|M.Sc Student||Dassa Oded|
|Subject||The Effect of the Lattice Planes in III-V Semiconductors on|
their Passivation by Organic Self Assembled
|Department||Department of Chemical Engineering||Supervisors||Professor Yaron Paz|
|Professor Dan Ritter|
One of the main problems of microelectronic devices based on InP and GaAs is poor electronic properties due to high density of surface states within the band gap. Standard passivation techniques, such as hydrogen plasma treatment and deposition of dielectric films such as Si3N4, SiO2 or polyimide, have quite a limited effect. Substantial improvement in the surface properties can be achieved by utilizing chemical treatments by inorganic sulfur compounds (Na2S.9H2O, (NH4)2S). However, practical implementation of sulfur passivation is often limited due to the instability of the passivating agent.
It was proposed that self-assembled monolayers of long-chain organo-sulfur compounds could be ideal for surface passivation of III-V semiconductors, since these materials may combine chemical bonding with the semiconductor's dangling orbitals together with close-packing and high stability.
Following previous work, which demonstrated the feasibility of this approach, this work presents a study on the effect of the lattice planes of III-V semiconductors (InP, InGaAs) on the density and structure of the monolayer. Of major interest were also the surface-electronic properties induced by this non-standard passivation technique, as well as the correlation between these properties and the structure of the organic monolayers.
The chemisorption of octadecylthiol (ODT) on different InP sidewalls planes [(100), (101) and (111)] was characterized by angle resolved Auger spectroscopy, revealing different thickness, coverage and stability of the monolayer on these planes. SAM’s on InGaAs epilayers, grown on InP (100) substrates, were also characterized by XPS, Auger Spectroscopy, FTIR and contact angle measurements. Here, Auger spectroscopy of InGaAs epilayers coated by SAM showed that a monolayer of octadecylthiol is sufficient to prevent oxygen penetration, at least for five days.
The influence of the presence of the SAMs on the electrical properties of the semiconductors’ surface was investigated by measuring the base-collector dark current in InGaAs/InP Heterojunction bipolar transistors (HBTs). The passivation, which was manifested by a dramatic reduction of as much as 3 orders of magnitude in the leakage current, depended on the device orientation relative to the wafer’s major flat. In this context, the ability of thiolated SAMs to perform an electrical passivation of InGaAs epilayers was demonstrated by enhancement of the photoluminescence (PL) signal. It was found that the intensity of the PL signal of InGaAs epilayers is stable over time compared to traditional inorganic coatings.