JP3570094B2 - Surface emitting semiconductor laser, method of manufacturing the same, and wavelength variable method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wavelength tunable surface emitting semiconductor laser.
In recent years, research on surface emitting lasers, which are key devices for optical interconnection and parallel optical links, has been active. The vertical cavity surface emitting laser has the following advantages.
[0002]
(1) Ultra-low threshold operation is possible because the cavity volume is small. (2) Single mode operation is easy because the cavity length is short. (3) Coupling with an optical fiber because the beam spread is narrower than that of a stripe laser. (4) Inspection in the wafer state is possible, and no cleaved surface is required on the structure.
[Prior art]
FIG. 6 shows a typical conventional example of a vertical cavity surface emitting laser.
In the figure, 1 is a one-conductivity type semiconductor substrate, 2 is a one-conductivity type semiconductor multilayer reflector, 3 is a microresonator, 4 is a dielectric multilayer reflector, 5 is an antireflection coating film, 6 is a current confinement layer, Reference numerals 7 and 8 denote electrodes.
[0004]
The multilayer mirrors 2, 4 are made by alternately laminating materials having a large difference in refractive index, and are manufactured so that the reflectance exceeds 99%. The reason is that the resonator length is short and the resonator loss increases.
[0005]
The vertical cavity surface emitting laser can be stacked and integrated with other optical functional devices, and can add a wavelength variable function.
The following method is available as a method for changing the wavelength of the vertical cavity surface emitting laser.
[0006]
(1) Temperature control (Peltier effect)
(2) Plasma effect by carrier injection (3) Refractive index change by application of electric field (4) Mechanical driving of external mirror
[Problems to be solved by the invention]
The above methods (1) of controlling the temperature and (2) of the method using carrier injection have problems of resistance heating and light absorption because current is injected into the device.
[0008]
Also, in the method using the refractive index change due to the electric field described in (3) above, a high voltage must be applied in order to perform tuning over a wide range.
In the method of (4), in which the external mirror is moved mechanically, there are a method in which the micrometer is moved manually and a method in which the external mirror is moved by using electrostatic attraction. Similarly, there is a problem that the tuning voltage becomes high.
[0009]
An object of the present invention is to tune the wavelength of a surface emitting laser with low power consumption.
[0010]
[Means for Solving the Problems]
The solution to the above problems is
1) One conductive type semiconductor multilayer mirror, one conductive type semiconductor layer, active layer, opposite conductive type semiconductor layer, laser electrode, dielectric multilayer reflective mirror, dielectric multilayer reflective surface A mirror driving stripe and wavelength tuning electrodes connected to both ends of the driving stripe are laminated in this order, and a surface in which a cavity is formed between the opposite conductive semiconductor layer and the dielectric multilayer reflector. 2) a wavelength at which the surface emitting semiconductor laser according to 1) is oscillated in a magnetic field and a current is applied to the driving stripe to apply a force to the dielectric multilayer mirror to mechanically move the mirror. A variable method, or 3) oscillating the surface emitting semiconductor laser described in 1 above in a magnetic field, keeping the magnetic field constant, and changing the amount of current flowing through the driving stripe to change the tuning amount. Or 4) a wavelength tunable method of oscillating the surface emitting semiconductor laser described in 1 above in a magnetic field, keeping the amount of current flowing through the driving stripe constant, and changing the amount of tuning by changing the intensity of the magnetic field, or 5). A) stacking on the one-conductivity-type semiconductor substrate at least one one-conductivity-type semiconductor multilayer mirror, one-conductivity-type semiconductor layer, an active layer, an opposite-conductivity-type semiconductor layer, and a sacrificial layer for forming a cavity; Etching a part of the sacrificial layer while leaving it, and then laminating a dielectric multilayer mirror and its driving stripe and tuning electrode on the substrate so as to cover the sacrificial layer; Forming a cavity by etching off the sacrificial layer.
[0011]
According to the present invention, a surface emitting laser is driven in a constant magnetic field or in a variable magnetic field, a current flows through a conductive stripe formed in close contact with the external mirror, and the external mirror is mechanically driven by Lorentz force. The wavelength tuning is performed by driving in a dynamic manner.
[0012]
FIG. 1 shows a principle diagram of the present invention.
