JPS60107886A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To enable a semiconductor laser to maintain low-noise characteristics even when a readout of recorded results is performed at lower-photo output by a method wherein plural lasers, whose oscillation threshold value currents different from each other, are formed on the same semiconductor substrate. CONSTITUTION:Buried semiconductor lasers A and B, whose mesa widths are different from each other at a ratio such that one side is about 1mum and the other side is about 2mum, for example, are formed on a semiconductor substrate 1 at a prescribed interval. As the widths of the active layers 4 of the lasers A and B different at a ratio such that one side is about 1mum and the other side is about 2mum, the oscillation threshold value currents of the lasers A and B become a respectively different oscillation threshold value current of about 25mA and about 50mA. In such the laser A, about -144dB/Hz of noise can be obtained when the oscillation threshold value current is 25mA and the output is 2mW, while in the laser B, about -130dB/ Hz of noise can be obtained when the oscillation threshold value current is 50mA and the output is 2mA, and about -160dB/Hz of noise can be obtained when the oscillation threshold value current is 50mA and the output is 20mW. Accordingly, when optical recording is performed, the region of the laser B is used, while in case the recorded results on a medium are read out under a photo output operating condition of 2mW or thereabouts, the region of the laser A is used. As a result, the semiconductor laser can be made to operate at a high S/N ration.

Description

[Detailed description of the invention] The present invention relates to a semiconductor laser device.

A multilayer semiconductor laser using a tilted structure such as AJGaAs or Ig+GaAse is capable of highly efficient laser oscillation operation and is widely used in applications such as optical fiber communication, and is also applicable to digital signal processing systems and analog signal processing systems. The area is expanding. In particular, it has a function of writing to and reading from a recording medium using optical signals. I) R.A.
W (1) direct TLead AfterWri
te) Application of semiconductor lasers to equipment Along with the significant improvement in recording density, it is possible to improve the speed of data processing and readout, and the expansion of information processing functions is expected. Writing/reading devices using semiconductor lasers use the same semiconductor laser light source, so they inherently have the disadvantage of being susceptible to noise. To illustrate this situation, the noise of the semiconductor laser will be briefly explained using FIG. Figure 1 shows the drive current (Il) and optical output (Ll characteristics) of a semiconductor laser, the noise components included in the optical output (Il, IN), and the drive current (Il characteristics). There is almost no change even if the ingredients are changed, and it is based on the oscillation principle of semiconductor lasers.
Noise component of 8-conductor laser ()1. It is known that it is large near the IN) tri oscillation threshold ('th), becomes smaller as the drive current increases (light output increases), and is expressed as nxNoc(I/Ith1)-3.

Therefore, the optical output of the semiconductor laser is approximately 20 mW -CNt
When recording on a medium and reading the recorded result with an output of about 2 mW, the noise component is 16 at an optical output of 20 mW.
0 d137Hz or less, which is a sufficiently small value, but about 2
When reading with mW output, the noise component is 1130d1
3/'1-1 z, and in a state where there are many voices of 30d1 and 12 or more (number 8), the disadvantage of easily causing a readout error was unavoidable.Here, when reading By increasing the optical output to about 10 mW, the noise component can be improved to about -150 dR/)lx, but if reading continues for a long time in this condition, the high optical output will cause the media listed above to deform. It is not possible to unnecessarily increase the optical output at the time of reading because this will result in a re-recording state.

An object of the present invention is to eliminate such drawbacks of the conventional structure and to provide a highly reliable semiconductor laser device that maintains low noise characteristics even when reading at low r'r and output. The semiconductor laser device of the present invention has a structure characterized in that a plurality of semiconductor lasers having at least 10 different oscillation thresholds are formed on a semiconductor substrate.

