JPH03174793A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To decrease leakage current even in a high temperature state by providing a third semiconductor layer wherein P-type impurities are added and which has the forbidden band wider than that of a semiconductor substrate and prevents leakage of electrons, or a third semiconductor layer wherein N-type impurities are added and which has the forbidden band width wider than that in the semiconductor substrate and prevents holes at one part of a semiconductor layer at the periphery of a light emitting part. CONSTITUTION:A light emitting region 1 including an active layer comprising InGaAsP is formed in a stripe shape on an N-type InP substrate 2. An InGaP layer 11, an InP layer 13 and an InGaP layer 12 are sequentially laminated on the substrate 2 on both sides of the light emitting region 1. Zn as P-type impurities is added in the layer 11, and the layer 11 has the forbidden band width wider than InP. The InP layer 13 is of a P-type and has the low impurity concentration. Se as N-type impurities is added into the layer 12. Namely, a layer having the broad forbidden band width in a current block layer is made to act as a barrier layer. Impurities which impart the polarity that is opposite to the conductivity of carriers whose leakage is to be prevented are added in the layer. The barrier layer is formed of the impurity added layer. In this constitution, the decreasing effect of leakage current at high temperature is enhanced, and the high-temperature operation can be performed.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a semiconductor laser, and more specifically, to a semiconductor laser structure in which a current blocking layer is provided near an active layer.

