Group III-Nitride Epitaxy
Nitride-based epitaxial growth at FBH is done in five different MOVPE reactors and one HVPE reactor. An MOVPE reactor AIX200/4-RF-S with a capacity of 1×2" is used to deposit epitaxial structures for blue-violet laser diodes on GaN substrate. Two planetary reactors AIX2600G3-HT with a capacity of 11×2" or 8x3"/4" are used. In this production-type reactors, high temperatures up to 1400°C can be reached. High-quality AlN can therefore be grown for example on sapphire for the use as templates for optoelectronic structures for UV-LEDs.
Further improvement of crystal quality can be achieved by annealing in an oven at up to 1700°C. A close-coupled showerhead reactors (6x2") is employed for growing layer structures for UV LEDs. A second reactor of the same type will be used for AlN-based heterostructure field-effect transistors (HFET) within the funding program of "Research Fab Microelectronics Germany". All MOVPE systems are equipped with in situ sensors (EpiCurveTT from LayTec). An HVPE reactor with temperatures up to 1300°C is used for hardware and process development to grow thick AlN layers with low absorption on low dislocation density as template for the growth of optoelectronic structures for the UVC emission range.
AlGaN/GaN heterostructure field-effect transistors (HFET) on 100 mm substrates are being developed for application in microelectronics. The semi-insulating SiC substrates offer a high thermal conductivity as compared to the cheaper sapphire. The layer structures for HFET devices usually consist 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 improved thermal properties in addition to higher breakdown voltage and improved linearity in the working range (lower dispersion).