JPH0927657A - Manufacture of semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser which is long in service life and high in reliability by a method wherein a PN junction diode of reverse direction is formed in parallel with a semiconductor laser on the same substrate. SOLUTION: A current block layer is formed on each side of a mesa stripe semiconductor laser, a P-type GaAs contact layer 30A is formed thereon, and a P-type InGaP layer 31, an N-type InGaP layer 32, and a GaAs contact layer 33 are successively grown thereon. The P-type InGaP layer 31, the N-type InGaP layer 32, and the GaAs contact layer 33 are partially removed by selective etching for the formation of an reverse bias diode A. An electrically isolating groove 37 is formed between a semiconductor laser B and the reverse bias diode A. Electrodes 39 to 42 are provided for positively biasing the contact layer 30B of the semiconductor laser and the N-type second contact layer 33 of the reverse bias diode A and negatively biasing a substrate 21 and the contact layer 30A of the reverse bias diode A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high power semiconductor laser as a light source for pumping an optical fiber amplifier of an optical communication system.

[0002]

2. Description of the Related Art Conventionally, there have been the following semiconductor lasers in such a field. When using a semiconductor laser, a metal heat sink (usually C
u, which is also called a header), is used by bonding a laser chip with metal solder or the like.

FIG. 5 is a diagram showing the structure of such a conventional semiconductor laser. That is, as shown in FIG.
Is an anode (+) and heat sink, 2 is an insulator, 3 is a cathode (beard), 4 is an anode (+) and heat sink 1
The excitation laser chip 5 mounted on the Au connects the excitation laser chip 4 and the cathode (−) (beard) 3 to each other.
Wires 6 are holes for screwing the anode (+) and heat sink 1.

In the device structure, as shown in FIG. 5B, the active layer 14 includes a p-type InGaP cladding layer 15 and an n-type In.
It has a pn junction sandwiched between GaP cladding layers 13. It is a current blocking layer composed of a p-type InGaP layer 16 and an n-type InGaP layer 17 on both sides of the active layer 14. Normally, when a laser is operated, current is efficiently injected only into the active layer portion (for example, “High”). Po
wer InGaAs-GaAs-InGaP Bur
ied Heterostructure Strai
Ned Quantum Well Lasers G
row byTwo Step MOVPE ”El
electronics Letters, author: Y. K.
Sin, H .; Horikawa, T .; Kamijoh,
21st, January 1993 Vol. 29
No. 2 pp. 240-241). Note that FIG.
In (b), 11 is an n-side electrode and 12 is n-type GaAs.
A substrate, 18 is a p-type GaAs contact layer, and 19 is a p-side electrode.

In FIG. 5A, since the heat sink side is the anode (+), it is used as the anode (+) and heat sink 1. When bonding the element shown in FIG. 5B, AuZn / Au ( The (+) 19 side is the anode (+) / heat sink 1 side, that is, the junction of the active layer 14 is on the lower side (usually referred to as junction down).

Further, the state in which the bias is applied is shown by a symbol as shown in FIG. 5 (c), in which a forward current is applied to the diode for operation.

[0007]

However, when the semiconductor laser chip is bonded to the heat sink by the above-mentioned method and used, surge current flows in the opposite direction during handling and measurement, or the element is removed due to static electricity discharge. There is a problem that it is easily destroyed. In particular, the semiconductor laser having GaAs on the substrate as shown in the above document is very weak in the application of the reverse direction and has a problem in reliability.

According to the present invention, the above problems are eliminated, and a reverse pn junction diode is formed in parallel with a semiconductor laser on the same substrate to prevent damage or deterioration of the device.
An object of the present invention is to provide a method of manufacturing a semiconductor laser having a long life and high reliability.

[0009]

In order to achieve the above object, the present invention forms a current block layer on both sides processed into a mesa stripe shape having an active layer forming a semiconductor laser portion, and further forms a current block layer thereon. First conductivity type (p type) GaAs
The step of forming a contact layer and the first conductivity type (p
Step of sequentially growing a first conductivity type (p type) InGaP layer, a second conductivity type (n type) InGaP layer, and a second conductivity type (n type) GaAs contact layer on a (type) GaAs contact layer And by selective etching, the first conductivity type (p type) InGaP layer and the second conductivity type (n type) are partially formed.
InGaP layer and the second conductivity type (n-type) GaA
a step of forming a reverse bias diode with the s contact layer left, a step of forming an electrical isolation groove between the semiconductor laser portion and the reverse bias diode, and a first conductivity type of the semiconductor laser portion ( p type) Ga
The As contact layer and the second conductivity type (n type) second contact layer of the reverse bias diode are positively biased, and the second conductivity type (n type) substrate and the first conductivity type of the reverse bias diode are biased. And a step of forming respective electrodes capable of negatively biasing the (p-type) first GaAs contact layer.

