MXPA99005516A - Semiconductor having large volume fraction of intermediate range order material - Google Patents

Abstract

A high quality non-single-crystal silicon alloy material including regions of intermediate range order (IRO) silicon alloy material up to but not including the volume percentage required to form a percolation path within the material. The remainder of the material being either amorphous or a mixture of amorphous and microcrystalline materials. The materials were prepared by CVD using differing amounts of hydrogen dilution to produce materials containing differing amounts of IRO material. Preferably the material includes atleast 8 volume percent of IRO material.

Description

SEMICONDUCTOR HAVING A LARGE VOLUME OF FRACTION OF ORDINATED MATERIAL OF INTERMEDIATE RANGE DESCRIPTION OF THE INVENTION This invention describes semiconductors in general. In particular, the invention describes a semiconductor material having a volume of ordered materials of intermediate range (size of crystals of 10-50 Angstroms) up to, but not including, the percentage of volume required to form a filtration path within of the material. Within a relatively short time, semiconductor materials have made possible the creation of a wide variety of optical and electronic devices which have played an important role in shaping our world. The impact of semiconductor devices has been felt from the battlefield to the playing field and from the kitchen to the cosmos. In the earliest stages, semiconductor technology was limited by the use of monocrystalline materials. These materials were necessarily highly pure and possessed a morphology with a long-range and extremely regular periodicity. The interdependent double limits of periodicity and this «quiometry restricted the degree of composition, and thus the physical properties of crystalline semiconductor materials. As a result, the devices monocrystalline were expensive, difficult to manufacture and limited in their properties. While conventional wisdom at this time dictated that the behavior of the semiconductor could only manifest itself in highly ordered materials, it was recognized by S.R. Ovshinsky that the requirements of periodicity could be solved and that the behavior of the semiconductor could be manifested by several disordered materials. In this regard, see "Reversible Electrical Switching Phenomena and Disordered Structures" by Stanford R. Ovshinsky; Physical Review Letters, vol. 21, No. 20, Nov. 11, 1968, 1450 (C) and "Simple Bond Model for Amorphous Semiconducting Alloys" by Morrel H. Cohen, H. Fritzsche and S. R. Ovshinsky; Physical Review Letters, vol. 22, No. 20, May 19, 1969, 1065 (C). Disordered materials were characterized by a lack of long-range periodicity. In disordered semiconductors, the limits of periodicity and stoichiometry are removed and as a result, it is now possible to place atoms in three dimensional configurations previously prohibited by the network constants of the crystalline materials. In this way, a completely new spectrum of semiconductor materials having novel physical, chemical and electrical properties has been made available. By choosing compositions of appropriate materials, the Disordered semiconductor properties can be manufactured according to needs over a wide range of values. Disordered semiconductors can be deposited by film techniques over relatively large areas at low cost, and as a result many types of new semiconductor devices that are commercially possible can be obtained. A first group of unordered semiconductors are generally equivalent to their crystalline counterpart while a second group manifests physical properties that can not be achieved with crystalline materials. As a result of the above, the disordered semiconductor materials have been widely accepted and a large number of devices that are manufactured from these are of significant commercial use. For example, wide-area photovoltaic devices are routinely manufactured from amorphous silicon and germanium-based alloys. Such materials and devices are described, for example, in the Patents of E.U.A. Nos. 4,226,898 and 4,217,374 of Ovshinsky et al. Disordered alloy materials have also been used to manufacture ranges of photodetectors for use in document scans, disk drives for LCD displays, cameras and the like. In this regard see the Patent of E.U.A. No. 4,788,594 to Ovshinsky et al. Disordered semiconductor materials have also been used in devices for high volume storage of optical and electronic information. Amorphous materials are currently used in a manner that takes advantage of the wide variety of interactions between atoms constituting molecules in contrast to the restricted number and types of interactions interposed by a crystal lattice. In the present invention, the advantages of crystalline and amorphous properties can be combined for those devices and applications in which periodicity is essential to physics. The periodicity can be placed in an amorphous matrix through the use of the present invention. The material may include spatially repeated units, atoms, groups of atoms or layers