JP4192293B2 - AlGaAs semiconductor laser manufacturing method, AlGaAs semiconductor device manufacturing method, and compound semiconductor growth method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for growing a compound semiconductor, and is particularly suitable for use in growing a group III-V compound semiconductor.
[0002]
[Prior art]
Among AlGaAs-based semiconductor lasers, one in which an active layer having a strained quantum well structure is realized by using GaInAs as an active layer is known. In an AlGaAs semiconductor laser having an active layer having such a strained quantum well structure, improvement in laser characteristics such as a lower threshold and higher reliability is expected.
[0003]
Here, in an AlGaAs semiconductor laser having an active layer having a strained quantum well structure using GaInAs as an active layer, AlGaAs or GaAs is used as a material for a cladding layer or an optical waveguide layer. However, the optimum growth temperature of GaInAs is different from the optimum growth temperature of AlGaAs or GaAs. For this reason, AlGaAs and GaAs can grow at about 780 ° C. to 800 ° C., whereas GaInAs generally has a lower growth temperature than AlGaAs and GaAs, specifically 750 ° C. or less, preferably 600 ° C. Must grow at ~ 750 ° C.
[0004]
The reason why GaInAs must be grown at a temperature lower than the growth temperature of AlGaAs or GaAs is because of the high vapor pressure of In. That is, when GaInAs is grown at a temperature as high as the optimal growth temperature of AlGaAs or GaAs, the re-evaporation (re-detachment) rate of In increases due to the high vapor pressure of In, and In is not taken into the crystal. In addition, when In once taken into the crystal is bolded up, pit-shaped irregularities are generated on the crystal surface, which deteriorates the surface morphology. When the GaInAs crystal in such a state is used for the active layer of the semiconductor laser, the internal loss becomes large, and the adverse effect on the increase of the oscillation threshold and the reliability becomes great.
[0005]
For example, samples having a structure in which a single-layer GaInAs film is provided on a GaAs substrate were prepared by changing the growth temperature in various ways, and the pit density on the surface of the GaInAs film was observed with an electron microscope for each sample. When the growth temperature was set to a temperature similar to the optimum growth temperature of AlGaAs or GaAs, for example, 820 ° C., circular pits were observed on the surface of the GaInAs film. The pits on the surface of the GaInAs film were generated with higher density as the In composition ratio increased. The pits on the surface of the GaInAs film are generated as a result of In re-evaporation as described above. In contrast, when the growth temperature of the GaInAs film is lower than the optimal growth temperature of AlGaAs or GaAs, for example, 750 ° C. or less, even if the In composition ratio is a large sample of 0.31, for example, The pits as described above are hardly seen. This shows that the crystallinity of the GaInAs film is improved by growing the GaInAs film at a lower temperature than the growth of AlGaAs or GaAs.
[0006]
Therefore, conventionally, when manufacturing an AlGaAs semiconductor laser having an active layer of a strained quantum well structure using GaInAs as an active layer, growth of AlGaAs constituting a cladding layer or the like is performed at a high temperature of about 750 ° C. to 800 ° C., A temperature control method for switching the growth temperature before and after the growth of the active layer has been used, such that the growth of GaInAs constituting the active layer is performed at a low temperature of 750 ° C. or less, for example, about 600 ° C. to 750 ° C.
[0007]
FIG. 12 shows a growth temperature profile when a semiconductor layer constituting a laser structure is grown by a conventional semiconductor laser manufacturing method. Here, a case will be described in which an GaAs (Separate Confinement Heterostructure) AlGaAs semiconductor laser having a cladding layer of AlGaAs, an optical waveguide layer of AlGaAs, and an active layer of GaInAs is manufactured.
[0008]
That is, in this semiconductor laser manufacturing method according to the prior art, as shown in FIG. 12, the growth temperature is set to 780 ° C. by metal organic chemical vapor deposition (MOCVD), and the n-type GaAs substrate is n-type. An AlGaAs cladding layer and an AlGaAs optical waveguide layer are grown sequentially. Next, the growth is interrupted and the growth temperature is lowered to 650 ° C. Next, when the growth temperature is stabilized at 650 ° C., a GaInAs active layer is grown on the AlGaAs optical waveguide layer. Next, the growth is interrupted again, and the growth temperature is raised to 780 ° C. again. Next, when the growth temperature is stabilized at 780 ° C., an AlGaAs optical waveguide layer and a p-type AlGaAs cladding layer are sequentially grown on the GaInAs active layer.
[0009]
According to this semiconductor laser manufacturing method according to the prior art, the growth of the AlGaAs cladding layer and the AlGaAs optical waveguide layer and the growth of the GaInAs active layer are performed at the respective optimum growth temperatures, whereby each of the components constituting the semiconductor laser structure. The crystallinity of the semiconductor layer, particularly the GaInAs active layer is improved.
[0010]
[Problems to be solved by the invention]
However, in the conventional semiconductor laser manufacturing method using the temperature control method as described above, after growing a GaInAs active layer at 650 ° C., an AlGaAs optical waveguide layer and an AlGaAs cladding layer are grown thereon. In the process of raising the growth temperature to 780 ° C., re-evaporation of In from the surface of the GaInAs active layer is inevitable. That is, the crystallinity of the obtained GaInAs active layer is deteriorated as in the case where the growth of the GaInAs active layer is performed in a state where the growth temperature is higher than the optimum growth temperature.
[0011]
Therefore, even if the temperature control method as described above is applied to manufacture an AlGaAs semiconductor laser having a strained quantum well structure and the GaInAs active layer is grown at the optimum growth temperature, the expected effect (GaInAs active layer) Improvement in crystallinity).
[0012]
When a semiconductor layer constituting a laser structure is grown using a temperature control method, the growth must be interrupted until the growth temperature is changed and the state is stabilized. There is also a problem that the semiconductor layer constituting the structure is contaminated by impurities or the like and the device characteristics are deteriorated.
[0013]
The above is for the case where GaInAs is grown on a substrate such as a GaAs substrate. However, in the case where a compound semiconductor that contains In and does not contain Al, such as GaInP and GaInAsP, is also grown on the substrate. I can say that.
