JPH03225325A - Light guide parts of semiconductor - Google Patents

Abstract

PURPOSE:To increase the efficiency of change of refractive index even at low voltage and to enable switching even to light having long wavelength by rendering a two-layered structure composed of an upper layer having high carrier concn. and a lower layer having low carrier concn. to an upper clad layer of an n-type semiconductor. CONSTITUTION:A two-layered structure composed of an upper layer 7b having high carrier concn. and a lower layer 7a having low carrier concn. is rendered to an upper clad layer 7 of an n-type semiconductor forming a light waveguide. Since ohmic contact is attained between the layer 7b and an upper electrode 9 and all of impressed reverse voltage acts effectively, the efficiency of change of the refractive index of a core layer 5 can be maximized even at low impressed voltage. The carrier concn. of the lower layer 7a is reduced by more than one figure as compared with the conventional concn., the light absorption loss of the layer 7a is also reduced and switching action to light having long wavelength is enabled even if the lower p-n junction face 10 of the layer 7a is brought close to the core layer 5.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a semiconductor optical guide comprising a ridge-loaded optical waveguide made of a semiconductor and having a pn junction surface formed in its upper cladding layer. More specifically, regarding waveguide components, the efficiency of changing the refractive index of the optical waveguide by voltage application or current injection into the optical waveguide is large, and absorption loss of injected carriers in the n-type semiconductor layer forming the pn junction surface is reduced. The present invention relates to a semiconductor optical waveguide component including an optical waveguide that can be made small.

(Prior art) Among optical circuit components made of semiconductors, such as directional coupler type optical switches, X-type total internal reflection optical switches, Y-type branching optical switches, optical multiplexers/demultiplexers, and optical modulators The device includes an optical waveguide loaded in a ridge shape on a semiconductor substrate,
It has a structure in which a pn junction surface is formed in the upper cladding layer.

Then, by applying a voltage to this pn junction surface, an electro-optic effect is exhibited, or by injecting a current into the pn junction surface to cause a plasma effect or a band filling effect, thereby forming a core layer in which light is guided. Changing the optical path by changing the refractive index.

It realizes functions such as wavelength separation, nine frequencies, and phase modulation.

The structure of such an optical waveguide will be explained with reference to FIG. 3 in the case of a directional coupler type optical switch in which two optical waveguides are formed close to each other in parallel.

In FIG. 3, the back surface of the lower electrode 1 made of an electrode material such as Ti/Pt/Au is
A substrate 2 of type semiconductor is formed.

On the semiconductor substrate 2, for example, a p layer with a thickness of about 0.5 μm is provided.
"p"G through the buffer layer 3 made of GaAs.
4. Lower cladding layer made of aAj7As and having a thickness of approximately 3.0 μm. Core layer made of p-GaAs and having a thickness of approximately 1.0 μm5. p-type upper cladding layer made of p-GaAjl'As6. An n-type upper cladding layer 7 made of GaAAAs is sequentially laminated to form ridge-shaped optical waveguides A and B. The entire surface of these optical waveguides A and B is covered with an insulating thin film 8 such as 5 iOz. A part of the insulating thin film 8 in the optical waveguides A and B of the switch part is removed in the form of, for example, a slit to form windows 8a and 8b, and this part is coated with AuGeNi by, for example, a vapor deposition method.
Upper electrodes 9a, 9b made of an electrode material such as /Au are attached.

In this way, the upper cladding layers of the optical waveguides A and H are composed of the p-type upper cladding layer 6 and the n-type upper cladding layer 7, and the interface between these layers forms the pn junction surface 10,
Further, the n-type cladding layer 7 is in contact with the upper electrodes 9a and 9b at its switch portion.

In the case of this optical switch, for example, when a voltage in the opposite direction is applied between the upper electrode 9a and the lower electrode l, a depletion layer spreads from the pn junction surface IO to the core layer 5 side due to the electro-optic effect, and the core layer 5 The refractive index changes. As a result, the optical waveguide A
No light is guided to the optical waveguide B, and the light is guided only through the optical waveguide B. That is, an optical path change occurs and a switching operation occurs.

(Problems to be Solved by the Invention) By the way, when trying to realize switching operation at low voltage in the optical switch of the conventional structure described above,
It is necessary to maximize the efficiency of changing the refractive index of the core layer 5 even when such a low voltage is applied.

