JPH06152073A - Evaluation of semiconductor laser and semiconductor laser wafer - Google Patents

Abstract

PURPOSE:To facilitate evaluation of optical output-current characteristic by having a construction provided with a plurality of phtodiodes arranged in the width direction of a laser element on the front of a resonator of the laser element to the evaluated for performing evaluation by driving a wafer element on wafer. CONSTITUTION:A semiconductor wafer 1 is placed on a wafer pro er, a current is made to flow through a laser element 12 so as to oscillate laser. Then, laser light 10 is radiated from an active region 4 on as to be incident on a plurality of photodiodes arranged in the front of the laser element 12. The photodiode arrays 31-3n are in advance independently impressed by reverse bias voltage so that laser light 10 radiated from the laser element 12 is absorbed by the active region 4 so as to be converted into an optical current. When the photodiodes 3k are subjected to the light having the strongest intensity of laser light 10, light within a radiation angle is received respectively and independently by the photodiodes 3k2... Accordingly, measurement in the on-wafer state is made possible by independently measuring optical currents of the photodiodes 31-3n.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser evaluation method and, more particularly, to a semiconductor laser evaluation method which enables on-wafer evaluation of optical output-current characteristics and the like.

[0002]

2. Description of the Related Art FIG. 6 is a view showing a conventional semiconductor laser wafer structure capable of on-wafer evaluation of a semiconductor laser device, and FIG. 7 is an enlarged view of a portion VII of FIG. In the figure, 1 is a semiconductor wafer, 2 is a laser element manufactured on the semiconductor wafer 1, 4 is an active region of the laser element 2, 5 is an end face of the laser element 2, and 6 is a laser element separated in the cavity length direction. A groove 8 is a groove for electrically separating adjacent laser elements. Reference numeral 21 is an upper electrode of the laser element 2. 12
Is a laser element of the laser element 2 that is evaluated on-wafer in the following description, and 22 is a laser element of the laser element 2 formed at a position facing the laser element 12. A laser beam 10 is emitted from the active region 4 of the laser element 12.

Next, a structure of a conventional semiconductor laser wafer and a conventional method for evaluating a semiconductor laser will be described. In this semiconductor laser wafer 1, crystals such as an active layer, a clad layer, a current blocking layer and an ohmic contact layer are grown on a compound semiconductor substrate such as GaAs or InP, and then electrodes are formed by a wafer process to form an element isolation groove 6 and 8 is formed to produce a plurality of laser elements 2 on the wafer. The laser element 2 has a dimension of, for example, a length of 30.
It has a width of 0 μm and a width of about 300 μm, and is electrically and optically separated from the front and rear laser elements by the etching groove 6, and is electrically separated from the adjacent laser element by the etching groove 8. Particularly, the groove 6 for separating the laser element in the cavity length direction.
Is formed by dry etching so as to be perpendicular to the wafer surface so that the end surface 5 of the laser element formed thereby becomes a mirror surface perpendicular to the wafer surface and functions as a laser resonator end surface. The separation groove 6 is usually about 10 μm deep and 20 to 5 wide.
It is about 0 μm. The laser element 2 is formed on the entire surface of the wafer 1 with the front and rear separation grooves 6 and the adjacent separation grooves 8 separated from each other. On-wafer evaluation using this laser wafer 1 is performed as follows.

A wafer is placed on a prober, and a current is passed through the laser element 12 to operate the laser. When the laser oscillates, it emits laser light 10 from the active region 4. By the way, the laser element 2 functions as a laser when a current is applied, but when light is received by the active region while a reverse bias voltage is applied, the laser element 2 absorbs the light and converts it into a current, and thus also functions as a photodiode. Therefore, if the laser element 22 arranged in front of the laser element 12 is used as a photodiode, the photocurrent detected by the laser element 22 changes rapidly before and after the oscillation of the laser element 12, so that the laser oscillation is performed on-wafer. It is possible to confirm and measure the oscillation threshold current. Each laser element is subjected to on-wafer evaluation as described above, and then divided into chips and used.

