RU2309502C1 - Semiconductor injection laser - Google Patents

Abstract

FIELD: quantum electronics; pumping solid-state lasers.

SUBSTANCE: proposed semiconductor injection laser has separate-confinement heterostructure incorporating quantum-size active region, waveguide top and bottom layers, p and n emitters. Emitter of p polarity of conductivity is made of solid Al_XpGa_1-Xp solution. Emitter of n polarity of conductivity is made of solid Al_XnGa_1-XnAs solution. Waveguide top layer is made of solid Al_YtGa_1-YtAs solution. Waveguide bottom layer is made of solid Al_YbGa_1-YbAs solution. Mole fraction of Xp in solid Al_XpGa_1-XpAs solution ranges between 0.5 and 0.7. Mole fraction of Xn in Al_XnGa_1-XnAs solution is between 0.3 and 0.4. Mole fraction of Yt in solid Al_YtGa_1-YtAs solution at p emitter boundary equals Xp value and monotonously reduces down to 0.25 ≤ Yt ≤ 0.30. Mole fraction of Yb in solid Al_YbGa_1-YbAs solution at n emitter boundary monotonously reduces down to 0.25 ≤ Yb ≤ 0.30. Waveguide top layer thickness is between 320 and 380 nm. Waveguide bottom layer thickness is between 470 and 530 nm.

EFFECT: reduces optical loss, enhance efficiency, reduced radiation power density at optical faces of laser, enhanced service life of device.

1 cl, 1 dwg, 1 tbl

Description

The invention relates to quantum electronic technology and can, in particular, be used to pump solid-state lasers, which requires a very high coefficient of performance (COP) and the radiation power of a semiconductor laser.

A semiconductor laser is known, including a quantum-well active region, waveguide layers in contact with the active region on both sides thereof, and a semiconductor substrate. An additional optical limitation is created by layers made of wide-gap optical material adjacent to the full-flowing layers and having the same type of conductivity, JP 2005191349.

The disadvantage of this technical solution is the very high density of radiation power on the optical edges of the laser and, as a consequence, the short life of the device. In addition, several transverse modes are generated in this laser, which results in insufficient stability and low total radiation power.

Known semiconductor injection laser containing a separate confinement heterostructure, including a multimode waveguide, the confining layers of which are simultaneously emitters of p- and n-type conductivity with the same refractive indices, the active region, consisting of at least one quantum-dimensional active layer, location wherein in the waveguide and the waveguide thickness satisfies the relationship: T ⁰ _QW / _QW T ^m> 1.7, wherein T ⁰ and T _QW ^m _QW - optical confinement factor for the active region of the zero mode fashion and m-g (Higher) order (m = 1, 2, 3 ...), respectively, reflectors, optical facets, ohmic contacts, an optical resonator; the active region is placed in an additional layer, the refractive index of which is greater than the refractive index of the waveguide, and the thickness and location in the waveguide are determined from the condition for the above relation to be fulfilled, and the distances from the active region to p and n emitters do not exceed the diffusion lengths of holes and electrons in the waveguide, respectively RU 2259620; According to the description of the present invention, heterostructure layers can be made of AlGaAs solid solution.

This technical solution is made as a prototype of the present invention.

The disadvantage of the prototype is the fact that the electromagnetic field of the main (zero) transverse mode is completely concentrated in an additional layer, which has a significantly smaller thickness in comparison with the waveguide layers. This leads to an excessively high radiation power density at the optical faces of the injection laser, which is the reason for its insufficient life. It should also be noted that the waveguide layers are made of a material whose composition is constant over the thickness of these layers. With a high level of injection of nonequilibrium carriers, this leads to large optical losses and, as a result, to a decrease in the efficiency of the device.

The objective of the present invention is to reduce optical loss and increase the efficiency of the device, as well as reducing the power density of the radiation on the optical faces of the laser and thereby increasing the life of the device.

According to the invention, the semiconductor injection laser comprises a separate confinement heterostructure including a quantum-well active region, upper and lower waveguide layers adjacent to them, respectively, p- and n-conductivity emitters, while the p-conductivity emitter is made of Al _Xp Ga solid solution _1-Xp As, the n-conductivity emitter is made from Al _Xn Ga _1-Xn As solid solution, the upper waveguide layer is made from Al _Yв Ga _1-Yв As solid solution, the lower waveguide layer is made from Al _Yн Ga _1-Yн As solid solution ; new in the present invention is that in the Al _Xp Ga _1-Xp As solid solution, the value of the molar fraction Xp is in the range from 0.5 to 0.7, in the Al _Xn Ga _1-Xn As solid solution, the molar fraction Xn is in in the range from 0.3 to 0.4, in the solid solution Al _Yв Ga _1-Yв As the value of the molar fraction of Yв on the border with the p-conductivity emitter is equal to the value of Хр and monotonically decreases to 0.25≤Yв≤0.30, in the solid the solution Al _Yн Ga _1-Yн As the value of the molar fraction of Yн at the boundary with the n-conductivity emitter is equal to the value of Xn and monotonically decreases to 0.25≤Yn≤0.30, while the thickness of the upper waveguide the layer is in the range of 320-380 nm, and the thickness of the lower waveguide layer is in the range of 470-530 nm.