[0014]
Therefore, the object of the present invention is to reduce surface re-evaporation of In from the growth layer when growing a compound semiconductor containing In and not containing Al, such as GaInAs, GaInP, and GaInAsP. It is an object of the present invention to provide a compound semiconductor growth method capable of obtaining a good growth layer.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, a compound semiconductor growth method according to the first invention of the present invention comprises:
During the growth of the compound semiconductor containing In and not containing Al, the first raw material used for the growth of the compound semiconductor is mixed with the second raw material containing Al, and at this time, the Al in the growth layer is grown. Concentration of 1 × 10 ¹⁸ / Cm ^Three In addition, the supply amount of the second raw material and the supply ratio of the second raw material to the first raw material are controlled so that the Al composition ratio in the growth layer is 0.1 or less.
It is characterized by this.
[0016]
In the first invention, a metal organic chemical vapor deposition method or a molecular beam epitaxy method is typically used for the growth of a compound semiconductor containing In and not containing Al. In the first invention, the compound semiconductor containing In and not containing Al is typically a III-V group compound semiconductor, and specifically, for example, GaInAs, GaInP, or GaInAsP.
[0017]
In the first aspect of the invention, the lower limit of the amount of Al added to the growth layer of the compound semiconductor containing In and not containing Al is the concentration of Al in the growth layer from the viewpoint of suppressing re-detachment of In from the growth layer. Is 1 × 10 ¹⁸ / Cm ^Three It is chosen to be above. In this case, in order to further reduce the re-detachment of In from the growth layer, the lower limit of the amount of Al added to the growth layer of the compound semiconductor containing In and not containing Al is preferably set to Al in the growth layer. Is selected so that the composition ratio of Al is 0.01 or more, and more preferably, the composition ratio of Al in the growth layer is 0.05 or more. As the amount of Al added to the growth layer of a compound semiconductor containing In and not containing Al increases, the effect of reducing the re-release of In increases, but the growth of the compound semiconductor containing In and not containing Al. The upper limit of the amount of Al added to the layer is, for example, that the Al composition ratio in the growth layer is 0.1 from the viewpoint of obtaining substantially the same properties as in the case where Al is not added to the growth layer. Selected to be: The upper limit of the amount of Al added to the growth layer of the compound semiconductor containing In and not containing Al is preferably selected so that the Al composition ratio in the growth layer is 0.08 or less.
[0018]
In the first aspect of the present invention, in the case of having a step of growing a compound semiconductor containing Al or not containing In before and / or after the growth of the compound semiconductor containing In and containing no Al, for example, The growth of compound semiconductors containing In and not containing Al and the growth of compound semiconductors containing Al or not containing In are optimal at a certain temperature, preferably compound semiconductors containing Al or not containing In. Do it at the growth temperature. In this case, the compound semiconductor containing In and not containing Al and the compound semiconductor containing Al or not containing In are typically III-V group compound semiconductors. The compound semiconductor that contains Al and does not contain Al is GaInAs, GaInP, or GaInAsP, and the compound semiconductor that contains Al or does not contain In is AlGaAs, AlGaInP, or GaAs. However, when the compound semiconductor containing In and not containing Al is GaInAs, it is preferable to use AlGaAs or GaAs as the compound semiconductor containing Al or not containing In, and a compound semiconductor containing In and not containing Al. Is a GaInP, it is preferable to use AlGaInP as a compound semiconductor containing Al or not containing In.
[0019]
In the first invention, after growing a compound semiconductor containing In and not containing Al, when growing a compound semiconductor containing Al or not containing In on the growth layer, for example, The growth of the compound semiconductor containing In and not containing Al is performed at the first temperature, and the growth of the compound semiconductor containing Al or not containing In is performed at the second growth temperature higher than the first temperature. To do. Here, the first temperature is preferably selected as an optimum growth temperature when a compound semiconductor containing In and containing Al is grown without mixing the second raw material into the first raw material. The temperature is preferably selected as the optimum growth temperature of the compound semiconductor containing Al or not containing In. In this case, the compound semiconductor containing In and not containing Al and the compound semiconductor containing Al or not containing In are typically III-V group compound semiconductors. The compound semiconductor that contains Al and does not contain Al is GaInAs, GaInP, or GaInAsP, and the compound semiconductor that contains Al or does not contain In is AlGaAs, AlGaInP, or GaAs. However, when the compound semiconductor containing In and not containing Al is GaInAs, it is preferable to use AlGaAs or GaAs as the compound semiconductor containing Al or not containing In, and a compound semiconductor containing In and not containing Al. Is a GaInP, it is preferable to use AlGaInP as a compound semiconductor containing Al or not containing In.
[0020]
According to the first aspect of the present invention configured as described above, when the compound semiconductor containing In and not containing Al is grown, the first raw material used for the growth of the compound semiconductor contains Al. In this case, the Al concentration in the growth layer is 1 × 10 6. ¹⁸ / Cm ^Three By controlling the supply amount of the second raw material and the supply ratio of the second raw material to the first raw material so that the Al composition ratio in the growth layer is 0.1 or less. The movement of In atoms is suppressed by the Al atoms added to the growth layer, and the re-detachment of In from the growth layer is suppressed.
[0021]
In this way, by suppressing the re-detachment of In from the growth layer of the compound semiconductor containing In and not containing Al, whether the compound semiconductor containing In and not containing Al (for example, GaInAs) contains Al? Alternatively, a growth layer of a compound semiconductor containing In and containing Al having good surface morphology can be obtained even when grown in a temperature range similar to the optimum growth temperature of a compound semiconductor containing no In (eg, AlGaAs or GaAs). be able to. As a result, when a compound semiconductor containing Al or not containing Al is grown before and / or after the growth of the compound semiconductor containing Al and not containing Al, the compound semiconductor containing In and Al is included. It is possible to perform growth of a compound semiconductor not containing Al and growth of a compound semiconductor containing Al or not containing In at a certain temperature, before and after the growth of the compound semiconductor containing In and not containing Al. This eliminates the need to perform growth temperature control with growth interruption.
[0022]
In addition, after a compound semiconductor containing In and not containing Al is grown at the first temperature, another compound semiconductor, for example, a compound semiconductor containing Al or not containing In is higher than the first temperature. In the case of having a step of growing at a temperature, after completion of the growth of the compound semiconductor containing In and not containing Al, in the temperature rising process of raising the growth temperature from the first temperature to the second temperature, the In containing and Al are contained. It is possible to reduce the re-detachment of In from the growth layer of the compound semiconductor that is not included.