By the way, in the above-described on-wafer evaluation, the laser light is emitted from the end face of the laser element with a spread as shown in FIG. Further, there is a light output-current characteristic as one element for evaluating the laser characteristics, but there is a case where nonlinearity (kink) occurs in the light output-current characteristic due to instability of the transverse mode. However, the laser device 2
Since the width of the active region 4 for receiving the laser light is small, for example, about 2 μm, the operation of the photodiode 2 of FIG. 2 is an operation of absorbing a part of the strongest portion of the laser light and converting it into a photocurrent. Therefore, in this conventional on-wafer evaluation method, the evaluation of the radiation pattern of the laser light,
The optical output-current characteristics cannot be evaluated.

[0006]

According to the conventional on-wafer evaluation method for semiconductor lasers, a pair of resonator end faces are formed on a semiconductor wafer as described above, and adjacent elements are electrically separated by a groove. In the state of a semiconductor laser wafer in which a plurality of laser element rows are arranged in parallel, since it is performed by using the laser element formed at the opposing position as a photodiode, it is difficult to determine the quality of the optical output-current characteristics, and There is a problem that the radiation pattern of the laser beam cannot be evaluated.

The present invention has been made to solve the above problems, and a semiconductor laser evaluation method capable of evaluating the optical output-current characteristics and the radiation pattern of a semiconductor laser device on-wafer, and The purpose is to obtain a semiconductor laser wafer for carrying out this.

[0008]

According to a semiconductor laser evaluation method of the present invention, a semiconductor laser wafer on which a semiconductor laser element is manufactured is separated by a predetermined distance from a cavity facet of the semiconductor laser element on the semiconductor wafer. At a position, a structure is provided with a plurality of independently drivable photodiodes arranged in the width direction of the semiconductor laser device so that the light incident surface thereof faces the cavity end face of the semiconductor laser device, and is in an on-wafer state. In order to evaluate the semiconductor laser element, the semiconductor laser element is driven to detect each output of the plurality of photodiodes arranged to face the cavity end face of the semiconductor laser element.

The semiconductor laser evaluation method according to the present invention further has a structure in which the semiconductor laser wafer is provided with another semiconductor laser element at a position facing the semiconductor laser element with the plurality of photodiodes interposed therebetween. ,
The other semiconductor laser device is driven in an on-wafer state, and the outputs of the plurality of photodiodes arranged facing the cavity end face of the other semiconductor laser device are detected to evaluate the other semiconductor laser device. It was something that I was supposed to do.

A semiconductor laser wafer according to the present invention is a semiconductor laser wafer in which a plurality of semiconductor laser elements used by being divided into individual chips are formed on the semiconductor wafer. A plurality of independently drivable elements that are arranged in the width direction of the semiconductor laser device at positions separated from the resonator end face by a predetermined distance so that the light incident surface faces the resonator end face of the semiconductor laser device. It is equipped with a photodiode.

[0011]

In the present invention, the semiconductor laser wafer is
As a structure provided with a plurality of photodiodes arranged in the width direction of the laser element in front of the cavity end face of the laser element to be evaluated, the laser element was driven on-wafer for evaluation, so that the laser element was measured in the width direction of the laser element. It is possible to separately receive the spread laser oscillation light at different positions in the laser element width direction, and the radiation pattern of the laser oscillation light can be evaluated on-wafer, and the light receiving area can be enlarged, so the optical output-current characteristics can be evaluated. Can be easy.

Further, in the present invention, the semiconductor laser wafer further has a structure in which another semiconductor laser element is provided at a position facing the semiconductor laser element with the plurality of photodiodes sandwiched therebetween, and the other semiconductor laser element is in an on-wafer state. Since the semiconductor laser device is driven to detect the respective outputs of the plurality of photodiodes arranged facing the cavity end face of the other semiconductor laser device, the other semiconductor laser device is evaluated. The utilization efficiency of the photodiode can be doubled, and more semiconductor laser devices can be manufactured on the wafer.

