JP4962178B2 - Method for fabricating a semiconductor optical device - Google Patents

Description

  The present invention relates to a method for fabricating a semiconductor optical device.

  Non-Patent Document 1 describes that GaInNAs lattice-matched to GaAs was grown by metal organic vapor phase epitaxy. A laser diode having a GaInNAs / GaInP double quantum well structure was fabricated. Dimethylhydrazine and arsine were used as Group V materials for GaInNAs, and the growth temperature of GaInNAs was 580 degrees Celsius or more and 680 degrees Celsius.

  Patent Document 1 describes that GaInNAs is grown on a substrate crystal in a temperature range of 350 degrees Celsius to 490 degrees Celsius for manufacturing a semiconductor laser. With this temperature, GaInNAs having good crystallinity is grown.

  Patent Document 2 describes a semiconductor laser including a group III-V mixed crystal semiconductor layer such as GaInNAs and an upper semiconductor layer grown thereon and including a cladding layer. In this manufacturing method, the growth temperature of the III-V mixed crystal semiconductor layer, for example, a temperature higher than 550 degrees Celsius, for example, Celsius, between the end of the growth of the III-V mixed crystal semiconductor layer and the end of the growth of the upper semiconductor layer. Including the step of 700 degrees. This period is provided before the start of growth of the upper semiconductor layer formed by doping impurities.

Patent Document 3 describes a heat treatment method for obtaining a GaInNAs crystal having excellent light emission characteristics. When heat-treating a GaInNAs semiconductor, the temperature is raised at a heating rate of 50 degrees Celsius / second or more and 500 degrees Celsius / second or less, and then heated at a holding temperature of 550 degrees Celsius or more and 900 degrees Celsius or less. ing.
Jpn. J. Appl. Phys. (1997) 36, pp.2671-2675 JP-A-11-87848 JP 2001-257430 A JP 2002-319548 A

A semiconductor optical device (for example, a semiconductor laser) having an active layer of Ga _0.66 In _0.34 N _0.01 As _0.99 has been developed. A GaInNAs crystal having this composition can emit light at a wavelength of 1.3 micrometers. However, it is not easy to obtain a GaInNAs crystal that realizes good laser characteristics. In addition, it is not easy to obtain sufficient emission intensity, and the oscillation threshold current density of the laser diode is high. Furthermore, with regard to long-term reliability, a sufficient lifetime of the laser diode is not obtained. To the knowledge of the inventor, there is no known document detailing the relationship between the lifetime and electrical characteristics of GaInNAs laser diodes and growth conditions. In the conventional method, after growing a dilute nitrogen III-V compound semiconductor typified by GaInNAs, a heat treatment (thermal annealing) of the dilute nitrogen III-V compound semiconductor is performed to relate to the improvement of the emission characteristics. The device life was improved. However, until now, the device life has not been applicable to products, and further improvement in device life has been desired.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method of manufacturing a semiconductor optical device using a III-V compound semiconductor containing nitrogen and arsenic as a V group. According to the method, the device life of the semiconductor optical device can be improved.

One aspect of the present invention is a method for fabricating a semiconductor optical device. The method includes the step of growing at a growth temperature T _A of the first III-V compound semiconductor layer for the active layer includes nitrogen and arsenic as (a) V group constituent element, (b) said first III (C) forming an epitaxial substrate by growing a plurality of remaining second III-V compound semiconductor layers for the semiconductor optical device after growing the -V compound semiconductor layer; Forming an opening in the insulating film, and (d) forming a p-electrode and an n-electrode on the epitaxial substrate after forming the insulating film, the maximum value of the growth temperature of the second III-V compound semiconductor layer is a temperature T _B, the film formation temperature of the insulating film is a temperature T _C, the process for forming the p electrode and n electrode The maximum temperature at Temperature _T P, is _{T N,} the temperature _{T B,} T C, when the maximum value of _{T P,} and _{T N} referred to as the maximum temperature _{T MAXA,} the growth temperature _{T A} is from the maximum temperature _{T MAXA} The temperature difference between the maximum temperature T _MAXA and the growth temperature T _A (T _MAXA −T _A ) is 70 degrees Celsius or less.

