Hydride vapor phase epitaxy using a solid germanium source

Abstract

Described herein are systems and methods which utilize solid, elemental germanium as a source for hydride vapor phase epitaxy (HVPE). These systems and methods may reduce costs by simplifying the growth process and reactor design and eliminate the need for expensive Ge gas precursors. Additionally, the described process may be useful as a way to recycle Ge, as Ge scarcity is a potential concern.

Description

HYDRIDE VAPOR PHASE EPITAXY USING A SOLID GERMANIUM SOURCECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. Provisional Patent Application No. 63 / 695,115, filed on September 16, 2024, the contents of which are incorporated herein by reference in their entirety.CONTRACTUAL ORIGIN

[0002] This invention was made with government support under Contract No. DE-AC36- 08G028308 awarded by the Department of Energy. The government has certain rights in the invention.SUMMARY

[0003] Described herein are systems and methods which utilize solid, elemental germanium as a source for hydride vapor phase epitaxy (HVPE). These systems and methods may reduce costs by simplifying the growth process and reactor design and eliminate the need for expensive Ge gas precursors. Additionally, the described process may be useful as a way to recycle Ge, as Ge scarcity is a potential concern.

[0004] Germanium growth through halide vapor phase epitaxy has been documented since the 1960s, Previous studies have predominantly relied on gaseous germanium, specifically germanium tetrachloride (GeCL) and germane (GeEL), as sources for epitaxial growth. As described herein, elemental germanium is used as the source for germanium epitaxy. Hydrogen chloride (HC1) is employed to create volatile Ge chlorides that transport to the substrate for growth. This step is more efficient under a nitrogen ambient, but this alone does not lead to Ge epitaxy. An additional molecule is necessary to effectively deposit germanium on the substrate, so hydrides, for example, arsine (AsHs), phosphine (PH3), and / or hydrogen selenium (H2Se) are used as assisting agents. These hydrides provide active hydrogen at the substrate surface which reduces the Ge chlorides allowing for the Ge to incorporate into the growth layer. It is noted that H2 does not lead to substrate growth.

[0005] In an aspect, provided is a method comprising: a) providing a solid germanium source; b) reacting the solid germanium source with an acid; c) flowing a hydrogen source over a surface of the germanium source, thereby generating a germanium-containing gas; and d) depositing the germanium containing gas on a substrate via hydride vapor phase epitaxy.

[0006] In an aspect, provided is a method comprising: a) providing a solid elemental germanium source; b) reacting the solid germanium source with HC1; c) flowing arsine, phosphine, hydrogen selenium or a combination thereof over a surface of the germanium source, thereby generating a GeCh gas; and d) depositing the germanium containing gas on a substrate via hydride vapor phase epitaxy.

[0007] In an aspect, provided is a system or reactor for performing any of the methods described herein, for example, as shown in Fig. 1.

[0008] For example, the acid may comprise HC1, the germanium-containing gas may comprise GeCh, the germanium source may comprise elemental germanium, and the hydrogen source may comprise arsine, phosphine, hydrogen selenium, or a combination thereof.

[0009] The methods may be performed in the presence of an inert gas, such as a carrier gas, including nitrogen, helium or argon.

[0010] The germanium source may be provided at a reaction temperature of about 800 °C or a temperature selected from the range of 600 °C to 850 °C, 700 °C to 850 °C or 700 °C to 800 °C. The substrate may be provided at a temperature of about 600 °C or a temperature selected from the range of 500 °C to 850 °C, 600 °C to 800 °C or 700 °C to 800 °C. The method or reactor pressure may be selected from the range of 50 torr to 500 torr, 150 torr to 550 torr, 200 torr to 500 torr or 300 to 400 torr.

[0011] The flow rates of the acid or the hydrogen source may be less than or equal to 10 seem, 9 seem, 8 seem, 7 seem, 6 seem, 5 seem or 4 seem.BRIEF DESCRIPTION OF DRAWINGS

[0012] Some embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than limiting.

[0013] Figure 1 illustrates an example of a single chamber halide vapor phase epitaxy utilizing a solid germanium source.

[0014] Figure 2A charts an equilibrium mole fraction simulation of different species in the vapor inside the reactor chamber for difference source temperatures under H2 and N2 carrier flows. Figure 2B provides an equilibrium mole fraction simulation of HC1 and GeCh showing their dependence on H2 concentration.