[0010]

According to the present invention, as described above, since the pn diode chip is formed in parallel with the semiconductor laser in the reverse direction on the same substrate, when some kind of reverse current flows through the element. Also in this case, no reverse current flows through the pumping semiconductor laser, and one reverse bias diode flows as a forward current, so that the element is not damaged and the deterioration speed does not increase.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. 1 is a sectional view of a semiconductor laser showing a first embodiment of the present invention, FIG. 2 is a sectional view of manufacturing steps of the semiconductor laser (No. 1), FIG. 3 is a sectional view of manufacturing steps of the semiconductor laser (No. 2), FIG. 4 is a sectional view (3) of the manufacturing process of the semiconductor laser.

First, a method of manufacturing a semiconductor laser according to the first embodiment of the present invention will be described with reference to FIGS. (1) First, as shown in FIG. 2A, an n-InGaP clad layer (carrier concentration 1
× 10 ¹⁸ / cm ³ , thickness 1 μm 22, GaAs (undoped 1000 Å) / InGaAs (undoped 70)
Å) / GaAs (undoped 1000 Å) strained quantum well active layer 23 (hereinafter, simply referred to as active layer), p-InGa
P first cladding layer (carrier concentration 1 × 10 ¹⁸ / cm ³ ,
MOVPE (Metal) with a thickness of 0.5 μm or less) 24 and a GaAs cap layer (undoped thickness of 0.1 μm) 25.
Organic Vapor Phase Epit
axy) method. However, p-InGaP
The thickness of the first clad layer 24 is used to bury it flat. The GaAs cap layer 25 is necessary as a protective layer for the p-InGaP first cladding layer 24 in the next etching process.

(2) Next, as shown in FIG.
An iO ₂ mask 26 is formed and processed into a mesa stripe shape. The etchant is HBr + H ₂ O ₂ + H ₂ O, and the etching depth is 1.5 μm. (3) Next, as shown in FIG. 2C, as a current blocking layer, a p-InGaP blocking layer (carrier concentration 1 ×
10 ¹⁸ / cm ³ , thickness 0.9 μm) 27, n-InGa
A P block layer (carrier concentration 1 × 10 ¹⁸ / cm ³ , thickness 0.6 μm) 28 is grown on both sides of the mesa stripe.

(4) Next, as shown in FIG.
The iO ₂ mask 26 is removed to remove the p-InGaP second cladding layer 29, the p-GaAs first contact layer 30, and the p-InGaP second cladding layer 29.
The InGaP diode layer 31, the n-InGaP diode layer 32, and the n-GaAs second contact layer 33 are sequentially grown. (5) Next, as shown in FIG. 3A, an etching mask 34 of SiO ₂ or the like is formed in a portion other than directly above the active layer 23, at least 10 μm away from the end of the active layer 23. The etching mask 34 has a stripe shape,
Alternatively, it is formed in an island shape. Considering wire bonding, the size is 100 μm × 100 μm or more in width.

(6) Next, as shown in FIG. 3B, the n-GaAs second contact layer 33, the n-InGaP diode layer 32, and the p-I are used as an etching mask.
The nGaP diode layer 31 is removed by etching, and p
-The GaAs first contact layer 30 is exposed. In this etching, the n-GaAs second contact layer 33
Is H ₂ SO ₄ + H ₂ O ₂ + H ₂ O, n-In
When it reaches the GaP diode layer 32, it stops automatically.
Next, selectively etching the n-InGaP diode layer 32, p-InGaP diode layer 31 with a HCl + H ₂ O. With this etchant, p-G
The etching automatically stops at the aAs first contact layer 30. In this way, a portion to be the reverse bias diode A is formed.

(7) Next, a SiO ₂ mask 35 is formed on the entire surface of the wafer, and element isolation is performed by photolithography between the stripe portion of the active layer 23 and the reverse bias diode A portion as shown in FIG. 3C. Etching windows 36 are formed. (8) Next, as shown in FIG. 4A, an electrical isolation groove 37 reaching the n-GaAs substrate 21 is formed in the etching window 36. HBr + H as an etchant
_{When 2} O ₂ + H ₂ O is used, etching can be performed without selectivity (etching for InGaP and GaAs) from the p-GaAs first contact layer 30 to the n-GaAs substrate 21. Here, the p-GaAs first contact layer 30 is the p-GaAs contact layer 30 of the laser portion B.
B and the p-GaAs contact layer 30A of the reverse bias diode A are separated.

