The subject matter described herein relates generally to semiconductor devices, specifically, optoelectronic semiconductor structures.
Some optoelectronic devices include perovskite layers. These layers are typically amorphous, resulting from fabrication by one of two methods that include vapor conversion of nuclei or co-deposition of precursors to form perovskite layers on a substrate, such as a polycrystalline layer on glass (typically TiO2, FTO, or ITO). Even in the case of formation on layers or substrates comprising single crystals of, for example, TiO2, the resulting perovskites formed thereon are polycrystalline in nature. While not limited to any particular theory, it is believed that this is due, in part, to such single crystals having tetragonal, orthorhombic or monoclinic crystal structures (i.e., structures that are not cubic) having lattice constants that are not compatible with the quasi-cubic lattice constant of perovskites, such as methylammonium lead iodide (CH3NH3PbI3). Accordingly, where the formation energy of a single crystalline layer of such quasi-cubic-structured perovskites is not favorable to the formation of many small grains, the formation energy of a polycrystalline perovskite thin-film layer comprising varying grain sizes is energetically favored when fabricated on a material having a non-cubic crystal structure.
Nonetheless, amorphous perovskite layers having thicknesses of about 100 nm to 1000 nm can be used as highly efficient semiconductor active layers in devices. However, perovskite active layers formed by conventional methods also suffer from limitations such as humidity degradation of the perovskite layer, hysteresis of light intensity-current-voltage (LIV) curve trace, temperature instability, and UV instability. While the root cause of these issues is the subject of current research, it is believed that the grain boundaries between device layers provide fast pathways for dissolution of the perovskite crystal and fast water diffusion pathways leading to intercalation or dissociation of the oxide layers that may underlie the polycrystalline perovskite active layer. Due to this degradation at grain boundaries, the use of amorphous perovskite active layers for optoelectronics devices is limited.
One method that has succeeded in producing stable perovskite active material is inverse temperature crystallization of single crystal perovskite layers. However, single crystal formation limits the device fabrication methods that require significant handling, cutting and polishing to produce devices. Further, single crystal perovskites are still small and difficult to produce. Improved epitaxial, single-crystal perovskites and methods for making the same would be welcome additions to the art.
A semiconductor device comprises a substrate comprising a single-crystal semiconductor; and at least one layer disposed on the substrate, wherein the at least one layer comprises an organometallic-halide ionic solid perovskite.
A method for making a semiconductor device, comprises: forming at least one perovskite layer on a substrate, wherein the substrate comprises a single-crystal semiconductor and the at least one perovskite layer comprises an organometallic-halide ionic solid perovskite; forming a first electrical contact in electrical communication with the substrate, the at least one perovskite layer or both; and forming a second electrical contact in electrical communication with the substrate, the at least one perovskite layer, or both.
While not limited to any particular theory it is believed that lattice matching between single crystal perovskites and underlying single crystal layers, such as the semiconductor substrate leads to a bandgap alignment and reduced resistivity between the perovskite layer and the and underlying single crystal layer. Other advantages of the examples will be set forth in part in the description which follows, and in part will be understood from the description, or may be learned by practice of the examples. The advantages will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. The materials used for the semiconductor layer and the materials used for the perovskite layers described herein can be lattice matched, thereby leading to enhanced electrical properties and increased device efficiencies.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the examples, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate examples of the present teachings and together with the description, serve to explain the principles of the disclosure.
Reference will now be made in detail to the examples which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the examples are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein are to be understood to encompass any and all sub-ranges subsumed therein. For example, a range of “less than 10” can include any and all sub-ranges between (and including) the minimum value of zero and the maximum value of 10, that is, any and all sub-ranges having a minimum value of equal to or greater than zero and a maximum value of equal to or less than 10, e.g., 1 to 5. In certain cases, the numerical values as stated for the parameter can take on negative values. In this case, the example value of range stated as “less that 10” can assume negative values, e.g. −1, −2, −3, −10, −20, −30, etc.
Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases. Furthermore, to the extent that the terms “including,” “includes,” “having,” “has,” “with,” or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” Additionally, in the discussion and claims herein, the term “on” used with respect to two materials, one “on” the other, means at least some contact between the materials, while “over” means the materials are in proximity, but possibly with one or more additional intervening materials such that contact is possible but not required. Neither “on” nor “over” implies any directionality as used herein. The term “at least one of” is used to mean one or more of the listed items may be selected. As used herein, the phrase “one or more of”, for example, A, B, and C means any of the following: either A, B, or C alone; or combinations of two, such as A and B, B and C, and A and C; or combinations of three A, B, and C.
The following examples are described for illustrative purposes only with reference to the Figures. Those of skill in the art will appreciate that the following description is exemplary in nature, and that various modifications to the parameters set forth herein could be made without departing from the scope of the present examples. It is intended that the specification and examples be considered as exemplary only. The various examples are not necessarily mutually exclusive, as some examples can be combined with one or more other examples to form new examples. It will be understood that the structures depicted in the figures may include additional features not depicted for simplicity, while depicted structures may be removed or modified.
Generally described herein are optoelectronic devices that include at least one epitaxially grown perovskite material layer, as opposed to amorphous or polycrystalline perovskite layers that suffer from limitations such as humidity degradation temperature instability, and UV instability, and corresponding methods for growing the at least one perovskite material layer, for example, on a semiconductor substrate. To overcome issues associated with amorphous or polycrystalline perovskites as described above, a method for single crystal perovskite fabrication includes forming an epitaxial single layer of the perovskite on a single crystal semiconductor substrate. That is, by selection of a single crystal semiconductor substrate having a lattice constant that is compatible with the quasi-cubic lattice constant of perovskites, the formation energy of such quasi-cubic-structured perovskites as a single crystalline layer is energetically favored when fabricated epitaxially on a substrate having a lattice matched crystal structure.
In an example, a semiconductor device comprises: a semiconductor substrate and at least one perovskite layer disposed on the substrate. The semiconductor substrate comprises a single-crystal semiconductor and the at least one perovskite layer comprises a single-crystal organometallic-halide ionic solid perovskite. In one implementation,
As described in more detail below, the semiconductor substrate 220 comprises a single-crystal semiconductor with a corresponding semiconductor crystal structure 20. The substrate single-crystal semiconductor may be configured as a polar crystal (e.g., in the case of a III-V semiconductor, polarized with surface group III atoms that are slightly positively charged respect to negative group V atoms). The semiconductor substrate 220 may be purchased or may be fabricated by known methods.
The perovskite layer 210 comprises a single crystal perovskite, such as an organometallic-halide ionic solid perovskite, that has a corresponding quasi-cubic perovskite crystal structure 10′. As described above for
As discussed above, the formation energy of a single crystalline layer, such as that for perovskite layer 210, is not favorable to the formation of many small crystalline grains such as those of a polycrystalline perovskite layer. Therefore, in order to reproduce the lattice spacing represented by lattice constant 24, 24′ of the semiconductor crystal structure 20 without forming multiple nuclei of the epitaxial layer material (which would lead to a polycrystalline layer instead of a single crystal), there must also be an epitaxial relationship between the quasi-cubic perovskite crystal structure 10′ of the perovskite layer 210 and semiconductor crystal structure 20 of the semiconductor substrate 220. That is, the perovskite material selected for epitaxial growth must be capable of forming a quasi-cubic perovskite crystal structure 10′ that has a lattice constant similar to the lattice constant of the underlying substrate's semiconductor crystal structure 20. In other words, the lattice mismatch between the quasi-cubic perovskite crystal structure 10′ and the semiconductor crystal structure 20 must not be too large. That is, the quasi-cubic perovskite crystal structure 10′ and the semiconductor crystal structure 20 are substantially lattice matched. In an example, the lattice mismatch between the quasi-cubic perovskite crystal structure 10′ and the semiconductor crystal structure 20 may be less than or equal to about 17%, such as less than or equal to about 8%, including less than or equal to about 5%, such as less than or equal to about 3%. Accordingly, as used here, the phrase “substantially lattice matched” includes a lattice mismatch between the quasi-cubic perovskite crystal structure 10′ and the semiconductor crystal structure 20 of less than or equal to about 17%, such as less than or equal to about 8%, including less than or equal to 5%, such as less than or equal to about 3%.
