JPH0423482A - Method for appreciation of refractive index difference - Google Patents

Abstract

PURPOSE:To appreciate readily and surely whether or not a desired refractive index difference is produced in an active layer by determining refractive index difference between an active layer and an impurity diffusion region on the basis of an impurity concentration in a known active layer and an impurity concentration in an impurity diffusion region which is found in advance. CONSTITUTION:Laser light is projected selectively to an action layer 2 part as it is and a P-type impurity diffusion region 4. PL wavelength is measured separately, and impurity concentration in a P-type impurity diffusion region 4 is obtained from the result. That is, since hole concentration po and PL wavelength are in positive correlation, hole concentration po can be known when the difference lambdaPL of PL wavelength values of the active layer 2 and the P-type impurity diffusion region 4 is obtained. Furthermore, since impurity concentration is known, the refractive index difference n between the P-type impurity diffusion region 4 and the active layer 2 can be obtained only by determining hole concentration po. Thereby, it is possible to appreciate readily and surely whether or not refraction factor difference is a proper value.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for evaluating a refractive index difference in an index-guided semiconductor laser in which an impurity diffusion region is selectively formed, At the stage of the wafer in which the impurity diffusion region is formed, the desired refractive index difference Δn is set in the active layer.
The purpose of this method is to easily and reliably evaluate whether or not a The active layer and the impurity diffusion region of the index-guided semiconductor laser that performs confinement are separately irradiated with laser light to measure their respective photoluminescence wavelengths, and then the difference between the two photoluminescence wavelengths is measured. The impurity concentration of the impurity diffusion region is derived from ΔλPL, and then the impurity concentration of the active layer and the impurity diffusion region is determined from the impurity concentration in the active layer known in advance and the impurity concentration in the impurity diffusion region derived earlier. The configuration is configured to derive the refractive index difference between.

[Industrial application field]

The present invention relates to a method for evaluating a refractive index difference in an index-guided semiconductor laser in which impurity diffusion regions are selectively formed.

Currently, there is a demand for higher output semiconductor lasers used in the visible short wave band, such as semiconductor lasers for laser printers or pumping semiconductor lasers.

[Conventional technology]

In general, as a type of semiconductor laser aiming at high output,
A refractive index waveguide type device having a so-called window structure in which an impurity diffusion region is formed by applying a selective diffusion method is known.

The window portion in this type of semiconductor laser is
Since it is transparent to laser light, accidents such as melting of the laser light emitting surface are unlikely to occur even during high-output oscillation, making it an extremely effective means for increasing the output power of semiconductor lasers. ing.

Now, in this refractive index guided semiconductor laser, an impurity diffusion region is formed using a selective diffusion method, and light is confined by utilizing the refractive index difference between the diffused and non-diffused areas. .

FIG. 6 is a diagram for explaining a refractive index guided semiconductor laser having an impurity diffusion region formed by applying a selective diffusion method, in which (A) is a cutaway front view of the main part, and (B) is a refractive index waveguide semiconductor laser. Each represents a line diagram showing the rate distribution.

In the figure, 11 is an n-type cladding layer, 12 is an n-type active layer, 13 is a p-type rad layer, 14 is a p-type impurity diffusion region,
Δn indicates the refractive index difference. In addition, (B) in the figure
Here, the vertical axis represents the refractive index, and the horizontal axis represents distance.

As shown in the figure, in this refractive index guided semiconductor laser, for example, zinc (Zn) is diffused from the surface side, and in particular,
By inverting a part of the n-type active layer 12 to p-type and increasing the refractive index, a refractive index difference Δn in the lateral direction is generated and light is confined.

FIG. 7 is a diagram for explaining changes in the refractive index depending on the electron concentration and the genuine plate concentration in GaAs, with the vertical axis representing the refractive index n and the horizontal axis representing the electron concentration n. and hole concentration p. are taken respectively.

As is clear from the figure, the electron concentration n. Or the hole concentration p
. When , the corresponding refractive index n also changes, so the refractive index difference Δn between the diffusing part (p type) and the non-diffusing part (n type) in the active layer is an effective value for confining light. It is necessary to control the p-type impurity concentration in the diffusion portion so that .

[Problem to be solved by the invention]

In the refractive index guided semiconductor laser in which impurity diffusion regions are selectively formed as described above, the refractive index difference Δn between the p-type part and the n-type part in the active layer is sufficient. In other words, the function as an index-guided semiconductor laser depends on whether the p-type impurity diffusion region sufficiently reaches the active layer and maintains a predetermined impurity concentration. will be affected.

However, since the stripe width of this p-type impurity diffusion region is very fine, on the order of several [μm], specifically on the order of 2 to 3 [μm], it is necessary to measure the impurity concentration in advance during manufacturing. Conventionally, after a semiconductor laser is completed, it is necessary to actually perform laser oscillation to determine whether it is a good product, that is, whether p-type impurity diffusion has been properly performed. It was impossible to determine. Moreover, such determination is also an indirect means and does not directly measure the impurity concentration. still,
It is also possible to form an impurity diffusion region for monitoring at a suitable location on a wafer on which an index-guided semiconductor laser is formed, and to observe the impurity concentration. This does not mean that it is being measured directly.

