CN107611780A - Si doping InAs/GaAs quantum dot lasers and preparation method thereof - Google Patents

Abstract

The invention discloses a Si-doped InAs/GaAs quantum dot laser and a preparation method thereof, wherein the quantum dot laser comprises a quantum dot active region (50), and the quantum dot active region (50) comprises Si A doped quantum dot layer (51); the preparation method of the quantum dot laser is to grow a buffer layer (20), a lower cladding layer (30), a lower waveguide layer ( 40), quantum dot active region (50), upper waveguide layer (60), upper cladding layer (70) and ohmic contact layer (80). The quantum dot laser provided by the invention effectively passivates the non-radiative recombination centers near the quantum dots by introducing Si atoms, thereby enhancing the optical properties of the quantum dot materials; at the same time, the electrons introduced by the Si atoms can reduce the threshold current of the laser device and improve the performance of the device. performance.

Description

Si-doped InAs/GaAs quantum dot laser and its preparation method

technical field

The invention belongs to the technical field of semiconductors, and in particular relates to a Si-doped InAs/GaAs quantum dot laser and a preparation method thereof.

Background technique

The continuous increase in the amount of information puts forward higher requirements for the light source of optical fiber communication. As the core component of the optical fiber communication system, the semiconductor laser plays a vital role in the performance of the whole system. Quantum dot materials have discrete energy levels similar to atoms, and the density of states is in the form of a delta function because the sizes in three dimensions are close to the de Broglie wavelength of electrons. Semiconductor quantum dot lasers exhibit superior characteristics such as low threshold current density, high differential gain, high temperature stability, high modulation rate, and low frequency chirp effect, and are expected to become important light sources for next-generation optical communication systems. And high-speed data exchange systems and other fields have important application prospects.

There are many methods for preparing quantum dots, and the following two are common:

(1) The method of combining microstructure material growth with microfabrication technology: that is, using molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MOCVD) technology to perform selective epitaxial growth or high-quality Epitaxial material growth, combined with high spatial resolution electron beam direct writing, dry or wet etching, and then epitaxial growth. The advantage of this method is that the size, shape and density of quantum dots (QD) are controllable, but due to the interface damage caused by processing and the impurity contamination introduced by the process, the device performance is far from the predicted value of the theory.

(2) The use of strained self-assembly mode (SK growth mode) to grow quantum dot materials is a commonly used preparation method for quantum dot materials. The SK growth mode is suitable for heterojunction material systems with large lattice mismatch but low surface and interface energy. The initial stage of SK epitaxial growth is two-dimensional layered growth, usually only a few atomic layers thick, called the wetting layer; as the layer thickness increases, the strain energy continues to accumulate, and when a certain critical thickness t _c is reached, the epitaxial growth Transition from two-dimensional layered growth to three-dimensional island growth, thereby reducing the energy of the system; the nanoscale islands formed in the initial stage of three-dimensional island growth are dislocation-free, if surrounded by materials with a large band gap In general, the carriers in the small islands are three-dimensionally confined, which are called quantum dots; on the basis of the grown single-layer quantum dots, the above growth process can be repeated to obtain a quantum dot superlattice structure. By controlling the growth conditions of quantum dots, high-quality quantum dot materials can be obtained. The disadvantage of this method is that its size, shape, distribution uniformity and density are more difficult to control.

Contents of the invention

(1) Technical problems to be solved

The invention provides a Si-doped InAs/GaAs quantum dot laser and a preparation method thereof. By introducing appropriate Si atoms into the InAs/GaAs quantum dot material, the optical performance of the quantum dot material is improved, thereby improving the performance of the quantum dot laser .

