JP2001189528A - Semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser element in which operating speed is increased sufficiently. SOLUTION: A carrier storage preventive layer 8 having a striped opening section in the top face of a ridge section, a low carrier concentration layer 9 and an N-current block layer 10 are formed successively on a P-clad layer 6 with a ridge section. The low carrier concentration layer 9 has carrier concentration lower than the N-current block layer 10. The band gap of the carrier storage preventive layer 8 is set between that of the p-clad layer 6 and that of the low carrier concentration layer 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser device having a refractive index waveguide structure.

[0002]

2. Description of the Related Art Conventionally, a semiconductor laser device having a refractive index waveguide structure in which a refractive index difference is given in a direction parallel to an active layer to form an optical waveguide has been developed. FIG. 23 is a schematic cross-sectional view of a conventional semiconductor laser device described in Japanese Patent Application Laid-Open No. 8-222801.

In a semiconductor laser device 120 shown in FIG. 23, an n-type cladding layer 122, an active layer 123, a p-type cladding layer 124, and a p-type contact layer 127 are sequentially formed on an n-type substrate 121, and the p-type contact layer 127 is formed. Then, the p-type cladding layer 124 is etched to form a ridge portion and flat portions on both sides of the ridge portion.

Furthermore, a low carrier concentration layer 125 is formed on a flat portion on both sides of the ridge portion of the p-type cladding layer 124, and the n-type current blocking layer 1 is formed on the low carrier concentration layer 125.
26 are formed. The p-type contact layer 12 is formed on the p-type contact layer 127 and the n-type current block layer 126.
8 are formed.

When the semiconductor laser device 120 is driven, a reverse bias is applied to a pn junction between the n-type current blocking layer 126 and the p-type cladding layer 124. Thereby, the current is cut off by the n-type current block layer 126,
The current is confined and injected into the ridge.

In general, a pn junction formed between an n-type current blocking layer and a p-type cladding layer has a large electric capacity, which hinders a high-speed operation of a semiconductor laser device. The electric capacity of the pn junction increases as the carrier concentration at the pn junction increases.

Therefore, the semiconductor laser device 120 shown in FIG.
, A low carrier concentration layer 125 is provided in order to reduce the electric capacity at the pn junction between the n-type current blocking layer 126 and the p-type cladding layer 124.

[0008] The low carrier concentration layer 125 has a lower carrier concentration than the n-type current blocking layer 126. Therefore, a depletion region is formed at the pn junction between the n-type current blocking layer 126 and the p-type cladding layer 124 by the low carrier concentration layer 125, and the electric capacity is reduced. Thereby, high-speed operation of the semiconductor laser device 120 becomes possible.

[0009]

However, in a semiconductor laser device having a complex refractive index waveguide structure, the band gaps of the n-type current blocking layer and the low carrier concentration layer are made smaller than the band gaps of the p-type cladding layer, and the active band gap is reduced. The lateral mode control is performed by absorbing the light generated by the layer in the n-type current blocking layer and the low carrier concentration layer.

FIG. 24 schematically shows an energy band diagram of a valence band of a p-type cladding layer and a low carrier concentration layer in a semiconductor laser device having a complex refractive index waveguide structure. As shown in FIG. 24, since the band gap of the low carrier concentration layer is sufficiently smaller than the band gap of the p-type cladding layer, carriers are easily injected from the p-type cladding layer to the low carrier concentration layer and accumulated. The accumulation of carriers in the low carrier concentration layer inhibits depletion at the pn junction. As a result, the electric capacity at the pn junction between the n-type current blocking layer and the p-type cladding layer increases, and high-speed operation cannot be sufficiently achieved.

An object of the present invention is to provide a semiconductor laser device capable of sufficiently operating at high speed.

[0012]

According to the semiconductor laser device of the present invention, a first cladding layer of a first conductivity type is provided on an active layer, and a first cladding layer is provided except for a current injection region.
A current blocking layer of the second conductivity type is provided on the cladding layer of the second type, and a low carrier concentration layer having a lower carrier concentration than the current blocking layer is provided on the current blocking layer side between the first cladding layer and the current blocking layer. A carrier accumulation preventing layer is provided on the first cladding layer side between the first cladding layer and the current blocking layer to prevent accumulation of carriers in the low carrier concentration layer.

In the semiconductor laser device according to the present invention, the accumulation of carriers from the first cladding layer to the low carrier concentration layer is prevented by the carrier accumulation preventing layer. Thereby, the depletion state of the low carrier concentration layer is maintained. Therefore, the electric capacitance between the current blocking layer and the first cladding layer is kept small, and the high speed operation of the semiconductor laser device is sufficiently achieved.

The band gap of the first cladding layer, the carrier accumulation preventing layer and the low carrier concentration layer may be reduced in this order.

Thereby, a carrier accumulation preventing layer having an intermediate band cap is provided between the first cladding layer having a large band gap and the low carrier concentration layer having a small band gap.

In this case, the energy difference between the first cladding layer and the carrier accumulation preventing layer is smaller than the energy difference between the first cladding layer and the low carrier concentration layer.
Carriers are less likely to be injected from the first cladding layer into the carrier accumulation preventing layer, and carriers are less likely to be injected into the low carrier concentration layer. In addition, since carriers are separately injected from the first cladding layer into both the low carrier concentration layer and the carrier accumulation preventing layer, the amount of carriers accumulated in the low carrier concentration layer is reduced. In this manner, the accumulation of carriers in the low carrier concentration layer can be prevented with a simple configuration in which the band gap of the carrier accumulation preventing layer is set to an intermediate value between the low carrier concentration layer and the first cladding layer. it can.

The first cladding layer has a flat portion formed on the active layer and a ridge portion formed on the flat portion in the current injection region. The carrier accumulation preventing layer has flat portions on both sides of the ridge portion. The low carrier concentration layer and the current blocking layer formed on the carrier and the side surface of the ridge may be sequentially formed on the carrier accumulation preventing layer.

In this case, the first layer is formed by the carrier accumulation preventing layer.
From the flat portion of the cladding layer is prevented from accumulating in the low carrier concentration layer. Thereby, the depletion state of the low carrier concentration layer is maintained, and the electric capacity between the flat portion of the first cladding layer and the current blocking layer is maintained small.

