JPH04372187A - Semiconductor device and driving method thereof - Google Patents

Abstract

PURPOSE:To provide a semiconductor device such as a tunable laser having a wide variable range of wavelength, a variable wavelength filter, etc. CONSTITUTION:A semiconductor device has an active layer 4 composed of at least one quantum well layer, which can be oscillated and has a plurality of quantum levels, and has a comb-shaped ultrasonic vibrator 10 to one part on an optical guide layer 3. Laser oscillation wavelength can be varied over a wide range by varying the wavelength of surface acoustic waves generated from the vibrator 10. Currents injected to electrodes 7, 9 are brought to an oscillation threshold or less, thus varying the selected wavelength over the wide range while amplifying incident light.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is used for wavelength multiplexing optical communication, processing, recording, etc., and in particular, semiconductor devices such as wavelength tunable lasers with a wide wavelength tuning range and wavelength tunable optical filters (filters), and methods for driving the same. Regarding.

0002

2. Description of the Related Art In recent years, with the advancement of technology in the fields of optical communications and optical processing, optical devices with wavelength tunable functions have become important. In particular, in wavelength multiplexing communication, a wavelength tunable laser and a wavelength tunable optical filter are required and are being developed as a receiving side.

[0003] As a typical conventional example, a mode is stabilized by forming a constant periodic collage on an optical guide layer.
Some devices have a wavelength tunable function by providing multiple electrodes or a phase adjustment region without collage (Laser Research 17 (11) November 1989 p. 40
, OQE88-65 p. 9th grade). In this method, the refractive index of the medium is changed by injecting a current, and the oscillation wavelength or filtering wavelength can be changed while keeping the single mode stable.

On the other hand, as an example in which no collagen is formed, a comb-shaped electrode ultrasonic transducer that generates surface acoustic waves is provided on the light guide layer, and the surface acoustic waves propagating on the light guide layer have the same effect as collagen. and the laser oscillation wavelength changes depending on the change in the frequency (Japanese Patent Application Laid-Open No. 1-5)
8876) has been proposed.

[0005]

[Problems to be Solved by the Invention] However, in the method of forming collagen, the wavelength tuning range is several n.
It is narrow, about m, and there is a limit to the degree of wavelength multiplexing. Furthermore, high-precision microfabrication is required for manufacturing, and crystals must be regrown on a substrate that has been processed in the atmosphere, which may lead to reductions in reproducibility, productivity, and service life.

On the other hand, when surface acoustic waves are used, the wavelength can be freely changed depending on the vibration frequency, and the wavelength variable range is wider than when using collage, and manufacturing is simpler. However, in a normal laser wafer, the gain of the active layer is
As shown in Figure 10, the wavelength range is limited and the center wavelength λ0
The gain decreases as you move away from. Therefore, the wavelength tunable range is limited to about several tens of nanometers, and if the wavelength is varied beyond that, the threshold value will rise, making it unusable.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a semiconductor device and a method for driving the same that solve the above-mentioned problems.

[0008]

[Means for Solving the Problems] A wavelength tunable semiconductor laser of the present invention that achieves the above object has an active layer consisting of at least one quantum well layer having a plurality of quantum levels capable of oscillation, and has an active layer formed on a light guide layer. A semiconductor device including a comb-shaped ultrasonic transducer in a part thereof is characterized in that the laser oscillation wavelength can be varied over a wide range by changing the wavelength of the surface acoustic wave generated from the transducer. Further, the wavelength tunable optical filter of the present invention has an active layer consisting of at least one quantum well layer having a plurality of quantum levels capable of oscillation, and a comb-shaped ultrasonic transducer is provided on a part of the optical guide layer. The semiconductor device is characterized in that by keeping the injected current below the oscillation threshold, the selected wavelength can be changed over a wide band while amplifying the incident light.

Furthermore, the method for driving a semiconductor device of the present invention has an active layer consisting of at least one quantum well layer having a plurality of quantum levels capable of oscillation, and a part of the optical guide layer is provided with comb-shaped ultrasonic vibrations. In a semiconductor device equipped with a vibrator, the laser oscillation wavelength is changed over a wide band by changing the wavelength of a surface acoustic wave generated from the vibrator while keeping the injected current equal to or higher than the oscillation threshold. Alternatively, the selected wavelength may be changed over a wide band while amplifying the incident light by changing the wavelength of the surface acoustic wave generated from the vibrator while keeping the injected current below the oscillation threshold.

