JPH04280493A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser that can operate favorably at a high temperature where the light-absorption will not increase and the resistivity will not increase by setting the density of Zn to a suitable range. A p-type InP substrate is used to manufacture a semiconductor light-emitting element capable of operating even at a high temperature. Conventionally, the characteristics are specified in relation to the density of the carrier when Zn is doped to make an p-type. However, by doing so, the density of Zn will be scattered. If the density of the Zn is high, it diffuses to the active layer during the epitaxial growth, resulting in the increase in the increased absorption of light, with reduced light-emitting efficiency. CONSTITUTION:If a p-type InP substrate is specified with carrier density, the density of Zn will be excessive. Thus, the characteristics of the p-type InP substrate are specified with the density of the Zn atoms to be 3X10<18>-7X10<18>cm<-3>, and the semiconductor laser is formed on this substrate.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser formed on a Zn-doped p-type InP substrate.

0002

[Prior Art] Light emitting devices such as light emitting diodes and semiconductor lasers are manufactured by epitaxially growing many layers of III-V group mixed crystal semiconductors on III-V group compound semiconductor substrates such as GaAs and InP. . The earliest semiconductor laser appeared on an n-type GaAs substrate.
A double heterostructure is formed by epitaxially growing a GaAs mixed crystal or a GaAs thin film. N-type cladding layer on n-type substrate, non-doped (or low concentration p-type)
An active layer, a p-type cladding layer, a p-type contact layer, etc. were laminated. The n-type has a lower specific resistance than the p-type, and the n-type substrate was more convenient for reducing the resistance caused by the substrate. Also, it is easier to form ohmic junction electrodes on n-type substrates.

[0003] GaAs-based light emitting elements have a thickness of 0.7 to 0.8μ.
It emits light with a wavelength of m, but an InP-based light emitting element is used to generate light with a long wavelength used for optical communication. Engineers who had originally been developing GaAs-based light-emitting devices decided to proceed with the development of InP-based light-emitting devices, so n-type InP
Layering thin films of InGaAsP and InP on the substrate
I tried to make an n-junction. Even now, semiconductor lasers and light emitting diodes using n-type InP substrates are mainstream.

However, in recent years, semiconductor lasers using p-type InP substrates have been attracting attention. This is because it can operate at higher temperatures. The reason why n-type InP substrate lasers malfunction at high temperatures is explained, for example, by Y. NAKA
NO & Y. NOGUCHI,”1.3μm
Buried-HeterostructureLas
ers on p-type InPSubst
Quantum Ele
ctoronics, vol. QE21, No. 5,p
．． 452-457 (1985). In the case of a buried semiconductor laser, both sides of a pn junction that contributes to light emission are covered with buried layers. This part is for concentrating current and light only on the pn junction, and has a pnpn thyristor-like structure. In other words, in the case of an n-type substrate, the buried layer becomes pn, and together with the n-type substrate and the p-type contact layer, an npnp structure is formed from the substrate side. The layer in contact with the substrate is a p-type thin film. This must be below the central active layer. This is because if the first buried layer is above the active layer, current will flow from the p-type cladding layer to the p-type buried first layer and from there to the n-type substrate. This current becomes a gate current and turns on the thyristor. This point is similar in the case of a p-type substrate, and buried layers are provided on both sides, but these are naturally np layers. The buried first layer in contact with the substrate is n-type. The buried first layer must be thin. In any case, the buried layer is pnp
This results in an n, npnp thyristor structure. Of these, the thinnest layer is the buried first layer directly above the substrate. This is because minority carriers are injected from the substrate, but a reverse biased pn junction with the buried second layer is formed, so current is blocked here. In the case of an n-type substrate, the buried first layer is p-type, the second layer is n-type, and the first layer
The pn junction of the layer will be reverse biased. In the case of a p-type substrate, the buried first layer is n-type, the second layer is p-type, and the np junction of the first and second layers is reverse biased. This is common not only to embedded type lasers but also to all semiconductor lasers. This is because it is necessary to concentrate current and light in a narrow region of the active layer.

Now, a majority of the minority carriers that have entered the first buried layer from the substrate are recombined with majority carriers and disappear, but a portion is diffused by the concentration difference potential and enters the second buried layer. This is a leakage current that travels through the buried layer. The lower the temperature of a semiconductor laser, the greater its emission power. This is well known. When the temperature becomes high, the slope of the increase in emitted light power with respect to the current becomes smaller, and the threshold voltage itself becomes higher. This is because the leakage current passing through both sides of the active layer increases as the temperature increases. This means that a semiconductor laser with a structure that has low leakage current at high temperatures can oscillate efficiently even at high temperatures.

