CN101540357B - Growth method for controlling nucleation of self-organization In-Ga-As quantum dots - Google Patents

Abstract

A growth method for controlling the nucleation of self-organized InGaAs quantum dots in the present invention is characterized in that it comprises the following steps: step 1: select a substrate; step 2: use molecular beam epitaxy or metal organic chemical vapor phase on the substrate The deposition method deposits a buffer layer to isolate impurities and dislocations in the substrate, and to make the growth surface smoother; step 3: deposit a stress relief layer on the buffer layer to relieve the buffer layer and InGaAs Strain between materials; step 4: sequentially deposit the first layer of InGaAs, ultra-thin AlAs and the second layer of InGaAs on the stress relief layer to form the InGaAs wetting layer and InGaAs Quantum dot layer to complete the preparation for growth.

Description

Growth method for controlling the nucleation of self-organized InGaAs quantum dots

technical field

The invention relates to a growth method for controlling the nucleation of self-organized indium gallium arsenic quantum dots. More precisely, an ultra-thin AlAs layer is introduced near the critical thickness of the InGaAs material from layer growth to island growth (2D-3D) transition during the growth of quantum dots to regulate the nucleation of quantum dots The growth method of the process.

Background technique

Because the confined electrons and photons in the nano-quantum structure present many physical connotations that are very different from those in the bulk material structure, and are very rich in new quantum phenomena and effects, this also provides new opportunities for the development of electronic and optoelectronic devices with new principles. Opportunities, such as the development of quantum wells, quantum wires and quantum dot lasers, modulators and detectors based on different application goals and working in different wavelength bands, etc., have many advantages due to their multi-dimensional limitations, such as quantum dot lasers have narrow emission Unique superior characteristics such as line width, high modulation frequency, high temperature stability and low threshold current density.

At present, new low-dimensional material growth technologies represented by molecular beam epitaxy and metal-organic chemical vapor deposition have made great progress, and a series of nanostructure materials have been successfully grown. After years of hard work, on the basis of these two technologies, a variety of preparation methods for semiconductor quantum dot materials have been developed, including "top-down", "bottom-up" and a combination of the two Preparation technology. Among them, the "top-down" method is to use electronic, ion or optical microfabrication technology to directly prepare quantum dots by etching. Although the size, shape and density of the quantum dots prepared by this method are controllable, the interface damage caused by processing and the impurity contamination introduced during the process make the related device performance far from the theoretical expectation. However, the combination of this method and the "bottom-up" method improves the performance of the device to a certain extent, but there is still a certain distance from the theoretical expectation. The "bottom-up" approach is also generally referred to as the self-organizing growth approach. This growth method uses the SK (Stranski-Krastanow) growth mode to grow quantum dots on a lattice-mismatched substrate. This kind of quantum dots has almost no dislocations and has good electrical and optical properties. However, the quantum dots grown by the self-organization method generally have a certain size distribution due to the randomness of the nucleation of quantum dots during the Sk transition (that is, from the layered growth mode to the island growth mode (2D-3D)), This results in a non-uniform broadening (20-100 meV) of the quantum dot spectrum. This size inhomogeneity effect destroys the excellent performance based on the unique zero-dimensional electronic energy state structure (delta function density of states) of quantum dots, so how to improve the uniformity of quantum dot size distribution has become one of the research hotspots in recent years. one.

In addition, low-density quantum dots can be used to prepare single-photon sources and single-electron devices, which has become one of the research hotspots in recent years. Single photon sources with photon energies around 1.3 μm and 1.5 μm (long wavelength) are especially widely used in the field of quantum communication. However, low growth rate, low arsenic pressure, and low growth temperature can achieve low-density quantum dots with room temperature fluorescence of about 1.3 μm, but the range of growth conditions is extremely narrow, and slight changes in growth conditions may lead to experimental failure.

