Heterogeneous material integration through guided lateral growth

Abstract

Methods are provided for generating a crystalline material. The methods comprise depositing a textured thin film in a growth seed area, wherein the textured thin film has a preferential crystallographic axis; providing a growth channel extending from the growth seed area, the growth channel permitting guided lateral growth; and growing a crystalline material in the growth channel along a direction that is substantially perpendicular to the preferential crystallographic axis of the textured thin film. A preferred crystalline material is gallium nitride, and preferred textured thin films are aluminum nitride and titanium nitride.

Claims

1. A method for generating a crystalline material, the method comprising: depositing a textured thin film of a nitride material in a growth seed area, wherein the textured thin film comprises fibrous grains having a majority oriented along a preferred crystallographic axis; providing a growth channel extending from the growth seed area, the growth channel permitting guided lateral growth; and growing a III-V crystalline material at a temperature of at least 900 C. in the growth channel along a direction that is perpendicular to the preferred crystallographic axis of the textured thin film, wherein the textured thin film has not undergone recrystallization up until the crystalline material begins to grow, wherein the crystalline material is gallium nitride.

2. The method of claim 1, further comprising: growing the crystalline material into a single crystalline region at an end of the growth channel wherein the crystalline material is single crystalline over an area as large as 200 square microns.

3. The method of claim 1 wherein the textured thin film comprises aluminum nitride or titanium nitride.

4. The method of claim 1, wherein the crystalline material is grown on an amorphous substrate such that the crystalline material and the substrate are heterogeneously integrated.

5. The method of claim 4, wherein the substrate comprises silicon dioxide.

6. The method of claim 1, further comprising the step of generating the crystalline material from a polycrystalline material by evolutionary selection within the growth channel, wherein the polycrystalline material is grown from the growth seed area.

7. The method of claim 1, wherein the method comprises selectively growing a polycrystalline material from the growth seed area and continuing through the growth channel such that the multiplicity of orientations in the polycrystalline material lessen as the growth extends farther from the growth seed area in the growth channel, thereby providing the crystalline material having a single orientation from the polycrystalline material.

8. The method of claim 1, wherein the growing of the crystalline material from the seed area into the growth channel is selected from metalorganic chemical vapor deposition, hydride vapor phase epitaxy, molecular beam epitaxy or liquid phase epitaxy.

9. The method of claim 1, wherein depositing the textured thin film comprises depositing the textured thin film such that a portion of the thin film is connected to the growth channel to provide a growth seed area.

10. The method of claim 9, wherein the portion of the thin film that provides the growth seed area is a side surface or a top of the textured thin film.

11. The method of claim 10, wherein the growth channel is formed by: patterning the textured thin film into one or more desired thin film patterns, covering said one or more thin film patterns with dielectric material to form a dielectric cover, wherein the dielectric cover has at least a first end and a second end; removing at least a portion of the first end of the dielectric cover so as to expose an edge of the thin film pattern, and removing a first portion of the textured thin film from under the dielectric cover to form a tunnel while leaving a second portion of the textured thin film within the second end of the dielectric cover, wherein the second portion of the textured thin film has a side surface; wherein the side surface of the thin film serves as the growth seed area.

12. The method of claim 10, wherein the portion of the thin film that provides the growth seed area is a top surface of the textured thin film, and wherein the growth channel is formed by: covering the textured thin film with a first dielectric layer having a top surface, opening a window to form the growth seed area, covering the top surface of the first dielectric layer and the growth seed area with a sacrificial layer, patterning the sacrificial layer into desirable shapes with one portion connected to the growth seed area, depositing a second dielectric layer on top of the sacrificial layer, performing another patterning to expose the edge of the sacrificial layer, and removing the sacrificial layer to form a channel defined by the first and second dielectric layers connected to the growth seed area.

13. A method for generating a crystalline material on a substrate, the method comprising: depositing a textured thin film of a nitride material in a growth seed area of a substrate, wherein the growth seed area has a first width and the textured thin film comprises fibrous grains having a majority oriented along a preferred crystallographic axis; providing a growth channel on the substrate connected to the growth seed area, the growth channel having a second width, wherein the second width is less than the first width; providing a growth area on the substrate connected to the growth channel, the growth area having a third width, wherein the third width is greater than the second width; and selectively growing gallium nitride crystalline material at a temperature of at least 900 C. from the growth seed area and continuing through the growth channel such that a multiplicity of orientations in the gallium nitride crystalline material lessen as the growth of the gallium nitride crystalline material extends farther from the growth seed area, wherein the gallium nitride crystalline material in the growth area has a single orientation and wherein the textured thin film has not undergone recrystallization up until selectively growing the gallium nitride crystalline material.

14. The method of claim 13, further comprising forming the growth channel by depositing a grooved dielectric layer on the textured thin film or a substrate.

15. The method of claim 13, further comprising depositing a vertical confinement layer above the growth channel and optionally above the growth area such that the growth of the crystalline gallium nitride material is vertically confined at least through the growth channel and optionally in the growth area.

16. The method of claim 13, wherein the crystalline material in the growth area is single crystal over an area as large as 200 square microns.