According to this method, the temperature _{T B, T C, T P} , the temperature difference between the maximum temperature _{T MAXA} and the growth temperature _{T A} of the _{T N (T MAXA} -T _A) is less than 70 degrees Celsius, The device lifetime of the semiconductor optical device using the first III-V compound semiconductor layer can be improved.

In the method according to the present invention, after growing the second III-V compound semiconductor layer, the first III-V compound semiconductor layer can further comprise the step of annealing at an annealing temperature T _D. Wherein when referred to as the annealing temperature _{T D} and the maximum temperature _T up to the temperature _{T MAXB} the maximum value among _MAXA, the growth temperature _{T A,} the maximum temperature _T less than _MAXB, the maximum temperature _{T MAXB} and the growth temperature _{T A} the difference between the _{(T MAXB} -T _a) is less than 70 degrees Celsius.

According to this method, the temperature _{T B, T C, T D} , T P, the temperature difference between the maximum temperature _{T MAXB} the growth temperature _{T A} of the _{T N (T MAXB} -T _A) is below 70 degrees Celsius Therefore, the device lifetime of the semiconductor optical device using the first III-V compound semiconductor layer can be improved.

In the method according to the present invention, the temperature difference _{(T MAXA} -T _A) is preferably less than or equal 55 degrees Celsius. According to this method, since the temperature difference (T _{MAXA -T A)} is less than 55 degrees Celsius, it is possible sufficiently improve the device life of the semiconductor optical device using a first III-V compound semiconductor layer.

The method according to the present invention, after growing the second III-V compound semiconductor layer, the first III-V compound semiconductor layer can further comprise the step of annealing at an annealing temperature T _D. When referred to a maximum temperature _{T MAXB} the maximum value of the annealing temperature _{T D} and the maximum temperature _{T MAXA,} the growth temperature _{T A} is less than the maximum temperature _{T MAXB,} the maximum temperature _{T MAXB} said the growth temperature _{T A} difference _{(T MAXB} -T _a) is less than 55 degrees Celsius.

According to this method, since the temperature difference (T _{MAXB -T A)} is less than 55 degrees Celsius, it is possible sufficiently improve the device life of the semiconductor optical device using a first III-V compound semiconductor layer.

  In the method according to the present invention, after the second III-V compound semiconductor layer is grown, the first III-V compound semiconductor layer is not annealed. According to this method, the device life can be improved even when the first III-V compound semiconductor layer is not annealed.

  In the method according to the present invention, the first III-V compound semiconductor layer may be composed of any one of GaInNAs, GNAs, GaNPAs, and GaInNAsSb. The above materials are exemplified as a dilute nitrogen III-V compound semiconductor containing nitrogen and arsenic as group V constituent elements.

  In the method according to the present invention, the active layer may have a quantum well structure, and the first III-V compound semiconductor layer may be a well layer for the active layer. According to this method, the device lifetime of a semiconductor optical device having an active layer having a quantum well structure can be improved.

  In the method according to the present invention, the growth temperature of the first III-V compound semiconductor layer is not less than 490 degrees Celsius, and the growth temperature of the first III-V compound semiconductor layer is not more than 520 degrees Celsius. be able to. According to this method, a III-V compound semiconductor layer having good crystal quality is grown.

  In the method according to the present invention, the semiconductor optical device includes a semiconductor laser, and the first III-V compound semiconductor layer is provided for a light emitting layer of the semiconductor laser. According to this method, the device life of the semiconductor laser can be improved.

  The above and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings.

  As described above, according to the present invention, a method of manufacturing a semiconductor optical device using a III-V compound semiconductor containing nitrogen and arsenic as a group V is provided, and the device lifetime of the semiconductor optical device manufactured by this method is provided. Is improved.

