Extension of Shockley's transmission line method (TLM) to characterize ohmic contacts

A method to extract the resistance of the metallic pad of ohmic contacts is presented. It utilizes the transmission line method array of ohmic contacts and measurements required to obtain their specific contact resistance plus just an additional current voltage measure. The method was applied to fully characterize, included their reliability, standard ohmic contacts on p-GaAs and n-GaInP thin epitaxial layers whose measured sheet resistances were 96 and 6.86 (Ohms Sq(-1)) respectively. Our extended method found contact pad sheet resistances of R-shMP = 0.9 and 0.09 (Ohms Sq(-1)) for those on p-GaAs and n-InGaP, respectively, giving a ratio of 1%-2%, in this case. For their reliability it was found that after 430 degrees C for a 30 min thermal anneal, those on n-InGaP strongly degrade. The degradation initiates increasing the metallic pad sheet resistance and then the contact resistance, while those on p-GaAs remain unchanged. This method should contribute to a better characterization of ohmic contacts.