the third semiconductor layer; and a means for injecting current leakage formed between the second semiconductor layer and the third semiconductor layer. a leak prevention layer that prevents leakage, and the leakage prevention layer
The present invention provides a semiconductor light emitting device characterized by having a quantum well structure in which a pseudomorphic strained semiconductor layer having a wider forbidden band width than the semiconductor layer and the third semiconductor layer is used as a barrier layer.

The active layer is a region where injected electrons and holes recombine to emit light, and these electrons and holes are transferred to P-type or It is implanted through an N-type semiconductor layer.

[0011] The pseudomorphic layer in the second and third inventions refers to a layer formed on a semiconductor layer by suppressing the thickness to a desired critical thickness or less, thereby elastically straining another semiconductor layer that is not lattice-matched. The in-plane lattice constants are made to match.

0012

[Operation] According to the first invention, the carrier overflow prevention layer interposed between the active layer and the P-type semiconductor layer has a higher energy level of the lowest quantum level of the conduction band for electrons than these layers. There is no fear that electrons injected into the active layer will leak beyond this carrier overflow prevention layer to the P-type semiconductor layer side. On the other hand, the energy level of the lowest quantum level of the valence band for holes in this carrier overflow prevention layer is substantially the same or smaller than that of the active layer or the P-type semiconductor layer, so carriers are removed from the P-type semiconductor layer. Holes are easily injected into the active layer through the overflow prevention layer. Therefore, many holes are injected into the active layer, and at the same time, there is less fear that the injected electrons will leak, increasing the recombination of holes and electrons, and improving luminous efficiency.

According to the second invention, in addition to the first invention, since a pseudomorphic strained semiconductor layer is used for the carrier overflow prevention layer, the energy level of the lowest quantum level of the conduction band for electrons can be made higher. Furthermore, since the energy level of the lowest quantum level of the conduction band for electrons in the multiple well layers in this carrier overflow prevention layer is higher than that of the active layer, electrons that do not have the corresponding energy cannot tunnel through the barrier layer, and carrier overflow due to tunneling can be prevented, and further improvement in luminous efficiency can be expected.

According to the third invention, the leakage prevention layer having a similar structure to the carrier overflow prevention layer is then added to the second layer.
, are interposed between the third semiconductor layers. As a result, the leak prevention layer prevents carriers from leaking between the second and third semiconductor layers other than the active layer, and further improvement in luminous efficiency from this aspect can be expected.

[0015]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a first embodiment, which is a first embodiment.
FIG. 2 is a cross-sectional perspective view of the distributed feedback semiconductor laser device according to the invention. FIG. 2 is a band diagram along the AA' cross section in FIG.
The solid line between 22 and 22 indicates the lowest quantum level energy level of the valence band for holes. 12 to 17 in Figure 1 are 1 in Figure 2
It corresponds to numbers 2 to 17.

This semiconductor laser device has a fourth semiconductor layer of In0.5218Ga0.0875Al0 with a thickness of 250A between the optical waveguide layer 15 and the quantum well active layer 13.
．． It is characterized in that a 3907As carrier overflow prevention layer 14 is interposed therebetween.

That is, an n-type In with a (100) main surface
On the P substrate 21, a second semiconductor layer with a thickness of 2 μm is formed.
InG via the InP type buffer (cladding) layer 12
aAs/InGaAsP multi-quantum well active layer 13, In0.5218Ga0.0875Al0. with a film thickness of 250A.
3907As carrier overflow prevention layer 14, In0.77Ga0.23As0.5P with a film thickness of 1000A
0.5 photoelectric wave layers 15 are sequentially laminated. active layer 1
3 is undoped In0.53Ga0.47 with a film thickness of 75A
Five As well layers, 100A thick undoped In0.
Six 77Ga0.23As0.5 P0.5 barrier layers are alternately laminated. A first-order phase shift structure diffraction grating 26 with a Bragg wavelength of 1.55 μm is formed in the optical waveguide layer 15. On top of that, a 1.5 μm thick P type InP cladding layer 17 is further formed as a P type third semiconductor layer, and a 0.8 μm thick InGaAs cladding layer 17 is formed as a P type third semiconductor layer.
A P contact layer 28 is laminated. These laminated structures are etched into mesa stripes perpendicular to the diffraction grating, and are filled with a p-type InP layer 29, an n-type InP layer 210, a p-type InP layer 211, and a p-type InGaAsP contact layer 212. and InGaAsP
A p-type ohmic electrode (Ti/Pt/A
u) 213 is formed, and an n-type ohmic electrode (Au/Ge) 214 is formed under the substrate 21. The contact layer 212 and the electrode 214 work together as carrier (electron) injection means. The same applies to the hole injection means.

