Boron nitride (BN) has numerous advantageous physical and electrical properties for mechanical and (opto-)electronic applications, yet growing large single crystals is challenging. The ammonothermal method has demonstrated its suitability for large single-crystal gallium nitride growth and is investigated for its ability to grow BN. The temperature-dependent solubility of BN in sodium-containing supercritical ammonia is previously demonstrated. Herein, the application of a temperature gradient across a baffled autoclave toward the continuous dissolution and crystallization of BN is examined. BN deposits on all wetted surfaces in the lower-temperature zone, predominantly on the autoclave walls as polycrystalline sheets and to a lesser degree on suspended seeds of cubic BN as oriented, micrometer-sized, repeated trapezoidal platelet units. Analysis of the grown BN crystals by Raman, X-ray diffraction, and transmission electron microscopy suggests the growth of sp2-hybridized BN, predominantly the rhombohedral crystal structure on nitrided NiCr alloy surfaces and rhombohedral and hexagonal crystal structures on the cubic BN seed crystal surfaces. The interfacial relationships between the cBN and the sp2-hybridized BN phases are examined, where favorable attachment sites are discovered between the dissimilar lattices, further supporting the observed crystal growth.

The hexagonal polymorph of boron nitride (hBN) is a material of great interest for electronic and optoelectronic applications. There is a demand for large-area single crystals both as a bulk material and as a source of 2D monolayers for quantum and 2D devices. Recent work has produced millimeter-scale lateral dimensions but thicknesses only in the range of tens to lower hundreds of micrometers. The temperature (1400-1800 °C) and/or pressure conditions (2.5-2500 MPa) for crystal growth by existing methods provide significant limitations to upscaling and tend to produce very thin crystals. This study describes the growth of hBN crystals via two routes from a flux of lithium boron nitride in a novel parameter space: around 1200 °C with 0.1-1.5 MPa of nitrogen overpressure. Analysis of the hBN crystals provides evidence for optical transparency without coloration, phase purity, chemical purity, a narrow Raman peak width (8.2 cm-1 for E 2g), and aspect ratios (thickness/width) of 0.1-0.25 for crystals with lateral widths in the c-plane of 0.5-1.5 mm, offering a path for the attainment of thicker crystals.

The state-of-the-art ammonothermal method for the growth of nitrides is reviewed here, with an emphasis on binary and ternary nitrides beyond GaN. A wide range of relevant aspects are covered, from fundamental autoclave technology, to reactivity and solubility of elements, to synthesized crystalline nitride materials and their properties. Initially, the potential of emerging and novel nitrides is discussed, motivating their synthesis in single crystal form. This is followed by a summary of our current understanding of the reactivity/solubility of species and the state-of-the-art single crystal synthesis for GaN, AlN, AlGaN, BN, InN, and, more generally, ternary and higher order nitrides. Investigation of the synthesized materials is presented, with a focus on point defects (impurities, native defects including hydrogenated vacancies) based on GaN and potential pathways for their mitigation or circumvention for achieving a wide range of controllable functional and structural material properties. Lastly, recent developments in autoclave technology are reviewed, based on GaN, with a focus on advances in development of in situ technologies, including in situ temperature measurements, optical absorption via UV/Vis spectroscopy, imaging of the solution and crystals via optical (visible, X-ray), along with use of X-ray computed tomography and diffraction. While time intensive to develop, these technologies are now capable of offering unprecedented insight into the autoclave and, hence, facilitating the rapid exploration of novel nitride synthesis using the ammonothermal method.

Boron nitride (BN) is a fascinating ultra-wide bandgap semiconductor offering extreme material properties that can be leveraged in a range of potential applications including (opto-)electronic and quantum devices. Availability of high-quality, large-area and volume, single-crystal material would provide a significant boon to the community facilitating or enabling development of devices. BN has been successfully grown using high pressure, high temperature presses and precipitation from a solvent on the order of a few millimeters. While these methods have yielded high-quality material, scaling of these approaches is challenging motivating the search for additional bulk synthesis methods. This talk will present foundational work being performed in the pursuit of bulk BN growth using two industrial scalable methods: the ammonothermal method and a flux-based approach. The ammonothermal method utilizes supercritical ammonia at temperatures and pressures around 400—600 °C and 100—250 MPa, respectively. One or more mineralizers are added to the solution to enhance the solubility of BN. This talk will demonstrate temperature-dependent solubility of BN in basic ammonothermal solutions containing alkali [1] and/or alkaline earth metals. Initial crystal growth experiments were performed using sodium as the mineralizer yielding the spontaneous nucleation and growth of sub-mm sized hexagonal and rhombohedral BN. The flux-based method uses a solvent exhibiting exceptionally high solubility of nitrogen and boron. A dedicated growth system has been developed and initial growth runs have demonstrated the solubility and growth of BN from solution. Preliminary growth campaigns have successfully demonstrated the growth of ~ >0.1 mm sized BN crystals after 1-2 days. This work has been supported by NSF DMR 1832824, NSF CAREER 2046468, ARL DEVCOM UWBG RF Electronics Center, and Lehigh Startup Funds. [1] Dooley, J., Stoddard, N., Landskron, K. & Pimputkar, S. On the solubility of boron nitride in supercritical ammonia-sodium solutions. J. Cryst. Growth 621, 127381 (2023). doi: 10.1016/j.jcrysgro.2023.127381