Preferably, the thickness of the carrier accumulation preventing layer is 10 nm or more. Thereby, the high-frequency characteristics of the semiconductor laser device are further improved.

The thickness of the carrier accumulation preventing layer is preferably at least 15 nm. Thereby, the high-frequency characteristics of the semiconductor laser device are further improved.

The carrier accumulation preventing layer is formed on the first cladding layer, a ridge-like second cladding layer of the first conductivity type is further provided on the carrier accumulation preventing layer in the current injection region, and a low carrier concentration is provided. The layer and the current blocking layer may be sequentially formed on the carrier accumulation preventing layer on both sides of the second cladding layer and on the side surface of the second cladding layer.

In this case, the first layer is formed by the carrier accumulation preventing layer.
The accumulation of carriers from the cladding layer of the above to the low carrier concentration layer is prevented. Thereby, the depletion state of the low carrier concentration layer is maintained, and the electric capacity between the first cladding layer and the current blocking layer is maintained small.

The thickness of the carrier accumulation preventing layer is preferably at least 15 nm. Thereby, the high-frequency characteristics of the semiconductor laser device are further improved.

The thickness of the carrier accumulation preventing layer is preferably at least 20 nm. Thereby, the high-frequency characteristics of the semiconductor laser device are further improved.

The carrier accumulation preventing layer, the low carrier concentration layer, and the current blocking layer are formed sequentially on the first cladding layer except for the current injection region. In the current injection region, the carrier accumulation preventing layer, the low carrier concentration layer, and the current blocking layer are formed. A second cladding layer of the first conductivity type may be provided so as to fill a space surrounded by the side surface of the layer and the upper surface of the first cladding layer.

In this case, the first layer is formed by the carrier accumulation preventing layer.
The accumulation of carriers from the cladding layer of the above to the low carrier concentration layer is prevented. Thereby, the depletion state of the low carrier concentration layer is maintained, and the electric capacity between the first cladding layer and the current blocking layer is maintained small.

The thickness of the carrier accumulation preventing layer is preferably at least 15 nm. Thereby, the high-frequency characteristics of the semiconductor laser device are further improved.

The thickness of the carrier accumulation preventing layer is preferably at least 20 nm. Thereby, the high-frequency characteristics of the semiconductor laser device are further improved.

The carrier accumulation preventing layer may have a single layer structure or a super lattice structure. The active layer is (Al _x1 Ga _1-x1 ) _y1
Including a layer made of In _1-y1 P, the carrier accumulation preventing layer is made of (Al _x2 Ga _1-x2 ) _y2 In _1-y2 P or Al _x2 Ga _1-x2
As, the low carrier concentration layer is (Al _x3 Ga _1-x3 )
_y3 In _1-y3 P or Al _x3 Ga consists _1-x3 As, the current blocking layer _{(Al x4 Ga 1-x4)} y4 In 1-y4 P or A
l _x4 Ga _{1 -x4} As, x1, x2, x3, x4,
y1, y2, y3 and y4 may each be 0 or more and 1 or less.

The active layer includes a layer made of Al _x1 Ga _1-x1 As, the carrier accumulation preventing layer is made of Al _x2 Ga _1-x2 As, the low carrier concentration layer is made of Al _x3 Ga _1-x3 As,
The current blocking layer is made of Al _x4 Ga _1-x4 As,
x2, x3 and x4 may each be 0 or more and 1 or less.

The active layer is made of In_x1Ga_1-x1N
Rear accumulation prevention layer is Al_x2Ga_1-x2Made of N, low carry
A concentration layer is Al_x3Ga_1-x3The current blocking layer made of N
Al _x4Ga_1-x4N, x1, x2, x3 and x
4 may be 0 or more and 1 or less.

The active layer is (Al _x1 Ga _{1 -x1} ) _y1 In _{1 -y1} P
And the carrier accumulation preventing layer includes (Al _x2 Ga
_1-x2 ) _{y2 In1 -y2} P, the low carrier concentration layer is Al
_{x3Ga1 -x3As} , and the current blocking layer is _Alx4Ga
1-x4 As, x1, x2, x3, x4, y1, and y2 are each 0 or more and 1 or less, and the first conductivity type is p.
And the second conductivity type is preferably n-type.

In this case, the carrier accumulation preventing layer prevents the accumulation of carriers from the first cladding layer into the low carrier concentration layer, so that the improvement of the high frequency characteristics becomes particularly remarkable.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) First Embodiment FIG. 1 is a schematic sectional view of a semiconductor laser device according to a first embodiment of the present invention.

In the semiconductor laser device shown in FIG.
On the n-GaAs substrate 1, n- (Al _0.7 Ga _0.3 )
_A 1500 nm thick n-cladding layer 2 made of _0.5 In _0.5 P and a light emitting layer 14 described later are formed in this order. On the light emitting layer 14, p- (Al _0.7 Ga _0.3 ) _0.5 I
1500 nm thick p-cladding layer 6 of n _0.5 P
Thickness 200nm consisting and p-Ga _0.5 In _0.5 P
Are formed in this order. The p-cladding layer 6 and the p-contact layer 7 are etched to form a ridge.

The carrier concentration of the n-GaAs substrate 1 is 1 ×
10¹⁸cm^-3, N-cladding layer 2 has a carrier concentration of 3 ×
10¹⁷cm^-3, The carrier concentration of the p-cladding layer 6 is 3 ×
10 ¹⁷cm^-3, P-contact layer 7 has a carrier concentration of 2
× 10¹⁸cm^-3It is.

Further, a carrier accumulation preventing layer 8 having a thickness t having a stripe-shaped opening on the upper surface of the ridge portion is formed on the p-clad layer 6. Thickness 1000n made of GaAs having a stripe-shaped opening on the upper surface of the ridge
A low carrier concentration layer 9 of m is formed on the carrier accumulation preventing layer 8. A 500 nm-thick n-current blocking layer 10 made of n-GaAs having a stripe-shaped opening on the upper surface of the ridge is formed on the low carrier concentration layer 9. The carrier concentration of the n-current blocking layer 10 is 8 × 10
¹⁷ cm ^-3 . The carrier concentration of the low carrier concentration layer 9 is lower than the carrier concentration of the n-current blocking layer 10.

