A Study of Deep Levels in MOCVD-Grown InP/Semi-Insulating InP Structure

Deep levels in undoped n-type InP epitaxial layers grown by MOCVD on Fe-doped InP substrates were investigated by DLTS and photo-excited DLTS. Two main electron traps, F1 and F2, were observed in the films. The concentration profile of F1 seems to be related to that of donors. The concentration of F2 increases as the substrate is approached, suggesting the out-diffusion of Fe from the Fe-doped substrate. The activation energy E n and the carrier capture cross section σ n were found to be 0.48 eV and ∼6×10 -19 cm 2 respectively for F1; and 0.78 eV and 10 -20 ∼10 -21 cm 2 respectively for F2 in the temperature range investigated. Another level was also detected in the Fe-doped substrate, and its E n and σ ∞ were found to be 0.24 eV and 2×10 -16 cm 2 , respectively. We speculate that either or both of these F1 and F2 traps are the origin of the substantial looping phenomenon in the drain I / V characteristics previously observed in InP MESFETs.