In the figure, 7 is a semiconductor substrate of one conductivity type, 8 is a mirror of a semiconductor multilayer film of one conductivity type, 9 is a semiconductor layer of one conductivity type, 10 is an active layer, 11 is a semiconductor layer of the opposite conductivity type, and 12 is a reflection of a dielectric multilayer film. Reference numeral 13 denotes a laser electrode, and 14 denotes a metal stripe for driving the dielectric multilayer film reflecting mirror and a tuning electrode.
[0013]
FIG. 2 is a cross-sectional view taken along a line AB in FIG. 1, and 15 is a current confinement layer.
In order to realize variable wavelength, the surface emitting laser having this structure is driven in a magnetic field in the direction of the vector B in FIGS. When a current is applied to the metal stripe 14 in the direction of the arrow (A), a downward force is applied to the dielectric multilayer mirror 12 by the Fleming's left-hand rule, so that the resonance wavelength becomes shorter. Conversely, when an electric current is applied to the metal stripe 14 in the direction of the arrow (B), an upward force is applied to the dielectric multilayer mirror 12 according to Fleming's left-hand rule, and the resonance wavelength becomes a long wave.
[0014]
Alternatively, by changing the direction of the magnetic field B while keeping the current flowing through the metal stripe 14 constant, it is possible to change the direction of the force acting on the dielectric multilayer mirror 12, that is, the direction of tuning.
[0015]
As described above, according to the present invention, the wavelength is tuned by mechanically moving the external mirror by the Lorentz force, so that there is no influence of absorption. Moreover, since the wavelength tuning is performed by passing a current through the metal stripe 14, a low voltage is applied. Tuning is possible. Therefore, tuning can be performed with low power consumption.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
An example in which the present invention is applied to a surface emitting laser in the 0.98 μm band will be described with reference to FIGS.
[0017]
3 (A) to 3 (C), 4 (D) and 4 (E) are explanatory views of the embodiment of the present invention.
The crystal growth in this example is performed by metal organic chemical vapor deposition (MOCVD), and the size of a single device is 300 μm square.
[0018]
In FIG. 3A, on an n-type (n−) GaAs substrate,
n-AlAs / GaAs (both have a thickness of λ / 4) 25.5 pairs of semiconductor multilayer reflector 8, n-cladding layer 9 of n-Al _x Ga _1-x As layer (x = 0.53) , Thickness 1047.5Å, impurity concentration 5 × 10 ¹⁷ cm ⁻³ ),
As the active layer 10,
Intrinsic (i-) Al _x Ga _1-x As layer of spacer layer (x = 0.53, thickness 300 °),
I-GaAs layer of barrier layer (thickness: 100 mm),
I-In _y Ga _1-y As layer of strained quantum well (y = 0.2, thickness 80 °)
I-GaAs layer of barrier layer (thickness: 100 mm),
An i-Al _x Ga _1-x As layer of a spacer layer (x = 0.53, thickness 300 °),
_{p-Al x Ga 1-x} As layer of the n-side cladding layer 11 (x = 0.53, thickness 1047.5A, impurity concentration 5 × ¹⁰ 17 ^cm -3),
I-GaAs layer of contact layer (thickness 200 mm) 21,
The sacrifice layer 22 is grown in the order of the i-InGaAs layer (thickness 9800Å).
[0019]
In FIG. 3 (B), a silicon dioxide (SiO ₂ ) film 23 is laminated on this substrate to a thickness of 1000 ° by a vapor phase epitaxy (CVD) method. The SiO ₂ film is patterned. After etching the uppermost i-InGaP layer 22 with hydrochloric acid using the patterned SiO ₂ film 22 as a mask, zinc (Zn) is thermally diffused in that state. A p-type diffusion layer 24 is formed.
[0020]
In FIG. 3C, a resist pattern 25 having a thickness of 5 μm and a diameter of 5 μm is provided at the center of the SiO ₂ mask 22, and protons are implanted at an energy of 150 KeV and a dose of 5 × 10 ¹⁴ cm ⁻² to form a current confinement layer. 15 are formed.
[0021]
Next, the resist mask and the SiO ₂ mask are removed, an SiO ₂ film is again laminated on the substrate, a window for a p-side electrode (reference numeral 13 in FIG. 1) is patterned and opened, and titanium (Ti) / platinum ( Pt) is deposited in this order, and a gold (Au) pad is formed thereon.
[0022]
Next, using the gold pad as a mask, Ti / Pt and SiO ₂ are removed by reactive ion etching (RIE) so that the i-InGaP layer 22 is completely exposed.
