JPH07249575A - Manufacture of semiconductor optical element - Google Patents

Abstract

PURPOSE:To provide a method of manufacturing a semiconductor optical element, which is small in element resistance and is small in optical loss. CONSTITUTION:When a P-type InP clad layer 6 doped with beryllium is formed using an organometallic molecular beam epitaxy method (an MOMBE method) using a hydrogen compound as a group V raw material and a gas source molecular beam epitaxy method (a GSME method), the doping amount of the beryllium is inhibited by changing the feed rate of phosphine, which is the group V raw material, in stages.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a p-type cladding layer in a semiconductor optical device.

[0002]

2. Description of the Related Art In a semiconductor optical device having a waveguide structure,
Light confinement is realized by using a clad layer having a smaller refractive index than the active layer. In a semiconductor optical device on an InP substrate, it is common to use an InP layer as a cladding layer. In a semiconductor optical device, it is effective to increase the carrier concentration in the clad layer in order to reduce the device resistance, but in the case of InP, the absorption coefficient of light increases due to the increase in carrier concentration, which is It was a loss. This optical loss is more problematic in p-type doped InP than in n-type (Applied Physics Letters Vol. 44, p. 82 [CH Casey
et al., Appl. Phys. Lett., 44 (1984) 82.], Journal of Crystal Growth, vol. 62, p.
AA Ballman et al., J. Crystal Growth, 62 (1983)
198.]).

Therefore, in a semiconductor optical device using p-type InP as a clad layer, a structure in which the p-type carrier concentration is changed in the InP clad layer is used in order to reduce the device resistance and the optical loss. Came.

An example of this structure is shown using the semiconductor laser structure shown in FIG. In FIG. 1, 1 is an n-type InP substrate, 2 is n
Type InP buffer layer, 3 is an InGaAsP guide layer, 4
Is an InGaAs / InGaAsP MQW active layer, 5 is an InGaAsP guide layer, 6 is a p-type InP cladding layer,
Reference numerals 7 respectively denote p-type InGaAsP contact layers.
In the case of the semiconductor laser structure of FIG. 1, the p-type carrier concentration in the p-type InP clad layer 6 is In as shown in FIG.
It becomes large in the region near the p-type InGaAsP contact layer 7 from the GaAsP guide 5. In the metalorganic molecular beam epitaxy method (MOMBE) or the gas source molecular beam epitaxy (GSMBE method), solid beryllium is used as a dopant material, and p-type In as shown in FIG.
When the P clad layer 6 is to be formed, the p-type InP
A method of continuously increasing the cell temperature of beryllium to increase the carrier concentration during the growth of the cladding layer, or II
The method of decreasing the growth rate by decreasing the supply amount of the group I raw material to increase the carrier concentration is mainly used.

[0005]

[Problems to be Solved by the Invention] As described above, MOMB
In the method E or the GSMBE method, in which the cell temperature of beryllium is raised to increase the p-type carrier concentration in InP, the temperature of the cell peripheral portion also rises due to the cell temperature rise of beryllium, so impurities other than beryllium ( For example, silicon) is mixed in the InP layer to deteriorate the film quality, and it takes time in minutes for the cell temperature of beryllium to stabilize at the set temperature.

Further, as described above, the MONBE method or G
In the SMBE method, the supply amount of group III raw material was reduced
With the method of increasing the type carrier concentration, it is difficult to control the film thickness of the clad layer because the growth rate of InP changes greatly depending on the supply amount of the group III raw material.

It is an object of the present invention to provide a method for manufacturing a semiconductor optical device on an InP substrate, in which a p-type InP clad layer having a small device resistance and a small optical loss is formed with good film thickness control. .

[0008]

A method for manufacturing a semiconductor optical device according to the present invention, which achieves the above object, is a metal organic molecular beam epitaxy method (MOMB) using a hydrogen compound as a group V raw material.
E method) and gas source molecular beam epitaxy method (GSM
In the BE method), when the InP layer doped with solid beryllium as a p-type dopant is grown, the supply amount of phosphine, which is a group V raw material, is changed to control the beryllium doping amount. Further, in the method for manufacturing a semiconductor optical device, the group V raw material is phosphine.