(2) Technical solutions

In order to achieve the above technical purpose, as an aspect of the present invention, the present invention provides a Si-doped InAs/GaAs quantum dot laser, including a substrate and an epitaxial layer grown thereon;

The lower part of the epitaxial layer includes a buffer layer, a lower cladding layer above the buffer layer, and a lower waveguide layer above the lower cladding layer;

The upper part of the epitaxial layer includes an upper waveguide layer, an upper cladding layer on the upper waveguide layer, and an ohmic contact layer on the upper cladding layer;

The middle part of the epitaxial layer includes a quantum dot active area, and the quantum dot active area includes a Si-doped quantum dot layer, a first capping layer on the top of the quantum dot layer, and a second capping layer on the top of the first capping layer. cycle structure.

As a further embodiment, the host material of the Si-doped quantum dot layer is InAs.

As a further embodiment, the material of the first capping layer is InGaAs or GaAs, and the material of the second capping layer is GaAs.

As a further embodiment, the main material of the substrate, the buffer layer, the lower waveguide layer, the upper waveguide layer and the ohmic contact layer is GaAs.

As a further embodiment, the substrate and the buffer layer are n-type doped GaAs; the lower waveguide layer and the upper waveguide layer are pure GaAs; the ohmic contact layer is p-type doped GaAs.

As a further embodiment, the host material of the lower cladding layer and the upper cladding layer is AlGaAs.

As a further embodiment, the lower cladding layer is n-type doped AlGaAs; the upper cladding layer is p-type doped AlGaAs. As a further embodiment, the period number of the periodic structure is 1-20.

As a further embodiment, the quantum dot growth thickness of the Si-doped quantum dot layer is 0 to 10ML, and the doping concentration of Si is 1×10 ³ to 1×10 ²⁴ cm ⁻³ (ML: monoatomic layer thickness, That is, the thickness of one atomic layer of the grown material).

As a further embodiment, the growth thickness of the first capping layer is 0-30 nm.

As a further embodiment, the growth thickness of the second capping layer is 0-30 nm.

In order to achieve the above technical purpose, as another aspect of the present invention, the present invention provides a method for preparing a Si-doped InAs/GaAs quantum dot laser, which is characterized in that it includes the following steps:

Step 1: Select a substrate;

Step 2: growing a buffer layer on the substrate;

Step 3: growing a lower cladding layer on the buffer layer;

Step 4: growing a lower waveguide layer on the lower cladding layer;

Step 5: growing a quantum dot active region on the lower waveguide layer, the quantum dot active region comprising a Si-doped quantum dot layer;

Step 6: growing an upper waveguide layer on the quantum dot active region;

Step 7: growing an upper cladding layer on the upper waveguide layer;

Step 8: growing an ohmic contact layer on the upper cladding layer.

As a further embodiment, the quantum dot active region first grows a Si-doped quantum dot layer, grows a first capping layer on the Si-doped quantum dot layer, grows a second capping layer on the first capping layer, and forms A periodic structure; the period number of the periodic structure is 1-20.

As a further embodiment, in the Si-doped quantum dot layer, the quantum dot growth thickness is 0-10ML, and the doping concentration of Si is 1×10 ³ to 1×10 ²⁴ cm ^-3 ;

As a further embodiment, the host material of the Si-doped quantum dot layer is InAs.

As a further embodiment, the material of the first capping layer is InGaAs or GaAs, and the growth thickness is 0-30 nm; the material of the second capping layer is GaAs, and the growth thickness is 0-30 nm.

As a further embodiment, the main material of the substrate, the buffer layer, the lower waveguide layer, the upper waveguide layer and the ohmic contact layer is GaAs.

As a further embodiment, the substrate and the buffer layer are n-type doped GaAs; the lower waveguide layer and the upper waveguide layer are pure GaAs; the ohmic contact layer is p-type doped GaAs.

As a further embodiment, the host material of the lower cladding layer and the upper cladding layer is AlGaAs.

As a further embodiment, the lower cladding layer is n-type doped AlGaAs; the upper cladding layer is p-type doped AlGaAs.