As described above, the present invention is equipped with a comb-shaped electrode ultrasonic transducer that generates surface acoustic waves, and furthermore, the gain range of the active layer is wideband from 50 to 100 nm.
Provided are a wavelength tunable laser and a wavelength tunable filter that can change wavelength to about 0 nm. The structure of the active layer has a plurality of different energy band gaps Eg1,
Quantum wells with 2 and 3 quantum wells are stacked via barrier layers with appropriate height and width, and as shown in Figure 9, the entire active layer is stacked with the gain corresponding to the band gap of each quantum well. Since the gain is determined, a uniform gain can be obtained over a very wide range. Therefore, by determining the selected wavelength based on the frequency of the surface acoustic wave, a tunable laser that oscillates in a single mode in a range of approximately 100 nm and a tunable filter that has a narrow bandwidth can be obtained.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a perspective view showing the structure of a wavelength tunable laser or wavelength tunable filter according to a first embodiment of the present invention. Moreover, FIG. 2 is a cross-sectional view of the waveguide portion. As can be seen in the figure, the device is divided into a current injection part and a current non-injection part.

The wafer structure of the current injection section is n-GaAs.
On the substrate 1, a 0.5 μm thick n-GaAs buffer layer (not shown) and a 1.5 μm thick n-Al0.5Ga0.
5As cladding layer 2, active layer 4, p-
Al0.25Ga0.75As light guide layer 3, thickness 1.
5 μm p-Al0.5Ga0.5As cladding layer 5,
A p-GaAs cap layer 6 with a thickness of 0.5 μm is laminated by molecular beam epitaxial method. Furthermore, an Au/Cr electrode 7 is deposited on the p-side, and an Au-Ge/Au electrode 9 is deposited on the n-side, and they are alloyed so that ohmic contact can be established.

The structure of the active layer is as shown in FIG.
quantum well layer W1 of aAs (thickness 80 Å) and Al0.08
A quantum well layer W2 of Ga0.92As (thickness 160 Å) and a quantum well layer W2 of Al0.3Ga0.7As (thickness 15 Å) separating them
0 Å) barrier layer B. Furthermore, GRIN-SCH layers G1 and G2 with a thickness of 400 Å are provided outside the quantum well.
l0.3Ga0.7As to Al0.5Ga0.5As
The Al mixed crystal ratio gradually changes up to the point where light and electrons are confined.

[0014] The current non-injection part has a comb-shaped electrode ultrasonic transducer (
G
After etching up to the aAs substrate 1, the cladding layer 2,
The optical guide layer 3 is regrown in this order, and the structure is such that there is no optical loss in this region. Further, an insulating film 8 is formed on the surface other than the cap layer 6 by sputtering.

The lateral structure perpendicular to the resonance direction of the semiconductor laser and filter of this embodiment uses a ridge waveguide structure as shown in FIG. A cut of .9 μm was made, and the ridge width was 3
It is μm. A light guide layer 3 is provided in the area where the IDT 10 is formed.
A notch of 0.1 μm is made with the same width to create a slight difference in refractive index.

Next, the operating principle of the apparatus according to the embodiment of the present invention will be briefly described. First, regarding the gain of the active layer 4, as shown in FIG.
As the value increases, the gain curve changes. That is, when the amount of current injection is small, oscillations tend to occur near λ1, and when the amount of current injection is large, oscillations tend to occur near λ2. In between, there are cases where the gain becomes uniform over λ1 to λ2. In the absence of a wavelength selection function such as collation, oscillation would occur at a wavelength that is likely to oscillate as the current changes, but in the present invention, surface acoustic waves (hereinafter referred to as SAW) generated by the IDT 10 are used to guide light. The light propagates through the layer 3, causing a refractive index distribution similar to collage, and has a wavelength selection function, so it can oscillate at an intended wavelength.

Now, the relationship between the oscillation wavelength λ and the period of the refractive index distribution, that is, the SAW wavelength Λ, is as follows: λ=2nΛ/m (1) n: equivalent refractive index near the optical guide layer m: Bragg diffraction It is the order. Further, when the propagation speed of the SAW is V and the frequency of the electromagnetic wave applied to the IDT 10 is ν, V=νΛ (2). (
From 1) and (2), λ=2nV/mν...(3) Therefore, if n=3.4 and V=3300m/s, 840nm oscillation is obtained by first-order diffraction (m=1). It can be seen that in order to achieve this, it is sufficient to set ν=26.71 GHz.

Furthermore, when the SAW wavelength is changed by ΔΛ, from (2), Δν=ΔΛ×(-ν2/V)... (4) Therefore, the change in oscillation wavelength Δλ is: Δλ=2nΔΛ/m =- It can be expressed as 2nV×(Δν/ν2m) (5). For example, it can be seen that in order to change the oscillation wavelength from 840 nm to 820 nm, it is sufficient to increase the applied frequency by Δν=0.64 GHz.

By the above method, the oscillation threshold value of 40 m
The oscillation wavelength can be changed in a single mode from about 850 nm to about 800 nm at about A.

Furthermore, if this device guides a wavelength-multiplexed signal by lowering the injection current below the oscillation threshold, only the signal with the Bragg wavelength determined by the SAW wavelength will be selectively amplified, and the signal will be transmitted to the side opposite to the input end face. It is emitted from. Signals of other wavelengths are scattered and not emitted, resulting in a broadband wavelength tunable optical filter. Assuming that the crosstalk required for wavelength division multiplexing communication is -10 dB, the -10 dB bandwidth in this device is about 10 Å, so a system using this device can perform optical multiplex communication of about 50 waves.

