JP2793464B2 - Semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly to a semiconductor laser for optical communication.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional DC-PBH (double
e channel planarburied he
1 shows a cross-sectional view of a semiconductor laser having a (structure) structure. In the conventional DC-PBH laser, the carrier concentration of the p-type current blocking layer is about 1 × 10 ¹⁸ cm ⁻³ , and the carrier concentration of the p-type cladding layer is 5 × 10 ¹⁷ cm ^−3.
And a channel width of about 7.0 μm (for example, literature IEE Journal of Light Technology, IEEE.LT-1 Vol . 195-202).
Page J. L. T. , Vol. LT-1, No. 1, p
p. 195 -202 (1983) Mito et al. "InGaA
sP Double-Channel-Planar-
Buried-Heterostructure La
ser Diode (DC-PBH LD) With
Effective Current Confin
element "). DC having such a structure
The operating current of the -PBH laser at a light output of 20 mW at 85 ° C. was 90 mA or more.

[0003]

SUMMARY OF THE INVENTION Optical Ti
me Domain Reflectmeter (OT
In a high-power semiconductor laser for DR) or an environment-resistant semiconductor laser used in an optical subscriber communication system, it is desirable that the drive current be as small as possible in order to suppress heat generation from the active layer.

It is an object of the present invention to provide a DC-DC converter having such a conventional structure.
An object of the present invention is to improve the high-output characteristics or the high-temperature characteristics of the environment-resistant laser by eliminating the drawbacks of the PBH laser and reducing the drive current.

[0005]

According to the present invention, there is provided a semiconductor laser comprising a DC laser formed on an n-type or p-type semiconductor substrate.
In the PBH laser, the carrier concentration of the p-type current blocking layer located beside the active layer is 3 × 10 ¹⁷ cm ⁻³ or more, and the carrier of the p-type cladding layer above the active layer or the p-type cladding layer below the active layer is The concentration is higher than or equal to the carrier concentration of the p-type current blocking layer.

Alternatively, in a semiconductor laser having a DC-PBH structure formed on an n-type or p-type semiconductor substrate, the lateral length of a channel portion beside the active layer is 3.0 μm or more at the top. 0.0 μm or less.

Alternatively, in a DC-PBH laser formed on an n-type or p-type semiconductor substrate, the carrier concentration of the p-type current block layer located beside the active layer is 3 × 10
¹⁷ cm ⁻³ or more, and the carrier concentration of the p-type cladding layer above the active layer or the p-type cladding layer below the active layer is the p-type.
The carrier concentration is higher than or equal to the carrier concentration of the type current block layer, and the length of the channel portion beside the active layer is 3.0 μm or more and 5.0 μm or less at the top.

Alternatively, in the above semiconductor laser, the active layer is an InGaAsP well having a composition of 1.40 μm,
And an MQW (multiple quantum well) structure comprising an InGaAsP barrier having a composition of 1.13 μm.

[0009]

In order to realize a low oscillation threshold current and a high slope efficiency in a semiconductor laser, it is important to reduce unnecessary leakage current flowing in portions other than the active layer. Leakage current flowing on both sides of the active layer is suppressed to some extent by the pnpn structure of the current block layer. However, it flows into the p-type current blocking layer from the p-type cladding layer above the active layer,
When the gate current flowing through the pn junction of the channel increases, the oscillation threshold current and the slope efficiency deteriorate.

In the conventional structure, generation of a gate current flowing from the p-type cladding layer above the active layer to the p-type current blocking layer was inevitable. Particularly at high temperatures, the tan-on voltage of the p-type current blocking layer is reduced, the oscillation threshold current is increased, and the slope efficiency is reduced.

Next, FIG. 3 shows the results of analyzing the dependence of the drive current and the leakage current on the carrier concentration of the p-type current block layer at 85 ° C. and 5 mW optical output using a two-dimensional optical device simulator. Here, the calculation was performed with the carrier concentration of the p-type cladding layer being 7 × 10 ¹⁷ cm ⁻³ .
From FIG. 3, at the carrier concentration of 3 × 10 ¹⁷ cm ⁻³ ,
It can be seen that the drive current and the leakage current increase on the low concentration side or the high concentration side.