[0015] Figure 3 A provides the growth rate of varying HC1 flow to Ge and hydride flow. Figures 3B-3D provide AFM surface images of Ge grown under an HC1 flow of 5 seem and AsFb flows of 4 seem (Figure 3B), 8 seem (Figure 3C) and 12 seem (Figure 3D) presenting a surface roughness of 2.3 nm, 3.8 nm and 27 nm, respectively.

[0016] Figure 4 provides the doping levels of As by the depth profile by different HC1 on Ge and ASH3flow measure by SIMS.

[0017] Figure 5 A provides measured Ge growth rates for different growth temperatures. Figure 5B shows a simulation of Ge growth rates for different growth temperatures.

[0018] Figure 6A shows Ge growth rates under varying the chamber pressures from 50 torr to 500 torr. Figures 6B-6E show AFM images of grown Ge surfaces at pressures of 50 torr (Figure 6B), 200 torr (Figure 6C), 350 torr (Figure 6D) and 500 torr (Figure 6E).

[0019] Figure 7 illustrates the growth rates of germanium at different AsH3 flow rates. Notably, there is no observable growth at 0 seem of AsH3, emphasizing the need for a hydride helper molecule in the germanium growth process. The black curve, illustrating the use of PH3 instead of AsH3 follows a similar trend, reinforcing the importance of a hydride helper molecule for germanium growth.

[0020] Figure 8 provides a photograph of the fragmented germanium substrates inside the hydride vapor phase epitaxy reactor boat. Hydrogen chloride is injected into the reactor boat to etch germanium and create volatile Ge chlorides, while hydrogen is utilized to transport the liberated germanium into the reactor growth chamber.DETAILED DESCRIPTION

[0021] The embodiments described herein should not necessarily be construed as limited to addressing any of the particular problems or deficiencies discussed herein. References in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, “some embodiments”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0022] As used herein the term “substantially” is used to indicate that exact values are not necessarily attainable. By way of example, one of ordinary skill in the art will understand that in some chemical reactions 100% conversion of a reactant is possible, yet unlikely. Most of a reactant may be converted to a product and conversion of the reactant may asymptotically approach 100% conversion. So, although from a practical perspective 100% of the reactant is converted, from a technical perspective, a small and sometimes difficult to define amount remains. For this example of a chemical reactant, that amount may be relatively easily defined by the detection limits of the instrument used to test for it. However, in many cases, this amount may not be easily defined, hence the use of the term “substantially”. In some embodiments of the present invention, the term “substantially” is defined as approaching a specific numeric value or target to within 20%, 15%, 10%, 5%, or within 1% of the value or target. In further embodiments of the present invention, the term “substantially” is defined as approaching a specific numeric value or target to within 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, or 0.1% of the value or target.

[0023] As used herein, the term “about” is used to indicate that exact values are not necessarily attainable. Therefore, the term “about” is used to indicate this uncertainty limit. In some embodiments of the present invention, the term “about” is used to indicate an uncertainty limit of less than or equal to ±20%, ±15%, ±10%, ±5%, or ±1% of a specific numeric value or target. In some embodiments of the present invention, the term “about” is used to indicate an uncertainty limit of less than or equal to ±1%, ±0.9%, ±0.8%, ±0.7%, ±0.6%, ±0.5%, ±0.4%, ±0.3%, ±0.2%, or ±0.1% of a specific numeric value or target.