[0018] Then, it is cut into chips with a length of 900 μm and a width of 300 μm, and a non-reflective coating film is formed on the end face. In reality, this laser chip is mounted in a module together with an optical isolator, a Peltier cooling element, an optical fiber pigtail, etc. The operation of this semiconductor laser device will be explained.

FIG. 3 shows In1 lattice-matched to the InP substrate.
-u Gau Asv P1-v (0≦v≦1), u
=0.1894v/(0.4184-0.013v)±
δ) and In1-s (Aa1-t Alt )s As
It is a figure which shows the band alignment based on the vacuum level of (0<=t<=1, S=0.47+0.01t). The lower end Ec of the conductor, which is the energy level of the lowest quantum level of the conduction band for electrons, is located at an energy level lower than the vacuum level by electron affinity x. The apex Ev of the valence band, which is the energy level of the lowest quantum level of the valence band for holes, is further extended from Ec to the forbidden band energy width E
It is located at a lower location by g.

From this figure, the positions of Ev almost match, and Ec is In1-s(Ga1-t Alt)s As(
0≦t≦1, S=0.47+0.01t), it is possible to obtain a combination in which the value is higher.

Here, by setting v=0.5 and t=0.817, there is almost no discontinuity in Ev (ΔEv=
0), and the Ec gap is ΔEc=0.3182eV
It is getting higher.

From FIG. 3, In1-u Gau Asv
P1-v and In1-s (Ga1-t Alt)
s In the As heterojunction, the positions of Ev are almost the same, and E
It can be seen that other combinations can be obtained in which c has a high value of In1-s (Ga1-t Alt)s As. For this example, i.e. v=0.5, t
A band diagram when =0.817 is shown in FIG.

By having such a band diagram, in the semiconductor laser device of the present invention, there is almost no discontinuity in Ev (ΔEv=0), and the gap ΔE in Ec is
The carrier overflow prevention layer 14 in FIG. 2 acts as a barrier to electrons, but does not act as a barrier to hole injection. Furthermore, since the carrier overflow prevention layer 14 has a thickness of 250 A, leakage of electrons due to tunnel current can also be prevented.

Electrons injected from the n-type cladding layer 12 into the active layer 13 are transferred to the In0.53Ga0.47As well layer 13.
Since the two-dimensional density of states in the conduction band 1 is small, it also overflows to the InGaAsP barrier layer 132 in the laser oscillation state. However, since the carrier overflow prevention layer 14 has a sufficiently large barrier ΔEc against electrons, overflow to the optical waveguide layer 15 is effectively prevented.

On the other hand, from the p-type cladding layer 12 to the active layer 13
The electrons injected into the active layer 13 pass through the optical waveguide layer 15 and the carrier overflow prevention layer 14 . At this time, since there is no barrier to holes in the optical waveguide layer 15, carrier overflow prevention layer 14, and active layer 13, holes can be efficiently injected into the quantum well layer 131. Since the two-dimensional density of states in the valence band of the In0.53Ga0.47As well layer 131 is sufficiently large, overflow of holes can be almost ignored.

In this way, the oscillation threshold can be lowered by the amount that recombination of electrons and holes in the optical waveguide layer can be reduced. Furthermore, the stimulated emission gain (differential gain) for carrier injection increases to the extent that electrons do not overflow into the optical waveguide layer 15. Therefore, the luminous efficiency is also improved. Furthermore, since the linewidth increase coefficient is inversely proportional to the differential gain, increasing the differential gain is also effective in reducing the linewidth increase coefficient.