(3) Beneficial effects

The method is a quantum device based on a low-dimensional semiconductor nanostructure quantum dot material. Compared with the prior art, the present invention has the following beneficial effects:

(1) Direct doping of Si atoms in InAs/GaAs quantum dot materials can effectively passivate the non-radiative recombination centers near the quantum dots. The reduction of the non-radiative recombination process is a very beneficial process for quantum dot lasers, which can enhance the quantum dots. The optical properties of the material;

(2) The electrons introduced by Si atoms can reduce the threshold current of the laser device and improve the device performance.

(3) The lasing wavelength of the quantum dot laser can be adjusted by controlling the thickness of the first capping layer and the ratio of the third main group metal element in the first capping layer.

Description of drawings

Fig. 1 is a schematic diagram of an epitaxial growth structure for preparing a quantum dot laser provided by an embodiment of the present invention.

Fig. 2 is a schematic diagram of a P-I curve of a semiconductor laser according to an embodiment of the present invention.

Fig. 3 is an optical power-current curve of an undoped InAs/GaAs quantum dot laser (undoped) and a Si-doped InAs/GaAs quantum dot laser (Si-doped) in an embodiment of the present invention.

Explanation of reference numbers:

10: Substrate

20: buffer layer

30: lower cladding

40: Lower waveguide layer

50: Quantum dot active area

51: Si-doped quantum dot layer

52: First cover layer

53: Second cap layer

60: Upper waveguide layer

70: upper cladding

80: Ohmic contact layer

detailed description

In order to further illustrate the specific technical content of the present invention and make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

According to the general inventive concept of the present invention, as an aspect of the present invention, a kind of Si-doped InAs/GaAs quantum dot laser is provided, as shown in Figure 1, quantum dot laser of the present invention comprises substrate 10 and grows on it The epitaxial layer; the bottom of the epitaxial layer includes a buffer layer 20, the lower cladding layer 30 on the top of the buffer layer 20, and the lower waveguide layer 40 on the top of the lower cladding layer 30; the upper part of the epitaxial layer includes an upper waveguide layer 60, an upper waveguide The upper cladding layer 70 on the upper part of the layer 60 and the ohmic contact layer 80 on the upper cladding layer 70; the middle part of the epitaxial layer includes a quantum dot active region 50, and the quantum dot active region 50 includes a Si-doped quantum dot layer 51 , a periodic structure formed by the first cover layer 52 on the top of the Si-doped quantum dot layer 51 and the second cover layer 53 on the top of the first cover layer 52; preferably, the host material of the Si-doped quantum dot layer 51 for InAs.

Preferably, the material of the first capping layer 52 is InGaAs or GaAs, and the material of the second capping layer 53 is GaAs.

Preferably, the main material of the substrate 10 , the buffer layer 20 , the lower waveguide layer 40 , the upper waveguide layer 60 and the ohmic contact layer 80 is GaAs.

More preferably, the substrate and the buffer layer are n-type doped GaAs; the lower waveguide layer and the upper waveguide layer are pure GaAs; the ohmic contact layer is p-type doped GaAs.

Preferably, the host material of the lower cladding layer 30 and the upper cladding layer 70 is AlGaAs.

More preferably, the lower cladding layer is n-type doped AlGaAs; the upper cladding layer is p-type doped AlGaAs.

Preferably, the period number of the periodic structure is 1-20.

Preferably, the Si-doped quantum dot layer 51 has a quantum dot growth thickness of 0-10ML, and a Si doping concentration of 1×10 ³ to 1×10 ²⁴ cm ⁻³ . Preferably, the growth thickness of the first capping layer 52 is 0-30 nm.

Preferably, the growth thickness of the second capping layer 53 is 0-30 nm.

According to the general inventive concept of the present invention, as another aspect of the present invention, a kind of preparation method of Si-doped InAs/GaAs quantum dot laser is provided, and specific process is as follows:

Step 1: Take a substrate 10;

Step 2: growing a buffer layer 20 on the substrate 10;

Step 3: growing a lower cladding layer 30 on the buffer layer 20;

Step 4: growing a lower waveguide layer 40 on the lower cladding layer 30;

Step 5: growing a quantum dot active region 50 on the lower waveguide layer 40, the quantum dot active region including a Si-doped quantum dot layer 51;

Step 6: growing an upper waveguide layer 60 on the quantum dot active region 50;

Step 7: growing an upper cladding layer 70 on the upper waveguide layer 60;

Step 8: growing an ohmic contact layer 80 on the upper cladding layer 70 .

