JPH0595157A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser which can control the oscillated wave length easily and the check the trouble such as that the short wavelength does not oscillate by the increase of the gain on an active region, by equipping it with a nondoped active layer, a mesa type ring-shaped second clad layer, a cap layer, a current block layer, an electrically isolating area, etc., which are severally specific. CONSTITUTION:This device is equipped with a substrate 1, a first clad layer 3, a light waveguide path layer 3, a nondoped active layer 4 having quantum well structure, and a mesa type ring-shaped second clad layer 5, which consists of first and second rings 5a and 5b widths several times as wide as the oscillated wavelength and diameters several hundred times as long as the oscillated wavelength and in which the intervals between the rings are tens of times as long as the oscillated wavelength. Furthermore, it is equipped with cap layers 6a and 6b made thereon, a current block layer 7, the first electrode 9, the second electrode 10, and an electric isolating area 8, which is made in the current block layer 7 between the first and second rings 5a and 5b, the second clad layer 5, the active layer 4, the light waveguide path layer 3, and the first clad layer 2 to reach the substrate 1.

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, and more particularly to a semi-circular ring double hetero structure multi-wavelength laser array 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, a wavelength tunable semiconductor laser using a reference level and a high-order level in a quantum well layer has been proposed as a method of making the wavelength tunable (JP-A-63-32985). This semiconductor laser is capable of oscillating at various quantum levels by dividing the current injection electrode into a plurality of parts and controlling the injection current level to each injection electrode independently. It is characterized by.

The principle of variable wavelength will be described below. In the case of an active layer having a quantum well structure, as the injection current increases, the gain curve in the active layer has a maximum gain of a low energy gap (hereinafter referred to as Eg) as shown in FIG.
It is well known to shift from the (long wavelength) side to the high Eg (short wavelength) side. As described above, in a semiconductor laser having an active layer having a quantum well structure, long-wavelength light oscillates when current is uniformly injected in the cavity direction. That is, the light corresponding to low Eg is oscillated in a state where the total loss in the resonator is low. 2 is a band diagram corresponding to FIG.

In addition, in this semiconductor laser, short-wavelength light oscillates when current is nonuniformly injected. On this occasion,
Since the gain is small in the loss region, a large amount of current is injected to increase the gain in the gain region. In particular, since the gain on the short wavelength side in the loss region is very small, the injection current into the gain region is made very large so that the total gain in the resonator becomes the maximum in the short wavelength light.

Here, the uniform injection in the resonance direction means a state in which light and electrons in the active layer are injected at the same current density in the resonance direction of the light in the active waveguide.
On the other hand, even if the current density is uniform over the length in the resonance direction in a certain region, non-uniform injection is a state in which the current density is different in each region in all resonators. Further, in order to make the injection current into each region different, a separation portion is required between the regions. No electric current is injected into this separated portion even during uniform injection. However, if this separation portion has a length of 10 μm or less, it can be regarded as a substantially uniform injection state in consideration of carrier spreading inside the active layer. As described above, the conventional variable wavelength method oscillates long-wavelength light during uniform injection and oscillates short-wavelength light during nonuniform injection.

[0006]

However, according to the prior art, the length of the absorption wavelength is very important, and if the absorption region at the time of nonuniform injection is long, the loss amount of short wavelength light becomes large,
Even if the gain of the active region is increased, the short wavelength light may not oscillate. The reason for this is that the gain on the short wavelength side in the loss region significantly decreases as the injection current decreases, but the gain on the short wavelength side in the gain region shows a saturation tendency as the injection current increases, and This is because a state in which the loss of the short wavelength light cannot be completely compensated occurs.

The present invention has been made in view of the above circumstances, and the semiconductor laser device can control the oscillation wavelength more easily than before and can prevent the case where the short wavelength light does not oscillate due to the increase in the gain of the active region. The purpose is to provide.

[0008]

The present invention provides a substrate, a first cladding layer formed on the substrate, an optical waveguide layer formed on the first cladding layer, and an optical waveguide layer on the optical waveguide layer. A non-doped active layer having a formed quantum well structure,
The first and second rings are formed on the active layer and have a width of several times the oscillation wavelength and a ring diameter of at least 100 times the oscillation wavelength. The spacing between the rings is at least several tens of times the oscillation wavelength. A mesa ring-shaped second clad layer, a cap layer formed on each of the first and second rings of the second clad layer, and a current block formed in a bottomed region and an outer peripheral region of the second clad layer. Layer, the current blocking layer, the first electrode formed on the cap layer, the second electrode formed on the back surface of the substrate, the current blocking layer between the first and second rings, the second cladding layer A semiconductor laser device comprising: an active layer, an optical waveguide layer, and an electrical isolation region formed so as to reach the substrate in the first cladding layer.

[0009]

In the present invention, the relationship between the semicircular ring diameter and the waveguide loss is an important parameter.
"GaAs-AIGaAs Half-Circular Ring Laser by High Concentration Zinc Diffusion" (GaAs-AIGaAs Half Ring Las)
er Fabricated by Deep Zn Diffusion) data is shown in FIG. Set the ring radius to the oscillation wavelength λ ₀ (0.85μ
m) is shown as standardized to show the optical loss as a normal stripe ray.
It is the figure standardized by the value of Z.