[0023]
A method for growing a compound semiconductor according to a second invention of the present invention comprises:
Growing a first compound semiconductor containing In and not containing Al at a first temperature at which In does not re-detach from the growth layer;
Growing a second compound semiconductor containing Al on the growth layer of the first compound semiconductor at a first temperature;
A step of growing a third compound semiconductor containing Al or not containing In at a second temperature higher than the first temperature on the growth layer of the second compound semiconductor.
It is characterized by having.
[0024]
A method for growing a compound semiconductor according to a third aspect of the present invention comprises:
By alternately growing a first compound semiconductor containing In and not containing Al and a second compound semiconductor containing Al at a first temperature at which In does not re-separate from the growth layer of the first compound semiconductor, Forming a stacked structure in which a growth layer of a first compound semiconductor is sandwiched between growth layers of a second compound semiconductor;
A step of growing a third compound semiconductor containing Al or not containing In at a second temperature higher than the first temperature on the second compound semiconductor growth layer in the uppermost layer of the stacked structure.
It is characterized by having.
[0025]
In the second and third inventions of the present invention, the growth of the first compound semiconductor, the second compound semiconductor, and the third compound semiconductor typically involves metal organic chemical vapor deposition or molecules. Line epitaxy is used. In the second and third aspects of the invention, the first growth temperature is preferably selected as the optimum growth temperature for the first compound semiconductor. The second temperature higher than the first temperature is a temperature at which In re-detaches from the growth layer of the first compound semiconductor, and is preferably selected as the optimum growth temperature of the third compound semiconductor. .
[0026]
In the second and third aspects of the invention, the first compound semiconductor, the second compound semiconductor, and the third compound semiconductor are typically III-V group compound semiconductors, specifically The first compound semiconductor is GaInAs, GaInP or GaInAsP, the second compound semiconductor is AlGaAs or AlGaInP, and the third compound semiconductor is AlGaAs, AlGaInP or GaAs.
[0027]
According to the second invention of the present invention, the step of growing the first compound semiconductor containing In and containing no Al at the first temperature at which In does not re-separate from the growth layer, and the first compound semiconductor A step of growing a second compound semiconductor containing Al on the first growth layer at a first temperature, and a third compound containing Al or not containing In on the growth layer of the second compound semiconductor. And growing the compound semiconductor at a second temperature higher than the first temperature, whereby the growth layer of the first compound semiconductor containing In and not containing Al is formed of the second compound semiconductor containing Al. Capped by the growth layer. Since the movement of In atoms is suppressed due to the presence of Al atoms in the growth layer of the second compound semiconductor, the In in the growth layer of the first compound semiconductor is changed to the growth layer of the second compound semiconductor. Evaporation can be suppressed through Therefore, after the growth of the second compound semiconductor is completed, the growth temperature of the first compound semiconductor is increased from the first temperature to the second temperature in order to grow the third compound semiconductor. In re-extraction of In can be reduced.
[0028]
According to the third aspect of the present invention, the first compound semiconductor containing In and not containing Al and the second compound semiconductor containing Al are not separated from the growth layer of the first compound semiconductor. By alternately growing at a temperature of 1, a stacked structure in which the growth layer of the first compound semiconductor is sandwiched between the growth layers of the second compound semiconductor, and on the growth layer of the second compound semiconductor, Al is formed. Growing a third compound semiconductor containing In or not containing In at a second temperature higher than the first temperature, thereby growing a first compound semiconductor containing In and not containing Al. The layer is capped by a second compound semiconductor growth layer comprising Al. Since the movement of In atoms is suppressed due to the presence of Al atoms in the growth layer of the second compound semiconductor, the In in the growth layer of the first compound semiconductor is changed to the growth layer of the second compound semiconductor. Evaporation can be suppressed through Therefore, after the growth of the second compound semiconductor is completed, the growth temperature of the first compound semiconductor is increased from the first temperature to the second temperature in order to grow the third compound semiconductor. In re-extraction of In can be reduced.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. Here, the case where the compound semiconductor growth method according to the present invention is applied to the manufacture of a semiconductor laser having an active layer having a strained quantum well structure will be described.
[0030]
First, a first embodiment of the present invention will be described. FIG. 1 is a cross-sectional view of an AlGaAs semiconductor laser having an active layer having a strained quantum well structure to be manufactured in the first embodiment. The AlGaAs semiconductor laser has an SCH structure, and the active layer has a single quantum well (SQW) structure.
[0031]
As shown in FIG. 1, in an AlGaAs semiconductor laser having an active layer of this strained quantum well structure, for example, an n-type AlGaAs cladding layer 2, a GaAs optical waveguide layer 3, an Al-doped GaInAs are formed on an n-type GaAs substrate 1. An active layer 4, a GaAs optical waveguide layer 5, a p-type AlGaAs cladding layer 6, and a p-type GaAs cap layer 7 are sequentially stacked.
[0032]
Here, the n-type AlGaAs cladding layer 2 and the p-type AlGaAs cladding layer 6 are, for example, Al _0.45 Ga _0.55 It consists of As. In addition, as described later, the Al-added GaInAs active layer 4 mixes a raw material containing Al (second raw material) with a raw material (first raw material) used for normal GaInAs growth during the growth of GaInAs. It is formed by performing growth, and consists of GaInAs as a main component and a predetermined amount of Al added to this GaInAs.
[0033]
The lower limit of the amount of Al added to the Al-added GaInAs active layer 4 is such that, for example, the doping concentration of Al in GaInAs is 1 × 10 6 so that re-evaporation of In from the Al-added GaInAs active layer 4 is suppressed. ¹⁸ / Cm ^Three It is chosen to be above, preferably Al _x Ga _1-xy In _y As is selected so that the Al composition ratio x in As is 0.01 or more, and more preferably, Al _x Ga _1-xy In _y The Al composition ratio x in As is selected to be 0.05 or more. It should be noted that as the amount of Al added to the Al-added GaInAs active layer 4 increases, the expected effect of suppressing the re-evaporation of In is greater. The upper limit of the amount of Al added is, for example, Al so that substantially the same properties as those obtained when not performed can be obtained. _x Ga _1-xy In _y As is selected so that the Al composition ratio x in As is 0.1 or less, preferably, Al _x Ga _1-xy In _y The Al composition ratio x in As is selected to be 0.08 or less. In this case, specifically, the Al-added GaInAs active layer 4 is made of, for example, Al _0.05 Ga _0.75 In _0.2 It is composed of As. The emission wavelength at this time is 0.94 μm. Incidentally, Ga instead of Al-added GaInAs active layer 4 _0.8 In _0.2 When the GaInAs active layer made of As is used, the emission wavelength is 0.98 μm.