[0027] Furthermore, an increase in the linewidth increase coefficient α due to the plasma effect of the optical waveguide layer can also be prevented. Therefore, it is possible to narrow the linewidth of the oscillation spectrum and reduce wavelength chirping during high-speed modulation.

Furthermore, it is possible to improve the performance of a DFB laser for 10 Gb/s class ultra-high speed optical communication and a semiconductor laser for coherent optical communication. This embodiment can be applied not only to lasers but also to LEDs without a resonator.

In the above embodiment, ΔEv=0, but in reality it is difficult to make the apexes of the valence bands completely coincide. However, the difference (barrier) is the thermal energy of the laser operating temperature kT (k is Boltzmann's constant, T is the absolute temperature)
If it is small compared to , most of the holes can overcome this heterobarrier. Here, when we say that there is virtually no barrier, we are referring to such a state, and it is not necessarily limited to ΔEv=0, but ΔEv=0.
Any material that satisfies Ev<kT is sufficient.

Next, a second embodiment of the present invention will be explained. This embodiment differs from the previous embodiment in the carrier overflow prevention layer. In the following, parts that are the same as those in the first embodiment are given the same numbers, and detailed explanation thereof will be omitted.

As shown in the band diagram of the laser of this embodiment in FIG. 4, holes are injected from the optical waveguide layer 15 to the carrier overflow prevention layer 44, and holes are injected from the carrier overflow prevention layer 44 to the barrier layer 132 of the active layer. If no valence band barrier is created for hole injection, ΔEv
=0 does not have to be the case. That is, it is effective if the energy level for holes at the upper end of the valence band decreases from the optical waveguide layer 15 to the active layer 13. Even in this case, the same effects as in the first embodiment can be achieved.

Note that in the above embodiment, the substrate is an n-type I
Although an nP substrate was used, it goes without saying that a p-type substrate may also be used. In that case, the vertical relationship of each layer may be reversed.

[0033] Here, the carrier overflow prevention layer 4
If 4 is too thick, there will be a layer with a low refractive index between the active layer with a high refractive index and the optical waveguide layer, which will adversely affect the optical waveguide characteristics. In addition, the carrier overflow prevention layer 44
By using a material that is not lattice-matched to the substrate, it is possible to make the barrier higher than a material that is lattice-matched, but in this case, in order to avoid deterioration of crystallinity, the thickness of the lattice-mismatched layer must be , it is necessary to set the in-plane lattice constant below a critical thickness at which elastic distortion occurs so as to match the substrate. If the carrier overflow prevention layer 44 cannot be made sufficiently thick for such reasons, overflow may occur due to tunnel current from the active layer 13 to the optical waveguide layer 15. FIG. 5 is a diagram showing a band diagram of a semiconductor laser device according to a second invention, which is a third embodiment, focusing on these points. This structure can also prevent carrier overflow due to tunnel current, and is similar to the first embodiment, but the carrier overflow prevention layer 5
4 is InGa consisting of a pseudomorphic strained semiconductor layer.
AlAs barrier layer 541 and InGaAsP well layer 542
, 543. The InGaAlAs layer 41 has a composition with less In and more Al than a composition that is lattice matched to InP, and as a result, a higher barrier can be achieved than when InGaAlAs that is lattice matched to InP is used. However, the thickness of each InGaAlAs layer 541 is set to 50 Å in order to avoid an increase in tunnel current through deep levels due to lattice mismatch and property deterioration due to crystal defects. In this case, the InGaAlAs layer 54
1 has in-plane tensile strain (compressive strain in the normal direction), so the degeneracy of heavy holes and light holes in the valence band is resolved,
The forbidden band width for light holes becomes narrower. Here InG
valence band peak Evlh, which is the energy level of the lowest quantum level of the valence band of light holes in the aAlAs layer 541;
is set to almost coincide with the valence band apex of the InGaAsP layers 542 and 543, so no barrier to holes is created. This valence band apex Evlh is the third
The energy level of the lowest quantum level for holes is lower than the valence band apex of the optical waveguide layer 55, which is a semiconductor layer, and higher than the valence band apex of the barrier layer 132 of the active layer. Therefore p
There is no barrier to hole injection from the type cladding layer 17 to the well layer 131. On the other hand, since a quantum well is formed for electrons injected through the second semiconductor layer, I
The energy level of the lowest quantum level for electrons in the nGaAsP layers 542 and 543 is higher than the conduction band edge of the active layer. Therefore, electrons that do not have energy corresponding to this lowest quantum level are transferred from the barrier layer 132 of the active layer to the InGaAsP layer 542.
It is not possible to tunnel through the lAs layer 541. Therefore, overflow due to tunnel current can be reduced. This lowest quantum level is the InGaAsP layer 542
The thinner the thickness of the InGaAsP layer 54, the higher the height.
2 is preferably made as thin as possible. Furthermore, by providing multiple quantum wells, the tunneling probability can be reduced. At this time, in order to prevent tunnel current from increasing due to resonance tunneling, it is preferable to set each quantum well layer to have different quantum level levels by changing the thickness, etc. In the example of FIG. 5, the first InGaA
The sP layer 542 is 40A thick and the second InGaAsP
The layer 543 is set to 25A. This effect causes
InGaAsP layer 542 to InGaAsP layer 543
As a result, carrier overflow due to tunnel current from the active layer 13 to the optical waveguide layer 15 can be almost prevented.

