Electronic and optical applications of diamond-like carbon

In this contribution emphasis is placed on examining the electronic and optical properties of a-C and a-C:H in their own right as those belonging to an amorphous semiconductor. It is shown that the electronic density of states in semiconducting a-C and a-C:H is very different from that of other group IV amorphous semiconductors due to the presence of π states associated with sp² hybridised bonds. Even in tetrahedral amorphous carbon (ta-C) with sp³ bonding of up to 70-80%, the π and π* states tend to determine the electronic and optical properties. Such π states are of course not present in diamond. This is in contrast to the mechanical properties of ta-C which can be very close to those of diamond. The presence of π bonding (in addition to the σ bonding) gives a-C and a-C:H some advantageous properties compared to a-Si and a-Ge. Passive use of a-C and a-C:H in applications such as IR windows and passivation layers and their potential for active use as electronic materials in optoelectronic devices are discussed. As examples of the latter, use of doped ta-C as a wide band-gap material with Si for heterojunctions and a-C:H in band-gap modulated amorphous superlattices are examined