Preferably, the quantum dot active region 50 is sequentially grown by the Si-doped quantum dot layer 51 , the first capping layer 52 , and the second capping layer 53 to obtain a periodic structure, and the period number of the periodic structure is 1-20.

Preferably, the growth thickness of the Si-doped quantum dot layer 51 is 0-10ML, and the doping concentration of Si is 1×10 ³ to 1×10 ²⁴ cm ⁻³ .

Preferably, the growth thickness of the first capping layer 52 is 0-30 nm.

Preferably, the growth thickness of the second capping layer 53 is 0-30 nm.

Preferably, the host material of the Si-doped quantum dot layer 51 is InAs.

Preferably, the material of the first capping layer 52 is InGaAs or GaAs, and the material of the second capping layer 53 is GaAs.

Preferably, the main material of the substrate 10 , the buffer layer 20 , the lower waveguide layer 40 , the upper waveguide layer 60 and the ohmic contact layer 80 is GaAs.

More preferably, the substrate and the buffer layer are n-type doped GaAs; the lower waveguide layer and the upper waveguide layer are pure GaAs; the ohmic contact layer is p-type doped GaAs.

Preferably, the host material of the lower cladding layer 30 and the upper cladding layer 70 is AlGaAs.

More preferably, the lower cladding layer is n-type doped AlGaAs; the upper cladding layer is p-type doped AlGaAs.

The technical solutions of the present invention will be further described below in conjunction with specific embodiments.

Example 1:

(1) Take a substrate 10, which is an n+-type GaAs substrate with a crystal orientation of (100), a doping element of Si, and a doping concentration of (0.5-5)×10 ¹⁸ cm ^-3 ;

(2) Epitaxially grow a layer of GaAs buffer layer 20 on the above-mentioned GaAs substrate 10, the buffer layer growth thickness is 0-800nm, it is n-type doped, the doping element is Si element, and the doping concentration is (0.5- 5)×10 ¹⁸ cm ^-3 ;

(3) Epitaxially grow the AlGaAs lower cladding layer 30 on the above-mentioned GaAs buffer layer 20, the growth thickness is 500-2000nm, and perform n-type doping on it, the doping element is Si element, and the doping concentration is (0.1-5)× 10 ¹⁸ cm ^-3 ;

(4) epitaxially growing the GaAs lower waveguide layer 40 on the above-mentioned AlGaAs lower cladding layer 30, with a growth thickness of 50-200 nm;

(5) epitaxially grow a Si-doped InAs quantum dot layer 51 on the GaAs lower waveguide layer 40, the growth thickness is 0-10ML, and the Si doping concentration is 1×10 ³ to 1×10 ²⁴ cm ^-3 , which is The key to improving the performance of quantum dot lasers.

(6) epitaxially grow the first capping layer 52 of InGaAs on the above-mentioned Si-doped InAs quantum dot layer 51, and the growth thickness is 0-30nm; by controlling the thickness of the first capping layer 52 of InGaAs and the ratio of In and Ga in InGaAs, Tuning the lasing wavelength of the quantum dot laser.

(7) Epitaxially grow the second GaAs capping layer 53 on the above-mentioned InGaAs first capping layer 52, the growth thickness of this layer is 0-30 nm.

(8) Obtain the InAs quantum dot active region 50 by above-mentioned steps (5)～(7); Steps (5)～(7) are repeated 1～20 times, form the multi-period InAs quantum dot active region 50 (1 ~20 cycles).

(9) Epitaxially grow the GaAs upper waveguide layer 60 on the above-mentioned multi-period InAs quantum dot active region 50 with a growth thickness of 50-200 nm.

