JP2004274090A - Semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser device of improved light emission characteristics at high temperatures. <P>SOLUTION: In the semiconductor laser element comprises an active layer which comprises a plurality of distorted quantum wells, the active layer comprises six or more distorted quantum well layers of GaInAsP compound semiconductor, and the total thickness of the distorted quantum well layers multiplied by distortion (%) is 20-40 nm, and oscillates up to 140°C as a laser device. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a semiconductor laser device having a strained quantum well.

A semiconductor laser device having a conventional strained quantum well has, for example, a structure as shown in FIG. In the figure, 1 is an n-InP substrate, 2 is an n-InP buffer layer, 3 is an active layer including a strained quantum well, 4a and 4b are p-InP cladding layers, 5 is a p-InP current blocking layer, and 6 is n -InP current blocking layer, 7 is a p-InGaAs contact layer. This semiconductor laser device is manufactured by the following steps. That is,
1) On an n-InP substrate 1, an n-InP buffer layer 2, an active layer 3, and a p-InP cladding layer 4a are stacked. As a growth method, for example, a metal organic chemical vapor deposition method is used.
2) Next, a mesa stripe having a width of about 1.5 μm is formed by ordinary photolithography and chemical etching using a SiNx mask (not shown).
3) Next, the p-InP current blocking layer 5 and the n-InP current blocking layer 6 are formed by the second crystal growth, and the SiNx mask is removed. Then, the p-InP cladding layer is formed by the third crystal growth. 4b, the p-InGaAs contact layer 7 is laminated to form a buried structure.

  FIG. 5B is a band diagram of the active layer 3 including the strained quantum well. The active layer 3 has a structure in which a 4 nm-thick GaInAsP well layer 9 (λg = 1.4 μm) is sandwiched by a 12 nm-thick GaInAsP optical waveguide layer 8 (λg = 1.1 μm). The GaInAsP well layer 9 has a composition in which the lattice constant is about 1% larger than that of the InP substrate 1, and the GaInAsP well layer 9 is subjected to compressive strain. The temperature dependence of the emission characteristics of a semiconductor laser device having this structure with a cavity length of 150 μm and a high reflection coating (reflectance: 85% to 95%) on both surfaces was measured. FIG. 6 shows the result. This device realizes a low threshold current of 2.0 mA at room temperature. FIG. 7 shows the temperature dependence of the luminous efficiency.

  However, in the above-described semiconductor laser device, as can be seen from FIG. 6, there is a problem that the threshold current increases as the temperature increases, and oscillation does not occur at 100 ° C. or higher.

  The present invention provides a semiconductor laser device that solves the above-described problems. The semiconductor laser device according to the present invention is an active laser device having an active layer including a plurality of strained quantum well layers on an InP substrate. The layer has six or more strained quantum well layers made of a GaInAsP compound semiconductor, and a product of the total thickness of the strained quantum well layers and the strain (%) is 20 nm or more and 40 nm or less, It is characterized by oscillating up to 140 ° C. as a laser element.

  In a semiconductor laser device having an active layer including a plurality of strained quantum well layers, the product of the total thickness of strained quantum well layers included in the active layer and strain (%) is 20 nm or more and 40 nm or less. There is an excellent effect that an increase in threshold current and a decrease in luminous efficiency at a high temperature can be prevented, and luminescence characteristics at a high temperature can be improved.

  It is known that, in a semiconductor laser device, the threshold current density decreases as the number of strained quantum well layers in the active layer increases. On the other hand, if the number of strained quantum well layers is excessively increased, lattice defects due to the strain are generated. Then, the total thickness of the strained quantum well layer and the influence of the strain on the temperature characteristics of the threshold current density were experimentally investigated, and new findings were obtained. The present invention shows a design standard for an active layer based thereon. That is, according to the experiments of the present inventors, when the product of the total thickness of the strained quantum well layers and the strain (%) is smaller than 20 nm and larger than 40 nm, the threshold current density at high temperature is reduced. It was found to increase. By the way, conventionally, the active layer is constituted by a product of the total thickness of the strained quantum well layer and the strain (%) is 20 nm or less.