17. The method of claim 16, wherein: the textured thin film comprises aluminum nitride or titanium nitride; and the substrate comprises silicon or silicon dioxide.

18. A method for producing a gallium nitride crystalline material, the method comprising: depositing a textured thin film of a nitride material in a growth seed area, wherein the textured thin film comprises fibrous grains having a majority oriented along a preferred crystallographic axis; providing a growth channel extending from the growth seed area, the growth channel permitting guided lateral growth; and growing the gallium nitride crystalline material at a temperature of at least 900 C. in the growth channel along a direction that is perpendicular to the preferred crystallographic axis of the textured thin film, wherein the textured thin film has not undergone recrystallization up until the crystalline material begins to grow.

19. The method of claim 18, wherein the textured thin film comprises aluminum nitride, zirconium nitride, or titanium nitride.

20. The method of claim 18, further comprising depositing the textured thin film on an amorphous substrate.

21. The method of claim 18, wherein the method comprises selectively growing a polycrystalline material from the growth seed area and continuing through the growth channel such that the multiplicity of orientations in the polycrystalline material lessen as the growth extends farther from the growth seed area in the growth channel, thereby providing gallium nitride crystalline material having a single orientation over an area as large as 200 square microns.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIGS. 1A to 1E are schematic drawings illustrating the idea of guided lateral overgrowth of a crystalline material.

(2) FIG. 2A shows an open channel configuration for ES-SAG growth, where (1) a SiO.sub.2 mask is photolithographically defined on a textured substrate, (2) SAG on the exposed template region, and (3) lateral overgrowth over the SiO.sub.2 channel, which is constrained in the opposite lateral direction. FIG. 2B) are inclined SEM images of growths performed with single crystal GaN as a template, with a lateral overgrowth length of about 2 m, with thickness of 400 nm (v.sub.lateral/v.sub.vertical<5).

(3) FIGS. 3A to 3E are top-view schematic drawings depicting growth and orientation selection during lateral guided growth.

(4) FIGS. 4A to 4C illustrate other embodiments of a method of generating a crystalline material within a growth channel (in this case, tunnels of various shapes).

(5) FIG. 5A shows inclined SEM of SiO.sub.2 stripe pattern tunnel substrates before and after lateral undercut etch of the sputtered AlN seed by TMAH. FIG. 5B shows a top view SEM, constrast from underneath the top SiO.sub.2 layer showing the depth of the AlN front and FIG. 5C before and after removing the SiO.sub.2 to expose the (0001) textured AlN seed that serves as the first orientation selection template for GaN.

(6) FIG. 6A shows 2 m width tunnel patterns 602, FIG. 6B shows 4 m width tunnel patterns 604, FIG. 6C shows 8 m width tunnel patterns 606 and FIG. 6D shows 16 m width tunnel patterns 608 1208 after GaN growth. GaN growth duration is long enough that the growth fills and extends outside the tunnel, (tunnel depth <5 m, 1 hr growth at 1030 C., 15 sccm TMGa, 2 slm NH3, 100 mbar).

(7) FIGS. 7A to 7C show morphological analyses and diffractive pole figures GaN growth on SiO.sub.2, on an AlN layer, and in a growth tunnel.

(8) FIGS. 8A to 8C show characterizations of GaN grown by evolutionary selection in a growth tunnel.

(9) FIGS. 9A and 9B provides photographs of transmission electron microscopy (TEM) performed on the GaN crystals.

(10) FIG. 10A shows laterally unconstrained growth of GaN from textured AlN seed. FIG. 10B is an EBSD characterization which shows the grain evolution.

(11) FIG. 11 shows an image of a growth seed area 1102 that permits evolutionary selection growth from a top surface rather than side of the AlN seeds into a growth channel 1104.

(12) FIGS. 12A to 12C show growth tunnels of various designs. FIG. 12A shows a growth tunnel with 60 bends 1202. FIG. 12B shows a growth tunnel with 90 bends 1204. FIG. 12C shows a growth tunnel with 120 bends 1206.

(13) FIG. 13A shows simulation of ES growth, vertical lines denoting grain boundaries, horizontal lines denoting growth fronts at different times. FIG. 13B shows the number of surviving grains as a percentage of original as film thickness increases. FIG. 13C shows the orientation distribution of grains at several film thicknesses, the sharpening of the peak around 90 shows the orientation selection of grains most closely oriented normal to the substrate. FIG. 13D shows average grain size as a function of thickness, display a (h/d.sub.0) dependence.

DETAILED DESCRIPTION

(14) The present disclosure provides methods for generating a crystalline material from a textured thin film, including methods for generating a single crystal material on an amorphous substrate. A textured thin-film as used herein refers to a film of crystalline grains of less than micrometer dimensions (less than 1 m), preferably nanometer dimensions (that is, of the scale of 10 to 500 nm) which have a preferential but non-uniform crystallographic orientation. The present disclosure provides methods for generating a crystalline material from a textured thin film, wherein the crystalline is grown along a direction that is substantially perpendicular to the preferential crystallographic axis of the textured thin film.