FIG. 6(a) is a structural sectional view of a semiconductor laser according to the third invention, which is a fourth embodiment. This semiconductor laser device consists of an n-type InP substrate 61 (also serving as a cladding layer) with a carrier density of 3 x 1018 cm-3, which is a second semiconductor layer, and a striped InGaAsP substrate with a width of 1.5 μm stacked thereon. (Wavelength 1.3 μm composition)
An active layer 63, a leak prevention layer 64 laminated on the part of the substrate 61 where the active layer 63 is not present, and a third semiconductor layer laminated on top of these, with a thickness of 1.5 μm and a carrier density of 1×.
A p-type InP cladding layer 66 of 1018 cm-3 is further laminated on top of the p-type InP cladding layer 66 with a thickness of 0.7 μm and a carrier density of 5×.
1018 cm-3 p-type InGaAsP contact layer 6
7. An n-side electrode 68 provided at the bottom of the substrate, a p-side electrode 69a provided at the top of the contact layer, and an insulating film 611 are formed. Furthermore, in order to reduce leakage current, a mesa 610 with a width of 16 μm and a height of 2.5 μm is formed along the active layer stripe. 69b is an electrode wiring. The current blocking layer 64 is
It has a quantum well structure in which a barrier layer 641 is made of In0.50Ga0.50P and a well layer 642 is made of InP. The thickness of the barrier layer 641 is 30A, the thickness of the first well layer is 50A from the bottom, and the thickness of the second well layer is 30A. In0
．． There is a lattice mismatch of about 3.7% between 50Ga0.50P and InP, but since the barrier layer 641 is thin, it is elastically strained and becomes a pseudomorphic strain layer. Then, it is cleaved into chips with a length of 300 μm and mounted on a module. The cleavage plane constitutes an optical resonator for laser oscillation.

FIG. 6(b) shows that in the laser shown in FIG. 6(a), B-
A band diagram along the B' section is shown. 61 in the diagram
66 correspond to 61 to 66 in FIG. 6(a). In
The forbidden band width of 0.50Ga0.50P in an unstrained state is about 1.87 eV. When tensile strain is applied to InP to achieve lattice matching, the forbidden band width narrows;
is larger than the forbidden band width of 1.35 eV, and the band discontinuity is large on the conduction band side. A quantization level is formed in the conduction bands of the first well layer 642 and the second well layer 642. The energy level of the quantization level is higher in the second well layer 642 having a narrower well width. The barrier layer 641 is 3
Since it is thin (0A), it cannot prevent electron tunneling, but electrons having energy lower than the quantization level of the well layer 642 cannot tunnel because there is no level at which the electrons can enter. In other words, electrons tunneling from the n-type cladding layer 61 to the well layer 642 must have energy higher than the quantization level of the well layer 642, and electrons tunneling from the first well layer 642 to the second well layer 642 must have energy higher than the quantization level of the well layer 642. The electrons are transferred to the second well layer 642.
must have a higher energy than the quantization level of Since the probability of the existence of high-energy electrons decreases exponentially, the current leaking through the leak prevention layer 64 can be significantly reduced. As a result of significantly reducing leakage current that does not contribute to laser oscillation, it is possible to achieve higher laser output, higher efficiency, lower threshold, and improved temperature characteristics.