[0021] Furthermore, a non-reflection coating is applied to the light output end where the current injection part is located, so as to suppress the Fabry-Perot mode.

In the first embodiment, since the active layer 4 is not included in the region where the IDT 10 is formed, there is an advantage that light absorption is small and the threshold value is low. However, there are some problems in terms of yield. Therefore, in the second embodiment, the laser cannot be used as a filter and has a higher threshold value than the first embodiment, but the manufacturing process is simplified.

FIG. 3 shows a sectional view of the waveguide portion of the device according to the second embodiment. There is also an active layer 4 in the area where the IDT 10 is formed, and since current cannot be injected into this region, this layer becomes a light absorption layer. However, when used as a wavelength tunable laser that extracts light from the current injection region side, it can be used satisfactorily. Since the crystal growth only needs to be done once, the manufacturing process is simple and the productivity is high.

FIG. 6 shows a structure of an active layer with a wide gain region.
It is also possible for the barrier layer B to be very thin, such as a few atoms (~10 Å). In this structure, two quantum wells W
Since the barrier between 1 and W2 is thin, electrons can move freely due to the tunnel effect. Therefore, if the injection density is low,
As shown in , there is a gain only in λ1, and the implantation density n0 at which the gains in λ1 and λ2 are at the same level is higher than that in the first embodiment.

The same effect can be expected even if the active layer has a single-layer quantum well structure. Regarding the lateral light and current confinement structure, the ridge type was used in the above embodiment, but it may also be a buried structure, a rib type, or a VSIS structure.
It may be a type, etc. Also, regarding semiconductor materials, GaA
InP/InGaAsP other than s/AlGaAs system, G
It may also be aAs/InGaAlP or the like.

[0026]

[Effects of the Invention] As explained above, the present invention provides:
Tunable lasers and wavelength tunable filters that can change the wavelength over a range of about 100 nm become possible, and wavelength multiplex communication with a wavelength multiplexing degree of about 100 waves becomes possible.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a waveguide portion of the first embodiment of the present invention.

FIG. 3 is a cross-sectional view of a waveguide portion of a second embodiment of the present invention.

FIG. 4 is an energy band diagram of the active layer of the first embodiment of the present invention.

FIG. 5 is a diagram showing a gain curve versus wavelength in the active layer of FIG. 4;

FIG. 6 is an energy band diagram of an active layer according to a third embodiment of the present invention.

7 is a diagram showing a gain curve versus wavelength in the active layer of FIG. 6. FIG.

FIG. 8 is a diagram showing an example of energy bands of the present invention.

9 is a diagram showing a gain curve versus wavelength in the active layer of FIG. 8. FIG.

FIG. 10 is a diagram showing a gain curve with respect to wavelength in a normal active layer.

[Explanation of symbols]

1 n-GaAs
Substrate 2 n-Al
0.5Ga0.5As cladding layer 3 p-Al0.
25Ga0.75As4
active layer 5
p-Al0.5Ga0.5As cladding layer

Claims (6)

[Claims] 1. A semiconductor device having an active layer consisting of at least one quantum well layer having a plurality of quantum levels capable of oscillation, and comprising a comb-shaped ultrasonic transducer on a part of the light guide layer, A wavelength tunable semiconductor laser characterized in that a laser oscillation wavelength can be varied over a wide range by changing the wavelength of a surface acoustic wave generated from the vibrator. 2. A semiconductor device having an active layer consisting of at least one quantum well layer having a plurality of quantum levels capable of oscillation, and comprising a comb-shaped ultrasonic vibrator on a part of the light guide layer, A wavelength tunable optical filter is characterized in that by reducing the injected current below the oscillation threshold, the selected wavelength can be changed over a wide band while amplifying the incident light. 3. The wavelength tunable semiconductor laser according to claim 1, wherein the active layer comprises a plurality of quantum well layers having mutually different quantum level structures. 4. The wavelength tunable optical filter according to claim 2, wherein the active layer comprises a plurality of quantum well layers having mutually different quantum level structures. 5. A semiconductor device having an active layer consisting of at least one quantum well layer having a plurality of quantum levels capable of oscillation, and comprising a comb-shaped ultrasonic vibrator on a part of the light guide layer, Driving a semiconductor device as a wavelength tunable semiconductor laser, characterized in that the laser oscillation wavelength is varied over a wide range by changing the wavelength of a surface acoustic wave generated from the vibrator while keeping the injected current equal to or higher than the oscillation threshold. how to. 6. A semiconductor device having an active layer consisting of at least one quantum well layer having a plurality of quantum levels capable of oscillation, and comprising a comb-shaped ultrasonic vibrator on a part of the light guide layer, A semiconductor device characterized by changing the selected wavelength over a wide band while amplifying the incident light by changing the wavelength of the surface acoustic wave generated from the vibrator while keeping the injected current below the oscillation threshold. How to drive it as a variable optical filter.