[0024] Halide vapor phase epitaxy (HVPE) shows promise for III-V device manufacturing because of its potentially lower costs and significantly faster growth rates compared to other growth methods. HVPE is known for using elemental sources as precursors, like gallium and indium, instead of more complex and expensive precursors. Germanium (Ge) is one useful semiconductor material that is typically grown using germanium tetrachloride (GeCh) or germane (GeH4) but has not been grown using an in-situ elemental Ge source. This would be a useful advancement for HVPE growth toward the development of, for example, an epitaxial bottom junction of an inverted triple junction solar cell, which helps enable substrate reuse, or as a sacrificial layer for epitaxial lift off. We also note that recycled Ge substrates can be used as source material, potentially mitigating use of this critical material. Therefore, we developed and sought to understand the growth of Ge from an elemental Ge source by HVPE. We used elemental Ge as source material for Ge growth, flowing anhydrous HC1 over Ge metal to forma volatile chloride, as is done for Ga and In in HVPE. Here, we show that it is possible to grow Ge using a N2 ambient at the Ge source to promote GeCh formation while separately providing a source of hydrogen at the substrate to encourage Ge deposition. We utilized arsine and phosphine gases as convenient sources of reactive hydrogen available in most III-V growth systems to prove the concept because our reactor cannot flow both N2 and H2 at the same time without significant modifications. Ge growths were performed at 350 Torr (-46.66 kPa) and at 800 °C, using elemental Ge, also held at 800 °C, in a N2 ambient. We intentionally supplied ASH3and PH3 to the growth to promote Ge deposition. We observed no Ge growth unless a supply of hydrogen was added to the system, consistent with the thermodynamic calculations described above. Ge growth from a chloride likely features a kinetic barrier similar to that observed for GaAs growth, namely the saturation of the surface with Cl atoms. Hydrogen from pyrolyzed hydrides reduces this surface chlorine, which forms HC1 and desorbs, opening surface sites for the continued deposition of Ge. We observed that by increasing the hydride flow and the Ge flow we can increase the growth rate up to a certain point for each flow combination before it starts to decrease. We attribute this growth rate decrease to surface etching, which was observed using atomic force microscopy of the Ge surface after growth, potentially caused by the same hydride source that contributes to growth. We also observed As or P concentrations in the Ge films, using secondary ion mass spectrometry, in the range of 3xl017- IxlO18atoms / cm3, which can drastically influence device characteristics. We note, however, that upon modifications to our system we were able to inject H2 gas directly toward the substrate, while still using the N2 ambient, and observe similar Ge growth rates without the group V contamination. This allows for the deposition of high-quality Ge for optoelectronic devices from an elemental source.Introduction

[0025] Halide Vapor Phase Epitaxy (HVPE) can potentially lower the cost of epitaxial III-V device manufacturing because of its potentially lower costs and by having a significantly faster growth rate when compared to the most common methods of III-V growth, metalorganic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE). HVPE is known for high growth rates, leading to high production throughput and the use of lower cost elemental precursors. The HVPE process uses elemental sources as precursors, like gallium and indium, instead of more complex and expensive precursors like trimethylgallium and trimethylindium which are widely used in other growth techniques. In HVPE, the elemental sources are converted to volatile chlorides by reacting them in situ with anhydrous HC1 to form the growth species.

[0026] Germanium (Ge) is a well-known semiconductor material that has been used for many applications for decades and it is typically deposited with a few different gaseous precursors, including germanium tetrachloride (GeCh) and germane (GeEh). ). The growth process using these gaseous sources can be complex. Focusing on growth from the chloride molecule, Ishii and Takahashi found that chemical vapor deposition using GeCh carried by H2 using growth temperatures from 490-565 °C led to Ge growth when the GeCh partial pressure was below 5xl0'3Torr and etching at higher partial pressures. They also proposed a growth mechanism to understand the Ge growth where the GeCh cracks into germanium dichloride (GeCh) and the GeCh molecule with an H2 molecule are adsorbed onto the growth surface where they react with each other to form HC1 and solid Ge. Park, et al. used reduced pressure chemical vapor deposition (RP-CVD) to grow Ge at a pressure of 3xl0'2torr. They observed a relatively constant growth rate between 500-750 °C (PECVD) for Ge deposition and proposed another mechanism for growth in a GeCh carrier and an activation energy about 1 kcal / mol. Lai et al. used plasma enhanced chemical vapor deposition in a H2 system where GeCh reacts with H2 on the growth surface to produce a chlorine terminated Ge surface and an HC1 molecule, followed by H2 then reacting with the chlorine on the surface to form HC1 and another H2 terminated surface. Cho et al. used a GeCh / Eh epitaxial system at 550 °C and 760 torr and reported growth rates of up to 190 nm / min with increasing growth rates at higher GeCh flow rates.

[0027] As described herein, we used an in-situ elemental Ge source could have multiple advantages. One benefit is that it potentially simplifies the growth process, which could lead to greater understanding of the process, in general. In situ generation of Ge chlorides preferentially results in the formation of GeCh at typical growth temperatures, as shown below, eliminating the need for the first reaction step involving a GeCh molecule. The HVPE process also opens the possibility of using scrap, i.e., broken from Ge wafers as the precursor material for Ge growth. This unconventional approach not only marks significant advancement but also offers several practical advantages and it is also a steady way of recycling Ge. Utilizing elemental Ge simplifies the growth process, making it more straightforward and accessible. This approach is also cost-effective, eliminating the need to purchase gases from suppliers. Ge is known as a critical material, since there are no sources of pure Ge on Earth, and its extraction is mainly made by collecting it from the remaining ashes of certain types of coal. Repurposing old Ge substrates not only contributes to sustainability but also addresses logistical challenges associated with sourcing specific gases for the growth process. Growth from elemental Ge alsoallows for easy integration into HVPE reactors that already use chloride transport, and that permits the straightforward growth of many device structures. For example, epitaxial Ge could be used as a 3rdjunction of a triple junction solar cell grown inverted to reuse the substrate. Currently, these triple junction structures are grown on Ge substrates with much of the Ge substrate ground or etched away to reduce weight. Direct epitaxial growth of the Ge junction would significantly reduce waste. Ge epitaxy by HVPE could also enable other substrate reuse technologies, such as either selective chemical etching or controlled spalling of a buried Ge layer under a III-V device

