JPH0856048A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To make a semiconductor photodiode for monitoring optical output unnecessary which has been necessary to be prepared individually from a laser element in the conventional device, when a semiconductor laser element module for providing controlled optical output is formed, by using a semiconductor element which is constituted of a resonator wherein a pair of end surfaces are used as reflecting mirrors, and applies the vicinity of an end surface to a non-excited region. CONSTITUTION:This semiconductor laser element is constituted of a resonator wherein a pair of end surfaces are used as reflecting mirrors, and the vicinity of the end surface is turned into a non-excited region. In the element, a ridge part, a photodiode 21, an insulating part 24, a gain region 22 and an end surface non-excited region 23 are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device in which a photodiode is laminated in a resonator.

[0002]

2. Description of the Related Art When using laser light emitted from a semiconductor laser device, it is required that the light output be constant in time as a specification. In order to realize the control, it is necessary to monitor the optical output of the laser element using an appropriate sensor. Conventionally, a semiconductor light receiving element, especially a two-terminal photodiode has been used as the sensor. FIG. 6 shows a block diagram for controlling the optical output of the semiconductor laser using the photodiode as a monitor.

A general semiconductor laser device is composed of a resonator composed of a pair of reflecting mirrors. The reflectivity of the reflecting mirror is less than 1, and as a result, laser light is output from both end faces of the resonator. In order to control the light output of this element, as shown in FIG. 6, only the radiated light from one end face is used as an output, and the radiated light from the other end face is received by a photodiode for light output monitoring. The module configuration is generally taken. As an optical output monitor photodiode, an independent element different from the semiconductor laser element has been conventionally used. A conventional practical semiconductor laser device is, for example, GaAs / A having a wavelength of 0.8 μm.
InGaAsP / In with a wavelength of 1.55 μm
Like P, it has a compound semiconductor heterostructure composed of three or more elements. On the other hand, it is necessary to select a photodiode with a high gain in the wavelength band used. The reason for this is that the end face on the photodiode side is subjected to high reflectance treatment in order to maximize the output of the utilized light, so that the incident light on the photodiode is small. As a specific example,
Si photodiodes are used for wavelengths of 1 μm or less, and Ge or InGaAs photodiodes are used for wavelengths of 1 μm to 1.6 μm.

In the semiconductor laser device, due to non-radiative recombination, a temperature rise is likely to occur especially near the end face where the photon density is high and laser light is likely to be reabsorbed. Therefore, element defects such as COD (Catastrophic Optical Damage) are particularly likely to occur near the end surface. A so-called end face non-excitation structure that suppresses temperature rise by not injecting drive current into the region near the end face is adopted as an effective means for significantly improving the end face resistance to device failure and improving the reliability of the device. Has been done. This region naturally becomes an absorption loss region without gain, which lowers the performance of the device such as efficiency and threshold value, but the gain region is overwhelmingly large in the commonly used laser device structure. The drop is hardly a problem.

[0005]

As described above, in the laser module using the conventional semiconductor laser element, it is necessary to use the semiconductor light receiving element different from the semiconductor laser element. This requires an increase in the number of parts and the module volume and the process required for mounting the light receiving element. Also, the mounting position of the parts is required to be accurate. As a result, the process becomes complicated and sophisticated, and the cost required for manufacturing the module is increased. It was also mentioned as one of the factors that reduce the yield and reliability of the module. In order to solve this problem, it has been conventionally proposed and tried to integrate a semiconductor laser and a light receiving element to realize one semiconductor laser element having an optical output monitoring function. However, in the conventional proposals, different semiconductor multilayer film structures are adopted for the laser section and the light receiving element section. The semiconductor multi-layered film structure here includes not only a hetero structure composed of different semiconductor layers, but also a laminated structure composed of layers composed of the same semiconductor and having different conductivity types, carrier concentrations, types and concentrations of dope species, and the like. In order to form different semiconductor multi-layered film structures on a single semiconductor substrate, there is only a method of first crystallizing the first structure and then forming the second structure by selective regrowth. It is difficult to improve the quality of a semiconductor crystal formed by re-growth, and the quality for practical use of a semiconductor device having a re-growth portion as an active layer has not yet been achieved. Also, the use of selective regrowth significantly increases the number of steps and raises the manufacturing cost of the device. Further, since heat and stress are applied to the device during the process, the yield and reliability are unavoidably deteriorated.

