Ferroelectric Gate on AlGaN/GaN Heterostructures

A PZT, Pb(Zr,Ti)O₃ (40:60), ferroelectric layer has been successfully deposited onto a Al_0.3Ga_0.7N/GaN heterostructure with a 2DEG, two dimensional electron gas. Due to the chemical and temperature stability of AlGaN/GaN it was possible to implement the concept of field-effect transistor with ferroelectric gate. The high temperature processing conditions for PZT were optimised in order to grow highly textured (111) PZT on the heterostructure without destroying the 2DEG. However, it was imperative to measure the transport properties in the 2DEG before and after the PZT deposition process in order to detect any degradation of the 2DEG due to diffusion. Hall measurements also enabled the observation of the partial depletion of electrons in the 2DEG, confirming the functionality of the ferroelectric gate. This depletion was due to a change of the spontaneous polarisation in the PZT layer when poled with a negatively biased voltage. These results are encouraging for the use of PZT as a ferroelectric gate on AlGaN/GaN heterostructures and may open new possibilities for semiconductor heterostructure nano-patterning by polarisation domain engineering.