(15) A growth channel as used herein refers to a channel, groove, tunnel or other confinement having a length greater than its width or height. Preferably the growth channel as a lateral to vertical ratio (v.sub.lateral/v.sub.vertical) that is greater than or equal to 5. In some embodiments, the growth channel has a width that is from 10 to 200 times, alternatively 10 to 50 times, the size of the nuclei (crystallites) of the textured thin film. The length of the growth may be based on the characteristic length in evolutionary selection and is sufficient to provide that the crystalline material growing at or near the far end of the channel consists of a single crystal. The growth channel is adapted to remove or lessen degrees of freedom in grain orientations of the textured thin film, for example, by removing one, two or three degrees of freedom. In some embodiments, the growth channel has an hour-glass shape or a narrower width in a middle portion. In some embodiments, the growth channel has bends having an angle between about 30 and about 150, alternatively between about 60 and about 120. More particularly, a growth channel in any of the embodiments has one or more bends having an angle of 30, 40, 45, 50, 60, 70, 75, 80, 90, 100, 105, 110, 120, 130, 135, 140, 145, and/or 150.

(16) FIGS. 1A to 1E show how a growth channel can be configured and an embodiment of a method of guided epitaxial growth can be carried out. FIG. 1A depicts how a growth window or seed area 102 (a via window exposing the underlying crystalline or textured layer 104) and an interconnected dielectric channel 106 (a shallow grooved pattern created into a dielectric layer) are created. The height difference between the channel and the seed area is around 100 nm. The seed layer 104 has a unique property; it is a strongly textured nature, sometimes called fiber-textured. See, for example, G. Abadias, Stress and preferred orientation in nitride-based PVD coatings, Surface and Coating Technology 202, 2225-2235 (2008). The majority of the grains are strongly orientated along a preferred axis but normally there is no in-plane alignment (see a graphic plan-view representation in FIG. 3A).

(17) During the subsequent growth, as the surface is largely masked by dielectric materials 108 with an inert surface (including both the bottom surface log and lateral surfaces 110 in FIG. 1A, selective-area growth will take place within only the seed area 102. Adatoms will only be added to the seed region through both vertical and horizontal growth, depicted as 112 in FIG. 1B. Growth conditions should be carefully selected to suppress the growth velocity along the fiber-texture axis while enhancing the growth velocities in the in-plane directions. While the height of the layer within the seed window only increases in a limited way, a substantial lateral growth is expected to take place within the channel (FIGS. 1C and 1D), thus the term guided growth is derived. Crystal growth in the growth channel will be along a direction that is substantially perpendicular to the preferred crystallographic axis of the textured thin film. The lateral growth of fiber-textured grains within the channel (FIGS. 1C and 1D) represents an important aspect of the present disclosure, as an orientation selection process (A. van der Drift, Evolutionary selection, a principle governing growth orientation in vapour-deposited layers, Philips Res Repts 22, 267-288 (1967) is expected to take place horizontally. In FIG. 1E, the crystalline material has grown into a growth area 114 having a width that is greater than the width of the growth channel 106. In the growth area 114, a single crystalline material can be formed as a layer or film.

(18) FIG. 2A also shows schematic drawings of a growth structure having a textured thin film 204 in a growth seed area, a growth channel 206, and a growth area 214. Adatoms 212 are initially added vertically on the textured thin film, followed by horizontal growth through the growth channel 206.

(19) The crystalline material grown through a laterally constrained open channel, as shown in the SEM images in FIG. 2B. With a textured seed, the c-oriented GaN will laterally extend over the amorphous mask by use of growth conditions to enhance the v.sub.lateral/v.sub.vertical growth rate ratio. The preferred maximum ratio of about 5 was obtained with growth conditions of 1100 C., 50 mbar, 5 sccm TMGa and 1 slm NH.sub.3 under N.sub.2 carrier gas. However, a prohibitively thick SiO.sub.2 mask would be required to constrain the growth and at the same time enable larger area GaN. Thus, vertical confinement is added in preferred embodiments of the method. Preferred growth conditions include temperatures in the range of about 900 C. to about 1100 C., alternatively about 1030 C., and pressures in the range of about 50 mbar to about 300 mbar, alternatively about 100 mbar.

(20) FIG. 3A illustrates a fiber-textured seed window 304 exposing oriented yet misaligned (in-plane) grains, denoted by different shading. FIGS. 3B & 3C illustrate initial stages of lateral guided growth since the growth channel 306 is the only viable space for layer growth; orientations with the fastest growth velocity will gradually dominate the growth front. FIG. 3D illustrates that, as the guided growth proceeds, there will be a gradual down selection or filtering of grains 308, eventually reaching a stage of single grain growth with an appropriate choice of the width and length of the guided channel 306. This phenomenon is sometimes called necking. FIG. 3E illustrates further development of the filtered grain into a large-area, single crystalline layer 316 in the targeted semiconductor-on-insulator region. The large-area, single crystalline layer is formed in the growth area 314.

