Drastic reduction of gate leakage in InAlAs/InGaAs HEMT's using a pseudomorphic InAlAs hole barrier layer

Impact ionization in the channel of InAlAs/InGaAs HEMT's was shown to be a reason for excess gate leakage current. Hot electrons in the high field region of the channel under the gate generate electron-hole pairs. The generated holes can reach the gate (gate leakage) as well as the source, the electrons flow to the drain (kink effect). The number of holes reaching the gate strongly depends on the valence band discontinuity. In order to increase this valence band discontinuity a thin pseudomorphic InAlAs layer with high Al-content was inserted in the spacer of an InAlAs/InGaAs HEMT. The efficiency of this hole barrier was measured by photocurrent and DC measurements, while its influence on transport characteristics was measured by Hall and RF measurements. A reduction of gate leakage by a factor of 200 is demonstrated.<
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