[0006]

SUMMARY OF THE INVENTION The present invention is intended to solve such a problem, and is constituted by a resonator having a pair of end faces as reflecting mirrors, and a non-excitation region near the end faces. In the semiconductor laser device, an electrode electrically independent of the laser driving upper electrode is formed in the end face non-excitation region as ohmic contact, and the region is used as a photodiode. Further, by using the photodiode as an optical output monitor, integration of the optical output monitor in a resonator is realized.

[0007]

In the semiconductor laser device according to the present invention, the photodiode is formed by using the semiconductor laser layer structure as it is. A typical layer structure used in a semiconductor laser device is shown in FIG. In FIG. 1, 5 is an active layer, 4 and 6 are optical confinement layers, 3 and 7 are cladding layers, 2 is a buffer layer,
Reference numeral 1 is a substrate, and 8 is an electrode contact layer. The energy gap increases in the order of the active layer, the light confinement layer, and the cladding layer, and the light confinement layer is designed to have a larger refractive index than the cladding layer. 1 on the substrate side with the active layer in between
4 is doped to p or n, and 6 to 8 on the surface side are doped to the conductivity type opposite to the substrate side. The active layer 5 is also doped with p or n, although the concentration is lower than the layers on both sides. The double hetero-type pn diode is configured as a whole, and electrons and holes are accumulated in the active layer by passing a current in the forward direction, and a gain is generated by stimulated emission due to radiative recombination. It is a well-known fact.

In this device, consider the case where the electrodes on the p-side and the n-side are short-circuited and light having a wavelength when the device is operated as a laser device is made incident on the active layer.
Since the active layer has an energy gap smaller than the energy of incident light, the incident light is absorbed and electron-hole pairs are generated. It can be considered that the pn junction surface of this device is located at the interface between the active layer and the optical confinement layer having a conductivity type different from that of the active layer. As is well known as the principle of photodiodes, among the electrons and holes generated by light absorption, those corresponding to minority carriers in the active layer, and in the depletion layer extending from the pn junction surface, and further in the depletion layer. Those located within the diffusion length of the carrier from the edge move to the optical confinement layer side beyond the pn junction surface, generating an electromotive force, and a photocurrent flows in the conducting wire short-circuited between the electrodes. As described above, the present invention is used as a photodiode by electrically insulating a part of a semiconductor laser device from other parts and applying a weak reverse bias to the 0 to pn junction to the voltage applied to that region. It is characterized by that.

The photodiode according to the present invention has a drawback that the gain is low due to the absence of carrier multiplication effect, the small absorption in the active layer, and the fact that only a part thereof contributes to the photocurrent. However, this photodiode is integrated in the resonator of the semiconductor laser device. When the laser is used as an optical output monitor as in the invention of claim 3, since the input light is sufficiently strong,
This problem can be solved by combining an appropriate preamplifier with the current measuring device. Further, the small absorption means that the loss of this device as a laser device is small, which is rather convenient. In the present invention, the photodiode is formed in the non-excitation region near the end face of the resonator. Since the photodiode is used without applying a voltage and the electromotive force due to absorption is small, the current density flowing in the photodiode is negligibly small with respect to the current density flowing in the gain region of the laser. Therefore, the photodiode region also has the function of the end face non-excitation region. Claim 3
When it is used as an optical output monitor as in the invention, it must be examined whether the characteristics of the photodiode are suitable for the application. In the active layer of the semiconductor laser device, the refractive index changes with respect to the photon density of light in the wavelength band of output light, and exhibits supersaturated absorption. Therefore, in this photodiode, as the input light intensity increases, the increase rate of the output current decreases, and the photodiode shows a characteristic of being saturated. However, if the photocurrent-light intensity characteristics of this photodiode monotonically increase within the rated output range of the laser element and the characteristics are reproducible and can be expressed by a linear or simple function, then It can be used as an optical output monitor. The correction of the photodiode characteristics required at that time is
As long as the present photodiode satisfies the above conditions, it can be easily realized by, for example, installing a silicon integrated circuit or the like in the laser element driving device shown in FIG.

