LOCAL TEMPERATURE INCREASES DURING ELECTRIC-FIELD-INDUCED TRANSISTOR FORMATION IN CUINSE2

Local p-n and p-n-p junction structures can be formed under room-tempe rature conditions, in CuInSe2 and related materials solely by applying strong electric fields through small contacts. Electromigration of na tive Cu ions, which was suggested as the mechanism for type conversion , assumes an enhancement in ion mobility of several orders of magnitud e. Electric-field-induced local heating was given as one possible caus e for such enhancement [Cahen et al., Science 258, 271 (1992)]. Theref ore, we have measured the average temperature of and around the contac ts to CuInSe2 and Cu0.95Ag0.05InSe2 crystals, during application of th e electric field. The measurements were done as a function of the acti ve power dissipated in the system, using two different techniques, viz . infrared emission and contact melting. We find that the temperature around the contact, during the tens of ms of actual structure formatio n (210-320-degrees-C), is insufficient for significant thermal diffusi on. We conclude that electromigration is the dominant mechanism.