[0028] Growth from an elemental source, which is then converted to a volatile precursor before depositing as the same element, requires a driving force. This can be created by a temperature difference between the source and deposition zones to increase the gas-phase supersaturation, but this is ineffective for growth from Ge chlorides. To grow we flowed anhydrous HC1 over Ge metal to form a volatile chloride that is transported to the substrate for growth, as is done for gallium and indium in HVPE. In-situ chlorination of elemental Ge with HC1 has been reported for n-type doping of GaN, however the growth of Ge from an elemental source has not been explored in existing literature. This approach was not used previously for Ge growth, because, while the thermodynamic driving force for GeCh generation from HC1 and Ge is high in an inert ambient such as N2, the driving force for growth is low. On the other hand, little GeCh is generated in-situ from HC1 and Ge in an H2 carrier, although the driving force for growth from an externally injected GeCk source is high. Here, we show that it is possible to grow Ge using a N2 ambient at the Ge source to promote GeCh formation while separately providing a source of hydrogen at the substrate to encourage Ge deposition. This application describes the impact of substrate and source temperature, reactor pressure, and the flow of HC1 to the Ge source to help understand the growth process and to determine their effect on Ge growth rate and surface morphology.

[0029] By following this approach, using elemental Ge for growth, it can be utilized into many different applications. From a simple epi-layer in a device to a more specific method like epitaxial lift-off (ELO). As an epi layer, it could be used to grow a 3rdjunction of a triple junction solar cell grown inverted to reutilize the substrate. Usually, triple junctions are grown on Ge substrates that only uses around 3 pm, out of the total 180-300 pm, as an active part of the 3rdjunction.

[0030] ELO can also be an application for Ge growth, commonly aluminum arsenide (AlAs) is used as a sacrificial layer for ELO, but it has a slow selective etching process (on the orderof 0.1 mm / h), that on a large scale can imply into a negative impact on production rate. By utilizing Ge as a sacrificial layer, it can be etched by using xenon difluoride (XeF?) which already proved to be a good solution for ELO, with lateral etching rates up to 9 mm / h for thin epitaxial Ge layers.

[0031] This application describes the growth of Ge from an in-situ elemental Ge source on an HVPE reactor. We studied the impact of substrate and source temperature, reactor pressure, Ge HC1 flow and hydride flows to determine their effect on Ge growth rate and surface morphology. We measured film thickness by measuring the growth step with a profilometer. To characterize the grown Ge we used specular ion mass spectrometer (SIMS) and atomic force microscopy (AFM).Experimental Methods

[0032] For this work, we used a single-growth chamber low pressure K50 III-V HVPE reactor (Kyma Technologies) to perform Ge growth. Fig. 1 shows a simplified schematic of the Ge growth configuration in the reactor. The substrate stage has 3 positions; after inserting the substrate into the reactor’s load lock, the pre-process is the first position that the substrate goes while the system’s temperature, gas flows and pressure are entering into equilibrium. The second position is the no-growth position, where we can perform annealing steps and where the substrate goes in between layers of different materials. And the growth position is where the actual growth happens. Furthermore, there are 3 zones of temperature where we can achieve a single temperature across the whole reactor or a gradient of temperatures. X °C zone is the temperature at the source, Y °C is the in between source and substrate temperatures and Z °C is the substrate zone temperature. HC1 is injected into the reactor’s boat to etch Ge and create volatile Ge chlorides, while a carrier gas is utilized to transport the free Ge into the reactor’s growth chamber. For our growths, we utilized N2 as a carrier gas rather than H2 like previously reported Ge growths because adding H2 would encourage the reverse reaction at the Ge source as can be seen in Equation 1.GeCh + H2 2HC1 + Ge(s) (Eq. 1)If H2 was used we would be limiting the production of GeCh and leading to no growth at the substrate, more information about it can be found on the results section. By using N2 as a carrier gas we are forcing the reaction to the forward direction, i. e. towards the chamber and, consequently, to the substrate. We could also control the flow of HC1 to the Ge source, effectively controlling how much GeCh reaches the substrate. Besides controlling the zonestemperatures and the HC1 flow that goes to the Ge, we are also able to control de pressure and the hydride flows through the center tube.

