AN ATOM-PROBE STUDY OF III-V COMPOUND SEMICONDUCTORS

GaAs tips prepared from commercially available wafers were analyzed using our focusing-type time-of-flight atom-probe. It was found that (1) The composition depends strongly on the experimental conditions, such as H2 partial pressure and netplane. (2) Even in good vacuum ( 5 x 10-11Torr) Ga concentration (Ga/Ga +As) is only 43% at the (111) plane and (3) Ideal concentration can be obtained using pulse ratio of 0.13 in the presence of 3 x 10-7Torr H2. We believe that vacancy cluster formation due to the preferential evaporation of As is responsible to the observed Ga depletion. GaAs-Ti interface was also studied. Our findings are (1) Ti partially diffuses into the substrate even at cryogenic temperature 50 K. and (2) at and above 1130 K Ti appears to form an intermetallic compound with GaAs, whose composition is Ga :As : Ti = 1 :1 :1 with a sharp interface with the underlying bulk.