Ohmic Contacts to ZnO

Kim et al. [23] have investigated nonaUoyed Al and Al/Pt ohmic contacts on n-type ZnO and found that the I-Vcharacteristics of as-deposited Al and Al/Pt contacts on n-type ZnO reveal a linear behavior with a specific contact resistivity of 8.0 x 10 and 1.2 X 10 Dcm, respectively. Pt overlayer on Al contact, compared to the case without the overlayer, has resulted in a large reduction in the specific contact resistivity on n-type ZnO. This reduction has been attributed to the prevention of surface oxide layer (Al-O) by the Pt metal, which is similar to the case of GaN. A nonaUoyed In-based ohmic contact, formed on a hydrothermally grown n-type ZnO substrate by KrF excimer laser irradiation with 0.3 J cm and metal deposition 

Ip et al. [30] could obtain a minimum specific contact resistance of 6 x 10 Q cm for Ti/Al/Pt/Au contacts on undoped (n = 10 cm ) bulk ZnO. The contacts did not show ohmic behavior in the as-deposited state and reached their minimum resistance after 250 °C annealing. This value was essentially independent of the surface cleaning procedure employed, including sequential solvent cleaning or H2 plasma 

Some of the various ohmic contact metallization approaches on n-type ZnO are summarized in Table 8.1 together with carrier concentration, specific contact resistance, and method used to measure the specific contact resistivity. A1 [33-35], 

---