JPH05327111A - Semiconductor laser and its manufacture - Google Patents

Abstract

PURPOSE:To obtain the manufacturing method of a semiconductor laser wherein variable range of wavelength is wide and gain characteristics scarcely have wavelength dependency, regarding the manufacturing method of a semiconductor laser device wherein clad layers and an active layer sandwiched by the clad layers are formed on a semiconductor substrate. CONSTITUTION:Mask layers 4 whose width continuously increases along the laser oscillation direction are formed on both sides of an active layer forming region 3 on a semiconductor substrate 2. When compound semiconductor is deposited from above by a vapor epitaxial method, raw material seed of the compound semiconductor to be deposited on the mask layers 4 diffuses in the lateral direction of the mask layers 4, and is deposited on the active layer forming region 3 sandwiched by the mask layers 4. The wider the mask layer 4 becomes, the larger the amount of the compound semiconductor deposited on the active layer forming region 3 becomes. Hence the compound semiconductor layer can be made thick by increasing the growth speed of the compound semiconductor layer along the laser oscillation direction.

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 clad layer and an active layer sandwiched by the clad layers are formed on a semiconductor substrate, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, as a signal light source of an optical communication system or a reference light source of a measurement system, a semiconductor laser device which oscillates at a single wavelength, has a narrow spectral line width, and has a wide wavelength tunable amount has been strongly demanded. There is. In order to realize a semiconductor laser device having such characteristics, conventionally, a method of providing a reflection mirror outside the semiconductor laser device to form an external resonator structure, a distributed feedback (DFB) laser, a distributed reflection type ( D
There has been a method of realizing a BR) laser by a semiconductor laser device alone.

In the conventional method using the external resonator structure, the wavelength tunable amount close to the gain bandwidth (about 200 to 250 nm) of the semiconductor laser device can be obtained by adjusting the external resonator. At the same time, it is possible to realize a very narrow spectral line width. Further, in the case of the method realized by the semiconductor laser device alone, although the wavelength tunable amount is not necessarily large (100 kHz and 10 nm, respectively), the device size is small as a whole and the handling is easy.

[0004]

However, in the method using the external resonator structure, the wavelength tunable width is limited to the gain band of the semiconductor laser device, and it is impossible in principle to extend the wavelength tunable range further. Is. Further, in the method using the external resonator structure, since the gain characteristic has a strong wavelength dependence, there is a problem that the threshold and the optical output change greatly when the wavelength is tuned.

Further, the method using a single semiconductor laser device has the problems that the gain band characteristic of the semiconductor forming the active layer is limited and the wavelength selectivity of the distributed feedback structure or distributed reflection structure is narrow. An object of the present invention is to provide a semiconductor laser device having a wide wavelength tunable amount and almost no wavelength dependence of gain characteristics, and a method for manufacturing the same.

[0006]

The principle of the present invention will be described with reference to FIGS. On the semiconductor substrate 2 on which the first cladding layer is formed, as shown in FIG. 1A, an active layer formation-scheduled region 3 made of silicon oxide or silicon nitride is formed.
Are formed, and mask layers 4 are formed on both sides of the active layer formation-scheduled region 3 so that the width thereof is continuously increased along the x direction (laser oscillation direction).

When a compound semiconductor is deposited from above by a vapor phase epitaxial method on the semiconductor substrate 2 on which the mask layer 4 having such a shape is formed, the compound semiconductor is selectively grown on the active layer formation planned region 3 having an opening. At the same time, the compound semiconductor to be deposited on the mask layer 4, in particular, the raw material species of the group III element diffuses in the lateral direction of the mask layer 4 and is deposited on the active layer formation scheduled region 3 sandwiched between the mask layers 4. .. As the width of the mask layer 4 is wider, more compound semiconductor is deposited in the active layer formation-scheduled region 3. Therefore, as shown in FIG. 1B, the growth rate of the compound semiconductor layer along the x direction (laser oscillation direction). And the compound semiconductor layer becomes thicker.

