Development of low resistance ohmic contact structures for GaAs based semiconductor devices

Ohmic contacts are an important component that affects the performance of GaAs-based semiconductor devices. Formation of low resistance contacts increase both the efficiency and longevity of the device. Determining the thermal stability as well as degradation of the contacts by measuring the resistance values with an appropriate method is viable for the development of the reliable and efficient metallization structures. In this thesis, using e-beam evaporation technique, Ti/Pt/Au and AuGe/Ni/Au were evaporated as an Ohmic contact structures for p- and n-type GaAs samples, respectively. Contact resistances of both fresh (un-aged) and thermally aged samples were measured using TLM method. Low specific contact resistivity values in the range of 10-6 Ω.cm² were obtained both for the p- and n-type contacts. The contacts were subjected to thermal aging in a high temperature furnace. Thermal aging studies revealed that, for the chosen contact structures, n-type contacts have much higher tolerance to the thermal aging compared to the p-type contact structures. From SEM and EDS measurements, oxidation and formation of high resistive phases due to metal diffusion to the p-GaAs layer were observed in the p-contacts. We came up with a conclusion that, different phases formations at the metal-semiconductor interface of the n-contacts has an adverse effect on the current conduction. However, we could get an efficient contacts having lowest contact resistance as well as with much enhanced aging tolerances. Moreover, using comparative aging tests we have observed that 150 hours of annealing at chosen aging temperature could not satisfy the contact degradation criteria.