JP2010098201A - Ridge type semiconductor laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ridge type semiconductor laser allowing a ridge to be formed by selective etching without separately adding an etching stopper layer, small in threshold current and excelling in efficiency. <P>SOLUTION: An n-type InP clad layer 12 (n-type clad layer), an InGaAsP multiquantum well layer 16 (InGaAsP active layer), a first p-type InP clad layer 20, a p-type Al(Ga)InAs electron barrier layer 22, a second p-type InP clad layer 24, and a p-type InGaAsP contact layer 26 (p-type contact layer) are sequentially formed on an n-type InP substrate 10 (substrate). A ridge 28 is formed by selectively etching the p-type InGaAsP contact layer 26 and the second p-type InP clad layer 24 by using the p-type Al(Ga)InAs electron barrier layer 22 as an etching stopper layer. The p-type Al(Ga)InAs electron barrier layer 22 is present on the whole surface between the ridge 28 and the first p-type InP clad layer 20. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a ridge type semiconductor laser used in an optical communication system or the like.

  In an optical communication system or the like, a ridge type semiconductor laser in which a semiconductor layer is etched into a ridge type for current confinement and horizontal light confinement is used. In the conventional ridge type semiconductor laser, for example, an n-type InP cladding layer, an n-type InGaAsP optical confinement layer, an InGaAsP multiple quantum well layer, a p-type InGaAsP optical confinement layer, and a p-type InP clad layer are formed on an n-type InP substrate. And a p-type InGaAsP contact layer are formed in order. A ridge is formed by etching from the p-type InGaAsP contact layer to the middle of the p-type InP cladding layer.

In order to oscillate a semiconductor laser, it is necessary to accumulate electrons in the multiple quantum well layer to form an inversion distribution. However, in the conventional ridge type semiconductor laser, the height of the conduction band barrier with respect to the multiple quantum well layer of the p-type InP cladding layer is as small as several tens meV. For this reason, when the electron density is close to 1E18 cm ⁻³ , a phenomenon (overflow) in which electrons overflow into the p-type InP cladding layer becomes significant. Therefore, there is a problem that the threshold current is large and the efficiency of the semiconductor laser is poor.

In order to prevent such overflow, a ridge type semiconductor laser in which a p ⁺ type InP carrier stop layer having a higher impurity concentration than the p type InP cladding layer is formed on the multiple quantum well layer has been proposed (for example, Patent Document 1).

JP 2004-95822 A

Since the p ⁺ -type InP carrier stop layer of Patent Document 1 has the same constituent material as the p-type InP clad layer, it cannot serve as an etching stopper layer when forming a ridge. Therefore, when the ridge is formed by selective etching, an etching stopper layer has to be added separately.

  The present invention has been made in order to solve the above-described problems, and its object is to form a ridge by selective etching without adding an additional etching stopper layer, which has a small threshold current and a high efficiency. A semiconductor laser is obtained.

  The present invention provides an n-type cladding layer, an InGaAsP active layer, a first p-type InP cladding layer, a p-type Al (Ga) InAs electron barrier layer, a second p-type InP cladding layer, and a p-type contact layer on a substrate. The p-type contact layer and the second p-type InP cladding layer are selectively etched using the p-type Al (Ga) InAs electron barrier layer as an etching stopper layer to form a ridge, and the ridge The p-type Al (Ga) InAs electron barrier layer is present on the entire surface between the first p-type InP cladding layer and the first p-type InP cladding layer. Other features of the present invention will become apparent below.

  According to the present invention, a ridge can be formed by selective etching without adding an additional etching stopper layer, and a ridge type semiconductor laser with a small threshold current and high efficiency can be obtained.

Embodiment 1 FIG.
FIG. 1 is a sectional view showing a ridge type semiconductor laser according to Embodiment 1 of the present invention. On an n-type InP substrate 10 (substrate), an n-type InP cladding layer 12 (n-type cladding layer), an n-type InGaAsP optical confinement layer 14, an InGaAsP multiple quantum well layer 16 (InGaAsP active layer), a p-type InGaAsP optical closure The buried layer 18, the first p-type InP clad layer 20, the p-type Al (Ga) InAs electron barrier layer 22, the second p-type InP clad layer 24, and the p-type InGaAsP contact layer 26 (p-type contact layer) are in this order. Is formed. Then, using the p-type Al (Ga) InAs electron barrier layer 22 as an etching stopper layer, the p-type InGaAsP contact layer 26 and the second p-type InP cladding layer 24 are etched to form the ridge 28. A p-type Al (Ga) InAs electron barrier layer 22 exists on the entire surface between the ridge 28 and the first p-type InP cladding layer 20.

A SiO ₂ insulating film 30 is formed on the p-type Al (Ga) InAs electron barrier layer 22 on both sides of the ridge 28 and on the side walls of the ridge 28. A Ti / Pt / Au anode electrode 32 is formed so as to be connected to the p-type InGaAsP contact layer 26 through the opening of the SiO ₂ insulating film 30 on the ridge 28. An AuGeNi cathode electrode 34 is formed on the bottom surface of the n-type InP substrate 10.