[0033] We identified the necessity for hydrogen (H) molecules to encourage Ge deposition onto the substrate after tests within the reactor’s growth chamber. To address this, we utilized hydrides available in most III-V growth systems, specifically arsine (Asfh) and phosphine (PH3), as deposition assisting agents. These hydrides played a crucial role in the deposition by providing reactive H at the substrate surface and reducing the Ge chlorides, allowing for Ge to incorporate into the growing layer. We used this approach to prove the concept because our reactor cannot flow both N2 and H2 at the same time without significant physical modifications. We do not observe Ge growth without the addition of a source of reactive H. The growths were done leaving the source temperature at 800 °C to keep the Ge elemental, since its melting point is 938 °C. The substrate temperatures were varied from 600 °C to 800 °C and the pressure was varied from 150 torr to 550 torr (~ 20.00 kPa to 73.32 kPa).

[0034] We grew Ge on a Ge substrate and utilized a quartz mask to cover part of the substrate to create a step so the layers could be discerned measured the thickness using a stylus profilometer (Veeco Dektak 8). We calculated growth rates by measuring the thickness of the grown Ge layers and dividing by the known growth time, which was 900 seconds for all samples. Besides being interested in Ge growth rates, we were also interested in the surface morphology of the grown Ge film since a smoother surface is known to produce a better device. An AFM (Veeco Dimension 3100) was used to identify the sample’s surface roughness and to observe the surface morphology. The samples were also depth profiled on a Cameca IMS 7f dynamic secondary ion mass spectrometer (SIMS) to check for potential background doping and to analyze the effects of hydrides on the Ge layer. The sample potential was -5kV with a cesium primary ion beam potential of 10 kV for a 15 kV impact energy. The elements of interest, like As, P, Ge, and H were quantified using relative sensitivity factors obtained from ion implanted standards. Thermochemical calculations were performed using HSC Chemistry software package to help understand the Ge growth process and the kinetics behind it to identify if the Ge growth was possible on our HVPE reactor under the standard conditions.Results

[0035] We performed thermodynamic equilibrium calculations to estimate the equilibrium mole fraction of different species formed in our reactor. To do so, we had to make some assumptions: the source reaction goes to completion; the diffusion to the surface is infinitelyfast; and the reactants have enough time to reach equilibrium before leaving the reactor chamber. These theorical assumptions are probably not exactly what is really happening inside the reactor, giving us an overestimate, but is sufficient for us to understand the reaction mechanisms for the growth. Fig. 2A presents the equilibrium calculation for solid Ge phase and a vapor phase with inputs of 10000 mole ambient of either N2 or H2, 10 moles of HC1 added. For the N2 case, 10 moles of H2 were also added. For the case of the H2 ambient (solid lines), the HC1 mole fraction remains nearly constant as a function of temperature, showing that only a few percent of the solid Ge is converted to a chloride even at the highest temperature. This indicates a preference for H-Cl bonds over Ge-Cl bonds in a hydrogen atmosphere. Conversely, the N2 ambient promotes significant Ge chloride formation (dashed lines). Notably, the concentration of the GeCh molecule starts to become dominant over GeCh at temperatures above ~ 500 °C. This indicates that Ge growth will require a N2 ambient to form volatile chlorides in the source region but will need a source of hydrogen at the substrate to provide a driving force to deposit as a solid. Fig. 2B shows the impact of varying the concentration of H2 injected to the deposition zone on generating Ge from HC1 with the source and substrate temperatures at 800 °C. It is possible to observe that H2 can be used as a promoter to reduce the concentration of the Ge species in the vapor by generating HC1 and allowing Ge to be deposited on the substrate. In other words, while the thermodynamic driving force for GeCh generation from HC1 and Ge is high in an inert ambient such as N2, the driving force for growth is low. On the other hand, little GeCh is generated in situ from HC1 and Ge in an H2 carrier, although the driving force for growth from an externally injected GeCk source is high. Here, we show that it is possible to grow Ge using a N2 ambient at the Ge source to promote GeCh formation while separately providing a source of hydrogen at the substrate to encourage Ge deposition. It is noteworthy to mention that in the simulations we used H2 as a hydrogen provider, but the same results can be achieved by using any hydride source, like AsH? and PH3. Our HVPE reactor is not designed to be able to use both N2 and H2 carrier gases in different parts of the reactor, so this presents a challenge to Ge growth. However, most IILV reactors use hydride gases such as arsine and phosphine, which are excellent sources of active hydrogen.