without inhibition of the total volume of the crystal periodicity. Also, individual atoms or groups of atoms in various configurations can be provided, which can be combined with other atoms or groups of atoms and be spent through the material. As mentioned, the individual atoms or groups of atoms in these materials do not need to be in a regular pattern, but may have a variable spatial pattern, as if they were graduated or without sequence through the material. By the proper choice of atoms or groups of atoms, their orbitals and isolated configurations can be produced, anisotropic effects not allowed in any type of material that could be produced. These procedures provide variable geometric environments for the same atom or a variety of atoms, so that these atoms can be linked to other surrounding atoms in different coordination configurations as well as unusual non-binding relationships resulting in entirely new chemical environments. The procedures provide means for arranging different chemical environments which can be distributed and located through the material in the desired spatial pattern. For example, a part or portion of a material may have local environments totally different from the other portions. The variable electronic states that result from the various spatial patterns which are formed and the various chemical environments which can be designated, can be reflected in many parameters as a type of density states or changes of states in the energy space of a semiconductor except that this density of states can be arranged spatially. In essence, the material of the invention is a material compositionally modulated using the mere concept of regularity, inhomegeneity, "disorder" or localized order which has been avoided in the prior art, to achieve benefits that are not exhibited in materials previous Local environments do not need to be repeated through the material in a periodic manner as in the compositionally modulated materials of the prior art. In addition, because the above-described effects of the specific types of disorder and their spatial pattern arrangements, the materials as described by this invention can not be thought of as truly amorphous materials as typically were produced by the prior art since the material it is more than a random placement of atoms. The placement of atoms and orbitals of a specific type that can either interact with their local environment or with another environment dependent on their placement through an amorphous material and an amorphous matrix can be achieved. The composite material seems to be homogeneous, but the positions of the orbitals of the atoms can have relations designed to emphasize a particular parameter, such as compensation or decompensation of spin. The materials thus formed give a new sense to the disorder based not only on the relations of the nearest neighbor, but "disorder" between functional groups, which can be layers or groups, at a scale of distance that can be as small as a single atomic diameter. This, a totally new class of "multidisciplinary synthetic unbalance" materials has become available.

It has been found that the properties of semiconducting materials in the disordered state will depend on their morphology and local chemical order and can be affected by various methods of preparation. For example, manufacturing techniques without equilibrium can provide a local order and / or morphology different from that achieved with equilibrium techniques; and as a result, the physical properties of the material can be changed. In most cases, an amorphous semiconductor will have a lower electrical conductivity than the corresponding crystalline material and in many cases the band gap energy, the optical absorption coefficient and the electronic activation energy of the corresponding crystalline and amorphous materials it will differ. For example, it has been found that amorphous silicone materials typically have a band space of approximately 1.6-1.8 eV while crystalline silicone has a band space of 1.1 eV. It is also important to note that the amorphous silicone materials have a direct band gap while the corresponding crystalline material has an indirect band gap and as a result, the optical absorption of the amorphous silicone is significantly higher than that of the crystalline silicone in or near from the edge of the band. It should also be noted that the dark electrical conductivity of the unpurified amorphous silicone is several orders of magnitude lower than that of crystalline silicone. It can thus be seen that the various physical properties of silicone strongly depend on its morphology and local order. Similar relationships are found in a large number of other semiconductor materials. The principle of the present invention resides in the ability to control the local order of a semiconductor material from that which corresponds to a completely amorphous phase through several other local organizations including the intermediate order to a state where the local order is so repetitively periodic that the material is in its monocrystalline state. The most important