Abstract The field of nitride‐based materials is producing some of the most promising and interesting candidates for advanced technology applications. Novel formulations and polymorphs are of interest for applications requiring one or more of: high hardness, high oxygen resistance at elevated temperatures, catalytic action, semiconductor light sources, and (ultra‐)wide band gap electronics. The synthesis of nitrides with excellent single crystal structural quality of an appreciable size is challenging whether working in solution growth techniques like ammonothermal and flux growth, or in vapor deposition techniques. This paper presents a perspective on recent developments in equipment and techniques for single crystal nitride synthesis with a view toward progress anticipated in the next 5–10 years.

Cubic boron nitride (cBN) is considered to be one of the leading candidates for next generation electronic devices yet has no current synthesis route for single crystals greater than a few mm in size leading to a lack of suitable substrates. New synthesis methods need to be explored, with the ammonothermal method being a potential candidate for synthesis of large area, thick cBN and hexagonal BN (hBN) single crystals. This paper investigates the solubility of BN in supercritical ammonia using sodium amide (NaNH2) as a mineralizer and cBN crystals as feedstock. Solubilities were measured based on mass loss of the feedstock at temperatures from 450-600 deg. C, with pressures of 150-190 MPa, using durations from 24-96 h and with varying amounts of Na. A positive solubility trend is demonstrated with respect to temperature with solubility varying from 0.017-0.050% molBN/ molNH3. Solubilities did not vary as a function of time or when>0.07 molNa/L mineralizer content was used suggesting both that equilibrium was reached and the solutions were saturated. These values are high enough to motivate further investigation for solution-based growth of BN.

Gallium nitride continues to be a material of intense interest for the ongoing advancement of electronic and optoelectronic devices. While the bulk of today’s markets for low-performance devices is still met with silicon and blue/UV LEDs derived from metal–organic chemical vapor deposition gallium nitride grown on foreign substrates such as sapphire and silicon carbide, the best performance values consistently come from devices built on bulk-grown gallium nitride from native seeds. The most prominent and promising of the bulk growth methods is the ammonothermal method of high-pressure solution growth. The state-of-the-art from the last five years in ammonothermal gallium nitride technology is herein reviewed within the general categories of growth technology, characterization and defects as well as device performance.

The Floating Silicon Method (FSM) has been established as a viable, stable method for growing single crystal ribbons directly from a silicon melt. With intense helium jet cooling to drive the linear progress of a [111] facet, pulled in the 110 direction, ribbons in the 0.6 - 3.0 mm thickness range can be grown at linear growth rates from 0.3 mm/s to > 6 mm/s as reported in the literature. We report on recent progress towards growing (100) oriented ribbons with a net thickness of < 200 mu m and a ribbon width up to 18 cm using a stable, continuous process in the Leading Edge prototype furnace. The 3D details of the single crystal growth are explained using the mechanics of the Limit Cycle Theory, with novel Internal Side Effect morphology described by a proposed Facet Flow Theory. Grown-in crystalline defect distributions are described as well as values of critical impurities like oxygen, carbon, dopants, and metals that are relevant for use as wafers for solar cells.

II-VI Aerospace & Defense currently supports the defense industry on several aerospace platforms by providing high quality, large, single crystal sapphire substrates and windows. There continues to be a rapidly increasing interest in large substrates capable of use in high energy laser (HEL) systems. Such applications require materials with high thermal conductivity and high thermal shock resistance, high strength, and near-zero defect levels. Laser damage-inducing defects include those which are incorporated in the substrate during crystal growth, as well as defects incurred during routine optical fabrication and finishing processes. In the following paper, II-VI A&D presents data for a-plane and cplane sapphire windows of sufficient size for projected HEL applications exhibiting laser-grade surface quality and surface roughness, while still maintaining low rms transmitted wavefront error. Included is a discussion evaluating the benefits of sapphire for envisioned HEL windows, as well as engineering challenges that should be considered.

Single crystal growth by the edge-defined film-fed growth method (EFG) has been commercially practiced for over 40 years. State of the art sapphire crystals can be over 300 mm wide, 10 mm thick and 1 m long. In addition to well-known defects such as bubble inclusions and bulk structure loss, we describe a crystalline defect occurring uniquely at the outer surfaces of the sapphire panel. Termed 'surface crystals', they penetrate less than 1 mm into the depth of the A-plane panel and can originate and terminate multiple times in a single panel. We report correlations with both temperature and ambient conditions and present micro-scale characterization to elucidate the nature of these defects.

There is an increasing industry need for high quality materials which can be used in high energy laser (HEL) applications. Currently, II-VI OS is growing large sapphire substrates for use in the defense industry on aerospace applications that operate in the visible and mid-wave infrared regions. II-VI OS is capable of producing a-plane and c-plane sapphire substrates of sufficient size for envisioned HEL applications, and in the following paper will present optical and material data on properties of interest. Specifically, data will be presented on BTDF and BRDF at 1.06 mu m in both s- and p-polarizations at angles of incidence (AOI) ranging from 0 to 60 degrees. These measurements are performed on a-plane and c-plane windows grown, fabricated and polished at II-VI OS Additionally, other critical properties evaluated include absorption at 1.06 mu m, as well as thermal expansion coefficient and Knoop hardness of c-plane sapphire.