[0034]
The upper layer portion of the p-type AlGaAs cladding layer 6 and the p-type GaAs cap layer 7 are patterned into a ridge stripe shape having a predetermined width extending in one direction. An n-type GaAs current confinement layer 8 is buried in both sides of the ridge stripe portion, thereby forming a current confinement structure.
[0035]
A p-side electrode 9 such as a Ti / Pt / Au electrode is provided on the p-type GaAs cap layer 7 and the n-type GaAs current confinement layer 8, while an AuGe / An n-side electrode 10 such as a Ni electrode is provided.
[0036]
As an example of the thickness of each semiconductor layer constituting this semiconductor laser, the thickness of the n-type AlGaAs cladding layer 2 is 2 μm, the thickness of the GaAs optical waveguide layers 3 and 5 is 100 nm, and the Al-doped GaInAs active layer 4 The thickness is 10 nm, the total thickness of the p-type AlGaAs cladding layer 6 is 1.5 μm, and the thickness of both sides of the ridge stripe portion of the p-type AlGaAs cladding layer 6 is 0.5 μm.
[0037]
The semiconductor laser manufacturing method according to the first embodiment in which an AlGaAs semiconductor laser having an active layer with a strained quantum well structure configured as described above is manufactured will be described below. In the semiconductor laser manufacturing method according to the first embodiment, the compound semiconductor growth method according to the first invention of the present invention is applied to the growth of the Al-added GaInAs active layer 4. In the first embodiment, the semiconductor layer constituting the laser structure is grown at a constant temperature. 2 to 4 are cross-sectional views for explaining the semiconductor laser manufacturing method according to the first embodiment.
[0038]
In the semiconductor laser manufacturing method according to the first embodiment, in order to manufacture the semiconductor laser described above, each semiconductor layer constituting the laser structure is formed by, for example, the MOCVD method. At this time, as a raw material of the III-V group compound semiconductor, trimethylaluminum (TMA), trimethylgallium (TMG), trimethylindium (TMIn), arsine (AsH) _Three For example, Si or Se as the n-type impurity, and Zn as the p-type impurity, for example.
[0039]
In the method of manufacturing the semiconductor laser according to the first embodiment, first, as shown in FIG. 2, the growth temperature is 780 ° C. or higher and 800 ° C. or lower, which is the optimum growth temperature for AlGaAs and GaAs. And an n-type AlGaAs cladding layer 2, a GaAs optical waveguide layer 3, an Al-doped GaInAs active layer 4, a GaAs optical waveguide layer 5, a p-type AlGaAs cladding layer 6 and a p-type GaAs cap layer. 7 are sequentially grown by MOCVD.
[0040]
Here, when the Al-added GaInAs active layer 4 is grown, a raw material (first raw material) used for the growth of GaInAs, that is, TMG as a Ga raw material, TMIn as an In raw material, and AsH as an As raw material. _Three In addition, TMA (second raw material) as an Al raw material is simultaneously led to the reaction tube of the MOCVD apparatus, and GaInAs is grown while adding Al. At this time, the Al concentration in the Al-added GaInAs active layer 4 is 1 × 10 6. ¹⁸ / Cm ^Three (Preferably the Al composition ratio in the Al-added GaInAs active layer 4 is 0.01 or more, more preferably the Al composition ratio in the Al-added GaInAs active layer 4 is 0.05 or more), and this Al addition The amount of TMA added, TMG, TMIn, and Al so that the Al composition ratio in the GaInAs active layer 4 is 0.1 or less (preferably the Al composition ratio in the Al-added GaInAs active layer 4 is 0.08 or less). AsH _Three The TMA supply ratio with respect to is controlled. In this case, for example, the composition of the growth layer is Al. _0.05 Ga _0.75 In _0.2 The growth is performed under the condition of As, and the Al-added GaInAs active layer 4 is formed. In this way, the second source material containing Al is mixed into the first source material used for the growth of GaInAs, and the growth of the Al-added GaInAs active layer 4 is performed under a condition where the V / III ratio is small. It is effective in suppressing
[0041]
Next, as shown in FIG. 3, the entire surface of the p-type GaAs cap layer 7 is made of SiO. ₂ A mask 11 is formed by forming a film or a SiN film and patterning it into a predetermined stripe shape. Next, using the mask 11 as an etching mask, the p-type AlGaAs cladding layer 6 is etched to a depth in the middle of the thickness direction by, for example, a wet etching method. As a result, the upper layer portion of the p-type AlGaAs cladding layer 6 and the p-type GaAs cap layer 7 are patterned into a predetermined ridge stripe shape.
[0042]
Next, as shown in FIG. 4, an n-type GaAs current confinement layer 8 is grown by MOCVD using the mask 11 as a growth mask so as to fill in the portions on both sides of the ridge stripe portion. Thereafter, the mask 11 is removed by etching.
[0043]
Next, as shown in FIG. 1, a p-side electrode 9 is formed on the p-type GaAs cap layer 7 and the n-type GaAs current confinement layer 8 by vacuum deposition or sputtering, and the n-type GaAs substrate 1 is formed. An n-side electrode 10 is formed on the back surface.
[0044]
In this way, an AlGaAs semiconductor laser having an active layer having a target strained quantum well structure is manufactured.
[0045]
Here, in order to verify the effect of suppressing the re-evaporation of In due to the addition of Al to GaInAs, a single layer of Al is formed on a GaAs substrate at 780 ° C. _x Ga _1-xy In _y Samples with grown As films were prepared by changing the Al composition ratio x in various ways. _x Ga _1-xy In _y The relationship between the Al composition ratio x and the pit density was examined by observing the pit density on the surface of the As film with an electron microscope. FIG. 5 is a graph showing the results. Here, Al _x Ga _1-xy In _y The In composition ratio y in the As film is 0.15.
