JPS60206132A - Crystal growing process - Google Patents

Abstract

PURPOSE:To form excellent semiconductor layers without damaging the waving shapes thereof by a method wherein, within a vapor epitaxial growing process, a substrate at the start of growing process is held at the temperature not to damage the waving shapes thereof by the heating capacity of temperature to finish the growing process at the temperature higher than the starting temperature corresponding to the growing process of semiconductor layers. CONSTITUTION:Cyclic waving shapes are formed on an n type InP substrate 16 by means of conventional photolithography. The waving InP substrate 16 thus formed is bonded to a substrate holder 18 held in reaction tube 15 to form an InGaAsP waveguide layer 32. The temperatures during growing process shall be changed from 550 deg.C at the start to 690 deg.C at 15min after the start further to 700 deg.C at the finish of growing process. During the process, the InGaAsP waveguide 32 is grown while the temperature is rising from 550 deg.C up to 650 deg.C likewise an InGaAsP active layer 33 and a P-InP clad layer 34 are grown while the temperature is rising from 650 deg.C up to 700 deg.C. Through such an epitaxial growing process, the excellent waveguide layer 32, active layer 33 and P-clad layer 34 may be grown while maintaining the normal waving shapes of N-InP.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application on Yanliang) The present invention relates to a method for forming semiconductor layers having different refractive indexes on a semiconductor substrate having unevenness formed thereon.

(Prior Art and its Problems) Forming a semiconductor layer on a semiconductor substrate having an uneven surface is performed in various fields such as semiconductor lasers. However, since semiconductor layers have conventionally been formed by liquid phase epitaxial growth, there is a phenomenon (
There were drawbacks such as meltback and the loss of the shape of the irregularities. When this conventional method is applied to fabricate a device, for example, a distributed feedback semiconductor laser, the uneven shape is impaired, so stable oscillation at a single wavelength cannot be achieved, and a device with good characteristics cannot be obtained.

In order to avoid the meltback phenomenon peculiar to liquid phase growth,
We have attempted to obtain semiconductor layers with different refractive indices on uneven semiconductor substrates by vapor phase epitaxial growth. According to our experiments, in the normal vapor phase growth method (where the growth temperature is kept constant during growth), when the substrate temperature (called the growth temperature) of a semiconductor substrate on which unevenness is formed is set high, the unevenness disappears and the growth rate increases. It has been found that when the temperature is set low, the unevenness is preserved, but the crystallinity of the epitaxially grown layer becomes extremely poor. As described above, it is well known that if the crystal layer of the epitaxially grown layer is poor, the characteristics of the obtained semiconductor device, such as a distributed feedback semiconductor laser, will be impaired. Therefore, when manufacturing fc devices by applying the conventional vapor phase epitaxial growth method that keeps the growth temperature constant, for example, in distributed feedback semiconductor lasers, if grown at a high growth temperature, a single wavelength is produced. It has the disadvantage that it is difficult to oscillate stably, and when grown at a low growth temperature, the luminous efficiency deteriorates.

(Object of the Invention) An object of the present invention is to provide a method for eliminating the above-mentioned drawbacks and forming a good semiconductor M without damaging the uneven shape.

(Structure of the Invention) The present invention is a vapor phase epitaxial growth method in which a semiconductor substrate having an uneven surface is heated in a reaction gas to form semiconductor layers having different refractive indexes on the semiconductor substrate, the method comprising:
At the start of growth, the substrate temperature of the semiconductor substrate is maintained at a temperature at which the uneven shape does not collapse due to heat, and as the semiconductor layer grows, the substrate temperature is increased to a temperature higher than the substrate temperature at the start of the growth. It is characterized by the fact that it stops growing.

(Operations and Effects of the Invention) The present invention solves nine problems of the prior art by adopting the above-described configuration. By using the vapor phase epitaxial growth method, which is the first feature of the structure of the present invention, it has been possible to solve the conventional problem of eliminating the uneven shape or reducing the height of the unevenness. This is because meltback, which is a phenomenon peculiar to W phase:r-kf-sial growth, does not occur in vapor phase epitaxial growth.

When this method is applied to device fabrication, it becomes possible to obtain a semiconductor device with good characteristics, such as a distributed feedback semiconductor laser that stably oscillates at a single wavelength. ° ゛--1'''- →1 Next, a method of increasing the growth temperature, which is the second feature of the structure of the present invention, will be explained. Set the temperature to no
This refers to a method in which most of the epitaxial film is grown by increasing the growth temperature as the uneven shape is filled up to a temperature that is sufficient to maintain good crystallinity. With such a method, the epitaxial layer formed on the uneven substrate has extremely good crystallinity.

(Example) Examples of the present invention will be described in detail below with reference to the drawings. Incidentally, in the examples, an example in which the present invention is applied to the production of a semiconductor laser is described. FIG. 1 is a diagram illustrating an embodiment of the present invention, and is a schematic diagram of an apparatus for performing a step of vapor phase epitaxial growth of a semiconductor layer having a refractive index different from that of the semiconductor on a periodically formed semiconductor. It is a diagram. Further, FIG. 2 is a diagram showing changes in the temperature of the substrate in the reactor obtained by controlling the heating section 14 shown in FIG. 1. Furthermore, FIG. 3 is a diagram showing the layer structure of a distributed feedback semiconductor laser that was actually manufactured.