According to the present invention, the light incident surface of the semiconductor wafer faces the cavity end surface of the semiconductor laser element at a position spaced a predetermined distance from the cavity end surface of the semiconductor laser element. Since the structure is provided with a plurality of photodiodes that can be independently driven and are arranged in the width direction of the semiconductor laser device, the radiation pattern of the laser oscillation light can be evaluated on-wafer, and the light receiving area can be increased. The output-current characteristics can be easily evaluated.

[0014]

【Example】

Example 1. 1 is a diagram showing a semiconductor laser wafer structure for carrying out a semiconductor laser evaluation method according to a first embodiment of the present invention, and FIG. 2 is an enlarged view of a portion indicated by II in FIG. In FIGS. 1 and 2, the same reference numerals as those in FIGS. 5 and 6 are the same or corresponding portions, 3 is a photodiode formed at a position facing the laser light emitting end face 5 of the laser element 2, and 7 is a laser element 2. A groove which separates the photodiode 3 in the direction of the resonator of the laser, and 9 is the adjacent photodiode 3
Is an electrically isolated groove, and 14 is an active region of the photodiode 3.

FIG. 3 is a diagram for explaining the operation of the on-wafer evaluation of this embodiment. In the figure, 3 _{1 to} 3 n are shown.
Is a photodiode formed in front of the laser element 12 to be evaluated.

Next, a wafer structure for carrying out the evaluation method of this embodiment will be described. For a semiconductor wafer 1, an active layer, a clad layer, a current blocking layer, an ohmic contact layer and the like are crystal-grown on a compound semiconductor substrate such as a GaAs or InP substrate to form an array of semiconductor laser elements 2 and photodiodes 3 on the same wafer. It was done. As can be seen from FIG. 1, an array of laser elements 2 arranged in one row and photodiodes 3 arranged in one row is alternately formed on the wafer 1. Here, for the sake of explanation, it is assumed that the semiconductor wafer 1 is an InGaAsP / InP-based wafer. Laser element 2 is made of InGaAsP / InP
The size of the laser is, for example, 300 μm width × 3 length
The width of the active region 4 is about 1 to 2 μm. The size of the photodiode 3 is, for example, 5 μm in width × 100 μm in length, and the separation groove 9 from the adjacent photodiode 3 is used.
Has a width of 3 μm, for example. In this case, the array of photodiodes 3 is arranged in front of the laser element 2 with the separation groove 7 interposed therebetween. The end surface 5 of the laser element 2 has a vertical mirror surface formed by dry etching or the like as in the conventional example. Here, as an example, the width of the separation groove 7 (distance between the laser element 2 and the photodiode 3) is 100 μm.

Next, an on-wafer evaluation method using this wafer will be described. The semiconductor wafer 1 is placed on a wafer prober, and a current is passed through the laser element 12 to cause laser oscillation. When oscillated, the laser light 10 is emitted from the active region 4 and is incident on a plurality of photodiodes arranged in front of the laser element 12. In FIG. 3, by applying a reverse bias voltage to the photodiode arrays 3 _{1 to} 3 n independently in advance, the laser light 10 emitted from the laser element 12 is absorbed in each active region 14 and converted into a photocurrent. . Here, as a typical example of the horizontal radiation angle (full width at half maximum) of the InGaAsP / InP laser, 25
Considering this case, the width within the radiation angle of the laser light at the position of the photodiode 3, that is, at the position 100 μm away from the laser emission end face is about 44 μm. Therefore, if the width of the photodiode and the width of the separation groove between the photodiodes are set to the above-mentioned dimensions, 5.5 of the plurality of photodiodes will be located within the radiation angle. If the photodiode 3k receives the light with the highest intensity of the laser light 10, the light within the radiation angle will be received independently by the photodiodes 3k2, 3k-1, 3k, 3k + 1, 3k + 2. Further, the weak light which spreads to the outside of the emission angle is independently received by the photodiodes 3 _{1 to} 3k-3 and 3k + 3 to 3n arranged outside the photodiodes 3k-2 to 3k + 2. Therefore, by independently measuring the photocurrents of the photodiodes 3 _{1 to} 3 n, the horizontal radiation pattern of the laser light 10 oscillated by the laser element 12 can be roughly measured in an on-wafer state. Further, by adding the photocurrents of all the photodiodes 3 _{1 to} 3 n (about 37 photodiodes according to the above dimensions) arranged so as to face the end face of the laser element 12, a larger photocurrent than the conventional example is obtained. Since the photocurrent can be obtained, not only the oscillation threshold current can be measured but also the outline of the optical output-current characteristics can be measured in the on-wafer state. Also, the optical output during laser operation −
In the case where the non-linearity (kink) of the current characteristic appears, the transverse mode movement occurs in this non-linear portion as shown in FIG.
Therefore, in the on-wafer evaluation operation, while increasing the light output, by measuring the change of the photocurrent of each of the photodiodes 3 ₁ 3n, kink light output can also be evaluated in the on-wafer. Further, it is possible to select good chips having the optical characteristics of the semiconductor laser on-wafer by checking the above-mentioned evaluation against the determination standard.