FIG. 7 shows an example in which the above-described leak prevention layer is applied to a light emitting diode. The layer structure is shown in Figure 6(a).
It is similar to On the n-type InP substrate 71, a diameter of 30 μm,
InGaAsP active layer 73 with a thickness of 0.8 μm, substrate 71
Leak prevention layer 7 laminated on the part without the upper active layer 73
4. A p-type InP cladding layer 76 with a thickness of 1 μm is laminated thereon, and a p-type InGa layer with a thickness of 0.5 μm is laminated thereon.
An AsP contact layer 77 is formed, and an opening is provided so that light can be extracted from the top surface. A non-reflection coating 75 is applied to the surface of the opening, a p-side electrode 79 is formed above the contact layer, and an n-side electrode 78 is formed below the substrate 71. Leak prevention layer 74 is In0.50Ga0.5
It has a multiple quantum well structure with 0P as a barrier layer and InP as a well layer. In this light emitting diode as well, the leakage current is reduced in the same way, and the same effect can be obtained.

FIG. 8 is a structural sectional view showing a surface emitting laser device according to the third invention, which is a fifth embodiment. n-type InP/InGaAsP (1.3
Distributed Bragg reflection (DBR) layer 82 consisting of
, thickness 40A undoped strain In0.70Ga0.30
As well layer 84 (3 layers) and undoped In with a thickness of 60A
An active layer 84 consisting of a GaAsP (1.3 μm composition) barrier layer 84 and a p-type InP/I constituting the third semiconductor layer
A stack of distributed Bragg reflection (DBR) layers 85 made of nGaAsP (1.3 μm composition) is formed. The period of the DBR layers 82 and 85 is set so that the oscillation wavelength is 1.55 μm. InGaAsP layer (1.3 μm composition) at the boundary between DBR layers 82, 85 and active layer 84
The thickness of the active layer 84 is set so as to give a phase shift of λ/4 to the DBR layers 82 and 85 together with the active layer 84. This stacked body is processed into a cylindrical shape with a diameter of 4 μm, and around it is formed an n-type InP constituting the second semiconductor layer.
Cladding layer 86, In0.50Ga0.50P barrier layer 8
81 (30A double layer) and InP well layer 882 (30A
a p-type InGaAsP cladding layer (1.05 μm composition) constituting the third semiconductor layer
89 is embedded and laminated. In0.50Ga
The 0.50P barrier layer 881 is distorted to be lattice-matched to the substrate and becomes a pseudomorphic layer, as in the fourth embodiment. The active layer 84 and the leak prevention layer 88 are adjusted so as to be located approximately in the same plane. A laminate 82 to 89 made up of these layers is processed into a cylindrical mesa 810 with a diameter of 8 μm, around which an insulating film 811, a p-side electrode 812, and an n-side electrode 813 are arranged and formed as shown in the figure. There is.

