Characterization of electron traps in ion-implanted GaAs MESFET's on undoped and Cr-doped LEC semi-insulating substrates

This paper presents the results of characterization of deep levels in ion-implanted layers on semi-insulating LEC GaAs substrates, using MESFET channel current DLTS and transient resistance techniques. Test devices on undoped substrates show six electron traps with activation energies ranging from 0.15 to 0.85 eV, and devices on lightly and heavily Cr-doped substrates show five-and two-electron traps, respectively. The well-known EL2 level is the dominant level in undoped and lightly Cr-doped material, and there are two-electron traps (0.22 and 0.85 eV) that exist only in undoped material, and with the addition of Cr they are suppressed and a new level at 0.64 eV emerges instead. A deep level at 0.53 eV was observed in all samples and whether this arises due to implantation and annealing or it is a characteristic of the LEC material is as yet unknown.