[Prior art] In semiconductor lasers, current confinement in the active layer,
In order to lower the threshold current and increase luminous efficiency, a structure in which a current blocking layer is provided around the active layer has become mainstream. However, current still flows into current blocking regions other than the active layer, and the injection current is not sufficiently confined, which is one of the causes of reduced luminous efficiency. Furthermore, when this leakage current increases, the element temperature increases, and in extreme cases, oscillation may stop. In order to reduce this leakage current, the regions other than the upper and lower regions of the active layer are buried with a cladding layer whose forbidden band width is larger than that of the active layer, and a reverse bias junction is formed in this buried region to reduce the leakage current. A semiconductor laser having a structure in which a p-type Hn-type crystal growth layer is provided on a type substrate is generally known. However, in the reverse bias junction configuration, there was contact between the P-type cladding layer on the active layer and the P-type layer in the buried region, and leakage current could not be completely prevented. A 4i# semiconductor laser is known that prevents leakage current by adding Fe to the surrounding embedded region other than the lower region (Patent Publication No. 2-179).
4.4). Even in this structure, leakage current cannot be completely prevented, and in addition to providing a Fe-doped high-resistance layer in the buried region, a structure that combines a TnGaP layer with a wider forbidden band width than InP of the cladding layer is used. Semiconductor lasers have been proposed3 (I.E. Journal of Quantum Electronics, Vol. 25, Nos. 1362 to 13).
68 pages IEEE Journey of El-sct
ronics Vol, 25 No, 6pp, 1362
-13681989"). [Problems to be Solved by the Invention] The above conventional technique of providing a barrier layer (current block M) with a wider forbidden band width than the cladding layer in the buried region is quite effective in reducing leakage current. However, when carriers with high energy (electrons or genuine cards) increase as the temperature rises, there is still a problem that leakage current occurs.The first object of the present invention is to create a current blocking layer with a wide forbidden band width It is an object of the present invention to realize a semiconductor laser that enhances the role of a current barrier and reduces leakage current even in a high temperature state.A second object of the present invention is to reduce leakage current in a high temperature state to a leakage region outside the active layer region. Furthermore, the third object of the present invention is to suppress the leakage current to the cladding layer on or below the active layer in a high temperature state. [Means for Solving the Problems 1] In order to achieve the first objective, the present invention adds an impurity to a layer having a wide forbidden band width (barrier layer) that gives it a polarity opposite to the conductivity of carriers, which acts as a barrier layer and prevents leakage. In other words, at least a part of the semiconductor layer provided in the light-emitting periphery of the semiconductor laser is doped with P-type impurities and has a forbidden band width wider than that of the semiconductor substrate. Prevent electron leakage or n
The third semiconductor layer is doped with type impurities, has a wider forbidden band width than the semiconductor substrate, and prevents holes. Furthermore, in order to achieve the second objective, a structure was adopted in which two conductive layers (barrier layers) having a wide forbidden band width were used in the buried region to prevent leakage of electrons or holes. Furthermore, in order to achieve the third objective, impurities are added between the cladding layer above or below the active layer and the active layer so that the conductivity is the same as that of each cladding layer. For example, a barrier layer doped with a P-type impurity is inserted between barrier layers having a p-type rad layer. [Operation] The operating principle of the barrier layer of the semiconductor laser according to the present invention will be explained using FIG. 2, FIG. 3, and FIG. 4. Figure 1 shows (a) impurities added to the barrier layer when a barrier layer with a wide forbidden band width is inserted into the junction of a p-n junction and a forward bias (negative bias on the n-type layer side) is applied. (b
) is an energy band diagram when p-type impurities are added to the barrier layer. When no p-type impurity is added, the energy barrier height of the barrier layer felt by conduction electrons in the n-type region is the conduction band energy difference ΔEC at the time of junction. On the other hand, in case (b) when p-type impurities are added, the junction energy difference ΔEc
In addition, band bending due to charge balance is added, resulting in an energy difference ΔEc', and the height of the energy barrier to conduction electrons is higher than the energy difference ΔEC in (a). In this case, the effective energy barrier to holes in the valence band becomes low, but conversely, when n-type impurities are added to the barrier layer, the barrier to holes becomes high. As the temperature increases, the number of conduction electrons with high energy increases according to the Fermi day rough distribution, and in the case of (a), the barrier height ΔEc
becomes easier to exceed. This becomes a leakage current, but when a P-type impurity is added, the barrier becomes higher as shown in (b) and becomes difficult to overcome. A case in which the above principle is applied not only to electrons but also to both electrons and holes will be explained using FIG. 3. Figure 3 shows an energy band diagram of a junction between n-type InP and p-type InP as an example.
P-type barrier layer from InP side, lightly doped p-type I
An energy band diagram is shown when an nP layer and an n-type barrier layer are inserted and a forward bias is applied. Electrons, which are the main carriers in n-type InP, have a high barrier of the p-type barrier layer (ΔE
c') The barrier ΔE c' cannot be exceeded even in a high temperature state. Furthermore, the barrier ΔE■ for holes in p-type InP is also large and cannot be exceeded. Therefore, recombination of electrons and holes does not occur, and no current flows even in a forward bias state at a high temperature. Further, a method and use of the above-mentioned principle for blocking the flow of electrons and allowing holes to pass will be explained using FIG. 4. FIG. 4 shows an energy band diagram when electrons are injected from the n-type InF' layer and holes are injected from the p-type InP layer with a forward bias applied to InGaAsP (active layer). At this time, if a p-type barrier layer with a wide forbidden band width is inserted between the active layer and the p-type InP layer, a barrier layer ΔEc' is created for electrons injected into the active layer, so the p-type InP layer leakage can be prevented at high temperatures. At the same time, the barrier layer hardly acts as a barrier layer for holes, and p
It is efficiently implanted from the InP type layer to the active layer. With this structure, electrons can be efficiently confined in the active layer while holes are injected into the active layer, and leakage to the p-type InP layer can be prevented. Furthermore, by inserting an n-type barrier layer between the n-type InP layer and the active layer, electrons are injected into the active layer, and holes are injected into the n-type InP layer.
It is possible to prevent leakage into the layer, improve the confinement of carriers in the -M active layer, and prevent leakage current at high temperatures. The material of this barrier layer is, for example, InP, which can be lattice matched to InA s.
As a strain system that cannot be matched, I n 1−xA Q
xA s (X>0.48) or InGaP, InG
This corresponds to a A sP type semiconductor or a II-VI group semiconductor. The above-mentioned application of impurity addition to the barrier layer is not limited to the InP type, but applies to all structures to which this principle can be applied.