In this example, a distributed feedback semiconductor laser that oscillates at a wavelength of 1.55 μm was manufactured. The periodic concavo-convex shape 35 was obtained on the n-type 1nP substrate 16 by a commonly used photolithography method that makes full use of laser interference fringes. AZ-1350 was used as the photoresist, and a helium-cadmium laser was used by Lasani. The interval between interference fringes was selected to be about 2400. This interval corresponds to the first-order diffraction interval of the wavelength oscillating at a wavelength of 1.55 μm. The uneven InP substrate 16 thus obtained was stretched onto a substrate boulder 18 held within the reaction tube 15 shown in FIG. The gas atmosphere inside the reaction tube includes Inct vapor produced by the reaction between the In melt 12 and hydrochloric acid gas, GaC vapor produced by the reaction between the Ga melt 13 and hydrochloric acid gas, and arsine (AsH3) fed from the thin tube 11. ) gas and phosphine (PH
4) Composed of gas. In this way, an InGaAsP waveguide layer 32 having a forbidden band width of 0.95 eV as shown in FIG. 3 was formed.

As shown in Figure 2, the growth temperature over time at this time was maintained at 550°C at the start of growth, raised to 690°C 15 minutes after the start of growth, and continued to grow at 700°C.
It finished growing. At this time, InGaAsP guide M32
grows during the temperature rise from 550°C to 650°C, and InG
The aAsP active layer 33 and the P-InP cladding layer 34 are 65
Growth occurred during the temperature increase from 0°C to 700°C.

When epitaxial growth is performed using such a method, a high-quality guide layer 32. Active layer 33. And it was possible to obtain a P-cladding layer 34. When electrodes were formed on the wafer thus obtained using a conventional method to produce a distributed feedback semiconductor laser, it emitted stably at a single wavelength and had sufficiently high luminous efficiency.

In the above example, the period of the unevenness is 240OA.
Although it was difficult to grow on a concavo-convex substrate with first-order diffraction of μm, according to our experiments, the manufacturing method was effective regardless of the period of concavo-convexities.

In the above embodiment, the guide layer 32° active layer 3 is placed on the uneven substrate.
3. Although the P-InP cladding layer 34 is formed, P-InP 45 may be obtained by vapor phase epitaxial growth according to the present invention on a substrate on which a concavo-convex shape 35 as shown in FIG. 4 is formed on the guide layer 44. At this time, the substrate includes an n-InP buffer layer 42 *InGa
The AaP active layer 43 and the InGaAsP guide layer 44 are epitaxially grown.

In the above embodiments, sInGaAsP/InP-based materials were used, but AtGaAs/GaAs-based materials, I
It is clear that nGaAaP/GaAs may be used, and the material is not limited to this material.

In the above embodiment, a halogen-based group (I) gas and a hydride-based group (V) gas were used as raw materials, but an organometallic group (I) gas may also be used.

(Effect of implementation row) In the distributed feedback semiconductor laser manufactured in the above example, the depth of the uneven substrate did not decrease in the epitaxial air a, and was sufficiently deep for about 1000 people.

Therefore, the reflection coefficient of the Bragg reflector was sufficiently good, and the obtained distributed feedback semiconductor laser oscillated stably at a single wavelength. Furthermore, the quality of the crystal of the epitaxial layer obtained on the uneven substrate was sufficiently high, and a distributed feedback semiconductor laser with good luminous efficiency could be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a single gas phase epitaxial device for realizing the present invention, FIG. 2 is a diagram of changes in substrate temperature explaining one embodiment of the present invention, and FIG. 3 is a diagram showing a first embodiment of the present invention. FIG. 4 is a structural diagram of the distributed feedback semiconductor laser obtained in the second embodiment of the present invention. In the figure, 11...a tube, 12...In melt, 13...Ga
Melt. 14...Heating section, 15...Reaction tube, 16.Irregularities n-I
nP substrate, 18-substrate holder, 32- InGaA
gP guide layer. 33-InGaAa activity N, 34 ・= p −
InP cladding layer. 35... uneven interface, 41... n-InP substrate, 42...
・・n-InP buffer layer + 43-InGaAs
P active layer, 44--InGaAsP guide layer, 4
5-p-InP cladding layers are shown, respectively. 71-1 Figure 72 Figure O 3 Mouth 34

Claims (1)

[Claims] This is a vapor phase epitaxial growth method in which a semiconductor substrate with an uneven surface is heated in a reactive gas to form a semiconductor layer with a different refractive index on the semiconductor substrate. Amorphous growth characterized by maintaining the temperature at which the uneven shape does not collapse due to heat, increasing the substrate temperature as the semiconductor layer grows, and ending the growth at a substrate temperature higher than the substrate temperature at the start of the growth. Method.