JP3257045B2 - Semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser having a small leakage current flowing in a buried layer by bypassing a mesa including an active layer.

2. Description of the Related Art In a semiconductor laser, a structure in which a mesa including an active layer is buried in a high-resistance layer and a current is concentrated on the mesa is often used in order to improve luminous efficiency, reduce a threshold current, and increase output. Have been.

In the semiconductor laser having such a structure, when the electric resistance of the buried layer is small, the leakage current bypassing the mesa increases and the luminous efficiency decreases. For this reason, it is possible to prevent a decrease in the resistance of the buried layer which occurs during the manufacture of the semiconductor laser,
It is necessary to reduce the leak current flowing in the buried layer bypassing the mesa.

[0004]

2. Description of the Related Art FIG. 3 is a sectional view of a conventional semiconductor laser, showing a buried semiconductor laser having a mesa stripe structure.

A conventional semiconductor laser is shown in FIG.
A stripe-shaped mesa 7 formed on the semiconductor substrate 1 is filled with a high-resistance layer 8, and an upper electrode 9 and a lower electrode 10 are provided on the upper surface of the mesa 7 and the lower surface of the substrate, respectively.

As the substrate 1, an n-type semiconductor crystal, for example, a compound semiconductor such as InP can be used. The mesa 7 comprises a guide layer 2 made of n-type InGaAsP, an active layer 3 made of InGaAsP 3, a p-type semiconductor layer 4 made of, for example, Zn-doped InP, and a p-type InGaAsP deposited as a cladding layer 4 on the substrate. Having a contact layer 5.

The high-resistance layer 8 in which the mesas 7 are buried is doped with an impurity for forming a deep acceptor level to reduce the carrier concentration.
P is used.

In such a buried semiconductor laser, the current flowing between the upper and lower electrodes 9 and 10 is blocked by the high resistance layer 8 and flows intensively into the mesa 7 including the active layer, so that the current utilization efficiency is high.

However, when the buried layer 8 is deposited, the p-type semiconductor layer 4 exposed on the side wall of the mesa 7 and the buried layer 8 come into contact with each other, so that impurities in the p-type semiconductor layer 4 are removed.
To spread.

Since the p-type impurity is not compensated by the deep acceptor in the buried layer 8, the buried layer 8 in the vicinity of the mesa 7 is converted into the p-type conductivity. The current increases.

[0011]

As described above, in the semiconductor laser having the conventional structure, the impurity in the p-type semiconductor layer contained in the mesa diffuses into the buried layer in contact with the mesa, and the resistance of the buried layer decreases. Therefore, there is a problem that the current blocking function of the buried layer is reduced and the leak current is increased.

According to the present invention, by adding an impurity which forms a deep acceptor level contained in a buried layer to a p-type semiconductor layer, diffusion of the p-type impurity into the buried layer is prevented, thereby lowering the resistance of the buried layer. Therefore, it is an object of the present invention to provide a semiconductor laser having a small leakage current flowing through a buried layer and having a high luminous efficiency.

[0013]

FIGS. 2A to 2D are cross-sectional views showing a manufacturing process of a semiconductor laser according to an embodiment of the present invention, and FIGS. 1 shows a cross section of a completed semiconductor laser.

In order to solve the above problems, the present invention is based on FIG.
Referring to (d), the first configuration is a mesa 7 formed on a semiconductor substrate 1 having a p-type semiconductor layer 4 and a III-V doped with an impurity for forming a deep acceptor level. A high-resistance buried layer 8 which is made of a compound semiconductor and embeds the mesa 7 in contact with an end face of the p-type semiconductor layer 4 exposed on the side wall of the mesa 7; The buried layer 8 is characterized by being doped with the impurity element forming a deep acceptor level. The second configuration is a semiconductor laser of the first configuration. Is made of InP, the p-type semiconductor layer 4 is made of a III-V compound semiconductor to which at least one of Zn, Cd and Mg is added as a p-type impurity, and the buried layer 8 is made of InP and GaAs. Or a mixed crystal thereof, The impurity element which forms an added deep acceptor level INCLUDED layer 8, Fe, Co, and C
It is characterized by being any element of u.