FIG. 4 is a diagram showing a structure of the current blocking layer at a position perpendicular to the active layer in the current blocking layer at a distance of 0.1 μm from the edge of the active layer.
5 is a plot of valence band edge energy at a temperature of 5 ° C. and an optical output of 5 mW. When the carrier concentration of the p-type current blocking layer is as low as about 5 × 10 ¹⁶ cm ⁻³ , p
It can be seen that the potential difference at the pn junction of the npn current blocking layer is reduced, and the current flowing through the pnpn channel region increases. However, when the carrier concentration of the p-type current blocking layer is increased to about 3 × 10 ¹⁷ cm ⁻³ , it can be predicted that the potential difference can be increased and the leakage current can be reduced.

FIG. 5 is a plot of the valence band edge energy at a temperature of 85 ° C. and an optical output of 5 mW at a position 0.1 μm above the active layer and parallel to the active layer.
When the carrier concentration of the p-type current blocking layer increases, the potential barrier between the p-type cladding layer and the p-type current blocking layer decreases, and the hole current from the p-type cladding layer to the p-type current blocking layer easily flows. I understand. Therefore, the carrier concentration of the p-type current blocking layer must be lower than the carrier concentration of the p-type cladding layer.

As described above, the p-type current flows from the p-type cladding layer if the carrier concentration of the block layer is 3 × 10 ¹⁷ cm ⁻³ or more and is lower than or equal to the carrier concentration of the p-type cladding layer. The leakage current can be suppressed, and the characteristics at high temperatures are improved.

FIG. 6 shows the channel width dependence of the drive current and the leakage current at 85 ° C. and an optical output of 5 mW. The drive current and the leakage current both have a minimum at a channel width of 3.0 μm, and tend to increase in a region where the channel width is narrower or wider.

FIG. 7 shows the breakdown of leakage current at 85 ° C. and an optical output of 5 mW. The total leakage current was plotted separately for the leakage current flowing through the channel and the leakage current flowing to the quaternary layers on both sides. As the channel width increases, the leakage current passing through the channel increases monotonically, and the total leakage current also increases accordingly. Conversely, as the channel width decreases, the leakage current flowing into both quaternary layers increases, and the total leakage current also increases.

The hole current flowing into the p-type current block layer tends to flow to the quaternary layers on both sides having a low potential. However, when the channel width increases, the distance from the p-type cladding layer to the quaternary layers on both sides increases, so that the electrical resistance between the p-type cladding layer and the quaternary layers on both sides increases, and the channel flows into the p-type current blocking layer. The leakage current flows into the n-type substrate through the channel portion. Since the leakage current corresponding to the gate current Ig of the pnpn structure increases, the tan-on voltage decreases and the driving current also increases. Conversely, when the channel width is narrow, the distance from the p-type cladding layer to the quaternary layers on both sides becomes short, so that the electrical resistance between the p-type cladding layer and the p-type current block layer decreases, and The leakage current flowing into the side quaternary layer increases, and the driving current increases accordingly.

From the above, it can be seen that when the channel width of the DC-PBH structure semiconductor laser is set to be 3.0 μm or more and 5.0 μm or less, high-temperature characteristics are improved.

[0019]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of an InGaAsP / InP-based MQW DC-PBH laser according to one embodiment.

First, an n-InP (001) substrate 1
On the n-InP buffer layer 2 using the MOVPE method
(Si: 1.2 × 10 ¹⁸ cm ^-3 dove) 0.5μ
m, 1.13 μm composition n-InGaAsP SCH layer (Si: 1.2 × 10 ¹⁸ cm ⁻³ doped) 600A
(Angstrom), 57 thick 1.40 μm composition In
GaAsP well (non-doped) and 100A thick 1.
Seven-layer MQW structure 9 composed of a 13 μm-composition InGaAsP barrier (non-doped), p-InP cladding layer 4 (Z
n: 7 × 10 ¹⁷ cm ⁻³ doped) 0.6 μm is grown, and an MQW wafer is grown. In this embodiment, MOVPE
The method is used, but this is also possible in the LPE method or the MBE method.