The growth methods of InGaAs quantum dot samples grown based on the prior art are also mainly divided into two categories, please refer to the schematic diagrams of the structure A sample and the structure B sample of the prior art shown in Fig. 1 (a) and (b). The growth steps of the sample of structure A in the prior art are as follows: a buffer layer 20' is deposited on the substrate 10' by molecular beam epitaxy or metal-organic chemical vapor deposition; a stress relief layer 30 is deposited on the buffer layer 20' '; Deposit InGaAs material on the stress relief layer 30' to form the InGaAs wetting layer 40' and the InGaAs quantum dot layer 50'. The growth steps of the prior art structure B sample are similar to the steps in Figure 1(a), except that the step of depositing the stress relief layer 30' is missing, and it can be seen from Figure 1(a) and (b) that the quantum dot layer 50' are uneven bumps. When growing InGaAs quantum dots based on the prior art, by adjusting the growth conditions of quantum dots (such as growth temperature, growth rate and arsenic pressure, etc.) and growth structure (dot-in-well structure or stacked quantum dot structure, etc.) The size, shape, density and composition of quantum dots can be regulated within a certain range. For example, using the method of growth pause, the size self-limiting effect of quantum dots can be used to improve the uniformity of quantum dot size distribution; in addition, quantum dots with narrow spectrum can also be obtained by using a stacked quantum dot structure. However, the method of introducing an ultra-thin aluminum arsenide layer in the process of growing quantum dots provided in this paper (introducing an ultra-thin aluminum arsenide layer when the thickness of indium gallium arsenide is near the critical thickness of 2D-3D transition), utilizes The mobility of aluminum atoms is lower than that of gallium atoms and the addition of aluminum atoms to the surface of indium gallium arsenic will increase the surface energy of these two properties, so as to change the surface conditions of the growth front, making the transition from layered growth mode to island growth The mode (2D-3D) transition is advanced and promotes the uniform nucleation of 3D islands in the Al-rich region, thereby adjusting the nucleation density of quantum dots and improving the uniformity of quantum dot size distribution. In addition, because this method can control the preferential nucleation of 3D islands in the Al-rich region, it is possible to broaden the growth conditions of low-density quantum dots with room temperature fluorescence around 1.3 μm by controlling the additional parameter of the ultra-thin AlAs layer. Available range. The method has a novel idea, and the corresponding growth process is easy to grasp and optimize.

Contents of the invention

The object of the present invention is to provide a growth method for controlling the nucleation of self-organized indium gallium arsenic quantum dots, which can realize the growth of In _y Ga _{1-y As quantum dots on the growth front of In x Ga 1-x As .} The change of the nuclear mechanism (0≤x<y≤1) promotes the uniform nucleation of the quantum dots, thereby realizing the improvement of the size uniformity of the self-organized InGaAs quantum dots and the regulation of the nucleation density.

The technical solution of the invention is:

The invention provides a growth method for controlling the nucleation of self-organized InGaAs quantum dots, which is characterized in that it comprises the following steps:

Step 1: Select a substrate;

Step 2: Deposit a buffer layer on the substrate by molecular beam epitaxy or metal organic chemical vapor deposition to isolate impurities and dislocations in the substrate and make the growth surface smoother;

Step 3: Depositing a stress relief layer on the buffer layer to relieve the strain between the buffer layer and the InGaAs material;

Step 4: Deposit the first layer of InGaAs, ultra-thin AlAs and the second layer of InGaAs in sequence on the stress relief layer to form an InGaAs wetting layer and an InGaAs quantum dot layer to complete the growth preparation.

Wherein said substrate is gallium arsenide or indium phosphide or silicon substrate.

The chemical formula of the InGaAs layer described therein is In _x Ga _1-x As, where 0<x≤1.

The thickness of the sequentially deposited first layer of InGaAs described therein is approximately the same as the critical thickness for transitioning from layered growth mode to island growth mode when the InGaAs material is grown on the stress relief layer.

The thickness of the ultra-thin aluminum arsenide is less than 1ML.

The invention provides a growth method for controlling the nucleation of self-organized InGaAs quantum dots, which is characterized in that it comprises the following steps:

Step 1: Select a substrate;

Step 2: Deposit a buffer layer on the substrate by molecular beam epitaxy or metal organic chemical vapor deposition to isolate impurities and dislocations in the substrate and make the growth surface smoother;

Step 3: Deposit the first layer of InGaAs, ultra-thin AlAs and the second layer of InGaAs on the buffer layer in sequence to form an InGaAs wetting layer and an InGaAs quantum dot layer to complete the growth preparation .