  The knowledge of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown as examples. Subsequently, an embodiment according to a method of manufacturing a semiconductor optical device using a III-V compound semiconductor containing nitrogen and arsenic as a group V according to the present invention will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

  1 to 5 are drawings showing main steps of a method of manufacturing a semiconductor optical device according to an embodiment of the present invention. The semiconductor optical device manufactured by this method is made of a III-V compound semiconductor, and crystal growth of the III-V compound semiconductor is performed using, for example, a metal organic chemical vapor deposition method. In addition, this semiconductor optical device has an active layer including a III-V compound semiconductor layer containing nitrogen and arsenic as a V group. In the following description, a method for manufacturing an edge-emitting laser diode as an example of a semiconductor optical device will be described.

  A semiconductor substrate 13 is set in a metal organic vapor phase growth furnace (hereinafter referred to as a growth furnace) 11. As gallium raw material, indium raw material, aluminum raw material, nitrogen raw material, phosphorus raw material and arsenic raw material, for example, triethylgallium (TEGa), trimethylindium (TMIn), trimethylaluminum (TMAl), dimethylhydrazine (DMHy), tertiary butyl, respectively. Phosphine (TBP) and tertiary butylarsine (TBA) are used.

  The semiconductor substrate 13 is made of a first conductivity type III-V compound semiconductor and is, for example, a Si-doped n-type GaAs substrate. As shown in FIG. 1A, the buffer layer 15, the cladding layer 17, and the optical confinement layer 19 are formed on the main surface 13 a of the semiconductor substrate 13. The buffer layer 15 and the cladding layer 17 are made of a first conductivity type III-V compound semiconductor, and the optical confinement layer 19 is made of a III-V compound semiconductor. On an example n-type GaAs substrate, an n-type GaAs buffer layer, an n-type AlGaAs cladding layer, and an undoped GaAs optical confinement layer are grown in this order. The growth temperature of the GaAs buffer layer is, for example, 550 degrees Celsius, the growth temperature of the AlGaAs cladding layer is, for example, 650 degrees Celsius, and the growth temperature of the GaAs optical confinement layer is, for example, 550 degrees Celsius.

  Next, as shown in FIG. 1B, a well layer 21a for the active layer is formed on the optical confinement layer 19 at the growth temperature T1. The well layer 21a is made of a III-V compound semiconductor containing nitrogen and arsenic as a V group. The well layer 21a can be made of, for example, an undoped GaInNAs layer, and the growth temperature T1 is, for example, not less than 490 degrees Celsius and not more than 540 degrees Celsius.

  In the subsequent process, after the well layer for the active layer is grown, the remaining plurality of III-V compound semiconductor layers for the semiconductor optical device are grown at respective growth temperatures to form an epitaxial substrate. After the formation of the well layer, as shown in FIG. 2A, the barrier layer 23 is formed on the well layer 21a at the growth temperature T2. The barrier layer 23 can be made of, for example, an undoped GaAs layer, and the growth temperature T1 is, for example, not less than 490 degrees Celsius and not more than 540 degrees Celsius. If necessary, the barrier layer 23 is added with a desired dopant. The material of the barrier layer 23 is not limited to GaAs, but can be composed of GaNAs, GaAsP, or the like.

  As shown in FIG. 2B, the well layer 21b is formed on the barrier layer 23 at the growth temperature T1 similarly to the well layer 21a. The well layer 21b can be composed of, for example, an undoped GaInNAs layer, like the well layer 21a. The material of the well layers 21a and 21b is not limited to GaInNAs, and can be any of GANAs, GaNPAs, and GaInNAsSb.

  As shown in FIG. 3A, the optical confinement layer 25 is formed on the well layer 21b at the growth temperature T3. For example, the optical confinement layer 25 may be undoped GaAs, and the growth temperature T3 is, for example, 490 degrees Celsius or more and 550 degrees Celsius or less.

  As shown in FIG. 3B, the cladding layer 27 made of the second conductivity type III-V compound semiconductor is formed on the optical confinement layer 25 at the growth temperature T4. For example, the clad layer 27 may be p-type AlGaAs, and the growth temperature T4 is, for example, 550 degrees Celsius or more and 650 degrees Celsius or less.

