JPH0590699A - Manufacture of multiple-wavelength semiconductor laser device - Google Patents

Abstract

PURPOSE:To obtain a multiple-wavelength semiconductor laser device having a low threshold, the degree of freedom of an oscillation wavelength, a high output and a clean buried interface by forming striped grooves having different width and depth. CONSTITUTION:Masks having striped opening sections having different width are formed onto a substrate 31 through a first etching stop layer 33, a growth layer 34, a second etching stop layer 35 and a non-doped growth layer 36. Each growth layer 34, 36 and the second stop layer 35 are vapor-phase etched, and striped grooves reaching the first and second stop layers 33, 35 and having different width and depth are formed. A lower clad layer 39, quantum well active layers 40,44, an upper clad layer 41 and cap layers 42, 46 are shaped successively into the striped grooves, and Ga ions are implanted up to the second stop layer 35 at positions except regions corresponding to the width of the striped grooves. Lastly, electrodes 48, 49a, 49b connected to the cap layers 42, 46 in each striped groove are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a multiwavelength semiconductor laser device for information processing.

[0002]

2. Description of the Related Art As is well known, a high-performance wavelength tunable function is important as a function required of a semiconductor laser such as an improvement in recording density by wavelength multiplexing in the field of optical recording.

By the way, as a semiconductor laser device for changing the wavelength, for example, one shown in FIG. 7 is known (Japanese Patent Laid-Open No. 1-276686). 1 in the figure is n-type GaA
s substrate. On this substrate 1, there is formed a current block layer 3 having two different widths and having a first groove 2a and a second groove 2b having a reverse tapered cross section. The first groove 2a
On the substrate 1, the n-type AI _0.3 Ga _0.7 As clad layer (lower clad layer) 4, the quantum well active layer 5, the p-type AI _0.3 Ga _0.7 As clad layer (upper clad layer) 6 and p ⁺ Type GaAs cap layer 7 is sequentially formed. An n-type AI is formed on the substrate 1 in the second groove 2b.
_0.3 Ga _0.7 As clad layer (lower clad layer) 8, quantum well active layer 9, p-type AI _0.3 Ga _0.7 As clad layer (upper clad layer) 10 and p ⁺ Type GaAs cap layer 11
Are sequentially formed. A p-side electrode 12a is formed on a part of the cap layer 7 and the current blocking layer 3, and a p-side electrode is formed on a part of the cap layer 11 and the current blocking layer 3.
12b is formed. An n-side electrode is provided on the back surface of the substrate 1.
13 are formed. Next, the operation of the laser device configured as shown in FIG. 7 will be described.

First, when current is injected into the laser device,
In the quantum well active layer 5, since the active layer width is narrow, the vertical mode is
Mode, the 0th order of the quantum level is saturated, and the vertical mode is 1 of the quantum level.
It oscillates at the next. Therefore, it oscillates on the high energy side, that is, at a short wavelength.

On the other hand, in the other quantum well active layer 9, the longitudinal mode normally oscillates in the 0th order of the quantum level. For example, if the width of the quantum well active layer 5 is 1 μm, the width of the quantum well active layer 9 is 2 μm, and the quantum well width is 10 nm, the oscillation wavelength is 810 nm in the quantum well active layer 5, and the quantum well active layer 9 is
, A wavelength difference of about 30 nm is obtained at 840 nm, and the threshold current in the first level oscillation is increased by about 30% in comparison with the zero order.

[0006]

However, since the conventional laser device has the same quantum well width, it has no choice but to use the 0th order and the 1st order of the quantum levels. Limited. Further, if the quantum levels of 1st order and 2nd order and higher levels are used, the oscillation wavelength becomes short, but the operating current increases. In particular, when the output is high, in the oscillation of a high level, the oscillation wavelength shifts to a higher level, so that the output efficiency decreases.

On the other hand, when the stripe width is narrowed to 1 μm or 2 μm, the crystal at the regrowth interface is deteriorated during regrowth filling, and the amount of leakage current flowing along the interface increases. In addition, since the width of the active layer is narrow, the deterioration of the crystals on both sides spreads inside, which significantly deteriorates the reliability.

The present invention has been made in view of the above circumstances, and provides a multi-wavelength semiconductor laser device having a low threshold value, oscillation wavelength freedom, high output, and a clean buried interface. With the goal.

[0009]

The present invention has different widths on a compound semiconductor substrate through a first etching stop layer, a growth layer containing impurities, a second etching stop layer and a non-doped growth layer. A step of forming a mask having a stripe-shaped opening, and vapor-phase etching each growth layer and the second etching stop layer using the mask to reach the first and second etching stop layers, and stripe width and depth. Forming stripe grooves having different widths, sequentially forming a lower clad layer, a quantum well active layer, an upper clad layer and a cap layer in the stripe grooves, and an effective width of each layer in the stripe grooves. A step of implanting Ga ions up to the second etching stop layer in a region other than the region corresponding to, and connecting to the cap layer in each stripe groove. Multiwavelength semiconductor laser characterized by comprising a step of electrodes respectively formed that - a method of manufacturing the laser device.