The substrate mentioned therein is gallium arsenide or indium phosphide substrate.

The indium gallium arsenic mentioned therein has a chemical formula of In _x Ga _1-x As, where 0<x≤1.

The thickness of the sequentially deposited first layer of InGaAs described therein is approximately the same as the critical thickness for transitioning from layered growth mode to island growth mode when the InGaAs material is grown on the buffer layer.

The thickness of the ultra-thin aluminum arsenide is less than 1ML.

The significance that the present invention has:

The invention provides a new method for changing the nucleation mechanism of self-organized InGaAs quantum dots by introducing an ultra-thin aluminum arsenide layer, and provides a new method for controlling the size, shape and density of quantum dots. The adjustable parameters improve the uniformity of the size distribution of self-organized InGaAs, and widen the selectable range of growth conditions for achieving low-density quantum dots (room temperature fluorescence at about 1.3 μm).

Description of drawings

In order to further illustrate the specific technical content of the present invention, below in conjunction with embodiment and accompanying drawing detailed description as follows, wherein:

Fig. 1 (a) is the structural representation of prior art structure A sample; (b) is the structural representation of prior art structure B sample;

Fig. 2 is the structural representation of the sample of the first embodiment of the present invention;

Fig. 3 is the structural representation of the sample of the second embodiment of the present invention;

Fig. 4 (a) is the atomic force photograph (2 * 2 μ m ) of prior art structure A sample and corresponding height distribution histogram; (b) is the atomic force photograph (2 * 2 μ m ) of the sample of the first embodiment of the present invention and corresponding Height distribution histogram;

Fig. 5 (a) is the comparison of the size scale distribution (solid square) of the small quantum dot set in the prior art structure A sample with the theoretical scaling function f ₁ (u) (dotted line); (b) is the prior art sample B Comparison of the size scaling distribution (solid squares) of medium and large quantum point sets with the theoretical scaling function f ₃ (u) (dashed line);

Fig. 6 is the comparison of the size scale distribution (solid square) of all quantum dots in the present invention with the theoretical scale function f ₃ (u) (dotted line);

Fig. 7 is the low-temperature fluorescence spectrum (80K) of the sample of the second embodiment of the present invention, in which the dotted line represents the Gaussian fitting peak;

Fig. 8 is the low-temperature fluorescence spectrum (80K) of the structure B sample in the prior art, and the dotted line in the figure represents the Gaussian fitting peak.

Detailed ways

Please refer to FIG. 2 , which is the first embodiment of the present invention.

A growth method for controlling the nucleation of self-organized indium gallium arsenic quantum dots of the present invention comprises the following steps:

Step 1: Select a substrate 10, the substrate 10 is a gallium arsenide (001) substrate;

Step 2: grow a buffer layer 20 on the substrate 10 by molecular beam epitaxy. The growth of the sample in this example is carried out in Riber 32p molecular beam epitaxy equipment, and the buffer layer 20 is a gallium arsenide buffer layer with a thickness of 400nm. The growth temperature is 610°C, and the gallium arsenide buffer layer grown at high temperature can make the growth surface as smooth as possible, and can minimize the influence of impurities and dislocations in the substrate material on the photoelectric properties of the quantum dot layer;

Step 3: Deposit a stress relief layer 30 on the buffer layer 20, the stress relief layer 30 is a 2nm thick In _0.15 Ga _0.85 As stress relief layer, the growth temperature is lowered to 510°C, and the stress relief layer 30 is The growth of the subtractive layer can reduce the interchange between indium atoms and gallium atoms;

Step 4: On the stress buffer layer 30, deposit the first layer of InGaAs, ultra-thin AlAs and the second layer of InGaAs in sequence to form the InGaAs wetting layer 40 and the InGaAs quantum dot layer 50 , to complete the preparation for growth. The indium gallium arsenide is selected as indium arsenide (the chemical formula is In _x Ga _1-x As, x=0), and the thickness of the first layer of indium gallium arsenide deposited sequentially is 0.9ML, so The thickness of the ultra-thin AlAs described above is 0.02ML, the thickness of the second layer of InGaAs is 0.2ML, the growth temperature in this step is still 510°C, and the deposition rates of InGaAs and AlAs are both 0.01ML/s.