(10) Epitaxially grow an AlGaAs upper cladding layer 70 on the above-mentioned GaAs upper waveguide layer 60, with a growth thickness of 500-2000 nm; perform p-type doping on the AlGaAs upper cladding layer 70, the doping element is Be element, and the doping concentration is It is (0.1～5)×10 ¹⁸ cm ^-3 .

(11) epitaxially grow GaAs ohmic contact layer 80 on the above-mentioned AlGaAs upper cladding layer, the growth thickness is 200nm; carry out p-type doping to described GaAs ohmic contact layer 80, doping element is Be element, and doping concentration is (0.01 ~1)×10 ²⁰ cm ⁻³ .

Performance Characterization

Optical power-current (P-I) characteristic test: The P-I characteristic indicates the relationship between the average output optical power of a semiconductor laser and the injection drive current, which is the most important characteristic of a semiconductor laser and an important basis for selecting a semiconductor laser. Fig. 2 is a schematic diagram of a P-I characteristic curve of a semiconductor laser.

Testing process

The P-I characteristic testing device used includes a direct current source, a pulse current source, a photodetector, a die test platform, a computer, and the like. During the test, the laser is fixed on the test platform, the current source provides continuous or pulse current, the output light of the device is collected by the photodetector, and then converted into the output optical power value by the program, and the data is collected and the result is displayed by the computer .

Test parameters

(1) Threshold current I _th

Semiconductor lasers can be regarded as an optical oscillator. To form optical oscillations, an optical amplification mechanism is necessary, that is, the active medium is in a population inversion distribution, and the resulting gain is sufficient to offset all losses. The condition at which a net gain begins to occur is referred to as a threshold condition. Generally, the injection current value is used to calibrate the threshold condition, that is, the threshold current I _th (the intersection point of the two line segments in FIG. 2 ). When the injection current I increases, the output optical power P increases accordingly; before the threshold current I _th is reached, the semiconductor laser emits spontaneously and outputs fluorescence; after reaching I _th , it is stimulated emission and outputs laser light.

(2) Slope efficiency dP/dI

Above the threshold current I _th , the laser works in stimulated emission and outputs laser light, and the power rises rapidly with the current, basically in a linear relationship. The current-voltage relationship of a laser is similar to that of a forward diode.

When selecting, the threshold current I _th should be selected as small as possible, the corresponding P value of I _th is small, and there is no kink point semiconductor laser. Such a laser has low working current, high working stability, large extinction ratio, and is not easy to generate optical signal distortion; moreover, the slope efficiency dP/dI of the PI curve is required to be appropriate, and if the slope is too small, the required driving current is too large, which will cause problems for the drive. The circuit is troublesome; if the slope is too large, optical reflection noise will appear, making automatic optical power control loop tuning difficult.

Fig. 3 is a P-I curve diagram of an undoped quantum dot laser and a Si-doped quantum dot laser. It can be seen from the figure that the threshold current of the Si-doped quantum dot laser is 175.6mA, which is much smaller than the threshold current of 217mA of the undoped quantum dot laser. Therefore, in the Si-doped InAs/GaAs quantum dot laser provided by the present invention, the electrons introduced by Si atoms can reduce the threshold current of the laser device and improve the performance of the device. Moreover, the lasing wavelength of the quantum dot laser can be adjusted by controlling the thickness of the first capping layer and the ratio of the third main group metal element in the first capping layer.

On the other hand, the slope efficiency dP/dI of the Si-doped quantum dot laser is about 0.34W/A, and the slope efficiency dP/dI of the undoped quantum dot laser is about 0.29W/A. The increase in slope efficiency is due to the fact that the introduction of Si atoms is beneficial to the passivation of the non-radiative recombination centers near the quantum dots, which improves the quality of the quantum dot materials.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the present invention. Within the spirit and principles of the present invention, any modifications, equivalent replacements, improvements, etc., shall be included in the protection scope of the present invention.