and interesting area of the present invention is the ability conferred on it to control the local order of a semiconductor material to produce a material that has valuable properties different from either amorphous or crystalline states. The various properties of amorphous and crystalline silicone confer different advantages on various devices. The high mobility of carriers in crystalline silicon is important in high-speed semiconductor circuits while the high level of optical absorption of amorphous silicon is ideal for photovoltaic devices since full absorption of light can be achieved by relatively thin layers of material, making a Light weight and low cost device. In some cases, a property of a local order and given semiconductor morphology may be ideal for a particular purpose while the value of another property of that same material may not also be adequate. For example, the high optical absorption of the amorphous silicone is ideal for a photovoltaic device, however, the adequately wide band gap of the amorphous silicon does not allow it to address the longest wavelength portions of the solar spectrum. The use of a narrower band gap crystalline material in photovoltaic devices increases the portion of the usable light spectrum and the high conductivity, high mobility and long diffusion length of minority long carrier in crystalline silicon decreases the series resistance of photovoltaic device , with which increases its total efficiency; but, the disadvantage is that the crystalline cells are relatively thick due to their low absorption and therefore they are fragile, bulky and expensive. Previously Ovshinsky, et al. they produced materials that included clusters of atoms, typically between 12 and 50 angstroms in diameter. See the Patent of E.U.A. No. 5,103,284, registered on April 7, 1992 and entitled "SEMICONDUCTOR WITH ORDERED CLUSTERS". The groupings or grains had a degree of order which is different from both crystalline and amorphous forms of the material. The small size and Sorting of the clusters allowed them to adjust their band structure- to thereby relax the vector selection rules K. Ovshinsky et al found that the various physical properties of the semiconducting materials decoupled from the morphology and local order when those materials were composed of organized groupings. This relaxation of selection rule occurred because the materials included a volume of fraction of intermediate materials which was high enough to form filtration paths within the material. The principle of the critical threshold value for the substantial change in the physical properties of the materials in the state of ordered grouping depends on the size, shape and orientation of the particular groupings. However, it is relatively constant for different types of materials. There are 1-D, 2-D and 3-D models which predict the volume of fraction of clusters necessary to reach the threshold value, and these models depend on the shape of the ordered clusters. For example, in a 1-D model (which can be analogized to the load carrier flow through a thin wire, the fraction volume of the groupings in the matrix must be 100% to reach the threshold value In the 2-D model (which can be seen as groupings in substantially conical shape that extend through the thickness of the matrix) the fraction volume should be around 45% to reach the threshold value, and finally in the 3-D model (which can be seen as substantially spherical groupings at a threshold of matrix material) the fraction volume needs to be about 16-19% to reach the threshold value. Therefore, the materials described and claimed in the Patent of E.U.A. No. 5,103,284 has at least 16-19 percent volume of order-range material-intermediate for spherical clusters, at least 45 percent volume for cone-shaped clusters, and 100-percent volume for clustering-in-form. of filament. The present inventors have found that materials that include any volume percent of intermediate range material (ie ordered arrays) will have properties which (while not necessarily decoupled) differ from materials that do not have rank order material. intermediate. These materials are particularly useful in the form of thin films * used in devices such as: in photovoltaic devices, thin film diodes, thin film transistors, photoreceptors, etc.

The present inventors have produced a high quality non-monocrystalline silicone alloy material which includes a volume percent of regions of intermediate-range silicon alloy material (IRO) up to, but not including, the percentage of volume required for form a filtration path within the material. The rest of the material is either amorphous or a mixture of amorphous and microcrystalline materials. The materials were prepared by PECVD using different amounts of hydrogen dilution to produce materials containing different amounts of IRO material. The silicone alloy material additionally includes hydrogen and / or halogen, as is fluorine. The material is preferably in the form of a thin film, which is useful in devices such as photovoltaic devices, diodes, transistors, and photoreceptors. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a luminous field electron transmission (TEM) micrograph of a reference silicone material produced without using a dilution of hydrogen; Figure 2 is a luminous field TEM of a reference hydrogenated silicone alloy material produced using a low dilution of hydrogen; Figures 3 and 4 are luminous field and dark field TEMs, respectively, of a hydrogenated silicone alloy material according to the present invention produced using a high dilution of hydrogen; Figure 5 is a luminous field TEM (magnification: 3.63 million x) of the hydrogenated silicone alloy material of Figures 3 and 4, specifically illustrating that the material of the present invention contains IRO material; Figure 6 is a luminous field TEM (magnification: 2.64 million x) of the hydrogenated silicone alloy material according to the present invention produced by a PECVD using a half dilution of hydrogen; and Figure 7 is a luminous field TEM (magnification: 3.52 million x) with a hydrogenated silicone alloy material according to the present invention produced by a PECVD using a high dilution of hydrogen. The existence of intermediate range order material (IRO) is known since at least 1981. See for example a paper of co-authors of one of the present inventors, SR Ovshinsky, entitled "THE NATURE OF INTERMEDIATE RANGE ORDER IN SI: F: H: (P) ALLOY SYSTEMS "Tsu et al., 'Journal de Physique Colloque C4, No. 10, 42, pp. C4-269-72, October 1981. The present inventors have been investigating the deposition of silicone materials by means of chemical vapor deposition enhanced with plasma (PECVD) of disilane (Si2H6) and hydrogen (H). More recently they have investigated the deposition using a high dilution of hydrogen. See for example "STABILITY STUDIES OF HYDROGENATED AMORPHOUS SILICON ALLOY SOLAR CELLS PREPARED WITH HYDROGEN DILUTION", Yang et al., Materials Research Society Symposium Proceedings, Vol. 336, p. 687-92, 1994; e "HIDROGEN DILUTION EFFECTS ON a-Si: H AND a-SiGe: H MATERIALS PROPERTIES AND SOLAR CELL PERFORMANCE", Xu et al., International Conference on Amorphous Semiconductors (ICAS 16), September 1995. The present inventors have now found that a very high dilution of hydrogen during CVD deposition of silicon results in materials having intermediate fraction order material (IRO) volumes. The present inventors have also found that these materials, while not having the decoupling properties of the materials of the 5,103,284 patent, have better properties compared to those materials that do not have IRO material. As used herein, the intermediate range order material (IRO) should be defined as a material having atomic aggregations of very short range periodicity, and comprising a plurality of relatively small, highly ordered, atomic aggregations, which typically they extend to no more than 50 atomic diameters. The exact dimensions of the aggregations in these materials will depend on the particular semiconductor material in question, but typically they are in the range of 10 to 80 angstroms and preferably around 30-50 angstroms. IRO materials have a periodicity and local order that differs from a totally crystalline or amorphous material. In IRO materials, the local order propagates but does not reach the point of becoming an order of rank long; and therefore, the network constants of the crystalline state do not become the factor for determining the properties of the materials. In IRO materials, bond lengths and angles are much more flexible than materials with a long range periodicity. 15"Samples were prepared by PECVD using different amounts of hydrogen dilution to produce materials containing different amounts of IRO material The deposition parameters of the samples are given in Table 1. TABLE 1 * Except sample RF 5357, which indicates the flow velocity of the mono-silane (SiH) While there are a variety of methods by which the materials of the present invention can be repaired (i.e., thin film deposition techniques) such as laser ablation, spraying, chemical vapor deposition, plasma deposition processes, and evaporation processes) the most preferred is chemical vapor deposition enhanced with plasma (PECVD). The present RF method PECVD is normal in most respects except that the temperature is controlled and the hydrogen dilution level is very high. For example, hydrogen for the degree of disilane is typically greater than about 98: 1 and preferably greater than 99: 1. 