[0046]
According to FIG. 5, Al is formed on a GaAs substrate at 780 ° C. _x Ga _1-xy In _y It can be seen that in the sample grown with As film, the pit density decreases as the Al composition ratio x increases. This is an effect obtained by suppressing re-evaporation of In by adding Al to GaInAs.
[0047]
According to the first embodiment configured as described above, in an AlGaAs semiconductor laser having an active layer having a strained quantum well structure, an Al-added GaInAs active layer 4 is used as an active layer, and this Al-added GaInAs active layer is used. 4 is a first raw material (TMG, TMIn and AsH used for the growth of GaInAs). _Three ) Is mixed with a second raw material (TMA) containing Al and grown by GaInAs growth while adding Al, so that the Al-added GaInAs active layer 4 can be formed. In reevaporation of In can be suppressed. Therefore, the Al-doped GaInAs active layer 4 can be grown at the optimum growth temperature of the n-type AlGaAs cladding layer 2, the GaAs optical waveguide layers 3 and 5, and the p-type AlGaAs cladding layer 6. Even when the growth is performed, there are almost no pits due to evaporation of In on the surface, and an Al-added GaInAs active layer 4 with good crystallinity can be obtained. This makes it possible to manufacture a semiconductor laser with good operating characteristics and high reliability.
[0048]
Further, the Al-doped GaInAs active layer 4 can be grown at the optimum growth temperature of the n-type AlGaAs cladding layer 2, the GaAs optical waveguide layers 3 and 5, and the p-type AlGaAs cladding layer 6, thereby forming a laser structure. Since the semiconductor layer can be grown at a constant temperature, there is no growth interruption due to a complicated growth process as in the case of using the temperature control method. This simplifies the manufacturing process and prevents the semiconductor layer constituting the laser structure from being contaminated by impurities due to the growth interruption.
[0049]
Next explained is the second embodiment of the invention. In the second embodiment, an AlGaAs semiconductor laser having an active layer having a strained quantum well structure shown in FIG. 1 of the first embodiment is manufactured.
[0050]
A method for manufacturing the semiconductor laser according to the second embodiment, in which an AlGaAs semiconductor laser having an active layer with a strained quantum well structure is manufactured, will be described below. In the semiconductor laser manufacturing method according to the second embodiment, the compound semiconductor growth method according to the first invention is applied to the growth of the Al-doped GaInAs active layer 4. In the second embodiment, the semiconductor layer constituting the laser structure is formed using a temperature control method that switches the growth temperature before and after the growth of the active layer. FIG. 6 is a schematic diagram showing a growth temperature profile when a semiconductor layer constituting a laser structure is grown in the semiconductor laser manufacturing method according to the second embodiment.
[0051]
That is, in the method of manufacturing the semiconductor laser according to the second embodiment, as shown in FIG. 6, the growth temperature is 780 ° C. or higher and 800 ° C. or lower, which is the optimum growth temperature for AlGaAs and GaAs. The n-type AlGaAs cladding layer 2 and the GaAs optical waveguide layer 3 are sequentially grown on the n-type GaAs substrate 1 by MOCVD. Next, the growth is interrupted, and the growth temperature is lowered to 600 ° C. or higher and 750 ° C. or lower, which is the optimum growth temperature of GaInAs, specifically to 650 ° C., for example. Next, when the growth temperature is stabilized at 650 ° C., an Al-added GaInAs active layer 4 is grown on the GaAs optical waveguide layer 3 by MOCVD. Since the growth method of the Al-added GaInAs active layer 4 is the same as that in the semiconductor laser manufacturing method according to the first embodiment except that the growth temperature is different, description thereof is omitted. Next, the growth is interrupted again, and the growth temperature is raised to 780 ° C. again. Next, when the growth temperature is stabilized at 780 ° C., the GaAs optical waveguide layer 5, the p-type AlGaAs cladding layer 6 and the p-type GaAs cap layer 7 are sequentially grown on the Al-added GaInAs active layer 4 by MOCVD.
[0052]
Thereafter, similarly to the semiconductor laser manufacturing method according to the first embodiment, the upper layer portion of the p-type AlGaAs cladding layer 6 and the p-type GaAs cap layer 7 are patterned into a ridge stripe shape, and portions on both sides of the ridge stripe portion are formed. After the n-type GaAs current confinement layer 8 is embedded in the current confinement structure to form a current confinement structure, a p-side electrode 9 is formed on the p-type GaAs cap layer 7 and the n-type GaAs current confinement layer 8, and An n-side electrode 10 is formed on the back surface. As described above, an AlGaAs semiconductor laser having an active layer having a target strained quantum well structure is completed.
[0053]
According to the second embodiment, re-evaporation of In from the Al-added GaInAs active layer 4 can be suppressed as in the first embodiment. For this reason, after the Al-added GaInAs active layer 4 is grown at 650 ° C., the Al-added GaInAs is raised in the temperature increasing process from 650 ° C. to 780 ° C. in order to grow the GaAs optical waveguide layer 5 and the like thereon. Since the re-evaporation of In from the active layer 4 can be reduced and the good crystallinity of the Al-added GaInAs active layer 4 can be maintained, the semiconductor layer constituting the laser structure can be formed using a temperature control method. You can maximize the benefits of growing. Thereby, a semiconductor laser having good operating characteristics and a long lifetime can be manufactured.
[0054]
Next explained is the third embodiment of the invention. FIG. 7 is a cross-sectional view of an AlGaAs semiconductor laser having an active layer having a strained quantum well structure to be manufactured in the third embodiment. The AlGaAs semiconductor laser has an SCH structure, and the active layer has a single quantum well structure. 7, parts that are the same as or correspond to those in FIG. 1 are given the same reference numerals.
[0055]
As shown in FIG. 7, in the AlGaAs semiconductor laser having the active layer of the strained quantum well structure, a GaInAs active layer 21 is used instead of the Al-added GaInAs active layer 4. In this case, the GaInAs active layer 21 is specifically made of, for example, Ga _0.8 In _0.2 It consists of As. An AlGaAs cap layer 22 is provided between the GaInAs active layer 21 and the GaAs optical waveguide layer 5. The AlGaAs cap layer 22 has such a thickness that carriers can tunnel, for example, a thickness of several atomic layers (several to several tens of tens).
