RU2787721C9 - Separate-confinement laser hetero-structure - Google Patents

Abstract

FIELD: semiconductor technology.

SUBSTANCE: invention relates to semiconductor technology, to planar laser heterostructures. The separate-confinement laser hetero-structure grown on a GaAs substrate of n-conductivity includes a quantum-dimensional active region, waveguide layers made of a solid solution of Al_xGa_1-xAs, emitter layers of n-conductivity and p-conductivity adjacent to the waveguide layers and made of a solid solution of Al_x'Ga_1-x'As. The heterostructure is provided with contact layers of n-conductivity and p-conductivity adjacent to the corresponding emitter layers of n-conductivity and p-conductivity, the waveguide layers contact directly with the quantum-dimensional active region and the emitter layers of n-conductivity and p-conductivity and are made of different thickness and are 2y and y, respectively, where y is within from 0.75 to 0.85 microns, the molar fraction of aluminum x solid solution Al_xGa_1-xAs in waveguide layers at the boundaries with emitter layers is 0.8x' and linearly decreases to 0.5x' at the boundaries with the quantum-dimensional active region, and in emitter layers the molar fraction of aluminum x' solid solution Al_x'Ga_1-x'As is in the range from 0.4 to 0.45.

EFFECT: present invention enables to improve the design of the laser heterostructure, to create an additional optical confinement between the emitter and waveguide layers.

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Description

The invention relates to semiconductor technology, in particular to planar laser heterostructures used for the manufacture of laser diodes with high output optical power.

Known laser heterostructure described in US patent No. 6996149, publ. 02/07/2006, under the title "Semiconductor laser and semiconductor laser module". The heterostructure contains an active region including at least one quantum well. The charge carrier confinement layers are located on either side of the active region. The optical confinement layers have a graded-gap structure and are located on both sides of the active region. The difference in the refractive indices of the active region layer and charge carrier confinement layers is no more than 0.02.

The disadvantages of the technical solution include:

- insufficient limitation of light radiation and an increase in the effective mode width due to a small difference between the refractive indices of the active region layer and charge carrier confinement layers (no more than 0.02), which worsens the characteristics of the resulting laser diodes for the following reasons:

- increasing the depth of radiation penetration into the doped layers, which increases the internal optical loss;

- a decrease in the optical limiting factor of the generated modes, which leads to an increase in the threshold current and a decrease in the efficiency of laser diodes.

Known laser heterostructure described in US patent No. 9042416, IPC H01S 5/00, H01S 5/34, publ. 05/26/2015, under the name "Powerful GRINSCH laser with low losses", which is a graded-gap heterostructure of separate limitation, consisting of an active region, layers of n- and p-contacts, n and p-emitter layers, multilayer sections n- and p- types of doping adjacent directly to the active region, n and p-subemitter layers.

The disadvantages of the technical solution include:

- reduced values of the efficiency of laser diodes due to high values of the threshold current and reduced differential efficiency due to the fact that the layers adjacent to the active region are doped. Since doping differs in type, at least one of the two adjacent layers in this heterostructure is intentionally doped, while additional doping in the layers that act as a waveguide increases the internal losses of the laser diode.

The closest and selected as a prototype is the design of a separate restriction laser heterostructure described in patent RU No. 2309501, IPC H01S 5/32, publ. October 27, 2007 under the name "Injection semiconductor laser", including a quantum-well active region, waveguide layers made of an Al _x Ga _1-x As solid solution, emitter layers of n- and p-conductivity adjacent to the waveguide layers and made from a solid solution of Al _x' Ga _1-x' As.

The disadvantages of the technical solution include:

- the concentration of Al in the presented solution corresponds to indirect-gap layers, in which phonon recombination takes place, which is the reason for the release of additional heat and a decrease in the efficiency of manufactured laser diodes;

- the symmetry of the structure, which causes a decrease in the selection of higher-order modes and, in turn, a decrease in the radiation power and efficiency of laser diodes based on the presented heterostructure.

The objective of the claimed invention is to improve the main characteristics of the manufactured laser diodes, namely the reduction of the threshold current, the increase in the output optical radiation power and the efficiency of laser diodes manufactured on the basis of the laser heterostructure design.

The technical result, which allows solving the problem, is to improve the design of the laser heterostructure due to its asymmetry and the presence of a graded-gap structure of the waveguide layers, as well as to create an additional optical limitation between the emitter and waveguide layers.