Next, using a stripe mask having a center interval of 3.2 μm for forming a DC-PBH mesa and a width of 1.0 μm in a double channel portion, a length in a lateral direction on an MQW wafer by a Br-methanol type etchant. Is at the top
A double channel 10 having a width of 0 μm (channel width) is formed. Then, the double channel 10 formed on the MQW wafer by the LPE method is formed by p-InP5 (Zn: 3 × 1).
0 ^{1 7} cm ^{- 3} doped), n-InP6 (Si: 7 × 1
0 ¹⁷ cm ^-3 dope) is sequentially grown.

When the p-side and n-side electrodes were formed on the wafer manufactured based on the above-described steps and evaluated,
The operating current at 5 ° C.-20 mW is 85 mA, which can be reduced by 5 mA or more compared to the conventional structure (about 90 mA).

The present invention relates to the InGaAsP /
AlGaAs as well as InP DC-PBH laser
Also applicable to / GaAs-based DC-PBH lasers.

[0024]

According to the DC-PBH laser of the present invention, the driving current can be reduced, and the high-output characteristics or high-temperature characteristics can be improved.

[Brief description of the drawings]

FIG. 1 shows an InGaAsP / InP MQW according to the present invention.
It is sectional drawing of a DC-PBH semiconductor laser.

FIG. 2 is a sectional view of a DC-PBH semiconductor laser having a conventional structure.

FIG. 3 is a diagram showing the dependence of the drive current and the leakage current on the carrier concentration of a p-type current block layer.

FIG. 4 is a diagram for explaining valence band edge energy.

FIG. 5 is a diagram for explaining valence band edge energy.

FIG. 6 is a diagram showing channel width dependence of drive current and leakage current.

FIG. 7 is a diagram showing channel width dependence of leakage current.

[Explanation of symbols]

Reference Signs List 1 n-InP (001) substrate 2 n-InP buffer layer 3 MQW structure 4 p-InP cladding layer (Zn: 7 × 10 ¹⁷ cm)
⁻³ doped) 5 p-InP current blocking layer (Zn: 3 × 10 ¹⁷⁾
cm ^{- 3} doped) 6 n-InP current blocking layer 7 p-InP layer 8 p-InGaAsP cap layer 9 MQW active layer 10 double channel (3.0 [mu] m width) 11 n-InP (001) substrate 12 n-InP buffer layer 13 MQW structure 14 p-InP cladding layer (Zn: 5 × 10 ¹⁷ cm
⁻³ doped) 15 p-InP current blocking layer (Zn: 1 × 10 ¹⁸⁾
cm ⁻³ doped) 16 n-InP current blocking layer 17 p-InP layer 18 p-InGaAsP cap layer 19 MQW active layer 20 double channel (7.0 μm width)

Claims (3)

(57) [Claims] In a semiconductor laser having a DC-PBH structure formed on a semiconductor substrate, a lateral length (channel width) of a channel portion beside an active layer is not less than 3.0 μm and not more than 5.0 μm at an uppermost portion. A semiconductor laser, comprising: 2. A DC-PBH laser formed on a semiconductor substrate, wherein the p-type current blocking layer located beside the active layer has a carrier concentration of 3 × 10 ¹⁷ cm ⁻³ or more, and is formed on the active layer or on the active layer. The carrier concentration of the p-type cladding layer below the layer is higher than or the same as the carrier concentration of the p-type current blocking layer, and the lateral length of the channel portion beside the active layer is 3.0 μm or more at the uppermost portion. A semiconductor laser having a thickness of 0 μm or less. 3. An InGaAs having an active layer of 1.40 μm composition.
3. The semiconductor laser according to claim 1, wherein the semiconductor laser has an MQW (multiple quantum well) structure including a P-well and an InGaAsP barrier having a composition of 1.13 [mu] m.