[0010]

In the present invention, an extremely thin film of a-Si film or SiO ₂ film is formed on the surface of the wafer including the first and second etching stop layers, and Ga ⁺ If the ion beam or the electron beam is narrowed down to less than μm and directly patterned, physical spattering can be performed by the same action (see FIG. 2). Then, as shown in FIG. 8, when vapor phase etching is performed with HCI gas in an As atmosphere, selectivity of the etching rate occurs due to the AI composition. The etching depth varies depending on this effect and the width of the window of the mask. In this state, MOVPE containing dimethylgallium chloride (DMGaCI) is used to selectively form a double heterojunction structure in the stripe groove. At this time, if the depth of the groove is large, the growth rate is high, that is, the quantum well width is large (see FIG. 4).

The quantum well width can be changed by changing the stripe width and the depth, and the effective active layer width is Ga ^+. Ion beams are implanted from the wafer surface to control the width. For a series of processes in the furnace, for example, when re-growing normally, a lower clad layer is grown to be relatively thick, and oxidation,
Although strain needs to be mitigated, the process of the present invention
It is possible to directly form the optical waveguide layer without the lower clad layer, and the device has excellent reliability.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a multiwavelength semiconductor laser device according to an embodiment of the present invention will be described below with reference to FIGS.

(1) First, a (100) n-type GaAs substrate 31
N-type AI _0.5 Ga _0.5 A by MOVPE technology
s layer 32, n-type AI _0.3 Ga _0.7 As etching stop layer (hereinafter referred to as the first stop layer) 33, n-type GaAs layer
34, n-type AI _0.5 Ga _0.5 As etching stop layer (hereinafter referred to as a second stop layer) 35, and non-doped G
The aAs layer 36 was sequentially grown. Here, the AI _0.5 G
a _0.5 As layer 32 is made of Si and has an impurity concentration of 1 × 10 ¹⁷ cm ^-3
The thickness is 2.0 μm, the first stop layer 33 is Si-doped, the impurity concentration is 1 × 10 ¹⁷ cm ⁻³ , the thickness is 0.1 μm, and the n-type GaAs is
Layer 34 is Si de - flop, the thickness at an impurity concentration of 1 × 10 ¹⁸ cm ^-3 0.
4 μm, the thickness of the second stop layer 35 is 0.05 μm, and the thickness of the non-doped GaAs layer 36 is 1.6 μm. Subsequently, plasma CVD is performed on the non-doped GaAs layer 36.
Then, an a-Si film 37 having a thickness of 3 nm was grown (FIG. 1).

(2) Next, a focusing G is formed on the a-Si film 37.
a ion beam (accelerating voltage 20 KeV, dose amount 5 × 10 ¹⁴
cm ⁻² ), parallel stripes having a width (W ₁ ) of 4 μm and a width (W ₂ ) of 8 μm are directly drawn at intervals of 80 μm (FIG. 2).

(3) Next, the wafer with the window opened is subjected to MOVPE.
It was transferred to a furnace and etched with HCI gas at 850 ° C. under As pressure. The etching depth is the depth at which the narrow stripe depth stops at the second stop layer 35. In this case, in a wide stripe, the second stop layer 35 is removed by over-etching, the n-type GaAs layer 34 having a high etching rate is removed, and the second stop layer 35 stops at the first stop layer 33 (FIG. 3). In the figure, 38a is a narrow stripe groove, 38b
Shows a wide stripe groove.

(4) Next, the temperature inside the MOVPE furnace is set to 700 ° C.
At a growth temperature of 10 Torr or less, and then a double heterostructure is grown in the groove by the MOVPE method including DEGaCI. That is, as described below, the layer thickness is controlled within the narrow stripe groove.

First, the n-type A is inserted into the narrow stripe groove 38a.
I _0.45 Ga _0.55 As clad layer (hereinafter referred to as lower clad layer) 39, active layer 40, p-type AI _0.45 Ga _0.55 As clad layer (hereinafter referred to as upper clad layer) 41, and p ⁺ A type GaAs cap layer 42 was selectively grown. However, the lower clad layer 39 is made of Si and has an impurity concentration of 1 × 10 ¹⁷
cm ^-3 with a thickness 0.4 .mu.m, the active layer 40 is GaAs quantum well width 5 nm, 2 cycle AIAs barrier width 5 nm, an upper clad layer 41 of Mg-de - flop, the thickness at an impurity concentration of 7 × 10 ¹⁷ cm ^-3 0 It is 0.4 μm.

In the selective growth under reduced pressure of 10 Torr or less, when the groove width is 10 μm or less and the depth is 1.5 μm or more, the growth rate is 1.5 to 2.0 as compared with the depth of 1 μm or less.
It is twice as fast. In the present invention, by utilizing this property, the thickness of the growth layer at the time of selective burying growth in the narrow stripe groove 38a is made variable. Therefore, the layer thickness parameters in the wide stripe groove 38b are as follows.