The growth of each step in this embodiment adopts As ₂ gas pressure, and keeps it at 3.6×10 ^-6 Torr.

For comparison, a prior art structure A sample (see FIG. 1(b)) similar to the sample structure of this embodiment was also grown, and the growth conditions of each step of the two samples were the same for comparison.

Before growing the sample, it has been determined in advance by the reflective high-energy electron diffraction device _{( RHEED} ) installed on the molecular beam epitaxy equipment. The critical thickness of 2D-3D transformation is between 0.9ML-1.0ML.

After the growth of the sample was completed, the substrate temperature was rapidly cooled to room temperature, and the sample was taken out for atomic force measurement. The results are shown in Figure 4.

According to Figure 4, it can be seen that the surface morphology of the two samples is very different. The surface quantum dots of the structure A sample in the prior art consist of two groups of quantum dots: one group is small quantum dots with a height of 0.9-3.5nm and a density of about 9.7×10 ⁹ cm ^-2 , and the other group is a group of small quantum dots with a height of 7-3.5 nm. 14nm large quantum dots, the density is about 5.3×10 ⁸ m ^-2 ; while the surface quantum dots of the sample of the first embodiment of the present invention only contain one mode, its density is about 5.5×10 ⁹ cm ^-2 , and the height distribution can be a Gaussian peak to fit.

The kinetic scaling theory was introduced to analyze the nucleation process of the two samples. According to the classical nucleation theory, if the size distribution of 3D islands obeys a certain scaling law, then

N(u)＝(θ/<s> ² )f(u)

where θ is the effective coverage of the epitaxial layer, u=s/<s>, <s> is the average size of 3D islands, N(u) is the number density of 3D islands with size s, f(u) is A scaling function that only depends on the size of u. When u=1, f(u) reaches its maximum value. Kinetic scaling theory was initially used to describe the nucleation process of 2D islands and was confirmed in theoretical simulations in homoepitaxial and heteroepitaxial as well as experimental studies. The size of the critical nucleation number i can be obtained by comparing the size distribution of the quantum dots measured experimentally with the theoretical function. In addition, it is deduced that when $i\&Greater\; Equal;1:f_i\left(u\right)=C_i{u}^i{e}^{-i{a}_i{\mathrm{<figure-callout\; id="1"\; label="u"\; filenames="S2008101021989E00022.png"\; state="\{\{state\}\}">u</figure-callout>}}^{1/a_i}},$ where C _i and a _i are constants. At the same time, some people applied this method to the analysis of 3D island growth of semiconductor heterojunction, and believed that s is the volume of 3D island.

Figure 5(a) and (b) show the size scale distributions of small quantum dots and large quantum dots in the structure A sample of the prior art, respectively. At the maximum value of the size scale distribution of the small quantum dot, u<1, its shape is between the scale function of i=0 and i=1. The critical nucleation number i=0 for a system means that In atoms nucleate spontaneously as soon as they are deposited on the growth surface. Such behavior may be due to the presence of defects in the growth surface, such as steps, etc. However, the size scale distribution of large quantum dots in the structure A sample of the prior art is completely different from that of small quantum dots, and its shape is close to the theoretical function f ₃ (u). The difference in the size scale distribution of large and small quantum dots indicates that the two are at different stages of evolutionary development and simultaneous nucleation is unlikely.

The size scale distribution of the quantum dots in the sample of the first embodiment of the present invention is provided in Fig. 4, and its shape is also a function of class i=3, which shows that all the quantum dots in the sample of the first embodiment of the present invention are at the same An evolutionary stage, possibly simultaneous nucleation.

