Nitride-based epitaxial processes are performed in four MOVPE reactors at FBH. A MOVPE reactor AIX200/4-RF-S with a capacity of 1×2" is used to deposit epitaxial structures for laser diodes. The reactor is equipped with a LayTec high resolution curvature sensor (EpiCurveTT-HR). Futhermore, two planetary reactors AIX2600G3-HT with a capacity of 11×2" or 8×3"/4" are used at FBH also equipped with in-situ sensors. In this production-type reactors, high temperatures up to 1600°C can be reached in the stainless steal reactor chamber. High-quality AlN can therefore be fabricated for the use as templates for optoelectronic structures for far-UV emission. A Close Coupled Showerhead reactor (6x2") is employed for fabricating UV LEDs.
For the development of electronic devices such as AlGaN/GaN heterostructure field-effect transistors (HFET) 100 mm semi-insulating SiC substrates are used. They offer a high thermal conductivity in comparsion to the cheaper sapphire. The layer structure for HFET devices usually consists of a highly resistive GaN buffer layer, a GaN channel, and an AlxGa1-xN-barrier layer with an Al content of x=0.15 to x=0.35. Due to the spontaneous piezo-electric polarization in the AlGaN-GaN material system, carriers accumulate at the interface resulting in a two-dimensional electron gas. Typical carrier mobilities for a layer concentration of 1x1013 cm-2 are in the range of 1600 cm2/Vs. For high voltage applications HFET structures with AlN buffer layers are developed, which feature higher breakdown voltages as well as improved thermal characteristics.
Optoelectronic layer structures are developed for laser diodes in the blue/violet spectral range (380 nm – 450 nm) as well as for UV light-emitting diodes and UV photodetectors (230 nm – 360 nm). The laser diodes are based on 2 - 7 nm thick InGaN quantum wells as light-emitting layers embedded in GaN and AlxGa1-xN layers for wave guiding on GaN substrates. LED structures are grown on sapphire and consist of light-emitting InyAlxGa1-x-yN layers sandwiched between AlxGa1-xN. Absorbing AlxGa1-xN layers on sapphire substrates are used for UV photodetectors.