JP4668529B2 - GaInNAs semiconductor laser - Google Patents

Description

  The present invention has a GaInNAs-based strained active layer that generates light on a GaAs substrate crystal and a resonator structure that obtains laser light from light generated from the active layer, and a structure in which a stress compensation layer is formed near the active layer. The present invention relates to a GaInNAs semiconductor laser.

  With the explosive growth of the Internet population in recent years, there has been a demand for rapid increase in information transmission and capacity, and optical communication will continue to play an important role in the future. In addition to performance requirements, it is important to provide semiconductor lasers that serve as light sources in optical communications at low cost. In particular, it is essential to reduce costs for access systems with short transmission distances and LAN optical links. Yes.

  GaInNAs semiconductor lasers that use GaInNAs-based materials developed in recent years for the active layer are different from conventional communication lasers formed on InP substrate crystals, and are low-cost because they are formed on inexpensive and large-diameter GaAs substrates. It is advantageous to make. GaInNAs-based materials are characterized by the addition of nitrogen, which has chemical properties that are significantly different from those of conventional III-V group semiconductors. The GaInNAs-based material in the present invention includes a material based on GaInNAs and containing a small amount of other elements such as phosphorus, antimony, and dopant.

Electronics Letters, vol. 36, No. 16, pp.1381-1382

  GaInNAs-based materials are characterized by the addition of nitrogen with significantly different chemical properties to conventional III-V group semiconductors. Addition of nitrogen makes it possible to form an active layer material with an emission wavelength suitable for optical communication on a GaAs substrate. However, the addition of nitrogen, which differs greatly in chemical properties, generally lowers the crystallinity of the parent group III-V semiconductor. Let The amount of nitrogen added is reduced as much as possible within the range where optical communication wavelengths can be realized, and is almost around 1%. Therefore, the composition of In in the active layer is 30 to 40%, and a compressive strain of 2% or more is applied to the active layer. The strain amount of the active layer of the conventional semiconductor laser is about 1.5% at maximum, and the strain of the active layer of the GaInNAs laser is very large.

  A large amount of strain generally has an adverse effect on device life and yield. In order to reduce this, it is conceivable to arrange a layer having an extension strain in the immediate vicinity of the compressive strain GaInNAs active layer as in the conventional semiconductor laser to compensate the stress. On the GaAs substrate, the material of the stress compensation layer having a tensile strain is basically GaPAs and GaNAs. In the crystal growth of GaPAs, it is difficult to switch the raw materials of arsenic and phosphorus, and it is difficult to obtain good quality crystals. On the other hand, in the case of GaNAs, crystal growth is relatively easy because a small amount of nitrogen may be added to GaAs as in the active layer.

  Livshits et al., In Electronics Letters, vol. 36, No. 16, pp. 1381-1382, reported a GaInNAs-based laser in which a GaInNAs compression-strained well layer is sandwiched between GaNAS stress compensation layers and an active layer is used as a quantum well. I'm getting results. However, when the inventors made additional trials, the device life and yield were not improved much. The reporters and others conducted an extensive investigation to find out that the absolute value of the strain difference at the interface between the GaInNAs compressive strained layer and the GaNAs strained layer is too large, and it is often impossible to form a good heterointerface. It was.

  An object of the present invention is to provide a stress-compensated GaInNAs semiconductor laser in which both a GaInNAs compressive strain active layer and a GaNAs stretch strain layer formed near the active layer have a good heterointerface.

  By inserting an intermediate layer with an intermediate strain amount between the GaInNAs-based compressive strain active layer and the GaNAs extensional strain stress compensation layer, the absolute amount of strain difference at the heterointerface can be reduced, thus forming a good heterointerface And the above objective can be achieved. As the material of the intermediate layer, GaAs, GaAsSb, and GaInAs are preferable. As usual, when compressive strain is expressed as + strain, if the amount of strain in the intermediate layer is too large on the + side, it is against the purpose of stress compensation, so a range of 0 to + 0.5% is preferable. If the thickness of the intermediate layer is too thin, there is no effect of insertion, and conversely if it is increased too much, the effect of stress compensation is reduced, so there is an optimum range.

  FIG. 2 shows the relationship between the intermediate layer thickness and the photoluminescence (PL) intensity from the active layer (experimental example). The material of the intermediate layer in this example is GaAs. As shown in the figure, increasing the thickness of the intermediate layer improves the heterointerface and increases the PL intensity. In addition, the PL strength decreases even if the thickness of the intermediate layer is excessively increased. Therefore, it can be seen that the thickness of the intermediate layer is preferably 0.5 to 2.5 nm.