  As shown in FIG. 4A, a contact layer 29 made of a second conductivity type III-V compound semiconductor is formed on the cladding layer 27 at a growth temperature T5. For example, the contact layer 29 may be p-type GaAs, and the growth temperature T5 is, for example, 500 degrees Celsius or higher and 550 degrees Celsius or lower. Through these steps, the epitaxial substrate E1 was formed.

  Next, if necessary, as shown in FIG. 4B, annealing 31 of the epitaxial substrate E1 is performed at a temperature T6 using the growth furnace 11. The annealing temperature T6 is, for example, not less than 550 degrees Celsius and not more than 750 degrees Celsius. The annealing 31 is performed, for example, in an atmosphere of tertiary butyl arsine (TBA). By this heat treatment, an epitaxial substrate E2 was formed.

  Thereafter, as shown in FIG. 5A, an insulating film 33 is formed on the contact layer 29 of the epitaxial substrate E2 by using a film forming apparatus 35, and an opening is formed in the insulating film 33 to form a protective layer. 33a is formed. The growth of the insulating film 33 is performed at the film formation temperature T7. The temperature T7 is, for example, 200 degrees Celsius or more and 300 degrees Celsius or less. The opening of the insulating film 33 is formed by photolithography.

Next, as shown in FIG. 5B, electrodes 35 and 37 are formed on the epitaxial substrate. In one example, the p electrode of the electrodes 35 and 37 is formed on the contact layer 29, and the n electrode of the electrodes 35 and 37 is formed on the back surface 13 b of the substrate 13. In this formation, the maximum temperatures in the process for forming the p electrode and the n electrode are temperatures T _P and T _N , respectively. In the following description, the smaller value of the temperatures T _P and T _N is referred to as the temperature T8. The temperature T8 is, for example, not less than 300 degrees Celsius and not more than 400 degrees Celsius.

  After forming the electrodes, a semiconductor laser was fabricated by opening the wafer wall. The cavity length of this semiconductor laser is, for example, 600 micrometers.

An example of a semiconductor laser manufactured by these processes is
Semiconductor substrate 13: Si-doped n-type GaAs
Buffer layer 15: Si-doped n-type GaAs, thickness 200 nm
Cladding layer 17: Si-doped n-type AlGaAs, thickness 1.5 μm
Optical confinement layer 19: undoped GaAs, thickness 140 nm
Well layers 21a, 21b: undoped GaInNAs, thickness 7 nm
Barrier layer 23: undoped GaAs, thickness 8 nm
Optical confinement layer 25: undoped GaAs, thickness 140 nm
Cladding layer 27: Zn-doped p-type AlGaAs, thickness 1.5 μm
Contact layer 29: Zn-doped p-type GaAs, thickness 200 nm
Insulating film 33: silicon oxide, thickness 100 nm
It is. The active layer can be composed of, for example, a light confinement layer 19, a well layer 21a, a barrier layer 23, a well layer 21b, and a light confinement layer 25. In the growth of the well layer (or bulk active layer), the flow rates of the organic metal raw materials TEGa, TMIn, DMHy, and TBAs are 3 × 10 ⁻⁵ mol / min, 2 × 10 ⁻⁵ mol / min, ^{They were} x10 ^<-2 > mol / min and 3 x 10 < ^-4 > mol / min. With this growth, the molar ratio of DMHy and TBAs supplied to the same group V atom is [DMHy]: [TBAs] = 100: 1.
It is. When the laser diode of the above example was fabricated under these growth conditions, the In composition and N composition of the well male were about 34% and about 1%, respectively, and the laser emission wavelength was 1.29 μm.

