JP2006203100A - Semiconductor laser and light transmitter module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a gain from a gain spectrum having wide range energy for Bragg wavelength in the overall temperature region of 0°C to 85°C. <P>SOLUTION: A semiconductor laser forms a quantum well layer constituted of three layers or more whose well widths are equal, and whose Eg difference is 18 meV or less in an active layer region. Each quantum well has different forbidden band width, and a gain spectrum 1 has gains within a wide wavelength range. Thus, it is possible to realize the uniformity of gains in a wide temperature range for Bragg wavelength 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor laser and an optical transmitter module, and more particularly to a semiconductor laser and an optical transmitter module having a wide operating temperature range.

  2. Description of the Related Art A semiconductor laser element is known as a basic element structure in which a double hetero structure in which an active layer is sandwiched between semiconductor layers having a forbidden band wider than the forbidden band of the active layer. Non-Patent Document 1 discloses that an active layer having a double hetero structure sandwiches an ultra-thin semiconductor layer with a narrow forbidden band between ultra-thin semiconductor layers with a wide forbidden band, and carriers in an ultra-thin semiconductor with a narrow forbidden band. It has been described that by adopting a quantum well structure that takes discrete energy states, the state density of carriers becomes discrete, low oscillation threshold, high light conversion efficiency, and good temperature characteristics. Yes.

N. Holonyak, jr., Et al., "Quantum-well heterostructure lasers", IEEE, Journal of Quantum Electronics, 1980, Vol.QE-16 pp.170-186

  In the distributed feedback semiconductor laser, the oscillation wavelength is a Bragg wavelength determined by the effective refractive index and the diffraction grating period, and its temperature characteristic is about 0.1 nm / K. On the other hand, the temperature characteristic of the gain wavelength determined by the quantum well active layer is about 0.4 nm / K.

  When a semiconductor laser is applied to a wide temperature range, the Bragg wavelength peak deviates from the gain wavelength peak due to the difference in temperature characteristics of the Bragg wavelength and the gain wavelength, the gain decreases, the oscillation threshold current increases, and the optical conversion Efficiency is reduced. For example, the maximum difference between the Bragg wavelength peak and the gain wavelength peak at 0 ° C. to 85 ° C. is about 25.5 nm.

  The quantum well active layer is provided with quantum wells having at least three wells having substantially the same width and different forbidden band widths, and the difference in the forbidden band widths of the quantum wells is about 18 meV. The quantum well active layer is provided with at least three quantum wells having different well widths and substantially equal forbidden band widths, and the difference in well width between the quantum wells is set to approximately 0.7 nm. Further, by combining them, the well width and / or the forbidden band width of the quantum well is adjusted so that the difference between the converted values of the forbidden band width of the quantum well is approximately 18 meV.

  By the above means, the Bragg wavelength can be gained from a gain spectrum having a wide range of energy in the entire temperature range from 0 ° C. to 85 ° C.

  Hereinafter, embodiments of the present invention will be described using examples with reference to the drawings. The same reference numerals are assigned to equivalent parts in the respective embodiments, and description thereof will not be repeated.

  A semiconductor laser according to a first embodiment of the present invention will be described with reference to FIGS. Here, FIG. 1 is a sectional view in the optical axis direction of a semiconductor laser having an active layer having a multiple quantum well structure. FIG. 2 is a diagram for explaining the energy gap of the quantum well. FIG. 3 is a diagram for explaining the wavelength dependence of gain.

  First, a semiconductor laser manufacturing process will be described with reference to FIG. In FIG. 1A, an n-type InAlAs optical cladding layer 4, an n-type InGaAlAs optical guide layer 5, an InGaAlAs well layer, and an InGaAlAs barrier layer are formed on an n-type InP substrate 3 by metal organic vapor phase epitaxy. A quantum well active layer 6, a p-type InGaAlAs light guide layer 7, a p-type InGaAsP etching stop layer 8, and a p-type InGaAsP diffraction grating layer 9 which are alternately stacked five times are crystal-grown. Next, as shown in FIG. 1B, a diffraction grating is formed on the p-type InGaAsP diffraction grating layer 9 by a photolithography technique.