【Example】

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. 1 shows a sectional view of a first embodiment of a semiconductor laser according to the present invention. In this embodiment, barrier layers based on the principle shown in FIG. 3 are provided in current blocking layers provided on both sides of a leading wave layer. The semiconductor laser of this example has I
A light emitting region 1 including an active layer made of nGaAsP is formed in a stripe shape extending perpendicular to the plane of the paper,
On the n-type InP substrate 2 and on both sides of the light emitting region 1, an InGaP layer 11 having a wider forbidden band width than InP doped with Zn as a p-type impurity and a p-type I with a low impurity concentration are formed.
nPM 13 and InG doped with Se as an n-type impurity
The aP barrier layer is sequentially laminated to form the light emitting region l and the In
P-type InP clad N3 on the entire upper surface of GaP[12,
An InGaAsP cap layer 7 is formed, and the InGaAsP
An SiO2 insulating film 6 is formed at a position on the upper surface of the a As P layer 7 excluding a portion corresponding to the upper surface of the light emitting region 1, and corresponds to the upper surface of the light emitting region 1 on the upper surface of the In Ga As P layer 7. A lower electrode 4 is formed on the SiO2 insulating film 6 and on the lower surface of the substrate 2 except for the portion where the lower electrode 4 is formed. A method of manufacturing the above semiconductor laser will be explained. A light emitting region 1 including an active layer made of InGaAsP is grown on an n-type 1nP substrate 2 by crystal growth. That is, the absorption edge wavelength is 1
．． 3 μm of In Ga As P 1-1 is approximately 0.15 μm thick and the absorption edge wavelength is 1.5 μm.
G a As P 1-2 with a thickness of about 0.15 μm,
(active M), and InGaA with an absorption edge wavelength of 1.3 μm
s P 1-3 is laminated to a thickness of about 0.15 μm. A protective film of Sin is placed on the light emitting region 1, and the photoresist is further patterned, and the SiO2 is etched with a hydrofluoric acid etching solution to leave a stripe shape of @1 μm. I was etched with a sulfuric acid-based etching solution using SiO2 as a mask.
The light emitting region 1 of nGaAsP is etched down to the substrate surface of the n-type InP layer 2 and removed. The SiO2 mask is left as is, and an InP layer is added as an n-type impurity, which has a forbidden band width 0.1 eV wider than that of the InP layer doped with Zn.
The GaP layer 11 is 0.015 μm thick and is p-type and 1×101
The InP layer 13 with a low impurity concentration of about 10l7" is
In with a thickness of 4 μm and Se added as an n-type impurity.
The GaP layer 12 is grown by a 0.015 μm thick organometallic vapor phase epitaxy method (
(MOVPE method) to grow crystals in regions other than SiO2. After this, the 5in2 mask was removed and the entire surface was covered with P type I.
In the nP cladding layer 3, an InGaAsP layer 7 having an absorption wavelength of 1.15 μm is grown. Incidentally, the above p-type and n-type impurity concentrations are all about IXI 18 cm-3 unless otherwise specified. S
The iO2 insulating film 6 is patterned, Zn is diffused into the window, and the p-electrode 5 and n-electrode 4 are deposited. InGaP barrier layers 11 and 12 at the laser oscillation wavelength of 1.54 μm
Although the refractive index of InP is smaller than that of InP, since it is thin at about 5 μm above O0O, it does not cause a large distortion in the optical electric field distribution compared to a conventional buried region made only of InP. In this embodiment, the current block is made according to the principle shown in FIG. 3, and by combining it with a barrier having the opposite conductivity, laser oscillation can be easily obtained even at temperatures of 100° C. or higher. Embodiment 2 FIG. 5 shows a cross-sectional view of a second embodiment of a semiconductor laser according to the present invention. In this embodiment, a barrier layer 14 based on the principle shown in FIG. 4 is disposed above the light emitting region 1 of the semiconductor laser shown in FIG. 1, and the other parts have the same structure. Light emitting area 1
Zn as a p-type impurity on top of I x 1018cm
An InGaP barrier layer 4 with a thickness of about 0.015 μm doped with about -' is formed at the same time as the crystal growth of the active layer 1 in the first crystal growth. By providing this barrier layer 14, the electron p-type 1nP
Leakage into the three layers is reduced and the current-to-light output conversion efficiency at 100° C. is increased. This allows for more stable laser oscillation at higher temperatures. Also, between the photoconductive layer l and the n-type InP substrate 2 in FIG.
By inserting an InGaP barrier layer doped with Se as a type impurity at an amount of approximately I x 10 cm-', leakage of holes to the n-type InP substrate 2 can be prevented. Embodiment 3 FIG. 6 shows a cross-sectional diagram of a third embodiment of the semiconductor laser according to the present invention.This embodiment has a second current blocking layer provided on both sides of the light emitting region. A barrier layer is provided based on the principle shown in Figure (b).The semiconductor laser of this example has a p
Type InPlil-1, undoped InGaAs P
Light emitting region 1 consisting of active layer 1-2 and n-type InP layer 1-3
A mesa is formed in the shape of a stripe extending perpendicularly to the plane of the paper, and a p-type InP layer 8, an n-type InP current blocking layer 13,
p-type In added with p-type impurities (1-52A, 4
．． An As current blocking layer 15 is stacked on the light emitting region l.
An n-type InP buried layer 3 is formed on the upper surface of the current blocking layer 15, and the light emitting region 1 on the upper surface of the n-type InP buried layer 3 is formed.
A 5in2 insulating film 6 is formed at a position excluding a portion corresponding to the upper surface, and an upper n is formed at a position excluding a portion corresponding to the upper surface of the light emitting region 1 on the upper surface of the buried layer 3 and an upper surface of the 5in2 insulating film 6.
An electrode 5 is connected to a lower p-electrode 4 on the lower surface of the n-type InP substrate 2.
is formed. A method of manufacturing the above semiconductor laser will be explained. First, a p-type InP layer 1-1 (thickness 1 μm) is formed on a p-type InP substrate 2 by the MOCVD method, and an undoped InGaP
Active layer 1-2 (thickness 0.14 pm), n-type InP layer 1-
3 (thickness: 0.3 μm), a mesa is formed by a normal wet etching method. Thereafter, p-type InP current blocking layer 8, n-type InP current blocking layer 13, and p-type InP current blocking layer 13 are formed using liquid layer growth.
n 11 * 4 s Ag current block Cl ivy layer 15, n
An InP type buried layer 3 is grown sequentially as shown in the figure. Thereafter, a 5i02 insulating film 6 is formed by the CVD method, contact holes are provided, and finally an n-type electrode 5 and a p-type electrode 4 are formed by using a vapor deposition method. The semiconductor laser of this example oscillates CW up to 160°C, and
The efficiency at 00°C was 0.08 nW/mA. Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and includes lasers in which the substrate is p-type and the conductivity type is reversed, distributed feedback (DFB) lasers, and Bragg reflection lasers (DBF). It is also applied to lasers, lasers with external resonators, etc.