(21) The microstructural evolution that takes place within the channel 306 is illustrated schematically in FIGS. 3C and 3D. It is expected that the misaligned grains adjacent to the channel will have the opportunities to grow laterally. In contrast to the typical orientation selection described in Van der Drift that takes place vertically, or parallel to the surface orientation, the guided growth here represents a novel implementation of orientation selection, where crystalline material is generated perpendicularly to the surface orientation of the textured thin film, ultimately causing the formation of a single crystalline region 314 that is some distance away from the original seed window 304.

(22) This process described above enables the preparation of single crystalline semiconductor from a textured thin-film, including a fiber-textured thin film. It is well known that many metal and nitride thin films, when deposited at low temperatures (<0.3 T.sub.M.P.) on amorphous or crystalline substrates, will develop into a fiber textured morphology. Taking advantages of such a known phenomenon (summarized in Abadias) in inducing crystallographic alignment along one axis on essentially arbitrary substrates, the guided, selective-area, and channeled growth (FIGS. 1-3) is utilized to drastically reduce the in-plane (orthogonal) misalignment to obtain single-crystalline device layers on essentially any substrates.

(23) While this principle can be applied to many possible sets of (substrates, fiber-textured layer, device layer) combinations, one preferred choice would be the preparation of device quality GaN through lateral guided growth on sputtered AlN ((0001) textured) or TiN ((111) textured) on oxide on Si (001) that will integrate two mainstream technologies, the silicon-based microelectronics and GaN-based opto- and power-electronics. As a preferred aspect, methods of generating single-crystalline GaN on amorphous templates are provided herein.

(24) The present disclosure demonstrates single crystal growth on amorphous oxide by exploiting evolutionary selection growth, which is responsible for the formation of polycrystalline and textured thin films. Another embodiment of a method of generating a crystalline material within a growth channel (a tunnel) is illustrated in FIG. 4. With the successive applications of evolutionary selection along two perpendicular axes (FIG. 4A). First vertically in Step 1 and then horizontally in Step 2, the degrees of freedom in grain orientations are removed, resulting in the preparation of single-crystalline GaN on a SiO.sub.2/Si(100) template. The conceptual model of evolutionary selection is confirmed by the modeling of growth dynamics and provides a universal procedure in forming crystalline layers on amorphous substrates.

(25) FIG. 4 shows the concept and fabrication of a SiO.sub.2 tunnel structure. FIG. 4A provides a schematic of the concept used here. Growth proceeds in two steps: (1) vertical deposition 401 of a textured AlN 416 on a SiO.sub.2/Si(100) substrate 418, and (2) longitudinal metal-organic chemical vapor deposition (MOCVD) growth 403 of GaN. In step (2) the initial nucleation is randomly oriented and polycrystalline, and will undergo an evolutionary selection process (left, after [10] van der Drift) that results in single crystalline GaN. Other techniques for growth can be used, such other chemical vapor deposition (CVD) techniques. FIG. 4B shows processing flow of the SiO.sub.2 tunnels. A layer of AlN 416 is deposited in the substrate 418, then patterned (using lithography or another technique) into one or more thin film patterns 420. The pattern 420 is then covered with a dielectric cover 422. At least a portion of a first end of the dielectric cover 422 is removed so as to expose an edge of the thin film pattern 406. A portion of the textured thin film is removed from under the dielectric cover to form a tunnel 424, but a portion is kept to provide a seed. Single crystalline GaN 426 is generated in the tunnel. FIG. 4C is inclined SEM images 430, 432, 434, 436 and 438 of the completed tunnel fabrication, with exposed AlN 431, 433, 435, 437 and 439 at the ends. Characterization of growth in patterns on the left are shown in FIG. 9, and results in the patterns on the right (angled at 60, 90 and 120 are shown in FIGS. 12A to 12C). The scale bar is 20 m.

(26) The present methods employ a dielectric cover fabricated to confine the subsequent growth in two directions. FIG. 5 shows a photograph of a fabricated SiO.sub.2 growth mask 502 defining several growth tunnels 506 after the AlN has been laterally undercut etched 503. The undercut AlN is better seen after the SiO.sub.2 has been removed 505.

(27) While single crystalline material is obtained within the tunnel as measured by EBSD, another indication of crystallinity can be seen by growth outside the tunnel, by an extended duration of MOCVD growth of GaN. FIG. 6 shows photographs of GaN crystals 601, 603, 605, and 607 generated in growth tunnels 602, 604, 606, and 608 and extending out of those tunnels. FIG. 6A shows growth tunnels 602 having a width of 2 m. Most of the crystals extend out of the tunnel exhibit one or more components with six-fold symmetry, reflecting the symmetry of the wurtzite GaN unit cell. Vertical facets (m-plane) bound the crystal. The number of crystals that are present at the opening of the tunnel increase with tunnel width (with mostly single crystal for the 2 m and 4 m tunnel width, and 2 or more crystals for 8 m and 16 m), which is due to incomplete filtering of the additional nucleated grains for the wide tunnels.

