Our aim is to produce small series of prototype substrates with tailored properties from semiconductor crystals with promising properties and to make these available to research partners to enable innovation in epitaxial and device processes or new applications. This requires not only the optimization of crystal growth and preparation processes with regard to technological capability, but also the development of standardized and efficient characterization methods for each specific material.
Monocrystalline aluminium nitride is a promising substrate material for the production of ultraviolet light-emitting diodes (UV LEDs), which are used for disinfection, among other things. We produce AlN substrates with low dislocation densities, high UV transparency and high surface quality which partners can use to develop new devices. The developed processes and technologies will later on be adjusted and optimized for other application-relevant materials.
The section also operates the "Chemical Metrology" and "Crystal Machining" support labs.
Aluminium nitride (AlN) crystals are grown by physical vapor phase transport (PVT) in crucibles of TaC or W and must have low dislocation densities and relevant diameters (1") regardless of the intended application. Prerequisites for the growth of AlN crystals of high crystalline quality are the availability of low-defect seeds, the avoidance of impurity precipitation during heating up and an optimal T-field design (e.g. high T).
Diameter increase is achieved by gradual seed increase in several successive growth runs with suppression of parasitic growth and slow lateral growth using suitable lateral T-gradients. For the application as a substrate for UV emitters (<= 280 nm) a sufficient transparency in the targeted wavelength range is required, which can be adjusted by specifically influencing the concentrations of the main impurities O, C and Si.
Carsten Hartmann, Lucinda Matiwe, Jürgen Wollweber, Ivan Gamov, Klaus Irmscher, Matthias Bickermann, Thomas Straubinger
Favourable growth conditions for the preparation of bulk AlN single crystals by PVT
CrystEngComm
DOI: 10.1039/c9ce01952a
Carsten Hartmann, Jürgen Wollweber, Sakari Sintonen, Andrea Dittmar, Lutz Kirste, Sandro Kollowa, Klaus Irmscher, Matthias Bickermann
Preparation of deep UV transparent AlN substrates with high structural perfection for optoelectronic devices
CrystEngComm
DOI: 10.1039/c6ce00622a
Andrea Dittmar, Jürgen Wollweber, Martin Schmidbauer, Detlef Klimm, Carsten Hartmann, Matthias Bickermann,
Physical vapor transport growth of bulk Al1−xScxN single crystals
Journal of Crystal Growth
DOI: 10.1016/j.jcrysgro.2018.07.022
Left: Facilities for growing AlN single crystals at IKZ; Middle: View into the sublimation growth facility; Right: AlN single crystal
At the IKZ the installation of a technology-ready processing line for the preparation and characterization of semiconductor substrates with diameters up to 2" is planned. Currently, the IKZ is already able to produce demonstrator substrates (e.g. aluminium nitride) with small diameters and high quality. For the production of prototypes and small series, the machining effort must be reduced and the process reproducibility must be improved.
Central technical or scientific challenges in the production of semiconductor substrates are:
Left: Wire sawing; Middle: Substrates on polishing carrier; Right: TEM images of an AlN substrate surface after chemical-mechanical polishing - Top: Crystal volume near the surface (dark) in low magnification - Below: Near-surface ordered atomic structure without damage in high resolution
Semiconductor crystals of group III-V (e.g. InP, AlN) are substrate materials of the future for microelectronic, photonic, and opto-mechanical components that find applications in areas such as mobile communication, sensing, medical technology, and automotive. Integrating them into mature Si or sapphire-based technology platforms has the potential to realize cost-effective semiconductor devices with superior properties.
To enable this fundamentally new and future-oriented device generation, we want to develop preparation and transfer processes for integration on Si and other target substrates for III-V bulk crystals grown at the IKZ. Our activities are conducted in close collaboration with the bulk crystal growth (VGF-III-V, Aluminium Nitride Crystal Growth) and Wafering research groups, the IKZ-IRIS joint lab „Layer Transfer" as well as partners specialized in device development.
The R&D activities include:
Process chain – from single crystal to III-V on Si integration; Left: III-V single crystals, 1’’ AlN and 4’’ InP; Centre left: 10 µm thin InP-layer with AFM image; Centre right: InP micro-platelets; Right: Schematic image of transferred micro-platelets on Si target substrate.