On the p-contact layer 7 in the stripe-shaped opening of the n-current block layer 10 and on the n-current block layer 10, a 3000 nm-thick p-contact layer 11 made of p-GaAs is formed. . The carrier concentration of the p-contact layer 11 is 3 × 10 ¹⁹ cm ⁻³ . p
A p-side electrode 12 having a thickness of 300 nm on the contact layer 11
Is formed. thickness of 300 on the back surface of the n-GaAs substrate 1
An n-side electrode 13 of nm is formed.

The light emitting layer 14 has a 30 nm thick guide layer 3 made of (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P formed on the n-cladding layer 2 and a quantum well active layer formed on the guide layer 3. layer 4, and a guide layer 5 of the quantum well active layer formed on the 4 (Al _0.5 Ga _{0. 5)} thickness 30nm consisting _0.5 in _0.5 P.

The quantum well active layer 4 is made of Ga _0.5 In _0.5 P
A plurality of 5 nm-thick quantum well layers 15 made of
It has a superlattice structure in which a plurality of barrier layers 16 of _0.5 Ga _0.5 ) _0.5 In _0.5 P having a thickness of 5 nm are alternately laminated. For example, the number of barrier layers 16 is two and the number of quantum well layers 15 is three.

Table 1 summarizes the above configuration.

[0042]

[Table 1]

FIG. 2 is a graph showing the relationship between p and p in the semiconductor laser device of FIG.
FIG. 3 is a diagram schematically illustrating an energy band diagram of a valence band of the cladding layer 6, the carrier accumulation preventing layer 8, and the low carrier concentration layer 9.

As shown in FIG. 2, the band gaps of the p-cladding layer 6, the carrier accumulation preventing layer 8, and the low carrier concentration layer 9 become smaller in this order. Therefore, the energy difference between the p-cladding layer 6 and the carrier accumulation preventing layer 8 in contact with the p-cladding layer 6 becomes smaller than the energy difference between the p-cladding layer 6 and the low carrier concentration layer 9. It becomes difficult to be injected into the accumulation preventing layer 8 and further to the low carrier concentration layer 9. As a result, the amount of carriers accumulated in the low carrier concentration layer 9 decreases. In addition, since carriers are separately injected into both the low carrier concentration layer 9 and the carrier accumulation preventing layer 8, the amount of carriers accumulated in the low carrier concentration layer 9 is reduced.

Since the amount of carriers accumulated in the low carrier concentration layer 9 decreases, the depletion state of the low carrier concentration layer 9 is maintained.
The electric capacitance between the semiconductor laser device and the cladding layer 6 is kept small, and the high-speed operation of the semiconductor laser device is sufficiently achieved.

As described above, with the simple configuration in which the band gap of the carrier accumulation preventing layer 8 is set to an intermediate value between the low carrier concentration layer 9 and the p-clad layer 6, the high frequency characteristics of the semiconductor laser device of FIG. Be improved.

FIGS. 3, 4 and 5 are schematic process sectional views showing a method of manufacturing the semiconductor laser device shown in FIG.

As shown in FIG. 3, MOCVD (organic metal
By a chemical vapor deposition method, on the n-GaAs substrate 1,
n- (Al_0.7Ga_0.3)_0.5In_0.5N- consisting of P
Clad layer 2, (Al_0.5Ga_0.5)_0.5In_0.5P
Guide layer 3, quantum well active layer 4, (Al_0.5Ga
_0.5)_0.5In_0.5P guide layer 5, (Al_{0. 7}
Ga_0.3)_0.5In_0.5P-cladding layer 6 composed of P
And p-Ga_0.5In _0.5P-contact layer made of P
Grow 7 in order.

As shown in FIG. 4, an SiO ₂ film is formed on the p-contact layer 7 and patterned to form a stripe-shaped SiO ₂ film 17. Then, the SiO ₂ film 17
Using p as a mask, part of p-contact layer 7 and p-cladding layer 6 are removed by etching to form a ridge portion.

[0050] Further, as shown in FIG. 5, SiO ₂ film 1
7 as a selective growth mask, carrier accumulation preventing layer 8 made of Ga _0.5 In _0.5 P on the p- type cladding layer 6 by MOCVD, composed of a low carrier concentration layer 9 and the n-GaAs consisting GaAs n-current blocking layer 10 Grow in order.

After removing the SiO ₂ film 17, as shown in FIG. 1, the p-contact layer 1 made of p-GaAs is formed on the n-current block layer 10 and the p-contact layer 7.
1 is formed by MOCVD, and the p-contact layer 11 is formed.
A p-side electrode 12 made of Cr / Au on the surface of
An n-side electrode 13 made of AuGe / Ni / Au is formed on the back surface of the n-GaAs substrate 1.

FIG. 6 is a diagram showing the measurement results of the cutoff frequency of the semiconductor laser device of Table 1 when the thickness t of the carrier accumulation preventing layer 8 is changed. Here, the cutoff frequency is a frequency at which the amplitude of the laser light on which the sine wave output from the semiconductor laser element to be measured is superimposed is lower by 3 dB than when the frequency is superimposed at a low frequency (in this example, when the superimposed frequency is 10 MHz or less). It is. In FIG. 6, ○ indicates a carrier accumulation preventing layer 8 having a single layer structure of Ga _0.5 In _0.5 P, and □ indicates (Al
_0.7 Ga _0.3 ) _0.5 In _0.5 P barrier layer and Ga _0.5 In
A carrier accumulation preventing layer 8 having a superlattice structure having _0.5 P well layers alternately (thickness t is the total value of the thicknesses of the well layers).
This shows a case where a carrier accumulation preventing layer 8 having a single layer structure made of l _0.45 Ga _0.55 As is used.

When the carrier accumulation preventing layer 8 was not formed, the cutoff frequency was 200 MHz, but by increasing the thickness of the carrier accumulation preventing layer 8, the cutoff frequency is improved, and the thickness t of the carrier accumulation preventing layer 8 is reduced. When the thickness exceeds 10 nm, the cutoff frequency is significantly improved, and the thickness t is almost saturated when the thickness t is about 20 nm. Therefore, the thickness t of the carrier accumulation preventing layer 8 is preferably 10 nm or more, more preferably 20 nm or more at which the rise of the cutoff frequency is saturated. If the thickness t of the carrier accumulation preventing layer 8 is 15 nm or more between 10 nm and 20 nm, there is a sufficient effect of improving high frequency characteristics.

