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GaN - Heterojunctions

AlGaN/GaN

AlxGa1-xN alloy is the most studied semiconductor for GaN microelectronics.

AlxGa1-xN alloy grown on GaN gives rise to fixed charges at the interface stemming from piezoelectric effects.
These charges induce the presence of free carriers called 2 dimension electron gas which flow can be controled by the gate of the transistor.

Despite tremendous achievements in the past years in many labs, the internal mechanical stress of the AlxGa1-x N/GaN heterojunction that appears as soon as aluminium is incorporated in GaN (see graph on the right: the lattice shrinks), might create reliability issue on long term operation.

InAlN/GaN

One can find a InAlN concentration such as the lattice constant is the same as the GaN one (see graph on the right). This cystalline lattice matching enables low stress level in the heterojunction.

Due to a strong spontaneous polarisation in the InxAl1-xN crystal, a stress-free fixed charge creation is naturally present at the interface (and then creating a 2D electron gas see upper). Efficient electrical transport is observed together with low mechanical stress. This last point is an advantage compared to AlGaN/GaN.