15 The critical element of any deposition process is the control of the size of the crystals to keep the material in the deposition regime of the intermediate rank order. In general, growth processes very slowly in a very large number of nuclei will produce a material that has a larger fraction volume of IRO material within it. For example, in the process of plasma deposition present, a direct reaction takes out in which the precursor gas species disilane is decomposed to produce a deposit of solid silicone. This process also includes a counter reaction in which the high concentration of hydrogen reacts with the silicone recently deposited to corrode that silicon and regenerate the gaseous species. The rate of deposition is a function of the balance of the direct and counter-reaction reactions. The addition of high concentrations of corrosion material (ie, hydrogen), accelerates the corrosion process and therefore moderates the deposition rate and improves the growth of IRO material. In addition to, or instead of the above, another species of corrosive as it is fluorine can be added to the process to likewise moderate the deposition rates. While increasing the dilution of hydrogen in the reaction gas mixture increases the volume of the intermediate range order in the deposited material, the present inventors have found that there is a limit to this effect. That is, beyond a certain level of hydrogen dilution, an increase in the level of hydrogen dilution causes microcrystalline materials to deposit in a constantly increasing volume of fraction. This in turn can lead to a reduction in the fraction volume of the IRO material. The present inventors have also seen that this dilution limit is sensitive to the temperature. That is, the dilution limit at a substrate temperature of 300 ° C appears to be much lower than the limit at about 150 ° C. Therefore by adjusting the hydrogen dilution, the substrate temperature and other deposition parameters which affect the rate of deposition, which can control the volume of the IRO material fraction in the deposited material. While the functions of fluorine as a corrosive material to moderate the growth of crystals and thus allow the preparation of the IRO material of the present invention, the effects of fluorine extend far beyond its simple corrosive role. Fluorine is a super halogen and as such exerts effects not obtainable by the use of a quantity of hydrogen or other halogens in the deposition atmosphere. The fluorine acts to provide a local, improved and improvised order in the material and to control the size and morphology of the intermediate range order material. Fluorine also reacts with morphological deviations and electrical states as they form in the material, thereby moderating the electrical properties of the material's volume. Therefore, when used in deposition, fluorine plays several important roles in the deposition of the material of the present invention, in the vapor or plasma state as well as in the surface of the IRO material, in the volume of the IRO material and at the interfaces between the IRO material and the rest of the material. It is also beneficial to reduce the density of defective states in the material space. Fluorine is a very active corrosive material and it is generally preferred that it be moderate, for example by dilution with hydrogen. Referring now to the characterization of the sample materials, Figure 1 is a micrograph Transmission of luminous field electrons (magnification: 3.63 million x) of the silicone alloy material (Sample # RF 5357) produced by PECVD at a substrate temperature of 300 ° C without using a dilution of hydrogen. From the circulation of the micrograph it is clear that the material is purely amorphous without signs of any order of long or intermediate range (a fact that comes from the Raman information presented here below). Figure 2 is a luminous field TEM (magnification: 3.63 million x) of the hydrogenated silicon alloy material (Sample # 8014) produced by PECVD at a substrate temperature of 300 ° C using a low dilution of hydrogen. From the circulation of the micrograph it is clear that the materialwhile it is still almost totally amorphous, it does not exhibit signs of intermediate rank order. Figures 3 and 4 are luminous and dark field TEMS, respectively, (magnification: 3.63 million x) of the hydrogenated silicon alloy material (Sample # 8013) produced by PECVD at a substrate temperature of 300 ° C using a high dilution of hydrogen. From the circulation of the micrograph it is clear that the material contains both microcrystalline and non-crystalline "amorphous" material. It should be noted that in this extension the IRO materials can not be seen. Figure 5 is a luminous field TEM (magnification: 3.63 million x) of the hydrogenated silicone alloy material of Figures 3 and 4. From the circulation of this micrograph it is clear that the material contains IRO, amorphous and microcrystalline material. The IRO material can be clearly seen in the lower left corner of the micrograph. Figure 6 is a luminous field TEM (magnification: 2.64 million x) of the hydrogenated silicone alloy material (Sample # LL 1208) produced by PECVD at a substrate temperature of 150 ° C using a half hydrogenated dilution. From the circulation of this micrograph it is clear that the material contains IRO material, which can also be seen as areas arranged in the form of serpentine in the micrograph. Figure 7 is a luminous field TEM (magnification: 3.52 million x) of hydrogenated silicon alloy material (Sample # LL 1234) produced by PECVD a a substrate temperature of 150 ° C using a high dilution of hydrogen. From the circulation of this micrograph it is clear that the material contains microcrystalline amorphous IRO material. The IRO material in the form