[0056]
Here, the cap layer provided between the GaInAs active layer 21 and the GaAs optical waveguide layer 5 must be configured using a material containing Al. This is because, for example, when a GaAs cap layer not containing Al is used instead of the AlGaAs cap layer 22, as will be described later, in the temperature raising process for raising the growth temperature in order to grow the GaAs optical waveguide layer 5, This is because In in the GaInAs active layer 21 evaporates through the GaAs cap layer.
[0057]
Since the other configuration of the semiconductor laser is the same as that of the semiconductor laser shown in FIG. 1 of the first embodiment, description thereof is omitted.
[0058]
A method for manufacturing the semiconductor laser according to the third embodiment, in which an AlGaAs semiconductor laser having an active layer with a strained quantum well structure shown in FIG. 7 is manufactured, will be described below. In the third embodiment, the compound semiconductor growth method according to the second invention of the present invention is applied to the growth of the semiconductor layer constituting the laser structure. FIG. 8 is a schematic diagram showing a growth temperature profile when a semiconductor layer constituting the laser structure is grown in the semiconductor laser manufacturing method according to the third embodiment.
[0059]
That is, in the third embodiment, as shown in FIG. 8, the growth temperature is set to 780 ° C. or more and 800 ° C. or less, which is the optimum growth temperature for AlGaAs and GaAs, specifically, for example, 780 ° C. An n-type AlGaAs cladding layer 2 and a GaAs optical waveguide layer 3 are sequentially grown on the GaAs substrate 1 by MOCVD. Next, the growth is interrupted, and the growth temperature is lowered to 600 ° C. or higher and 750 ° C. or lower, which is the optimum growth temperature of GaInAs, specifically to 650 ° C., for example. Next, when the growth temperature is stabilized at 650 ° C., a GaInAs active layer 21 made of GaInAs and an AlGaAs cap layer 22 are sequentially grown on the GaAs optical waveguide layer 3 by MOCVD. Next, the growth is interrupted again, and the growth temperature is raised to 780 ° C. again. Next, when the growth temperature is stabilized at 780 ° C., the GaAs optical waveguide layer 5, the p-type AlGaAs cladding layer 6 and the p-type GaAs cap layer 7 are sequentially grown on the AlGaAs cap layer 22 by MOCVD. In this case, since each semiconductor layer constituting the laser structure is grown at the respective optimum growth temperature, the crystallinity is good.
[0060]
Thereafter, similarly to the semiconductor laser manufacturing method according to the first embodiment, the upper layer portion of the p-type AlGaAs cladding layer 6 and the p-type GaAs cap layer 7 are patterned into a ridge stripe shape, and portions on both sides of the ridge stripe portion are formed. After the n-type GaAs current confinement layer 8 is embedded in the current confinement structure to form a current confinement structure, a p-side electrode 9 is formed on the p-type GaAs cap layer 7 and the n-type GaAs current confinement layer 8, An n-side electrode 10 is formed on the back surface. As described above, an AlGaAs semiconductor laser having an active layer having a target strained quantum well structure is completed.
[0061]
According to the third embodiment, after the GaInAs active layer 21 is grown at 650 ° C., which is the optimum growth temperature of GaInAs, and before the growth temperature is increased to grow the GaAs optical waveguide layer 5, that is, GaInAs. When the growth of the active layer 21 is completed, the AlGaAs cap layer 22 is grown on the GaInAs active layer 21 at 650 ° C., so that the temperature is raised from 650 ° C. to 780 ° C. In the process, re-evaporation of In from the GaInAs active layer 21 can be reduced, and good crystallinity of the GaInAs active layer 21 can be maintained. Therefore, a semiconductor that forms a laser structure using a temperature control method You can maximize the benefits of growing layers. Thereby, a semiconductor laser having good operating characteristics and a long lifetime can be manufactured.
[0062]
Next explained is the fourth embodiment of the invention. FIG. 9 is a cross-sectional view of an AlGaAs semiconductor laser having an active layer having a strained quantum well structure to be manufactured in the fourth embodiment. This semiconductor laser has an SCH structure, and the active layer has a multiple quantum well (MQW) structure. FIG. 10 is an energy band diagram of the semiconductor laser shown in FIG. In FIG. _C Indicates the energy at the bottom of the conduction band.
[0063]
As shown in FIGS. 9 and 10, in an AlGaAs semiconductor laser having an active layer of this strained quantum well structure, for example, an n-type AlGaAs cladding layer 32, an AlGaAs optical waveguide layer 33, an n-type GaAs substrate 31, An MQW structure active layer 34 in which GaInAs quantum well layers 34 a and AlGaAs barrier layers 34 b are alternately stacked, an AlGaAs optical waveguide layer 35, a p-type AlGaAs cladding layer 36, and a p-type GaAs cap layer 37 are sequentially stacked.
[0064]
Here, the n-type AlGaAs cladding layer 32 and the p-type AlGaAs cladding layer 36 are, for example, Al _0.45 Ga _0.55 For example, AlGaAs optical waveguide layers 33 and 35 are made of As. _0.1 Ga _0.9 It consists of As. The GaInAs quantum well layer 34a constituting the active layer 34 of the MQW structure is, for example, Ga _0.8 In _0.2 The AlGaAs barrier layer 34b is made of, for example, Al. _0.1 Ga _0.9 It consists of As. In this case, the barrier layer in the active layer 34 of the MQW structure must be configured using a material containing Al, such as AlGaAs.
[0065]
The upper layer portion of the p-type AlGaAs cladding layer 36 and the p-type GaAs cap layer 37 have a predetermined ridge stripe shape extending in one direction. An n-type GaAs current confinement layer 38 is buried on both sides of the ridge stripe portion, thereby forming a current confinement structure.
[0066]
A p-side electrode 39 such as a Ti / Pt / Au electrode is provided on the p-type GaAs cap layer 37 and the n-type GaAs current confinement layer 38, while an AuGe / An n-side electrode 40 such as a Ni electrode is provided.
[0067]
As an example of the thickness of each semiconductor layer constituting the semiconductor laser, the thickness of the n-type AlGaAs cladding layer 32 is 2 μm, the thickness of the AlGaAs optical waveguide layers 33 and 35 is 100 nm, and the thickness of the GaInAs quantum well layer 34a. The thickness of the AlGaAs barrier layer 34b is 5 nm, the total thickness of the p-type AlGaAs cladding layer 36 is 1.5 μm, and the thickness of both sides of the ridge stripe portion of the p-type AlGaAs cladding layer 36 is 0. 5 μm.
