JPS61239686A - Semiconductor laser device and manufacture thereof - Google Patents

Abstract

PURPOSE:To stabilize an oscillation wavelength, and to obtain a large optical output by arranging a plurality of light-emitting regions having quantum well type structure in series and constituting a residual region by a semiconductor having the man composition of two kinds of compound semiconductors organizing the same structure. CONSTITUTION:A P-type semiconductor layer 2 is formed onto a P-type semiconductor 1 as a lower clad layer. An active layer 4 is shaped onto the layer 2. A plurality of striped light-emitting regions 8a, 8b having quantum well type structure are disposed in series with the direction of a laser resonator at the center of the layer 4 at regular intervals 6b. The left and right both regions 6a of the regions 8a, 8b and the interval 6b are constituted by a semiconductor having the mean composition of two kinds of compound semiconductors organizing quantum well type structure. Consequently, the forbidden band width of the regions is made larger than that of the light-emitting regions, and a refractive index thereof is made smaller than those of the light-emitting regions. An N-type semiconductor layer 3 is formed onto the layer 4 as an upper clad layer. According to such formation, an oscillation wavelength is stabilized, and a large optical output is acquired by small modulation currents.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a semiconductor laser device having a quantum well structure as an active layer, in which a plurality of light emitting regions are arranged in series in the cavity direction, and its manufacture. It is about the method.

(Prior Art) Conventionally, a semiconductor laser device for transverse single mode oscillation has a buried heterostructure in which an active region is surrounded by a semiconductor having a large forbidden band width. This buried heterostructure laser device is manufactured using two liquid phase growth methods and mesa etching. That is, a double heterostructure crystal is created in the first liquid phase growth, and this crystal is chemically etched into a mesa/stripe shape, and then the mesa/stripe becomes a forbidden zone in the second liquid phase growth. Embedded by a wide semiconductor.

:' + , -'+ -3-4゛1t ■ ・Thus, in view of the above, the applicant constructed a quantum well type structure above and below the active layer of the quantum well type structure. The average composition of the two types of semiconductors is larger than the average composition of the two types of semiconductors, and zinc is diffused into a quantum well structure on the left and right sides of the active layer. A laser device was proposed.

This semiconductor laser device has a structure similar to a buried double heterostructure with a quantum well structure as an active layer, and can easily be created by simply performing an impurity diffusion process on a multilayer semiconductor crystal growth layer formed by epitaxial growth. (Japanese Unexamined Patent Publication No. 59-21084).

(Problems to be solved by the invention) Semiconductor laser devices are easily affected by temperature: Length of oscillation region, ? L: 112...an integer), noise occurs when the value jumps, that is, when the wavelength chirps. Semiconductor laser devices with the above-mentioned quantum well structure as an active layer have less temperature dependence than normal semiconductor laser devices, but wavelength chirping may occur when used for direct modulation, making it difficult for long-distance optical transmission and optical In analog transmission, etc., transmission characteristics may deteriorate.

An object of the present invention is to provide a semiconductor laser device that has small temperature dependence, stable oscillation wavelength, and can provide a large forward output power with a small modulation current, and a method for manufacturing the same.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a semiconductor laser device having a quantum well structure as an active layer, in which a plurality of stripe-shaped light emitting quantum well structures are provided in the center of the active layer. The regions are arranged in series in the direction of the laser resonator with a predetermined gap,
The remaining region υ provides a semiconductor laser device constituted by a semiconductor having an average composition of two types of compound semiconductors constituting a quantum well structure.

(effect) oscillates. The oscillation wavelength 2 of the laser beam oscillated in each region is represented by two wavelengths as described above. Oscillation η$ If there are two oscillation regions, the length of each oscillation region is 2? L/
Ll 2nlL2 Saori, , L wise, j, =- and Suen = , 1r
Laser oscillation occurs when ν1 and O□ become equal.

Therefore, the degree of freedom is reduced compared to the case where there is only one oscillation region, but on the other hand, oscillation occurs only under specific conditions, so the oscillation wavelength is stabilized. As the number of oscillation regions increases, the stability of the oscillation wavelength increases, and the occurrence of wavelength chirping is suppressed.

Furthermore, as mentioned above, a tandem laser device in which multiple light emitting regions are arranged in series has hysteresis in the first-input and first-output characteristics, and the current-light output characteristic may exhibit sharp rises and falls. As is known, a large optical output can be obtained with less modulation current than a normal semiconductor laser device.