(28) Deposition of thin films on amorphous substrates does not need to be, as one might expect, always disordered and amorphous. There are instances that textured thin films can be formed spontaneously on arbitrary substrates.sup.4,5,6,7. These textured films consist of fibrous grains with a preferential axis oriented along the growth direction yet with no in-plane (transverse) alignment. The origin of the spontaneous formation of orientation with the increase of film thickness was explained by the model of evolutionary selection (ES).sup.8. According to this model the randomly oriented nuclei grow and undergo a competitive, geometric selection process; nuclei with their fastest growing axis oriented obliquely from surface normal are blocked (or filtered out) by adjacent nuclei with better on-axis alignment, thus creating a survival of the fastest phenomenon. While these textured thin films are in essence polycrystalline and have not been considered for active devices, the mechanism associated with their formation offers a unique pathway to non-epitaxial growth of single crystalline layers on amorphous substrates.

(29) FIG. 7 shows GaN growth under differing conditions. FIG. 7A is a photograph of the direct deposition of GaN on SiO.sub.2. Pole figure, bottom, indicates random orientation of GaN crystals. FIG. 7B is a photograph of GaN grown on sputtered AlN and it forms c-axis oriented grains following the orientation of the AlN template. A distinct [0001] orientation, but random in-plane orientation, of the GaN is shown in the pole figure below. FIG. 7C shows that the present methods can be used to grow single crystals of GaN of defined location and size. The pole figure of one of these crystal is shown below. The scale bar for SEM images is 20 m.

(30) The orientation of an arbitrary grain possesses three degrees of freedom: polar, azimuthal, and rotational/twist.sup.8. This can be seen by typical growth of semiconductors on oxide or amorphous templates, which result in the formation of randomly oriented crystallites, as shown in FIG. 7A for GaN deposited on SiO.sub.2. The surface exhibits large isolated discrete crystallites nucleated on the SiO.sub.2 mask, and the pole figure (FIG. 7A) confirms their random orientation. No mechanism rendering orientational guidance exists for the GaN crystallites during nucleation or growth on SiO.sub.2, thus all three degrees of freedom in orientation are retained. The challenge of growing crystal on amorphous templates is formulated as a task to control and reduce the degree of freedom from three (completely random) to zero (single crystalline) with no need of crystalline underlayers. This disclosure discusses the concept and results of successive applications of evolutionary selection, along two orthogonal axes, such that single crystalline layers within a confined geometry can be obtained on an amorphous surface. This concept is illustrated in FIG. 4A. Without a loss of generality, GaN was chosen as an example for the evolutionary selection study. The importance of GaN in opto- and power electronics is well established.sup.9,10. A particular need that has received much attention but has not been solved before the present disclosure is the heteroepitaxial integration of GaN with mainstream Si technology. This aspiration faces major challenges including mismatches in lattice and thermal expansion constants.sup.11, the problem of chemical reactivity.sup.12, and the current leakage through conductive Si substrates.sup.13. By combining two processes in thin-film growth: evolutionary selection and selective-area growth (ES-SAG), the possibility is hereby validated of a non-epitaxial route to crystalline layers through the demonstration of dislocation-free, device quality GaN on amorphous SiO.sub.2 on Si(100).

(31) To implement the concept of evolutionary selection for the growth of GaN on SiO.sub.2, a textured AlN thin film was initially deposited. It has been shown that during the sputtering of nitride films, including TiN.sup.14,15, ZrN.sup.16 and AlN.sup.14,17, a preferred orientation develops as the film grows thicker. The formation of such a fibrously textured thin film effectively reduces the degrees of freedom from three to one. However, morphological analysis and the diffractive pole figure of GaN grown on such AlN layer (FIG. 7B) indicate the orientation distribution along c-axis is retained, but the same random in-plane orientation exists. The fact that in-plane alignment is not established makes such textured layers generally unsuitable for device applications, with the exception of micro-arrayed devices reported recently.sup.18.

(32) To eliminate the remaining degree of freedom, evolutionary selection growth of GaN was considered along a direction perpendicular to the first growth axis while using the initial AlN template as a textured seed. To facilitate the filtering process, horizontal (perpendicular) ES growth was carried out with a confined geometry, as depicted in FIG. 4, where the confined incorporation of reactants is enabled by the principle of selective area growth (SAG). A growth tunnel 424 with an additional vertical confinement is used, due to the limited vertical-to-horizontal ratios in growth rates.sup.19 (v.sub.vertical/v.sub.horizontal5, FIG. 3) which inhibit the ability to form large enough area within a reasonable film thickness.sup.20,21. In this way, the thickness of the layer produced by ES growth can be controlled to remain thin, but the distance of ES growth (along what we call the longitudinal axis) will have no practical limit in length.

(33) A schematic diagram of a fabrication process flow for growth tunnels and the subsequent ES-SAG growth as a method of generating a crystalline material is illustrated in FIG. 4B. Briefly, a PECVD SiO.sub.2 layer 402 is deposited on top of lithographically defined AlN stripes of different patterns 404 (FIG. 4B (iii)). The SiO.sub.2 layer 402 is removed at the ends of the patterns to expose a portion of the AlN 406 (FIG. 4B (iv)). Examples of fabricated AlN tunnels are shown in FIG. 3b, with the exposed AlN shown 406. AlN is then selectively etched underneath the SiO.sub.2 mask 402, resulting in a growth tunnels 424 bound by SiO.sub.2 in transverse (lateral and vertical) directions (FIG. 5), allowing only longitudinal SAG. A portion of AlN is retained to serve as a textured thin film seed. The fabricated tunnels are then cleaned and loaded into a MOCVD reactor for GaN growth. The sputtered AlN thus serves dual purposes as a filler (cast) to define the tunnel geometry and as a seed for horizontal ES growth.

