JPH02309303A - Semiconductor device having heterostructure - Google Patents

Abstract

PURPOSE:To obtain the device having high transmittance and high efficiency by specifying the transverse size and waveform characteristics of a core formed of a GaP core layer and an AlxGa1-xP clad layer to prescribed values. CONSTITUTION:The 1st clad layer 2 consisting of the AlxGa1-xP (where, for example, x=0.095) is grown by a liquid phase growth method due to a temp. difference on a GaP substrate crystal 1 having a (100) face orientation. The GaP core layer 3 is then grown by applying an optimum phosphorus vapor pressure P onto a soln. to obtain the core layer 3 having less defects. This layer is then etched to a stripe shape having 50mum or smaller width by a reac tive on-etching method using a gaseous PCl3 discharge and further, a 2nd clad layer 4 consisting of the AlxGa1-xP is formed and a buffer layer 5 consisting of GaP is formed thereon by an ordinary wet etching. The loss of this optical waveguide is small as the absorption of the GaP itself is small. The device which is extremely small by the scattering and absorbing of the heterobounary of the GaP and the AlxGa1-xP and is small in the absorption loss from 600nm to 1.6mum wavelength, i.e. from visible to near IR regions is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a semiconductor optoelectronic lunar light waveguide, and particularly to a high transmittance leading waveguide used for optical modulation/demodulation, optical switching, optical nonlinear mixing, etc.

[Problems to be solved by conventional technology and invention]

Conventionally, various devices having optical waveguide structures of compound semiconductors, particularly GaAs-GaAgAs, have been proposed as devices for modulation/demodulation of light waves, optical switching, etc. These devices use effects such as electro-optic effects, absorption modulation effects, and optical nonlinear effects within compound semiconductors, but these effects are very small and require a considerable length of 1 mm to 10 mm or more. It was necessary to interact within a waveguide that has a light confinement effect with a certain degree of strength. However, such a long GaAs-GaA2As optical waveguide was impractical because absorption was large within the crystal and at the heterointerface, making it difficult to transmit light substantially without attenuation over a length of 10 mm. In particular, when the transmitted light wave is light from a GaAs laser diode, the light wave coincides with the absorption edge of the medium, so almost no light is transmitted, making it impractical. The present invention provides a semiconductor guided waveguide that solves the above-mentioned problems, and has an extremely high light transmittance, a light confinement effect comparable to that of the GaAs-GaAAAs system, an electro-optic effect, an absorption modulation effect, and an optical waveguide. The effects used, such as nonlinear effects, are also of comparable magnitude. According to the present invention, zero
．． A device is provided that produces the various interaction effects over 10 mm with substantially no attenuation of 5 db/cm or less, that is, a loss of 10% or less (Means for Solving the Problems) FIG. The optical waveguide has a GaP epitaxial layer as the optical waveguide section or core, and Ga, -, A
J□P is a cladding layer surrounding the core, which is formed on a GaP crystal substrate. The GaP core layer has a low carrier density, i.e. 2X10, to minimize internal crystal absorption.
It is desirable to have a carrier density of /am-3 or less.

In addition, in the G a, -, A J-z P layer, a crystal layer with a light confinement effect and good crystallinity can be obtained when the composition X of A, // is in the range of 0°25 to 0.03. However, in order to achieve a high transmittance, which is the objective of the present invention, that is, a loss of 0.5 db/cm or less, the range should be 0.1>x<0.03. In FIG. 1, 1 is a GaP substrate, 2 is a first cladding layer, 3 is a GaP core layer, 4 is a second cladding layer, and 5 is a GaP substrate.
This is a P buffer layer.

[Effect]

Since both GaP and G a+-z"l P are indirect transition semiconductors, their transmittance at wavelengths longer than the fundamental absorption edge is extremely high compared to direct transition semiconductors up to wavelengths very close to the absorption edge. is 550 nm, and has high transmittance for the wavelength of 840 nm of GaAs laser diode.Also, since it is an IV group compound semiconductor like GaAs, it has high transmittance such as electro-optical wave effect, absorption modulation effect, and various optical nonlinear effects. The various effects also have similarly large values.Furthermore, Ga
The relative lattice constant difference between P and AnoP is 3 x JO-3, and the lattice constant difference between GaAs and AZAs is τ = 1.5X10
The lattice matching degree is extremely high compared to that of all other 1-V group compound semiconductors in which the difference between binary systems is on the order of 10 or more. Therefore, it is possible to almost eliminate deep levels, dislocations, and other causes of loss and deterioration at the heterointerface, thereby eliminating interface loss of the waveguide structure. Furthermore, since the degree of lattice matching is high, distortion is small, and bad effects such as changes in polarization direction due to photoelastic effects can be avoided. In particular, in order to maximize the aforementioned effects, it is necessary not only to make the thickness of the core layer 10 μm or less, but also to make the stripe width as small as possible, 50 μm or less. Even though the combination of , -EP is extremely excellent, when propagating over a length of 10 mm, a loss of several tens of percent or more occurs due to light scattering holes and light leakage at the hetero interface, especially on the sides. .

