JP2004165486A - Semiconductor laser diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a semiconductor laser diode of high output and a small working current by restraining an increase of a laser working current caused by inner loss due to optical absorption in a contact layer and obtaining electrical contact of a low resistance. <P>SOLUTION: The semiconductor laser diode of an edge face light emission type has an n-type GaAs substrate 101, a first clad layer 103 formed of n-type AlGaInP formed on the substrate, an active layer 104 formed on the first clad layer, a second clad layer 105 formed of p-type AlGaInP formed on the active layer, and a p-type contact layer 106 formed on the second clad layer. In the semiconductor laser diode, the p-type contact layer 106 is formed of GaP. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a visible light semiconductor laser diode having a large light output.
[0002]
[Prior art]
Semiconductor laser diodes (LDs) are widely used as light sources for optical disks and laser printers. In particular, AlGaInP-based LDs used as light sources for writable DVD-Rs, DVD-RWs, and DVD-RAMs are required to have high output, low operating current, and high reliability.
[0003]
Conventionally, a cladding layer having a ridge structure laminated on a semiconductor substrate on which a predetermined semiconductor material layer including an active layer is formed, a cap layer having a ridge structure laminated on the cladding layer, and formed on both sides of the cladding layer There is a semiconductor laser diode including a current block layer (for example, see Patent Document 1).
[0004]
FIG. 2 shows an example of a conventional semiconductor laser diode (LD) using an AlGaInP-based semiconductor material. In the figure, reference numeral 201 denotes an n-type GaAs substrate, and 202 denotes a first clad layer formed on the substrate 201 and made of n-type AlGaInP. 203 is an active layer made of AlGaInP. Reference numeral 204 denotes a second cladding layer made of p-type AlGaInP. That is, the mixed crystal ratio is set so that the energy gap of the AlGaInP active layer 203 is smaller than the energy gaps of the AlGaInP cladding layers 202 and 204, and a double hetero structure is formed. 206 is a contact layer. 205 is a current blocking layer made of GaAs. The current block layer 205 is provided for the purpose of so-called current confinement in order to obtain a current density required for laser oscillation.
[0005]
[Patent Document 1]
JP-A-2000-244066 (FIG. 3 (i))
[0006]
[Problems to be solved by the invention]
The major issues for increasing the output power of an AlGaInP-based LD are firstly a reduction in operating current, and secondly, the suppression of degradation (COD; Catastrophic Optical Damage) at the laser end face. The methods for reducing the operating current include (1) a method of increasing the gain in the active layer by making the active layer a strained quantum well structure, and (2) increasing the carrier concentration of the p-type cladding layer to increase the leakage from the p-type cladding layer. (3) A method for reducing internal loss by forming a current blocking layer with a material transparent to laser light, (4) A method for forming a contact layer (cap layer) above a laser transparent to laser light. And (5) increasing the distance between the active layer and the cap layer by increasing the thickness of the p-type cladding layer to reduce the influence of absorption in the contact layer. .
[0007]
As the method (4), an example using AlGaAs as the contact layer has been reported (Applied Physics Society Fall 2001, 14P-B-3). The contact layer must have as low a resistance as possible, but AlGaAs has a lower activation rate than a GaAs layer that has been widely used in the past, and thus has a problem that it is difficult to reduce the resistance.
[0008]
For example, Zn-GaAs doped with zinc (Zn) at 1 × 10 ¹⁹ cm ⁻³ as a p-type dopant has a hole mobility of about 80 cm ² / V · s and a resistivity of 7.8 × 10 ⁻³ Ω · cm. On the other hand, Zn—Al _0.5 Ga _0.5 As doped with the same amount of Zn has a hole mobility of about 30 cm ² / V · s and a resistivity of about 2.7 times that of Zn—GaAs. 0.1 × 10 ⁻² Ω · cm.
[0009]
As described above, since the AlGaAs layer has a lower carrier mobility than the GaAs layer, the carrier concentration for obtaining the same resistivity is higher in AlGaAs than in GaAs. Therefore, in order to reduce the resistance of the AlGaAs contact layer to the same level as that of the GaAs contact layer, it is necessary to dope at a higher concentration than the GaAs contact layer. In the laser element, which degrades the characteristics of the laser element. For example, the diffusion of unactivated Zn causes the pn junction position to be shifted to the n side from the light emitting layer, resulting in abnormal current-voltage characteristics and increasing the threshold current of the laser.
[0010]
On the other hand, AlGaAs is grown by MOVPE under appropriate growth conditions (for example, at a substrate temperature of about 600 ° C. or less, and the molar supply of group V raw material is 30 times or less of the molar supply of group III raw material). It is known that a large amount of C is contained in the crystal and exhibits p-type conductivity. However, a large amount of oxygen is simultaneously mixed in the crystal because Al is easily oxidized, and a low-resistance film is obtained. Is very difficult.