According to the experiments by the inventors, the growth temperature of a III-V compound semiconductor layer (for example, a GaInNAs layer) for an active layer containing nitrogen and arsenic as a group V, and after growing this III-V compound semiconductor layer It has been found that the difference from the maximum temperature in the thermal history is closely related to the lifetime of the laser diode. FIG. 6 is a drawing showing the relationship between the temperature difference and the lifetime (relative value) of the laser diode. The experimental condition for the life of the laser diode is the time when the emission intensity is reduced by 20% when the applied current is a constant value with continuous energization. Five plots P1, P2, P3, P4 and P5 are drawn on the graph. The straight line L1 determined by the least squares method uses the independent variable X on the horizontal axis and the dependent variable Y on the vertical axis,
LOG (Y) = − 0.0292X + 6
(LOG represents a logarithmic function). According to the knowledge of the inventors, the practical value in the lifetime of the laser diode is about 10,000 in terms of the value on the vertical axis of the graph. The temperature difference corresponding to this converted value (10000) is 70 degrees Celsius. The temperature difference corresponding to the plot P4 is 55 degrees Celsius.

  In the fabrication of laser diodes, it is believed that the maximum processing temperature is during the epitaxial growth process after growing a III-V compound semiconductor layer (eg, a GaInNAs layer) for the active layer containing nitrogen and arsenic as the V group. This is because the processing temperature in the metallization process for forming electrodes (for example, the processing temperature for alloying) is generally lower than the maximum processing temperature during the epitaxial growth process. Further, in a process after the metallization process (for example, a cleavage process for forming a laser bar), the laser diode is not exposed to a temperature that affects metallization. Therefore, in the following, in order to facilitate understanding, description will be made in the range of processing temperatures in the epitaxial growth process and the metallization process.

Experimental results are measured Temperature difference Relative life Minimum temperature Maximum temperature Annealing temperature Clad temperature P1: 210 degrees 1 490 degrees 700 degrees 700 degrees 550 degrees P2: 160 degrees 10 490 degrees 650 degrees 650 degrees 550 degrees P3: 130 degrees 400 520 degrees 650 Degree 650 degrees 550 degrees P4: 55 degrees 42000 520 degrees 575 degrees 575 degrees 550 degrees P5: 30 degrees 100000 520 degrees 550 degrees None 550 degrees.

From this result, it referred to as the growth temperature T _A III-V compound semiconductor layer for the active layer includes nitrogen and arsenic as group V (e.g. GaInNAs layer). After forming the III-V compound semiconductor layer, the remaining plurality of III-V compound semiconductor layers are grown to form an epitaxial substrate. The maximum value of these growth temperature referred to as the temperature T _B. Further, an insulating film in the film formation temperature T _C in the epitaxial substrate. Further, the maximum temperature in the process for forming the p electrode and the n electrode is denoted as temperature T8. When the maximum value among the temperatures T _B , T _C , T _P , and T _N is denoted as the maximum temperature T _MAXA , the growth temperature T _A is smaller than the maximum temperature T _MAXA . Then, as already described, the temperature difference between the maximum temperature _{T MAXA} and the growth temperature _{T A (T MAXA} -T _A) is less than 70 degrees Celsius. Further, the temperature difference _{(T MAXA} -T _A) is more preferably equal to or less than 55 degrees Celsius.

Moreover, as already explained, the growth temperature _{T A,} the maximum temperature _{T MAXB} smaller of the annealing temperature _{T D} and the maximum temperature _{T MAXA} annealing the epitaxial substrate. Then, the difference between the maximum temperature _{T MAXB} and the growth temperature _{T A (T MAXB} -T _A) is preferably less than 70 degrees Celsius. Further, the temperature difference _{(T MAXB} -T _A) is more preferably equal to or less than 55 degrees Celsius.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. In the present embodiment, for example, a semiconductor optical device such as a semiconductor laser has been described. However, the present invention is not limited to the specific configuration disclosed in the present embodiment. In the present embodiment, the semiconductor laser is described as an example, but it may be a light receiving element or a photodetector. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

