Spontaneous and piezoelectric polarization effects in III-V nitride heterostructures

The role of spontaneous and piezoelectric polarization in III-V nitride het erostructures is investigated. Polarization effects and crystal polarity ar e reviewed in the context of nitride heterostructure materials and device d esign, and a detailed analysis of their influence in nitride heterostructur e field-effect transistors is presented. The combined effects of spontaneou s and piezoelectric polarization are found to account well for carrier conc entrations observed in AlGaN/GaN transistor structures with low to moderate Al concentrations, while the data for higher Al concentrations are consist ent with defect formation in the AlGaN barrier. Theoretical analysis sugges ts that incorporation of In into the barrier and/or channel layers can subs tantially increase polarization charge at the heterojunction interface. The use of polarization effects to engineer Schottky barrier structures with l arge enhancements in barrier height is also discussed, and electrical chara cteristics of transistors with conventional and polarization-enhanced Schot tky barrier gates are presented. The polarization-enhanced barrier is found to yield a marked reduction in Sate leakage current, but to have little ef fect on transistor breakdown voltage. (C) 1999 American Vacuum Society. [S0 734-211X(99)05804-7].