  When the InGaAlAs well layer of the quantum well active layer 6 is grown, the composition ratio of the film thickness (6.3 nm) and In and As is constant for each growth time, and the Ga composition ratio is increased every time. Reduce the Al composition ratio every time.

  1C, a p-type InP clad layer 10 and a p-type InGaAs contact layer 11 are crystal-grown, a p-electrode 12 is formed on the substrate surface, an n-electrode 13 is formed on the back surface of the substrate, cleaved, and then the front end surface of the device A non-reflective film 14 was formed on the back surface, and a highly reflective film 15 was formed on the rear end face. The resonator length was 150 μm.

  As shown in FIG. 2, the quantum well active layer of this device structure has five quantum wells having the same well width and different forbidden band widths. The forbidden band widths of the quantum wells were Eg1 = 0.972 eV, Eg2 = 0.967 eV, Eg3 = 0.963 eV, Eg4 = 0.958 eV, and Eg5 = 0.954 eV, respectively.

  In FIG. 3, the gain has five peaks corresponding to the difference in the forbidden bandwidth. This means having gain over a wide energy range. As a result, the gain cannot be reduced over a wide temperature range. Since Eg1−Eg5 = 18 meV, the gain peak difference (predetermined value) between Eg1 and Eg5 is 26 nm. This predetermined value can be calculated from the temperature range to be used, the temperature characteristic of the Bragg wavelength peak, and the temperature characteristic of the gain wavelength peak.

  This semiconductor laser device has an oscillation threshold temperature characteristic of 100 K, an optical conversion efficiency temperature dependency of 1.1 dB, an oscillation threshold temperature characteristic of 70 K when the element band is constant, and an optical conversion at an element temperature of 0 ° C. to 85 ° C. The temperature dependence of efficiency was improved from 2.0 dB.

  When the InGaAlAs well layer of the quantum well active layer 6 is grown, the film thickness and the composition ratio of In and As are constant for each growth time, and the Al composition ratio is increased each time to increase the Ga composition ratio. It may be reduced every time. It may be different at random. When the number of well layers is two, dip occurs. Therefore, the number of well layers is preferably 3 or more, and more preferably 5 or more. Further, as can be easily understood by those skilled in the art, the conductivity type (p-type or n-type) may be reversed. This is the same in the following embodiments.

Example 2 of the semiconductor laser will be described with reference to FIGS. 1, 3, and 4. FIG. Here, FIG. 4 is a diagram for explaining the structure of the quantum well.
The structure of the semiconductor laser of Example 2 is basically the same as that shown in FIG. However, in Example 1, when the InGaAlAs well layer was grown, the composition ratio of Ga and Al was changed with the film thickness being constant, whereas the film thickness (that is, well width) was changed with the composition of InGaAlAs being constant. Specifically, the number of well layers is five, and the width W of each well is W1 = 6.0 nm, W2 = 6.2 nm, W3 = 6.3 nm, W4 = 6.5 nm, and W5 = 6.7 nm.

  As shown in FIG. 4, the quantum well structure of this embodiment is expressed by five wells having a constant forbidden band width (0.963 eV) and different widths. Further, the wavelength dependency of gain (FIG. 3) described in the first embodiment is also common to the second embodiment. That is, the gain peak difference between the converted Eg1 and the converted Eg5 is 26 nm.

This semiconductor laser device obtained an oscillation threshold temperature characteristic of 100 K and a temperature dependency of light conversion efficiency of 1.1 dB at an element temperature of 0 ° C. to 85 ° C.
The width of the well may be increased initially and gradually reduced. Further, the well width may be changed randomly. The number of well layers is preferably 3 or more, and more preferably 5 or more.

  Furthermore, a combination of the well width and the forbidden band width may be a three-layer well having a difference of about 18 meV in terms of the forbidden band width. In other words, the well width or / and the forbidden band width may be adjusted to convert the forbidden band width into at least three wells having a difference of about 18 meV.