  Next, a method for manufacturing the ridge type semiconductor laser according to the first embodiment of the present invention will be described. 2 and 3 are cross-sectional views for explaining the method of manufacturing the ridge type semiconductor laser according to the first embodiment of the present invention.

  First, as shown in FIG. 2, on an n-type InP substrate 10, an n-type InP cladding layer 12, an n-type InGaAsP optical confinement layer 14, an InGaAsP multiple quantum well layer 16, a p-type InGaAsP optical confinement layer 18, One p-type InP cladding layer 20, a p-type Al (Ga) InAs electron barrier layer 22, a second p-type InP cladding layer 24, and a p-type InGaAsP contact layer 26 are formed in order. Then, a resist pattern 36 is formed on the p-type InGaAsP contact layer 26 by photolithography or the like.

  Next, as shown in FIG. 3, the p-type InGaAsP contact layer 26 and the second p-type InP cladding layer 24 are formed using the resist pattern 36 as a mask and the p-type Al (Ga) InAs electron barrier layer 22 as an etching stopper layer. The ridge 28 is formed by dry etching or wet etching. As a chemical solution for wet etching, a mixed solution of hydrochloric acid and phosphoric acid can be used. Further, as an etching gas for dry etching, a mixed gas of methane, hydrogen, and oxygen can be used. In any case, InP can be selectively etched with respect to Al (Ga) InAs.

Thereafter, the resist pattern 36 is removed. Further, as shown in FIG. 1, the ridge type semiconductor laser according to the present embodiment is manufactured by forming the SiO ₂ insulating film 30, the Ti / Pt / Au anode electrode 32, and the AuGeNi cathode electrode.

  The effect of the ridge type semiconductor laser according to the present embodiment will be described in comparison with a reference example. FIG. 4 is a cross-sectional view showing a ridge type semiconductor laser according to a reference example. FIG. 5 is a diagram showing the relationship between the current and laser output of the ridge type semiconductor laser according to the reference example, and FIG. 6 shows the relationship between the current and laser output of the ridge type semiconductor laser according to Embodiment 1 of the present invention. FIG.

  In the reference example, the p-type Al (Ga) InAs electron barrier layer 22 does not exist as compared with the first embodiment, and the ridge 28 is formed by etching from the p-type InGaAsP contact layer 26 to the middle of the p-type InP cladding layer 38. Has been. On the other hand, in the first embodiment, the p-type Al (Ga) InAs electron barrier layer 22 exists on the entire surface between the ridge 28 and the first p-type InP cladding layer 20.

  The p-type Al (Ga) InAs electron barrier layer 22 can increase the barrier height against electrons by a maximum of about 100 meV compared to InP by reducing the amount of Ga added. For this reason, the p-type Al (Ga) InAs electron barrier layer 22 becomes a barrier layer against electrons from the InGaAsP multiple quantum well layer 16 toward the second p-type InP cladding layer 24. Therefore, electrons are easily accumulated in the InGaAsP multiple quantum well layer 16 when current is injected into the semiconductor laser. As a result, as shown in FIGS. 5 and 6, the semiconductor laser according to the first embodiment has a smaller threshold current than the semiconductor laser according to the reference example. Therefore, an efficient ridge type semiconductor laser can be obtained.

  Further, when the ridge 28 is formed, the p-type Al (Ga) InAs electron barrier layer 22 is also used as an etching stopper layer, so that the ridge 28 can be formed by selective etching without adding an additional etching stopper layer.

In addition, it is preferable that the p-type dopant Zn is doped so that the carrier concentration of the p-type Al (Ga) InAs electron barrier layer 22 is 0.7E18 cm ⁻³ or more. Thereby, a sufficient barrier height against electrons can be obtained. However, the carrier concentration of the p-type Al (Ga) InAs electron barrier layer 22 is suitably 1.0E19 cm ⁻³ or less that is normally used.

Further, it is preferable that the InGaAsP multiple quantum well layer 16 is doped n-type and the carrier concentration is 1.0E18 cm ⁻³ or more. Thereby, the injection current required to reach the electron and hole carrier density (1.0 to 2.0E18 cm ⁻³ ) necessary for the quantum well to obtain optical gain can be reduced, and the semiconductor laser The threshold current can be reduced. However, the carrier concentration of the InGaAsP multiple quantum well layer 16 is suitably 1.0E19 cm ⁻³ or less which is usually used.

The carrier concentration of the first p-type InP clad layer 20 is preferably 2.0E18 cm ⁻³ or more. This makes it difficult for an electron current to flow into the first p-type InP clad layer 20, so that electrons can easily accumulate in the InGaAsP multiple quantum well layer 16, and the threshold current of the semiconductor laser can be reduced. However, the carrier concentration of the first p-type InP cladding layer 20 is suitably 1.0E19 cm ⁻³ or less which is normally used.

