JPH0214320B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to epitaxial growth using InP as a substrate.

InGaAsP-based semiconductors are widely used as materials for light-emitting and light-receiving elements for optical communications. Such light-emitting/light-receiving elements are generally manufactured from wafers obtained by crystal growth using liquid phase or vapor phase epitaxial growth methods. Incidentally, various structures have been proposed in the past in order to control the transverse mode or longitudinal mode of the oscillated light of a semiconductor laser, and to provide a filter effect (wavelength selectivity) in a light receiving element. The structure of such an element is
It is obtained by growing crystals on a complexly processed substrate, but during crystal growth, this substrate is left under high temperature while the melt is sufficiently melted. As a result, in substrates using InP or InGaAsP, problems arise in that the P component in particular dissociates, resulting in roughening of the surface of the substrate and deformation of intricately processed parts.

For example, in a distributed feedback laser (hereinafter abbreviated as DFB laser), periodic irregularities are formed along the direction of light propagation in the light emitting layer or a layer close to the light emitting layer in order to achieve a single longitudinal mode. This unevenness provides selectivity of the oscillation wavelength. To be more specific, it is formed on an n-type InP substrate with a period of 2360 Å and a height of about 1000 Å.
On top of this, n-type InGaAsP is formed.
layer (λg=1.3μm, λg: wavelength corresponding to forbidden band width)
0.1μm thick, undoped InGaAsP layer (λg=1.55μ
m) is 0.1 μm, undoped InGaAsP layer (λg = 1.3 μm)
If we fabricate a laser using a wafer with 0.1 μm of m) and approximately 2 μm of p-type InP layer, and inject a current,
A laser that oscillates in a single longitudinal mode at 1.55 μm can be obtained. The threshold of this oscillation mainly depends on the height of the unevenness, but because the crystal is left at high temperatures for about an hour during crystal growth, the uneven surface may become rough or deformed, or in the worst case, the unevenness may become uneven. It often disappeared. The same thing happens even when left in an atmosphere containing a sufficient amount of P, so this is not only due to the phenomenon of P dissociating from the surface, but also due to the phenomenon of minimizing the surface energy of uneven parts. It is considered that a reaction occurs in the solid phase and gas phase, and a phenomenon in which In and P in the convex portions move to the concave portions is also occurring at the same time. Further, a similar problem occurred with the above-mentioned light receiving element.

Conventionally, to prevent the above problems, PH ₃ gas or InP crystals were used as a cover for the substrate, but it was difficult to prevent deformation of a microfabricated substrate with good reproducibility. Ta.

The present invention provides a crystal growth method that suppresses the transport phenomenon in the solid phase-vapor phase and prevents deformation of microfabricated portions even when crystallization is initiated.

A feature of the present invention is that in the epitaxial crystal growth method in which a desired semiconductor is grown on a substrate made of InP containing P as a constituent element as the first element with high vapor pressure and having microfabrication on the surface, Before starting, the InP substrate is housed in an atmosphere containing the first element and As as a second element having a lower saturated vapor pressure than the first element.

The present invention will be explained in detail below.

The figure shows a cross section of a graphite boat for crystal growth. The boat includes melt reservoirs 1, 2, 3, 4, a boat body 7 in which a cavity 6 is formed for accommodating a carbon basket 5 having a number of holes with a diameter of 0.5 to 1 mmφ at the bottom, and an InP substrate 8. The substrate holder 9 is slidable in close contact with the substrate holder 9. Here, carbon basket 5 contains InP and
Add 10% of the Sn melt in which InAs has been dissolved. Each component is, for example, 5g of Sn, 150mg of InP, 50mg of InAs.
shall be. Further, the melt reservoirs 1, 2, 3, and 4 are filled with melt according to the growth composition. For example, 11 is n type
Melt for InGaAsP layer (λg = 1.3 μm), 12 is melt for undoped InGaAsP layer (λg = 1.55 μm), 1
3 is a melt for an undoped InGaAsP layer (λg=1.3 μm), and 14 is a melt for a p-type InP layer. Now, in the actual crystal growth process, after the substrate, melt, etc. are all placed in a boat, this is put into a quartz tube.
While flowing H ₂ gas, the temperature was raised to about 620°C and left for about 30 minutes. After the melts 11 to 14 became sufficiently uniform, the temperature was lowered and the substrates 8 were sequentially brought into contact with the melt to form the desired shape. Perform crystal growth of components and film thickness. Now,
Before the substrate and the melt come into contact, the substrate 8 is covered with carbon.
It is held under the basket 5. Sn melt 1
The P component evaporated from the InP substrate reaches the substrate holder 9 through the hole at the bottom of the basket, and serves to protect the P component from dissipating from the InP substrate surface. Furthermore, the As component also evaporates from the same Sn melt,
This As component forms a thin film consisting of In, P, and As on the substrate surface, and this causes phenomena such as migration of In and P from convex areas to concave areas due to reactions in the solid phase and gas phase. hindering.