(Example) To explain this invention based on an illustrated example, / is p
type semiconductor substrate, on which a lower cladding layer is formed as a stripe-shaped light emitting region gα of a quantum well type structure, which will be described later.

jrb (two in the illustrated embodiment) align a predetermined gap 6b. They are arranged in series in the direction of the laser resonator while maintaining

This quantum well type structure is constructed by alternately stacking three or more ultrathin films of two types of compound semiconductors with different compositions, each having a thickness of several tens to several hundreds of times.The compound semiconductors constituting this quantum well type structure include Gaks, GaAlAs.

G(zA5P, G(L'n"8 + 'nG(LA
Examples include binary, six-element, and four-element semiconductors such as 8P, which have different forbidden band widths.

The illustrated embodiment shows a case where there are two light-emitting regions, but there are six light-emitting regions.
You can arrange books or more. It is preferable that the length ratio of each light emitting region is not an integer.

Striped light emitting region zaα, both left and right regions 6α of gb,
6α and the gap 6b between the two light emitting regions ga and tb, there exists a semiconductor having an average composition of two types of compound semiconductors constituting a quantum well structure. Therefore, in this region, the forbidden band width becomes larger than in the light emitting region, and the refractive index becomes smaller. In this gap 6mm, there is a high n-type semiconductor layer 3. On the upper surface of the upper cladding layer 3, where the light-emitting regions gα and gb are present, the cladding layer also has a narrow stripe-like forbidden band width.
'N-type semiconductor left α and Sb are provided.

Striped n-type semiconductor Sα,s on the upper cladding layer 3
The insulating film 9 is covered except for the area where b is provided. An n-side electrode IO is independently provided on the top surface of the n-type semiconductor Sα, and an n-side electrode IO is independently provided on the top surface of the n-type semiconductor sb.
A common p-side electrode // is formed on the bottom surface of the semiconductor laser device as shown in FIG.

In this semiconductor laser device, when an electron current is supplied to the n-side electrode 10°/2 and a hole current is supplied to the p-side electrode //, the current is concentrated in the light emitting regions gα and zab of the active layer 3, and the oscillation region gα The optical gain is maximum at a wavelength where the gains of the oscillation longitudinal mode in the oscillation region gb and the oscillation longitudinal mode in the oscillation region gb match, and the laser oscillates.

Both sides of the light emitting regions gα and zab are composed of impurity diffusion regions in which quantum well structures are alloyed, so the refractive index is smaller than that of the light emitting regions, and the upper and lower cladding layers 3. This region also has a smaller refractive index than the light emitting region, so the oscillated laser light has a single mode in the lateral direction.

If a p-type semiconductor layer with a lower refractive index than the lower cladding layer is interposed as a light guide layer between the lower cladding layer and the active layer, light will be confined and the forbidden band width of the semiconductor constituting the active layer will be reduced. A layer a of p-type GaAs with a large thickness is formed.

Next, three or more layers of two types of compound semiconductor thin films having different forbidden band widths are alternately laminated on the lower two rad layers λ to a thickness of several tens to several hundreds of times, thereby forming an active layer with a quantum well structure. . Subsequently, on the active layer, an n-type GaAs layer a layer 3, which has a large forbidden band width compared to a semiconductor and constitutes a quantum well type structure, is formed as an upper cladding layer to form a so-called double heterojunction structure.

Next, an n-type GaAs layer having a narrower forbidden band width than the upper cladding layer is grown on the upper cladding layer 3 in order to connect it to the ohmic electrode. If necessary, a p-type GaAs layer or p-type GcLA is provided between the substrate crystal l and the lower cladding layer.
The IAs layer may be provided as a buffer layer.

Once the multilayer structure is formed as described above, the top three n-type GaA layers are etched into a mesa shape using n-type aahs and glue to form a shape similar to a mask. A heated p-type impurity such as zinc (Zs) is diffused until it reaches at least the very thin semiconductor film at the bottom of the quantum well structure forming the active layer. In FIG. 2, impurity diffusion regions are indicated by diagonal lines. The depth and lateral diffusion of impurities is controlled by the impurity diffusion temperature and diffusion time. Furthermore, due to the diffusion of impurities, the active layer's impurity diffusion region constitutes a quantum well type.

The two compound semiconductors are alloyed and an impure valve train is formed.
,.

In the striped light emitting regions Ia and Jrl below the diffusion regions, that is, the n-type GaAs layers Sα and Sb, the forbidden band width is large and the refractive index is small.

Next, the mask is removed and the impurity diffusion region is covered with an insulating film 9. From above the n-type GαA 8 layers sa and rb, A
A uGeNi alloy /θ, /2 is deposited to form an n-side electrode.