[0006] The first buried layer is thin, and if the current passing through it by diffusion reaches the second buried layer and exceeds this potential, it becomes a leakage current. However, when the temperature increases, the luminous efficiency decreases due to an increase in Auger non-radiative recombination absorption in the active layer and an overflow of carriers from the active layer to the InP cladding. It is necessary to increase the applied voltage. This makes it easier for minority carriers to overcome the potential barrier between the first buried layer and the second buried layer. Therefore, if a large number of minority carriers pass through the buried first layer due to diffusion, leakage current will increase, further reducing luminous efficiency.

As shown in FIG. 13, in the n-type substrate, an npnp thyristor structure is formed from the n-type substrate/buried first layer (p)/buried second layer (n)/p cladding layer, and the buried first layer is - Corresponds to Among them, if we focus on the npn transistor including the gate, the collector current Ic
is equal to the current leak IL. As is well known,
Ratio of collector current Ic to gate current Ic/IG,
In other words, the current amplification factor is proportional to the mobility of minority carriers in the gate region. In the npn transistor, the minority carriers in the first buried layer (p), which is the gate region, are electrons. As shown in FIG. 14, a pnpn thyristor structure is similarly formed on the p-substrate from p-substrate/buried first layer (n)/buried second layer (p)/n cladding layer, but the gate This is the buried first layer (n) and includes the gate.
Minority carriers in the gate n-layer of a p-transistor are holes. The mobility depends on the temperature, but in the case of InP, the hole mobility is much smaller than the electron mobility, 1/20 to 1/30.
Therefore, the current amplification factor of a pnp transistor with a p-substrate is 1/20 to 1/30 smaller than that of an npn transistor with an n-substrate, and the collector current, that is, the leakage current, is also The board is 1 more than the n board.
/20 ~ 1/30 It can be seen that it is small.

For this reason, semiconductor lasers with p-type substrates have less leakage current at high temperatures and can therefore operate at high temperatures. P-type substrate InP lasers began to attract attention around 1984 to 1985, and many proposals regarding them have been made. However, all of these improvements were made to the active layer and buried layer. For example, K.
Imanaka, H. Horikawa, A. Mato
ba, Y. Kawai, &M. Sakuta,”H
high power output,lowthr
eshold, inner stripe GaI
nAsP laser diode on a
p-type InP substrate”,A
ppl. Rhys. Lett. vol. 45(3), p.
282 (1984) introduced Zn into the active layer InGaAsP.
It is proposed to dope the material to make it p-type. It is a V-groove type semiconductor laser rather than a buried type (BH) type. Although the layer is grown by liquid phase epitaxy, the active layer I
The optimal doping amount of Zn in nGaAsP (0.2 μm thick) is being determined. Since it is liquid phase epitaxy, the dopant Zn is mixed into the liquid phase in which Ga, In, As, and P are present. It is said that the optimum atomic ratio of Zn in the solution is 7 x 10-6. If the Zn concentration in the active layer is lower than this, the resistance will increase, which is undesirable. If the Zn concentration in the active layer is higher than this, light absorption will increase, which is undesirable. This refers to the active layer, not the substrate. The substrate is Zn-doped and has a carrier concentration of 5.times.10.sup.18 cm.sup.-3.

[0009] Japanese Patent Application No. 60-044640 is a p-type substrate I.
We are proposing a method to reduce leakage current transmitted through the buried layer of an nP buried semiconductor laser. The buried layer has a pnp three-layer structure (the one described above has two np layers), and an n-type buried layer is added to eliminate leakage current that propagates from the n-type buried layer to the n-type cladding layer (center) above the active layer. This layer is interposed between the n-type buried layer and the n-type cladding layer. Since the n-type buried layer has low resistance, if it is in contact with the n-type cladding, current will flow between the layers. To prevent this, a p-type layer with high resistance is inserted between the n-type buried layer and the n-type cladding layer to form a three-layer buried layer. However, if this is done, a leakage current flows from the newly added p-type buried layer to the n-type cladding layer. JP-A-1-
In order to prevent this, No. 300581 proposes four buried layers of p+pnp. The p+ p layer separates the n-type buried layer and the n-type cladding layer. The p+ inverts both sides of the n-type cladding layer to p-type, increasing the high-resistance p-type region. It is stated that both effects reduce leakage current. This is also an improvement of the buried layer, and there is nothing to say about the substrate.

