Formation of pinning-free Schottky barriers on InP and related materials by novel in-situ electrochemical process and its mechanism

Recently the so-called InP-based materials such as InP, In_0.52Al_0.48As and In_0.53Ga_0.47 As have become important materials for high speed electronic and optoelectronic devices. A common drawback of these materials is, however, that Schottky barrier heights (SBHs) on n-type materials are generally low. Typical SBH values are 0.45 eV, 0.60 eV and 0.20 eV for n-InP, In_0.52Al_0.48As and In_0.53Ga_0.47As, respectively. Technologically low SBH values are problematic and impose severe limitations on the realizability of MESFETs and MSM photodetectors, and performance and reliability of HEMTs. In an attempt to overcome this difficulty, we have recently found that the SBH value of the Pt/n-InP Schottky diode can be increased up to 0.86 eV by using a novel in-situ electrochemical process, and have succeeded in realization of well-behaved InP MESFETs for the first time. The purpose of the present paper is further to understand and optimize the electrochemical process in view of its possible application to formation of fine Schottky gate electrodes for InP-based HEMTs utilizing InAlAs/InGaAs/InA1As/InP heterostructures. First, electrodeposition conditions and metal selection were optimized for InP for higher SBHs. Then, applicability of the electrochemical process for formation of Schottky gate was confirmed directly on HEMT wafers. Finally, the possible mechanism for the observed SBH increase is briefly discussed