According to FIG. 5, the loss is 10 times (up to 250 cm ^-1 ) at a radius of 150 μm, while the loss is 2.0 at a radius of 300 μm.
It is remarkably reduced by a factor of two (up to 50 cm ^-1 ), and at a radius of 800 μm or more, the substantially striped waveguide and its loss do not change at all. Therefore, the oscillation wavelength can be made variable by the waveguide loss estimated from the ring diameter, and the current injection method can be uniform.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

Reference numeral 1 in the figure is an n-type (100) GaAs substrate (Si doped, impurity concentration 2 × 10 ¹⁸ cm ^-3 ). On the substrate 1, an n-type AI _0.45 Ga _0.55 having a thickness of 1.5 μm is formed.
As first cladding layer 2 (Si doping, impurity concentration 2 × 10 ¹⁷
cm ^-3 ) are formed. An n-type AI _0.3 Ga _0.7 As optical waveguide layer 3 having a thickness of 50 nm is formed on the first cladding layer 2.
(Si doping, impurity concentration 2 × 10 ¹⁷ cm ⁻³ ) is formed. A non-doped active layer 4 having a quantum well structure (a single quantum well structure having a GaAs well width of 10 n is formed on the optical waveguide layer 3).
m) has been formed. A thickness of 1.5 is formed on the active layer 4.
A μm-thick p-type AI _0.45 Ga _0.55 As second cladding layer 5 (Mg doped, impurity concentration 5 × 10 ¹⁸ cm ⁻³ ) is formed. Here, the second cladding layer 5 is in the shape of a mesa ring, and the upper portion is the first ring 5a and the second ring 5b whose width is several times the oscillation wavelength and whose ring diameter is at least 100 times the oscillation wavelength or more. Therefore, the distance between the rings 5a and 5b is at least several tens of times the oscillation wavelength.

On the first ring 5a and the second ring 5b, a p ⁺ -type GaAs cap layer 6a having a thickness of 1 μm,
6b (Mg doping, impurity concentration 5 × 10 ¹⁸ cm ⁻³ ) is formed. In the bottomed region and the outer peripheral region of the second cladding layer 5, a current blocking layer 7 (Si doping, impurity concentration 3) is formed.
× 10 ¹⁸ cm ^-3 ) are formed. The current blocking layer 7, the second cladding layer 5, the non-doped active layer 4, the optical waveguide layer 3 and the first cladding layer 2 between the first and second rings are electrically separated so as to reach the substrate 1. Ga ⁺ as a region
An ion implantation region 8 is formed. A p-type electrode 9 as a first electrode is formed on the current blocking layer 7 and the cap layers 6a and 6b. An n-type electrode 10 as a second electrode is formed on the back surface of the substrate 1.

Next, a method of manufacturing a laser array having such a structure will be described. (1) First, the first cladding layer 2, the optical waveguide layer 3, the non-doped active layer 4, the second cladding layer 5 and the cap layers 6a and 6b are successively grown on the substrate 1 in sequence. Next, a 400 nm-thick Si film was formed by CVD on the entire surface of the grown wafer.
An O ₂ film is attached, and a circular double ring pattern having a ring width of 6 μm, a ring radius of 150 μm and a ring radius of 300 μm is formed by photolithography. Next, the thickness of the bottom portion of the second cladding layer 5 is 0.3 μm with a phosphoric acid-based etching solution.
Remove the remaining m.

(2) Next, using the MOVPE growth technique,
The current blocking layer 7 is buried in a mesa ring shape by selective burying growth. Next, a 400 nm-thick Si film was formed on the entire surface by CVD.
An O ₂ film is attached and a ring-shaped window having a width of 20 μm is formed in the central portion of the double ring by photolithography. Then, the current blocking layer 7, the second cladding layer 5, the non-dope active layer 4, the optical waveguide layer 3 and the first cladding layer 2 between the first and second rings are reached until reaching the substrate 1 through this window. the Ga ⁺ de in - ion-implanted with's weight ^{4 × 10 14 cm -2, 700} ℃, 20 minutes anneal in arsenic atmosphere - and Le, Ga ⁺
The ion implantation region 8 is formed. After that, the SiO ₂ film is removed.

(3) Next, the cap layers 6a and 6b on the surface are removed by etching by 0.5 μm to form the cap layers 6a and 6b. Subsequently, the n-type electrode 10 is formed on the back surface of the substrate 1. Further, after cleaving at the center of the ring of the wafer, an oxidation protection film (not shown) is formed on the cleaved end face to form a laser array.