FIG. 7 is a diagram showing the effect of improving the cutoff frequency when the carrier accumulation preventing layer 8 of the semiconductor laser device of FIG. 1 is doped. The horizontal axis represents the ratio of the carrier concentration of the carrier accumulation preventing layer 8 to the carrier concentration of the p-clad layer 6, and the vertical axis represents the cutoff frequency. The carrier accumulation preventing layer 8 of this semiconductor laser device is made of p-type GaInP and has a thickness t of 25 nm.

As shown in FIG. 7, the carrier accumulation preventing layer 8
When the carrier concentration is higher than the carrier concentration of the p-cladding layer 6, the effect of improving the cutoff frequency is small, but when the carrier concentration of the carrier accumulation preventing layer 8 is lower than the carrier concentration of the p-cladding layer 6, The effect of improving the cutoff frequency is great. Therefore, the carrier concentration of the carrier accumulation preventing layer 8 is preferably lower than that of the p-clad layer 6.

(2) Second Embodiment Next, a semiconductor laser device according to a second embodiment of the present invention will be described.

The configuration of the semiconductor laser device according to the second embodiment is the same as the configuration shown in FIG. 1, except that the material, thickness and carrier concentration of each layer are different. Table 2 shows the material, thickness, and carrier concentration of each layer of the semiconductor laser device of the present embodiment.

[0058]

[Table 2]

FIG. 8 is a graph showing the measurement results of the cutoff frequency of the semiconductor laser device shown in Table 2 when the thickness t of the carrier accumulation preventing layer 8 is changed. In FIG. 8, ○ indicates Al
The carrier accumulation preventing layer 8 having a single-layer structure of _0.25 Ga _0.75 As, and □ are an Al _0.45 Ga _0.55 As barrier layer and an Al _0.25 Ga
_This figure shows a case where a carrier accumulation preventing layer 8 having a superlattice structure alternately having _0.75 As well layers (film thickness t is the total thickness of the well layers) is used.

When the carrier accumulation preventing layer 8 was not formed, the cutoff frequency was 400 MHz, but by increasing the thickness of the carrier accumulation preventing layer 8, the cutoff frequency is improved, and the thickness t of the carrier accumulation preventing layer 8 is reduced. When the thickness exceeds 10 nm, the cutoff frequency is significantly improved, and the thickness t is almost saturated when the thickness t is about 20 nm. Therefore, the thickness t of the carrier accumulation preventing layer 8 is preferably 10 nm or more, more preferably 20 nm or more at which the improvement of the cutoff frequency is saturated. If the thickness t of the carrier accumulation preventing layer 8 is 15 nm or more between 10 nm and 20 nm, there is a sufficient effect of improving high frequency characteristics.

(3) Third Embodiment Next, a semiconductor laser device according to a third embodiment of the present invention will be described.

The configuration of the semiconductor laser device according to the third embodiment is the same as the configuration shown in FIG. 1, except that the material, thickness and carrier concentration of each layer are different. Table 3 shows the material, thickness, and carrier concentration of each layer of the semiconductor laser device of the present embodiment.

[0063]

[Table 3]

FIG. 9 is a graph showing the measurement results of the cutoff frequency of the semiconductor laser device shown in Table 3 when the thickness t of the carrier accumulation preventing layer 8 is changed. In FIG. 9, ○ indicates Al.
The carrier accumulation preventing layer 8 having a single-layer structure of _0.07 Ga _0.93 N, and □ are Al _0.15 Ga _0.85 N barrier layer and Al _0.07 Ga _0.93
The case where a carrier accumulation preventing layer 8 having a superlattice structure having alternately N-well layers (film thickness t is the total value of the thicknesses of the well layers) is used.

When the carrier accumulation preventing layer 8 was not formed, the cutoff frequency was 320 MHz, but the cutoff frequency is gradually improved by increasing the thickness of the carrier accumulation preventing layer 8. When t exceeds 10 nm, the cutoff frequency is significantly improved, and the thickness t is about 20 nm.
And almost saturated. Therefore, the thickness t of the carrier accumulation preventing layer 8 is preferably 10 nm or more, more preferably 20 nm or more at which the improvement of the cutoff frequency is saturated. The thickness t of the carrier accumulation preventing layer 8 is 15n between 10 nm and 20 nm.
If m or more, there is a sufficient effect of improving high frequency characteristics.

(4) Fourth Embodiment FIG. 10 is a schematic sectional view showing a semiconductor laser device according to a fourth embodiment of the present invention.

In the semiconductor laser device shown in FIG. 10, similarly to the semiconductor laser device shown in FIG.
Each layer 2 to 5 is formed on the s substrate 1.

On the guide layer 5, p- (Al_0.7Ga_0.3)
_0.5In_0.5200 nm thick p-clad made of P
Layer 61 and Ga_0.5In_0.5Carrier accumulation consisting of P
An accumulation preventing layer 62 is formed in order. p-cladding layer 6
The carrier concentration of 1 is 3 × 10 ¹⁷cm^-3It is.

P- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P
A ridge-shaped p-cladding layer 63 of 1300 nm is formed on the carrier accumulation preventing layer 62.
The carrier concentration of the p-cladding layer 63 is 3 × 10 ¹⁷ cm ⁻³
It is. p-Ga _0.5 In is formed on the upper surface of the p-cladding layer 63.
_A p-contact layer 7 of _0.5 P is formed.

A low carrier concentration layer 9 made of GaAs having a stripe opening on the upper surface of the p-contact layer 7 and having a thickness of 1000 nm is formed on the carrier accumulation preventing layer 62 on both sides of the p-cladding layer 63 and the p-cladding layer 63. Is formed on the side surface.

Further, n-GaAs having a thickness of 500 nm and made of n-GaAs having a stripe-shaped opening on the upper surface of the ridge portion.
The current blocking layer 10 is formed on the low carrier concentration layer 9; A p-contact layer 11 is formed on p-contact layer 7 and n-current block layer 10.

Table 4 summarizes the above configuration.