  In general, it is difficult to improve the crystallinity of the active layer as the thickness of the hetero layer formed under the active layer increases. The effect of stress compensation is greater in a surface-emitting laser with a multilayer mirror thickness of about 5 μm than an edge-emitting laser with a cladding layer of about 1.5 μm. Therefore, the effect of the present invention is also remarkable in the surface emitting laser.

  Note that the GaNAs stress compensation layer in the present invention includes a case where a trace amount of other elements such as antimony and dopant is added based on the GaNAs material.

  According to the present invention, the absolute amount of strain difference at the heterointerface can be reduced by inserting an intermediate layer having an intermediate strain amount between the GaInNAs-based compression strain active layer and the GaNAs stretch strain layer clad layer, A stress compensated GaInNAs semiconductor laser having a good heterointerface can be provided.

  Embodiments of the present invention will be described below with reference to FIGS.

In the first embodiment, the present invention is applied to a 1.3 μm band edge emitting semiconductor laser. FIG. 1 (a) shows a cross-sectional structure, and FIG. 1 (b) shows an enlarged view of the active layer. On n-GaAs substrate 1, GaAs buffer layer 2, n-Al _0.3 Ga _0.7 As cladding layer (layer thickness 1500 nm) 3, GaAs light guide layer (layer thickness 150 nm) 10, GaN _0.01 As _0.99 stress compensation layer (layer thickness) Strain compensated quantum well active layer 4 consisting of 5 nm) 11, GaAs intermediate layer (layer thickness 2 nm) 12, and Ga _0.6 In _0.4 N _0.005 As _0.995 well layer 13 (layer thickness 5 nm), p-Al _0.3 Ga _0.7 As A clad layer (layer thickness 1500 nm) 5 and a p-GaAs capping layer (layer thickness 200 nm) 6 were successively crystal-grown by a GS-MBE (gas source molecular beam epitaxy) method to produce a multilayer structure. Metal aluminum, metal gallium, and metal indium were used as Group III element materials. Nitrogen and metal arsenic activated by RF plasma were used as the raw materials for group V elements. Metal arsenic was attached to a normal molecular beam cell, heated and sublimated, and supplied as an As ₄ molecular beam. Si was used as the n-type dopant, and Be was used as the p-type dopant. Layers 2, 3, 5, and 6 were grown at 600 ° C. On the other hand, the active layer 4 was grown at a low temperature of 480 ° C. in order to suppress phase separation.

As shown in FIG. 1 (a), a SiN _x nitride film was deposited on the fabricated multilayer structure to form a current confinement layer 7. After forming the p-side electrode 8 and the n-side electrode 9, a laser element having a resonator length of about 400 μm was obtained by a cleavage method. The stripe width was 5 μm. A low reflection film made of SiO _{2 having} a thickness of λ / 4 (λ: oscillation wavelength) was formed on the front surface of the element, and a high reflection film made of a four-layer film made of SiO ₂ and amorphous Si was formed on the rear surface of the element. Thereafter, the element was bonded onto the heat sink with the pn junction surface facing down.

This laser oscillated continuously at room temperature with a threshold current density of 0.5 kA / cm ² and an oscillation wavelength of 1.3 μm. In this laser, the GaInNAs well layer 13 and the GaNAs stress compensation layer 11 both have a good heterointerface due to the intermediate layer 12, so that the crystallinity of the active layer 4 is good, and the device lifetime is longer than 100,000 hours. In addition, the distribution within the wafer was small, and the yield was very good.

In this embodiment, the present invention is applied to a 1.3 μm band-emitting semiconductor laser. Hereinafter, a description will be given with reference to FIG. FIG. 3 (a) shows a cross-sectional structure, and FIG. 3 (b) shows an enlarged view of the active layer. n-GaAs substrate 1, n-type semiconductor multilayer reflector 20, GaAs spacer layer 21, GaN _0.01 As _0.99 stress compensation layer (layer thickness 5 nm) 41, GaAs _0.99 Sb _0.01 intermediate layer (layer thickness 1.5 nm) 42, Double quantum well active layer 24 composed of Ga _0.6 In _0.4 N _0.005 As _0.995 well layer (layer thickness 6 nm) 43 and GaN _0.01 As _0.99 stress compensation barrier layer (layer thickness 7 nm) 44, GaAs spacer layer 25, GaAs A p-Ga _0.5 In _0.5 P cladding layer 26 and a p-GaAs contact layer 27 lattice-matched to the substrate were sequentially grown by the GS-MBE method. Metal aluminum, metal gallium, and metal indium were used as Group III element materials. Nitrogen, phosphine, and metal arsenic activated by RF plasma were used as Group V element materials. Metal arsenic was attached to a valved cracker type molecular beam cell and As ₄ molecules obtained by heating and sublimation were cracked at a higher temperature and supplied as a beam of As ₂ molecules. Further, Si was used as the n-type dopant, and C (carbon) was used as the p-type dopant.

