JP3268560B2 - Method for manufacturing optical semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical semiconductor device which performs an optical logic / optical switch operation which can be used for an optical switching / optical repeater which is expected to constitute an optical communication / optical information processing system. Things.

[0002]

2. Description of the Related Art FIG. 1 is a structural view of a resonance type optical switch in which a semiconductor quantum well layer 1 is used as an optical nonlinear material and sandwiched between high reflection films 2, and FIG. In the optical switch having this structure, when the control light pulse 3 is not irradiated, the transmission spectrum of the resonator becomes a solid line in FIG. 2, and the signal light pulse 4 is not transmitted. On the other hand, when the control light pulse 3 is irradiated, the refractive index of the quantum well layer 1 changes, so that the resonance peak shifts as shown by the dotted line, so that the signal light 4 is transmitted.

[0003]

As described above by taking the above-mentioned resonator type optical switch as an example, in all conventional optical semiconductor devices having an optical switch operation function, carriers are excited by irradiating control light. , Changing the refractive index of the material, resulting in an optical switch operation. The lifetime of carriers excited at this time is as long as several nanoseconds. Therefore, in the conventional optical semiconductor device, the recovery to the state before the irradiation of the control light is delayed, and it is difficult to perform a high-speed switching operation. Therefore, in the conventional optical semiconductor device, in order to perform a high-speed optical switch operation, it is necessary to extremely shorten the life of excited carriers. This is the problem to be solved by the present invention. That is, an object of the present invention is to provide a manufacturing method for obtaining an optical semiconductor device capable of extremely shortening the lifetime of carriers excited by irradiation with control light.

[0004]

Features of the present invention a method Means for Solving the Problems] is lower temperature than the normal growth temperature of the optical nonlinear material, namely, Ri near the use of the InGaAs quantum well layer grown at 0.99 ° C. to 400 ° C. And this InGaAs
During the low temperature growth of the quantum well layer, a p-type element or
Other Ru near the addition of Be.

[0005]

[0006] Additional features of the method of the invention, after the low temperature growth of the quantum well layer is to annealed.

[0007]

The gas source molecular beam epitaxy (MB)
E) In the device, the quantum well layer is grown at about 500 ° C. At this time, the excited carriers become dominant in the light emitting recombination process, and thus the obtained optical semiconductor device is extremely useful for application to light emitting devices such as lasers. However, on the other hand, the carrier lifetime due to the radiative recombination process is
Since it is extremely long and several to several tens of nanoseconds, in this optical semiconductor device, recovery to the initial state is slow, and it is difficult to create a high-speed switch.

On the other hand, when the temperature is lowered and the growth is performed at 150 ° C. to 400 ° C. as in the present invention, it is considered that a recombination center is formed at a deep level. Speed up to about 100 picoseconds. If the growth of the quantum well layer is performed at less than 150 ° C., it is considered that the wavelength of the absorption by the exciton does not change. Therefore, it is difficult to use as a growth temperature. Further, when the growth temperature exceeds 400 ° C., the carrier life starts to be prolonged.
Are not available. Further, when a p-type element or Be is introduced during growth, the carrier lifetime can be reduced to about 1 picosecond. Further, when the grown quantum well layer is annealed at a temperature of about 500 ° C., the doped acceptor is activated, and a carrier generated during the low-temperature growth is compensated, so that the quantum well layer has an extremely high resistance. be able to. Therefore, if this quantum well layer is used as an optical nonlinear material of the optical semiconductor device, it is possible to produce an extremely high-speed all-optical switch.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Example 1 A quantum well layer suitable for use in an optical semiconductor device intended in the present invention was grown by a molecular beam epitaxy method. The equipment used was
It is a well-known molecular beam epitaxy apparatus and was performed under the following growth conditions. Note that Be was doped as the acceptor.

(I) Group III source: In, Ga, Al (metal) (ii) Group V source: AsH ₃ gas (flow rate 2 cc)
m) (iii) Degree of vacuum during growth: 1.3 × 10 ^-5 Torr (iv) Substrate rotation speed: 20 rpm (v) Growth speed: 2.6 μm / h (vi) Growth temperature: 200 ° C. As described above. FIG. 3 shows an example in which a change in the transmittance of an InGaAs / InAlAs quantum well layer grown at 200 ° C. by a gas source molecular beam epitaxy apparatus and doped with Be as an acceptor was measured by a pump-probe method. This absorption recovery time reflects the carrier lifetime, and means that the quantum well layer recovers to the initial state in a few picoseconds.

Under the same conditions as above, only the growth temperature is set to 15
The quantum well layer was grown at 0, 200, 300, 400 and 600 ° C. When the carrier lifetime of the quantum well layer grown at each temperature was measured, the result of FIG. 4 was obtained. As is clear from the figure, the growth temperature is 4
If the temperature exceeds 00 ° C., the carrier lifetime starts to be prolonged. Therefore, the growth temperature is preferably 400 ° C. or less. Also, 150
In the vicinity of ° C., there is no problem in the value of the carrier lifetime,
If the temperature is lower than 0 ° C, there is a large possibility that the wavelength of the absorption by the exciton will not change. Therefore, the growth at a temperature lower than 150 ° C should be avoided.

Next, in order to investigate the effect of the change of the Be doping amount on the carrier lifetime, only the Be doping amount was changed from the doping amount of 0 cm ^-3 to about 8 c
The quantum well layer was grown in four different ways up to m ^-3 , and the carrier lifetime of each was measured. The result is shown in FIG. For comparison, the change in carrier lifetime with respect to the change in doping amount of the quantum well layer grown at a growth temperature of 500 ° C. is also shown in FIG. As is clear from the figure, in the growth at 200 ° C., the carrier lifetime is sharply shortened by doping with Be.