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.
The structure of the semiconductor laser device of this embodiment is the same as that of FIG. 5A used in the description of the prior art, except for the active layer. As shown in FIG. 1, the active layer 13 has a strained multiple quantum well composed of a GaInAsP well layer 9 having a thickness of 4 nm (λg = 1.4 μm) and a GaInAsP barrier layer 10 having a thickness of 12 nm (λg = 1.1 μm). It has a structure, and the number of well layers 9 is six. In this case, the product of the strain and the total thickness of the well layers is 1% × 4 nm × 6 = 24 nm. The resonator length was 170 μm, and the reflectance on both sides was 85% and 95%. FIG. 2 shows the emission characteristics of this device. As can be seen from FIG. 2, the threshold current was 2.5 mA at room temperature and 6.5 mA at 100 ° C., and it was confirmed that the laser oscillated up to 150 ° C. or higher. Further, the deterioration of the luminous efficiency due to the temperature rise was smaller than in the conventional case. For example, the temperature at which the luminous efficiency is reduced to half is 145 ° C. in the present embodiment, as shown in FIG. 3, but is around 85 ° C. in the conventional example as shown in FIG.

  In the above embodiment, the relationship between the product of the strain and the total thickness of the well layers and the threshold current was measured by changing the number of the quantum well layers while setting the thickness of each quantum well layer to 40 nm and the strain to 1%. did. The result is shown in FIG. As can be seen from FIG. 4, when the product of the strain and the total thickness of the well layer is smaller than 20 nm or larger than 40 nm, the threshold current rapidly increases at a high temperature of 150 ° C. or higher. Therefore, it is desirable to design the active layer so that the product of the strain and the total thickness of the well layers is in the range of 20 nm or more and 40 nm or less.

FIG. 8 shows the results of photoluminescence measurement at liquid nitrogen temperature (77 K) of wafers having different numbers of quantum wells. When the product of the strain and the total thickness of the well layers exceeds 40 nm, the half-width increases and the peak wavelength becomes longer. This indicates the deterioration of crystallinity due to relaxation of strain due to the critical film thickness. It has been confirmed that the deterioration of the crystallinity has an adverse effect on the reliability of the element, and that the reliability of the device is also reduced. From such a viewpoint, it is important that the product of the strain and the total thickness of the well layers is 40 nm or less.
Note that the present invention is not limited to the above embodiment, and can be applied to an InGaAlAs / InP system, an InGaP / AlInGaP system, and the like.

FIG. 3 is a diagram showing a band gap structure of an active layer in one embodiment of the semiconductor laser device according to the present invention. It is a figure which shows the relationship between the electric current and light output of the said Example. It is a figure which shows the relationship between the electric current and luminous efficiency of the said Example. FIG. 7 is a diagram illustrating a relationship between a product of strain and a total thickness of well layers and a threshold current. (A) is a sectional view of a conventional semiconductor laser device, and (b) is a diagram showing a band gap structure of an active layer thereof. It is a figure which shows the relationship between the conventional electric current and light output. It is a figure which shows the relationship between the conventional electric current and luminous efficiency. It is a figure which shows the relationship between the product of distortion and the total thickness of a well layer, and the photoluminescence half value width.

Explanation of reference numerals

Reference Signs List 1 n-InP substrate 2 n-InP buffer layer 3, 13 active layer 4a, 4b p-InP cladding layer 5 p-InP current blocking layer 6 n-InP current blocking layer 7 p-InGaAs contact layer 8 optical waveguide layer 9 well Layer 10 Barrier layer

Claims (2)

  In a semiconductor laser device having an active layer including a plurality of strained quantum well layers above an InP substrate, the active layer has six or more strained quantum well layers made of a GaInAsP compound semiconductor, and A semiconductor laser device wherein the product of the total thickness and the strain (%) is 20 nm or more and 40 nm or less, and oscillates up to 140 ° C. as a laser device.   2. The semiconductor laser device according to claim 1, wherein the temperature at which the luminous efficiency at 1/2 of the luminous efficiency at 40 ° C. is 140 ° C. or higher.

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