Embodiments of the present invention will be described below with reference to the drawings. FIGS. 2 and 3 are a cross-sectional view of the structure of a semiconductor laser device in which the present invention is implemented, and its current (Il - light output (Ll) 2 is a diagram showing current (Il-noise (RIN) characteristics. The structure of the semiconductor laser device of the example is as shown in FIG. 2. First, an n-type GaAs
On substrate m, n-type A/~iGa fi:t(・As layer (2), n-type AI!, Jo, Ga7,7As layer (3),
At>/i Ga 7 houses A3 layer (4), which becomes the active layer.
p-type Al! ), (! Ga7 (pattern ΔS layer (5), p-type G
AAs layers (6) are sequentially formed. The thickness of each layer is 1.
0μm, 0.7μm, 0.111m, 1.0μm1
After obtaining the ioL using a standard value of 05 μm, mesa etching is performed using a chemical etching solution (Hs PO4 + HtOt +3 CHsOH) to a depth that reaches the 0aks substrate (1) as shown in Figure 2 to form a band-shaped mesa region having an active region. Form multiple pieces. In this embodiment, as a typical example of different oscillation threshold currents, FIG. 2 shows an example having two mesa regions with different widths, and a narrow mesa region (arrow A on the left side of the figure). The active layer width of the active layer is about 1 μm1 in the wide mesa region (arrow 8 on the right side of the figure). 41
Kii is approximately 2μm, and the distance between both mesas is 1M'? + is about 50
μm〇Next, as shown in Fig. 2, in the second crystal growth process, as shown in Fig. 2, the side surface of the mesa region is covered with n-type A, zeOax7
lil(71, p Jjl At p, j Ch ′
I, 7ΔS layer (8), n-type Ali age (, + a p2.
After sequentially forming the As layer (9), a p-type impurity diffusion layer 0111. is formed by Zn diffusion. 8i for electrode separation
02) Possessing θ force and p-type memic °1! lL pole Q4
．． A semiconductor laser device according to the present invention is formed by forming an 11-type ohmic 1←, pole Q: Li.

In the tree structure -r#J:, 50 at intervals on the same semiconductor substrate
Two different buried 81J seat lasers A and B with a mesa width of about 1 μm and a width of about 2 μm are formed, each having an independent semiconductor laser operation using a separated p-type ohmic electrode. You can have the righteousness to act. Here, since the active layer widths of semiconductor lasers A and 8 are different, each being about 1 μm and the other about 2 μm, the currents of the oscillation 1rAl lfj will be different, about 25 mA and about 50 mA. In the A and 13th generations, the respective drive current (I) - optical output (Ll characteristics and drive current (Il - noise (
RIN) characteristics. In semiconductor laser A, the noise (IN) when the oscillation threshold current is 25 mA and 2 mW output is approximately -144 dB/Hz, while in semiconductor laser B, the noise when the oscillation threshold current is 50 mA and 2 mW output is approximately -144 dB/Hz. (
RIN) is approximately -130dB/It-1x, 20m
The sound of W output (R, IN) is approximately -160dB/Hz
Therefore, the optical output was reduced to about 20 mW.
When performing optical recording on a recording medium at a high power output of about 2 mW, laser recording is performed using the B region of the semiconductor laser according to this embodiment. By using the A region of the semiconductor laser, the noise at 2 mW output (⇠IN
) to approximately -140dQ/1 (z, high 87N
This enabled us to create a long-term semiconductor laser light source with little readout error. As shown in this example, in a semiconductor laser in which the oscillation threshold current is reduced by reducing the mesa width and the noise component is reduced,
In addition to the low-output readout operation (about 20mW high-output operation), when the optical recording operation is performed, the active WI
Because the width is narrow and the cross section of the excavated light is small, the reflective mirror surface of the semiconductor laser and the phase separation in its vicinity are destroyed by the heat generation phenomenon caused by high optical output density operation (this is called destruction due to high optical output density operation, and is an essential phenomenon in semiconductor lasers. There is), the third
As shown in the figure, the maximum optical output of the KA domain semiconductor laser is 12
It should be noted that the limit is approximately 13 mW. In addition, in the semiconductor laser of this example, since the distance between the two laser regions is narrow, approximately 50 μm, the two light beams can be collimated and focused using a commonly used optical system as is. It has a % characteristic.