[0036] Therefore, we grew a series of Ge layers on a Ge substrates, using a pressure of 350 torr and 800 °C for both the source and deposition zones, varying the HC1 flow to the Ge source from 5 to 45 seem and varying the AsH? flow from 0 to 25 seem. In Fig. 3A, a graph illustrates the growth rates of Ge at different hydride flow rates. We never observed Ge growth unless a supply of hydrogen was added to the system which is consistent with the thermodynamiccalculations described above. Ge growth from a chloride likely features a kinetic barrier similar to that observed for GaAs growth, namely the saturation of the surface with Cl atoms. Hydrogen from pyrolyzed hydrides reduces the surface chlorine, which forms HC1 and desorbs, opening surface sites for the continued deposition of Ge. The Ge growth rate initially increases with increasing hydride flow, but then begins to decrease. The maximum growth rate reached increases with increasing HCloe, indicating some influence of mass flow on the overall growth rate. The peak growth rate also shifts to higher hydride flow rates with higher HCloe, and this might indicate a competition between growth and etching processes.

[0037] Arsine is known to etch Ge surfaces. The AFM images shown in Fig. 3B-3D reveal an increasing density of pits in the surface with increasing arsine flow, with the sample that is past the growth rate peak becoming totally rough. With higher AsHs flows the surface becomes rougher, with the root mean square (RMS) roughness varying from 2.3 nm to 27 nm. The highest growth rate observed in this samples set, while maintaining a flat and pit-free surface, was 48.5 nm / min while using HCloe = 10 seem and AsH? = 8 seem. The behavior observed for Ge growth by HVPE is reminiscent of GaAs growth in the hydride-enhanced growth regime [refs throughout this section]. At relatively low growth temperatures, GaAs growth is limited by stable As-Ga-Cl complexes on the surface that block available sites for As incorporation. Adding a source of active hydrogen, such as uncracked arsine, to this process reduces the surface chlorine, opening sites for As adsorption and continued growth. Something similar appears to be happening for Ge growth. The thermodynamic calculations suggest stronger Ge- C1 bonds than H-Cl bonds when in a N2 atmosphere. This might indicate there is a stable Ge- C1 complex on the surface that plays a similar role to limiting Ge growth as in the case for GaAs. We speculate that the addition of active hydrogen to the surface, again in this case in the form of pyrolyzed hydrides, reduces the Cl from the surface and allows for continued Ge growth. We use the term “active hydrogen” because separate experiments that added molecular H2 to the growth did not lead to Ge deposition. We note that the stable surface Cl impedes growth even at this relatively high deposition temperature of 800°C, at which point the analogous GaAs growth already proceeds through other Cl reduction mechanisms

[0038] Since we are using hydrides as the source of H to complete the reaction to grow Ge. We wanted to investigate the effects of the molecules like As and P on the Ge growth. We performed SIMS measurements to identify other effects that As could be causing on Ge. Fig. 4 presents a graph of As doping versus depth profile for different AsHi seem and HC1 on Ge flows. Despite the surface etching with high flows of AsHi shown on Fig. 3A, As is also dopingGe in the range of 3xl017to 4xl018with a doping peak of ~ IxlO19at the interface between the substrate and the Ge layer. By increasing the AsHs flow we are also increasing As doping but in a very small rate, the doping levels matches with As solubility values on Ge found on literature, around IxlO20at 800 °C. This amount of doping can influence the performance of a device and needs to be considered for future applications. The observed doping peak at the interface is probably due to the AsHs dissociation at the Ge surface suggesting a high incorporation of As at the surface layer that diffuses into the substrate. Besides etching and doping of Ge, by using hydrides as helping molecules in the Ge growth, we did not observe any different type of material structure that could possibly be grown rather than just Ge, like germanium arsenide (GeAs) or germanium phosphide (GeP). All the observed defects can be avoided by using molecular H within the center tube and N2 as carrier gas. In our reactor, without making impactful changes, this is only possible by manually flow H2 through some other line that is not in use for the growth. We did manual experiments using H2 and PbSe as helper molecules and we measured an average growth rate of 83 nm / min and 295.8 nm / min respectively.