[0009]

The present invention utilizes the property that when a beryllium-doped InP layer is grown by the MOMBE method or the GSMBE method, the p-type carrier concentration is increased by increasing the supply amount of V group raw material such as phosphine. Then, the p-type doping amount is changed in the p-type InP cladding layer. Therefore, it differs from the prior art in that the p-type doping amount in the InP load can be increased or decreased without increasing or decreasing the cell temperature of beryllium or the supply amount of the group III raw material.

[0010]

The preferred embodiment of the present invention will be described below.

Organometallic molecular beam epitaxy method (MOMBE) using phosphine (PH ₃ ) as a group V raw material and trimethyl indium (TMIn), triethylindium (TEIn) or another organic metal as a group III raw material.
Method), the p-type carrier concentration in the p-type InP clad layer is increased / decreased by increasing / decreasing the supply amount of phosphine which is a group V raw material.

When the beryllium-doped InP is grown by the MOMBE method, the p-type carrier concentration increases as the supply amount of phosphine increases. In this case p
Even if the phosphine supply amount is increased so that the mold carrier concentration is increased to about twice, the change in the growth rate can be suppressed within about 10%.

As shown in FIG. 3, under the condition that the cell temperature of beryllium is constant and the supply amount of trimethylindium as the group III material is constant, the supply pressure of the phosphine as the group V material is 6 T.
When InP was epitaxially grown by increasing from orr to 9 Torr, the p-type carrier concentration in InP increased from 4 × 10 ¹⁷ cm ⁻³ to 1 × 10 ¹⁸ cm ⁻³ . In this case, the growth rate of the InP epitaxial film was 1 μm / h, which was constant regardless of the phosphine supply pressure.

Using the semiconductor laser structure shown in FIG. 1, p
A method of forming the type InP clad layer will be described. In the n-type InP substrate 1, the n-type InP buffer layer 2, In
GaAsP guide layer 3, InGaAs / InGaAsP
After growing a beryllium-doped InP cladding layer 6 on the heteroepitaxial structure consisting of the MQW active layer 4 and the InGaAsP guide layer 5 while gradually or continuously increasing the phosphine supply amount, beryllium-doped p-type InGaAsP The contact layer 7 is continuously grown.

As described above, the p-type carrier concentration in beryllium-doped InP increases / decreases as the amount of phosphine supplied increases / decreases. Therefore, the InP clad layer 6 described above
InG by increasing the phosphine supply
The p-type carrier concentration increases from the aAsP guide layer 5 side toward the p-type InGaAsP contact layer 7 side. In the growth of the emitted light from the active layer 4 in the p-type InP clad layer 6, since the supply amount of phosphine, which is a group V material, is small, the p-type carrier concentration is small, and the optical loss due to the p-type carrier can be suppressed to be small. On the other hand, the resistance of the p-type InP clad layer 6 as a whole layer can be increased by increasing the p-type carrier concentration in the region of the p-type InP clad layer 6 close to the p-type InGaAsP contact layer 7, so that the phosphine supply amount is not increased. However, it can be made smaller.

On the other hand, also in the gas source molecular beam epitaxy method (GSMBE method) using phosphine as the group V source and metal indium as the group III source, the p-type carrier concentration in InP doped with beryllium is the same as in the case of the MOMBE method. Is increased by increasing phosphine. Under the phosphine supply pressure of 9 Torr,
After adjusting the cell temperature of indium so that the growth rate of InP is 1 μm / h, the supply pressure of the phosphine, which is a group V raw material, is from 6 Torr to 9 Torr under the condition that the cell temperature of beryllium is constant and the cell temperature of indium is constant. If InP is grown epitaxially, M
Similar to the OMBE case, the p-type carrier concentration in InP increased from 4 × 10 ¹⁷ cm ⁻³ to 1 × 10 ¹⁸ cm ⁻³ . The growth rate of the InP epitaxial film in this case is 1
It was μm / h and was constant regardless of the phosphine supply pressure.

