Ohmic contacts to n-type and p-type ZnSe

Stable Ohmic contacts are essential for reliable operation of electronic devices. Such contacts have been made to n-type and p-type ZnSe. Au, Pd, Cu and Se for p-type N-doped ZnSe (1 × 10¹⁷ cm^-3) and AuGe, In, Yb and Mg for n-type Cl-doped ZnSe (4.5 × 10¹⁸ and 1.15 × 10¹⁹ cm^-3) grown by molecular beam epitaxy (MBE) on (100) semi-insulating GaAs substrates have been deposited by thermal evaporation. Annealing techniques at different temperatures, chemical etching and cleaning prior to metallization and reactive ion etching (RIE) in a N₂ plasma and a Ar plasma for p-ZnSe have been studied. The electrical characteristics for the contacts were examined by the current versus voltage curves and the specific contact resistance was determined by use of the transmission line method (TLM). The current transport mechanisms for the Mg/Au contact to n-type ZnSe and the Cu/Au contact to p-type ZnSe have been studied by the current versus voltage for different temperatures (I-V-T) measurements. In/ Au was best for n-type and Cu/Au for the p-type materials. Plasma treatment of the ZnSe surface prior to metallization was proven to lower the contact resistance to p-type ZnSe. The lowest specific contact resistance values of 1.67 × 10^-1 Ω cm² for the Cu/Au contact to p-type ZnSe with a N₂ plasma treatment and 1.04 × 10^-2 Ω cm² for the In/Au contact to n-type ZnSe were achieved. Two different current flow mechanisms were shown for the Cu/Au contact to low doped p-ZnSe (1 × 10¹⁷ cm^-3) and three for Mg/Au contact to highly doped n-ZnSe (1.15 × 10¹⁹ cm^-3). The Cu/Au contact to p-ZnSe and Mg/Au contact to n-ZnSe have been observed to be especially stable and reproducible.