Furthermore, FIG. 4 shows another embodiment according to the present invention. In the structure shown in Figure 4, unlike the previous example, 1
In the case of an O+IAs substrate (1) showing an application example of the present invention, which can be formed by multiple liquid phase crystal growth steps,
Standard photoresist process and selective chemical etching (
A V-shaped groove with a width of about 3 μm and a depth of about 1 μm and a width of about 51
Concave grooves with a depth of 1 m and approximately 111 m are formed at intervals of approximately 50 μm. After this, a liquid phase crystal growth process is performed to form n-type grooves.
, a OII'e, 7" H (31, kl゛2.
yOrito As1 (41, p type A/ip, J (ja d
y As layer (81, n-type GaAs layer 0 → is formed sequentially 0ζ where the layer thickness of each layer is n-type AZ p, ・a' Ga
>, 7 As jf't (31 is about 0.2 μm outside R1, Al t), 'l' Ga Il,
P'As 1tii (41 is α1μm% p-type Al
'pJOa azAs j comparison (s+ is about 1.5 μm,
The thickness of the n-type 0aAs layer was approximately 1.0 μm. Next, similarly to the above-mentioned structure example shown in FIG.
Another embodiment of the present invention is formed by forming an impurity diffusion layer 0 (l), 8i02 scraps ◇υ for electrode separation, and a p-type ξ oak cloth frame θ and an n-type ohmic electrode a1.

In this structure, as shown in FIG. 4, the groove width of the semiconductor laser in region A is narrow, and the emission spot is approximately 1.2 mm.
In addition to being on the order of μm, the p-type impurity diffusion width is approximately 3 μm.
Due to the narrow width of m, the oscillation threshold current is approximately 30mA, and the optical output is 2m~V.
Time noise (TIIN) approximately -140dB/1-1x K
On the other hand, the semiconductor laser in region B has a wide groove and a large emission spot of about 2511 m.
In addition, since the p-type impurity diffusion width is as wide as approximately 6 μrl+, the opening (
, Shak]n i reconnaissance, flow rate 6 (l woA with high output 1 mountain production d'i'JfJhi becomes about "l OmW
By using semiconductor lasers A and 8 in close proximity to each other, write and read data with high S/N characteristics can be obtained. It has a row that can be formed by four consecutive growth steps.

- laser and a semiconductor laser that enables high output operation of about 20 mW are formed on the same substrate in close proximity to each other. Therefore, multiple optical systems are prepared to combine each laser beam into one ? Since light does not need to be focused and can be focused with a single optical system, it is possible to use a conductor with excellent noise characteristics for both rock-in and R>F-extrusion operations. can be provided.

In the above embodiments, an example using an AlGaAs-based semicircular material is described, and ft is In0aAsP.
It goes without saying that the same effect can be obtained by using other semiconductor materials such as thread, but in the above embodiment, as a means of differentiating the detection flow from one another, the width of the stripes in the active region is varied. However, there are other methods, such as (
The same effect as in the above embodiment can be obtained by (b) changing the thickness of the active layer, (b) changing the lifetime fc of carriers in the active layer (changing the impurity concentration, introducing a deep level, etc.).

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the drive current-optical output characteristics and drive current-noise characteristics of a semiconductor laser, FIG. 2 is a cross-sectional view of the structure of an embodiment of the semiconductor laser device according to the present invention, and FIG. FIG. 4 is a diagram showing drive current-optical output characteristics and drive current-noise characteristics of a semiconductor laser according to an embodiment, and is a structural sectional view of another embodiment according to the present invention. In each figure, 1: n-type GaAs substrate 2: n-type Alj near Ga 4.6 As layer 3:
nm, At h, C3*,? , Z As layer 4
: Al #','/'Ga'7. pAs f@
5: p-type Aed, 7 Gap, (Asso: p-type GaA
S layer 7: n-type A/ #, 'd'' (1a 6., y As layer 8: p-type Al p, ?C1a /, 7 As layer 9: n
Type A/>, J Ga I, p, 7. As layer 10:p
type impurity diffusion layer 11: 8i02 layer 12: p-type ohmic electrode 13: n-type ohmic electrode 14: n-type GRAS layer. Figure 1 lN 2O3046506070θθ qo to. 1 (MA) Fig. 2 A f3 Fig. 3 IN zo so 40so 6o 'to no qot
o. 1, (fllA)

Claims (1)

[Claims] A semiconductor laser device characterized in that a plurality of semiconductor lasers having at least different oscillation threshold currents are formed on a semiconductor substrate〇