JP-A-1-287985 is also an improvement for reducing leakage current. A p-type InP separation layer is grown on the n-type cladding layer above the active layer, a buried layer is grown, and then the separation layer is etched from above to the center and the n-type cladding layer is grown there. be. A p-type separation layer exists on the side surface of the n-type cladding layer, which blocks contact between the buried layer and the n-type layer. Therefore, no leakage current flows from the buried n-type layer to the n-type cladding layer. This is also an improvement of the buried layer, and there is nothing to say about the substrate.

[0011]

Problems to be Solved by the Invention Unlike the case of n-type InP substrates, new problems arise with p-type InP substrates. As already mentioned, research on the buried layer and active layer is active, but sufficient consideration has not been given to the substrate itself. Since the electron mobility is 20 to 30 times the hole mobility, n
In the case of a type substrate, the resistance is low and the amount of dopant may be small. However, if a p-type InP substrate is used, it is necessary to add a large amount of dopants to make it low resistance. Since the substrate is much thicker than the epitaxial film, it must have a particularly low resistance.

Since light is not emitted from the substrate, there should be no problem with light absorption, and it was thought that the only problem would be the electrical characteristics of the substrate. For this reason, substrate characteristics have been evaluated solely by carrier concentration. For example, the above-mentioned Appl. Rhys. Lett. 45(3), p2
82 (1984) is Zn-doped and has a carrier concentration of 5×1.
It was stated that an InP substrate of 0.018 cm-3 was used. The carrier concentration can be easily measured by Hall measurement. However, even if the carrier concentration is similarly defined, the characteristics of semiconductor lasers fabricated on the same substrate vary. Some emit light well, while others have low luminous efficiency. Conventionally, it has been made by liquid phase epitaxy, but when trying to make it by MOCVD, the problem of variation becomes particularly noticeable.

This means that there are unknown variables that are not controlled. The inventor repeated various experiments and found that Zn, which is a dopant, was removed from an InP substrate.
However, we have discovered a phenomenon in which the particles become more mobile and diffuse toward the active layer when heated. To make a semiconductor laser (BH type), epitaxial growth is performed three times. After the first epitaxy to form the active layer, the second epitaxy to form the buried layer, and the third epitaxy to form the contact layer. FIG. 1 schematically shows the manufacturing process of a semiconductor laser. (a) shows the state in which the active layer has been grown. On the p-InP substrate, p-In
P first cladding layer, p-GaInAsP active layer, n-I
An nP second cladding layer and an n-GaInAs contact layer are provided. Liquid phase epitaxial growth (LPE), organic metal vapor phase epitaxy (OMVPE), etc. can be used. (b) shows the state of mesa formation. Both sides of the epitaxially grown layer are removed by etching. In (c), a buried layer and a contact layer are grown. (d) shows a state in which electrodes are formed. A p-side electrode is formed on the substrate, and an n-side electrode is formed on the n-type contact layer. Many of the above-described devices are manufactured on InP wafers. (e) shows this. After this, the device is assembled and evaluated.

After the active layer is thus formed, epitaxy is performed twice. At this time, the substrate is heated to a high temperature. For example, in the case of liquid phase epitaxy, the heating state continues at about 600° C. for about 2 hours. Therefore, as shown in Figure 2, Zn
diffusion occurs. Zn from the substrate passes through the p-InP cladding layer and enters the InGaAsP active layer.

[0015] When a high concentration of Zn is introduced into the substrate, the value differs from the initial design value. If the amount of Zn is too large, the absorption of light propagating through the active layer will increase. This deteriorates the oscillation characteristics. In other words, the threshold current increases and the quantum efficiency decreases. In severe cases, the p-n junction shifts upward and the n-In
In some cases, the P cladding layer emits weak light. To the best of the inventor's knowledge, the diffusion of Zn from the substrate to the active layer has not been considered a problem. The p-InP cladding layer is of course p-type doped with Zn, but it is not a big problem because the Zn concentration is lower than that of the substrate and the total amount of Zn atoms is also smaller. However, it is a fact discovered by the present inventors that due to the diffusion of Zn from the substrate, the properties of the active layer deviate from the desired properties, and the absorption of light increases and the oscillation properties deteriorate. p-InP
It would be better if the cladding layer was thicker, but in the case of liquid phase epitaxy, the growth rate is fast, so a p-InP layer with a thickness of 2 to 3 μm is required.
Even if it is possible to stack the cladding layer, the growth rate is slow when using MOCVD, so the thickness can only be about 0.5 to 1 μm. P-InP cladding layers tend to become thinner and thinner and are less useful in preventing Zn diffusion.