[0073]

[Table 4]

FIGS. 11, 12 and 13 are schematic process sectional views showing a method of manufacturing the semiconductor laser device shown in FIG.

As shown in FIG. 11, the MOCVD method
N- (Al) on the n-GaAs substrate 1_0.7G
a_0.3)_0.5In_0.5An n-cladding layer 2 made of P;
(Al_0.5Ga _0.5)_0.5In_0.5Guide layer made of P
3, quantum well active layer 4, (Al_0.5Ga _0.5)_0.5In
_0.5P guide layer 5, (Al_0.7Ga_0.3)_0.5
In_0.5P-cladding layer 61 made of P, Ga_0.5In
_0.5P carrier accumulation preventing layer 62, p- (Al
_0.7Ga_0.3)_0.5In_0.5P-cladding layer made of P
63 and p-Ga_0.5In_0.5P-contour consisting of P
Are grown in order.

As shown in FIG. 12, p-contact layer 7
An SiO ₂ film is formed thereon and patterned to form a stripe-shaped SiO ₂ film 64. Thereafter, using the SiO ₂ film 64 as a mask, the p-contact layer 7 and the p-cladding layer 63 are removed by etching to form a ridge.

Further, as shown in FIG. 13, using the SiO ₂ film 64 as a selective growth mask, a low carrier concentration of GaAs is formed on the carrier accumulation preventing layer 62 on both sides of the ridge portion and the side surface of the p-cladding layer 63 by MOCVD. Layer 9
And an n-current blocking layer 10 of n-GaAs is grown in order.

After removing the SiO ₂ film 64, a p-contact layer 11 made of p-GaAs is formed on the n-current block layer 10 and the p-contact layer 7 by MOCVD as shown in FIG. A p-side electrode 12 made of Cr / Au is formed on the surface of the p-contact layer 11, and AuGe / Ni / Au is formed on the back surface of the n-GaAs substrate 1.
Is formed.

FIG. 14 shows the thickness of the carrier accumulation preventing layer 62.
Cut-off circumference of the semiconductor laser device of Table 4 when t is changed
It is a figure showing a measurement result of a wave number. In FIG.
Ga _0.5In_0.5Prevention of carrier accumulation of single layer structure composed of P
Stop layer 62, □ is (Al_0.7Ga_0.3)_0.5In_0.5P failure
Wall layer and Ga_0.5In_0.5Super case with P well layer alternately
Carrier accumulation preventing layer 62 having a child structure (film thickness t is the thickness of a well layer
Total thickness), △ is Al_0.45Ga_0.55Single layer made of As
The case where a carrier accumulation preventing layer 62 having a structure is used is shown.
You.

When the carrier accumulation preventing layer 62 was not formed, the cutoff frequency was 200 MHz. However, by increasing the thickness of the carrier accumulation preventing layer 62, the cutoff frequency gradually increased, and the thickness of the carrier accumulation preventing layer 62 was reduced. t is 15n
m, the cutoff frequency is significantly improved, and the thickness t is about 2
Almost saturated at 0 nm. Therefore, the thickness t of the carrier accumulation preventing layer 62 is preferably 15 nm or more, and more preferably 20 nm or more at which the improvement of the cutoff frequency is saturated. If the thickness t of the carrier accumulation preventing layer 62 is 18 nm or more between 15 nm and 20 nm, there is a sufficient effect of improving high frequency characteristics.

(5) Fifth Embodiment Next, a semiconductor laser device according to a fifth embodiment of the present invention will be described.

The configuration of the semiconductor laser device of the fifth embodiment is the same as the configuration shown in FIG.
The film thickness and carrier concentration are different. Table 5 shows the material, film thickness, and carrier concentration of each layer of the semiconductor laser device of the present embodiment.

[0083]

[Table 5]

FIG. 15 shows the thickness of the carrier accumulation preventing layer 62.
Cutoff circumference of the semiconductor laser device of Table 5 when t is changed
It is a figure showing a measurement result of a wave number. In FIG. 15,
Al _0.25Ga_0.75Single layer carrier accumulation of As
Prevention layer 62, □ is Al_0.45Ga_0.55As barrier layer and Al
_0.25Ga_0.75Of a superlattice structure having alternating As well layers
Carrier accumulation preventing layer 62 (film thickness t is the total thickness of well layers)
(Value).

When the carrier accumulation preventing layer 62 is not formed, the cutoff frequency is 400 MHz, but the cutoff frequency is gradually improved by increasing the thickness of the carrier accumulation preventing layer 62, and the thickness t of the carrier accumulation preventing layer 62 is reduced. Is 15 nm
Is exceeded, the cutoff frequency is significantly improved, and the thickness t is about 20.
It is almost saturated at nm. Therefore, the thickness t of the carrier accumulation preventing layer 62 is preferably 15 nm or more, and more preferably 20 nm or more at which the improvement of the cutoff frequency is saturated. If the thickness t of the carrier accumulation preventing layer 62 is 18 nm or more between 15 nm and 20 nm, there is a sufficient effect of improving high frequency characteristics.

(6) Sixth Embodiment Next, a semiconductor laser device according to a sixth embodiment of the present invention will be described.

The structure of the semiconductor laser device according to the sixth embodiment is the same as that shown in FIG.
The film thickness and carrier concentration are different. Table 6 shows the material, thickness, and carrier concentration of each layer of the semiconductor laser device of the present embodiment.

[0088]

[Table 6]

FIG. 16 shows the thickness of the carrier accumulation preventing layer 62.
Shut-off circumference of the semiconductor laser device of Table 6 when t is changed
It is a figure showing a measurement result of a wave number. In FIG. 16, ○ indicates
Al _0.07Ga_0.93Carrier accumulation prevention of single layer structure consisting of N
Stop layer 62, □ is Al_0.15Ga _0.85N barrier layer and Al_0.07G
a_0.93Superlattice structure carrier having N well layers alternately
The accumulation preventing layer 62 (the thickness t is the total thickness of the well layers) is used.
It shows the case where there was.