The difference between the atomic force morphology and the scale distribution of the quantum dots in the prior art structure A sample and the first embodiment sample of the present invention shows that the ultra-thin aluminum arsenide does change the self-organized indium gallium arsenide quantum dots The nucleation process in the initial stage of 2D-3D transformation changes the nucleation density of quantum dots, promotes uniform nucleation of quantum dots, and improves the uniformity of quantum dot size distribution.

Please refer to FIG. 3 , which is a second embodiment of the present invention (wherein the same parts of the second embodiment and the first embodiment use the same reference numerals).

A growth method for controlling the nucleation of self-organized indium gallium arsenic quantum dots of the present invention comprises the following steps:

Step 1: Select a substrate 10, the substrate 10 is a gallium arsenide (001) substrate;

Step 2: On the substrate 10, a buffer layer 20 is deposited by molecular beam epitaxy. The growth of the sample in this example is carried out in a Riber 32p molecular beam epitaxy device. The buffer layer 20 is a gallium arsenide buffer layer with a thickness of 400nm. The growth temperature is 610°C, and the gallium arsenide buffer layer grown at high temperature can make the growth surface as smooth as possible, and can minimize the influence of impurities and dislocations in the substrate material on the photoelectric properties of the quantum dot layer;

Step 3: sequentially depositing a first layer of InGaAs, an ultra-thin AlAs and a second layer of InGaAs on the buffer layer 20 to form the InGaAs wetting layer 40 and the InGaAs quantum dot layer 50 . The indium gallium arsenide is selected as indium arsenide (the chemical formula is In _x Ga _1-x As, x=0), and the thickness of the first layer of indium gallium arsenide deposited sequentially is 1.6ML, so The thickness of the ultra-thin AlAs described above is 0.02ML, the thickness of the second layer of InGaAs is 0.3ML. The growth temperature in this step is still 490°C, and the deposition rate of InGaAs is 0.00375ML/s. The aluminum deposition rate is 0.01ML/s.

After completing the growth in step 3, a 5nm-thick In _0.15 Ga _0.85 As and a 10nm-thick GaAs low-temperature cap layer were grown sequentially at a growth temperature of 490°C, and then the temperature was raised to 610°C to continue to grow 240nm of arsenic GaN high-temperature spacer layer to complete the sample preparation. The purpose of this step of growth is to make the sample more conducive to the study of the optical properties of the quantum dots of the present invention.

The growth of each step in this embodiment adopts As ₂ gas pressure, except that the As ₂ gas pressure in step 3 is kept at 0.9×10 ^-6 Torr, and the other steps are kept at about 4×10 ^-6 Torr.

For comparison, a prior art structure B sample similar to the sample structure of this embodiment was also grown (see FIG. 1(b)), and the growth conditions of each step of the two samples were the same for comparison.

While growing the sample, observe the reflective high-energy electron diffraction device (RHEED) installed on the molecular beam epitaxy equipment, and know the critical thickness of the 2D-3D transition of the indium arsenide material on the gallium arsenide when the substrate temperature is 490°C Slightly larger than 1.6ML.

After the sample growth was completed, the substrate temperature was rapidly cooled to room temperature, and the sample was taken out for plane transmission electron microscopy and low-temperature photoluminescence measurement (80K).

In this embodiment, the growth of the InGaAs wetting layer 40 and the InGaAs quantum dot layer 50 adopts the conditions of low growth temperature, low growth rate and low arsenic pressure. The role of nuclear growth methods in growing long-wavelength low-density quantum dots.

After the plane transmission electron microscope test was carried out on the sample, it was found that the areal density of the quantum dots in the sample of the second embodiment of the present invention was about 5×10 ⁹ cm ^-2 , while the areal density of the quantum dots in the sample of structure B of the prior art was about 1.5× 10 ¹⁰ cm ^-2 . It can be seen that the density of the latter is about three times that of the former, and the introduction of ultra-thin aluminum arsenide effectively reduces the areal density of quantum dots.

Fig. 7 shows the low-temperature fluorescence spectrum (80K, excitation power is 10mW) of the sample of the second embodiment of the present invention, through Gaussian fitting, it is found that the spectrum comprises E0 (peak position=1.26 μm, full width at half maximum=28meV) and E1 (peak Bit=1.18μm) two peaks, by comparing with the spectrum under high excitation power, it is found that E0 is the quantum dot ground state light emission, and E1 is the quantum dot excited state light emission, which shows that there are only single-mode distribution quantum dots in the sample of the second embodiment .

