Degradation of d.c. parameters in enhancement mode WN_X self-aligned gate GaAs MESFETs under high temperature stress

摘要

The effect of thermal stress on the d.c. parameter degradation of enhancement mode tungsten nitride (WN_x) selfaligned gate GaAs MESFETs was investigated. Threshold voltage, surce-drain current and transconductance were measured during the tests. The physicla roperties of the device aftr thermal stress were analyzed by means of Auger electron spectroscopy (AES), X-ray diffractometry to identify the degradation mechanism. The d.c. failure mode consists of an increase in the threshold voltage and a decrease in the current and transoconductance of the FETs. The device simulator was also used for analyticla understanding of the d.c. parameter degradation. The simulated results showed that d.c. parameter degradation was mainly attributed to the increase in source and drain ohmic contact resistances. Frod the AES analysis, we found that the incresase of contact resistance was due to carrier compensation, which was caused by Ga outdiffusion and Ni indiffusion under the ohmic contact layer. Therefore the thermally activated carrier compensation effects by trap generation are proposed to be the main failure mechanism for d.c. parameter degradation of enhancement mode WN_x self-aligned gate GaAs MESFETs.