When the active layer has a multiple quantum well structure in which well layers and barrier layers having different band gaps are alternately laminated, the thickness of the well layer and the barrier layer is x depending on the change of the width of the mask layer 4. It continuously changes along the direction (laser oscillation direction) as shown in FIG. As the width of the mask layer 4 becomes wider, the well layer and the barrier layer become thicker. When the thickness of the well layer and the barrier layer is increased, the quantum level of the active layer of the multiple quantum well structure is lowered, the band gap is narrowed, the band gap energy is lowered, and the band gap wavelength is lengthened. That is, as shown in FIG. 2A, as the width of the mask layer 4 becomes wider, the bandgap wavelength of the active layer finally becomes longer.

Therefore, as shown in FIG. 1 (a), x
When the active layer is formed by using the mask layer 4 whose width is continuously wide along the direction (laser oscillation direction), regions having different oscillation wavelengths are arranged along the x direction (laser oscillation direction). Become. Therefore, as shown in FIG. 2B, the gain characteristics of the active layer are obtained by overlapping the gain characteristics (dotted lines) in the regions having different oscillation wavelengths, and a semiconductor laser device having a wide gain bandwidth can be realized.

As is apparent from the above-mentioned principle of the present invention, an object of the present invention is to form a semiconductor substrate, a first clad layer formed on the semiconductor substrate, and a first clad layer formed on the first clad layer. In a semiconductor laser device having an active layer and a second cladding layer formed on the active layer, the forbidden band width of the active layer continuously changes from one end face side to the other end face side. It is achieved by the semiconductor laser device.

Another object of the present invention is to form a first cladding layer on a semiconductor substrate, and to form a first cladding layer on the first cladding layer.
A mask layer is formed around the active layer formation scheduled region, the active layer formation scheduled region being open, and a mask layer having a width that continuously changes along the laser oscillation direction is formed. A multiple quantum well structure is formed by alternately stacking well layers and barrier layers that are deposited and alternately change in thickness in accordance with a change in the width of the mask layer in the active layer formation region on the first clad layer. Is formed, and a second cladding layer is formed on the active layer.

[0012]

According to the present invention, the forbidden band width of the active layer is made to continuously change from the one end surface side to the other end surface side. Since the characteristics overlap, a semiconductor laser device having a wide gain bandwidth can be realized.

[0013]

EXAMPLE A semiconductor laser device according to an example of the present invention will be described with reference to FIG. 3A is a cross-sectional view of the semiconductor laser device, and FIG. 3B is a cross-sectional view of the active layer as seen along the laser oscillation direction from one end face side to the other end face side. As shown in FIG. 3A, the impurity concentration is 1 × 10 ¹⁸ c
An impurity concentration of 1 μm with a thickness of 1 μm on the n − InP substrate 5 of m ⁻³
× 10 ¹⁷ cm n-InP cladding layer 6 of ^-3 is formed, n-InP on the cladding layer 6 is formed a multiple quantum well active layer 8, 0 thickness on the multiple quantum well active layer 8 ．
A p-InP cladding layer 9 having an impurity concentration of 5 × 10 ¹⁷ cm ^{−3 and} a thickness of 4 μm is formed. The p-InP clad layer 9 and the multiple quantum well active layer 8 are processed into a mesa shape having a stripe long in the laser oscillation direction.

Multiple layers with the mesa-shaped p-InP clad layer 9
The quantum well active layer 8 has a thickness of 0.5 μm and an impurity concentration of 5 × 1.
0¹⁷cm^-3Embedded by the p-InP buried layer 7 of
It Impurity with a thickness of 0.5 μm on the p-InP buried layer 7
Material concentration 5 × 10¹⁷cm^-3N-InP current blocking layer 1
0 is formed. p-InP clad layer 9 and n-
Impurity on InP current blocking layer 10 is 0.3 μm thick
Material concentration 5 × 10¹⁷cm ^-3Of the p-InP buried layer 11 of
Is made.