The active layer 24 has a stress compensated quantum well structure having a GaAsSb intermediate layer 42. The thickness of the GaAs spacer layer was adjusted so that the total thickness of the GaAs spacer layer 21, the double quantum well active layer 24, and the GaAs spacer layer 25 was equal to the wavelength in the semiconductor. In the semiconductor multilayer mirror 20, the high refractive index GaAs layer having a quarter wavelength thickness in the semiconductor and the low refractive index AlAs layer having a quarter wavelength thickness in the semiconductor are alternately laminated. In order to make the reflectivity 99% or more, the number of reflector layers was 22 pairs. n-type semiconductor multilayer reflector 20 is 600 ° C., GaAs spacer layer 21, double quantum well active layer 24, and GaAs spacer layer 25 is 450 ° C., p-Ga _0.5 In _0.5 P cladding layer 26, p-GaAs contact Layer 27 was grown at 500 ° C.

Next, a circular SiO ₂ film with a diameter of 10 μm (not shown in the figure for removal in a later process) is formed by chemical vapor deposition and photoresist processes. Wet etching to halfway to form mesa. Thereafter, while a chemical vapor deposition process leaving the SiO ₂ mask is formed of SiO ₂ protective layer 28, a polyimide 29 is coated and cured. Next, the polyimide 29 is etched by reactive ion beam etching until the SiO ₂ mask is exposed, and the SiO ₂ mask on the top of the mesa is removed as shown in the figure to obtain a flat surface. Thereafter, a ring-shaped p-side electrode 31 was formed by a lift-off method, a dielectric multilayer film reflecting mirror 30 was further formed by a sputter deposition method, and an n-side electrode 32 was formed. The dielectric multilayer mirror 30 is formed by alternately laminating a high refractive index TiO ₂ layer having a quarter wavelength thickness in a dielectric and a low refractive index SiO ₂ layer having a quarter wavelength thickness in a dielectric. Produced. In order to achieve a reflectance of 99% or more, the number of layers was set to 5 pairs.

  When current was injected into the surface emitting laser, continuous operation was successful up to a high temperature of 85 ° C. The laser light was emitted from the dielectric multilayer film reflecting mirror side, and the wavelength was about 1.3 μm. Further, since this laser has good crystallinity of the active layer, it has a long device life of 10,000 hours or more sufficient for practical use of a surface emitting laser. In addition, the yield during device fabrication was high, and a significant cost reduction was achieved.

FIG. 3 is a diagram showing an element structure of the semiconductor laser of Example 1. The figure which shows the relationship between intermediate | middle layer thickness and the photoluminescence (PL) intensity | strength from an active layer. FIG. 5 is a diagram showing an element structure of a semiconductor laser of Example 2.

Explanation of symbols

1: n-GaAs substrate, 2: GaAs buffer layer, 3: n-Al _0.3 Ga _0.7 As cladding layer (layer thickness 1500 nm), 4: strain compensation quantum well active layer, 5: p-Al _0.3 Ga _0.7 As cladding layer (Layer thickness 1500 nm), 6: p-GaAs capping layer (layer thickness 200 nm), 10: GaAs light guide layer (layer thickness 150 nm), 11: GaN _0.01 As _0.99 stress compensation layer (layer thickness 5 nm), 12: GaAs intermediate Layer (layer thickness 2 nm), 13: Ga _0.6 In _0.4 N _0.005 As _0.995 well layer (layer thickness 5 nm).

Claims (4)

GaAs having a compressive strain active layer made of a GaInNAs material and a stress compensation layer made of a GaNAs material on a GaAs substrate, and having a strain intermediate between the compressive strain active layer and the stress compensation layer , A GaInNAs semiconductor laser, wherein an intermediate layer made of GaAsSb or GaInAs is inserted.   2. The GaInNAs semiconductor laser according to claim 1, wherein the strain of the intermediate layer is a compressive strain and the amount of strain is in the range of 0 to + 0.5%. 3. The GaInNAs semiconductor laser according to claim 1, wherein the intermediate layer has a thickness in a range of 0.5 nm to 2.5 nm. The GaInNAs semiconductor laser according to any one of claims 1 to 3 , further comprising a multilayer reflector below and above the compressive strain active layer.

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