ON SPACE-CHARGE-LIMITED CONDUCTION IN SEMI-INSULATING GAAS

We have measured the tempertture dependence of Cr doped semi-insulating (SI) GaAs in planar and point contact configurations at various fields ranging between 10 and 10**6 v/m. In a planar configuration the transport is ohmic up to approximately 10**4 v/m with an activation energy of approximately 0. 75 ev. At higher fields we have observed a space-charge-limited (SCL) transport with an activation energy of about 0. 47 ev. In a point contact configuration a quasi-ohmic and a transitional region have been found, both having an activation energy of approximately 0. 47 ev. Such behaviour is in qualitative agreement with Lampert's theory of SCL conduction. Some deviations from this theory are accounted for by the existence of macroscopic screening length in SI-GaAs.