JPH03148889A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To enlarge the temperature range of single wavelength oscillation and an injection-quantity flow region, and to increase working speed by forming semiconductor small-gage wires in length and breadth of several nm while making a refractive index thereof higher than that of a region surrounding an active layer in the vertical direction to the progressive direction of light and shaping a diffraction grating in the progressive direction of light. CONSTITUTION:A rectangular laser base body is prepared by an InP substrate 1, an InP buffer layer 2, an InGaAaP optical guide layer 3 and an InGaAs active layer 4, a mask having a small-gage wire pattern, which is cyclic approximately at a pitch of 15nm and is 10nm wide, is shaped onto the laser base body, and only the layer 3 is etched selectively, thus forming quantum small-gage wires 5 composed of InGaAs. The structure of a quantum box 6 consisting of InGaAs small gage wires 5 in 10nm length and 10nm breadth is formed in two-dimensional structure, an InGaAsP optical guide layer 7 is grown on the quantum box 6, the small-gage wires 5 are buried completely, and the whole surface is covered with an lnGaAsP guide layer 8. An InP layer 10 and an InGaAsP layer 10 are laminated onto the layer 8 through a diffraction grating 9. The refractive index of the small-gage wires is increased and the grating is shaped in the progressive direction of light at that time.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention enables high-speed direct modulation of light intensity and obtains oscillated light with high spectral purity by wavelength selectivity using a diffraction grating. It relates to semiconductor lasers.

(Prior art) The direct modulation speed of a semiconductor laser is determined by the electrical limit determined by the element resistance and parasitic capacitance caused by the laser structure, and by the resonant frequency determined by the lifetime of carriers injected into the laser and the lifetime of photons. It has been determined from Currently, the maximum modulation speed of semiconductor lasers is reported to be 17 GHz due to the reduction of element resistance and parasitic capacitance. 10G
For high speed modulation above Hz, the limits of modulation are determined by the resonant frequency. The resonant frequency f is expressed by the following equation based on the rate equation of the number of photons and the number of injected carriers.

1 /cpξ dg where C is the speed of light, P is the optical output, ξ is the optical confinement rate in the active layer, n is the effective refractive index, ■ is the volume of the active layer, η is the differential quantum efficiency, d g/d N is is the differential gain coefficient. Figure 8 shows Asada, etaj! (Gain andT
Threshold of Three-Dimens
sional Quantus-BoxLasers
, IEEE Journal of Quant
umElectronics.

Vol1. GE-22, No. 91986. ap1
915-1921), which shows the relationship between the injected carrier density and the maximum gain. By forming the active region into a quantum box structure and a quantum wire structure, the differential gain is approximately It's 50 times bigger. Substituting this relationship into equation (1), the resonant frequency of quantum box and quantum wire lasers becomes about 7 times wider than that of normal bulk lasers, which is 20 Gllz to 30 Gllz.
High-speed direct modulation of z becomes possible. In addition, in Figure 8,
τi7 is the in-band relaxation time, Fiβm is the quantum thin film, B
OX represents a quantum box, and BuIl represents a bulk.

(Problems to be Solved by the Invention) An object of the present invention is to provide a distributed feedback type semiconductor laser that operates at high speed and includes a guiding waveguide layer having a diffraction grating and an active region having a quantum wire structure.

(Means for Solving the Problems) In the semiconductor laser of the present invention, a plurality of vertical semiconductor thin wires with a diameter of nm perpendicular to the direction in which light travels are made of a semiconductor having a smaller refractive index than the semiconductor constituting the thin wires. Either a diffraction grating is provided in the enclosed active region in the direction in which the light travels, or a semiconductor that generates light with a box structure of several nanometers on a side perpendicular to the direction in which the light travels is placed in a box. A diffraction grating is provided in the direction in which light travels in an active region surrounded by a semiconductor having a lower refractive index than the semiconductor constituting the structure.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

1 to 7 are diagrams showing the manufacturing process of the semiconductor laser of the present invention, and as shown in FIG. 1, the (100) plane In
An n-type InP buffer layer 2 having a length of 2μ was formed on a P substrate 1 (Sn-doped, N=1×10”cm−).
The InGaAsP optical waveguide layer 3 having a composition of Cl pta is 0.
．． 51111 Grow. After that, InG becomes the active layer.
The aAs layer 4 is grown for about 10 ns.

Here, Metal Organic-V is used as the growth method.
aporPhase Epitaxy (abbreviated as MO-
VPf? ) method (organometallic vapor phase epitaxy) was used. Triethylinsium and triethylgallium are used as the raw materials for the M group, and phosphin and arsine are used as the raw materials for the II group.

Diethyl zinc was used as the p-type dopant, and hydrogen selenide was used as the n-type dopant. The growth temperature was 630°C and 50 Torr.
Growth is performed under reduced pressure of r.

