Modification of electronic properties of metal/semiconductor contacts

The objective of this study is to understand and to control the interfacial electrical and metallurgical properties of metal/semiconductor contacts. Desired contact electrical properties were obtained by the modulation of carrier transport across the contacts, resulting from the modification of the semiconductor energy band profile near the contact interfaces. This method of controlling the metal/semiconductor electrical properties has been utilized to modulate the barrier height of Schottky diodes and to fabricate low-resistance ohmic contacts. Modelling of the carrier transport was made to correlate the metallurgical properties and the electrical characteristics of the contacts.;The first part of this work emphasizes the modulation of the effective barrier height of Ge Schottky diodes by a thin highly doped surface layer. Lowering of barrier height on metal/n-Ge contact and enhancement of barrier height on metal/p-Ge contact have been achieved. Experimentally observed barrier height and ideality factor were compared to those from the computer modeling.;Similar idea used to lower the effective barrier height of a Schottky diode can be used to fabricate ohmic contacts. Low-resistance non-spiking ohmic contacts to p-GaAs using layered structures of Si/Ni(Mg)/p-GaAs and Pd/Sb(Mn)/p-GaAs were studied. Metallurgical investigation indicated that the formation of ohmic contact can be correlated to the solid-phase regrowth of a highly doped semiconductor layer on the p-GaAs substrate, resulting in a low resistance tunneling junction. This correlation was assured by the computer modeled and experimentally observed temperature dependence of the contact resistivity.;To preserve contact characteristics of Schottky diodes under severe process condition was also a part of our interest. The metallurgical and electrical stability of high temperature annealed TaSi;Controlled interfacial reactions of metal/n-GaAs contact can be utilized to adjust the threshold voltage of GaAs metal-semiconductor field-effect transistors (MESFETs). The design principles of a self-limiting advancing gate technology were discussed. Enhancement mode GaAs MESFETs with precise control of threshold voltage and improved long term stability were fabricated using this technique.