As described above, when an InP substrate is left at a high temperature, the substrate surface can be well protected by using an atmosphere containing an As component with a slightly lower vapor pressure in addition to the P component. The protective film on the substrate surface made of As components is extremely thin, and since the layer that grows directly on the substrate contains As, rearrangement occurs during crystal growth, so the effect of this film on the entire growth layer is small. rare. The protection of such a substrate is
It is not possible to achieve sufficient results with only the component alone or with the As component alone, but by using both P and As components,
This is possible for the first time.

For example, when performing the above experiment using an InP substrate on which a diffraction grating with a depth of 800 Å and a period of 2400 Å was formed, the depth deformed to less than 50 Å without the As component, but when the As component was added When this was done, a diffraction grating with a depth of about 300 Å was obtained with good reproducibility.

In the above embodiments, As and P components were dissolved in the Sn melt, but melts of metals other than Sn, such as In, Ga, Pb, Bi, Cd, Zn, or a combination of these, may also be used. You may use it by dissolving As and P components in it.

Also, instead of using As and P components that evaporate from the solution, if a single crystal wafer such as InP _x As _1-x or In _1-y Ga _y P _x As _1-x is used as a cover for the substrate. Since the As and P components are dissociated from this Kaba crystal, the same effect as when using the metal melt described above can be obtained.

As yet another method, a compound gas of As or P, such as AsH ₃ or PH ₃ , may be used. In this case, AsH ₃ and PH ₃ decompose at high temperatures,
Since As ₄ , P _{4 ,} etc. are generated, similar effects can be obtained.

These methods may be used alone or in combination. For example, a method may be used in which a solution of As and P dissolved in Sn melt is used, and at the same time, PH ₃ and AsH ₃ gases are flowed, and As and P components generated from both are used.

In addition, similar protection laws apply not only to substrates containing P, but also to
For example, it is also applicable to substrates containing As or S.

As explained above, in the present invention, deformation and roughness of the substrate can be effectively prevented by housing the substrate containing an element that is easily liberated in an atmosphere containing both the element and an element with low vapor pressure. It can be prevented and its industrial value is great.

[Brief explanation of drawings]

The figure is a sectional view of a carbon boat to which the present invention is applied. 1, 2, 3, 4...Melt reservoir, 5...Carbon basket, 6...Cavity, 7...Boat body, 8...InP substrate, 9...Substrate holder, 10...
Sn melt, 11, 12, 13, 14...melt for crystal growth.

Claims (1)

[Claims] 1. Before the step of epitaxial crystal growth on a substrate made of InP and having microfabrication on the surface,
A crystal growth method comprising the step of housing the substrate in an atmosphere containing P and As. 2 The atmosphere containing the above P and As is the atmosphere containing the above P and the above
Formed by dissolving As in a metal melt of Sn, In, Ga, Pb, Bi, Cd, Zn, or a combination thereof, and using the P and As that evaporate from the solution. A crystal growth method according to claim 1, characterized in that: 3. The crystal according to claim 1, wherein the atmosphere containing the P and the As is formed using the P and the As by dissociation from a compound semiconductor containing the P and the As. How to grow. 4. The atmosphere containing the P and the As is formed using the P and the As decomposed from a compound gas containing the P and the As. Crystal growth method.