(9) Further, as shown in FIG.
An insulating SiO ₂ mask 38 is formed on the entire surface of the wafer, a window for forming an electrode of the laser portion B is opened by photolithography, and an electrode of the n-GaAs second contact layer 33 of the reverse bias diode A and a reverse bias are formed. A window for the electrode of the p-GaAs contact layer 30A of the diode A is also opened.

Finally, the electrodes on the contact layer side of the respective parts, that is, the p-GaAs first contact electrode (ohmic electrode) 39, the n-GaAs second contact electrode (ohmic electrode) 40, and the reverse bias diode A. The p-side electrode (ohmic electrode) 41 is formed. An electrode (ohmic electrode) 42 is formed on the n-GaAs substrate 21 side.

In this way, a semiconductor laser as shown in FIG. 1 can be manufactured. The operation of the semiconductor laser according to the present invention will be described below. In the normal operation, the electrode 39 of the p-GaAs contact layer 30B of the laser portion B and the electrode 40 of the n-GaAs second contact layer 33 of the reverse bias diode A are positively biased, and the n-GaAs substrate 21 side. And the p-side electrode 41 of the p-GaAs contact layer 30A of the reverse bias diode A are negatively biased.

As a result, a normal forward bias is applied to the semiconductor laser portion B, a current is injected into the active layer 23, and laser oscillation occurs. When the reverse bias is applied with a reverse voltage and the reverse breakdown voltage is about 2 V or more of the operating voltage of the laser,
It doesn't flow to that part. When a reverse bias is applied due to a surge or the like, the reverse bias diode A becomes a forward bias, and it is possible to prevent a current from flowing through this portion and flowing into the semiconductor laser.

In the embodiment of the present invention, the case where the n-GaAs substrate is used has been described. However, by inverting all conductivity types, it is possible to manufacture an element using the p-GaAs substrate. Further, the present invention is not limited to the above-described embodiments, and various modifications are possible based on the gist of the present invention, and these are not excluded from the scope of the present invention.

[0022]

As described above in detail, according to the present invention, the pn diode chip is formed in parallel with the semiconductor laser in the opposite direction, so that the pn diode chip is formed in the opposite direction to the element. Current does not flow in the pumping semiconductor laser in the reverse direction even when the current flows, the element is damaged or the deterioration rate is deteriorated because the current flows in one of the reverse bias diodes as the forward current. It never gets faster.

Therefore, a semiconductor laser having a long life and high reliability can be obtained.

[Brief description of drawings]

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

FIG. 2 is a sectional view of a semiconductor laser manufacturing process showing the first embodiment of the present invention (No. 1).

FIG. 3 is a manufacturing process sectional view (No. 2) of the semiconductor laser according to the first embodiment of the present invention.

FIG. 4 is a sectional view (No. 3) of the manufacturing steps of the semiconductor laser according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a conventional semiconductor laser.

[Explanation of symbols]

21 n-GaAs substrate 22 n-InGaP clad layer 23 GaAs / InGaAs / GaAs strained quantum well active layer 24 p-InGaP first clad layer 25 GaAs cap layer 26, 35 SiO ₂ mask 27 p-InGaP block layer 28 n-InGaP Block layer 29 p-InGaP second clad layer 30 p-GaAs first contact layer 30A p-GaAs contact layer of reverse bias diode A 30B p-GaAs contact layer of laser part B 31 p-InGaP diode layer 32 n-InGaP diode layer 33 n-GaAs second contact layer 34 etching mask 36 isolation etching window 37 electrically separating groove 38 insulating SiO ₂ mask 39 p-GaAs first contact electrode 40 n-GaAs second contactor p-side electrode 42 substrate side electrode of the use electrode 41 reverse biased diode A

Claims (1)

[Claims] 1. A step of: (a) forming a current blocking layer on both sides processed into a mesa stripe shape having an active layer forming a semiconductor laser portion, and forming a GaAs contact layer of a first conductivity type on the current blocking layer. , (B) Ga of the first conductivity type
A second conductivity type InGaP layer on the As contact layer;
A step of sequentially growing a conductive type InGaP layer and a second conductive type GaAs contact layer, and (c) selective etching to partially form the first conductive type InGaP layer and the second conductive type InGaP layer.
A step of forming a reverse bias diode while leaving the conductive type InGaP layer and the second conductive type GaAs contact layer; and (d) forming an electrical isolation groove between the semiconductor laser portion and the reverse bias diode. Forming step, and (e) GaA of the first conductivity type of the semiconductor laser portion.
s contact layer and the second contact type second contact layer of the reverse bias diode are positively biased, and the second conductivity type substrate and the first of the reverse bias diode are
And a step of forming respective electrodes capable of negatively biasing the conductivity type first GaAs contact layer.