Siddha Pimputkar

• B.S. Mechanical Engineering, Ph.D. Materials
• Professor (Assistant) at Lehigh University

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 facilitat...

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...

Highly indium-rich group-III nitrides are attracting attention for advancing our capacity to create highly effective optical emitters at extended visible/IR wavelengths or for enhancing bandgap engineering possibilities within the group-III nitride material framework. Current methods of synthesis are constrained in their efficacy, partially owing t...

High indium-content group-III nitrides are of interest to further expand upon our ability to produce highly efficient optical emitters at longer visible/IR wavelengths or to broaden bandgap engineering opportunities in the group-III nitride material system. Current synthesis approaches are limited in their capabilities, in part due to the low decom...

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...

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 sapphir...

Titanium zirconium molybdenum (TZM) is a high strength at high temperature alloy with favorable properties for use in high temperature structural applications. Use of TZM in high pressure, gas-containing autoclave systems was recently demonstrated for the ammonothermal method. Use of indium (In) in the system is desired, though there is a general l...

The design of a new super-atmospheric pressure metal organic chemical vapor deposition (MOCVD) reactor with spatially separated source zones and rotating susceptor is proposed and analyzed using computational fluid dynamics (CFD) techniques to determine fluid transport phenomena and suitability for thin-film synthesis of group III nitrides. This Hi...

Thermodynamic modeling of the ammonia decomposition under ammonothermal conditions (T > 600 K, P > 100 MPa) is presented given recent advances in developing a new, simple equation of state (EOS) describing ammonia, hydrogen, nitrogen and their mixtures under these conditions. The simplified EOS is based on the traditional form of the Beattie-Bridge...

The ammonothermal method has been extensively studied for the last two decades because of its potential to produce high-quality bulk gallium nitride (GaN) boules at low cost. Currently, the ammonothermal literature lacks in situ, internal fluid temperature measurements during the crystal growth process. This study reports on internal fluid temperat...

Native bulk gallium nitride (GaN) has emerged as an alternative for sapphire and silicon as a substrate material for III-N devices. While quasi-bulk GaN substrates are currently commercially available, single crystal GaN substrates are considered essential for future high performance light emitters and power devices. The ammonothermal method is cur...

The ammonothermal method is one of the most promising candidates for large-scale bulk GaN growth due to its scalability and high crystalline quality. However, emphasis needs to be put on understanding the incorporation and effects of impurities during growth. This article discusses how impurities are incorporated in different growth zones in basic...

Due to the disparity between observed gallium nitride (GaN) growth under conditions for which literature reports normal solubility, GaN solubility in supercritical NH3-Na containing solutions was re-evaluated. Isothermal gravimetric experiments on polycrystalline GaN were performed in the temperature range (T =415–650 °C) for which retrograde growt...

We report recent results of bulk GaN crystal growth using the sodium flux method in a new crucible-free growth system. We observed a (0001) Ga face (+c-plane) growth rate >50 µm/hr for growth at a N2 overpressure of ~5 MPa and 860 °C, which is the highest crystal growth rate reported for this technique to date. Omega X-ray rocking curve (ω-XRC) mea...

Single crystal, bulk gallium nitride (GaN) crystals were grown using the basic ammonothermal method in a high purity growth environment created using a non-hermetically sealed molybdenum (Mo) capsule and compared to growths performed in a similarly designed silver (Ag) capsule and capsule-free René 41 autoclave. Secondary ion mass spectrometry (SIM...

This paper discusses promising materials for use as internal, non-load bearing components as well as molybdenum-based alloys for autoclave structural components for an ammonothermal autoclave. An autoclave was constructed from the commercial titanium-zirconium-molybdenum (TZM) alloy and was found to be chemically inert and mechanically stable under...

Though several methods exist to produce bulk crystals of gallium nitride (GaN), none have been commercialized on a large scale. The sodium flux method, which involves precipitation of GaN from a sodium-gallium melt supersaturated with nitrogen, offers potentially lower cost production due to relatively mild process conditions while maintaining high...

Polarization controlled Fourier transform infrared (FTIR) absorption measurements were performed on a high quality m-plane ammonothermal GaN crystal grown using basic chemistry. The polarization dependence of characteristic absorption peaks of hydrogen-related defects at 3000–3500 cm−1 was used to identify and determine the bond orientation of hyd...

Improvements to the growth of nitride crystals in ammonothermal growth environments can be achieved through improved autoclave designs, purity, and use of in situ monitoring techniques. Given the limited data available on the stability of materials in supercritical ammonia solutions, this study intends to broaden the known dataset by experimentally...

Erhebliche Energieeinsparungen sind dank einer einzigen Erfindung möglich: der blauen Leuchtdiode. Die Forschung an GaN-basierte blauen LEDs resultierte nicht nur in einer effizienten weißen Lichtquelle, sondern hat viele weitere Anwendungs- und Forschungsperspektiven eröffnet. Die an der Entwicklung der blauen LED in erster Linie beteiligten Forsc...

Significant gains in energy savings now underway can be traced to a single invention-the blue light emitting diode. GaN-based blue LED technology not only resulted in efficient white light sources, but continues to enable a host of applications and scientific inquiries. The researchers primarily responsible for the development of the blue LED were...

Gallium Nitride (GaN) and its alloys form a promising material system for optoelectronic and electronic devices. Heteroepitaxial growth of GaN on sapphire and SiC, while viable, introduces threading dislocations (between 1E8 – 1E11 cm^-2), mismatches in thermal expansion coefficients, and limitations on available growth orientations other than the...

Boron-containing compounds, gasses and fluids are used during ammonothermal growth of group-Ill nitride crystals. Boron-containing compounds are used as impurity getters during the ammonothermal growth of group-Ill nitride crystals. In addition, a boron-containing gas and/or supercritical fluid is used for enhanced solubility of group-Ill nitride i...

Light-emitting diodes (LEDs) fabricated from gallium nitride (GaN) have led to the realization of high-efficiency white solid-state lighting. Currently, GaN white LEDs exhibit luminous efficacy greater than 150 lm W−1, and external quantum efficiencies higher than 60%. This has enabled LEDs to compete with traditional lighting technologies, such as...

New scintillators for high-resolution gamma ray spectroscopy have been identified, grown and characterized. Our development efforts have focused on two classes of high-light-yield materials: europium-doped alkaline earth halides and cerium-doped garnets. Of the halide single crystals we have grown by the Bridgman method-SrI₂, CaI<sub>2</...

Solid-state lighting using light-emitting diodes (LEDs) has the potential to reduce energy consumption for lighting by 50% while revolutionizing the way we illuminate our homes, work places, and public spaces. Nevertheless, substantial technical challenges remain in order for solid-state lighting to significantly displace the well-developed convent...