The applicant has not identified any technical solutions identical to the claimed, which allows us to conclude that the invention meets the criterion of "novelty."

Due to the implementation of the p-conductivity emitter from the Al _Xp Ga _1-Xp As solid solution, subject to the condition: 0.5≤Xr≤0.7, the electromagnetic field practically does not penetrate this emitter, as a result of which optical losses are reduced and the laser efficiency is increased . Due to the implementation of the n-conductivity emitter from the Al _Xn Ga _1-Xn As solid solution, subject to the condition: 0.3 n Xn 0 0.4, light scattering on free carriers decreases, which also contributes to an increase in efficiency. In addition, due to this, there is a very significant decrease in the concentration of the electromagnetic field in and around the active region and, accordingly, a decrease in the radiation power density at the optical edges of the laser and an increase in its service life.

It should be noted that, at values of the Chr molar fraction of AlAs in the Al _Xp Ga _1-Xp As solid solution of less than 0.5, the optical losses on free carriers increase significantly, and at Xp> 0.7, an additional fast degradation of the laser characteristics arises due to the oxidation of optical faces.

When Xn is less than 0.3, nonequilibrium carriers are ejected from the active region into the waveguide layers and the n-conductivity emitter, which leads to a sharp decrease in the efficiency. At Xn greater than 0.4, optical losses increase in the n-conductivity emitter.

Due to the fact that the upper and lower waveguide layers are respectively made of Al _Yв Ga _1-Yв As and Al _Yн Ga _1-Yн As solid solutions, in which the values of Yв and Yн at the boundaries with the emitters of p-conductivity and n-conductivity are respectively equal to Xp and Xn and monotonically decrease to 0.25≤Yв≤0.30 and 0.25≤Yн≤0.30, the effect of the "pulling field" in the waveguide layers. This effect consists in increasing the speed of displacement of nonequilibrium carriers in these layers. As a result, the concentration of injected carriers in the waveguide layers decreases and, as a result, the optical loss decreases and the laser efficiency increases. At Yb and Yn less than 0.25, nonequilibrium carriers are ejected into the waveguide layers from the active region, which sharply reduces the efficiency of the device. With Yb and Yn greater than 0.30, the pulling field effect becomes insufficiently expressed.

When the thickness of the upper waveguide layer (d _BB ) is less than 320 nm, a significant penetration of the electromagnetic field into the p-conductivity emitter occurs, which leads to an increase in optical losses. When d _{BB is} more than 380 nm, the value of the optical optical limitation factor of the laser decreases, the threshold and operating currents increase, and, as a result, the efficiency decreases. When the thickness of the lower waveguide layer (d _HB ) is less than 470 nm, a redistribution of the electromagnetic field in the heterostructure occurs, which reduces the value of the optical limiting factor of the laser and its efficiency; in addition, an excess concentration of the electromagnetic field arises in and around the active region, which leads to a decrease in the laser life. With an increase in d _HB over 530 nm, the electromagnetic field to an unacceptably large extent goes beyond the active region, which leads to a decrease in efficiency.

The applicant has not identified any sources of information in which there would be information about the characteristics indicated in the characterizing part of the claims, and the technical result achieved through their implementation. This circumstance, according to the applicant, allows us to conclude that the invention meets the criterion of "inventive step".

The invention is illustrated in the drawing, which shows the heterostructure of a semiconductor injection laser in section.