[0011]
Therefore, in order to obtain a low-resistance AlGaAs layer as a contact layer, it is necessary to intentionally add Zn or the like, which has caused the above-mentioned diffusion.
[0012]
Therefore, an object of the present invention is to solve the above-described problems, suppress an increase in laser operating current due to internal loss due to light absorption in a contact layer, and obtain a low-resistance electrical contact, thereby achieving high output and operating current. Is to provide a semiconductor laser diode having a small value.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is configured as follows.
[0014]
The semiconductor laser diode according to the present invention includes an n-type GaAs substrate, a first cladding layer made of n-type AlGaInP formed on the substrate, an active layer formed on the first cladding layer, In an edge-emitting semiconductor laser diode including a second clad layer made of p-type AlGaInP formed on an active layer and a p-type contact layer formed on the second clad layer, the p-type contact layer is made of GaP. It is characterized by becoming.
[0015]
According to a second aspect of the present invention, in the semiconductor laser diode according to the first aspect, a main element defining the conductivity of GaP of the p-type contact layer is carbon (C).
[0016]
According to a third aspect of the present invention, in the semiconductor laser diode according to the first or second aspect, the second cladding layer and the p-type contact layer have a ridge structure, and a current blocking layer is provided on the left and right sides of the ridge structure. It is characterized by having.
[0017]
<Action>
SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks, and has as its object to obtain a semiconductor laser diode having a high output and a small operating current.
[0018]
Therefore, in the present invention, an n-type GaAs substrate, an n-type AlGaInP cladding layer formed on the substrate, an active layer formed on the n-type AlGaInP cladding layer, and a p-type AlGaInP cladding layer formed on the active layer And a p-type GaP contact layer formed on the p-type AlGaInP cladding layer, thereby achieving the intended semiconductor laser diode.
[0019]
In the above, the target semiconductor laser diode was achieved by setting C as the main element that determines the conductivity of the GaP layer.
[0020]
GaP is an indirect transition type semiconductor, has an energy band gap of about 2.28 eV, and is a transparent material with respect to an oscillation wavelength of about 650 nm of a visible light laser diode for DVD. The hole mobility of C-GaP doped with C at 1 × 10 ¹⁹ cm ⁻³ is about 40 cm ² / V · s, and Zn-Al _0.5 Ga _0.5 As doped with the same amount of Zn is used. Since it has a mobility higher than the hole mobility of about 30 cm ² / V · s, it is easy to obtain a film having a lower resistance than at least AlGaAs. Further, C has a property that it is difficult to diffuse as compared with Zn or the like, so that C can be doped with a concentration exceeding 1 × 10 ¹⁹ cm ⁻³ , and furthermore, unlike AlGaAs, which does not contain Al, the effect of oxygen is less. As a result, a low resistivity equivalent to that of the GaAs layer can be realized.
[0021]
Therefore, by using GaP instead of GaAs as the contact layer, internal loss can be reduced by eliminating loss due to light absorption of laser light in the contact layer, and good electrical contact can be obtained because resistivity can be lowered. As a result, a laser diode having a large light emission output can be obtained.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described based on the illustrated embodiments.
[0023]
FIG. 1 shows a semiconductor laser diode LD according to an embodiment of the present invention. In this LD, an n-type GaAs buffer layer 102 and an n-type AlGaInP lower cladding layer (first cladding layer) 103 are sequentially epitaxially grown on an n-type GaAs substrate 101, and a strain quantum having a multilayer structure of AlGaInP and GaInP is formed thereon. It has a double hetero structure in which an active layer 104 having a well structure, a p-type AlGaInP upper cladding layer (second cladding layer) 105, and a p-type GaP contact layer (cap layer) 106 are sequentially grown. The p-type AlGaInP upper cladding layer 105 and the p-type GaP contact layer have a ridge structure, and n-type AlInP current blocking layers 107 are provided on the left and right sides of the ridge structure. The p-type GaP contact layer 106 has a structure in which C is heavily doped as an element that determines the conductivity of the GaP layer.
[0024]
In the semiconductor laser diode of this embodiment, GaP, which is a transparent material for the oscillating laser light, is used for the p-type contact layer and is doped with C at a high concentration, so that the p-type contact layer has a lower resistance than AlGaAs. Layers can be obtained. Further, since GaP does not contain Al, the influence of oxygen is small, and as a result, low resistivity similar to that of the GaAs layer can be realized.
[0025]
Therefore, by using GaP instead of GaAs as the contact layer, it is possible to suppress an increase in laser operation current due to internal loss due to light absorption in the p-type contact layer, and to enable low-resistance electrical contact, thereby achieving high output and high output. Moreover, a semiconductor laser diode having a small operating current can be obtained.