[0039] We grew a set of samples varying the substrate temperature from 600-800 °C with a chamber pressure of 350 torr, a Ge HC1 flow of 5 seem and AsHs flow of 4 seem, which are one of the flows configurations that presented the best samples, to understand how the controllable variables within the reactor influence the growth rate. Fig. 5A presents the growth rates for different growth temperatures alongside with Fig. 5B that presents a thermodynamic simulation for growth rate versus temperature, assuming a source temperature of 800 °C, a pressure of 350 torr, Ge HC1 flow of 5 seem and AsHs flow of 4 seem. According to the thermodynamic predictions, the growth rate should theoretically decrease with increasing temperature. This is attributed to the reduced thermodynamic driving force for Ge deposition as the substrate temperature rises. However, our experimental data contradicts this prediction. Instead, it reveals that as temperature increases, so does the Ge growth rate, as show in Fig. 5A. This discrepancy suggests that the thermodynamic by itself does not fully explain the growth process. It implies the presence of additional factors, likely a kinetic nature, influencing the growth behavior.

[0040] We also wanted to understand the effects of pressure during growth. Fig. 6A shows the GR for a set of samples grown at 800 °C with a Ge HC1 flow of 5 seem, AsH? flow of 4 seem and, varying the pressure from 50 to 500 torr. It is possible to observe that the GR increases as pressure increases until it reaches a pressure around 300 torr. For pressures higher than that weobserved a decrease in the GR. Figs. 6B-6E shows the AFM images of the grown Ge surfaces at different chamber pressures. It is possible to observe that as the pressure increases, the roughness also increases, with many pits being formed at the grown surface. The only exception was the sample grown at 350 torr, which presented a homogeneous surface with low RMS roughness of 1.9 nm, being the most suitable chamber pressure value for growth. We believe that there are two regimes ruling the surface etching by As; since AsH3 cracks faster at low pressures, we have more As hitting the Ge surface thus etching it faster; while at high pressures the AsH3 is hitting the surface faster which also contributes to increase the surface etching. There is a pressure equilibrium region where the growth is possible without etching the surface, that in our case corresponds to the region around 350 torr. We did not observe a clear trend in surface roughness or morphology as the pressure increases. Indeed, the sample grown at 350 Torr displayed a smooth surface with a low RMS roughness of 1.9 nm, while the samples at somewhat higher and lower pressures were quite rough. This behavior is likely highly dependent on the nature of the reactor used and sensitive to the competition between hydrogen reduction of Cl promoting growth and arsine leading to etching. For example, changing pressure in our reactor will necessarily change the gas velocity, which will in turn impact arsine pyrolysis. That is, a lower pressure should lead to less time the arsine spends in a hot zone, leading to lower cracking. However, lower pressures should also lead to increased diffusion of arsine toward the hot reactor walls, potentially increasing cracking.Conclusion

[0041] In summary, we showed for the first time that it is possible to grow Ge from an elemental source by introducing hydrides together with Ge. However, the group V atoms from the hydride source act as dopants onto Ge and the hydride flows needs to be within a certain range to avoid surface etching leading to increased roughness. To avoid the down effects of hydrides introduction, it is possible to grow Ge by simply introducing a source of active H2 inside the reactor, allowing the pure Ge growth. We also showed that both pressure and temperature play an important role on the Ge growth by changing the GR and its surface morphology, meaning that these variables need to be well controlled for a proper pristine surface quality.

[0042] The provided discussion and examples have been presented for purposes of illustration and description. The foregoing is not intended to limit the aspects, embodiments, or configurations to the form or forms disclosed herein. In the foregoing Detailed Description for example, various features of the aspects, embodiments, or configurations are grouped togetherin one or more embodiments, configurations, or aspects for the purpose of streamlining the disclosure. The features of the aspects, embodiments, or configurations, may be combined in alternate aspects, embodiments, or configurations other than those discussed above. This method of disclosure is not to be interpreted as reflecting an intention that the aspects, embodiments, or configurations require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment, configuration, or aspect. While certain aspects of conventional technology have been discussed to facilitate disclosure of some embodiments of the present invention, the Applicants in no way disclaim these technical aspects, and it is contemplated that the claimed invention may encompass one or more of the conventional technical aspects discussed herein. Thus, the following claims are hereby incorporated into this Detailed Description, with each claim standing on its own as a separate aspect, embodiment, or configuration.

[0043] The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments, exemplary embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims. The specific embodiments provided herein are examples of useful embodiments of the present invention and it will be apparent to one skilled in the art that the present invention may be carried out using a large number of variations of the devices, device components, methods steps set forth in the present description. As will be obvious to one of skill in the art, methods and devices useful for the present methods can include a large number of optional composition and processing elements and steps.