This is achieved by the fact that the separate limitation laser heterostructure, which includes a quantum-well active region, waveguide layers made of an Al _x Ga _1-x As solid solution, emitter layers of n- and p-conductivity adjacent to the waveguide layers and made of a solid solution Al _x' Ga _1-x' As, according to the invention, is provided with contact layers of n- and p-conductivity adjacent to the corresponding emitter layers of n- and p-conductivity, the waveguide layers are in direct contact with the quantum-well active region and the emitter layers of n- and p-conductivity and are made of different thicknesses on the side of the emitter layers of n- and p-conductivity and are 2y and y, respectively, where y is in the range from 0.75 to 0.85 μm, the mole fraction of aluminum x of the solid solution Al _x Ga _{1- x} As in the waveguide layers at the boundaries with the emitter layers is 0.8x' and decreases linearly to 0.5x' at the boundaries with the quantum-well active region, and in the emitter layers the mole fraction of aluminum x' of the solid solution Al _x' Ga _{1-x '} As ranges from 0.4 to 0.45.

The analysis of the state of the art carried out by the applicant, including the search for patent and scientific and technical sources of information and the identification of sources containing information about analogues of the claimed invention, made it possible to establish that the applicant did not find an analogue characterized by features identical to all essential features of the claimed invention, and the definition from the list identified analogues of the prototype, as the closest analogue in terms of the set of features, made it possible to identify a set of distinctive features in the claimed object that are significant in relation to the technical result perceived by the applicant and set forth in the claims.

Therefore, the claimed invention meets the requirement of "novelty" under the current legislation.

To verify the compliance of the claimed invention with the condition of inventive step, the applicant conducted an additional search for known solutions in order to identify features that coincide with the features of the claimed invention that are distinctive from the prototype, the results of which show that the claimed invention does not follow for a specialist in an obvious way from the known technical level of technology.

Therefore, the claimed invention meets the requirement of "inventive step".

The invention is illustrated in the following drawing, which shows the design of a separate restriction laser heterostructure.

The following positions are entered on the drawing:

1 - quantum-dimensional active region;

2, 3 - waveguide layers;

4 - emitter layer of n-conductivity;

5 - emitter layer of p-conductivity;

6 - contact layer of n-conductivity;

7 - contact layer of p-conductivity.

Separate-confinement laser heterostructure grown on an n-conductivity GaAs (100) substrate includes a quantum-well active region 1, waveguide layers 2 and 3 made of an Al _x Ga _1-x As solid solution, n-conductivity emitter layers 4 and p -conductivity 5 adjacent to the waveguide layers 2 and 3 and made of a solid solution of Al _x' Ga _1-x' As. Separate limitation laser heterostructure is equipped with contact layers of n-conductivity 6 and p-conductivity 7 adjacent to the corresponding emitter layers of n-conductivity 4 and p-conductivity 5, waveguide layers 2 and 3 are in direct contact with quantum-well active region 1 and emitter layers n -conductivity 4 and p-conductivity 5. The laser heterostructure of separate limitation is made asymmetric, since waveguide layers 2 and 3 are made of different thicknesses on the side of the emitter layers of n-conductivity 4 and p-conductivity 5 and are 2у ^⋅ and y, respectively, where y is within from 0.75 to 0.85 µm. The structure of waveguide layers 2 and 3 is graded-gap, since the mole fraction of aluminum x solid solution Al _x Ga _1-x As in waveguide layers 2 and 3 at the boundaries with emitter layers of n-conductivity 4 and p-conductivity 5 is 0.8x' and linearly decreases to 0.5x' at the boundaries with the quantum-well active region 1. In the emitter layers of n-conductivity 4 and p-conductivity 5, the mole fraction of aluminum x' of the solid solution Al _x' Ga _1-x' As is in the range from 0, 4 to 0.45.

The indicated compositions of solid solutions Al _x' Ga _1-x' As and Al _x Ga _1-x As, from which emitter layers of n-conductivity 4 and p-conductivity 5 and waveguide layers 2 and 3, respectively, are made, make it possible to achieve a difference in refractive indices Δn =0.03-0.09 at the boundaries between the emitter layers of n-conductivity 4 and p-conductivity 5 and waveguide layers 2 and 3, which creates an additional optical limitation that ensures efficient return of optical modes refracting from waveguide layers 2 and 3 to the emitter layers of n-conductivity 4 and p-conductivity 5.

Due to the fact that the waveguide layers 2 and 3 are made of different thicknesses on the side of the emitter layers of n-conductivity 4 and p-conductivity 5 and are 2у ^⋅ and y, respectively, and also taking into account the fact that the value of y is in the range from 0.75 to 0 .85 µm, provides optimal asymmetry of the design of the laser heterostructure separate limitation, which allows a high selection of modes of higher order.

An increase in the thickness y leads to an increase in the series resistance of the layers of the laser heterostructure of a separate limitation, which reduces the efficiency of the manufactured laser diodes. A decrease in the thickness y, in turn, leads to an increase in internal optical losses, as well as to an increase in the leakage of radiation from waveguide layers 2 and 3 into the emitter layers of n-conductivity 4 and p-conductivity 5 and, as a consequence, a decrease in the output power of laser radiation. diodes based on the proposed design.