Further, on the p-InP buried layer 11, p-InGa having a thickness of 1 μm and an impurity concentration of 1 × 10 ¹⁸ cm ⁻³ is formed.
The AsP cap layer 12 is formed, and p-InGaAsP is formed.
A p-side electrode 13 made of Ti / Pt / Au is formed on the cap layer 12. An n-side electrode 14 made of Au / Ge is formed on the bottom surface of the n-InP substrate 5.

The multiple quantum well active layer 8 has a multiple quantum well structure having five quantum wells in which InGaAs well layers 8a and InGaAsP barrier layers 8b are alternately formed, and as shown in FIG. 3 (b). , Has a characteristic structure in which the film thickness gradually increases along the laser oscillation direction. That is, the thickness of the InGaAs well layer 8a is 5 nm (see FIG.
The thickness of the InGaAsP barrier layer 8b varies continuously in the range of (b) the leftmost side to 10 nm (the rightmost side of FIG. 3B), and the thickness of the InGaAsP barrier layer 8b is 7 nm (the leftmost side of the FIG. 3B) to 10 nm (FIG. 3B).
(B) The rightmost range is continuously changing.

In the multi-quantum well active layer 8 of this embodiment, the quantum level rises on the leftmost side in FIG. Becomes On the other hand, on the rightmost side in FIG. 3B, which is the thickest, the quantum level is lowered, the forbidden band width is narrowed to 0.802 eV, and the band gap wavelength is 15
It becomes 45 nm.

Therefore, the gain band of the semiconductor laser device of this embodiment extends to approximately 1350 to 1670 nm due to the overlap of the gain characteristics in the regions having different bandgap wavelengths.
It is possible to realize a gain characteristic over a wide wavelength range of about 320 nm. By providing an external reflecting mirror to form an external reflector type structure, it is possible to realize a semiconductor laser device having a very narrow spectral line width and a wide wavelength tunable range. Moreover, since the gain characteristics of regions having different bandgap wavelengths are overlapped with each other, there is almost no wavelength dependence of the gain characteristics.

A method of manufacturing a semiconductor laser device according to an embodiment of the present invention will be described with reference to FIGS. First, n
An n-InP clad layer 6 that serves as a hole barrier is formed on the -InP substrate 5 (FIG. 5A). Next, a silicon oxide layer is deposited on the entire surface of the n-InP cladding layer 6 by a thermal CVD method or a sputtering method, and the deposited silicon oxide layer is patterned to form a mask layer 15. As shown in FIGS. 4 (b1) and 4 (b2), the mask layer 15 has an active layer formation scheduled region 16 having a width of 2 μm opened, and a laser beam having a length of 300 μm is provided on both sides of the active layer formation scheduled region 16. The width is continuously changed from 4 μm to 10 μm along the oscillation direction.

Next, using the mask layer 15 formed on the n-InP cladding layer 6 as a mask, the compound semiconductor material for forming the InGaAs layer and the InGaAsP layer is alternately supplied by the MOVPE method. The InGaAs well layer 8a and the InGaAsP barrier layer 8b are selectively grown on the active layer formation planned region 16 opened in the mask layer 15. At this time, InGaAs or InGaAs is formed on the mask layer 15.
Although P does not grow, the group III element, particularly In, supplied on the mask layer 15 is laterally diffused on the mask layer 15 and deposited on the active layer formation planned region 16 sandwiched between the mask layers 15. As the width of the mask layer 15 becomes wider, the amount of InGaAs or InGaAsP deposited in the active layer formation planned region 16 increases, and as shown in FIG. 5C2, the InGaAs well layer in which the film thickness gradually increases along the laser oscillation direction. 8a and I
The nGaAsP barrier layers 8b are alternately stacked.

In this embodiment, the InGaAs well layer 8a
Thickness is from 5 nm (leftmost side in Figure 5 (c2)) to 10 nm
It changes continuously in the range of (the rightmost side in FIG. 5 (c2)).
The GaAsP barrier layer 8b has a thickness of 7 nm (the leftmost side in FIG. 5 (c2)) to 10 nm (the rightmost side in FIG. 5 (c2)). Then, p-I is formed as an electron barrier on the multiple quantum well active layer 8.
The nP clad layer 9 is selectively grown (FIG. 5 (c1)).