It has been found that since Zn in the substrate is thermally diffused into the active layer during the two epitaxy steps, the amount of Zn in the active layer increases, light absorption increases, and the laser characteristics deteriorate. But if this is the case, why do the same carrier concentrations (e.g. p
= 5 x 1018 cm-3), are some good products and others defective? This is the problem. Conventionally, it was thought that [Zn concentration] = [hole concentration]. Therefore, the carrier (hole) concentration is 5×101
If it is 8cm-3, the concentration of Zn is also 5×1018cm-3
It was thought that Since Zn replaces In in the InP lattice and generates one hole, the above equation should hold true. In the case of a Si semiconductor, it is doped with B, p-type, and A
A, P, and Sb are doped to make it n-type, but in this case, the carrier concentration and dopant concentration are almost the same except in the vicinity of the pn junction. In the case of InP as well, it was thought that the Zn concentration and holes matched unless the concentration was extremely high. Carrier concentration can be easily measured by Hall measurement, but Zn
Atomic measurements are carried out using atomic emission spectroscopy or SIMS, which is a destructive test and is sometimes difficult to carry out. The inventors have discovered that the above equation does not actually hold, and that a significant portion of Zn does not emit holes. When Zn is added to an InP substrate, up to about 3 x 1018 cm-3, Zn
The concentration and the hole concentration become equal. However, even if the amount of Zn doped is increased beyond that, the hole concentration does not increase much. In other words, the hole concentration becomes saturated. The saturation concentration of holes is 5×
The present inventor also discovered for the first time that it is about 1018 cm-3. Then, when the hole concentration is defined as 5×10 18 cm −3 , the Zn concentration is not uniquely determined, and the Zn concentration may be small or large.

The reason for this is thought to be as follows. Zn
When the concentration becomes low, Zn does not replace In sites in the InP lattice, but instead occupies interatomic positions. In this case, it is considered that Zn does not have the effect of attracting electrons and does not generate a single hole. In other words, Zn becomes dormant and does not generate carriers. However, since it is not in a stable state, it diffuses according to the concentration gradient when heated. Since no carriers are generated, Hall measurement is not performed. This can only be understood through atomic emission spectroscopy. Also S
It can also be measured by IMS. p=5×10
Even if the substrates are selected by specifying 18 cm -3 , there will be some with a high Zn concentration, and if epitaxy is performed on this substrate twice, Zn will significantly diffuse into the active layer. What this shows is that the carrier concentration (p) should not be used to specify the quality of a Zn-doped p-type InP substrate, but the Zn concentration must be used instead. Another is that the Zn concentration should not be too high. In order to prevent Zn from diffusing into the active layer, the Zn concentration must be limited to an appropriate range. p- with Zn as a dopant
A semiconductor laser formed on an InP substrate,
It is an object of the present invention to provide a semiconductor laser that exhibits less light absorption by n and operates well even at high temperatures.

[0018]

[Means for Solving the Problems] A semiconductor laser of the present invention includes a p-InP first cladding layer on a p-InP substrate;
In a buried semiconductor laser having a p-GaInAsP active layer, an n-InP second cladding layer, an n-GaInAsP contact layer, and buried layers on both sides thereof,
The p-InP substrate is characterized in that the atomic concentration of zinc, which is a p-type dopant, is 3 to 7×10 18 cm −3 . More preferably, the atomic concentration of zinc, which is a p-type dopant, in the p-InP substrate is 4 to 5×10 18 cm −3 . Defining other structures in more detail, the semiconductor laser of the present invention has a p-InP first cladding layer, a p-GaInAsP active layer, an n-InP second cladding layer, and an n-InP second cladding layer on a p-InP substrate.
a cladding layer and an n-GaInAsP contact layer;
It has a buried layer on both sides, p-InP substrate and n-G
In a buried semiconductor laser having an electrode in an aInAs contact layer, the atomic concentration of zinc, which is a p-type dopant in a p-InP substrate, is set to 3 to 7 x 1018 cm-3,
If the thickness of the p-InP first cladding layer is 1.5 μm or less, p-InP
Mold carrier concentration is 2 x 1017 to 1 x 1018 cm-3
and the thickness of the p-GaInAsP active layer is 0.02~
At 0.2 μm, the p-type carrier concentration is 2×1017 to 1×1
018 cm-3, and n of the n-InP second cladding layer
The type carrier concentration is 2 x 1018 cm-3 or less, and the position of the p-n junction is between the p-GaInAsP active layer and the n-I
It is characterized by being located at the interface with the nP second cladding layer.