【Effect of the invention】

According to the present invention, an impurity is added to the current blocking layer to provide a layer (barrier layer) having a wide forbidden band width with a polarity opposite to that of the conductivity of the carriers to act as a barrier layer and prevent leakage. Composed of layers. Therefore, the effect of reducing leakage current is particularly enhanced at high temperatures, and high-temperature operation is possible.

[Brief explanation of drawings]

Figures 1, 5, and 6 are all cross-sectional structural diagrams of embodiments of the semiconductor laser according to the present invention, Figure 2 is an energy band diagram showing the principle of the present invention, and Figure 3 is an electron and hole diagram. FIG. 4 is an energy band diagram when an impurity-doped barrier wall is applied to both. FIG. 4 is an energy band diagram when an impurity-doped barrier wall is applied to block electrons and allow holes to pass. DESCRIPTION OF SYMBOLS 1... Light emitting part including active layer, 2... N-type InP substrate, 3... P-type InP cladding layer, 4... N-electrode, 5
...p electrode, 6-8iO2 insulating film, 7-I n G
a A s P layer, 11-p-type InGaP barrier wall, 1
2- n-type 16- nGaP barrier wall, 13...p-type InP layer with low impurity concentration, 14... p-type InGaP barrier wall.

Claims (1)

[Claims] 1. On a semiconductor substrate, a first semiconductor of a first conductivity type having a forbidden band width that is the same as or narrower than that of the semiconductor substrate, an active layer having a forbidden band width narrower than that of the first semiconductor, and a second semiconductor substrate. a light emitting section comprising a second semiconductor of a second conductivity type and having a forbidden band width wider than the active layer and the same as or narrower than the semiconductor substrate;
In a semiconductor laser having a semiconductor layer provided in a peripheral area of the light emitting part, a part of the semiconductor layer provided in a peripheral part of the light emitting part is doped with p-type impurities and has a forbidden band width wider than that of the semiconductor substrate. A semiconductor laser comprising a third semiconductor layer which prevents leakage of electrons or which is doped with n-type impurities and has a wider forbidden band width than the semiconductor substrate and prevents holes. 2. In claim 1, the semiconductor device is characterized in that a layer having a wide forbidden band width doped with impurities of a second conductivity type is inserted between the active layer and the second semiconductor layer. semiconductor laser. 3. In claim 1, a layer having a wide forbidden band width doped with impurities of a first conductivity type is combined with the active layer
A semiconductor laser characterized in that it is inserted between semiconductor layers. 4. Claim 1, 2 or 3, wherein the third or fourth semiconductor layer is in contact with or near a side surface of the active layer, and a region in contact with the first semiconductor is of a second conductivity type. 1. A semiconductor laser characterized in that the semiconductor laser is inserted such that the semiconductor laser has a first conductivity type, or the semiconductor laser is inserted such that a region in contact with the second semiconductor has a first conductivity type. 5. In the first, second or third claim, the semiconductor layer provided around the light emitting part is formed on the substrate in contact with a side surface of the light emitting part, and is laminated in sequence on the substrate. a fourth, a fifth, and a sixth semiconductor layer, the fourth and sixth semiconductor layers doped with impurities of second and first conductivity types, respectively, and have a wider range of impurities than the first and second conductivity type semiconductors; The fifth semiconductor layer is a semiconductor having a band width, and the fifth semiconductor layer is made of a semiconductor whose forbidden band width is wider than the forbidden band width of the active layer and narrower than the forbidden band width of the fourth and sixth semiconductor layers. semiconductor laser.