Next, FIG. 2 shows a growth wafer in which a fine line pattern of 10 nm width with a period of about 15 n- is formed using an X-ray exposure method using an electron beam exposure method, an interference exposure method, or a tank mask made by an electron beam exposure method. I n(; a
A thin line 5 of rnGaAs is formed using an etching solution that selectively etches only the As layer.

After that, as shown in Figure 3, 10 ns vertically and 10 r horizontally
A two-dimensional structure of an InGaAs quantum box 6 is formed. The manufacturing method is the same as the method for forming the thin wire described above.

Next, as shown in Figure 4, 1.1 um Mi InG
The aAsP optical waveguide layer 7 is grown to a thickness of 0.1 μm, and the InGa
The As quantum box 6 or quantum wire 5 is completely embedded. Thereafter, an InGaAsP guide layer 8 of 0.12 ova is grown in 1.3 tries.

After that, as shown in FIG. 5, I
A diffraction grating 9 with a period of about 240 nm is formed on nGaAsP N using a photolithography technique using an interference exposure method and etching.

After that, as shown in FIG.
= 5 x 10f'IC11-) to 1.555%
P” type nGaAsP layer 11 (P= 2×10”cm
- was grown to a thickness of about 0.5 g, and Au was grown on each of the p side and n side.
Electrodes are formed by thinly depositing Zn and AuGe, and a laser structure is formed depending on the thickness. The oscillation wavelength is 1.55 pta
, reduced oscillation threshold, high efficiency, and high-speed modulation of about 20 GHz can be expected.

Figure 7 shows a phase shift of 1 in the diffraction grating in the center of the laser cavity.
2 is added, and when forming a diffraction grating on the rnGaAs-light guide N8 in FIG. Institute of Electronics and Communication Engineers Research Technical Report, QQE 85
-60 ), a phase shift can be formed. Note that in FIG. 7, arrows indicate the traveling direction of light.

FIG. 9 is a diagram showing a gain spectrum with respect to wavelength according to ^sada etal, where N indicates the injection carrier density.

When a quantum (2) or quantum wire structure is used, the gain spectrum becomes larger and the width of the spectrum becomes narrower for the same injection current. Therefore, the difference in gain required for oscillation between modes determined by the laser oscillation conditions increases, and it is also possible to widen the temperature range and injection current range for single wavelength oscillation.

These structures are similar to other crystal systems, e.g. GaAs-A I
GaAs-based or GaAsSb-GaAsA I
It can also be applied to Sb system, InA I GaAs system, etc., with a structure in which p and n are reversed, and an active layer and a guiding waveguide layer are reversed, and a diffraction grating is formed on the substrate crystal, and a guiding waveguide is formed on it. A form in which the active layer is grown through layers is also possible.

In addition, although we have described the case where the quantum box and quantum wire are formed of a single layer of semiconductor, we have also described the case where the quantum box and quantum wire are formed with a single layer of semiconductor, but we have also
5 nm, InGaAsP (wavelength composition 1.3
A quantum wire or a quantum box may be constituted by an active layer formed by a multi-quantum well structure with 4 to 5 periods of 10 nm.

(Effects of the Invention) As described above, the semiconductor laser of the present invention has the advantage that the temperature range of single wavelength oscillation and the injection current range are widened, and that it operates at higher speed than the conventional semiconductor laser.

[Brief explanation of the drawing]

Figures 1 to 7 are diagrams showing the manufacturing process of the semiconductor laser of the present invention. Figure 8 is a diagram showing the relationship between the injected carrier density and gain in the bulk, quantum well thin film, quantum wire, and quantum box. Figure 9 is a diagram showing gain spectra in bulk, quantum well thin film, quantum wire, and quantum box. 1... InP substrate 2... InP buffer layer 3- 1nGaAsP optical waveguide N (wavelength composition 1.1g
m) 4...InGaAs active layer 5...Quantum wire 6...Quantum box? ---InGaAsP optical waveguide layer (wavelength composition 1.17
711 ) 8 ・-rnGaAsP guide layer (wavelength composition 1.3.us) 9... Diffraction grating 10-
p-type 1nP layer 11-P” type 1nGaAsPii 1
;”Phase shift. Fig. 1] Fig. 2 Fig. 3 ≠ ≦ ≦ Zudo i~-1mF law 2-It+ P/I, 71 layer 1f 4-- k Gt As layer, 6 5-one quantum box 8- I, + Aslκite view*t a glance (c@-RitoJ

Claims (2)

[Claims] 1. Multiple vertical and horizontal numbers n perpendicular to the direction in which the light travels
A semiconductor laser characterized in that a diffraction grating is provided in the direction in which light travels in an active region in which m semiconductor thin wires are surrounded by a semiconductor having a lower refractive index than the semiconductor constituting the thin wires. 2. ．． A semiconductor that generates light has a plurality of box structures with sides of several nanometers perpendicular to the direction in which the light travels. A semiconductor laser characterized in that a diffraction grating is provided in the direction of propagation.