[0019]

[Operation] Increase the hole concentration in the p-type InP substrate to 5×1018c
Rather than specifying the Zn concentration as 3 to 7×10
It is specified as 18 cm-3. As already mentioned, it was vaguely believed that Zn-doped InP substrates
The equation [concentration] = [hole concentration] does not hold. Even if it is defined based on the hole concentration, it does not mean that the Zn concentration is correctly defined.

FIG. 3 shows the Z
The measurement results of Zn atomic concentration and carrier (hole) concentration in an n-doped InP single crystal are shown. The horizontal axis represents the Zn atomic concentration, which is measured by atomic emission spectrometry. The vertical axis represents the hole concentration of the same single crystal, measured by Hall measurement. Zn atomic concentration is 2
．． In the case of 4 x 1018 cm-3, 3.8 x 1018 cm-3, the hole concentration is 2.4 x 1018 cm-3, 3.7
×1018 cm-3. However, the Zn concentration is 4×1
If it exceeds 018 cm-3, the hole concentration will deviate greatly from the Zn concentration.

[0021] When the Zn concentration is 4.8 x 1018 cm-3, the hole concentration (carrier concentration) is 4.4 x 1018 cm.
-3, and the latter is 0.4 x 1018 cm-3 lower. When the Zn concentration is 5.4 x 1018 cm-3,
The hole concentration is 4.8 x 1018 cm-3. In this case, there is a difference of 0.6×10 18 cm −3 . Zn concentration is 7.
In the case of 4 x 1018 cm-3, the carrier concentration is 5.1
× 1018 cm-3, and 2.3 × 1018 cm-3
There is a difference. Looking at this only from the carrier concentration,
p=4.4×1018cm-3, p=5.1×1018
cm-3, the carrier concentration is 0.7 x 1018 cm
Although the difference is only -3, the Zn atomic concentration is 4.8×101
8cm-3 and 7.4x1018cm-3, which means that the latter contains 1.5 times as much Zn as the former. Therefore, the inventor named [carrier concentration]/[Zn concentration] the activation rate, and calculated Z for the same data as in Figure 3.
The activation rate is shown in FIG. 4 as a function of n atom concentration. Zn
When the concentration is below 3 x 1018 cm-3, the activation rate is 100
%. When the Zn concentration is 3 to 5 x 1018 cm-3, the activation rate is about 97 to 95%. However, the Zn concentration was 5
When it exceeds x1018 cm-3, the activation rate decreases rapidly. When [Zn] = 5.4 x 1018 cm-3, the activation rate is 85%, when [Zn] = 6.2 x 1018 cm-3, the activation rate is 77%, [Zn] = 7.4 x 1018 cm
-3, the activation rate is 67%.

[0022] As defined by the present invention, the Zn concentration is between 3 and 7.
×1018 cm-3, the activation rate is 70% or more. Further, the carrier concentration is 4.9×10 18 cm −3 or less. 7×10 18 cm −3 is the upper limit at which light absorption in the active layer does not increase excessively due to thermal diffusion of Zn. 3×1
018 cm-3 is the lower limit to prevent the electrical resistance of the p-type substrate from becoming too high. Conventional p-type (Zn doped)
InP substrates have low hole mobility (1/20 to 1/20 of electrons).
/30) Since the resistance tends to be high, it was attempted to lower the resistance by doping as much Zn as possible. The aforementioned Appl. R
hys. Lett. 45(3), p282 (1984)
Also used a p-type InP substrate with p=5.0×10 18 cm −3 . If the manufacturing method is the same as the method of the present inventor, the Zn concentration will be 7.2×10 18 cm −3 or more. Since the hole concentration is saturated above this, the Zn concentration is 8 to 10×
It may be 1018 cm-3. Like this Z
When the n concentration is high, Zn reaches the active layer due to thermal diffusion and deteriorates the light emitting characteristics.