Next, the mask layer 15 is peeled off, and the mesa-shaped p-InP cladding layer 9 and the multiple quantum well active layer 8 are p-typed.
It is embedded by the InP burying layer 7. Then, n-InP
The n-InP current blocking layer 10 is formed on the cladding layer 6 and the p-InP cladding layer 9 by a normal embedding process.
A p-InP buried layer 11 is grown, and further p-In
A p-InGaAsP cap layer 12 is formed on the P buried layer 11.
Grow.

Next, p-
Ti / P is formed on the InGaAsP cap layer 12 (p side).
The p-side electrode 13 of t / Au is formed, and the n-side electrode 14 of Au / Ge is formed on the bottom surface of the n-InP substrate 5 (FIG. 5).
(D)). As described above, according to the present embodiment, the thickness of the multiple quantum well active layer can be changed in the laser oscillation direction only by changing the width of the mask layer, and a semiconductor laser device with a wide wavelength tunable amount can be manufactured. it can.

The present invention is not limited to the above embodiment, but various modifications are possible. For example, although the active layer has a multi-quantum well structure in the above embodiment, other structures may be used as long as the forbidden band width continuously changes along the laser oscillation direction. Further, although the above-mentioned embodiment is the Fabry-Perot type semiconductor laser device, even in the distributed feedback type semiconductor laser device having the distributed feedback structure on the substrate, the distributed reflection type semiconductor laser having the distributed reflection structure on both sides of the active layer. It may be a device.

[0025]

As described above, according to the present invention, the forbidden band width of the active layer is continuously changed along the laser oscillation direction, so that the gain characteristics of the active layer are in the regions having different oscillation wavelengths. The gain characteristics are overlapped, and a semiconductor laser device having a wide gain bandwidth can be realized.

[Brief description of drawings]

FIG. 1 is a principle diagram (1) of the present invention.

FIG. 2 is a principle diagram (2) of the present invention.

FIG. 3 is a sectional view of a semiconductor laser device according to an embodiment of the present invention.

FIG. 4 is a process chart (1) showing the method for manufacturing the semiconductor laser device according to the embodiment of the present invention.

FIG. 5 is a process diagram (2) showing the method for manufacturing the semiconductor laser device according to the embodiment of the present invention.

[Explanation of symbols]

 2 ... Semiconductor substrate 3 ... Active layer formation planned region 4 ... Mask layer 5 ... n-InP substrate 6 ... n-InP clad layer 7 ... p-InP buried layer 8 ... Multiple quantum well active layer 8a ... InGaAsP well layer 8b ... InP Barrier layer 9 ... p-InP clad layer 10 ... n-InP current blocking layer 11 ... p-InP buried layer 12 ... p-InGaAsP cap layer 13 ... p-side thin film 14 ... n-side electrode 15 ... mask layer 16 ... active layer formation Scheduled area

Claims (3)

[Claims] 1. A semiconductor substrate, a first clad layer formed on the semiconductor substrate, an active layer formed on the first clad layer, and a second clad layer formed on the active layer. A semiconductor laser device having a clad layer, wherein the band gap of the active layer continuously changes from one end face side to the other end face side. 2. The semiconductor laser device according to claim 1, wherein the active layer has a multiple quantum well structure in which well layers and barrier layers having different band gaps are alternately laminated, and the active layer has the multiple quantum well structure. A semiconductor laser device, wherein the thicknesses of the well layer and the barrier layer continuously change from one end face side to the other end face side. 3. A first clad layer is formed on a semiconductor substrate, an active layer formation planned region is opened on the first clad layer, and is formed around the active layer formation planned region. A mask layer having a width that continuously changes along with, and a compound semiconductor is deposited from above by a vapor phase epitaxial method to form the mask layer in the active layer formation planned region on the first cladding layer. To form an active layer having a multi-quantum well structure by alternately stacking well layers and barrier layers whose thickness changes according to the change in the width, and forming a second cladding layer on the active layer. A method of manufacturing a characteristic semiconductor laser device.