That is, the n-type AI _0.45 Ga _0.55 As layer 43 is 0.6 to 0.8 μm, and the active layer 44 is the GaAs quantum well width 8
nm, AIAs barrier width becomes 8 nm, and p-type AI _0.45 G
a _0.55 As clad layer 45 is 1 μm, the last p ⁺ Type GaA
The thickness of the s-cap layer 46 remains 0.4 μm (FIG. 4).

(5) Next, the insulating film 47 made of SiO ₂ was selectively patterned to a thickness of 500 nm, leaving a width of 2 μm only in the central portion of the stripe. Then, from above the insulating film 47, Ga ⁺ Ion beams (dose amount 4 × 10 ¹⁴ cm ^-2 ) were injected up to the first stop layer 33 (FIG. 5).

(6) Next, after removing the insulating film 47, a p-side electrode 48 is formed on the back surface of the substrate 31. Subsequently, a p-side electrode 49 was formed on the non-doped GaAs layer 36 and the cap layers 42 and 46. Further, the p-side electrode 49 is formed of an insulating film 50.
Divided into p-side electrodes 49a and 49b, a multiwavelength semiconductor laser composed of two elements was manufactured (FIG. 6).

The operation of the thus obtained multi-wavelength semiconductor laser device is as follows. That is, the p-side electrode 49
Carriers injected from a and 49b are Ga ⁺ Since the ion implantation region (dotted region in FIG. 6) is a high resistance region, it flows into the active layers 40 and 44. In these active layers, the light generated by recombination of carriers spreads horizontally and laterally because the refractive index is lowered due to disordering on both sides of the active layer, so that light absorption is small and resonance occurs. Optical feedback is repeated on the end face of the device, optical amplification is performed, and laser oscillation eventually occurs.

However, according to the above embodiment, mass productivity,
MOVPE technology with excellent controllability can be used. Focused ion beam direct writing, stripe grooves 38a and 38b are formed by vapor-phase etching with HCI gas, and then a selective process of double heterojunction structure is possible. Is. Therefore, since the process flows continuously without exposing the wafer to the air, deterioration of the crystal interface caused by regrowth can be prevented.

[0024]

As described above in detail, according to the present invention, it is possible to provide a multi-wavelength semiconductor laser device having a low threshold value, oscillation wavelength freedom, high output, and a clean buried interface.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a state in which each growth layer is formed on a substrate, showing one step in a method for manufacturing a multiwavelength semiconductor laser device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a step in a method of manufacturing a multi-wavelength semiconductor laser device according to an embodiment of the present invention, showing a state in which stripes having a predetermined width are drawn with a focused Ga ion beam. ..

FIG. 3 is a cross-sectional view showing a step of a method for manufacturing a multi-wavelength semiconductor laser device according to an embodiment of the present invention, in which stripe grooves are formed using HCI gas.

FIG. 4 is a cross-sectional view showing a step of a method for manufacturing a multi-wavelength semiconductor laser device according to an embodiment of the present invention, showing a state in which each growth layer is formed in a stripe groove.

FIG. 5 shows one step in a method of manufacturing a multi-wavelength semiconductor laser device according to an embodiment of the present invention, in which Ga ions are implanted in a predetermined region for the purpose of controlling the effective active layer width. FIG.

FIG. 6 is a cross-sectional view showing a step in a method for manufacturing a multi-wavelength semiconductor laser device according to an embodiment of the present invention, showing a state in which electrodes are formed on the back surface and the front surface side of a substrate respectively.

FIG. 7 is a sectional view of a conventional multi-wavelength semiconductor laser device.

FIG. 8 is a characteristic diagram showing the relationship between etching depth and etching time when etching each growth layer in FIG. 2 using HCI gas.

[Explanation of symbols]

31 ... n-type GaAs substrate, 32 ... n-type AI _0.5 Ga _0.5 As
Layer 33 ... first stop layer 34 ... n-type GaAs layer 35 ... second stop layer 36 ... non-doped GaAs layer 37 ... a-
Si film, 38a, 38b ... Stripe groove, 39 ... Lower clad layer, 40, 44 ... Active layer, 41 ... Upper clad layer, 42, 46 ...
p ⁺ Type GaAs cap, 43 ... n type AI _0.45 Ga _0.55 A
s layer, 45 ... p-type AI _0.45 Ga _0.55 As clad layer, 47 ...
Insulating film, 48 ... N-side electrode, 49a, 49b ... P-side electrode.

Claims (1)

[Claims] 1. A mask having stripe-shaped openings having different widths on a compound semiconductor substrate through a first etching stop layer, a growth layer containing impurities, a second etching stop layer and a non-doped growth layer. And forming a stripe groove in which the growth layers and the second etching stop layer are vapor-phase etched using the mask to reach the first and second etching stop layers and stripe widths and depths are different from each other. And a step of sequentially forming a lower clad layer, a quantum well active layer, an upper clad layer and a cap layer in the stripe groove, and a step except a region corresponding to the effective width of each layer in the stripe groove. Implanting Ga ions to the second etching stop layer,
And a step of forming an electrode connected to the cap layer in each of the stripe grooves, respectively.