In FIG. 4D, a dielectric multilayer film reflecting mirror 12 is formed on the p-side. A resist pattern 1 shown in FIG. 5A is formed on the p-side, and five pairs of SiO ₂ / Si (each having a film thickness of λ / 4) are vapor-deposited. A resist is further applied thereon to form a resist pattern 2 shown in FIG. 5 (B), and a drive electrode of the dielectric multilayer mirror 12 and Ti / Pt / Au to become a stripe 14 are sequentially deposited, and lift-off is performed. I do.
[0023]
In FIG. 4E, the i-InGaP layer 22 is completely removed by etching with hydrochloric acid to form a gap (cavity) 23 between the semiconductor layers 8 to 21 and the dielectric multilayer mirror 12, thereby completing the device. I do. In this device, a two-wavelength resonator (resonator whose resonator length is twice the oscillation wavelength) is formed by the gap between the semiconductor layer and the dielectric multilayer mirror, the semiconductor cladding layer, and the active layer.
[0024]
5A and 5B are plan views of a resist pattern used in a manufacturing process.
FIG. 5A shows a resist pattern 1 which is a mask for forming the dielectric multilayer reflector 12, and FIG. 5B shows a resist pattern 2 which shows the drive electrodes of the dielectric multilayer reflector 12 and the stripes 14. Is a mask that forms The hatched portions in the figure indicate the shielding portions of the mask.
[0025]
Next, when the surface emitting laser is driven in a magnetic field of 0.1 T and a current of 300 mA (the voltage at this time is 0.1 V) is passed through the tuning electrode, the dielectric multilayer film reflecting mirror moves by 150 nm. As a result, a tuning of 150 nm could be performed. At this time, the Lorentz force changes even if the magnetic field or the current flowing through the tuning electrode is changed, and as a result, the displacement of the dielectric multilayer mirror can be changed.
[0026]
【The invention's effect】
According to the present invention, tuning can be performed with low power consumption in a surface emitting laser.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating the principle of the present invention (1).
FIG. 2 is a diagram (2) for explaining the principle of the present invention.
FIG. 3 is an explanatory diagram (1) of the embodiment of the present invention.
FIG. 4 is an explanatory diagram (2) of the embodiment of the present invention.
FIG. 5 is a plan view of a resist pattern used in a manufacturing process. FIG. 6 is an explanatory view of a conventional example.
7 One-conductivity-type semiconductor substrate 8 One-conductivity-type semiconductor multilayer reflector 9 One-conductivity-type semiconductor layer 10 Active layer 11 Opposite-conductivity-type semiconductor layer 12 Dielectric multilayer reflector 13 Laser electrode 14 For driving dielectric multilayer reflector Metal stripe and tuning electrode 22 Sacrificial layer 23 Cavity

Claims (5)

On one conductivity type semiconductor substrate, one conductivity type semiconductor multilayer reflector, one conductivity type semiconductor layer, active layer, opposite conductivity type semiconductor layer, laser electrode, dielectric multilayer reflector, A driving stripe and wavelength tuning electrodes connected to both ends of the driving stripe are laminated in this order, and a cavity is formed between the opposite conductive type semiconductor layer and the dielectric multilayer mirror. Surface emitting semiconductor laser. 2. The surface emitting semiconductor laser according to claim 1, oscillated in a magnetic field, and a current is applied to the driving stripe to apply a force to the dielectric multilayer mirror to mechanically move the mirror. Tunable method. A wavelength tuning method, wherein the surface emitting semiconductor laser according to claim 1 is oscillated in a magnetic field, the magnetic field is kept constant, and a tuning amount is changed by changing an amount of current flowing through the driving stripe. 2. A wavelength tuning method, wherein the surface emitting semiconductor laser according to claim 1 is oscillated in a magnetic field, the amount of current flowing through the driving stripe is kept constant, and the tuning amount is changed by changing the intensity of the magnetic field. Stacking at least one semiconductor multilayer reflector, one semiconductor layer, an active layer, an opposite semiconductor layer, and a sacrificial layer for forming a cavity on a semiconductor substrate of one conductivity type in this order;
Next, a step of etching and removing a part of the sacrificial layer,
Next, a step of laminating a dielectric multilayer mirror, a driving stripe thereof, and tuning electrodes on the substrate so as to cover the sacrificial layer;
Forming a cavity by removing the sacrificial layer by etching.

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