Study of ohmic contact formation on AlGaN/GaN HEMT with AlN spacer on silicon substrate

This paper deals with the analyse of ohmic contact formation on GaN, AlGaN/GaN and AlGaN/AlN/GaN. TEM measurement was carried out on these last structures to explain the ohmic contact formation for Ti and Ti/Al contact. The difficulties to achieve an ohmic contact on AlGaN/AlN/GaN structures leads to etch the AlGaN barrier to obtain rapidly and easily an ohmic behaviour. At last, it is shown that TLM and TLTLM are necessary to characterise the ohmic contact when an alloy is formed under the metallisation. In this case, the transport is governed by tunnel effect assisted by field effect (FE) via deep levels.