[0044] As used herein and in the appended claims, the singular forms "a", "an", and "the" include plural reference unless the context clearly dictates otherwise. Thus, for example, reference to "a cell" includes a plurality of such cells and equivalents thereof known to those skilled in the art. As well, the terms "a" (or "an"), "one or more" and "at least one" can be used interchangeably herein. It is also to be noted that the terms "comprising", "including", and"having" can be used interchangeably. The expression “of any of claims XX- YY” (wherein XX and YY refer to claim numbers) is intended to provide a multiple dependent claim in the alternative form, and in some embodiments is interchangeable with the expression “as in any one of claims XX- YY.”

[0045] When a group of substituents is disclosed herein, it is understood that all individual members of that group and all subgroups, are disclosed separately. When a Markush group or other grouping is used herein, all individual members of the group and all combinations and subcombinations possible of the group are intended to be individually included in the disclosure. For example, when a device is set forth disclosing a range of materials, device components, and / or device configurations, the description is intended to include specific reference of each combination and / or variation corresponding to the disclosed range.

[0046] Every formulation or combination of components described or exemplified herein can be used to practice the invention, unless otherwise stated.

[0047] Whenever a range is given in the specification, for example, a density range, a number range, a temperature range, a time range, or a composition or concentration range, all intermediate ranges and subranges, as well as all individual values included in the ranges given are intended to be included in the disclosure. It will be understood that any subranges or individual values in a range or subrange that are included in the description herein can be excluded from the claims herein.

[0048] All patents and publications mentioned in the specification are indicative of the levels of skill of those skilled in the art to which the invention pertains. References cited herein are incorporated by reference herein in their entirety to indicate the state of the art as of their publication or filing date and it is intended that this information can be employed herein, if needed, to exclude specific embodiments that are in the prior art. For example, when composition of matter is claimed, it should be understood that compounds known and available in the art prior to Applicant's invention, including compounds for which an enabling disclosure is provided in the references cited herein, are not intended to be included in the composition of matter claims herein.

[0049] As used herein, “comprising” is synonymous with "including," "containing," or "characterized by," and is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. As used herein, "consisting of' excludes any element, step, or ingredient not specified in the claim element. As used herein, "consisting essentially of' doesnot exclude materials or steps that do not materially affect the basic and novel characteristics of the claim. In each instance herein any of the terms "comprising", "consisting essentially of and "consisting of may be replaced with either of the other two terms. The invention illustratively described herein suitably may be practiced in the absence of any element or elements, limitation or limitations which is not specifically disclosed herein.

[0050] All art-known functional equivalents, of any such materials and methods are intended to be included in this invention. The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention that in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims.

Claims

CLAIMSWhat is claimed is:

1. A method compri sing : providing a solid germanium source; reacting the solid germanium source with an acid; flowing a hydrogen source over a surface of the germanium source, thereby generating a germanium-containing gas; and depositing the germanium containing gas on a substrate via hydride vapor phase epitaxy.

2. The method of claim 1, wherein the acid comprises HC1 and the germanium- containing gas comprises GeCh.

3. The method of claim 1 or 2, wherein the solid germanium source is elemental germanium.

4. The method of any of claim 1-3, wherein the hydrogen source is arsine, phosphine, hydrogen selenide or a combination thereof.

5. The method of any of claims 1-4, wherein the method is performed in an inert gas environment.

6. The method of claim 5, wherein nitrogen creates the inert gas environment.

7. The method of any of claims 1-6, wherein the germanium source is provided at a temperature of about 800 °C.

8. The method of any of claims 1-7, wherein the substrate is provided at a temperature selected from the range of about 600 °C to 800 °C.

9. The method of any of claims 1-8, wherein the method is performed at a gauge pressure selected from the range of about 150 torr to 550 torr (about 20.0 kPa to 73.3 kPa).

10. The method of any of claims 1-9, wherein the acid is provided to the germanium source at a flow rate less than or equal to 10 seem (standard cm3 / min).

11. The method of any of claims 1-10, wherein the hydrogen source is provided to the germanium source at a flow rate less than or equal to 10 seem.

2. A method compri sing : providing a solid elemental germanium source; reacting the solid germanium source with HC1; flowing arsine, phosphine, hydrogen selenium or a combination thereof over a surface of the germanium source, thereby generating a GeCh gas; and depositing the germanium containing gas on a substrate via hydride vapor phase epitaxy.

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