Now, on the Zn-doped p-type InP substrate, I
When manufacturing a buried semiconductor laser using nGaAsP as an active layer, how Zn diffuses depending on the zinc Zn concentration of the substrate will be explained. FIG. 5 shows the Zn distribution after two liquid phase epitaxies when the Zn concentration of the substrate is 3 to 7×10 18 cm −3 as defined in the present invention. The horizontal axis indicates the height taken upward from the bottom of the substrate. The vertical axis is the Zn atomic concentration. From the bottom: p-InP substrate,
p-InP first cladding layer, InGaAsP active layer, n
-InP second cladding layer and n-InGaAsP contact layer. Since the diffusion of Zn into the buried layer is not a problem here, it is not shown here. This is the distribution along the center line of the laser. The dots indicate the Zn concentration when forming up to the first active layer. Here, the Zn concentration in the substrate is assumed to be 4×10 18 cm −3 . p-
0.8×1018 cm-3 for the InP cladding layer, In
GaAsP active layer has a lower concentration of 0.5-0.6
It is approximately ×1018 cm−3. However, when a buried layer is then formed and epitaxy is performed to form a contact layer, Zn diffuses from the substrate toward the active layer, as shown by the thick solid line. However, originally p-In
Since the Zn concentration in the P substrate is not very high, the Zn concentration on the side of the p-InP first cladding layer in contact with the substrate increases only a little, and the Zn concentration in the InGaAsP active layer hardly increases. The Zn concentration in the active layer remains at the design value of 0.5 to 0.6×1.
It is about 018 cm-3. The boundary between the active layer and the n-InP second cladding layer directly above the active layer forms a pn junction.

FIG. 6 shows a case where the Zn concentration of the substrate is 7×1018 cm.
If it exceeds -3 (7 x 1018cm-3 in this example)
The diffusion of Zn will be explained. In the first epitaxy process up to the active layer, the p-InP first cladding layer was 0.8
×1018cm-3, InGaAsP active layer is 0.5~
At a Zn concentration of 0.6 x 1018 cm-3 this is the same as in Figure 5 (indicated by dots). However, when epitaxy is performed twice, a high concentration of Zn diffuses from the substrate as shown by the thick solid line, and the Zn concentration of the entire p-InP first cladding layer increases to 2 x 1018 to 4.5 x 1018 cm-3. Put it away. The concentration of the active layer is also 1.6 to 2 x 1018 cm.
Increases to around -3. In addition, since Zn diffuses into the n-InP second cladding layer, a part of it is inverted to p-type and a pn junction enters the InP cladding layer. In this case, the light is not emitted from InGaAsP, but from InP.
Because it emits light, the emission wavelength changes. Furthermore, since there is a high concentration of Zn, light absorption increases. This makes it difficult to oscillate at high temperatures, and the light emission power decreases even at low temperatures.

[0025]

Embodiment A wafer is used as a substrate, which is obtained by thinly slicing a p-type InP single crystal doped with Zn and pulled by the liquid-encapsulated Czochralski method (LEC), and then subjected to processing such as etching and polishing. Substrates with different Zn concentrations were prepared.