  Example 3 of the semiconductor laser will be described with reference to FIG. FIG. 5 is a sectional view in the optical axis direction of a semiconductor laser having an active layer having a multiple quantum well structure.

  FIG. 5 is a sectional view in the optical axis direction of the distributed reflection type semiconductor laser. The semiconductor laser manufacturing process will be described with reference to FIG. Quantum in which an n-type InAlAs optical cladding layer 4, an n-type InGaAlAs light guide layer 5, an InGaAlAs well layer, and an InGaAlAs barrier layer are alternately stacked five times on an n-type InP substrate 3 by metal organic chemical vapor deposition. A well active layer 6, a p-type InGaAlAs light guide layer 7, and a p-type InGaAsP etching stop layer 8 are grown. Here, when the InGaAlAs well layer of the quantum well active layer 6 is grown, the film thickness and the composition ratio of In and As are constant for each growth time, and the composition ratio of Al is increased by increasing the Ga composition ratio every time. Is reduced every time.

  Next, the central active layer portion is masked, and the layers of the optical output waveguide portions on both sides are removed by etching up to the n-type InGaAlAs light guide layer 5. Next, an InGaAlAs passive waveguide 15 serving as a bad joint part is crystal-grown on both sides of the active layer to form an optical output waveguide 16. This optical output waveguide 16 is optically coupled to the quantum well active layer 6. An etching stop layer 8a and a p-type InGaAsP diffraction grating layer 17 are formed on the optical waveguide portion and the butt joint portion. A diffraction grating is formed on the p-type InGaAsP diffraction grating layer 17 by photolithography.

  Subsequently, the p-type InP clad layer 10 and the p-type InGaAs contact layer 11 were crystal-grown, and a device was fabricated through p-electrode 12 formation, back surface polishing, n-electrode 13 formation, and cleavage steps. An antireflective film 14 was formed on the front rear end face of the element. The resonator length was 150 μm for the active layer portion and 200 μm for each of the two optical output waveguide portions sandwiching the active layer.

  As shown in FIG. 1, the quantum well active layer in this device structure was formed with a plurality of quantum well layers having the same well width and different composition wavelengths. The quantum well layers are five layers, and the forbidden band widths are set to Eg1 = 0.972 eV, Eg2 = 0.967 eV, Eg3 = 0.963 eV, Eg4 = 0.958 eV, and Eg5 = 0.954 eV. At this time, the gain peak difference between Eg1 and Eg5 is 26 nm as shown in the first embodiment.

The semiconductor laser device of this structure obtained an oscillation threshold temperature characteristic of 70 K and a temperature dependency of optical conversion efficiency of 2.0 dB at an element temperature of 0 ° C. to 85 ° C.
Similar to Example 2, the same characteristics were obtained even when the quantum well active layers had the same composition wavelength and different well widths.

  An optical transmitter module according to the second embodiment of the present invention will be described with reference to FIG. Here, FIG. 6 is a circuit block diagram of the optical transmitter module.

  An optical transmitter module 200 shown in FIG. 6 is obtained by mounting the semiconductor laser elements 100 and 100 ′ of the first to third embodiments on an optical transmitter module. The optical transmitter module 200 includes a semiconductor laser element 100, a photodiode 101, a thermistor 102, and a driver IC 103 inside a grounded metal case 107. A power source line 106 and a DATA input line 104 are connected to the driver IC 103, and the semiconductor laser element 100 is directly modulated. An optical signal emitted from the front end of the semiconductor laser element 100 is coupled to an optical fiber transmission line (not shown) and transmitted. On the other hand, the optical signal emitted from the rear end of the semiconductor laser element 100 is incident on the photodiode 101 and the front output of the semiconductor laser element 100 is monitored. A thermistor 102 is provided in the metal case 107 to monitor that the semiconductor laser element temperature is in the range of 0 ° C. to 85 ° C.

This optical transmitter module 200 realized a characteristic that can be operated at all temperatures from 0 ° C. to 75 ° C. (case temperature) and that has a small change in oscillation threshold and a change in light conversion efficiency.
According to this embodiment, an optical transmitter module that does not require a temperature control device in the metal case can be realized.