Holes injected from the electrode 812 flow from the p-type cladding layer 89 to the p-type DBR layer 85 to the active layer 84. On the other hand, the electrons injected from the electrode 813
1→n-type cladding layer 86 and n-type DBR layer 82→active layer 84. In0.70Ga0.30As layer 84
Stimulated emission gain occurs due to holes and electrons injected into 2, and light emission occurs. Light is buried in the crat layers 86 and 89
is confined in a direction perpendicular to the substrate 81. DBR
Since the layers 82 and 85 constitute a Bragg optical resonator corresponding to a wavelength of 1.55 μm, single mode laser oscillation is obtained. The oscillated light can be extracted from the window of the upper electrode 812 or from the bottom of the substrate 81. The leakage prevention layer 88 prevents leakage current from flowing between the upper and lower cladding layers 86 and 89, realizing effective current confinement in the active layer. That is, a single In0.50Ga0.50P barrier layer 881 cannot prevent current leakage due to tunneling, but since the quantum level created in the InP well layer 882 is higher than the band edge of the p-type InGaAsP cladding layer 89, leakage due to tunneling cannot be prevented. This means that the current can be significantly reduced. As a result, the oscillation threshold and efficiency can be significantly improved, and heat generation due to reactive current can also be reduced. Since the leak prevention layer of the present invention is thin, it can be said to have a structure suitable for such a microscopic light emitting device. Mesa 81 like this
By arranging a large number of 0s on the substrate 81, a two-dimensional surface emitting laser array can be created. According to the present invention, since power consumption is reduced, it is possible to improve the density and expand the scale of a two-dimensional array. In the case of integration, the n-side electrode may be formed on the n-type cladding layer 86 using the substrate 21 as a semi-insulating substrate. By performing appropriate element separation, each laser output can be controlled independently. Further, the present invention can be applied to, for example, an optical arithmetic element that inputs light from the bottom of the substrate and outputs it from the top.

FIG. 9 is a cross-sectional structural diagram of a semiconductor laser device according to the second and third inventions, which is a sixth embodiment. This laser has a p-type InAlAsP electron barrier layer 9 with a thickness of 30A on a p-type InP substrate 91 which is a third semiconductor layer.
21 (Black area) Three layers and p-type InP quantum well layer 922
An electron blocking layer 92 consisting of (white area) is formed. The composition of the p-type InAlAsP barrier layer 921 is In
It is selected so that P and the top of the valence band almost coincide. Therefore, the blocking layer 92 does not act as a barrier to holes. This InAlAsP barrier layer 92 does not lattice match with the substrate, but since it is as thin as 30A, it becomes a pseudomorphic strained semiconductor layer. Of the two layers, the thickness of the p-type InP quantum well layer 922 is 30 Å on the side closer to the substrate 91 and 50 Å on the side farther away. Etch stop layer 923 is used to control the etching formation of mesas 94 and 95. On top of this is an inverted mesa shape with a bottom width of 1.5 μm and a thickness of 0.14 μm.
InGaAsP active layer 94 with a wavelength of 1.3 μm
and an n-type I with a thickness of approximately 1.5 μm constituting the second semiconductor layer.
An nP cladding layer 95 is laminated. This mesa 94,
The left and right portions of 95 are buried almost flat with an Fe-doped semi-insulating (SI) InP layer 96 with a thickness of about 1.2 μm and an n-type InP layer 97 with a thickness of about 0.4 μm forming the second semiconductor. It is. On the whole, there is an n-side electrode 98,
A p-side electrode 99 is formed at the bottom of the substrate. The whole was cleaved to a length of 300 μm and mounted in a module. The cleavage plane forms an optical resonator for laser oscillation.

FIG. 10(a) shows a band diagram along the C-C′ cross section including the active layer 94 under the laser oscillation bias of this semiconductor laser, and the SI-I in the vicinity
A band diagram along the DD′ cross section including the nP layer 96 is shown in FIG. 10(b). 91 to 96 in the figure are 9 in FIG.
It corresponds to 1 to 96. In FIG. 10(a), the electron blocking layer 92 extends from the active layer 94 to the p-type cladding layer (substrate) 91.
acts as a layer to prevent electron overflow. p-type In
The quantum level of electrons formed in the P quantum well layer 922 can be formed at a position higher than the bottom of the conduction band of bulk InP, so even though the electron blocking layer 92 is thick enough to allow electron tunneling, the electron cladding Overflow to the layer can be effectively prevented. Furthermore, since the inner well layer 922 on the substrate side of the two well layers 922 is thin, that is, the quantum level of electrons is high, even if there are electrons tunneled into the well layer 922 on the active layer side, the substrate side well layer 922
This can prevent tunneling to the p-type cladding layer 91 via the p-type cladding layer 91. As described above, this electron blocking layer 92 does not become a barrier to hole injection from the p-type cladding layer 91 to the active layer 94, so that highly efficient radiative recombination in the active layer 94,
Stimulated emission can be achieved. Note that since holes have a heavier effective mass than electrons, overflow of holes from the active layer 94 to the n-type cladding layer 95 can be ignored. The current is narrowed to the active layer 94 by the SI-InP buried layer 96, but n
In the vicinity of the active layer 94 where the distance between the InP-type InP cladding layer 95 and the p-type InP cladding layer 91 is close, leakage current is likely to occur due to a high electric field. In particular, the effective mass is small n
There is a concern about leakage of electrons with a high pseudo-Fermi level in the mold cladding layer 95. In contrast, in the present invention, FIG.
Since the band arrangement will be as shown in 0(b), Fig. 10(a)
As in the case of , the electron blocking layer 92 acts as an effective barrier against electrons. Therefore, leakage current can also be effectively prevented. Therefore, the electron blocking layer 92 functions as both a carrier overflow prevention layer and a leakage prevention layer, and can prevent both overflow current and leakage current.
A combined effect of the third and fourth embodiments can be obtained, and a high-output semiconductor laser with excellent efficiency, oscillation threshold value, temperature characteristics, etc. can be realized.