[0068]
A method for manufacturing a semiconductor laser according to the fourth embodiment, in which a semiconductor laser having an active layer with a strained quantum well structure configured as described above, is described below. In the fourth embodiment, the compound semiconductor growth method according to the third aspect of the present invention is used for the growth of the semiconductor layer constituting the laser structure. FIG. 11 is a schematic diagram showing a growth temperature profile when a semiconductor layer constituting a laser structure is grown in the semiconductor laser manufacturing method according to the fourth embodiment.
[0069]
That is, in the fourth embodiment, as shown in FIG. 11, the growth temperature is set to 780 ° C. or more and 800 ° C. or less, which is the optimum growth temperature for AlGaAs and GaAs, specifically, for example, 780 ° C. An n-type AlGaAs cladding layer 32 and an AlGaAs optical waveguide layer 33 are sequentially grown on the GaAs substrate 31 by MOCVD. Next, the growth is interrupted, and the growth temperature is lowered to 600 ° C. or higher and 750 ° C. or lower, which is the optimum growth temperature of GaInAs, specifically to 650 ° C., for example. Next, when the growth temperature is stabilized at 650 ° C., an active layer 34 having an MQW structure is grown on the AlGaAs optical waveguide layer 33. At this time, first, an AlGaAs barrier layer 34b is grown on the AlGaAs optical waveguide layer 33, and thereafter, a GaInAs quantum well layer 34a and an AlGaAs barrier layer 34b are alternately grown, and the uppermost layer of the active layer 34 of the MQW structure is formed. The AlGaAs barrier layer 34b is formed. Next, the growth is interrupted again, and the growth temperature is raised to 780 ° C. again. Next, when the growth temperature is stabilized at 780 ° C., the AlGaAs optical waveguide layer 35, the p-type AlGaAs cladding layer 36, and the p-type GaAs cap layer 37 are MOCVDed on the uppermost AlGaAs barrier layer 34b of the active layer 34 of the MQW structure. Growing sequentially by law.
[0070]
Thereafter, as in the semiconductor laser manufacturing method according to the first embodiment, the upper layer portion of the p-type AlGaAs cladding layer 36 and the p-type GaAs cap layer 37 are patterned into a ridge stripe shape, and portions on both sides of the ridge stripe portion are formed. After the n-type GaAs current confinement layer 38 is buried in the current confinement structure to form a current confinement structure, a p-side electrode 39 is formed on the p-type GaAs cap layer 37 and the n-type GaAs current confinement layer 38 and the n-type GaAs substrate 31 is formed. An n-side electrode 40 is formed on the back surface. As described above, an AlGaAs semiconductor laser having an active layer having a target strained quantum well structure is completed.
[0071]
According to the fourth embodiment, when the active layer 34 having the MQW structure is formed, the GaInAs quantum well layer 34a is sandwiched between the AlGaAs barrier layers 34b. Thereafter, the growth temperature is changed from 650 ° C. to 780 ° C. Since the re-evaporation of In from the GaInAs quantum well layer 34a can be reduced in the temperature raising process raised to 0 ° C., the same effect as in the third embodiment can be obtained.
[0072]
Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications based on the technical idea of the present invention are possible. For example, the growth temperature, numerical value, material, laser structure, manufacturing process, and the like given in the embodiment are merely examples, and the present invention is not limited thereto. Specifically, for example, in the first to fourth embodiments described above, the semiconductor layer constituting the laser structure is grown by the MOCVD method. However, the semiconductor layer constituting the laser structure is a molecular beam. You may make it grow by an epitaxy (MBE) method.
[0073]
In the first to fourth embodiments, the conductivity types of the semiconductor layers constituting the substrate and the laser structure may be reversed. In the first to third embodiments described above, GaAs is used as the material of the optical waveguide layer. As the material of the optical waveguide layer, AlGaAs may be used according to the band gap of the active layer. Is possible.
[0074]
In the fourth embodiment described above, the growth from the n-type AlGaAs cladding layer 32 to the p-type GaAs cap layer 37 may be performed by the following growth process. That is, the growth temperature is set to 780 ° C. or more and 800 ° C. or less, for example, 780 ° C., and the n-type AlGaAs cladding layer 32 is grown on the n-type GaAs substrate 31 by the MOCVD method. Next, the AlGaAs optical waveguide layer 33 is continuously grown on the n-type AlGaAs cladding layer 32 at 780 ° C. by a first thickness smaller than the thickness to be finally formed. Next, the growth is interrupted, the growth temperature is lowered to 600 ° C. or more and 750 ° C. or less, for example, 650 ° C., and when the growth temperature is stabilized at 650 ° C., the remaining portion of the AlGaAs optical waveguide layer 33 and the active layer of MQW structure Grow 34. Next, at a temperature of 650 ° C., an AlGaAs optical waveguide layer 35 is grown on the active layer 34 by a second thickness smaller than the thickness to be finally formed. Next, the growth is interrupted again, and the growth temperature is raised to 780 ° C. again. Next, when the growth temperature is stabilized at 780 ° C., the remaining portion of the AlGaAs optical waveguide layer 35, the p-type AlGaAs cladding layer 36, and the p-type GaAs cap layer 37 are sequentially grown by MOCVD. Also by such a growth process, the same effect as in the fourth embodiment can be obtained.
[0075]
In the first to third embodiments described above, an n-type GaAs optical waveguide layer and a p-type GaAs optical waveguide layer may be used instead of the GaAs optical waveguide layers 3 and 5. In the fourth embodiment, an n-type AlGaAs optical waveguide layer and a p-type AlGaAs optical waveguide layer may be used instead of the AlGaAs optical waveguide layers 33 and 35.
[0076]
In the first to fourth embodiments described above, the method for growing a compound semiconductor according to the present invention is performed using GaInAs as an example in the case of manufacturing an AlGaAs semiconductor laser having an active layer having a strained quantum well structure. Although the case where the present invention is applied to the growth of the AlGaAs-based material including the above has been described, the compound semiconductor growth method according to the present invention can also be applied to the growth of the AlGaInP-based material including the growth of GaInP, for example.