Therefore, when the above-mentioned Be-doped low-temperature-grown quantum well layer is used as an optical nonlinear material for the above-mentioned resonant optical switch, it becomes possible to produce an optical switch three orders of magnitude faster than conventional devices.

Example 2 A Be-doped low temperature growth quantum well layer was formed in the same manner as described above, and an optical switch having the structure shown in FIG. 6 was formed using this quantum well layer as an optical waveguide. FIG. 7 is a diagram illustrating the principle of the optical switch. As shown in the figure, this optical switch has an InGaAs / InAlAs functioning as an optical waveguide between InP layers 5 and 6.
It has a structure in which a quantum well layer 7 is formed, and a diffraction grating 8 is formed in a part of the quantum well layer 7 which is an optical waveguide. As described above, since the diffraction grating 8 is formed in a part of the optical waveguide of the optical switch, only the optical signal corresponding to the Bragg wavelength is reflected. Now, if the wavelength of the signal light pulse 9 is adjusted to this Bragg wavelength, the output light will be in a zero state as shown in FIG. 7 (solid line). At this time, when the excitation pulse 10 is applied to the diffraction grating 8 to excite the carriers, the refractive index of the diffraction grating 8 changes, so that the Bragg wavelength also shifts as indicated by the dotted line. Therefore, the input light shifts to the transmission state, and the output light can be obtained. The diffraction grating 8 is composed of a Be-doped low temperature growth quantum well layer 7
, The excited carriers disappear at a high speed as described above. Therefore, the quantum well layer 7
Can be quickly relaxed to the initial state, resulting in a high-speed optical switch.

(Embodiment 3) As shown in FIG.
A Mach-Zehnder optical switch using the same Be-doped low temperature growth quantum well layer 7 as an optical waveguide was formed. In the figure, 1
Reference numerals 1 and 12 are InP layers, and 13 is a ridge. As shown in the figure, since the optical waveguide forms a Mach-Zehnder interferometer that branches in the middle and then recombines, the phase of the multiplexed signal light pulse 15 is one when the excitation light pulse 14 is not irradiated. Therefore, it is output as it is. An excitation light pulse 1 is applied to one of the branched optical waveguides.
When 4 is irradiated to excite the carriers, the refractive index of that portion changes, and the optical path length changes. As shown in FIG.
The change amount ΔnL at that time (Δn: the change amount of the refractive index, L:
If the length of the excitation light irradiating section is adjusted so as to match the half wavelength of the signal light, the phase of the combined signal light is reversed, so that the signal light is not output. Since the optical waveguide portion is formed of the Be-doped low-temperature-grown quantum well layer 7, the excited carriers are quickly eliminated as described above, and are quickly relaxed to the initial state, thereby enabling a high-speed optical switch.

In the above embodiment, the InGaAs / InAlAs system has been described as a crystal material.
InGaAs / In (Ga) AlAs system, InGaAs
/ GaAs strained superlattice system, InGaAs / InGaAsP
Needless to say, the same effect can be realized also in a strained superlattice system.

Further, in the above embodiment, the production was carried out by the gas source molecular beam epitaxy method, but the present invention can of course be applied to the ordinary molecular beam epitaxy method.

[0019]

As described above, according to the method of the present invention, as an optical nonlinear material, a low-temperature grown InG doped with a p-type element or Be, which has a large nonlinearity and relaxes very quickly.
The optical semiconductor device is formed using the aAs quantum well layer. Since the excited carriers disappear as described above at high speed, the carriers are quickly relaxed to the initial state, and a high-speed optical switch can be realized .

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a conventional resonant optical switch.

FIG. 2 is a graph illustrating the principle of a conventional resonant optical switch.

FIG. 3 is a graph for explaining an example of the present invention and is a graph showing a measurement result of a saturable absorption recovery time of a Be-doped low temperature growth quantum well layer by a pump probe method.

FIG. 4 is a graph for explaining an example of the present invention and showing a relationship between a growth temperature of a quantum well layer and an excited carrier thereof in an optical semiconductor device formed by the method of the present invention.

FIG. 5 is a graph for explaining the present invention and showing the relationship between the amount of Be doped into the quantum well layer and the relaxation time (carrier lifetime) of the quantum well layer to an initial state after excitation.

FIG. 6 is a configuration diagram of a waveguide type optical switch having a diffraction grating formed by the method of the present invention.

FIG. 7 is a graph illustrating the principle of a waveguide type optical switch having a diffraction grating formed by the method of the present invention.

FIG. 8 is a configuration diagram of a Mach-Zehnder optical switch formed by the method of the present invention.

FIG. 9 is a graph illustrating the principle of a Mach-Zehnder optical switch formed by the method of the present invention.

[Explanation of symbols]

 5,6 InP layer 7 InGaAs / InAlAs quantum well layer 8 Diffraction grating 9 Signal light pulse 10 Excitation light pulse 11,12 InP layer 13 Ridge 14 Excitation light pulse 15 Signal light pulse

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshiaki Kagawa 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) Reference European Patent Application Publication 541304 (EP, A1) Appl. Phys. Lett. Vol. 59, no. 12, (1991) p. pp. 1491-1493 Optics Letters, Vol. 17, No. 7, (1992) p. p. 505-507 (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02F 1/35 G02F 1/017 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. A method of manufacturing an optical semiconductor device in which an InGaAs quantum well layer is stacked on a semiconductor substrate to form an active layer, wherein the growth of the InGaAs quantum well layer is performed at 150 ° C. to 400 ° C. layer
P-type element or Be added as dopant during the growth of
A method of manufacturing an optical semiconductor device. 2. The method of manufacturing an optical semiconductor device according to claim 1, further comprising a step of performing an annealing process after forming the InGaAs quantum well layer.