[0026]
[Example]
By an MOVPE method, an n-type GaAs buffer layer 102, an n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P lower cladding layer 103, and an (Al _{0. 5} Ga _0.5 ) _0.5 In _0.5 P and an active layer 104 having a strained quantum well structure having a multilayer structure of Ga _0.45 In _0.55 P, and a p-type (Al _0.7 Ga _0.3 A semiconductor laser diode having a _0.5 In _0.5 P upper cladding layer 105, an n-type Al _0.5 In _0.5 P current blocking layer 107, and a contact layer (cap layer) 106 made of p-type GaP is used. Produced. As the Ga, Al, and In raw materials, triethylgallium or trimethylgallium, trimethylaluminum, and trimethylindium were used. Phosphine (PH ₃ ) was used as the P raw material. Arsine (AsH ₃ ) was used as the As raw material.
[0027]
First, a GaAs substrate 101 was placed in a growth furnace, and a GaAs buffer layer 102 having n-type conductivity and a thickness of 0.5 μm was formed at a substrate temperature of 700 ° C. Further, a (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P lower cladding layer 103 having n-type conductivity and a thickness of 1.0 μm, and (Al _0.5 Ga _0.5 ) _0. An active layer 104 having a strained quantum well structure composed of a multilayer structure of ₅ In _0.5 P and Ga _0.45 In _0.55 P, a p-type conductive layer of (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P upper cladding layer 105 was sequentially formed.
[0028]
Next, the substrate temperature was set to 600 ° C., and the p-type GaP contact layer 106 was formed. The carrier concentration of the p-type GaP contact layer 106 was (5 to 20) × 10 ¹⁸ cm ⁻³ , and the thickness was 0.5 μm. For comparison, a laser diode wafer having a GaAs contact layer instead of the p-type GaP contact layer 106 was also manufactured.
[0029]
Next, the epitaxial wafer having the crystal grown to the contact layer 106 is taken out of the growth furnace, and a pattern is formed with silicon oxide. Then, reactive ion etching (RIE) and etching with an etching solution containing potassium hexacyanoiron (III) are performed. Then, a ridge was formed. An AlInP current blocking layer 107 having n-type conductivity was formed on the ridge-formed epitaxial wafer, and buried growth was performed.
[0030]
A laser diode chip was manufactured from the laser diode epitaxial wafer thus obtained. The width of the chip was 400 μm, and the length of the resonator was 1000 μm. The laser end face was subjected to Zn diffusion processing in order to suppress the end face destruction. When a threshold current value was measured by applying a current to this laser chip, the threshold current value of the laser diode having the GaP contact layer (cap layer) was 50 mA, and the threshold current value of the laser diode having the GaAs contact layer (cap layer) Of 60 mA.
[0031]
Further investigation of kink-free output revealed that the kink-free output of the laser diode having the GaP contact layer (cap layer) of the present example was 120 mW, and the kink-free output of the laser diode having the GaAs cap layer of the comparative example was 90 mW. The kink-free output could be increased by about 30%. It should be noted that no significant difference was observed between the two when the reliability was measured when the battery was energized for 1000 hours.
[0032]
【The invention's effect】
As described above, according to the present invention, GaP, which is a transparent material for oscillation laser light, is used for the p-type contact layer, so that loss due to light absorption of laser light in the contact layer is eliminated and internal loss is reduced. Can be done. Also, by using GaP, the p-type contact layer can be doped with C at a concentration exceeding 1 × 10 ¹⁹ cm ⁻³ , so that a p-type contact layer having a lower resistance than AlGaAs can be obtained. Further, since GaP does not contain Al, the influence of oxygen is small, and as a result, low resistivity similar to that of the GaAs layer can be realized.
[0033]
Therefore, by using GaP instead of GaAs as the contact layer, the loss due to the absorption of laser light in the contact layer can be eliminated and the internal loss can be reduced, and the resistivity can be lowered, so that good electrical contact can be obtained. As a result, a laser diode having a large light emission output can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing a structure of a semiconductor laser diode of the present invention.
FIG. 2 is a diagram showing a structure of a conventional semiconductor laser diode.
[Explanation of symbols]
101 n-type GaAs substrate 102 n-type GaAs buffer layer 103 n-type AlGaInP lower cladding layer 104 active layer 105 p-type AlGaInP upper cladding layer 106 p-type GaP contact layer (cap layer)
107 n-type AlInP current block layer

Claims (3)

an n-type GaAs substrate, a first cladding layer made of n-type AlGaInP formed on the substrate, an active layer formed on the first cladding layer, and a p-type AlGaInP formed on the active layer. An edge-emitting type semiconductor laser diode comprising two clad layers and a p-type contact layer formed on the second clad layer,
A semiconductor laser diode, wherein the p-type contact layer is made of GaP. The semiconductor laser diode according to claim 1,
A semiconductor laser diode, wherein a main element defining the conductivity of GaP of the p-type contact layer is carbon (C). The semiconductor laser diode according to claim 1 or 2,
A semiconductor laser diode, wherein the second cladding layer and the p-type contact layer have a ridge structure, and a current blocking layer is provided on the left and right sides of the ridge structure.

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