Further, after polishing the back surface of the substrate, a Crku alloy is deposited to form a p-side electrode. Finally, both end faces of the multilayer structure formed are placed between the bones to form a semiconductor layer of 1゜ or - type semiconductor layer, and on top of that, an n-type impurity is implanted into the active layer by implanting a conductivity type opposite to that described above. Even if a diffusion region is formed, a semiconductor laser device having the same functions as those described above can be constructed.

Next, embodiments of this invention will be described.

Using a molecular beam epitaxy method on a p-type GaA substrate crystal that has been subjected to organic cleaning and chemical etching, a p-type G(z(1,5Alo, Bi12 layer) is formed as a lower cladding layer.
A 100A thick GaAs layer and a 7OA thick G(LIl, 7A
A total of 10 layers of 8 I0.8A layers were formed alternately, followed by a 1.5 μm thick n-type Gα layer as an upper cladding layer. , 6A1g
, 5A8 layers and a 0.5 μm thick n-type AAHS layer were crystal grown. After coating silicon nitride on the top surface of this multilayer structure, the central coaxial line has a width of about 4 μm and a length of 50 μm.
Two stripe-like regions of 250 .mu.m and 250 .mu.m were formed by photolithography with a gap of 5 .mu.m maintained.

Using these two striped regions of silicon nitride as a mask, the top n-type GaAs layer was mesa-etched, and then molten zinc heated to 600°C was applied from the top layer to the bottom of the active layer. It spread until it reached The width of the non-diffusion region of zinc in the active layer was narrower than the mask width and was approximately 2.5 μm due to the presence of lateral diffusion. Next, side-etch the part where zinc is diffused in the top n-type Gα ~ layer.
,.

Then, an oxide film was formed on the exposed one-third of the n-type Gakl layer and the s layer using an anodic oxidation method, and the silicon nitride used as a mask was removed, and two straight lines were formed. The n-type GaAs layer was removed and an insulating film was overcoated, and then a hwaeNt alloy was deposited on each of the n-type GcLA8 layers to form an n-side electrode. In addition, the bottom surface of the p-type Gaks substrate was polished and Crku was deposited on it to form a p-side electrode, and both end surfaces were made into a bone and cut to a length of about 100 yen. A semiconductor laser device with a width of 100 μm and a width of about 400 μm was obtained.

A current of 20 mA was supplied to the longer light emitting region, and a modulation current was supplied to the shorter light emitting region, and when the current was gradually increased and exceeded 45 mA, laser oscillation occurred. Moreover, when the supply current became 557FLA or less, oscillation stopped and hysteresis was exhibited. The oscillation wavelength is 8340 A at 25°C.
The semiconductor device according to the invention has a longitudinal mode temperature dependence of 0.7 A/l, which is as low as that of a DFB (distributed feedback) laser (effect of the invention). A crystal growth process for multilayer structures using molecular beam epitaxial growth or vapor phase epitaxial growth with good properties, mask formation using photolithography, and self-alignment (Selfline) that does not require difficult mask alignment techniques. By using an extremely simple impurity diffusion process, a laser diode type buried laser device was obtained in which multiple light-emitting regions with a striped quantum well structure were arranged in series, and oscillation was achieved.
゛Stable wavelength//J゛Large optical output with 7 modulation currents
; is expected to be used as a laser light source for long-distance optical transmission and analog optical transmission.

[Brief explanation of the drawing]

FIG. 1 shows a semiconductor laser device according to the present invention. , ', 1 A partially cutaway perspective view showing one embodiment, FIG. 2 shows the state of the manufacturing process of the above semiconductor laser device, and shows the state in which impurities are diffused into the multilayer structure -/S- Upper cladding layer, da...active layer, Sα, sb...n
type semiconductor, 6α, bb... impurity diffusion region of active layer,
Zaα.

Claims (2)

[Claims] (1) In a semiconductor laser device having a quantum well structure as an active layer, a plurality of striped light emitting regions having a quantum well structure are arranged in series in the laser cavity direction with a predetermined gap maintained in the center of the active layer. A semiconductor laser device characterized in that the remaining region is composed of a semiconductor having an average composition of two types of compound semiconductors constituting a quantum well structure. (2) A lower cladding layer, an active layer with a quantum well structure, and an upper cladding layer are sequentially crystal-grown on a semiconductor substrate, and a plurality of striped masks are placed on the top surface of the formed multilayer structure with a predetermined gap maintained for resonance. The impurity is diffused from the top surface of the multilayer structure until it reaches at least the bottom layer of the quantum well structure, and an electrode is deposited on each of the formed striped impurity non-diffused regions. A method for manufacturing a featured semiconductor laser device.