[0015]

FIG. 1 is an explanatory view of the principle of the present invention, and shows the impurity concentration distribution in the depth direction of a p-type semiconductor layer and a buried layer deposited thereon. The impurity concentration distribution in FIG.
It is the result of having measured the sample described below by SIMS (secondary ion mass spectrum) method, and it was made clear by the inventor of the present invention. In the drawing, the Zn and Fe concentrations are clearly indicated by the symbols of Zn and Fe, respectively.

As a sample, a 2 μm-thick p-type semiconductor layer made of InP containing Zn as a p-type impurity is deposited on an InP substrate by MOCVD (metal organic chemical vapor deposition), and subsequently, Fe is deposited by MOCVD. Of 1 μm thick made of InP containing impurities as impurities for forming a deep acceptor level
m buried layers were deposited.

FIG. 1A shows the case where Fe is added to the p-type semiconductor layer at the same concentration as that of the buried layer. No diffusion of Zn occurs at the interface between the p-type semiconductor layer and the buried layer. On the other hand, FIG. 1B shows a case where Fe is not added to the p-type semiconductor layer. Zn impurities in the p-type semiconductor layer are diffused in the buried layer in contact with the p-type semiconductor layer.

The conventional semiconductor laser has a structure in which a buried layer to which Fe is not added is deposited in contact with the p-type semiconductor layer, as in the case where Fe is not added to the p-type semiconductor layer. The p-type impurity diffuses into the buried layer, and the resistance of the buried layer decreases.

The present invention has been devised based on this fact. That is, according to the present invention, referring to FIG. 2 (d), an impurity which forms a deep acceptor level is added to the buried layer 8 to increase the resistance, while the same deep acceptor is previously formed in the p-type semiconductor layer 4. The impurity which forms a level is added, thereby preventing the p-type impurity in the p-type semiconductor layer 4 from diffusing into the buried layer 8.

It should be noted that even if an impurity which forms a deep acceptor level is added to the p-type semiconductor layer 4, it is not compensated because the impurity is of the same conductivity type, and the conductivity type of the p-type semiconductor is changed. No inconvenience occurs.

Therefore, according to the present invention, since the resistance of the buried layer 8 does not decrease and the buried layer 8 having a high resistance is always maintained, the leakage current flowing through the buried layer 8 bypassing the mesa 7 is small. . Therefore, a semiconductor laser having high luminous efficiency is realized.

When Fe is added to the above-described p-type semiconductor layer, the diffusion of the p-type impurity into the buried layer is prevented.
The following mechanism is considered by the inventor of the present invention. Referring to FIG. 1B, Fe in the buried layer is diffused into the p-type diffusion layer at a uniform concentration. On the other hand, Zn as a p-type impurity in the p-type diffusion layer is diffused into the buried layer in exchange for the diffusion of Fe.

This fact suggests that Fe, which is an impurity forming a deep acceptor level, easily diffuses into the p-type semiconductor, and that Zn diffuses into the buried layer by mutual diffusion with the diffusion of Fe. are doing.

In the present invention, since Fe is previously added to the p-type semiconductor layer, the difference in Fe concentration from the buried layer is small, and the diffusion of Fe from the buried layer to the p-type semiconductor layer is suppressed. Therefore, Zn diffused by interdiffusion with Fe
Again, diffusion is suppressed.

The above-mentioned diffusion in InP containing Fe is caused by other p-type impurities, such as Cd and Be, by J. Crystal Gr.
owth vol. 11 (1992) p75 describes that the same occurs. For Mg, Paper presented of 6th Semi-in
sulating III-V Materials, Toront, Canada, (1990) p137
It is described in.

Therefore, the diffusion mechanism described above for Zn is the same for Cd, Be and Mg, and the present invention can be applied. Further, the above-mentioned diffusion may be caused by impurities which become deep acceptors in compound semiconductors, in particular, III-V compound semiconductors such as GaAs or InPaAs or group II impurities which replace group III in mixed crystals thereof, such as Co and Cu, in addition to Fe. Occurs similarly.