For that purpose, the carrier concentration in the core layer 5 must be set to I
It is possible to maintain a low concentration state of about 10 cm 2 , thereby allowing the depletion layer below the pn junction surface IO to expand to the entire core layer 5 even if the applied voltage is low. is necessary.

Therefore, it is preferable that the pn junction plane IO be as close to the core layer 5 as possible.

Further, in order for all the applied voltage to effectively act on the pn junction surface, the contact between the upper electrode 9a (or 9b) and the upper surface of the n-type upper cladding layer 7 needs to be ohmic contact.

In order to realize such ohmic contact, the carrier concentration in the n-type upper cladding layer 7 must be set to 3X 10''.
It is said that it is necessary to set the distance to be equal to or greater than cm"-'.

However, when the carrier concentration of the n-type upper cladding layer 7 is increased to a high concentration of 3 x 10 "cm-" or more, the absorption loss in the n-type upper cladding layer of the optical waveguide becomes large. .55 μm light is no longer guided.

Furthermore, in the case of light having a wavelength of 1.3 μm, although it is possible to guide the light, when the above-mentioned pn junction surface IO is brought close to the core layer 5, the propagation loss of the light increases. arise.

In this way, in optical waveguides with conventional structures, it is impossible to realize switching operation at low voltage (and therefore small current) by bringing the pn junction surface close to the core layer while suppressing absorption loss to a small level. Met.

The present invention solves the above-mentioned problems and makes it possible to maximize the efficiency of changing the refractive index of the core layer even by applying a low voltage or injecting a small current, while at the same time reducing the absorption loss in the n-type upper cladding layer. An object of the present invention is to provide a semiconductor optical waveguide component including an optical waveguide having a structure that can minimize the amount of noise.

(Means for Solving the Problem) In order to achieve the above-mentioned object, in the present invention, a p-type semiconductor substrate formed on the back surface of a lower electrode is
A lower cladding layer of type semiconductor, a core layer of p-type semiconductor, and an upper cladding layer of n-type semiconductor.

A semiconductor optical waveguide component having at least one optical waveguide in which an upper cladding layer of an n-type semiconductor is sequentially formed, and an upper electrode for voltage application or current injection is attached to the upper surface of the n-type semiconductor, A semiconductor optical waveguide component is provided, wherein the upper cladding layer of the n-type semiconductor has a two-layer structure including an upper layer with high carrier concentration and a lower layer with low carrier concentration.

In the optical waveguide of the present invention, the n-type upper cladding layer has a two-layer structure, of which the upper layer is composed of an n-type semiconductor layer with a high carrier concentration, and the lower layer is composed of an n-type semiconductor layer with a low carrier concentration. There is no difference from the structure of the conventional optical waveguide shown in FIG. 3, except for the fact that

In this optical waveguide, the carrier concentration in the upper layer is approximately 3
The carrier concentration in the lower layer is about I x 10 "cm".

(Function) In the case of the optical waveguide of the semiconductor optical waveguide component of the present invention, the n
Since the mold upper cladding layer has the above structure, ohmic contact is achieved between the upper layer with high carrier concentration and the upper electrode, and all of the applied reverse voltage can be effectively applied. Even when a low voltage is applied, the efficiency of changing the refractive index of the core layer due to the electro-optic effect can be maximized.

In addition, since the carrier concentration in the lower layer is more than an order of magnitude lower than in the conventional case, the absorption loss of light in this lower layer is reduced, and even if the lower surface of the lower layer, that is, the pn junction surface, is brought close to the core layer, Switching operation for long wavelength light becomes possible.

(Example) Hereinafter, an example of the present invention will be described based on the drawings. 1st
This figure is a sectional view of an optical waveguide corresponding to one optical waveguide in the directional coupler type optical switch shown in FIG. 3.

In FIG. 1, the lower electrode l such as Ti/Pt/Au
On the p'' GaAs substrate 2 formed on the back surface of the
．． Through a 5 μm p”GaAs buffer layer 3,
p"A1 o, +Gao,. Lower cladding layer 4 made of As (carrier concentration 5 x 10"cm" + thickness 3.0 μm), core layer 5 made of p-GaAs (carrier concentration lXl0"CIl+-', thickness 1 .0μm),
A p type upper cladding layer 6 (carrier concentration I o, +Gao, sAs
Lower layer 7a of n-type upper cladding layer consisting of (carrier concentration 1×10110l7”, thickness 0.7 μm) and n”
Upper layer 7b of the n-type upper cladding layer consisting of A1 o, +Gao, Js (carrier concentration 3 x 10"cm-
3, 0.2 μm thick), and the entire surface is covered with Si.
It was coated with an Ox thin film 8. A portion of the thin film 8 is removed to form a window 8a.
After forming AuGeNi/Au, the upper electrode 9a was attached thereto. The other optical waveguide provided in parallel was also formed in the same manner.

