Working Group Aluminium Nitride - Summary

Aluminium nitride (AlN) is considered as the preferential substrate material for AlGaN-based UV-optoelectronic devices (LEDs, lasers, sensors). In order to prepare efficient devices fort the deep-UV range (210-280 nm), in particular, excellent structural quality of the active layers is required. This is currently possible only by depositing the layers on AlN bulk crystal substrates having the same excellent structural quality. AlN bulk crystals have further potential fields of application as direct semiconductors with very high thermal conductivity, e.g. as substrates for high frequency and power devices, and for pressure or temperature sensors working at elevated temperatures (> 800°C).

The group Aluminium Nitride is focused on developing PVT growth technology (see Methods) to prepare AlN bulk crystals and substrates relevant for applications. A key aspect is to provide techniques that are suitable for industrial adoption (Advanced UV for Life). Important fields of activity are the iterative increase of the single-crystal diameter to industrially relevant sizes while maintaining the high structural quality, the further improvement of reproducibility and yield, and the adjustment of desired electrical and optical properties (e.g. high deep-UV transparency) of the crystals by controlling impurity incorporation during crystal growth.

Working Group Aluminium Nitride - Methods

Growth of AlN bulk single crystals:

• Preparation of high-purity AlN bulk single crystals with up to 15 mm diameter and 12 mm length, using the sublimation-recondensation (physical vapor transport, PVT) technique in inductively heated reactors at growth temperatures above 2000°C in N2 atmosphere (300-900 mbar)
• Preparation of particularly doped AlN bulk crystals and solid solutions, using various methods for dopant addition
• Preparation of TaC-based crucible materials by cold isostatic pressing and sintering
• Numerical modeling of the PVT growth process to optimize thermal gradients and mass transport in the crucible, using the software VirtualReactor
• Thermodynamic calculations and experiments to test and select proper set-up materials (in collaboration with the group Chemical & Thermodynamic Analysis)
• Preparation of AlN surfaces for use as seeds in PVT growth, and chemo-mechanical polishing (CMP) to produce substrates with epi-ready surface finish (in collaboration with the group Crystal Machining)
• Design and construction of AlN growth reactors and reactor components (in collaboration with the group Plant Engineering & Construction)
  
  

Characterization of AlN bulk single crystals and substrates (in collaboration with the department of Simulation & Characterization)

• Structural characterization by optical microscopy, electron microscopy, and X-ray methods and analysis, as well as by atomic force microscopy and defect-selective etching
• Chemical analysis to investigate impurity and dopant incorporation by EDS, XRF, and ICP-OES (in-house) as well as by SIMS and inert gas fusion (external),
• Evaluation of the influence of impurities and dopants in AlN crystals using spectroscopic and electrical methods and analysis, e.g. optical absorption, FTIR, EPR, cathode- and photoluminescence, temperature-dependent conductivity, and impedance

Working Group Aluminium Nitride - Publications

F. Langhans, S. Kiefer, C. Hartmann, T. Markurt, T. Schulz, Ch. Guguschev, M. Naumann, S. Kollowa, A. Dittmar, J. Wollweber, M. Bickermann
Precipitates Originating from Tungsten Crucible Parts in AlN Bulk Crystals Grown by the PVT Method.     
CRYST RES TECHNOL 51 (2016) 129 - 136            
doi:10.1002/crat.201500201

C. Hartmann, J. Wollweber, S. Sintonen, A. Dittmar, L. Kirste, S. Kollowa, K. Irmscher, M. Bickermann
Preparation of Deep UV Transparent AlN Substrates with High Structural Perfection for Optoelectronic Devices.
CRYSTENGCOMM (2016) 3488 - 3497
doi:10.1039/C6CE00622A

M. Bickermann
Growth and Properties of Bulk AlN. 
In: M. Kneissl and J. Rass (eds.), III-Nitride Ultraviolet Emitters - Technology and Applications, Springer Series in Materials Science 227 (2016), S. 27 - 46
doi:10.1007/978-3-319-24100-5_2

W. Guo, J. Kundin, M. Bickermann, H. Emmerich
A Study of the Step-flow Growth of the PVT-grown AlN Crystals by Multi-scale Modeling Method.
CRYSTENGCOMM 29 (2014) 6564 - 6577
doi:10.1039/C4CE00175C

C. Hartmann, A. Dittmar, J. Wollweber, M. Bickermann
Bulk AlN Growth by Physical Vapour Transport.
SEMICOND SCI TECH  29 (2014) 084002
doi:10.1088/0268-1242/29/8/084002

M. Woll, M. Burianek, D. Klimm, S. Gorfman, M. Mühlberg
Characterization of (Bi_0.5Na_0.5)_1-xBaxTiO₃ Grown by the TSSG Method.
_{J CRYST GROWTH 401 (2014) 351 - 354}
doi:10.1016/j.jcrysgro.2013.11.102

Martens, F. Mehnke, C. Kuhn, C. Reich, V. Kueller, A. Knauer, C. Netzel, C. Hartmann, J. Wollweber, J. Rass, T. Wernicke, M. Bickermann, M. Weyers, M. Kneissl
Performance Characteristics of UV-C AlGaN Quantum Well Lasers Grown on Sapphire and Bulk AlN Substrates.
IEEE PHOTONIC TECH L 26 (2014) 342 - 345
doi:10.1109/LPT.2013.2293611

T. Paskova, M. Bickermann
Vapor Transport Growth of Wide Bandgap Materials.
In: P. Rudolph (ed.), Handbook of Crystal Growth, Bulk Crystal Growth - Basic Technologies, 2^nd Edition, Vol. 2a (2014), 209 - 240
doi:10.1016/B978-0-444-63303-3.00016-X