When the carrier accumulation preventing layer 62 was not formed, the cutoff frequency was 320 MHz. However, by increasing the thickness of the carrier accumulation preventing layer 62, the cutoff frequency gradually increased, and the thickness of the carrier accumulation preventing layer 62 was reduced. t is 15n
m, the cutoff frequency is significantly improved, and the thickness t is about 2
Almost saturated at 0 nm. Therefore, the thickness t of the carrier accumulation preventing layer 62 is preferably 15 nm or more, and more preferably 20 nm or more at which the improvement of the cutoff frequency is saturated. If the thickness t of the carrier accumulation preventing layer 62 is 18 nm or more between 15 nm and 20 nm, there is a sufficient effect of improving high frequency characteristics.

(7) Seventh Embodiment FIG. 17 is a schematic sectional view of a semiconductor laser device according to a seventh embodiment of the present invention.

In the semiconductor laser device shown in FIG. 17, as in the semiconductor laser device shown in FIG.
Each layer 2 to 5 is formed on the s substrate 1.

On the guide layer 5, p- (Al _0.7 G
_a0.3 ) 200 nm thick p- layer composed of _{0.5 In0.5} P
A cladding layer 91 is formed. p-cladding layer 91
Has a carrier concentration of 3 × 10 ¹⁷ cm ⁻³ .

On the p-cladding layer 91, Ga _0.5 In
_A carrier accumulation preventing layer 92 of _0.5 P, a low carrier concentration layer 93 of 1000 nm thick made of GaAs, and n
A 500 nm-thick n-current blocking layer 94 made of -GaAs is formed in order.

The central regions of the carrier accumulation preventing layer 92, the low carrier concentration layer 93, and the n-current block layer 94 are removed to form a striped opening. n-
The carrier concentration of the current blocking layer 94 is 8 × 10 ¹⁷ cm ⁻³
It is. The carrier concentration of the low carrier concentration layer 93 is lower than the carrier concentration of the n-current blocking layer 94.

The p-type is formed so as to fill the stripe-shaped opening.
On the cladding layer 91 and the n-current blocking layer 94, p
_{-Thickness 1 of} (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P
A 300 nm p-cladding layer 95 is formed. p
The carrier concentration of the cladding layer 95 is 3 × 10 ¹⁷ cm ⁻³ ;

Thickness 20 of p-Ga _0.5 In _0.5 P
A 0 nm p-contact layer 96 is formed on the p-cladding layer 95. Thickness 3000 made of p-GaAs
A p-contact layer 97 of nm is formed on the p-contact layer 96. The carrier concentration of p-contact layer 96 is 2 × 10 ¹⁸ cm ⁻³ . The carrier concentration of p-contact layer 97 is 3 × 10 ¹⁹ cm ⁻³ .

Table 7 summarizes the above configuration.

[0099]

[Table 7]

FIGS. 18 and 19 are schematic process sectional views showing a method of manufacturing the semiconductor laser device shown in FIG.

As shown in FIG. 18, the MOCVD method
N- (Al) on the n-GaAs substrate 1_0.7G
a_0.3)_0.5In_0.5An n-cladding layer 2 made of P;
(Al_0.5Ga _0.5)_0.5In_0.5Thickness 30 consisting of P
nm guide layer 3, quantum well active layer 4, (Al_0.5Ga
_0.5)_0.5In_0.5Guide layer made of P and having a thickness of 30 nm
5, p- (Al_0.7Ga_0.3)_0.5In_0.5P from p
-Cladding layer 91, Ga_0.5In _0.5Carry consisting of P
A storage prevention layer 92, a low carrier concentration layer made of GaAs
93, and an n-current blocking layer made of n-GaAs
94 are grown in order.

A mask (not shown) is formed on the n-current block layer 94, and is patterned so as to have a stripe-shaped opening. Thereafter, as shown in FIG.
The central portions of the current blocking layer 94, the low carrier concentration layer 93, and the carrier accumulation preventing layer 92 are removed by etching to form a striped opening.

Further, as shown in FIG.
According to the D method, p- (Al _0.7 G) is formed on the n-current block layer 94 and the p-cladding layer 91 in the stripe-shaped opening.
a _{0. 3)} consisting of _0.5 In _0.5 P p- cladding layer 95,
consisting p-Ga _0.5 In _0.5 P p- contact layer 9
6, and p-contact layer 97 made of p-GaAs
Are formed in order. The surface of p-contact layer 97 has Cr /
A p-side electrode 12 made of Au is formed, and an n-side electrode 13 made of AuGe / Ni / Au is formed on the back surface of the n-GaAs substrate 1.
To form

FIG. 20 shows the thickness of the carrier accumulation preventing layer 92.
Cutoff circumference of the semiconductor laser device of Table 7 when t is changed
It is a figure showing a measurement result of a wave number. In FIG. 20, ○ indicates
Ga _0.5In_0.5Prevention of carrier accumulation of single layer structure composed of P
Stop layer 92, □ is (Al_0.7Ga_0.3)_0.5In_0.5P failure
Wall layer and Ga_0.5In_0.5Super case with P well layer alternately
Carrier accumulation preventing layer 92 having a child structure (film thickness t is the thickness of a well layer
Total thickness), △ is Al_0.45Ga_0.55Single layer made of As
The case where a carrier accumulation preventing layer 92 having a structure is used is shown.
You.

When the carrier accumulation preventing layer 92 is not formed, the cutoff frequency is 200 MHz, but the cutoff frequency is gradually improved by increasing the thickness of the carrier accumulation preventing layer 92, and the thickness t of the carrier accumulation preventing layer 92 is increased. Is 10 nm
Is exceeded, the cutoff frequency is significantly improved, and the thickness t is about 20.
It is almost saturated at nm. Therefore, the thickness t of the carrier accumulation preventing layer 92 is preferably 15 nm or more, and more preferably 20 nm or more at which the improvement of the cutoff frequency is saturated. If the thickness t of the carrier accumulation preventing layer 92 is 18 nm or more between 15 nm and 20 nm, there is a sufficient effect of improving high frequency characteristics.

(8) Eighth Embodiment Next, a semiconductor laser device according to an eighth embodiment of the present invention will be described.

The structure of the semiconductor laser device according to the eighth embodiment is the same as that shown in FIG.
The film thickness and carrier concentration are different. Table 8 shows the material, film thickness, and carrier concentration of each layer of the semiconductor laser device of the present embodiment.