Claims (10)

1. a kind of Si adulterates InAs/GaAs quantum dot lasers, including substrate (10) and growth epitaxial layer thereon；

The bottom of the epitaxial layer include cushion (20), cushion (20) top under-clad layer (30) and under-clad layer (30) on The lower waveguide layer (40) in portion；

The top of the epitaxial layer includes upper ducting layer (60), the top covering (70) and top covering on upper ducting layer (60) top (70) ohmic contact layer (80) on top；

The middle part of the epitaxial layer includes quantum dot active region (50), and the quantum dot active region (50) includes the quantum dot of Si doping Layer (51), the first cover (52) on quantum dot layer (51) top and second cap rock on first cover (52) top of Si doping (53) periodic structure formed.

2. Si according to claim 1 adulterates InAs/GaAs quantum dot lasers, it is characterised in that the quantum of Si doping The material of main part of point layer (51) is InAs.

3. Si according to claim 1 adulterates InAs/GaAs quantum dot lasers, it is characterised in that the first cover (52) material is InGaAs or GaAs, and the material of second cap rock (53) is GaAs.

4. Si according to claim 1 adulterates InAs/GaAs quantum dot lasers, it is characterised in that the substrate (10), Cushion (20), lower waveguide layer (40), the material of main part of upper ducting layer (60) and ohmic contact layer (80) are GaAs；Its In, the substrate (10) and cushion (20) they are that n-type adulterates GaAs；The lower waveguide layer (40) and upper ducting layer (60) are pure GaAs；The ohmic contact layer (80) is that p-type adulterates GaAs.

5. Si according to claim 1 adulterates InAs/GaAs quantum dot lasers, it is characterised in that the under-clad layer (30) and the material of main part of top covering (70) is AlGaAs；Wherein described under-clad layer (30) is that n-type adulterates AlGaAs；On described Covering (70) is that p-type adulterates AlGaAs.

6. Si according to claim 1 adulterates InAs/GaAs quantum dot lasers, it is characterised in that：

The periodicity of the periodic structure is 1~20；

Its Quantum Dots Growth thickness of the quantum dot layer (51) of the Si doping is 0~10ML, and Si doping concentration is 1 × 10³~1 ×10²⁴cm^-3；

The growth thickness of the first cover (52) is 0~30nm；

The growth thickness of second cap rock (53) is 0~30nm.

7. a kind of preparation method of Si doping InAs/GaAs quantum dot lasers, it is characterised in that comprise the following steps：

Step 1：Take a substrate (10)；

Step 2：One layer of cushion (20) is grown on substrate (10)；

Step 3：Under-clad layer (30) is grown on cushion (20)；

Step 4：Lower waveguide layer (40) is grown on under-clad layer (30)；

Step 5：The growth quantum point active area (50) on lower waveguide layer (40), the quantum dot active region include the quantum of Si doping Point layer (51)；

Step 6：Upper ducting layer (60) is grown on quantum dot active region (50)；

Step 7：Top covering (70) is grown on upper ducting layer (60)；

Step 8：Ohmic contact layer (80) is grown on top covering (70).

8. the preparation method of Si doping InAs/GaAs quantum dot lasers according to claim 7, it is characterised in that institute Quantum dot layer (51), first cover (52), the second cap rock (53) that quantum dot active region (50) is adulterated by Si is stated to grow successively A cycle is formed, the periodicity is 1~20.

9. the preparation method of Si doping InAs/GaAs quantum dot lasers according to claim 8, it is characterised in that institute Quantum dot layer (51) its Quantum Dots Growth thickness for stating Si doping be 0~10ML, and Si doping concentration is 1 × 10³~1 × 10²⁴cm^-3。

10. the preparation method of Si doping InAs/GaAs quantum dot lasers according to claim 8, it is characterised in that institute The growth thickness for stating first cover (52) is 0~30nm；The growth thickness of second cap rock (53) is 0~30nm.