Fig. 8 has provided the low-temperature fluorescence spectrum (80K, excitation power is 10mW) of prior art structure B sample, finds through Gaussian fitting, spectrum comprises E0 (peak position=1.27 μ m, full width at half maximum=29meV), E`0 (peak position=1.16μm, full width at half maximum=17meV), E1 (peak position=1.19μm) and E`1 (peak position=1.16μm) two peaks, by comparing with the spectrum under high excitation power, it is found that E0 and E`0 is the ground state luminescence of two quantum dot sets in the sample respectively, and E1 and E`1 are the excited state luminescence of the two quantum dot sets in the sample respectively, which shows that the distribution of quantum dots in the prior art structure B sample is double Die.

After the above analysis, it can be shown that the introduction of ultra-thin aluminum arsenide does effectively reduce the surface density of quantum dots and improve the uniformity of quantum dot size distribution, which is conducive to the realization of long-wavelength and low-density quantum dots.

While the present invention has been described in detail with reference to the foregoing embodiments, it is to be understood that the invention is not limited to the disclosed embodiments and that various changes in form and details will occur to those skilled in the art. The present invention is intended to cover modifications within the spirit and scope of the appended claims.

Claims (8)

1. A growth method for controlling the nucleation of self-organized indium gallium arsenic quantum dots, characterized in that, comprising the steps: Step 1: Select a substrate; Step 2: Deposit a buffer layer on the substrate by molecular beam epitaxy or metal organic chemical vapor deposition to isolate impurities and dislocations in the substrate and make the growth surface smoother; Step 3: Depositing a stress relief layer on the buffer layer to relieve the strain between the buffer layer and the InGaAs material; Step 4: Deposit the first layer of InGaAs, the ultra-thin AlAs with a thickness of less than 1ML, and the second layer of InGaAs on the stress relief layer in sequence to form the InGaAs wetting layer and the InGaAs quantum dots layer to complete the preparation for growth. 2. The growth method for controlling the nucleation of self-organized InGaAs quantum dots according to claim 1, wherein the substrate is GaAs or InP or Si substrate. 3. The growth method for controlling the nucleation of self-organized InGaAs quantum dots according to claim 1, wherein the chemical formula of the InGaAs layer is In _x Ga _1-x As, where 0<x ≤1. 4. The growth method for controlling the nucleation of self-organized InGaAs quantum dots according to claim 1, wherein the thickness of the first layer of InGaAs deposited sequentially is not the same as the growth rate of the InGaAs material. The critical thickness for transition from layered growth mode to island growth mode is about the same on the stress relief layer. 5. A growth method for controlling the nucleation of self-organized indium gallium arsenic quantum dots, characterized in that it comprises the following steps: Step 1: Select a substrate; Step 2: Deposit a buffer layer on the substrate by molecular beam epitaxy or metal organic chemical vapor deposition to isolate impurities and dislocations in the substrate and make the growth surface smoother; Step 3: Deposit the first layer of InGaAs, the ultra-thin aluminum arsenide with a thickness less than 1ML, and the second layer of InGaAs on the buffer layer in sequence to form an InGaAs wetting layer and an InGaAs quantum dot layer, Complete the preparation for outgrowth. 6 . The growth method for controlling the nucleation of self-organized InGaAs quantum dots according to claim 5 , wherein the substrate is a gallium arsenide or indium phosphide substrate. 7. The growth method for controlling the nucleation of self-organized InGaAs quantum dots according to claim 5, wherein said InGaAs has a chemical formula of In _x Ga _1-x As, where 0<x ≤1. 8. The growth method for controlling the nucleation of self-organized InGaAs quantum dots according to claim 5, wherein the thickness of the first layer of InGaAs deposited sequentially is not the same as the growth rate of the InGaAs material. The critical thickness for transition from layered to island growth mode is approximately the same when on the buffer layer.

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