FIG. 1 is a drawing showing main steps of a method of manufacturing a semiconductor optical device according to an embodiment of the present invention. FIG. 2 is a drawing showing main steps of a method of manufacturing a semiconductor optical device according to an embodiment of the present invention. FIG. 3 is a drawing showing main steps of a method of manufacturing a semiconductor optical device according to an embodiment of the present invention. FIG. 4 is a drawing showing main steps of a method of manufacturing a semiconductor optical device according to an embodiment of the present invention. FIG. 5 is a drawing showing the main steps of a method for manufacturing a semiconductor optical device according to an embodiment of the present invention. FIG. 6 is a drawing showing the relationship between the temperature difference in the thermal history and the lifetime (relative value) of the laser diode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 13 ... Semiconductor substrate, 15 ... Buffer layer, 17 ... Cladding layer, 19 ... Light confinement layer, 21a, 21b ... Well layer, 23 ... Barrier layer, 25 ... Light confinement layer, clad layer 27 ..., 29 ... Contact layer, 31 ... Annealing, 33 ... Insulating film

Claims (9)

A method for producing a semiconductor optical device, comprising:
A step of growing at a growth furnace in the first III-V compound semiconductor layer at a growth temperature T _A for the active layer includes nitrogen and arsenic as a group V constituent element,
After growing the first III-V compound semiconductor layer, growing a plurality of remaining second III-V compound semiconductor layers for the semiconductor optical device in the growth furnace to form an epitaxial substrate When,
Forming an insulating film on the epitaxial substrate and forming an opening in the insulating film;
Forming a p-electrode and an n-electrode on the epitaxial substrate after forming the insulating film ;
With
Maximum value among the growth temperature of the plurality of second III-V compound semiconductor layer is a temperature T _B,
Deposition temperature of the insulating film is a temperature T _C,
Maximum temperatures in the process for forming the p electrode and the n electrode are temperatures T _P and T _N , respectively.
Said temperature _{T B,} T C, when the maximum value of _{T P,} and _{T N} referred to as the maximum temperature _{T MAXA,} the growth temperature _{T A} is less than the maximum temperature _{T MAXA,}
The maximum temperature _{T MAXA} the temperature difference between the growth temperature _{T A (T MAXA} -T _A) is less than 70 degrees Celsius,
The method, after growing the second III-V compound semiconductor layer, further comprising the step of annealing the first III-V compound semiconductor layer in the annealing temperature T _D,
Wherein when the maximum value of the annealing temperature _{T D} and the maximum temperature _{T MAXA} the referred to as the maximum temperature _{T MAXB,} the growth temperature _{T A} is less than the maximum temperature _{T MAXB,}
The maximum temperature _{T MAXB} the difference between the growth temperature _{T A (T MAXB} -T _A) is less than 70 degrees Celsius,
The growth temperature _{T A} is equal to or greater than 490 degrees Celsius, or less 540 degrees Celsius,
Serial annealing temperature T _D is wherein the at least 550 degrees Celsius. 2. The method according to claim 1, wherein the growth of the first III-V compound semiconductor layer and the plurality of second III-V compound semiconductor layers is performed by metal organic vapor phase epitaxy. . The method according to claim 1, wherein the annealing is performed using the growth furnace. The method according to any one of claims 1 to 3, wherein the annealing is performed in an atmosphere of tertiary butylarsine. The method according to claim 1, wherein the active layer emits light in a 1.3 μm band.   6. The method according to claim 1, wherein the first III-V compound semiconductor layer is made of any one of GaInNAs, GNAs, GaNPAs, and GaInNAsSb. The active layer has a quantum well structure;
The method according to any one of claims 1 to 6, wherein the first III-V compound semiconductor layer is a well layer for the active layer. A step of growing a barrier layer of a III-V compound semiconductor containing at least one of GaAs, GANAs, and GaAsP;
The active layer has a quantum well structure;
The growth temperature of the barrier layer of the III-V compound semiconductor is 490 degrees Celsius or higher,
The method according to claim 1 , wherein a growth temperature of the barrier layer of the III-V compound semiconductor is 540 degrees Celsius or less . The semiconductor optical device includes a semiconductor laser,
The method according to claim 1, wherein the first III-V compound semiconductor layer is provided for a light emitting layer of the semiconductor laser.

Images