Due to the fact that the mole fraction of aluminum x in the waveguide layers 2 and 3 at the boundaries with the emitter layers of n-conductivity 4 and p-conductivity 5 is 0.8x' and decreases linearly to 0.5x' at the boundaries with the quantum-well active region 1 , provide an optimal profile of the aluminum content in the solid solution from which the waveguide layers 2 and 3 are made. This profile establishes the variability of the design of the waveguide layers 2 and 3, which is necessary to prevent leakage of refractive modes into the emitter layers of n-conductivity 4 and p-conductivity 5, and , as a consequence, to obtain increased values of the output optical power of laser diodes at a given pump current, as well as reduced values of the threshold current. In addition, in combination with the fact that in the emitter layers of n-conductivity 4 and p-conductivity 5 the mole fraction of aluminum x' is in the range from 0.4 to 0.45, the condition of additional optical limitation is achieved due to the difference in refractive indices by the boundary between the emitter layers of n-conductivity 4 and p-conductivity 5 and waveguide layers 2 and 3, component Δn=0.05-0.09, which also provides an effective return of optical modes and a decrease in the threshold current values of the separate limitation laser heterostructure.

An example of a specific implementation can be a separate limitation laser heterostructure grown on a GaAs (100) substrate of n-conductivity, including a quantum-well active region 1, waveguide layers 2 and 3, made from a solid solution of Al _x Ga _1-x As, emitter layers n -conductivity 4 and p-conductivity 5 adjacent to the waveguide layers 2 and 3 and made of a solid solution of Al _x' Ga _1-x' As. Separate limitation laser heterostructure is equipped with contact layers 6 and 7 of n- and p-conductivity, adjacent to the corresponding emitter layers of n-conductivity 4 and p-conductivity 5, waveguide layers 2 and 3 are in direct contact with quantum-well active region 1 and emitter layers n -conductivity 4 and p-conductivity 5 and are made of different thickness on the side of the emitter layers of n-conductivity 4 and p-conductivity 5 and are 1.5-1.7 µm and 0.75-0.85 µm, respectively, the mole fraction of aluminum x solid solution of Al _x Ga _1-x As in waveguide layers 2 and 3 at the boundaries with the emitter layers of n-conductivity 4 and p-conductivity 5 is 0.32-0.36 and decreases linearly to 0.2 at the boundaries with the quantum-well active region 1, and in the emitter layers of n-conductivity 4 and p-conductivity 5, the mole fraction of aluminum x' of the Al _x' Ga _1-x' As solid solution ranges from 0.4 to 0.45.

The use of this invention shows that the design of a separate restriction laser heterostructure with an additional restriction formed between the waveguide and emitter layers of n- and p-conductivity leads to a decrease in the threshold current of laser diodes by 20-40% for different cavity lengths, compared with a structure having homogeneous asymmetric waveguide. The decrease in the threshold current can be explained by an increase in the optical confinement factor in the waveguide layers of the heterostructure, which, in turn, is explained by an increase in the mole fraction of aluminum in the emitter layers, which causes a jump in the refractive index at the interface between the emitter and waveguide layers.

A decrease in the threshold current makes it possible to increase the maximum operating current of laser diodes by 20–40% and, as a result, to increase their maximum output optical power compared to laser diodes made from a heterostructure with a uniform waveguide. In addition, a graded-gap waveguide provides an increase in the output radiation power by 10–15% compared to a structure with a uniform asymmetric waveguide, since this type of waveguide contributes to the return of refractive modes from the waveguide to the emitter layers. On the whole, a decrease in the threshold current and an increase in the output radiation power contribute to an increase in the efficiency of laser diodes.

For the claimed invention in the form as it is described in the claims, the possibility of its implementation using the above-described design solutions and the ability to achieve the specified technical result is confirmed. Therefore, the claimed invention meets the condition of "industrial applicability".

Claims (1)

Laser heterostructure of separate limitation, including a quantum-well active region, waveguide layers made of a solid solution of Al _x Ga _1-x As, emitter layers of n- and p-conductivity adjacent to the waveguide layers and made of a solid solution of Al _x' Ga _{1 -x'} As, characterized in that it is equipped with contact layers of n- and p-conductivity adjacent to the corresponding emitter layers of n- and p-conductivity, the waveguide layers are in direct contact with the quantum-well active region and the emitter layers of n- and p- conductivity and are made of different thickness on the side of the emitter layers of n- and p-conductivity and are 2y and y, respectively, where y is in the range from 0.75 to 0.85 μm, the mole fraction of aluminum x of the Al _x Ga _1-x As solid solution in waveguide layers at the boundaries with the emitter layers is 0.8x' and decreases linearly to 0.5x' at the boundaries with the quantum-well active region, and in the emitter layers the mole fraction of aluminum x' of the Al _x' Ga _1-x' As solid solution is ranging from 0.4 to 0.45.

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