[0077]
In the first to fourth embodiments described above, the case where the compound semiconductor growth method according to the present invention is applied to the manufacture of a semiconductor laser has been described. However, the compound semiconductor growth method according to the present invention includes a semiconductor laser. In addition to the manufacture of the light emitting element as described above, the present invention can be applied to manufacture of a light receiving element and an electron traveling element, that is, manufacture of a semiconductor device in general.
[0078]
【The invention's effect】
As described above, according to the compound semiconductor growth method of the first aspect of the present invention, the movement of In atoms is suppressed by Al atoms added to the growth layer, and the re-detachment of In from the growth layer is suppressed. Therefore, it is possible to obtain a compound semiconductor growth layer containing In and containing Al with good surface morphology.
[0079]
According to the method for growing a compound semiconductor according to the second invention of the present invention and the method for growing a compound semiconductor according to the third invention, the growth layer of the first compound semiconductor that contains In and does not contain Al contains Al. Since the movement of In atoms is suppressed by the presence of Al atoms in the growth layer of the second compound semiconductor that is capped by the growth layer of the second compound semiconductor, In in the growth layer of the first compound semiconductor is Evaporation through the growth layer of the second compound semiconductor can be suppressed. Therefore, in the temperature rising process for raising the growth temperature from the first temperature to the second temperature in order to grow the third compound semiconductor containing Al or not containing In, the growth from the growth layer of the first compound semiconductor The re-detachment of In can be reduced, and a first compound semiconductor growth layer having a good surface morphology can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an AlGaAs semiconductor laser having an active layer having a strained quantum well structure to be manufactured in a first embodiment of the present invention.
FIG. 2 is a cross-sectional view for explaining the method of manufacturing the semiconductor laser according to the first embodiment of the invention.
FIG. 3 is a cross-sectional view for explaining the method of manufacturing the semiconductor laser according to the first embodiment of the invention.
FIG. 4 is a cross-sectional view for explaining the method of manufacturing the semiconductor laser according to the first embodiment of the invention.
FIG. 5 shows Al on a GaAs substrate at 780 ° C. _x Ga _1-xy In _y Al composition ratio x in the sample grown with As film and Al _x Ga _1-xy In _y It is a graph which shows the relationship of the pit density of the surface of As film | membrane.
FIG. 6 is a schematic diagram showing a growth temperature profile when a semiconductor layer constituting a laser structure is grown in the semiconductor laser manufacturing method according to the second embodiment of the present invention.
FIG. 7 is a cross-sectional view of an AlGaAs semiconductor laser having an active layer with a strained quantum well structure to be manufactured in a third embodiment of the present invention.
FIG. 8 is a schematic diagram showing a growth temperature profile when a semiconductor layer constituting a laser structure is grown in the semiconductor laser manufacturing method according to the third embodiment of the present invention.
FIG. 9 is a cross-sectional view of an AlGaAs semiconductor laser having an active layer having a strained quantum well structure to be manufactured in a fourth embodiment of the present invention.
10 is an energy band diagram of an AlGaAs semiconductor laser having an active layer having a strained quantum well structure shown in FIG.
FIG. 11 is a schematic diagram showing a growth temperature profile when a semiconductor layer constituting a laser structure is grown in the semiconductor laser manufacturing method according to the fourth embodiment of the present invention;
FIG. 12 is a schematic diagram showing a growth temperature profile when a semiconductor layer constituting a laser structure is grown in a semiconductor laser manufacturing method according to a conventional technique.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,31 ... n-type GaAs substrate, 2, 32 ... n-type AlGaAs clad layer, 3, 5 ... GaAs optical waveguide layer, 4 ... Al addition GaInAs active layer, 6, 36 ... p-type AlGaAs cladding layer, 7, 37... p-type GaAs cap layer, 8, 38... n-type GaAs current confinement layer, 9, 39... p-side electrode, 10, 40. , 21... GaInAs active layer, 22... AlGaAs cap layer, 33 and 35... AlGaAs optical waveguide layer, 34... MQW structure active layer, 34 a... GaInAs quantum well layer, 34 b.・ AlGaAs barrier layer

Claims (6)

Growing an Al-added GaInAs active layer to which Al is added in a composition ratio of 0.01 or more and 0.1 or less by metal organic chemical vapor deposition;
A step of growing an AlGaAs or GaAs layer on the Al-added GaInAs active layer by metal organic chemical vapor deposition.
A method of manufacturing an AlGaAs semiconductor laser, wherein the growth of the Al-added GaInAs active layer and the growth of the AlGaAs or GaAs layer are sequentially performed by setting the growth temperature to a constant temperature of 780 ° C. or higher and 800 ° C. or lower . 2. The method of manufacturing an AlGaAs semiconductor laser according to claim 1, wherein the Al composition ratio of the Al-added GaInAs active layer is 0.05 or more and 0.08 or less. A step of growing an Al-added GaInAs layer to which Al is added in a composition ratio of 0.01 or more and 0.1 or less by a metal organic chemical vapor deposition method;
A step of growing an AlGaAs or GaAs layer on the Al-added GaInAs layer by metal organic chemical vapor deposition,
A method of manufacturing an AlGaAs semiconductor device, wherein the growth of the Al-added GaInAs layer and the growth of the AlGaAs or GaAs layer are sequentially performed by setting the growth temperature to a constant temperature of 780 ° C. or higher and 800 ° C. or lower. 4. The method of manufacturing an AlGaAs semiconductor device according to claim 3, wherein the Al composition ratio of the Al-added GaInAs layer is 0.05 or more and 0.08 or less. A step of growing an Al-added GaInAs layer to which Al is added in a composition ratio of 0.01 or more and 0.1 or less by a metal organic chemical vapor deposition method;
A step of growing an AlGaAs or GaAs layer on the Al-added GaInAs layer by metal organic chemical vapor deposition,
A growth method of a compound semiconductor in which the growth of the Al-added GaInAs layer and the growth of the AlGaAs or GaAs layer are sequentially performed by setting a growth temperature to a constant temperature of 780 ° C. or higher and 800 ° C. or lower. 6. The method for growing a compound semiconductor according to claim 5, wherein the Al composition ratio of the Al-added GaInAs layer is 0.05 or more and 0.08 or less.

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