A patterned controllable droplet epitaxy method for semiconductor molecular beam epitaxy

Abstract

The present invention belongs to the field of semiconductor technology and relates to a patterned controllable droplet epitaxy method for semiconductor molecular beam epitaxy. The method comprises the following steps: maintaining the temperature of the substrate below the melting point of the target droplet material; depositing the target droplet material on the surface of the substrate to form a metal coating layer, the deposition thickness of which is higher than the critical thickness of the target droplet material when normally forming droplets; in-situ introducing laser interference pulse irradiation to act on the metal coating layer to achieve the patterned orderly construction of the target droplets. The method of the present invention can realize the patterned preparation of group III element droplets. The principle and implementation process of the method are fully compatible with the traditional droplet epitaxy process, there is no risk of introducing any material defects, and there is no selection of substrate types, thereby solving the problems commonly existing in the current existing patterning technology, including potential damage to the quality of the material crystal, poor consistency of the droplet composition, and the type of droplets being directly limited by the selected substrate.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor technology and relates to a patterned controllable droplet epitaxy method, in particular to a patterned controllable droplet epitaxy method for semiconductor molecular beam epitaxy. Background Art

[0002] Semiconductor technology is a crucial enabler of continuous progress in our current economy, society, national defense, and scientific research. Therefore, technological innovation related to semiconductors is crucial to the economic and technological development of a nation. Since its invention, molecular beam epitaxy (MBE), a key method for growing semiconductor materials and quantum structures, has significantly boosted the development of the semiconductor industry. In particular, high-quality quantum structures fabricated using this technology have led to the successful fabrication and development of various semiconductor devices for optoelectronics, optomagnetic systems, microelectronics, and logic computing.

[0003] Among them, the droplet epitaxy technology developed based on molecular beam epitaxy has always attracted much attention due to its ability to flexibly prepare various quantum structures including quantum dots, quantum rings, nanowires, concentric rings and quantum dot pairs. The process of this technology can be simply summarized into two steps: 1. In the absence of an atmosphere of group V elements (N, P, As, Sb), a certain thickness of group III elements (Ga, In) is deposited to form metal droplets on the surface of the substrate; 2. These pre-formed droplets are used as crystallization nuclei to subsequently start group V crystallization or induce the growth of various quantum structures. It can be seen that the position of the droplet formation in the first step determines the position of the subsequent quantum structure. However, the existing conventional molecular beam epitaxy process of obtaining droplets is a uniform deposition process, and the position of the droplet formation is a thermodynamically random process, which cannot achieve effective control of its position.

[0004] However, with the continuous development of semiconductor quantum information technology, more and more application scenarios (single-photon sources, quantum bits, intermediate-band solar cells) have put forward strong requirements for the orderly construction of quantum structure positions. Therefore, for droplet epitaxy technology, the realization of patterned and controllable droplet preparation is extremely important. To date, attempts to achieve ordered droplets have involved using high-energy lasers or ion beams to ablate and heat the substrate surface, causing the group V elements in the substrate to decompose and leave behind the group III metals. However, this approach has several limitations: First, the ablation process inevitably damages the underlying substrate lattice, introducing defects that degrade the crystal quality of the resulting quantum structure after subsequent crystallization. Second, the droplets formed after ablation are not guaranteed to be pure group III elements and may contain random contaminants of V that have not yet completely dissociated. The degree and distribution of this residual group V contaminant in the droplets are random and lack consistent stability, potentially compromising the controllability of subsequent quantum structure crystallization. Furthermore, a significant limitation is that this method can only produce droplets of the same group III element as the substrate. This means that GaAs substrates can only be ablated to form Ga droplets, not In droplets. In practical applications, heteroepitaxial growth is often required. Therefore, developing a process for safely and efficiently patterning droplets that is compatible with conventional molecular beam epitaxy (MBE) droplet formation, independent of substrate material, is of paramount importance. Summary of the Invention

[0005] The present invention aims to solve the above problems and provides a patterned controllable droplet epitaxy method for semiconductor molecular beam epitaxy, which can realize the patterned preparation of group III element droplets. The principle and implementation process of this method are fully compatible with the traditional droplet epitaxy process, there is no risk of introducing any material defects, and there is no selection for substrate type, thereby solving the problems commonly existing in current existing patterning technologies, including potential damage to material crystal quality, poor consistency of droplet composition, and the type of droplets being directly limited by the selected substrate.

[0006] According to the technical solution of the present invention, the patterned controllable droplet epitaxy method includes the following steps:

[0007] S1: maintaining the temperature of the substrate below the melting point of the target droplet material, wherein the target droplet material is a Group III metal material;

[0008] S2: depositing the target droplet material on the substrate surface to form a metal coating layer, wherein the deposition thickness is higher than the critical thickness of the target droplet material when the droplet is normally formed;

[0009] S3: In situ introduction of laser interference pulse irradiation to act on the metal coating layer to achieve the graphical and orderly construction of target droplets.

