Interfacial electrical properties of diamond-like carbon/gallium arsenide heterostructures

Deposition onto GaAs of dielectric film with good interfacial properties is difficult owing to the high surface state densities at the GaAs surface. Study of diamond-like carbon (DLC)/GaAs heterostructures is worthwhile because of the advantageous properties of insulating DLC film and the low temperatures involved in its preparation. In this paper, we compare the electrical interfacial properties of DLC/GaAs with those of DLC/Si and DLC/Ge structures. The DLC films were prepared by r.f. plasma-assisted chemical vapour deposition using a mixture of propane and n-butane. Capacitance measurements were taken in the frequency range 400 Hz to 1 MHz. The interface trap density distribution N_ss(E) was estimated for the DLC---Si interface using Terman's method. Compared with the DLC---Si and DLC---Ge interfaces, the DLC---GaAs interface shows qualitatively different behaviour. There is an indication that the interfacial layer at the DLC---GaAs interface is more conducting than the DLC film, giving rise to Maxwell-Wagner type relaxation. As a result, the effective permittivity of the DLC film is one order of magnitude higher. The formation of this interfacial layer could be related to pre-etching of the GaAs substrate using argon plasma.