[0010]

EXAMPLES Next, examples of the present invention will be described. A case where the present invention is applied to a conventional ridge-type end face non-pumped semiconductor laser device will be described. FIG. 2 is a cross-sectional view perpendicular to the cavity vertical direction, which is common to (b) a conventional semiconductor laser device and (a) a semiconductor laser device in which a photodiode according to the present invention is integrated. FIG. 3 is a perspective view of the same. Figure 2
In the figure, 5 is an active layer, 4 and 6 are optical confinement layers, 3 and 7 are cladding layers, 8 is an electrode contact layer, 2 is a buffer layer, and 1 is a substrate. The conduction type and the structure of the laser device of this multilayer film structure are the same as those described with reference to FIG. Further, in FIG. 2, the upper convex portion hits the ridge, constricts the current and acts as a waveguide, and realizes the horizontal transverse mode control of the laser light. The film 9 is an insulator film for preventing a current from flowing in the portion other than the ridge. And 10 and 11 are upper and lower electrodes.

In FIG. 3, reference numeral 22 is a gain region, and 21 is a photodiode portion added in the present invention. 21 is not present in conventional devices. FIG. 2A shows 2 of FIG.
In the cross section of the portions 1 and 22, the contact layer 8 and the electrode 10
And form an ohmic junction. Therefore, in this portion, current flows and operates as an element. On the other hand, 22 in FIG.
End face non-excitation region 23 between the laser and the laser end face, and 21 and 2
The electrical isolation portion 24 between the two has the cross section of FIG.
In this portion, the insulating film 9 exists between 8 and 10 and is insulated, so that no current flows.

Next, in this device example, top views of specific layers of the conventional device and the device according to the present invention are shown in FIGS. 4 and 5, respectively. In these figures, the position of the ridge is between the two broken lines. 4 and 5, (a) shows the insulating film layer 9 in FIG. 2, and (b) shows the upper surface electrode layer 10 similarly. In FIG. 4A and FIG. 5A, the insulating film exists in the portion indicated by 25. In these figures, 21 and 22 correspond to the photodiode portion 21 and the gain region 22 of FIG. 3, and show that windows are opened in the insulating film on each ridge, and correspond to FIG. 2 (a). ing.
Further, in (a) of FIGS. 3 and 5, a part 24 between 21 and 22 is a part for separating the photodiode part and the gain region, 22
The end face non-excitation region (23 in FIG. 3) is between the end face and the end face, and these have the cross section of FIG. 2 (b). In order to ensure the electrical insulation between the photodiode and the gain region, ions are added to the contact layer 8, the cladding layer 7, and possibly the optical confinement layer 6 shown in FIG. High resistance is achieved by injection. The depth of ion implantation is determined within a range in which the damage associated therewith does not reach the active layer 5. In FIG. 5B, reference numeral 26 is an upper surface electrode of the photodiode. Further, in FIGS. 4B and 5B, 27 indicates the upper surface electrode in the gain region, and 28 indicates the region where the upper surface electrode does not exist. Note that the example of the present invention in FIG. 5 is an example in which one photodiode is formed in one of the non-excitation regions on both end faces of the resonator. It is sufficient to provide two photodiodes.