Embodiment 2. FIG.
FIG. 7 is a vertical sectional view in the cavity direction of the ridge type semiconductor laser according to the second embodiment of the present invention. This semiconductor laser is a distributed feedback semiconductor laser in which a diffraction grating 40 is formed in the first p-type InP cladding layer 20. The diffraction grating 40 is doped p-type. Other configurations are the same as those of the first embodiment, and the same effects as those of the first embodiment can be obtained.

Embodiment 3 FIG.
FIG. 8 is a vertical sectional view in the cavity direction of the ridge type semiconductor laser according to the third embodiment of the present invention. This semiconductor laser is a distributed feedback semiconductor laser in which a diffraction grating 40 is formed in the second p-type InP cladding layer 24. The diffraction grating 40 is doped p-type. Other configurations are the same as those of the first embodiment, and the same effects as those of the first embodiment can be obtained.

Embodiment 4 FIG.
FIG. 9 is a vertical sectional view in the cavity direction of the ridge type semiconductor laser according to the fourth embodiment of the present invention. This semiconductor laser is a distributed feedback semiconductor laser in which a diffraction grating 40 is formed on an n-type InP cladding layer 12. The diffraction grating 40 is doped n-type. Other configurations are the same as those of the first embodiment, and the same effects as those of the first embodiment can be obtained.

Embodiment 5 FIG.
FIG. 10 is a vertical sectional view in the resonator direction of the optical integrated circuit according to the fifth embodiment of the present invention. This optical integrated circuit integrates a distributed feedback semiconductor laser and an optical modulator. On the n-type InP cladding layer 12, an n-type InGaAsP optical confinement layer 42 of an optical modulator, an InGaAsP multiple quantum well optical absorption layer 44 of an optical modulator, a p-type InGaAsP optical confinement layer 46 of an optical modulator, an optical modulation A p-type InP cladding layer 48 is formed in sequence. Even in such an optical integrated circuit, the same effect as in the first embodiment can be obtained.

1 is a cross-sectional view showing a ridge type semiconductor laser according to a first embodiment of the present invention. It is sectional drawing for demonstrating the manufacturing method of the ridge type semiconductor laser which concerns on Embodiment 1 of this invention. It is sectional drawing for demonstrating the manufacturing method of the ridge type semiconductor laser which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the ridge type semiconductor laser which concerns on a reference example. It is a figure which shows the relationship between the electric current of a ridge type semiconductor laser concerning a reference example, and a laser output. It is a figure which shows the relationship between the electric current and laser output of a ridge type semiconductor laser which concerns on Embodiment 1 of this invention. FIG. 6 is a vertical sectional view in the cavity direction of a ridge type semiconductor laser according to a second embodiment of the present invention. It is a vertical sectional view of the cavity direction of the ridge type semiconductor laser according to the third embodiment of the present invention. FIG. 6 is a vertical sectional view of a ridge type semiconductor laser according to a fourth embodiment of the present invention in the cavity direction. FIG. 10 is a vertical sectional view in the resonator direction of an optical integrated circuit according to a fifth embodiment of the present invention.

Explanation of symbols

10 n-type InP substrate 12 n-type InP cladding layer 14 n-type InGaAsP optical confinement layer 16 InGaAsP multiple quantum well layer 18 p-type InGaAsP optical confinement layer 20 first p-type InP cladding layer 22 p-type Al (Ga) InAs Electron barrier layer 24 second p-type InP cladding layer 26 p-type InGaAsP contact layer 28 ridge 40 diffraction grating

Claims (5)

An n-type cladding layer, an InGaAsP active layer, a first p-type InP cladding layer, a p-type Al (Ga) InAs electron barrier layer, a second p-type InP cladding layer, and a p-type contact layer are sequentially formed on the substrate. And
Using the p-type Al (Ga) InAs electron barrier layer as an etching stopper layer, the p-type contact layer and the second p-type InP cladding layer are selectively etched to form a ridge,
A ridge-type semiconductor laser, wherein the p-type Al (Ga) InAs electron barrier layer is present on the entire surface between the ridge and the first p-type InP cladding layer. 2. The ridge type semiconductor laser according to claim 1, wherein a carrier concentration of the p-type Al (Ga) InAs electron barrier layer is 0.7E18 cm ⁻³ or more and 1.0E19 cm ⁻³ or less. 2. The ridge type semiconductor laser according to claim 1, wherein the InGaAsP active layer is n-type and has a carrier concentration of 1.0E18 cm ⁻³ or more and 1.0E19 cm ⁻³ or less. 2. The ridge type semiconductor laser according to claim 1, wherein a carrier concentration of the first p-type InP cladding layer is 2.0E18 cm ⁻³ or more and 1.0E19 cm ⁻³ or less.   2. The ridge-type semiconductor according to claim 1, wherein a diffraction grating is formed in any one of the first p-type InP clad layer, the second p-type InP clad layer, and the n-type clad layer. laser.

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