The present invention aims to easily and reliably evaluate whether or not a desired refractive index difference Δn is generated in an active layer at the stage of a wafer in which a selective impurity diffusion region for generating a refractive index difference Δn is formed. I try to make it possible.

[Means to solve the problem]

FIG. 1 shows a cutaway front view of essential parts of a refractive index guided semiconductor laser for explaining the present invention in detail.

In the figure, l is an n-type cladding layer, 2 is an active layer, and 3 is a p-type cladding layer.
type cladding layer, 4 indicates a p-type impurity diffusion region, respectively.

In the present invention, a laser beam narrowed to a minute spot is used as an excitation light source for the index-guided semiconductor laser when the configuration shown in the figure is fabricated on a wafer. The active layer 2 itself and the p-type impurity diffusion region 4 formed in the active layer 2 are irradiated to emit photoluminescence.
nce:pI-) wavelength is measured (1), and the refractive index difference is evaluated from the measurement results.

From the above, in the refractive index difference evaluation method according to the present invention, (1) selectively forming an impurity diffusion region (for example, the p-type impurity diffusion region 27) in the active layer (for example, the n-type GaAs active layer 23); A laser beam is separately irradiated onto the active layer and the impurity diffusion region in the refractive index waveguide semiconductor laser which generates a refractive index difference (for example, refractive index difference Δn) and lateral optical confinement by forming the active layer and the impurity diffusion region. Then, from the difference between the two photoluminescence wavelengths, the impurity concentration (for example, hole concentration p.) of the impurity diffusion region is derived. Deriving the refractive index difference between the active layer and the impurity diffusion region from the known impurity concentration in the active layer and the previously derived impurity concentration in the impurity diffusion region, or (2) In (1) above, when the active layer and impurity diffusion region of the index-guided semiconductor laser are irradiated with laser light, the surface side semiconductor layer (for example, the n-type GaAs cap layer 26) that easily absorbs the laser light is ) is removed in advance, or

[Effect]

In the present invention, a laser beam that excites the active layer is selectively irradiated to a portion where p-type impurities are not diffused, that is, a portion of the active layer 2 as it is and the p-type impurity diffusion region 4, respectively. The PL wavelength is measured, and the impurity concentration in the p-type impurity diffusion region 4 is determined based on the result.

That is, the hole concentration p. (!: Since there is a positive correlation with the PL wavelength, if the difference ΔλPL between the PL wavelength values of the active layer 2 and the p-type impurity diffusion region 4 is known, the hole concentration p can be found.

Figure 2 shows the hole concentration p. This is a diagram for explaining the relationship between the difference ΔΔ in PL wavelength value between the p-type impurity diffused part and the non-diffused part, with the vertical axis representing the original card concentration po, and the horizontal axis representing the PL wavelength value. The differences in wavelength values Δ and Δ are respectively taken.

If you have this diagram, and you know the difference Δλ, L between the PL wavelength values of the active layer 2 and the p-type impurity diffusion region 4, you can determine the hole concentration P. can be easily found. Incidentally, it is easy to create such a correlation diagram in advance.

Here, since the impurity concentration in the active layer 2 itself is known, the hole concentration p is determined as described above. Once this is known, the refractive index difference Δn between the p-type impurity diffusion region 4 and the active layer 2 can be determined with reference to FIG.

〔Example〕

FIGS. 3 and 4 are cutaway front views of essential parts for explaining a refractive index guided semiconductor laser that is in the process of being manufactured and used in an embodiment of the present invention.

First, I will explain how to prepare the sample for evaluation. I will clarify.

In FIG. 3, 21 is an n-type GaAs substrate, 22 is an n-type AffiGaAs cladding layer 23 is an n-type Cr
24 is an n-type Al2GaAs cladding layer, 25 is a p-type AIGaAs current confinement layer, 26 is an n-type GaAs cap layer, and 27 is a p-type impurity diffusion region. can be easily made using conventional techniques. That is, after each semiconductor layer is laminated and grown on the n-type GaAs substrate 21, the p-type impurity diffusion region 27 is formed, and at that stage the wafer is folded to form a wafer as shown in the figure.

As seen in FIG. 4, the top layer of the wafer, ie, the n-type GaAs cap layer 26, is selectively etched away. This is to prevent the laser light from being greatly attenuated before reaching the n-type GaAs active layer 23 since GaAs absorbs the laser light. In addition, the base of this etching is AI! Since it is GaAs, for example, by applying a wet etching method using a mixture of ammonia (NH3) and hydrogen peroxide (H20□) as an etchant, it is possible to easily selectively etch only GaAs. be.

■ N-type GaAs active layer 23 and p-type impurity diffusion region 27
The PL wavelengths are measured separately by irradiating the laser beams on the PL wavelengths.