Comparing the conventional device of FIG. 4 with the device of the present invention of FIG. 5, the difference is that the insulating film layer is absent at the portion 21 except for the high resistance treatment applied to the insulating portion 24. The presence of the electrode 26 is only two points. By the way, using photolithography for both the insulating film and the electrodes,
Processing is generally and easily performed by a method in which an unnecessary portion is removed after the element is once formed on the entire surface. In photolithography, the shape is determined according to the mask pattern. That is, the structures shown in FIGS. 4 and 5 can be realized in exactly the same process as long as the mask pattern is changed. Moreover, when the resistance is increased by ion implantation, the technique is a well-established technique that is generally used, and there is no fear that the quality will be reduced at low cost.

As described above, according to the present invention, a semiconductor laser in which a photodiode is integrated can be realized with almost no increase in the process and cost required for manufacturing an element and without lowering the yield or reliability of the element. . Furthermore, if a semiconductor laser module is manufactured using this element,
By using the photodiode integrated with the laser element as the optical output monitor, a separate photodiode which has been conventionally required can be eliminated. As a result, the process and cost required for manufacturing the module are reduced, the reliability is improved, and the module can be further downsized.

(Specific Example) The case where the present invention is applied to an InGaAs / AlGaAs strained quantum well ridge waveguide semiconductor laser capable of obtaining an oscillation wavelength of about 1 μm will be described below as an example. FIG. 1 shows a semiconductor multilayer film structure of the device of this example. In the figure, 1 is an n-GaAs substrate, 2 is n-
GaAs buffer layer (thickness 0.2 μm), 3 is n-Al
_0.3 Ga _0.7 As clad layer (thickness 2 μm), 4 is n-
Al _0.2 Ga _0.8 As optical confinement layer (thickness 0.2 μm)
Is. 5 is an InGaAs active layer, and one layer of InGaA
The s-strained layer or several InGaAs strained quantum well layers and a GaAs barrier layer separating them. In this example, an In _0.2 Ga _{0.8 As} 2 layer having a thickness of 10 nm is used. 6 is a p-Al _0.2 Ga _0.8 As optical confinement layer (having a thickness of 0.2 μm).
m), 7 is a p-Al _0.3 Ga _0.7 As clad layer (thickness 2 μm), 8 is a p-GaAs cap layer (thickness 0.2 μm).
m). The layers up to this point are all semiconductor layers and can be easily realized by using either crystal growth method of metalorganic chemical vapor deposition (MOCVD) or molecular beam epitaxial growth (MBE).

First, the semiconductor multilayer film structure of FIG. 1 is produced by crystal growth. Next, the resistance increasing process as described above is performed under 24 of FIG. The mask of the non-implanted portion is patterned by photolithography, and protons are selectively implanted into 24. After removing the mask, thermal annealing is performed, and this step is completed. Next, in order to process the ridge structure shown in FIGS. 2 and 3, patterning is performed by photolithography, and parts other than the ridge portion are removed by wet or dry etching. Next, a SiO ₂ insulator film 9 is formed and processed into the structure shown in FIG. 2 by photolithography and etching. The SiO ₂ film is formed by a magnetron sputtering method or the like. Subsequently, 10 p-type electrodes are subjected to electron beam evaporation, patterned by photolithography, and a lift-off method is used to realize a structure as shown in FIG. Finally, the back surface n-type electrode 11 is vapor-deposited, and ohmic sintering is performed to complete the electrode.

A crystal was grown by the MOCVD method as a prototype of this example. In FIG. 4, the resonator length was 1 mm, and the length of the semiconductor gain region 22 when viewed in the resonator direction was 850 μm. And the distance from one end face to 22 is 100μ
m, and a photodiode section 2 with a length of 50 μm in between
1 was set. The length of the non-excitation region on the other end face side is 5
0 μm. After finishing the above-mentioned previous process, the element was cut out from the substrate by cleavage. When the cleaved surface was used as a reflecting mirror as it was, and a current of 200 mA was applied to the gain region without particular end face treatment, laser oscillation occurred at a threshold current of less than 30 mA, and wavelengths of 0.98 μm and 150
A laser light output of mW or more was obtained. This is equivalent to the performance of a conventional laser device having an equivalent structure without a photodiode. The photocurrent-laser light output characteristics of the photodiode of this device were measured. The photocurrent rises abruptly near the threshold, but then linearly increases monotonically. Moreover, similar characteristics were obtained from a plurality of elements, and reproducibility was confirmed. The above results show that the present invention can realize a semiconductor laser device integrated with an optical output monitor.