To avoid this, set the composition X of A7 to 0.03≦X by 0.1
If it is limited to the range of A total internal reflection critical angle can be obtained due to the refractive index difference.

[Example 1] A first cladding layer of ALo, oqsGao, and qoxP is grown on a GaP substrate crystal having a (100) plane orientation by a temperature difference liquid phase growth method. In the temperature difference liquid phase growth method, since slow cooling is not performed during growth, the Ox fold number of component A-6 can be kept constant during growth, and the A/e composition can be determined by measurements such as the EPMA method. The aforementioned values can be maintained with good reproducibility.

Next, the core layer GaP is grown by adding in phosphorus vapor pressure PoPc onto the solution. As a result, defects in the core layer are significantly reduced, carrier density is also minimized, and a core layer with extremely low internal absorption due to these is obtained. Next, put this on pc
, g, etched into stripes with a width of 50 μm or less using gas discharge or active ion etching (RIE), and then through a normal wet etching process to form “o, o9sG” o9o! .

By growing a second cladding layer of P and, if necessary, a buffer layer of GaP thereon, a leading waveguide as shown in cross section in FIG. 1 is formed. The loss of the leading wavepath formed in this way is due to the small absorption of GaP itself, and
'-z, GaH-zP losses due to scattering and absorption at the heterointerface are also extremely small. The GaP cladding layer is un
In the case of dope, it is less than lXl0 am, and the absorption loss due to this is 1 from a length of 10 mm and a wavelength of 600 nm.
．． 5 μm over 6 μm, i.e. in the visible to near-infrared region.
%, and the loss due to the hetero interface is about 5%, so the total loss is 10%/cm or 0.46db/cm
is obtained. Light may be introduced into this optical waveguide using an optical fiber or an objective lens in a manner similar to that shown in FIG. 5, that is, from the end surface. In the above example where x=0.095, NA(num
erical aperture) 0. Even if the light is incident at 6, complete optical confinement is achieved.

The vapor pressure control temperature difference method for GaP, especially the relationship between the optimal vapor pressure and growth temperature, is discussed in J. Nishizawa and Y4 Okuno, “Liquid phase epitaxy of GaP”.
Temperature Chart Difference Method Under Condroldo Baber Pressure Pa I E E E E E E I E E I E E I E E I E E I E E I E E I E E I E E I E E I E E I E E I E E E I E E I E E I E E E E E E E E E I E E I E I E E E E E E E I E E I E E I E E E E E E E E L E D thaner Ed-22 Page 716 (197
5) (J, NiN15hiza and Y,
0kuno.

”Liquid Phase Epitaxy of
GaP by a Temperature Diff
erence Method tinder Cont
rolled Vapor Pressure+' IE
EE Transactions on Electr
on Devices, Vol, ED-22P,
71B (1975)). In the above example, the growth temperature is 850°C and the carrier density of the core GaP layer is n=l.
X10"cdm, the applied a3am vapor pressure is 150 T Or'
It is r'. The thickness of each layer of the first cladding, core, and second cladding is 0.5μ to 2μ, 5μ to 10μ, and 0.5μ to
It is 2μ. Since the GaP layer grown by the vapor pressure controlled temperature difference method has virtually no deep levels responsible for absorption, the remaining absorption is caused by free carriers, and therefore the internal absorption is approximately proportional to the free carrier density. This free carrier density also becomes minimum at the highest vapor pressure, but the minimum carrier density becomes smaller as the growth temperature is lowered [Example 2] The general outline of the growth method is the same as in Example 1, but the loss is further reduced. The composition X of A and e- is set to 0.06 in order to lower it. Also,
Growth temperature 770° to reduce internal absorption of GaP core layer
C maximum phosphorus vapor pressure is 40 TOrr, carrier density is 0.5
Obtain xlOam. As a result, the optical loss was further reduced compared to Example 1, and the internal absorption loss of the core layer was 1.3% when the stripe width was 10μ, the core thickness was 1μ to 2μ, and the cladding layer thickness was 0.5μ to 1μ. Scattering and absorption loss at the hetero interface is 2% or less, total 2.3%/cm, 0.1db/
A low value below am is returned. Of course, by making X smaller, the refractive index difference necessary for light confinement becomes smaller, and N
At A=0.6, light confinement is not perfect, but at NA=0.
The incident light at about 4 can be completely confined, which is sufficient for input from a multimode optical fiber.