In the above embodiment, the photodiode 3
Has a width of 5 μm, and the separation groove 9 between the adjacent photodiodes 3 is
Is 3 μm, the width of the separation groove 7 between the laser element 2 and the photodiode 3 is 100 μm, and the horizontal emission angle of the laser beam 10 is 25 °. However, the width of the photodiode 3 is x, and the adjacent photodiodes 3 are The width of the separation groove 9 between them is y, the width of the separation groove 7 between the laser element 2 and the photodiode 3 is z, the horizontal radiation angle of the laser beam 10 is θ, and the number of the photodiodes 3 that fall within the radiation angle is n. Then, there is a relationship of n · (x + y) = 2z · tan (θ / 2) between them, and in order to increase the resolution of measurement, it is necessary to set x, y, z so that n is increased. Good. Further, for lasers having different θ, it is sufficient to set x, y, and z suitable for evaluation to manufacture a wafer.

Example 2. FIG. 4 is a diagram showing a semiconductor laser wafer structure used in the method for evaluating a semiconductor laser according to the second embodiment of the present invention, and FIG. 5 is an enlarged diagram of a portion indicated by V in FIG. In the figure, the same reference numerals as those in FIG. 1 and FIG.
The laser element 100 is arranged at a symmetrical position on the opposite side to the laser element 12 with respect to the array No.

The semiconductor wafer 1 according to the second embodiment is
As shown in FIG. 4, one array of photodiodes 3 and one array of laser elements 2 arranged symmetrically on both sides of the array are used as a set of three element rows. The set is formed over the entire wafer. Here, the operation and effect of the array of the laser element 12 and the photodiode 3 are exactly the same as those in the first embodiment. In the present embodiment, the on-wafer evaluation of the optical characteristics of the laser element 32 arranged on the side opposite to the laser element 12 with respect to the array of photodiodes 3 is further performed.
Laser beam 30 from the opposite side to the array can be performed.

As described above, in the second embodiment, two rows of laser elements are arranged for one row of the photodiode array, and the photodiodes 3 are used from the front and back sides. The utilization efficiency can be doubled, more laser elements can be arranged on the wafer as compared with the first embodiment, and the productivity can be improved.

Incidentally, in the first embodiment, the wafer structure in which the end face of the photodiode 3 on the side for receiving the laser light is coated with a non-reflective (low reflection) coating on both end faces of the photodiode 3 in the second embodiment. When the above is manufactured, the amount of light received by the photodiode increases, and it becomes possible to more accurately perform on-wafer evaluation of optical characteristics.

In the above embodiment, InGaAsP /
Although an InP-based semiconductor laser wafer has been described as an example, a semiconductor laser wafer using another compound semiconductor may be used as a material, and the same effect as that of the above-described embodiment is obtained.

[0024]

As described above, according to the present invention, a semiconductor laser wafer is provided with a plurality of photodiodes arranged in the laser element width direction in front of the end face of the resonator of the laser element to be evaluated. Since it is driven on-wafer for evaluation, it is possible to separately receive the laser oscillation light expanded in the laser element width direction at different positions in the laser element width direction. Can be evaluated, and non-defective devices can be selected on-wafer, and the light receiving area can be increased, so that there is an effect that the optical output-current characteristics can be easily evaluated.