[0018]

As described above, according to the present invention, a semiconductor laser integrated with a photodiode can be used without substantially increasing the steps and costs required for manufacturing an element and without lowering the yield or reliability of the element. realizable. Furthermore, if a semiconductor laser module is manufactured using this element, a separate photodiode, which was conventionally required, can be eliminated by using a photodiode integrated in the laser element as an optical output monitor. As a result, the process and cost required for manufacturing the module are reduced, the reliability is improved, and the module can be further downsized.

[Brief description of drawings]

FIG. 1 shows an example of a semiconductor multilayer film structure common to the present invention and a conventional device.

FIG. 2 shows a cross-sectional view of an example of a ridge-guided end face non-pumped semiconductor laser device according to the present invention and a conventional type. The part that protrudes upward is the ridge waveguide. (A) is an element part,
(B) shows a non-excitation part.

FIG. 3 shows a perspective view of an example of a ridge waveguide type end face non-pumped semiconductor laser device according to the present invention. The part that protrudes upward is the ridge waveguide. The conventional type has a photodiode section 2
1 does not exist.

FIG. 4 is a top view of a specific layer of an example of a conventional ridge waveguide type end face non-pumped semiconductor laser device. The position of the ridge waveguide is between the two dotted lines. (A) is an insulator film, (b) is an upper surface electrode.

FIG. 5 is a top view of a specific layer of an example of a ridge waveguide type end face non-pumped semiconductor laser device according to the present invention. The position of the ridge waveguide is between the two dotted lines. (A) is an insulator film, (b) is an upper surface electrode.

FIG. 6 shows a block diagram for controlling the optical output of a semiconductor laser using a photodiode as a monitor.

[Explanation of symbols]

1 substrate (n-GaAs) 2 buffer layer (n-GaAs, 0.2 μm) 3 clad layer (n-Al _0.3 Ga _0.7 As,
2 μm) 4 Optical confinement layer (n-Al _0.2 Ga _0.8 As,
0.2 μm) 5 active layer (In _0.2 Ga _0.8 As quantum well 2 layers, GaAs barrier layer) 6 optical confinement layer (p-Al _0.2 Ga _0.8 As,
0.2 μm) 7 Clad layer (p-Al _0.3 Ga _0.7 As,
2 μm) 8 Electrode contact layer (p-GaAs, 0.2 μm) 9 Insulator film (SiO ₂ ) 10 Top surface electrode (p-type electrode) 11 Bottom surface electrode (n-type electrode) 21 Photodiode part (without insulation layer on ridge) ) 22 gain region (without insulating layer on ridge) 23 end face non-excitation region (insulating layer on ridge) 24 insulating region between gain region and photodiode (insulating layer on ridge) 25 insulating layer 26 upper surface of photodiode Electrode 27 Gain area top electrode 28 Electrode non-formation part

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Akihiko Nishitani 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. A semiconductor laser device comprising a resonator having a pair of end faces as reflecting mirrors and having a non-excitation region near the end faces, wherein an electrode electrically independent from a laser driving upper electrode is provided in the end face non-excitation region. In the semiconductor laser device, an ohmic contact is formed with respect to the laser driving upper electrode, and the non-excitation region is a photodiode. 2. A semiconductor device having an upper electrode and a lower electrode, wherein a convex ridge is formed on the upper part of the device,
A gain region is provided in the center of the ridge, a photodiode is provided on one side of the gain region via an insulating portion, and an end face non-excitation region is provided on the other side, and the photodiode is provided on the upper electrode. 2. The semiconductor laser device according to claim 1, which is in ohmic contact. 3. A semiconductor laser device, wherein the photodiode according to claim 1 is used as an optical output monitor to enable integration of the optical output monitor in a resonator.