(34) FIG. 8 shows characterization of GaN growth. FIG. 8A contains an electron backscatter pattern from a single spot about 6 m from the interface, and mapping to wurtzite GaN crystal is shown below. FIG. 8B shows GaN growth in a straight tunnel shape (such as FIGS. 1C, 4C top left), top view SEM and corresponding inverse pole figure measured by EBSD. FIG. 8C shows GaN growth in an hour-glass designed tunnel shape (such as FIG. 4C, bottom left), narrowing in width (2.2 m) from the initial width of the AlN seed (4.5 m), and extending back out in width. The scale bar is 2 m.

(35) FIGS. 8A and 8B summarize the characterization of a particular ES-grown GaN having a tunnel geometry of 4 m, 0.65 m and 20 m in the lateral and vertical dimensions and depth, respectively. An electron backscatter pattern is obtained approximately 6 m from the interface with the presence of clear and higher order Kikuchi bands confirming the single crystallinity and providing orientational indexing of GaN (c-axis oriented in agreement with the preferred axis of AlN). The dynamics of ES growth is revealed by EBSD inverse pole figure (IPF) mapping along the entire length of the GaN stripe, tracing the evolution from polycrystalline nucleation on AlN to a uniformly single-crystalline grain over a distance of 4 m by evolutionary selection. A clear c-axis alignment juxtaposed with in-plane six-fold symmetry in the pole figure of mapped spots (FIG. 4C) indicate that single crystallinity is achieved on an amorphous template. Increasing growth time, the crystal extending out of the tunnel opening exhibits the expected six-fold symmetry of single crystal wurtzite GaN (FIG. 6). In addition to straight tunnel patterns, variations have been designed, as shown in FIG. 4C and FIG. 12, to affect the evolution of grains from the seed. Design considerations have included the filtering of grains by an hour-glass shaped constriction in the tunnel width, as demonstrated in FIG. 8C, and the subsequent enlargement of width to allow large areas of GaN. In a preliminary study, single-crystalline GaN as large as 1020 m.sup.2, subject to the initial mask designs, can be routinely obtained on SiO.sub.2.

(36) FIG. 9 shows Transmission electron microscopy (TEM) analysis of the single crystalline GaN generated by the present methods. FIG. 9A is a plan-view bright-field TEM image taken in [0001] zone-axis orientation, showing sputtered AlN 902, a dislocation cluster 904, and GaN 906. FIG. 9B is a plan-view HR-TEM image of GaN. Near the interface between GaN and sputtered AlN seed, clusters and array of dislocations were observed. Dislocations created at the interface, due to lattice mismatch, can propagate through single crystal grains and interact with each other. Grain boundaries usually hinder the movement of dislocations, creating a pile-up at the boundary.sup.22. No dislocations were observed for the samples imaged several m away from the interface. Selected area electron diffraction (FIG. 9A inset) and plan-view high-resolution TEM confirms single-crystallinity of the GaN and show the hexagonal six-fold arrangement of wurtzite GaN.

(37) FIG. 10 shows laterally unconstrained growth of GaN from textured AlN seed. Thus, the ES-SAG growth of GaN has no lateral (in-plane) confinement, but still retains an upper ceiling for vertical confinement. FIG. 10A is an SEM image and FIG. 10B is an EBSD characterization which shows the grain evolution. The orientation and grain information obtained from EBSD is input into simulation obeying ES growth rules, and overlayed on the SEM image in FIG. 10A. The solid lines denote grain boundaries, and the dashed lines and shading denote the growth front in the longitudinal direction.

(38) It is clear that the thin film remains polycrystalline across the entire length of the growth, thus underscoring the necessity of lateral confinement. From EBSD, the position and specific in-plane orientation of each grain (FIG. 10B) are found, and these initial conditions are input into simulation of growth obeying ES selection rules.sup.8,23 (FIG. 13), and overlayed with the SEM (FIG. 10A). The agreement of the simulated grain morphology based on the EBSD orientation map provides a quantitative support to the claim that evolutionary selection is responsible for the realization of single crystalline GaN on SiO.sub.2.

(39) Non-epitaxial formation of single-crystalline GaN on SiO.sub.2 has been reported by combining the concept of evolutionary selection (ES) with selective area growth (SAG). The ES-SAG method lifts the requirement for an epitaxial template to be present for the formation of device quality semiconductor layers. While the single-crystalline GaN is not a continuous layer at present, its size and position is precisely controlled by lithography and the area can exceed tens to hundreds of square micrometers, thus is uniquely suitable for the heterogeneous integration effort of III-V semiconductors and Si CMOS. Thus, a method of generating a crystalline material having an area greater than 10 m.sup.2, alternatively greater than 20 m.sup.2, alternatively greater than 50 m.sup.2, alternatively greater than 100 m.sup.2, alternatively greater than 200 m.sup.2, alternatively greater than 500 m.sup.2, is provided. The crystalline material can be a III-V material such as GaN, and/or can be heterogeously integrated with a substrate such as silicon semiconductors.