[0108]

[Table 8]

FIG. 21 shows the thickness of the carrier accumulation preventing layer 92.
Shutdown circumference of the semiconductor laser device of Table 8 when t is changed
It is a figure showing a measurement result of a wave number. 21. In FIG.
Al _0.25Ga_0.75Single layer carrier accumulation of As
Prevention layer 92, □ is Al_0.45Ga_0.55As barrier layer and Al
_0.25Ga_0.75Of a superlattice structure having alternating As well layers
Carrier accumulation preventing layer 92 (film thickness t is the total thickness of well layers)
(Value).

When the carrier accumulation preventing layer was not formed, the cutoff frequency was 400 MHz, but the cutoff frequency was gradually improved by increasing the thickness of the carrier accumulation preventing layer 92, and the thickness t of the carrier accumulation preventing layer 92 was reduced. When the thickness exceeds 15 nm, the cutoff frequency is remarkably improved, and is substantially saturated when the thickness t is 20 nm or more. Therefore, the thickness t of the carrier accumulation preventing layer 92 is preferably 15 nm or more, and more preferably about 20 nm at which the improvement of the cutoff frequency is saturated. If the thickness t of the carrier accumulation preventing layer 92 is 18 nm or more between 15 nm and 20 nm, there is a sufficient effect of improving high frequency characteristics.

(9) Ninth Embodiment Next, a semiconductor laser device according to a ninth embodiment of the present invention will be described.

The configuration of the semiconductor laser device of the ninth embodiment is similar to the configuration shown in FIG.
The film thickness and carrier concentration are different. Table 9 shows the material, film thickness, and carrier concentration of each layer of the semiconductor laser device of the present embodiment.

[0113]

[Table 9]

FIG. 22 shows the thickness of the carrier accumulation preventing layer 92.
Shut-off circumference of the semiconductor laser device of Table 9 when t is changed
It is a figure showing a measurement result of a wave number. In FIG. 22, ○ indicates
Al _0.07Ga_0.93Carrier accumulation prevention of single layer structure consisting of N
Stop layer 92, □ is Al_0.15Ga _0.85N barrier layer and Al_0.07G
a_0.93Superlattice structure carrier having N well layers alternately
The accumulation preventing layer 92 (the thickness t is the total thickness of the well layers) is used.
It shows the case where there was.

When the carrier accumulation preventing layer 92 was not formed, the cutoff frequency was 320 MHz, but by increasing the thickness of the carrier accumulation preventing layer 92, the cutoff frequency is gradually improved, and the thickness of the carrier accumulation preventing layer 92 is reduced. t is 15n
m, the cutoff frequency is significantly improved, and the thickness t is about 2
Almost saturated at 0 nm. Therefore, the thickness t of the carrier accumulation preventing layer 92 is preferably 15 nm or more, and more preferably 20 nm or more at which the improvement of the cutoff frequency is saturated. If the thickness t of the carrier accumulation preventing layer 92 is 18 nm or more between 15 nm and 20 nm, there is a sufficient effect of improving high frequency characteristics.

Note that the active layer, the carrier accumulation preventing layer,
The material of the carrier concentration layer and the current block layer
It is not limited to the form. For example, (Al_x1Ga_1-x1)_y1
In _1-y1Active layer of P, (Al_x2Ga_1-x2)_y2In
_1-y2P or Al_x2Ga_1-x2Carrier accumulation consisting of As
Prevention layer, (Al_x3Ga_1-x3)_y3In_1-y3P or Al _x3
Ga_1-x3Low carrier concentration layer made of As and (Al_x4
Ga_1-x4)_y4In_1-y4P or Al_x4Ga_1-x4From As
Use any combination of current blocking layers
it can. Here, x1, x2, x3, x4, y1, y
2, y3 and y4 are each 0 or more and 1 or less.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a semiconductor laser device according to a first embodiment of the present invention.

2 is an energy band diagram of a valence band of a p-clad layer, a carrier accumulation preventing layer, and a low carrier concentration layer in the semiconductor laser device of FIG. 1;

FIG. 3 is a schematic process sectional view illustrating the method for manufacturing the semiconductor laser device of FIG.

FIG. 4 is a schematic process sectional view illustrating the method for manufacturing the semiconductor laser device of FIG. 1;

FIG. 5 is a schematic process sectional view illustrating the method for manufacturing the semiconductor laser device of FIG. 1;

FIG. 6 is a diagram showing a measurement result of a relationship between a cutoff frequency of the semiconductor laser device of the first embodiment and a thickness of a carrier accumulation preventing layer.

FIG. 7 is a diagram showing an improvement effect of a cutoff frequency when doping is performed on a carrier accumulation preventing layer of the semiconductor laser device of the first embodiment.

FIG. 8 is a diagram showing a measurement result of a relationship between a cutoff frequency and a thickness of a carrier accumulation preventing layer of the semiconductor laser device according to the second embodiment.

FIG. 9 is a diagram illustrating a measurement result of a relationship between a cutoff frequency and a thickness of a carrier accumulation preventing layer of the semiconductor laser device according to the third embodiment.

FIG. 10 is a schematic sectional view of a semiconductor laser device according to a fourth embodiment of the present invention.

11 is a schematic process sectional view showing the method of manufacturing the semiconductor laser device of FIG. 10;

12 is a schematic process sectional view illustrating the method for manufacturing the semiconductor laser device of FIG.

13 is a schematic process sectional view illustrating the method for manufacturing the semiconductor laser device of FIG.

FIG. 14 is a diagram illustrating a measurement result of a relationship between a cutoff frequency and a thickness of a carrier accumulation preventing layer of the semiconductor laser device according to the fourth embodiment.

FIG. 15 is a diagram illustrating a measurement result of a relationship between a cutoff frequency and a thickness of a carrier accumulation preventing layer of the semiconductor laser device according to the fifth embodiment.

FIG. 16 is a diagram illustrating a measurement result of a relationship between a cutoff frequency and a thickness of a carrier accumulation preventing layer of the semiconductor laser device according to the sixth embodiment.

FIG. 17 is a schematic sectional view of a semiconductor laser device according to a seventh embodiment of the present invention.