From the values of the two PL wavelengths, the difference Δλ, L between them is obtained, and the p-type impurity diffusion region 27 is determined using the values and FIG.
The hole concentration at p. can be found.

Since the electron concentration n0 in the n-type GaAs active layer 23 is known in advance, the hole concentration po in the p-type impurity diffusion region 27 obtained as described above and from FIG.
The refractive index difference Δn between the type impurity diffusion region 27 and the n-type GaAs active layer 23 can be obtained.

FIG. 5 shows an explanatory diagram of the main parts for explaining the apparatus used to measure the PL wavelength described in (3) above.

In the figure, 31 is a laser light source, 32 is a lens, 33 is a mirror, 34 is a half mirror, 35 is a lens, 36 is a sample, 37 is a lens, 38 is a chopper, 39 is a spectrometer,
40 is a detector, 41 is a lock-in amplifier, and 42 is a recorder.

In the illustrated apparatus, the laser beam R31 is a Kr'' laser with a wavelength of 647.1 (nm), for example, a wavelength of 488.0 (nm) or 514.5 (nm).
An "Ar" laser can be used, and in this case, the selection criteria is a laser that can select a wavelength that passes through the cladding layer and is absorbed only by the active layer, or a laser that is close to that. Irradiate the sample 36. The spot diameter of the laser beam is set to 5 to 10 [μm].The detector 40 can be a silicon Lumin photodiode or a photomultiplier tube.The PL from the sample 36 is spectrally separated by a spectrometer 39, and the P The measurement results of the L wavelength are recorded on the recorder 42.

In the above embodiment, the active layer is made of GaAs, but even if the active layer is made of Δ12 Ga As or other materials, if a correlation such as ΔλPL+ no + P O+ n is obtained, the above It goes without saying that evaluation can be carried out in the same manner as .

〔Effect of the invention〕

In the refractive index difference evaluation method according to the present invention, the active layer and impurity diffusion region of an index-guided semiconductor laser are separately irradiated with laser light, and the photoluminescence wavelength of each is measured. Difference between two photoluminescence wavelengths ΔλP
The impurity concentration of the impurity diffusion region is derived from L, and the impurity concentration between the active layer and the impurity diffusion region is derived from the previously known impurity concentration in the active layer and the previously derived impurity concentration in the impurity diffusion region. The refractive index difference is derived.

By employing the above method, the refractive index can be changed during the manufacture of the refractive index guided semiconductor laser, that is, at the stage of the wafer in which the impurity diffusion region that generates the refractive index difference for lateral optical confinement is formed. It is possible to easily and reliably evaluate whether the difference is an appropriate value, and therefore, it is possible to use the evaluation results to decide whether or not to continue the subsequent manufacturing process, thereby reducing wasteful manufacturing. This greatly contributes to reducing work.

[Brief explanation of drawings]

FIG. 1 is a cutaway front view of essential parts of a refractive index guided semiconductor laser for explaining the present invention in detail, and FIG. 2 is a diagram showing the hole concentration p. Against P
Diagrams 3 and 4 for explaining the relationship of the difference Δλpt in PL wavelength value between the type impurity diffused part and the non-diffused part
The figure is a cut-away front view of the essential parts to explain the refractive index guided semiconductor laser in the process of being manufactured used in one embodiment of the present invention, Figure 5 is an explanatory diagram of the essential parts of the device for measuring the PL wavelength, and Figure 6 is the selected part. FIG. 2 is a diagram for explaining a refractive index guided semiconductor laser having an impurity diffusion region formed by applying a diffusion method, in which (A) is a cutaway front view of the main part, and (B) is a diagram showing the refractive index distribution. , Figure 7 shows Ga
Each of these diagrams shows a diagram for explaining the change in refractive index depending on the electron concentration and hole concentration in As. In the figure, 21 is an n-type GaAs substrate, 22 is an n-type AffiGaAs cladding layer 23 is an n-type GaAs substrate, and 22 is an n-type AffiGaAs cladding layer 23.
24 is an n-type Aj2GaAs cladding layer 25 is a p-type Aj2GaAs current confinement layer, and 26 is an n-type GaAs active layer.
27 indicates an As cap layer, and a p-type impurity diffusion region. Patent Applicant Fujitsu Co., Ltd. Representative Patent Attorney Shoji Aitani

Claims (2)

[Claims] (1) A refractive index waveguide semiconductor laser in which lateral optical confinement is achieved by selectively forming an impurity diffusion region in the active layer to generate a difference in refractive index. Light is irradiated separately to measure each photoluminescence wavelength, and then the impurity concentration of the impurity diffusion region is derived from the difference between the two photoluminescence wavelengths. A refractive index difference evaluation method comprising deriving a refractive index difference between the active layer and the impurity diffusion region from the impurity concentration in the active layer and the previously derived impurity concentration in the impurity diffusion region. (2) A claim characterized in that, when irradiating the active layer and impurity diffusion region of an index-guided semiconductor laser with laser light, the surface-side semiconductor layer that easily absorbs the laser light is removed in advance. Item 1. The refractive index difference evaluation method according to item 1.