[0010] Specifically, the patterned controllable droplet epitaxy method can be performed in a molecular beam epitaxy system.

[0011] Furthermore, the substrate is selected from one or more of GaAs, InP, GaN, AlAs, Si and Ge.

[0012] Furthermore, in step S1, the temperature T of the substrate is maintained at 5-10° C. lower than the melting point of the target droplet material.

[0013] Furthermore, the target droplet material is a single substance or an alloy. Specifically, the single substance may be In, Ga, etc., and the alloy may be an In-Ga alloy, etc.

[0014] Furthermore, in step S2, the deposition thickness is 1-3 atomic layers higher than the critical thickness of the target droplet material when the droplet is normally formed.

[0015] Furthermore, in step S3, laser interference pulse irradiation is introduced in situ to act on the metal coating layer, so that the temperature of the interference enhancement zone is higher than the melting point of the target droplet material, the temperature of the interference destructive zone is lower than the melting point of the target droplet material, and the transient average temperature before the energy of the laser interference pulse irradiation is completely dissipated is higher than the melting point of the target droplet material.

[0016] Furthermore, in step S3, the pulse width of the laser interference pulse is 5-50 ns, the polarization mode is S wave, and the energy is 10-40 mJ.

[0017] The technical solution of the present invention has the following advantages over the existing technology: the method of the present invention does not impose any restrictions on the required substrate, which fundamentally ensures that the method can be applied to all semiconductor material systems and provides the possibility for the free construction of various quantum structures; secondly, the entire implementation process can be implemented in situ in the molecular beam epitaxy equipment. Compared with the traditional droplet epitaxy technology, only one pulse interference exposure is added in the process, and the entire process takes only a few seconds. Obviously, it has the same high efficiency as the current molecular beam droplet epitaxy technology; in addition, since the substrate temperature during droplet preparation is designed to be below the melting point of the droplet metal, which is far lower than the growth temperature of the substrate material during thermodynamic epitaxy, the substrate material is in a very stable state. In addition, the laser only heats the thin layer of group III metal deposited on the surface, so the risk of damaging the underlying substrate material is extremely low. In summary, the above three points can prove that the method of the present invention is fully compatible with traditional droplet epitaxy technology and can safely and efficiently realize the patterned construction of droplets, which is bound to provide a key technology for the development and industrialization of new semiconductor quantum devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the process and principle of the method of the present invention.

[0019] Figure 2 This is an atomic force scanning image of the material obtained in Example 1.

[0020] Figure 3 This is an atomic force scanning image of the material obtained in Example 2.

[0021] Figure 4 This is an atomic force scanning image of the material obtained in Example 3. DETAILED DESCRIPTION

[0022] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0023] According to the principle of the current traditional droplet epitaxy technology, when preparing droplets, the temperature of the substrate is generally set to several hundred degrees (this temperature is much higher than the melting point of the corresponding group III metal material, such as the melting point of Ga is only 29.76℃, and the melting point of In is only 156.6℃). Then, in an atmosphere without group V elements, as long as a certain amount of group III metal elements is continuously deposited, when the thickness is higher than a certain critical thickness L C (Generally, in a few to a dozen atomic layers) under the action of surface energy and tension, the original two-dimensional film will self-organize and condense to form randomly distributed metal droplets (granular).

[0024] The present invention provides a patterned controllable droplet epitaxy method for semiconductor molecular beam epitaxy, such as Figure 1 As shown, the following steps are included:

[0025] First, if Figure 1 As shown in (a): Select any substrate A (such as GaAs, InP, GaN, AlAs, Si, Ge, etc.) and set the substrate temperature to T (i.e., the original substrate surface temperature curve T is distributed in a straight line). Unlike the traditional process, the setting value of T should be lower than the melting point T of the target droplet material B to be prepared (the target droplet material B is a Group III metal material, which can be a single substance or an alloy, such as In, Ga, or an In-Ga alloy, etc., referred to as B or metal B). m (Specifically, it can be about 5-10 ° C lower), and then, in the absence of group V elements, a layer of target droplet material B with a thickness of L is deposited. The thickness L is greater than the critical thickness L when the target droplet material B normally forms a droplet. C The substrate temperature is lower than the melting point of the target droplet material B (T <T m), so the target droplet material B is not in a flowing molten state, but a stable solid state. Therefore, even if the thickness L is higher than L C , and it cannot spontaneously condense to form droplets, but remains a metal coating layer (B film).

[0026] Then, if Figure 1 As shown in (b), when the laser interference pulse is introduced in situ to irradiate the surface of film B, due to the photothermal effect, the surface temperature distribution curve (T1) at the moment of the pulse action will change from the original uniform straight line distribution (T) to the laser interference pattern distribution curve (T1). m 5-10℃ smaller, so T1 in the interference enhancement region will be instantaneously higher than T m , the B film in this area becomes molten, and L>L C Therefore, the melting zone will quickly form droplets; while the temperature of the interference destructive zone is still maintained at the melting point (T m ) below and avoid the formation of droplets, so on the microscopic time scale, the laser interference enhancement area will advantageously form droplets in advance.