When the contact state between the upper electrode 9a and the upper layer 7b was examined by electrode contact resistance measurement and IV characteristic measurement, it was found that they were in an ohmic contact state.

An inverted Δβ directional coupler type optical switch and a -like Δβ directional coupler type optical switch equipped with this optical waveguide were fabricated, and their switching characteristics and propagation loss were evaluated using light at a wavelength of 1.3 μm. For comparison, the n-type upper cladding layer does not have a two-layer structure but has a carrier concentration of 3 x 10 "an-" and a thickness of 0.
．． A similar evaluation test was also conducted on a conventional device having a 5 μm layer and a 1.0 μm thick p-type cladding layer underneath.

The propagation loss in the optical switch of the present invention is approximately 6 dB/cm
In the case of the conventional one, it was about 15 dB/cm.

Further, the results of the switching characteristics are shown in FIG. In the figure, the marks -○- indicate the optical switch of the present invention, and the marks . . . indicate the optical switch of the conventional structure. As is clear from FIG. 2, in the case of the optical switch having the structure of the present invention, the switching voltage can be lowered by about 24 V compared to the conventional one.

(Effects of the Invention) As is clear from the above explanation, the semiconductor optical waveguide component of the present invention includes a lower cladding layer of an n-type semiconductor, a lower cladding layer of an n-type semiconductor, a substrate of an n-type semiconductor formed on the back surface of a lower electrode, A core layer of a semiconductor, an upper 4° rad layer of an n-type semiconductor, and an upper cladding layer of an n-type semiconductor are sequentially formed, and an upper electrode for voltage application or current injection is attached to the upper surface of the n-type semiconductor. A semiconductor optical waveguide component having at least one optical waveguide, characterized in that the upper cladding layer of the n-type semiconductor has a two-layer structure of an upper layer with a high carrier concentration and a lower layer with a low carrier concentration. Therefore, even at low voltages (small currents), the pn junction in the upper cladding layer acts effectively, maximizing the refractive index change efficiency of the core layer, and furthermore, reducing light in the n-type upper cladding layer. Absorption loss is also small, and switching operation can be realized even for long wavelength light.

Therefore, the component of the present invention has low loss, does not cause destruction of the pn junction surface due to application of high voltage or injection of large current, operates with low power consumption, and is highly reliable. Therefore, it has great industrial value as an optical circuit component element such as an optical switch or an optical modulator.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of the switch portion of the optical waveguide included in the component of the present invention, Fig. 2 is a graph showing the switching characteristics of a directional coupler type optical switch, and Fig. 3 is a cross-sectional view of the switch section of the optical waveguide included in the component of the present invention. FIG. 3 is a cross-sectional view of the switch section of the optical waveguide. l...lower electrode, 2...n-type semiconductor substrate, 3...
- Buffer layer of n-type semiconductor, 4... Lower cladding layer of n-type semiconductor, 5... Core layer of n-type semiconductor, 6...
Upper cladding layer of n-type semiconductor, 7... Upper cladding layer of n-type semiconductor, 7a... Lower layer of n-type upper cladding layer,
7b... Upper layer of n-type upper cladding layer, 8... Insulating thin film, 8a, 8b... Window, 9a, 9b... Upper electrode,
IO... pn junction surface.

Claims (1)

[Claims] On the p-type semiconductor substrate formed on the back surface of the lower electrode,
Lower cladding layer of p-type semiconductor, core layer of p-type semiconductor, p
An upper cladding layer of a type semiconductor and an upper cladding layer of an n-type semiconductor are sequentially formed, and at least one optical waveguide having an upper electrode for voltage application or current injection attached to the upper surface of the n-type semiconductor is formed. 1. A semiconductor optical waveguide component comprising: an upper cladding layer of the n-type semiconductor having a two-layer structure including an upper layer with a high carrier concentration and a lower layer with a low carrier concentration.