Next, buried semiconductor lasers were fabricated by liquid phase epitaxy on five types of p-type InP substrates having different Zn concentrations. FIG. 11 shows the structure of a semiconductor laser. This is the well-known and simplest Fabry-Perot type, and the cleavage planes at both ends are mirror surfaces, which constitute a resonator. The substrate is Zn-doped p-InP. The central part has the structure described many times before. This is illustrated in FIG. The buried layers are a p-InP layer, an n-InP layer, a p-InP layer, an n-I
It is an nP layer. Additionally, there are grooves on both sides to electrically separate the central part of the stripe from the parts on both sides. Such structures are known. Now, the central part of the element, which is the part formed first, is as shown in FIG. ■ p-InP cladding layer (first cladding layer) Zn concentration 6 to 7 x 1017 cm-3, thickness 0
．． 5μm ■ p-InGaAsP active layer (In0.73Ga0.27As0.57P0.43)
Zn concentration 4-5 x 1017 cm-3, thickness 0.
12μm ■ n-InGaAsP guide layer (In0.93Ga0.07As0.14P0.86)
Si concentration 6~7x1017cm-3, thickness 0.
14μm■ n-InP cladding layer (second cladding layer) Si concentration 8 to 10 x 1017cm-
3. Thickness 0.5μm■ Non-doped InGaAsP cap layer, thickness 0.05μm (In0.79Ga0.21As0.44P0.56)
It is. The simplest Fabry-Perot semiconductor (BH
) laser, length is 300 μm, reflectance of both end faces is 0.
31 and 0.9. The light is emitted from the 0.31 direction. Generally, it is desirable that the p-InP first cladding layer (2) has a thickness of 1.5 μm or less. Carrier concentration is 2 x 1017 cm-3 to 1 x 1018 cm-3
so that it is. The p-GaInAsP active layer of
Mold carrier concentration is 2 x 1017 cm-3 ~ 1 x 1018
cm-3, and the thickness is 0.05 to 0.2 μm. ■
The n-InP second cladding layer has an n-type carrier concentration of 7×
It should be 1017 cm-3 or more. The Zn concentration of the p-type InP substrate is (a) 2 x 1018 cm-3 (b)
3 x 1018cm-3 (c) 4.5 x 1018cm
-3 (d)6.5x1018cm-3 (e)7
．． It is 5 x 1018 cm-3. Ambient temperature 20℃~8
The current and light output characteristics at each temperature were measured and graphed. Figure 7 shows (a) [Zn]=2
An example of x1018 cm-3 is shown. Figures 8, 9, and 10 are (b) [Zn] = 3 x 1018 cm-3, (c), respectively.
[Zn] = 4.5 x 1018 cm-3, (d) [Zn]
= 6.5 x 1018 cm-3. Among these, the one with the best properties is (c) [Zn] = 4.5 × 10
This is a laser using a 18 cm-3 substrate. The slope of the curve represents luminous efficiency, but the slope is extremely large. 6 at 20℃
The optical power is 20 mW with an injection current of 0 mA. The threshold voltage is also low. Furthermore, it oscillates even at 80° C., and the threshold current is 40 mA. 8.3 for 100mA injection current
It has a light emission output of mW. The next best is (d) [Zn]=
This laser uses a substrate of 6.5 x 1018 cm-3. The luminous efficiency is lower than the example in (c), and the threshold is higher at 80°C.
But it oscillates. The optical power becomes 20 mA with an injection current of 110 mA at 20°C. The threshold current at 80° C. is 55 mA, and there is a light emission output of 4 mA for a current of 100 mA. The third best is (b) [Zn] = 3 x 1018 cm-
This uses the No. 3 board. The optical power becomes 20 mW with an injection current of 130 mA at 20°C. The threshold current at 80° C. is 45 mA, and the light emission output for a current of 100 mA is 4 mW. The fourth one is (A) [Zn] = 2 × 1
This is a laser fabricated on a substrate of 0.018 cm-3. 25
℃ threshold is 30mA and injection current of 100mA is 10m
There is only W output. Although the threshold value at 80° C. oscillates at 80 mA, the optical output is about 1 mW for a current of 100 mA. This is considered to be because the substrate contains too little Zn and the resistance is too high. (e) [Zn]=7.5×10
The one with a diameter of 18 cm-3 did not oscillate. Since no laser oscillation is performed, a graph of current-light output characteristics is not shown. Although a slight amount of light emission is observed, the wavelength corresponds to the InP hand gap, and it can be seen that the pn junction is shifted toward the n-InP cladding layer.

From these results, it is clear that the Zn of the p-type InP substrate
It is understood that a concentration of 4 to 5×10 18 cm −3 is best, and sufficient laser oscillation can be achieved even at 80° C. if the concentration is 3 to 7×10 18 cm −3 . Outside these ranges, the threshold current will be high and the luminous efficiency will be low.

[0028]

[Effect of the invention] Semiconductor lasers are manufactured using p-type InP substrates, but since quality evaluation was conventionally performed using carrier concentration, hidden parameters were overlooked, making it possible to manufacture devices with constant characteristics with good reproducibility. was difficult. In the present invention, when an InP substrate is doped with Zn above a certain level, the carrier concentration becomes saturated with respect to the Zn concentration, and even if the carrier concentration is specified near the saturation concentration, the concentration of Zn atoms is unique. It has been made clear that this is not specified. In addition, since the Zn concentration is 3 to 7 x 1018 cm-3, Zn does not diffuse into the active layer even after epitaxy twice, and the resistance of the substrate is small, making it possible to create a semiconductor laser with extremely high luminous efficiency, low threshold current, and the ability to oscillate even at high temperatures. can be provided.

[Brief explanation of the drawing]

[Figure 1] Semiconductor laser manufacturing process diagram

FIG. 2 is a diagram showing how Zn diffuses from the substrate to the active layer by subsequent epitaxial growth.

FIG. 3 is a graph showing measured values of Zn atomic concentration and carrier concentration doped into an InP substrate.

FIG. 4 is a graph showing measured values of Zn atom concentration and activation rate when an InP substrate is doped with Zn.

FIG. 5 is a diagram for explaining the diffusion of Zn from the InP substrate of the present invention.