FIG. 18 is a schematic process sectional view illustrating the method of manufacturing the semiconductor laser device of FIG. 17;

FIG. 19 is a schematic process sectional view illustrating the method of manufacturing the semiconductor laser device of FIG. 17;

FIG. 20 is a diagram showing a measurement result of a relationship between a cutoff frequency and a thickness of a carrier accumulation preventing layer of the semiconductor laser device according to the seventh embodiment.

FIG. 21 is a diagram showing a measurement result of a relationship between a cutoff frequency and a thickness of a carrier accumulation preventing layer of the semiconductor laser device according to the eighth embodiment.

FIG. 22 is a diagram showing a measurement result of a relationship between a cutoff frequency and a thickness of a carrier accumulation preventing layer of the semiconductor laser device according to the ninth embodiment.

FIG. 23 is a schematic sectional view showing the configuration of a conventional semiconductor laser device.

FIG. 24 is an energy band diagram of a valence band of a p-type cladding layer and a low carrier concentration layer in a semiconductor laser device having a complex refractive index waveguide structure.

[Explanation of symbols]

 8,62,92 Carrier accumulation preventing layer 9,93 Low carrier concentration layer 10,94 n-current blocking layer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Kunio Takeuchi 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Yasuhiko Nomura 2-5-5 Keihanhondori, Moriguchi-shi, Osaka No. 5 F-term in Sanyo Electric Co., Ltd. (reference) 5F073 AA09 AA13 AA20 AA45 AA51 AA71 AA74 CA05 CA07 CA14 EA14

Claims (14)

[Claims] A first conductive type first cladding layer provided on the active layer; a second conductive type current blocking layer provided on the first cladding layer except for a current injection region; A low carrier concentration layer having a lower carrier concentration than the current blocking layer is provided on the side of the current blocking layer between the first cladding layer and the current blocking layer, and the first cladding layer and the current blocking layer are provided. A carrier accumulation preventing layer for preventing accumulation of carriers in the low carrier concentration layer is provided on the side of the first cladding layer between the first and second cladding layers. 2. The semiconductor laser device according to claim 1, wherein the band gaps of said first cladding layer, said carrier accumulation preventing layer and said low carrier concentration layer become smaller in this order. 3. The carrier accumulation preventing layer, wherein the first cladding layer has a flat portion formed on the active layer, and a ridge portion formed on the flat portion in the current injection region. Are formed on the flat portion and on the side surfaces of the ridge portion on both sides of the ridge portion, and the low carrier concentration layer and the current block layer are sequentially formed on the carrier accumulation preventing layer. 3. The semiconductor laser device according to claim 1, wherein 4. The carrier accumulation preventing layer has a thickness of 10 n.
4. The semiconductor laser device according to claim 3, wherein m is not less than m. 5. The carrier accumulation preventing layer has a thickness of 15 n.
5. The semiconductor laser device according to claim 4, wherein m is not less than m. 6. The carrier accumulation preventing layer is formed on the first cladding layer, and is formed on the carrier accumulation preventing layer in the current injection region in a ridge-like second conductive type.
The low carrier concentration layer and the current blocking layer are further provided on the carrier accumulation preventing layer on both sides of the second cladding layer and the second blocking layer.
3. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is formed on a side surface of the cladding layer. 7. The carrier accumulation preventing layer, the low carrier concentration layer, and the current blocking layer are sequentially formed on the first cladding layer except for the current injection region, and the carrier accumulation preventing layer is formed in the current injection region. A second conductivity type second cladding layer is provided so as to fill a space surrounded by the layer, the low carrier concentration layer, the side surfaces of the current blocking layer, and the upper surface of the first cladding layer. 3. The semiconductor laser device according to claim 1, wherein: 8. The carrier accumulation preventing layer has a thickness of 15 n.
8. The semiconductor laser device according to claim 6, wherein m is not less than m. 9. The carrier accumulation preventing layer has a thickness of 20 n.
9. The semiconductor laser device according to claim 8, wherein m is not less than m. 10. The carrier accumulation preventing layer has a single-layer structure or a superlattice structure.
The semiconductor laser device according to any one of the above. 11. The method according to claim 1, wherein the active layer comprises (Al_x1Ga_1-x1)_y1I
n_1-y1A layer comprising P, wherein the carrier accumulation preventing layer comprises
(Al_x2Ga_1-x2)_y2In_1-y2P or Al _x2Ga_1-x2
As, and the low carrier concentration layer is made of (Al_x3Ga
_1-x3)_y3In_{1- y3}P or Al_x3Ga_1-x3From As
The current blocking layer is (Al_x4Ga_{1- x4})_y4In
_1-y4P or Al_x4Ga_1-x4As1, the x1,
The x2, the x3, the x4, the y1, the y2,
Y3 and y4 are each 0 or more and 1 or less.
The half according to any one of claims 1 to 10, characterized in that:
Conductive laser element. 12. The active layer includes a layer made of Al _x1 Ga _1-x1 As, and the carrier accumulation preventing layer is made of Al _x2 Ga
_1-x2 As, and the low carrier concentration layer is Al _{x 3} Ga
_1-x3 As, wherein the current blocking layer is Al _{x 4} Ga
11. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is made of _1-x4 As, and each of x1, x2, x3, and x4 is 0 or more and 1 or less. 13. The active layer comprises In _x1 Ga _1-x1 N, the carrier accumulation preventing layer comprises Al _x2 Ga _1-x2 N, and the low carrier concentration layer comprises Al _x3 Ga _1-x3 N. The current blocking layer is made of Al _x4 Ga _1-x4 N,
The said x1, the said x2, the said x3, and the said x4 are each 0 or more and 1 or less, The said 1st characterized by the above-mentioned.
The semiconductor laser device according to any one of the above. 14. The active layer is composed of (Al _x1 Ga _{1 -x1} ) _y1I.
a layer comprising n _1-y1 P, wherein said carrier accumulation preventing layer comprises (Al _x2 Ga _1-x2 ) _y2 In _1-y2 P; said low carrier concentration layer comprises Al _x3 Ga _1-x3 As; The current block layer is made of Al _x4 Ga _{1 -x4} As, and the x1, x2, x3, x4, y1, and y2
Is a number from 0 to 1 respectively, the first conductivity type is p-type, and the second conductivity type is n-type.
11. The semiconductor laser device according to any one of items 10 to 10.