[0027] On this basis, if Figure 1 As shown in (c), due to the existence of lateral heat conduction, the original patterned temperature curve will be re-uniformed. This process can be understood as evenly distributing the photothermal effect to all parts of the surface. Before the laser injection energy is completely dissipated, a transient T2 temperature field will be formed on the surface, while T2 is still higher than T m At this time, the B thin layer that was previously in the interference destructive zone also began to melt. However, since the droplet nucleus has been formed in the interference enhancement zone next to it, these existing droplets will absorb and gather the molten atoms in the destructive zone on both sides in real time. With this continuous transport of B atoms in the interference destructive zone to the droplets in the interference enhancement zone, it will result in the equivalent thickness of the B thin layer in this area (interference destructive zone) L t Less than L C , completely preventing the subsequent formation of droplets, thus ultimately achieving stable graphical and orderly construction of droplets.

[0028] The method of the present invention has no special requirements for the wavelength of the pulsed laser used, as long as it can be absorbed by the target droplet material B. The pulse width is preferably 5-50ns, the polarization mode is preferably S wave, and the energy range is preferably 10-40mJ.

[0029] Example 1

[0030] In the molecular beam epitaxy system, the GaN substrate temperature was set to 24 ° C, and then the Ga shutter was opened to deposit a 6-atomic-layer-thick Ga atomic metal layer (larger than the L-thick Ga droplet). CThickness 1ML), then introduce a double beam pulse laser exposure with energy of 20mJ in situ, the laser wavelength is 532nm, polarization is S wave, the pulse width is about 10ns, then take out the sample, the atomic force test results are as follows Figure 2 As shown, orderly arranged Ga droplets can be seen.

[0031] Example 2

[0032] In the molecular beam epitaxy system, the GaAs substrate temperature was set to 20°C, and then a Ga shutter was opened to deposit a 7-atomic-layer-thick Ga atomic metal layer (larger than the L-thick Ga droplet). C Thickness 2ML), then introduce a double beam pulse laser exposure with energy of 35mJ in situ, the laser wavelength is 532nm, polarization is S wave, the pulse width is about 10ns, then take out the sample, the atomic force test results are as follows Figure 3 As shown, orderly arranged Ga droplets can be seen.

[0033] Example 3

[0034] In the molecular beam epitaxy system, the GaAs substrate temperature is set to 165 degrees, and then the In shutter is opened to deposit a 10-atomic-layer-thick In atomic metal layer ((L than the In droplet formation) C Thickness 1.5ML)), then introduce a double-beam pulse laser exposure with an energy of 30mJ in situ, the laser wavelength is 532nm, the polarization is S wave, the pulse width is about 10ns, and then take out the sample, the atomic force test results are as follows Figure 4 As shown, orderly arranged In droplets can be seen.

[0035] In summary, the method of the present invention can realize the graphical preparation of group III element droplets, which can ensure the consistency of the droplet composition. At the same time, the type of prepared droplets will not be limited by the selected substrate, and will not cause damage to the material crystal quality, and has good application prospects.

[0036] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A patterned controllable droplet epitaxy method for semiconductor molecular beam epitaxy, characterized in that: The following steps are included: S1: maintaining the temperature of the substrate at 5-10° C. lower than the melting point of the target droplet material, wherein the target droplet material is a Group III metal material; S2: depositing the target droplet material on the substrate surface to form a metal coating layer, the deposition thickness of which is 1-3 atomic layers higher than the critical thickness of the target droplet material when normally forming droplets; S3: In-situ introduction of laser interference pulse irradiation to act on the metal coating layer to achieve patterned and orderly construction of target droplets; wherein, in-situ laser interference pulse irradiation is introduced to act on the metal coating layer so that the temperature of the interference enhancement area is higher than the melting point of the target droplet material, and the temperature of the interference destructive area is lower than the melting point of the target droplet material; The pulse width of the laser interference pulse is 5-50ns, the energy is 10-40mJ, and the polarization mode is S wave.

2. The patterned controllable droplet epitaxy method according to claim 1, wherein: The substrate is selected from one or more of GaAs, InP, GaN, AlAs, Si and Ge.

3. The patterned controllable droplet epitaxy method according to claim 1, wherein: The target droplet material is a single substance or an alloy.

4. The patterned controllable droplet epitaxy method according to claim 3, wherein: The target droplet material is In, Ga or In-Ga alloy.

5. The patterned controllable droplet epitaxy method according to claim 1, wherein: In step S3, after the laser interference pulse irradiation is introduced in situ to act on the metal coating layer, the transient average temperature before the energy of the laser interference pulse irradiation is completely dissipated is higher than the melting point of the target droplet material.

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