The perovskite layer 210 may comprise an organometallic halide ionic solid perovskite, for example, a single-crystal organometallic-halide ionic solid perovskite. In an example, the organometallic halide ionic solid perovskite comprises an epitaxially grown single crystal. Generally, the organometallic halide ionic solid perovskite may be represented by the formula, ABX3, where A comprises an organic ion, B comprises a group-IV ion, and X comprises a halide ion. The organic ion may comprise methylammonium (MA), formamidine (FA), at least one alkali metal, or combinations thereof, wherein the alkali metal may comprise cesium (Cs), rubidium (Rb) or both. The group-IV ion may comprise Pb+, Sn+, or a combination thereof and the halide ion may comprise Br, P, or combinations thereof. In an example, the organometallic halide ionic solid perovskite comprises methylammonium lead iodide (CH3NH3PbI3), methylammonium lead bromide (CH3NH3PbBr3), methylammonium lead chloride (CH3NH3PbCl3), methylammonium tin bromide (CH3NH3SnI3), methylammonium tin bromide (CH3NH3SnBr3), formamidinium lead iodide (NH2CH═NH2PbI3), or mixtures thereof.
In order to be substantially lattice matched to an underlying semiconductor substrate so as to be, for example, capable of epitaxially growing as a single crystal, exemplary organometallic halide ionic solid perovskites can include those having quasi-cubic lattice constant (aperovskite) of between 5.2 Å to about 6.6 Å, or for example, between about 5.6 Å to about 6.4 Å, including between about 5.6 Å to about 5.8 Å, between about 5.8 Å to about 6.0 Å, or between about 6.0 Å to about 6.4 Å. As used herein the term “quasi-cubic lattice constant” refers to a non-directional average of all of the lattice constant dimensions of semiconductors having multiple crystallographic forms (e.g., in the case of III-V structures, cubic and hexagonal). Additionally, the at least one perovskite layer may comprise more than one perovskite layer stacked, one over the other, either on one another or with one or more intervening layers between each of the more than one perovskite layers. In an implementation, the at least one perovskite layer may comprise a thickness of equal to or less than about 10 microns, for example, in order to serve as the active layer in a semiconductor device.
The semiconductor substrate 220 comprises a material having a crystal structure similar to that of the perovskite's crystal structure. That is, the semiconductor substrate may comprise a semiconductor crystal structure having a cubic or hexagonal lattice constant (asubstrate) of between 5.2 Å to about 6.6 Å, or for example, between about 5.3 Å to about 6.5 Å, including between about 5.3 Å to about 5.5 Å, between about 5.6 Å to about 5.7 Å, between about 5.8 Å to about 6.0 Å, or between about 6.4 Å to about 6.5 Å. As discussed above with respect to
The first and second electrodes may be any conductive material capable of forming an ohmic contact with the perovskite of the at least one perovskite layer 210 and with the semiconductor substrate 220. Exemplary electrode materials include metals such as Al and Ag; metal alloys such as AlAg, carbon-based ohmic contacts, conductive oxides such as indium tin oxide (ITO) or fluorine-doped tin oxide (SnO2:F); or mixtures thereof. The first and second electrodes may be formed according to standard electrode processing methods known in the art.
A first implementation of the polar alignment in the quasi-cubic perovskite crystal structure 10′ and the epitaxial relationship between quasi-cubic perovskite crystal structure 10′ and semiconductor crystal structure 20 are visualized in the (110) edge-on view 230a of the inset 230 in
In addition to being polar-aligned with the surface of the semiconductor substrate 220's semiconductor crystal structure 20, as described above with respect to
A second implementation of the polar alignment in the quasi-cubic perovskite crystal structure 10′ and the epitaxial relationship between quasi-cubic perovskite crystal structure 10′ and semiconductor crystal structure 20 are visualized in the (110) edge-on view 230b in
In addition to being polar-aligned with the surface of the semiconductor substrate 220 semiconductor crystal structure 20, as described in the example above for the group V-terminated, III-V compound semiconductor as shown in
While the examples have been illustrated respect to one or more implementations, alterations and/or modifications can be made to the illustrated examples without departing from the spirit and scope of the appended claims. In addition, while a particular feature of the examples may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular function.
Other examples will be apparent to those skilled in the art from consideration of the specification and practice of the descriptions disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the examples being indicated by the following claims.