SolarWorld has developed a new entrant in the field of crystal growth for silicon photovoltaic substrates. The NeoGrowth technique is a contactless bulk crystal growth method for producing single crystal ingots. NeoGrowth material can be produced at a throughput on par with G5 multicrystalline silicon, but with p‐type as‐grown minority carrier lifetimes exceeding 600 microseconds for a 1.5‐ohm cm resistivity. The silicon has low oxygen, and light‐induced degradation is measured at 0.5% to 0.7% in passivated emitter rear contact–based modules. In the first report of results from this technique, p‐type resistivity can be managed within a range of 1.5 to 2.0 ohm cm over the entire ingot. Dislocation density is shown to be typically in the 10 4 to 10 5 /cm 2 range but can be managed down to even lower levels. After cell processing steps, minority carrier lifetime can exceed 1.5 milliseconds for p‐type material and cell efficiencies on industrial cells range up to 20.9%.

In this work, we are showing that iron (Fe) related defects in mono-silicon have very different recombination characteristics depending on the doping element employed. While the defect characteristics of the Fe in its dissociated state is comparably the same in the materials of investigation, the defect characteristics of the associated state vary considerably. By using, defect parameter contour mapping (DPCM), a newly developed method for analyzing temperature and injection dependent lifetime data, we have for the first time, been able to show that in the case of gallium doping it is the orthorhombic state of the Fe-acceptor complex that is dominating the lifetime.

Spalling is a promising kerfless method for cutting thin silicon wafers while doubling the yield of a silicon ingot. The main obstacle in this technology is the high total thickness variation of the spalled wafers, often as high as 100% of the wafer thickness. It has been suggested before that a strong correlation exists between low crack velocities and a smooth surface, but this correlation has never been shown during a spalling process in silicon. The reason lies in the challenge associated to measuring such velocities. In this contribution, we present a new approach to assess, in real time, the crack velocity as it propagates during a low temperature spalling process. Understanding the relationship between crack velocity and surface roughness during spalling can pave the way to attain full control on the surface quality of the spalled wafer.

Gallium (Ga) doped silicon (Si) is becoming a relevant player in solar cell manufacturing thanks to its demonstrated low light-induced degradation, yet little is known about Ga-related recombination centers. In this paper, we study iron (Fe)-related recombination centers in as-grown, high quality, directionally solidified, monocrystalline Ga-doped Si. While no defect states could be detected by deep level transient spectroscopy, lifetime spectroscopy analysis shows that the minority carrier lifetime in as-grown wafers is dominated by low levels of FeGa related defect complexes. FeGa pairs have earlier been shown to occur in two different structural configurations. Herein, we show that in terms of recombination strength, the orthorhombic pair-configuration is dominant over the trigonal pair-configuration for FeGa. Furthermore, the defect energy level in the band gap for the orthorhombic defect center is determined to be EV + 0.09 eV, and the capture cross-section ratio of the same defect center is determined to be 220.

U.S. C. CPC .......... HOIL 31/03685 (2013.01); C30B II/00 (2013.01); C30B II/14 (2013.01); C30B 28/06 (2013.01); C30B 29/06 (2013.01); HOIL 31/182 (2013.01); C30B II/003 (2013.01); Y02E 10/546 (2013.01); Y10S 117/917 (2013.01) USPC ................ 117/13; 117/73; 117/921; 117/917 (58) Field of Classification Search USPC .............................................. 117/13, 73,971 See application file for complete search history.

In this work we show that the high minority carrier lifetime in as-grown Ga-Si wafers is dominated by low levels of iron contamination incorporated during silicon growth. Upon phosphorous diffusion iron is however effectively removed, increasing the bulk carrier lifetime from a few hundred micro-seconds to well above one milli-second. Lifetime spectroscopy in combination with Shockley Read Hall theory was used to determine the concentrations of Fei and FeGa complexes in the course of the FeGa association. Finally, we use the estimated concentrations of FeGa as a function of time of storage in the dark to validate that FeGa association follows the laws of coulombic attraction similar to FeB.

Single crystal production of silicon for solar cell substrates has relied on the Dash neck technique developed more than 50 years ago. The technique is simple and repeatable and enables truly dislocation free crystal growth. It does have drawbacks, however, including limits on throughput and some structural difficulties. It has long been assumed that dislocation-free growth is not possible by any other method. In the 'quasi-mono' crystal growth technique, one of the key elements is the use of large area single crystal seeds. By melting the seeds at near-equilibrium conditions, it is feasible to avoid the production of dislocations during melting. We will review the dislocation relevant details of the large area seeding process and present best case results for dislocation density, including measured minority carrier lifetimes in excess of 1 ms on p-type material. We will focus on dislocation density exclusive of seed boundaries, but we will also present a potential best-case limit for the technique.