Characterization of impact-ionization in InAlAs/InGaAs/InP HEMT structures using a novel photocurrent-measurement technique

A detailed analysis of the gate-leakage current in InAlAs/InGaAs/InP high electron mobility transistor (HEMT) structures is carried out. The different leakage contributions are studied experimentally and theoretically for the evaluation of an optimized layer structure to be used in low-noise optical receivers. The focus is on the additional gate-leakage current due to impact-ionization in the small-bandgap channel material. To reduce the gate-leakage caused by impact-ionization the authors introduced a strained In_0.1Al _0.9As layer within the spacer layer section of a conventional HEMT layer structure. To demonstrate the efficiency of this hole-barrier a photocurrent measurement technique was employed. Using this novel layer structure, a drastic reduction of gate leakage near pinch off bias was achieved