(40) FIG. 11 shows the fabrication process flow for evolutionary selection growth from a top surface rather than side of the AlN seed material 1106. A window 1102 for selective area growth is provided above the top surface of the AlN textured thin film 1106. A material can crystallize (likely by forming textured crystallites) on the top surface of the AlN seed 1106, and then grow laterally through a growth channel such as the lateral growth guide 1104 shown in FIG. 11. The lateral growth guide 1104 can be formed by covering the textured thin film with a first dielectric layer 1108 having a top surface, opening a window to form a growth seed area, covering the top surface of the first dielectric layer and the growth seed area with a sacrificial layer, patterning the sacrificial layer into desirable shapes with one portion connected to the growth seed area, depositing a second dielectric layer 1110 on top of the sacrificial layer, performing another patterning to expose the edge of the sacrificial layer, and removing the sacrificial layer to form a channel defined by the first and second dielectric layers connected to the growth seed area.

(41) The ability to change the growth filtering process by changing the tunnel shape is demonstrated in FIGS. 12A through 12C. Here, the tunnel has bends 1202 of 60, in order manipulate the length in which the single crystal dominates. FIG. 12A shows a growth tunnel designed with a 4 m width and 60 bends 1202. FIG. 12B shows a growth tunnel designed with a 4 m width and 90 bends 1204. FIG. 12C shows a growth tunnel designed with a 4 m width and 120 bends 1206. It is seen with a sharper bending angle, the distance in which all the grains are eliminated is reduced (from 8 m to 5.3 m to 2.1 m for bending angle reduced from 120 to 90 to 60, respectively). Due to the shadowing effect, grains closer to the side perpendicular to the growth direction interact with the SiO.sub.2 sidewall and are blocked from propagation. In FIGS. 12A to 12C, SEM and corresponding EBSD analysis of the grains show that the bending angle is effective in reducing the length in which a single crystal grain of GaN dominates.

(42) The concepts explored here are expected to provide universal and flexible integration of semiconductor materials with a new range of substrates, including oxides, metals, ceramics and glass. The evolutionary growth dynamics have been analyzed both analytically and by computer simulation, mainly with regards to crystalline diamond growth.sup.23. Here, for GaN nuclei bounded by {1011} facets and hexagonal symmetry, the growth from a random distribution of nuclei with average spacing d.sub.0, with a film thickness of h was modeled in Matlab. Each nuclei and grain boundary are set as points which extend upwards at a direction determined by the nuclei growth orientation or by the neighboring points. In FIG. 13, 2000 such points are used (only a portion is shown, for clarity). For each set of neighboring points, the time for intersection is precalculated, and the growth evolves to the next intersection. The grain or grain boundary is annihilated based on the geometry, and the direction is recalculated. With this simulation, the inverse-quadratic dependence of grain size over the distance of evolutionary selection d/d.sub.3.sup.oc (h/d.sub.0).sup.1/2, where d is the average grain size, d.sub.0 is the average initial nuclei spacing and h is the film thickness, is recovered. This relation implies that the geometric filtering tends to be slow beyond the initial growth, thus competing grains could co-exist over a long distance.sup.23. Also shown is the increasing sharpness with thickness of the orientation distribution function around the direction normal to the substration. In FIG. 13B, the x-axis is thickness (h/d.sub.0) and the y-axis is number of grains (N/N.sub.0). In FIG. 13C, the x-axis is orientation (degrees) and the y-axis is P(theta). In FIG. 13D, the x-axis is thickness (h/d.sub.0) and the y-axis is average grain size (d/d.sub.0). This simulation program, in FIG. 10(b) is used analyze the growth evolution of laterally unconfined growth from a wide AlN seed.

(43) The crystalline material generated by the methods herein, particularly single crystal gallium nitride, can be used in a wide variety of applications, including but not limited to optical devices and high-temperature and high-power devices, such as light-emitting devices. The GaN layer can be an un-doped layer or may be doped to form a n-type GaN layer or a p-type GaN layer.

EXAMPLES

(44) The following methods were used to generate and evaluate the single crystal GaN and other materials described and shown above and in the figures.

(45) MOCVD growth of GaN on SiO.sub.2: A low temperature (LT) GaN nucleation step (550 C.) was employed to deposit equivalent planar thickness 30 nm of material on SiO.sub.2 on Si(001). The temperature was ramped to typical GaN growth temperature of 1030 C. for 15 minutes (at a planar growth rate of 2 m/hr). Without the LT GaN step, the surface is completely clear of GaN crystallites, as desorption of Ga precursors on the mask occurs before critical nuclei size is reached under the growth conditions used. The nuclei formed during the low temperature deposition are enlarged with further growth at high temperature, with no coalescence of crystals as the nucleation density is too low due to the inert nature of SiO.sub.2 and the high nucleation barrier.