The semiconductor injection laser contains a separate confinement heterostructure, including a quantum-well active region 1 made of InGaAlAs solid solution, the composition of which provides a laser generation wavelength of 808 ± 3 nm, an active region thickness of 10 nm. The upper 2 and lower 3 undoped waveguide layers are adjacent to the active region 1; the thickness of the upper waveguide layer is from 320 to 380 nm, the thickness of the lower waveguide layer is 470-530 nm. The p-conductivity emitter 4 and the n-conductivity emitter 5 are adjacent, respectively, to the waveguide layers 2 and 3. The emitter 4 is made of a solid solution Al _Xp Ga _1-Xp As, where the value of the mole fraction Xp is in the range from 0.5 to 0 , 7. The material of the emitter 4 is doped with zinc to a concentration of acceptors, providing a hole concentration of p = 2 * 10 ¹⁷ cm ^-3 . The emitter 5 is made of a solid solution Al _Xn Ga _1-Xn As, where the molar fraction of Xn is in the range from 0.3 to 0.4. The material of the emitter 5 is doped with silicon to a donor concentration that provides an electron concentration of n = 2 * 10 ¹⁷ cm ^-3 . The waveguide layer 2 is made of a solid solution Al _Yв Ga _1-Yв As. The value of the molar fraction of Yв on the border with emitter 4 is equal to the value of Хр and monotonically decreases to 0.25≤Yв≤0.30. The waveguide layer 3 is made of a solid solution Al _Yn Ga _1-Yn As. The value of the molar fraction of Yн at the boundary with emitter 5 is equal to the value of Xn and monotonically decreases to 0.25≤Yn≤0.30. The substrate 7 is made of n-type GaAs with an electron concentration of n = 2 * 10 ¹⁸ cm ^-3 . The buffer layer 6 is made of n-type GaAs with a thickness of 0.3 μm with an electron concentration of n = 2 * 10 ¹⁸ cm ^-3 . The contact layer 8 is made of p-type GaAs with a hole concentration of p = 1 * 10 ¹⁹ cm ^-3 .

For testing, laser heterostructures were grown by the method of MOS hydride epitaxy at subatmospheric pressure and temperatures from 700 to 900 ° C; electron and hole concentrations were measured based on the Hall effect on individual samples. An ohmic strip p-contact 9 formed of an Au-Zn alloy with a width of 200 μm is formed on the upper surface of the heterostructure, and an n-contact 10 is formed on the lower surface of the heterostructure of the Au-Ge alloy. Multilayer dielectric coated coatings forming interference mirrors with reflection coefficients of 90% (“blind” mirror) and 20% (output mirror).

To measure the current – voltage and current – voltage characteristics of the laser, the sample was mounted on a cooled module equipped with a Peltier microcooler. Using a thermostabilizer, the module temperature was set to + 20 ° С. The pump current I was determined using a calibrated resistance of 0.01 Ohms, connected in series in the laser power circuit. A voltage signal at this resistance was applied to the input of a Tektronix TDS1002 digital oscilloscope. The total radiation power P was determined using a calibrated photodetector FD-24K, the signal from which was also fed to the input of a digital oscilloscope. The magnitude of the operating voltage U was measured directly at the contacts of the laser using a digital oscilloscope. The laser efficiency (hereinafter efficiency) was calculated as the ratio of the radiation power to the consumed electric power according to the formula

Efficiency = P / (I · U)

To measure the laser radiation pattern, injection lasers were mounted on a rotating base connected to a stepper motor, which, in turn, was controlled by a personal computer. A slotted diaphragm with a width of 500 μm, installed at a distance of 20 cm from the laser, ensured a measurement accuracy of 0.2 °. The width of the radiation pattern was characterized by its width at half maximum intensity.

The service life (MTBF) of the injection laser was determined by the following procedure. A laser was considered to be out of order if its total radiation power at the operating current was reduced by 20% relative to the initial value. Studies of MTBF for 10,000 hours have shown that a decrease in the radiation power at a fixed current is gradual and monotonous. Therefore, an extrapolation technique was used to quickly evaluate the service life, according to which the time was measured, during which the radiation power fell by 2% relative to the initial value, and the MTBF corresponded to ten times the measured time. Upon reaching the extrapolated lifetime of 10,000 hours, the tests were terminated.

The characteristics of injection lasers were measured for a fixed total radiation power of 2 W.

The characteristics of semiconductor injection lasers obtained as a result of the tests are shown in Table 1.

Examples 1, 2 and 3 correspond to the heterostructure parameters of the injection laser lying within the limits indicated in the claims. Examples 4 and 5 illustrate the deterioration of the characteristics of the laser when the deviation of the composition of the p-conductivity emitter from those indicated in the claims. Examples 6 and 7 demonstrate the deterioration of the characteristics of the laser when the deviation of the composition of the emitter of n-conductivity from those specified in the claims. Examples 8, 9, and 10, 11 show how deviations in the thickness of the upper and lower waveguide layers, respectively, beyond the limits indicated in the claims, negatively affect the characteristics of injection lasers. The deviation of the molar fractions of Yb and Yb at the boundary of the waveguide layers and the active region beyond the limits indicated in the claims also lead to a deterioration in the characteristics of injection lasers, as shown in examples 12 and 13. Example 14 corresponds to the prototype device.