of a serpentine can be clearly seen in the center of the micrograph. In addition to the evidence of the TEMs, the present inventors have used Raman scattering to characterize the deposited samples. The peaks of the transverse optical silicon Raman spectrograph (TO) for four specimens of thin film hydrogenated silicone produced by PECVD at a substrate temperature of 300 ° C and varying degrees of hydrogen and silane. One of the samples was deposited without using silane hydrogen dilution (Sample # RF 5357). The other samples are silicon deposited using different hydrogen dilution values of the syllable in a deposition mixture (ie Samples 8013, 8035 and 8014 respectively). From the Raman spectrographs, the inventors have discovered that as the hydrogen dilution of the silane increases, the TO peaks change from the typical "amorphous" 474 cm'1 to approximately 482.3 cm "1 for the highly diluted sample (i.e. 8013) Additionally, the highly diluted sample (8013) shows another peak centered around 517 cm-1 This additional peak is attributable to the microcrystalline inclusions, which are formed in the sample of high dilution at high temperature. discussion of the TEM photomicrograms mentioned above). The change of the TO peak from 474c? Rf1 to approximately 482. Sem "1 seems to be an unrecognizable feature so far, this feature seems to indicate the presence of IRO material, that is, the Raman information indicates the presence of an area of disordered materials that are less than and different from the microcrystalline inclusions, it is believed that the IRO inclusions are 10-80 Angstrom of crystals grouped in chain in the form of serpentine A comparison of both TO peaks of the sample of high dilution of hydrogen (8013), and the undiluted hydrogen sample (RF 5357) superimposed and aligned by the laser plasma lines on the same graph show that the TO peak of the high dilution hydrogen sample (8013) includes a microcrystalline peak of approximately 517 cm "1 which can not be seen in the sample without hydrogen dilution (RF 5357). The comparison also shows an additional peak of approximately 490cm "1 which can not be seen in the sample without hydrogen dilution (RF 5357) .Similar comparisons for samples with medium and low dilution of hydrogen respectively indicate that the peak of 490cm ~ 1 truly exists.

Another sample (LL 1208) was made using a high dilution of hydrogen and a low substrate temperature (150 ° C). This material has a TO peak of about 482 cm-1 and it does not have a microphoto crystalline peak. The Raman clearly indicates. a peak of IRO material. The semiconductors of the present invention can be prepared from a large number of materials and can be applied to a wide variety of semiconductor devices. While the previous discussion first had to do with silicon alloy devices for photovoltaic applications, it will also be appreciated that the principles described here can similarly be extended to other types of devices, such as: thin film diodes, film transistors thin, photoreceptors, etc. and other materials, such as: silicon alloys with germanium, carbon, oxygen, etc. and silicone lubricant. The drawings, discussions and previous descriptions are not intended to be limitations on the practice of the present invention but illustrations of this. They are the following claims, including all equivalents, which define the field of use of the invention.

Claims (9)

1. CLAIMS 1. A high quality non-monocrystalline silicone alloy material characterized in that it comprises: regions of intermediate order material up to but not including the percentage of volume required to form a filtration path within the material; and the rest of the material being either amorphous or a mixture of amorphous and microcrystalline materials.
2. 2. The silicone alloy material according to claim 1, characterized in that said silicone alloy material additionally includes at least one hydrogen and one halogen.
3. 3. The silicone alloy material according to claim 2, characterized in that said halogen is fluorine.
4. 4. The silicone alloy material according to claim 1, characterized in that said alloy material is in the form of a thin film.
5. 5. The silicone alloy material according to claim 4, characterized in that said thin film is incorporated into a photovoltaic device.
6. 6. The silicone alloy material according to claim 5, characterized in that said thin film is incorporated into one of a diode, transistor or photoreceptor.
7. 7. The silicone alloy material according to claim 4, characterized in that said regions of intermediate range order are serpentine-shaped groupings. The silicone alloy material according to claim 1, characterized in that said regions of silicone alloy material of intermediate range order are either 1-D and their volume percentage varies from 8 to less than 100%; 2-D and its percentage of volume varies from 8 to less than 45%; or 3-D and its volume percentage varies from 8 to less than 19%. 9. The silicone alloy material according to claim 1, characterized in that said silicone alloy material also includes at least germanium, carbon and oxygen.