Further, according to the present invention, the semiconductor laser wafer is further provided with another semiconductor laser element at a position facing the semiconductor laser element with the plurality of photodiodes sandwiched therebetween, and the semiconductor laser wafer is in an on-wafer state. Another semiconductor laser element is also driven, and the outputs of the plurality of photodiodes arranged facing the cavity end face of the other semiconductor laser element are detected to evaluate the other semiconductor laser element. Therefore, the utilization efficiency of the photodiode can be doubled, and more semiconductor laser elements can be manufactured on the wafer.

Further, according to the present invention, in a semiconductor laser wafer in which a plurality of semiconductor laser elements used by being divided into individual chips are formed on the semiconductor wafer,
On the semiconductor wafer, at a position separated from the cavity end surface of the semiconductor laser element by a predetermined distance, in the width direction of the semiconductor laser element so that the light incident surface faces the cavity end surface of the semiconductor laser element. Since it has a structure with a plurality of photodiodes that can be independently driven and arranged,
There is an effect that the radiation pattern of the laser oscillation light of the semiconductor laser device and the optical output-current characteristics can be evaluated on-wafer.

[Brief description of drawings]

FIG. 1 is a diagram showing a semiconductor laser wafer structure used in a semiconductor laser evaluation method according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of a portion II in FIG.

FIG. 3 is a diagram for explaining an on-wafer evaluation operation of the semiconductor laser evaluation method according to the first embodiment.

FIG. 4 is a diagram showing a structure of a semiconductor laser wafer used in a method for evaluating a semiconductor laser according to a second embodiment of the present invention.

FIG. 5 is an enlarged view of a V portion of FIG.

FIG. 6 is a diagram showing a structure of a conventional semiconductor laser wafer capable of on-wafer evaluation.

7 is an enlarged view of part VII of FIG.

FIG. 8 is a diagram for explaining an on-wafer evaluation operation in a conventional semiconductor laser evaluation method.

FIG. 9 is a diagram showing how transverse mode movement occurs when the optical output is increased.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor wafer 2 Laser element 3 Photodiode 7 Separation groove between laser element and photodiode 8 Separation groove between adjacent laser elements 9 Separation groove between adjacent photodiodes 12 Laser element 32 Laser element

Claims (4)

[Claims] 1. A semiconductor laser evaluation method for evaluating a semiconductor laser device, which is formed on a semiconductor wafer and then divided into individual chips to be used, wherein the semiconductor laser device on which the semiconductor laser device is prepared is Arranged in a width direction of the semiconductor laser device on the wafer at a position separated from the resonator end face of the semiconductor laser device by a predetermined distance so that the light incident surface faces the resonator end face of the semiconductor laser device. In addition, each semiconductor laser element is driven in an on-wafer state, and each output of the plurality of photodiodes arranged opposite to the cavity end face of the semiconductor laser element is driven. A method for evaluating a semiconductor laser, which comprises detecting and evaluating the semiconductor laser element. 2. The method for evaluating a semiconductor laser according to claim 1, wherein the semiconductor laser wafer further comprises another semiconductor laser element at a position facing the semiconductor laser element with the plurality of photodiodes sandwiched therebetween. And driving the other semiconductor laser device in an on-wafer state, detecting each output of the plurality of photodiodes arranged facing the cavity end face of the other semiconductor laser device, and detecting the other semiconductor laser device. A method for evaluating a semiconductor laser, which further comprises: 3. The method for evaluating a semiconductor laser according to claim 1, wherein the semiconductor laser device or another semiconductor laser device is evaluated with a non-reflective or low-reflective coating applied to the light incident surface of the photodiode. A method for evaluating a semiconductor laser, which comprises: 4. A semiconductor laser wafer in which a plurality of semiconductor laser devices, which are used by being divided into individual chips, are formed on a semiconductor wafer, wherein a predetermined distance from a cavity end face of the semiconductor laser device on the semiconductor wafer is provided. A plurality of independently drivable photodiodes arranged in the width direction of the semiconductor laser device so that their light incident surfaces face the cavity end faces of the semiconductor laser device are provided at positions spaced apart from each other. Characteristic semiconductor laser wafer.