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-temperature conditions, in CuInSe₂ and related materials solely by applying strong electric fields through small contacts. Electromigration of native Cu ions, which was suggested as the mechanism for type conversion, assumes an enhancement in ion mobility of several orders of magnitude. Electric-field-induced local heating was given as one possible cause for such enhancement [Cahen et al., Science 258, 271 (1992)]. Therefore, we have measured the average temperature of and around the contacts to CuInSe₂ and Cu_0.95Ag_0.05InSe₂ crystals, during application of the electric field. The measurements were done as a function of the active 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 formation (210-320°C), is insufficient for significant thermal diffusion. We conclude that electromigration is the dominant mechanism.