JPH0237305A - Optical waveguide and its manufacturing method - Google Patents

Abstract

PURPOSE:To obtain the light guide in which light can be effectively confined by laminating a clad layer consisting of a group II-VI compd. semiconductor on a substrate and a waveguide layer consisting of a group II-VI compd. semiconductor having the refractive index larger than the refractive index of the clad layer to a part on this clad layer. CONSTITUTION:This light guide has the structure composed of the GaAs substrate 1, the clad layer 2 consisting of ZnS and the waveguide 3 consisting of ZnSe. While the refractive index of the ZnSe of the waveguide 3 is 2.34, the refractive index of the ZnS of the clad layer 2 in the lower part is 2.31 and the refractive index of the upper part is 1.0, the difference in the refractive index is sufficiently large in the direction perpendicular to the boundary. The difference in the refractive index is sufficiently large in the direction parallel with the boundary as well because of the structure in which the waveguide layer 3 having 2.34 refractive index is sandwiched by the atm. of 1.0 refractive index. Since the difference in the refractive index between the waveguide layer 3 and the circumference thereof is large, the confinement of the light in the waveguide layer 3 is effectively executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to an optical waveguide of a II-Vl group compound semiconductor used as a component of an optical integrated circuit or an optoelectronic integrated circuit.

[Prior art] The optical waveguides of group II to Vl compound semiconductors that have been reported so far are based on Tosha Yokogaff 5 Applied Physics.
Letter (Toshiya Yokogawa, App
lPhys, Leff) Vol, 52. No
, 2 f1988) 120. FIG. 3 is a schematic diagram of the optical waveguide, and 5 is a G
aAs substrate, 6 is a cladding layer made of ZnS, 7 is Zn
5 is a waveguide layer made of an e-ZnS superlattice, and 8 is a stripe of SiO□. This optical waveguide becomes a single mode for light with a wavelength of 0.633 μm when the sin stripe width is 6 μm and the thickness of the waveguide layer is 0.4 to 124 μm, and the transmission loss is 0. It is reported to be 71 dB/cm.

(Problem to be Solved by the Invention) However, the optical waveguide of the prior art described above creates an effective refractive index step in the direction parallel to the interface by forming striped SiO□ on the waveguide layer. Therefore, there is a problem when the step in the refractive index between the waveguide region and the cladding region in this direction is small and light confinement cannot be performed effectively. Therefore, the present invention is intended to solve such problems, and its purpose is to create an If structure that effectively confines light.
- An optical waveguide made of a Vl group compound semiconductor and a method for manufacturing the same are provided.

[Means for Solving the Problems] The optical waveguide of the present invention includes a cladding layer made of a II-Vl group compound semiconductor on a substrate, and a portion of the cladding layer having a II-Vl compound semiconductor having a larger refractive index than the cladding layer. - It is characterized by having a structure in which waveguide layers made of a Vl group compound semiconductor are laminated. Furthermore, the method for manufacturing the optical waveguide includes a step of forming a cladding layer on a substrate, a step of forming a mask on the cladding layer, and a step of selectively applying the waveguide layer to a part of the cladding layer using the mask. and a step of removing the mask.

(Embodiment) FIG. 1 is a schematic cross-sectional view of an optical waveguide made of a II-Vl group compound semiconductor in an embodiment of the present invention. 1 is a GaAs substrate, 2 is a cladding layer made of ZnS, and 3 is a guide made of Zn5e. In this structure number, in the direction perpendicular to the interface, the refractive index of Zn5e in the waveguide layer is 2.34, whereas the refractive index of ZnS in the lower cladding layer is 2.31, and the refractive index in the upper part is 2.34. Since the atmosphere has a refractive index of 1.0, the difference in refractive index is sufficiently large, and even in the direction parallel to the interface, the waveguide layer with a refractive index of 2°34 is sandwiched between the atmosphere with a refractive index of 1.0. Therefore, the difference in refractive index is sufficiently large.As the difference in refractive index between the waveguide layer and its surroundings is large, the light is effectively confined in the waveguide layer.At a wavelength of 0.6328 μm, When the propagation loss of the optical waveguide was measured using light, it was 0.
, 5 dB/Cm or less, resulting in low loss. This is because, as mentioned above, light is effectively confined within the waveguide layer, so light seepage into the GaAs substrate is small.
This shows that absorption within the As substrate is small. Further, as will be described later, since there is no need to etch the waveguide layer in the manufacturing process of the optical waveguide, the surface of the waveguide layer is flat and the scattering loss is small, which also contributes to the low loss. ZnS and Zn
II-Vl group compound semiconductors such as 5e have a GaA substrate.
Since it has the same zincblende crystal structure as s, it can be easily epitaxially grown on a GaAs substrate. Furthermore, since optical devices and electronic devices such as light emitting elements and light receiving elements can be fabricated on GaAs substrates, the optical waveguide of the present invention can be easily integrated into optical integrated circuits or optoelectronic integrated circuits that integrate these devices. It can be applied. Also, as a substrate
In addition to aAS, a III-V group semiconductor substrate such as InP can also be used. Further, II-Vl group compound semiconductors as shown in Table 1 can also be used as materials for the waveguide layer and the cladding layer.