FIG. 6 is a diagram for explaining the diffusion of Zn from an InP substrate in a conventional example.

[Figure 7] The Zn concentration of the InP substrate is set to 2 x 1018 cm-3.
FIG. 2 is a diagram of current and light output characteristics depending on temperature of a semiconductor laser when a semiconductor laser is manufactured using this as a substrate.

[Figure 8] The Zn concentration of the InP substrate is set to 3 x 1018 cm-3.
FIG. 2 is a diagram of current and light output characteristics depending on temperature of a semiconductor laser when a semiconductor laser is manufactured using this as a substrate.

[Figure 9] Zn concentration of InP substrate is 4.5 x 1018 cm
-3 and a semiconductor laser is manufactured using this as a substrate.

[Figure 10] Zn concentration of InP substrate is 6.5×1018c
FIG. 3 is a diagram showing the current and light output characteristics of a semiconductor laser depending on the temperature when a semiconductor laser is manufactured using this as a substrate.

FIG. 11 is a schematic perspective view of a semiconductor laser according to an embodiment of the present invention.

FIG. 12 is a schematic diagram showing a film structure at the center of a semiconductor laser according to an embodiment of the present invention.

FIG. 13 is a diagram illustrating the structure of a buried layer in the case of an n-type substrate and current leakage in the buried layer using a thyristor equivalent circuit.

FIG. 14 is a diagram illustrating the structure of a buried layer in the case of a p-type substrate and current leakage in the buried layer using a thyristor equivalent circuit.

Claims (4)

[Claims] 1. On a p-InP substrate, a p-InP first cladding layer, a p-GaInAsP active layer, an n-InP
In a buried semiconductor laser having a second cladding layer, an n-GaInAsP contact layer, and buried layers on both sides, the atomic concentration of zinc, which is a p-type dopant in the p-InP substrate, is set to 3 to 7 x 1018 cm. A semiconductor laser characterized by -3. 2. On a p-InP substrate, a p-InP first cladding layer, a p-GaInAsP active layer, an n-InP
In a buried semiconductor laser having a second cladding layer, an n-GaInAsP contact layer, and buried layers on both sides, the atomic concentration of zinc, which is a p-type dopant in the p-InP substrate, is set to 4 to 5 x 1018 cm. A semiconductor laser characterized by -3. 3. On the p-InP substrate, a p-InP first cladding layer, a p-GaInAsP active layer, an n-InP
It has a second cladding layer, an n-GaInAsP contact layer, and a buried layer on both sides thereof, and has a p-InP substrate and an n-GaInAsP contact layer.
- In a buried semiconductor laser having an electrode in a GaInAs contact layer, the atomic concentration of zinc, which is a p-type dopant in the p-InP substrate, is set to 3 to 7 x 1018 cm-3, and the p-InP first cladding layer is The thickness is 1.5 μm or less and the p-type carrier concentration is 2 x 1017 to 1 x 1018 cm.
-3, and the thickness of the p-GaInAsP active layer is 0.0.
At 2-0.2 μm, the p-type carrier concentration is 2×1017-1
x 1018 cm-3, the n-type carrier concentration of the n-InP second cladding layer is 2 x 1018 cm-3 or less, and the position of the p-n junction is between the p-GaInAsP active layer and the n-type carrier concentration of the n-InP second cladding layer.
- A semiconductor laser characterized by being located at an interface with an InP second cladding layer. 4. On the p-InP substrate, a p-InP first cladding layer, a p-GaInAsP active layer, an n-InP
It has a second cladding layer, an n-GaInAsP contact layer, and a buried layer on both sides thereof, and has a p-InP substrate and an n-GaInAsP contact layer.
- In a buried semiconductor laser having an electrode in a GaInAs contact layer, the atomic concentration of zinc, which is a p-type dopant in the p-InP substrate, is set to 3 to 7 x 1018 cm-3, and the p-InP first cladding layer is The thickness is 1.5 μm or less and the atomic concentration of zinc is 2 x 1017 to 1 x 1018 cm-
3, and the thickness of the p-GaInAsP active layer is 0.02.
At ~0.2 μm, the atomic concentration of zinc is 2 x 1017 ~ 1 x 1
018 cm-3, and n of the n-InP second cladding layer
The type carrier concentration is 2 x 1018 cm-3 or less, and the position of the p-n junction is between the p-GaInAsP active layer and the n-I
A semiconductor laser characterized by being located at an interface with an nP second cladding layer.