Laser Stimulated Desorption from Compound Semiconductors, Dimerization Enhanced Phase Transition

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Abstract
Laser stimulated desorption (LSD) of neutral particles has been investigated in compound semiconductors MX of GaN, GaP, GaAs and CdS. No effects of crystallographic orientations on the characteristics of LSD, desorption yields, mean kinetic energies, and speed ratios have been recognized among (111) and (100) orientations in GaP and GaAs. This fact suggests that LSD does not follow the unimolecular dissociation of locally excited surface bonds, but occurs via a bulky event involving a phase transtion. The threshold laser powers for LSD were correlated to the crystal bond ionicities f i, which are good measures for the structural stability of tetrahedral covalent solids. It was found that with increasing f i of the solids, threshold laser powers tend to decrease. The dominant species ejected from MX were found to be in the forms of monomer M and X as well as dimer X2. The ratio of the yields of X2 to those of X increases as the single-bond energy of X2 increases. Considering these experimental results, we propose a model of a non-local electronic excitation mechanism for LSD; namely, LSD occurs via the dimerization enhanced phase transition in a high-density electron-hole plasma.