[Example 3] FIG. 2 shows a cross section of a leading waveguide in this example. Although the growth method and the like may be any of those in Examples 1 and 2, the heterointerface corners of the cross section are made to have a rounded structure without sharp corners.

In the case of such a rectangular corner with no roundness, as shown in FIG. 3, the scattering or leakage loss of light due to the corner cannot be ignored, and the effect is remarkable even when the cross section is small. To manufacture the structure shown in Fig. 2, wet etching after the RIE process described in Example 1 was performed to form HN○,: HF: H2O:
=1: 1: When etching is performed for a relatively long time, for example, about 3 minutes using a 1 solution, the vicinity of the hetero interface is particularly etched and becomes rounded. Furthermore, the growth rate of the second cladding layer was reduced to 5 μm, slower than the normal 20 μm/hr.
/ hr, the upper edge of the core layer also becomes rounded during growth, resulting in the shape shown in FIG. 2.

By doing this, the stripe width can be narrowed to about 20μ compared to Example 1, and also Example 2
For example, the stripe can be reduced to about #13μ. This roundness can be achieved by appropriately controlling the etching time and growth rate so that the radius of curvature is sufficiently large relative to the wavelength of light, for example, R~2 .mu.m.

In order to use the optical waveguide of the present invention for a modulator, a double-N unit, difference frequency mixing by optical nonlinear effect, sum frequency mixing, etc., a commonly known method may be used.

For example, in an optical modulator using an electro-optic effect having a structure in which the pn junction is reverse biased as shown in FIG. 4, the core GaP is an n-type undoped layer as in the previous embodiment, and the second cladding layer 4 is made of Alternatively, the p-type layer (p=3XIOcm') doped with Zn, the first cladding layer 2 is Te-doped n-type GaP (1x 1017cm-3), and the p-type layer, Lxaa, - A pmlE electrode 6 is formed on the p-type GaP buffer layer of the n-type (n-
1xlO”cm-3) n-shaped fi7 on the back side of the GaP substrate
By applying a reverse bias of 1 to 3 cm, the Qa of the core layer can be reduced.
P is depleted, and a high electric field is applied to the transmitted light 8 from the GaAs laser diode, which can be modulated by the electro-optic effect. Since the 4tL selection rule for the effect to be utilized is known, the orientation of the substrate crystal and the crystal orientation of the stripe direction can be appropriately selected using it.In actual IM example 2, the composition of hL is further reduced to 0.03. Although it is possible to do so, it becomes difficult for large amounts of light to enter the NAO. In such a case, as shown in Figure 5, the multimode optical fiber and the optical waveguide end may be
Light can be introduced by bringing the light close to the order of μm and filling the middle with a high refractive index liquid for matching.

In the case of differential frequency mixing, two laser beams of different frequencies are introduced through the fiber 6. For example, the wavelength is 860 nm
Then, light from a GaAs-Ga1gAs laser diode with a wavelength of 800 nm is introduced, and far-infrared light with a wavelength of 11.5 μ is emitted. In FIG. 5, 6 is an optical fiber, 7 is a GaP wafer having a waveguide, 8 is a stripe of the waveguide according to the present invention, and 9 is a high refractive index liquid.

〔Effect of the invention〕

As shown above, the device of the present invention has a high transmittance, and in particular does not absorb much of the output light from GaAs-based and other +11-V group compound semiconductor laser diodes.
It is a high-efficiency leading waveguide device that efficiently generates electro-optic effects, optical nonlinear effects, absorption modulation effects, etc. comparable to those of aAs itself.

[Brief explanation of the drawing]

FIG. 1 shows a leading waveguide of the present invention, and FIG. 2 shows an embodiment of the method of the present invention, in which the core has rounded corners.

Claims (3)

[Claims] (1) It has an optical waveguide formed of a GaP core layer and an Al_xGa_1_-_xP cladding layer, the core width being 50 μm or less, the wavelength being 600 nm or more, and the loss of guided light in the near-infrared region being small. Semiconductor heterostructure device. (2) The semiconductor heterostructure device according to claim 1, wherein the composition x of Al is 0.03≦x<0.1. (3) The semiconductor heterostructure device according to claim 1 or 2, wherein the corners of the core cross section are rounded.