The present invention can be modified and applied in various ways other than the embodiments described above. For example, semiconductor lasers include not only Fabry-Perot lasers in which a resonator is formed by a cleavage plane, but also distributed feedback (DFB) lasers, DBR lasers, composite cavity lasers, external cavity lasers, window structure lasers, etc. good. The output end face may be coated with a high reflection coating, a non-reflection coating, or the like, or the laser may have an etched end face. Optical waveguide layers may be formed above and below the active layer. In addition, multi-electrode lasers with multiple electrodes in the axial direction, wavelength tunable lasers, bistable lasers, optical ICs integrated with other optical elements such as optical modulators, OEICs integrated with electronic circuits, phase-locked lasers It can also be applied to arrays, etc. The active layer is preferably a quantum well structure, a double quantum structure, a double barrier structure, other multiple quantum well structures, or a structure having internal strain. Further, this active layer is not limited to a quantum well structure, and may be composed only of an undoped semiconductor layer. Materials include InP, InGaAsP, InGaAs, InA
lAs, InGaAlAs, InAlAsP, GaAs
, AlGaAs, AlAs, GaP, InGaP, In
GaAlP, InAlP, InAs, InAsSb, G
aSb, InGaAsSb, InGaAlSb, GaA
lAsSb, GaAlPSb, ZnSeS, CdSeS
, ZnCdSe, ZnCdTe, HgCdTe, Si,
SiC, SiGe, chalcopyrite structure semiconductors, etc.
Various combinations are possible.

The laser motion direction confinement structure is not limited to the above-mentioned structure, but may also include a planar buried hetero (PB) structure.
H) structure, self-aligned (SA) structure, ridge waveguide structure, and various modifications thereof. Of course, in addition to semiconductor laser devices, there are also light emitting diodes (LEDs), semiconductor laser amplifiers, carrier injection type optical modulators/optical switches,
A similar effect can be obtained even when applied to optical calculation/functional devices, etc., and the luminous efficiency can be improved by about 2 to 3 times compared to the conventional technology. In addition, the present invention can be implemented with various modifications without departing from the spirit thereof.

[0043]

According to the present invention, since reactive currents such as leakage current and overflow current can be effectively prevented, a semiconductor light emitting device with excellent luminous efficiency can be realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a band diagram of a semiconductor laser device according to a first embodiment.

FIG. 2 is a cross-sectional perspective view of the semiconductor laser device according to the first embodiment.

FIG. 3 In1-u Gau AsV P1-v (0≦
v≦1, u=0.1894v/(0.4184-0.0
13v)±δ) and In1-s (Ga1-t Alt
)s As (0≦t≦1, S=0.47+0.01t)
A diagram showing band alignment based on the vacuum level of .

FIG. 4 is a diagram showing a band diagram of a semiconductor laser device according to a second embodiment.

FIG. 5 is a diagram showing a band diagram of a semiconductor laser device according to a third embodiment.

FIG. 6 is a diagram showing a structural cross-sectional view and a band diagram of a semiconductor laser device according to a fourth embodiment.