Therefore, even when the GSMBE method is used,
As in the case of using the MONBE method, InP in FIG.
The clad layer 6 is formed from the InGaAsP guide layer 5 side by increasing the supply amount of phosphine.
The p-type carrier concentration increases as it approaches the AsP contact layer 7 side. The light intensity distribution of the light emitted from the active layer 4 in the p-type InP layer 6 is determined by the InGaAsP guide layer 5
However, in the growth of this region, the supply amount of phosphine, which is a group V raw material, is small, so that the p-type carrier concentration is low, and the optical loss due to the p-type carrier is suppressed to be small. On the other hand, the resistance of the p-type InP clad layer 6 as a whole layer can increase the p-type carrier concentration in the region of the p-type InP clad layer 6 close to the p-type InGaAsP contact layer 7, so that the supply amount of phosphine is increased. It can be made smaller than when not.

Next, one specific example of forming the semiconductor laser structure shown in FIG. 1 according to the present invention will be described.

As shown in FIG. 1, n = 2 × 10 ¹⁸ cm ^-3
After growing the Sn-doped InP buffer layer 2, the non-doped InGaAsP guide layer 3, the InGaAs / InGaAsP MQW active layer 4, and the non-doped InGaAsP guide layer 5 on the InP substrate 1 by the MOMBE method,
At a growth temperature of 500 ° C. and a beryllium cell temperature of 950 ° C., the phosphine (PH ₃ ) supply pressure is gradually increased to 6 Torr, 7.5 Torr, 9 Torr as shown in FIG. 4, and under each phosphine pressure, Beryllium-doped InP layer is grown for 30 minutes and the film thickness is 500 n
After forming the p-type InP clad layer 6 having a structure in which each m was grown, a p-type InGaAsP contact layer 7 was grown to 0.3 μm.

The phosphine supply pressure is 6 Torr, 7.
Beryllium-doped I in the case of 5 Torr and 9 Torr
Each of the p-type carrier concentration in nP, as shown in FIG. ^{4, 4x10 17 cm -3, 7x10} 17 cm -3, 1x10 18
It was cm ^-3 .

Active layer region width 2 μm, resonator length 300 μm
The device resistance of the ridge stripe laser is 8 ohms,
The threshold current was 17 mA.

As described above, the MONBE method or G
When the beryllium-doped InP layer is grown by the SMBE method, the property that the p-type carrier concentration is increased by increasing the supply amount of V group raw material, for example, phosphine, is utilized in the p-type InP clad layer. The p-type doping amount can be changed. It should be noted that in the present embodiment, phosphine (PH ₃ ) was used as the group V raw material, but the present invention is not limited to this, and for example, InG
In the production of the aAs layer, it is preferable to use arsine (AsH ₃ ) as the V group raw material.

[0023]

As described above, according to the present invention, M
By the OMBE method and the GSMBE method, by changing the supply amount of phosphine as the V group raw material during the growth of the beryllium-doped p-type InP clad layer, it is possible to realize a semiconductor optical device having a small device resistance and a small optical loss. The present method is useful for a laser diode device, a light modulation device, an optical device having a p-type InP clad layer for a light receiving device, and an integrated optical device combining these.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a semiconductor laser structure.

FIG. 2 is a diagram showing a p-type carrier concentration distribution in a semiconductor.

FIG. 3 is a diagram showing a change in p-type carrier concentration in beryllium-doped InP with respect to a phosphine supply pressure.

FIG. 4 is a cross-sectional view showing the structure of a p-type InP clad layer manufactured according to the present invention.

[Explanation of symbols]

 1 n-type InP substrate 2 n-type InP buffer layer 3 InGaAsP guide layer 4 InGaAs / InGaAsP MQW active layer 5 InGaAsP guide layer 6 p-type InP clad layer 7 p-type InGaAsP contact layer

Claims (2)

[Claims] 1. When a beryllium-doped p-type InP layer is formed by using a metalorganic molecular beam epitaxy method (MOMBE) and a gas source molecular beam epitaxy method (GSMBE method) in which a hydrogen compound is used as a group V raw material, A method for manufacturing a semiconductor optical device, characterized in that the doping amount of beryllium is controlled by changing the supply amount of a group V raw material. 2. The method for manufacturing a semiconductor optical device according to claim 1, wherein the group V raw material is phosphine.