Search

We have investigated electrical and microstructural properties of W-capped Er Ohmic contact to n-type In0.53Ga0.47As channel using (I-V) current-voltage characteristics, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The interfacial reaction between Er and In0.53Ga0.47As driven by rapid thermal annealing (RTA) process led to the formation of Er-InGaAs alloy. The increase in the RTA temperature resulted in the degradation of surface and interface morphologies of Er-InGaAs alloy film, which could be associated with the reduction of its surface energy combined with intense interfacial reaction between Er and In0.53Ga0.47As. The specific contact resistivity of Er-InGaAs alloy film extracted using four-point (Kelvin) probe technique was investigated as a function of RTA temperature. The specific contact resistivity was found to vary with the variation in RTA temperature. Such a dependency of specific contact resistivity on RTA temperature could be attributed to the phase evolution surface/interface morphologies of Er-InGaAs alloy film. A minimum specific contact resistivity of ~ 10-6 Ωcm2 was achieved after RTA process at 400 °C.

We have investigated the microstructural evolution and electrical property of self-aligned Ni-germanide thin film formed on n-type GaAs (100) substrate as a function of rapid thermal annealing at temperatures in the range of 300 – 600 °C. The heteroepitaxial growth of Ge on GaAs (100) substrates was carried out using rapid thermal chemical vapor deposition (RTCVD) method. The Ge epitaxial layers were formed by the decomposition of GeH4 in a H2 ambient at substrate temperatures of 400 – 500 °C. The specific contact resistivity was extracted using four-point (Kelvin) probe technique. The specific contact resistivity values of the Ni-germanide films varied with variation in annealing temperature and were comparable to those obtained for Ni-germanide. A low specific contact resistivity of the order of 2.1 × 10-6 Ωcm2 was obtained for the Ni-germanide film formed at annealing temperature of 500 °C. The variation in the specific contact resistivity with annealing temperature could be associated with the phase evolution, surface and interface morphologies of Ni-germanide that occur at different annealing temperatures.

Depinning of the Fermi-level at metal/Ge Schottky junctions was achieved by Se treatment at room temperature. Due to the strong Fermi-level pinning close to the valence band edge in Ge, Schottky and Ohmic behaviors were observed in conventional Al Schottky contacts to n- and p-type Ge, respectively. However, Al Schottky contacts to n- and p-type Ge with Se treatment became Ohmic and Schottky, respectively. Electron and hole barrier heights calculated using Richardson plots were found to be 0.15 eV for of Al contacts to Se-treated n- type Ge, and 0.33 eV for Al contacts to Se-treated p-type Ge, respectively. The transmission electron microscopy (TEM) examination combined with X-ray photoemission spectroscopy (XPS) analysis showed that Se treatment at room temperature yielded the formation of a fairly uniform Se-Ge alloy film with partially ionic binding nature caused by the chemical reaction between Se and Ge. This led to the reduction of surface states of Ge surface along with the passivation of dangling bonds by the incorporation of Se atoms, which was responsible for Fermi-level depinning at Al/Ge junctions.

We have investigated the electrical and microstructural properties of Cu-germanides formed on p-type Ge substrate as a function of rapid thermal annealing (RTA) temperature. As increasing RTA temperatures, Cu films reacted with Ge and formed Cu-germanides. The Cu3Ge phase appears to be the dominant phase along with Cu5Ge2 phase at annealing temperatures of 500 and 600 °C. The sheet resistance and specific contact resistivity were investigated as a function of germanide formation temperature. A minimum specific contact resistivity value of 6.19´10-6 Wcm2 is obtained after annealing at 400 °C associated with the formation of low stoichiometric Cu3Ge phase. The sheet resistance and specific contact resistivity increased after rapid thermal annealing at temperatures >500 °C, indicated the degradation of the contact properties and could be associated with the formation of copper rich Cu5Ge2 phase and the loss of structural integrity with increasing annealing temperature.