PULSE LASER ATOM PROBE STUDY OF GaP

Gap tips prepared f ran whiskers grown by the vapour phase reaction, were analyzed using our ctmbined-type atom-probe FIM by laser pulse operation instead of high voltage pulse operation. It was found that ( 1 ) The mposition is Ga : P=l : l at cryogenic temperature 45K in vacuum of better than 1 x 10-Ptorr. ( 2 ) Much more cluster ions of phosphorus atan in laser pulse mode are detected in canparison to that in high voltage pulse mode. (3) Mass resolution for laser pulse operation is high enough to resolved the hydride ions even at linear type mode. We also make clear the influences of laser beam power density irradiated on the tip for field evaporation. The TOF atcan-probe technique has only been applied to metallic samples due to the difficulty to transmit the nano-second high-voltage pulse through sample tips of low electrical conductivity. Another problem is distortion or reflection of high voltage pulse which result in anenergy spread of the fieXd eeMprated ions. Kellogg and Tsong proved that laser-assisted field evaporation can be used for TOF atom probe operation / l / . Using laser pulses, as v e d to high-voltage pulses, for TOF atan-probe operation eleiminates the above-mentioned problems and gives applicability to low-conductivity materials. The field evaporation of silicon in ultrahigh vacuum and at cryogenic temperature is qualitatively the same as for metal /2/, /3/. Recently, Cerezo et a1 show a pulse laser atan probe (PLAP) /l / mass spectrum for a GaAs whisker, giving a stoichimtry of &/AS = 0.99 0.03 /4/. They also give that the value obtained for Inks whisker is In/& = 0.97 + 0.05 /4/. We have also done nearly the same experiment for Gap whisker. As the sample of the atom probe, GaP whiskers withfhe [TT71 growth orientation were used in the same m e r as the previous experiments /5/. The resistivity of GaP was estimated to be more than 0.004nan. The sharp emitters of GaPwereprepared by dipping the specimens for a few minites in the hot solution of HNOj : HC1 (1 : 3). Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1986244