For the manufacture of injection lasers, the most widely used growth technology and standard industrial equipment are used, which determines the compliance of the invention with the criterion of "industrial applicability".

Table 1 Example No. Parameters of the heterostructure of the injection laser Laser Life (h) Efficiency (%) Half width of the radiation pattern (degrees) one Хр = 0.5, Xn = 0.32, Yв = 0.5 → 0.26,
Yн = 0.32 → 0.26, d _BB = 340 nm, d _HB = 500 nm > 10,000 35 28 2 Хр = 0.7, Xn = 0.35, Yв = 0.7 → 0.29,
Yн = 0.35 → 0.29, d _BB = 320 nm, d _HB = 530 nm > 10,000 34 29th 3 Хр = 0.6, Xn = 0.40, Yв = 0.6 → 0.25,
Yн = 0.40 → 0.25, d _BB = 350 nm, d _HB = 500 nm > 10,000 36 27 four Хр = 0.9, Xn = 0.35, Yв = 0.9 → 0.30,
Yн = 0.35 → 0.30, d _BB = 330 nm, d _HB = 510 nm 60 12 32 5 Хр = 0.4, Xn = 0.35, Yв = 0.4 → 0.30,
Yн = 0.4 → 0.30, d _BB = 320 nm, d _HB = 530 nm > 10,000 25 23 6 Хр = 0.6, Xn = 0.25, Yв = 0.6 → 0.25,
Yн = 0.25, d _BB = 350 nm, d _HB = 510 nm, > 10,000 23 19 7 Хр = 0.6, Xn = 0.50, Yв = 0.6 → 0.27,
Yн = 0.50 → 0.27, d _BB = 340 nm, d _HB = 520 nm 6000 22 34 8 Хр = 0.6, Xn = 0.35, Yв = 0.6 → 0.27,
Yн = 0.35 → 0.27, d _BB = 290 nm, d _HB = 530 nm 4500 thirty 35 9 Хр = 0.6, Xn = 0.35, Yв = 0.6 → 0.28,
Yн = 0.35 → 0.28, d _BB = 450 nm, d _HB = 530 nm 4200 25 28 10 Хр = 0.6, Xn = 0.40, Yв = 0.6 → 0.26,
Yн = 0.40 → 0.26, d _BB = 350 nm, d _HB = 400 nm 8000 twenty 34 eleven Хр = 0.6, Xn = 0.40, Yв = 0.6 → 0.26,
Yн = 0.40 → 0.26, d _BB = 330 nm, d _HB = 580 nm 5100 23 eighteen 12 Хр = 0.6, Xn = 0.40, Yв = 0.6 → 0.20,
Yн = 0.40 → 0.20, d _BB = 350 nm, d _HB = 510 nm 800 8 24 13 Хр = 0.6, Xn = 0.35, Yв = 0.6 → 0.35,
Yн = 0.35 → 0.35, d _BB = 350 nm, d _HB = 400 nm > 10,000 21 thirty fourteen Хр = 0.38, Xn = 0.38, Yв = 0.3 (const),
Yн = 0.3 (const), d _BB = 2000 nm, d _HB = 2000 nm 1100 eighteen 13

Claims (1)

A semiconductor injection laser containing a separate confinement heterostructure, including a quantum-well active region, upper and lower waveguide layers adjacent to them p and n conductivity emitters, respectively, while the p conductivity emitter is made of Al _Xp Ga _1-Xp solid solution As, the n-conductivity emitter is made from Al _Xn Ga _1-Xn As solid solution, the upper waveguide layer is made from Al _Yв Ga _1-Yв As solid solution, the lower waveguide layer is made from Al _Yн Ga _1-Yн As solid solution, characterized in in solid solution Al _Xp Ga _1-Xp As, the molar fraction of Хр is in the range from 0.5 to 0.7, in the Al _Xn Ga _1-Xn As solid solution, the molar fraction of Xn is in the range from 0.3 to 0.4 , in the Al _Yв Ga _1-Yв As solid solution, the value of the Yв molar fraction at the interface with the p-conductivity emitter is equal to the value of Хр and monotonically decreases to 0.25≤Yв≤0.30; in the Al _Yн Ga _1-Yн As solid solution, the value the molar fraction of Yн at the boundary with the n-conductivity emitter is equal to the value of Хн and monotonically decreases to 0.25≤Yn≤0.30, while the thickness of the upper waveguide layer is in the range 320-380 nm, and the thickness of the lower waveguide layer is in the range 470-530 nm.