FIG. 3 is a cross-sectional view in the optical axis direction of a semiconductor laser having an active layer having a multiple quantum well structure. It is a figure explaining the energy gap of a quantum well. It is a figure explaining the wavelength dependence of a gain. It is a figure explaining the structure of a quantum well. FIG. 3 is a cross-sectional view in the optical axis direction of a semiconductor laser having an active layer having a multiple quantum well structure. It is a circuit block diagram of an optical transmitter module.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Gain spectrum, 2 ... Bragg wavelength, 3 ... n-type InP substrate, 4 ... n-type InAlAs optical cladding layer, 5 ... n-type InGaAlAs optical guide layer, 6 ... quantum well active layer, 7 ... p-type InGaAlAs optical guide layer 8 ... p-type InGaAsP etch stopper layer, 9 ... p-type InGaAsP diffraction grating layer, 10 ... p-type InP cladding layer, 11 ... p-type InGaAs contact layer, 12 ... p-electrode, 13 ... n-electrode, 14 ... non-reflective film , 15 ... InGaAlAs passive waveguide, 16 ... InGaAlAs optical output waveguide, 17 ... p-type InGaAsP diffraction grating, 100 ... semiconductor laser element, 101 ... photodiode, 102 ... thermistor, 103 ... driver IC, 104 ... DATA line, 105 Optical output 106 Power line 107 Metal case 200 Optical transmitter module

Claims (5)

A first conductivity type optical cladding layer, a first conductivity type InGaAlAs light guide layer, an InGaAlAs quantum well active layer, and a second conductivity type InGaAlAs light guide on a first conductivity type semiconductor substrate. A semiconductor laser in which a layer, an optical cladding layer of a second conductivity type, a diffraction grating layer, and a contact layer are laminated,
The InGaAlAs quantum well active layer is provided with quantum wells having different forbidden band width conversion values of at least three layers, and the well width of the quantum well or the difference of the forbidden band width conversion values of the quantum wells becomes a predetermined value. A semiconductor laser device having a forbidden bandwidth adjusted. A first conductivity type optical cladding layer, a first conductivity type InGaAlAs light guide layer, an InGaAlAs quantum well active layer, and a second conductivity type InGaAlAs light guide on a first conductivity type semiconductor substrate. A semiconductor laser in which a layer, an optical cladding layer of a second conductivity type, a diffraction grating layer, and a contact layer are laminated,
The InGaAlAs quantum well active layer is provided with quantum wells having at least three wells having substantially the same width and different forbidden band widths, and the difference in the forbidden band widths of the quantum wells is set to about 18 meV. . A first conductivity type optical cladding layer, a first conductivity type InGaAlAs light guide layer, an InGaAlAs quantum well active layer, and a second conductivity type InGaAlAs light guide on a first conductivity type semiconductor substrate. A semiconductor laser in which a layer, an optical cladding layer of a second conductivity type, a diffraction grating layer, and a contact layer are laminated,
The InGaAlAs quantum well active layer is provided with at least three quantum wells having different well widths and substantially equal forbidden band widths, and the difference between the well widths of the quantum wells is approximately 0.7 nm. element. A semiconductor laser device according to any one of claims 1 to 3,
A semiconductor laser characterized in that the first conductivity type is n-type. A first conductivity type optical cladding layer, a first conductivity type InGaAlAs light guide layer, an InGaAlAs quantum well active layer, and a second conductivity type InGaAlAs light guide on a first conductivity type semiconductor substrate. A layer, a second-conductivity-type optical cladding layer, a diffraction grating layer, and a contact layer, and the InGaAlAs quantum well active layer includes at least three quantum wells having different forbidden band width conversion values. A semiconductor laser device, wherein a well width or / and a forbidden band width of the quantum well is adjusted so that a difference in a forbidden band width converted value of the quantum well is approximately 18 meV;
An optical transmitter module comprising a case for housing the semiconductor laser element.

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