P-GaN-substrate sprouted giant pure negative electrocaloric effect in Mn-doped Pb(Zr0.3Ti0.7)O3 thin film with a super-broad operational temperature range

Highlights: • Agiant negative EC effect was obtained in Mn-doped Pb(Zr_0.3Ti_0.7)O₃ thin film. • P-GaN-substrates prouted the structural phase transition between T and R. • P-GaN-substrate with high carrier concentration benefits the perovskite. Ferroelectric thin films simultaneously possessing large positive and negative electrocaloric (EC) effects are attractive to the solid-state temperature-controlled devices which can be used in many fields, such as modern electronics, communications, medical and military, etc. Here, it is demonstrated that the giant positive EC effect (△T_max ~ 44.5 K and △S_max ~ - 42.8 JK⁻¹ kg⁻¹ at ~ 313 K) of the Mn-doped Pb(Zr_0.3Ti_0.7)O₃ (PZT-Mn) thin film deposited by a sol-gel method on the Pt/TiOx/SiO₂/Si can be tailored into a pure negative EC effect (△T_max ~ - 23.5 K and △S_max ~ 16.3 JK⁻¹ kg⁻¹) with a recorded super-broad operational temperature range (~ 150 K) by directly depositing on the p-GaN-substrate that has a high carrier concentration (n = 4 × 10¹⁷). Under the sprouting of the p-GaN-substrate, an electric-field induced structural phase transition (nano-scaled tetragonal phase to rhombohedral phase) plays a key role in obtaining the recorded pure negative EC effect. It is concluded that direct deposition of ferroelectric thin film on the p-GaN-substrate can be used as a universal-simple-effective strategy to generate a pure negative EC effect in a broad operational temperature range (≥ 100 K).