Measurement of piezoelectrically induced charge in GaN/AlGaN heterostructure field-effect transistors

Electron concentration profiles have been obtained for ${\mathrm{Al}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N/GaN}$ heterostructure field-effect transistor structures. Analysis of the measured electron distributions demonstrates the influence of piezoelectric effects in coherently strained layers on III-V nitride heterostructure device characteristics. Characterization of a nominally undoped ${\mathrm{Al}}_{\mathrm{0.15}}{\mathrm{Ga}}_{\mathrm{0.85}}\mathrm{N/GaN}$ transistor structure reveals the presence of a high sheet carrier density in the GaN channel which may be explained as a consequence of piezoelectrically induced charges present at the ${\mathrm{Al}}_{\mathrm{0.15}}{\mathrm{Ga}}_{\mathrm{0.85}}\mathrm{N/GaN}$ interface. Measurements performed on an ${\mathrm{Al}}_{\mathrm{0.15}}{\mathrm{Ga}}_{\mathrm{0.85}}\mathrm{N/GaN}$ transistor structure with a buried ${\mathrm{Al}}_{\mathrm{0.15}}{\mathrm{Ga}}_{\mathrm{0.85}}\mathrm{N}$ isolation layer indicate a reduction in electron sheet concentration in the transistor channel and accumulation of carriers below the ${\mathrm{Al}}_{\mathrm{0.15}}{\mathrm{Ga}}_{\mathrm{0.85}}\mathrm{N}$ isolation layer, both of which are attributable to piezoelectric effects.