O

Scheme 1. Chemical aspects of multisource precursor (MSP) and single-source precursor (SSP) processes.

Scheme 1. Chemical aspects of multisource precursor (MSP) and single-source precursor (SSP) processes.

In this context, the SSP containing predetermined metal-ligand interactions (e.g., metal-carbon for carbides, metal-nitrogen for nitrides, metal-oxygen for oxides, etc.) are an attractive choice for obtaining materials that are homogeneous at the atomic level. The superior potential of molecular-level synthesis has been demonstrated in several cases. For instance, the metal organic chemical vapor deposition (MOCVD) of group III nitrides (AlN, GaN, InN) has traditionally been carried out with mixtures of the corresponding metal alkyls with ammonia (NH3). However, the high thermal stability of NH3 (<5% pyrolyzed at 700 °C) necessitates very high substrate temperatures (>1000 °C), and high NH3:MR3 (M = Al, Ga, In) ratios (e.g., 2000:1) are required to inhibit nitrogen desorption. This severely limits the choice of substrate material, and the inefficient use of toxic ammonia demands gas-scrubbing systems. On the other hand, the use of molecular sources [Me2AlNH2]3 and [Et2GaNH2]3 containing preformed aluminum-nitrogen and gallium-nitrogen bonds gives crystalline AlN and GaN films at 400-800 and 650 °C, respectively.

0 0

Post a comment