Table 1 The method for manufacturing the optical waveguide of the present invention is shown below in Figures 2(a) to (
This will be explained using d). First, a ZnS layer to be a lower cladding layer is epitaxially grown on a GaAs substrate by MOCVD, and then mask 4 8102 is deposited by thermal CVD or the like. This state is shown in FIG. 2(a).

Other epitaxial growth methods for ZnS include MBE method,
There are MOMBE method, hot wall epitaxy method, etc., and it is possible to form a ZnS cladding layer in the same way by these methods as well. Next, the SiO2 film is patterned by photolithography, and in this case, the SiO□ film in the portion where the waveguide layer is to be formed is removed by etching. This state is shown in FIG. 2(b). A waveguide layer of Zn5e was formed by selective epitaxial growth using the patterned 5iO= as a mask, as shown in Fig. 2(c).
). Selective epitaxial growth of Zn5e can be performed by the following method. Organic compounds of Zn and Se are used as raw materials, the growth pressure is 100 Torr or less, the growth temperature is 400°C or more and 700°C or less, and the raw material supply molar ratio of Group Vl raw material and Group II raw material is 6 or less. Alternatively, after forming a waveguide layer of Zn5e using the MOMBE method, 5102 is removed using a hydrofluoric acid-based etchant to complete an optical waveguide as shown in FIG. 2(d). In the above example, SiO□ was used as the mask, but other dielectric thin films such as 5i=N, W, etc. can be used in the same way.

Further, in the case of selective epitaxial growth of CdS, ZnTe, CdSe, etc., each organic compound of Cd, S, Zn, Te, and Se is used as a raw material.

[Effects of the Invention 1 As described above, the optical waveguide of the II-VI group compound semiconductor of the present invention has the following effects.

1) Light can be effectively confined in the optical waveguide structure of the present invention.

1i) i) makes it possible to effectively use optical nonlinear effects.

1ii) Low loss for visible light.

iv) Since it has the same crystal structure as the III-V compound semiconductor constituting the light emitting element and the light receiving element, it is possible to easily fabricate the optical waveguide of the present invention on the same substrate as these optical devices. This means that the optical waveguide of the present invention is suitable as a component of an optical integrated circuit or an optoelectronic integrated circuit.

Furthermore, the method for manufacturing an optical waveguide of the present invention has the following effects.

V) The optical waveguide having the above structure can be easily manufactured by a self-line process.

vi) Since the etching process of the waveguide layer is unnecessary, it is possible to prevent surface roughness that inevitably occurs due to etching, and to produce an optical waveguide with low scattering loss.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of an optical waveguide made of a II-Vl group compound semiconductor in an embodiment of the present invention. FIGS. 2(a) to 2(d) are schematic cross-sectional views showing the manufacturing process of the optical waveguide of the TI-Vl group compound semiconductor of the present invention. FIG. 3 is a schematic diagram of a conventional II-Vl group compound semiconductor optical waveguide.・GaAS substrate ・ZnS cladding layer Zn5e waveguide layer SiO□ mask GaAs substrate ZnS cladding layer Zn5e-ZnS superlattice waveguide layer in2 Hurry up

Claims (2)

[Claims] (1) A cladding layer made of a II-VI compound semiconductor is laminated on a substrate, and a waveguide layer made of a II-VI compound semiconductor having a larger refractive index than the cladding layer is partially laminated on the cladding layer. An optical waveguide characterized by having a structure. (2) forming a cladding layer on the substrate; forming a mask on the cladding layer; and selectively forming a waveguide layer on a portion of the cladding layer using the mask; A method for manufacturing an optical waveguide, the method comprising the step of removing a mask.