Therefore, the present invention is also applicable to a case where the above-mentioned III-V compound semiconductor is used as a buried layer or a p-type semiconductor layer and a group II impurity which replaces the above-mentioned group III, which becomes a deep acceptor, is added. It is.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the manufacturing steps of the embodiments. To manufacture a mesa stripe embedded semiconductor laser according to the present invention, referring to FIG. 2A, first, an MOCVD (organic metal chemical vapor deposition) method is performed on a semiconductor substrate 1 made of, for example, n-type InP. As a result, Sn
Is added to 1 × 10 ¹⁷ cm ⁻³ and a 0.2 μm-thick n-type InG
aAsP is used as an active layer 3 with an n-type In layer having a thickness of 0.1 μm.
GaAsP is used as a p-type semiconductor layer 4 to be a cladding layer, 1.5 μm thick InP to which Zn is added at 5 × 10 ¹⁷ cm ⁻³ and Fe is added at 6 × 10 ¹⁶ cm ⁻³ , and Zn is used as a contact layer 5. 0.2 μm thick In added with 1 × 10 ¹⁹ cm ⁻³
GaAs is sequentially deposited.

Then, referring to FIG. 2B, a stripe-shaped SiO ₂ mask 6 having a width of 2 μm is formed on the contact layer 5, and the above-mentioned process is performed using a sulfuric acid-based and hydrochloric acid-based etchant using the mask 6. A mesa 7 having a height of 2 μm and a width of 1.5 μm is formed by selective etching of the deposited layer.

Next, referring to FIG. 2C, InP for burying the sidewall of the mesa 7 is deposited by MOCVD to form a buried layer 8. At this time, the mask 6 is also used for selective deposition of the buried layer. The deposition temperature is, for example, 600 ° C.
It can be. The buried layer 8 is doped with, for example, Fe having a concentration of 6 × 10 ¹⁶ cm ⁻³ to provide a carrier-compensated high-resistance semiconductor.

Next, referring to FIG.
After the removal, a metal is deposited, for example, to form an electrode 9 in contact with the upper surface of the mesa 7 and extending on the surface of the buried layer 8 and an electrode 10 in close contact with the back surface of the substrate. Further, the semiconductor laser is completed as a chip having a cavity length of 300 μm by cleavage along a plane perpendicular to the mesa 7.

The maximum output of the semiconductor laser according to the present embodiment was 30 mW. This is 20% higher than the maximum output of 25 mW of the conventional semiconductor laser of the same shape.

[0033]

According to the present invention, the diffusion of the p-type impurity in the buried layer is suppressed by adding the same impurity as the compensation impurity added to the buried layer to the p-type semiconductor layer included in the mesa. This can prevent a decrease in the resistance of the buried layer, and can provide a semiconductor laser with a high luminous efficiency, with a small leakage current flowing through the buried layer bypassing the mesa including the active layer, thereby improving the performance of electronic devices. It greatly contributes to improvement.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is a process diagram of an embodiment of the present invention.

FIG. 3 is a sectional view of a conventional semiconductor laser.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 guide layer 3 active layer 4 p-type semiconductor 5 contact layer 6 mask 7 mesa 8 buried layer 9, 10 electrode

Claims (2)

(57) [Claims] 1. A a p-type and main support formed on a semiconductor board on a semiconductor layer, a deep acceptor level III-V compound impurities which form is added semiconductor, side該Me Sa writing <br/> Me embedding the該Me support in contact with the end face of the p-type semiconductor layer exposed in <br/> walls and a high resistance of the buried layer, the p-type semiconductor layer,該埋inclusive layer a semiconductor laser, characterized in that the impure product to form a deep acceptor level is added is added to. 2. A semiconductor laser according to claim 1, wherein said semiconductor base plate is made of InP, the p-type semiconductor layer, Zn as p-type impurity, Cd and M
g of a III-V compound semiconductor to which at least one element is added. The buried layer is made of any one of InP and GaAs or a mixed crystal thereof, and has a deep acceptor level added to the buried layer. the <br/> impure product to be formed, a semiconductor laser which is a one element selected from Fe, Co and Cu.