FIG. 7 is a cross-sectional view of the structure of a light emitting diode according to a fourth example.

FIG. 8 is a cross-sectional view of the structure of a surface emitting laser device according to a fifth embodiment.

FIG. 9 is a cross-sectional view of the structure of a semiconductor laser device according to a sixth embodiment.

10 is a diagram showing a band diagram of the semiconductor laser device shown in FIG. 9. FIG.

FIG. 11 is a cross-sectional perspective view of a conventional semiconductor laser.

FIG. 12 is a diagram showing a band diagram of a conventional semiconductor laser.

[Explanation of symbols]

1...Energy level of the lowest quantum level of the conduction band for electrons 2...Energy level of the lowest quantum level of the valence band for holes 12...N-type InP buffer layer 13...InGaAs/InGaAsP multiple quantum well active layer 14, 44 ... InGaAlAs carrier overflow prevention layer 15 ... InGaAsP optical waveguide layer 17 ... p-type InP cladding layer 21 ... InP substrate 26 ... phase shift structure diffraction grating 28 ... InGaAsP contact layer 29 ... p-type InP layer 54 ... pseudomorphic strained semiconductor layer 64 ...Leak prevention layer 210...n-type InP layer 211...p-type InP layer

Claims (7)

[Claims] 1. An active layer consisting of a first semiconductor layer, an N-type second semiconductor layer and a P-type third semiconductor layer formed to sandwich the active layer, and a third semiconductor layer formed in the active layer. means for injecting electrons through the second semiconductor layer and holes through the third semiconductor layer; and a fourth semiconductor layer formed between the active layer and the third semiconductor layer. The carrier overflow prevention layer has an energy level of the lowest quantum level of the conduction band for electrons that is higher than that of the active layer and the third semiconductor layer, and a valence band of the conduction band for holes. The energy level of the lowest quantum level is higher than the active layer, and the third
A semiconductor light emitting device characterized in that the semiconductor layer has a thickness substantially equal to or lower than that of a semiconductor layer. 2. The semiconductor light emitting device according to claim 1, wherein the active layer has a quantum well structure consisting of a well layer and a barrier layer. 3. The carrier overflow prevention layer has a quantum well structure consisting of a well layer and a barrier layer, and the well layer has a lower energy level of the lowest quantum level of a conduction band for electrons than the active layer. Claim 1
Alternatively, the semiconductor light emitting device according to claim 2. 4. An active layer consisting of a first semiconductor layer, an N-type second semiconductor layer and a P-type third semiconductor layer formed to sandwich the active layer, and a third semiconductor layer formed in the active layer. means for injecting electrons through the second semiconductor layer and holes through the third semiconductor layer; and a fourth semiconductor formed between the active layer and the third semiconductor layer. a carrier overflow prevention layer consisting of a layer, and the carrier overflow prevention layer has the lowest quantum level of the valence band for holes so as not to become a barrier when holes are injected from the third semiconductor layer into the active layer. A semiconductor light emitting device characterized in that it has a quantum well structure in which a pseudomorphic strained semiconductor layer having a wider forbidden band width than the active layer serves as a barrier layer and acts as a barrier to electrons. . 5. The semiconductor light emitting device according to claim 4, wherein the quantum well structure is a multi-quantum well layer in which each adjacent well layer has a different energy level of the lowest quantum level of a conduction band for electrons. Device. 6. An active layer consisting of a first semiconductor layer, an N-type second semiconductor layer and a P-type third semiconductor layer formed to sandwich the active layer, and the second semiconductor layer. and means for injecting electrons and holes into the active layer through a third semiconductor layer; and a leak prevention layer formed between the second semiconductor layer and the third semiconductor layer to prevent current leakage. A semiconductor light emitting device, characterized in that the leak prevention layer has a quantum well structure in which a pseudomorphic strained semiconductor layer having a wider forbidden band width than the second semiconductor layer and the third semiconductor layer is used as a barrier layer. Device. 7. The quantum well structure is a multi-quantum well structure in which each of the well layers adjacent to each other with the barrier layer in between has a different energy level at the lowest quantum level of a conduction band for electrons. 6. The semiconductor light emitting device according to 6.