(46) Fabrication of SiO.sub.2 tunnels on patterned AlN: A 650 nm thick AlN film was deposited on a thermally oxidized (500 nm thick SiO.sub.2) 4 silicon wafers with (100) orientation by alternating current reactive magnetron sputtering (OEM Group Inc). This film has an (0001) texture, with an XRD rocking curve (0002) FWHM of 1.72. The grain size is less than 100 nm with random in-plane orientation. The AlN is patterned, by standard photolithography and reactive-ion etching using SiO.sub.2 as a mask into stripes with various widths (from 1 m to 32 m) and shapes. Alternatively, other suitable patterning and etching techniques can be used. 1 m SiO.sub.2 was then deposited by plasma enhanced chemical vapor deposition to cover the AlN patterns. A second photolithography was performed to open the ends of the tunnel by removing the SiO.sub.2 on the sides of the AlN patterns using 5:1 buffered oxide etch. AlN is then undercut etch into the tunnel using 25% tetramethylammoniumhydroxide (TMAH) at 65 C. The lateral etch rates are between 0.5-1.5 m/hr, with etch selectivity over SiO.sub.2>50:1. Alternate etch rates are 0.1-7.5 m/hr. The substrates are then cleaned in piranha (5 min) and HCl diluted with DI water 1:1 (5 min) and rinsed in DI water.

(47) Selective area MOCVD growth of GaN in tunnel substrates: After substrates are dried, they are loaded into a metal-organic chemical vapor deposition (MOCVD) reactor (Aixtron 200-4 RF/S) for GaN growth. Trimethylgallium (TMGa) and ammonia (NH.sub.3) are used as source precursors, and H2 as a carrier gas. The substrates are ramped up to a growth temperature of 1030 C. in mixture of H.sub.2 (6.5 slm) and NH.sub.3 (3 slm), and held for 4 minutes for thermal cleaning and nitridization of surfaces in preparation for selective area growth. The growth temperature may be between 900 C.-1160 C. TMGa is introduced into the chamber at growth conditions between 900 C.-1070 C., 60-300 mbar, and 0.5-2 slm NH.sub.3. Typical longitudinal growth rates of GaN inside the tunnel are in the range of 4 to 12 m/hr.

(48) Characterization: To characterize growth, Nomarski optical microscopy was used to see GaN growth lengths within the tunnel. Scanning electron microscope was used to image the GaN crystals after removing the top SiO.sub.2 confined mask by BOE. The crystal structure and orientation was analyzed by electron backscatter diffraction (EBSD) using a FEI Quanta 3D field emission SEM equipped with a TSL Hikari high speed EBSD camera. Measurements were performed at an electron accelerating voltage of 20 kV, and data was processed using OIM Data Analysis software and Matlab using the MTEX toolbox for inverse pole figure mapping and pole figure plots. Transmission electron microscopy samples were prepared by conventional mechanical polishing followed by ion milling down to electron transparency. Plan-view bright field image of GaN stripe is taken in [0001] zone-axis orientation.

(49) The mechanism of evolutionary selection employed in this work is classified within the broader phenomena occurring during the spontaneous development of thin-film morphology, which have been classically organized within structure zone models (SZM).sup.5,6. Substrate temperature was identified as of particular importance as it primarily influences the growth mechanisms including adsorption, surface diffusion, grain growth, bulk diffusion, and desorption.sup.5,6,14. This classification is based on the distinct microstructural morphologies observed, and is generally classified into three zones. In zone I, the film structure is characterized by either a porous or amorphous microstructure, due to ballistic aggregation, usually when T<0.3TM (TM is the melting point), as a result of insufficient adatom mobility.sup.6. In zone II, the film consists of non-equiaxed columnar grains, often exhibiting a preferred orientation. It is in this zone, that sufficient surface diffusion is present such that the anisotropy of facet growth rates and direction of growth with respect to the substrate determine the grain growth rate, resulting in an evolutionary selection process between graine. Above zone II temperatures, the film becomes dominated by equiaxial grains, often related to grain growth processes due to suitably high temperatures for grain boundary migration.sup.7. Since the majority of vapor phase epitaxy takes place at 0.40.5 T.sub.m, surface diffusion of adatoms is sufficient for migration across islands and facets, and temperatures are not sufficient to activate grain growth in these materials.sup.8,14, which allow ES growth to take place under conventional VPE.

(50) With respect to the compositions described in the specification, it is intended that the specification also provides a description of methods of using any of those compositions in the described methods. With respect to the methods of manufacture described in the specification, it is intended that the specification also provides a description of the manufacture of any of the compositions described herein.

(51) All of the references cited herein, including patents, patent applications, and publications, are hereby incorporated in their entireties by reference.

(52) While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, of course, that the invention is not limited thereto since modifications can be made by those skilled in the art without departing from the scope of the present disclosure, particularly in light of the foregoing teachings.

(53) Although the dependent claims have single dependencies in accordance with U.S. patent practice, each of the features in any of the dependent claims can be combined with each of the features of other dependent claims or the main claim.

REFERENCE

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