The laser array having the above construction operates as follows. The carriers injected from the p-type electrode 9 are injected only into the central portion of the mesa because both sides of the mesa ring are covered with the current block layer 7. In this structure, since the quantum well structure is used for the active layer 4, the wavelength loss of the differential gain causes the waveguide loss to be 1 / th that of the ordinary bulk.
It is 2 to 1/3, and the light generated by carrier recombination in the active layer 4 is efficiently returned by repeating the return at both end faces of the ring.
The oscillation. In the above-mentioned embodiment, 4 μ in the narrow mesa width portion.
m, residual amount of the second cladding layer is 0.3 μm, active layer thickness, guide layer thickness, the effective refractive index difference between the central portion of the mesa and the horizontal direction is estimated to be 8 × 10 ^−3, and a stable single Mode
This is the condition under which the de-oscillation is obtained.

Hirayama et al., "Electrical characteristics of Ga ion beam-implanted GaAs epilayers", published in 1985, European Society of Applied Physics, Vol. 24, p. 965 (Japan. J.
Applied Physics, vol24. L965, "Electrical
Properties of GaIon Beam Implanted GaAa
According to "Epilayer", when Ga ⁺ ion implantation is performed and annealing is performed at 700 ° C., the crystal damage is recovered, but the resistance value rises by five digits, and the state does not change. It can be completely separated from the ring.

By the way, the size of the inner ring diameter and the outer ring diameter bends to cause a large difference in waveguide loss, and in the case of bulk, a difference of 5 times occurs, and the total waveguide loss of the inner ring is 250 cm. ^-1 , which is 1/2 to 1 in the quantum well structure
Since it is reduced to / 3, it is estimated to be around 100 cm ^-1, and the total waveguide loss of the outer ring laser is estimated to be equivalent to the waveguide loss of a normal mesa stripe laser. Therefore, in the ring laser shown in Fig. 4, the waveguide loss is 100 cm ^-1 , and the oscillation wavelength is estimated to be around 800 nm. On the other hand, in the outer ring laser, the waveguide loss is estimated to be 30 cm ^-1 or less,
The oscillation wavelength is considered to be around 850 nm, and a dual wavelength laser can be expected.

According to the laser array according to the above embodiment,
The active layer has a quantum well structure, the differential quantum gain becomes steep, and an element having high efficiency and good temperature characteristics can be realized while having a structure in which the MOVPE technology excellent in controllability and mass productivity can be used.

Further, since the waveguide has a ring shape, a radiation mode easily exists in addition to the waveguide mode, but the waveguide loss can be reduced to 1/2 to 1/3 of the bulk. Furthermore, by changing the ring diameter, the transition between low level transitions changes to high level transitions, that is, multiple wavelengths can be achieved, and a long resonator laser is realized to increase the diameter to reduce loss. It is also effective in achieving high efficiency and high output, and it is considered that there is not much difference in operating current in practical use between the inner and outer ring lasers. It can be expected that there is no significant difference in operating current in consideration of the correspondence between the waveguide loss and the resonator length.

Further, as a quantum well, the well width of GaAs is changed, a modulation well width structure and a multi-wavelength semi-circular ring laser array are expected to be used as a light source for a parallel multi-wavelength read / write optical disk.

[0023]

As described above in detail, according to the present invention, the semiconductor laser device can control the oscillation wavelength more easily than before and can prevent the case where the short wavelength light does not oscillate due to the increase in the gain of the active region. Can be provided.

[Brief description of drawings]

FIG. 1 is a perspective view of a semi-circular ring double hetero structure multi-wavelength laser array according to an embodiment of the present invention.

FIG. 2 Conventional semicircular ring double heterostructure multiwavelength laser
FIG. 3 is a characteristic diagram showing the relationship between gain and wavelength in the array.

FIG. 3 is a band diagram corresponding to FIG.

FIG. 4 is a characteristic diagram showing the relationship between wavelength and gain in the outer and inner ring lasers.

FIG. 5: GaAs-AIGaAs by high-concentration zinc diffusion
The characteristic view which shows the relationship between the standard optical bending loss in a semicircle ring laser, and the standard radius.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... GaAs substrate, 2 ... 1st cladding layer, 3 ... Optical waveguide layer, 4 ... Non-dope active layer, 5 ... 2nd cladding layer, 5
a, 5b ... Ring, 6a, 6b ... Cap layer, 7 ... Current blocking layer, 8 ... Ga ⁺ ion implantation region, 9 ... P-type electrode, 10 ... N-type electrode.

Claims (1)

[Claims] 1. A substrate, a first cladding layer formed on the substrate, an optical waveguide layer formed on the first cladding layer, and a quantum well structure formed on the optical waveguide layer. A non-doped active layer and formed on the active layer,
A second mesa-type ring-shaped cladding layer having a width of several times the oscillation wavelength and a first and second ring having a ring diameter of at least 100 times the oscillation wavelength and an interval between the rings of at least several tens of times the oscillation wavelength. And the first and second clad layers
A cap layer formed on each of the rings, a current blocking layer formed in a bottomed region and an outer peripheral region of the second cladding layer, a first electrode formed on the current blocking layer and the cap layer, and The second electrode formed on the back surface of the substrate, the current blocking layer between the first and second rings, the second cladding layer, the active layer, the optical waveguide layer, and the first cladding layer are formed to reach the substrate. And an electrically isolated region.